nitrogen plant automation using plc and scada project report (travancore cochin chemicals)

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Roman family

NITROGEN PLANT AUTOMATIONUSING PLC AND SCADA

A MAIN PROJECT REPORT

Submitted by

JAMSHEER M I (REAMEAE009)PRANAV RAMACHANDRAN (REAMEAE020)AJEESH V N (REAMEAE028)SUDHEESH S (REAMEAE037)

in partial fulfillment for the award of the degree of

BACHELOR OF TECHNOLOGYIN

APPLIED ELECTRONICS AND INSTRUMENTATION

ENGINEERING

ROYAL COLLEGE OF ENGINEERING & TECHNOLOGYAKKIKAVU

UNIVERSITY OF CALICUTMARCH 2016

ROYAL COLLEGE OF ENGINEERING &

TECHNOLOGY AKKIKAVU

Department of Applied Electronics &Instrumentation Engineering

CERTIFICATE

Certified that this project report “NITROGEN PLANT AU-TOMATION USING PLC AND SCADA” is the bonafidework of “JAMSHEER M I (REAMEAE009), PRANAV RAMACHAN-DRAN (REAMEAE020), AJEESH V N (REAMEAE028), SUDHEESH S(REAMEAE037)” of Department of Applied Electronics & InstrumentationEngineering in partial fulfillment of the requirements for the award of thedegree of Bachelor of Technology in Applied Electronics & InstrumentationEngineering under the University of Calicut during the year 2015-2016.

Guide Coordinator Head of the Department

Place: AkkikavuDate:

Acknowledgement

Every success stands as a testimony not only to the hardship but also to hearts behind

it. Likewise, the present project work has been undertaken and completed with direct and

indirect help from many people and I would like to acknowledge the same.

First and foremost I take immense pleasure in thanking the Management and respected

principal, Dr. B. Priestly Shan, for providing me with the wider facilities. I express

my sincere thanks to Prof. V K Sreehari, Head of Department of Applied Electronics

and Instrumentation Engineering for giving me opportunity to present this project and for

timely suggestions.

I wish to express my deep sense of gratitude to the project coordinators Prof. V K

Sreehari, Head of Department and Ms. Sherin Thomas, Asst Professor, Department

of Applied Electronics and Instrumentation Engineering, who coordinated in right path.

Words are inadequate in offering my thanks to Guide Ms. Nicy V B, Asst Professor of

Applied Electronics and Instrumentation Engineering, for her encouragement and guidance

in carrying out the project.

I express my sincere gratitude to the Mrs. Sreedevi K, Assistant General Manager

(Human Resource and welfare) TCC ltd. for her enterprising attitude, timely suggestions

and support that made the project successfully. I would like to thank Mr. C.T. Pradeep,

Chief Engineer, Instrumentation department and also I thank my Plant Guide Mr. Nikhil

K Joshi for his presence and support.

iii

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Needless to mention that the teaching and the non-teaching faculty members had been

the source of inspiration and timely support in the conduct of my project. I would like to

express ny heartfelt thanks to my beloved parents for their blessings, my classmates for

their help and wishes for the successful completion of this project.

Above all I would like to thank the Almighty God for the blessings that helped me to

complete the venture smoothly.

Contents

Contents v

Abstract viii

List of Figures ix

List of Tables xi

1 INTRODUCTION 11.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.3 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.4 Scope of the project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.5 Report organisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2 LITERATURE SURVEY 42.1 Design for dynamic performance: air separation unit . . . . . . . . . . . . 42.2 Nitrogen generation by pressure swing adsorption . . . . . . . . . . . . . . 52.3 Reactions and separations - producing nitrogen via PSA . . . . . . . . . . 52.4 A review of air separation technology & their integration with energy con-

servation process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52.5 Stability analysis of a process swing adsorption process . . . . . . . . . . . 6

3 DESIGN CONSIDERATIONS 73.1 Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

3.1.1 Air compressor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83.1.2 Air receiver tank . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93.1.3 Pressure switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103.1.4 Tower-1 & Tower-2 or PSA Unit . . . . . . . . . . . . . . . . . . . . 133.1.5 Nitrogen surge vessel . . . . . . . . . . . . . . . . . . . . . . . . . . 133.1.6 Oxygen analyser . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143.1.7 Nitrogen storage tank . . . . . . . . . . . . . . . . . . . . . . . . . 18

3.2 Hardware discription . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183.2.1 Pre-filter & air inlet header . . . . . . . . . . . . . . . . . . . . . . 18

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CONTENTS vi

3.2.2 Vent valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183.2.3 Pressure Holding Valve (PHV) . . . . . . . . . . . . . . . . . . . . . 193.2.4 Solenoid valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193.2.5 Bourdon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223.2.6 Rotameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243.2.7 Pressure switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263.2.8 Air filter regulator . . . . . . . . . . . . . . . . . . . . . . . . . . . 283.2.9 Three way vent valve . . . . . . . . . . . . . . . . . . . . . . . . . . 31

3.3 Software description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323.3.1 Programmable Logic Controller (PLC) . . . . . . . . . . . . . . . . 323.3.2 Why PLC is used instead of relay . . . . . . . . . . . . . . . . . . . 333.3.3 Advantages of PLC . . . . . . . . . . . . . . . . . . . . . . . . . . . 333.3.4 Some procedures of PLC . . . . . . . . . . . . . . . . . . . . . . . . 333.3.5 PLC block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . 343.3.6 Different types of PLCs . . . . . . . . . . . . . . . . . . . . . . . . 363.3.7 Programming documentation . . . . . . . . . . . . . . . . . . . . . 363.3.8 PLC installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373.3.9 Ladder diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 383.3.10 Control relays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 383.3.11 Features of ALLEN BRADLEY’S SLC 503 . . . . . . . . . . . . . . 423.3.12 RS Logix500 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 453.3.13 Benefits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 453.3.14 RS-Linx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 473.3.15 RS Emulate 500 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 473.3.16 Supervisory Control And Data Acquistion (SCADA) . . . . . . . . 473.3.17 Elements of SCADA system . . . . . . . . . . . . . . . . . . . . . . 483.3.18 SCADA implementation . . . . . . . . . . . . . . . . . . . . . . . . 483.3.19 Communication in SCADA . . . . . . . . . . . . . . . . . . . . . . 483.3.20 Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

3.4 Flowchart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 523.5 Specification of equipments . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

4 RESULTS AND DISCUSSIONS 574.1 Experimental setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 574.2 Results and inference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 584.3 Advantages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 584.4 Disadvantages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 584.5 Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 594.6 Future scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

5 CONCLUSION 60

Bibliography 61

CONTENTS vii

A LADDER DIAGRAM 62

Abstract

This project deals with Nitrogen plant automation using PLC and SCADA. A pro-

grammable logic controller (PLC) is a digital computer used for automation of electrome-

chanical processes, such as control of machinery on factory assembly lines, amusement

rides, or light fixtures.

The entire process of extracting nitrogen gas from the atmosphere by a system that

consists of following device like solenoids valves, air compressor, air filter regulator, ro-

tameter, bourdon tube, and pressure switch etc. atmospheric air with various impurities

admitted and compressed through air compressor and send to an air receiver, then to the

system.

Plant has two tanks of similar capacity constituting with different solenoid valves and

other associated paraphernalia. When the pressure in compressor exceeds 7 kg/cm2, it

admits to the first tank through appropriate valves. Now, oxygen and other impurities are

adsorbed by CMS (carbon molecular sieve) and the nitrogen is separated. The first tank

works for 58seconds, meanwhile, the second one regenerates. Within another two seconds

both tank equalize the pressure. Nitrogen generated in first tank pass to storage tank,

through appropriate solenoid valves and surge vessel by releasing the impurities. Then

the operation is repeated in the second tank. Both tanks operate simultaneously one after

another with an interval of 58 seconds. So that the process is continued and nitrogen

storage tank is filled as required.

viii

List of Figures

3.1 Block diagram of proposed system . . . . . . . . . . . . . . . . . . . . . . . . 7

3.2 Reciprocating air compressor . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

3.3 Air receiver tank . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

3.4 Solenoid valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

3.5 Bourdon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

3.6 Rotameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

3.7 Pressure switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

3.8 Pressure regulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

3.9 Three way vent valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

3.10 Block diagram of PLC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

3.11 Example for control relay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

3.12 Symbol Control relay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

3.13 Symbol CR1 (NO) and CR1 (NC) . . . . . . . . . . . . . . . . . . . . . . . . . 39

3.14 Symbol Time relay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

3.15 symbol TR1 (NO) and TR1(NC) . . . . . . . . . . . . . . . . . . . . . . . . . 39

3.16 Symbol Motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

3.17 Symbol SOL1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

3.18 Symbol Light . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

3.19 Symbol PB1 (NO) and PB1 (NC) . . . . . . . . . . . . . . . . . . . . . . . . . 41

ix

List of Figures x

3.20 Symbol LS1 (NO) and LS1 (NC) . . . . . . . . . . . . . . . . . . . . . . . . . 42

3.21 Symbol PS1 (NO) and PS1 (NC) . . . . . . . . . . . . . . . . . . . . . . . . . 42

3.22 Modems and Protocols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

3.23 Flow chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

List of Tables

xi

Chapter 1

INTRODUCTION

1.1 Background

This project deals with Nitrogen plant automation using PLC and SCADA. A pro-

grammable logic controller or programmable controller is digital computer used for au-

tomation of electro mechanical processes, such as control of machinery on factory assem-

bly lines, amusement rides, or light fixtures. Unlike general –purpose computers, the PLC

is designed for multiple inputs and output arrangements, extended temperature ranges,

immunity to electrical noise, and resistance to vibration and impact. Programs to control

machine operation are typically stored in battery – backed –up or non-volatile memory.

The entire processes of extracting nitrogen gas from the atmosphere by a system that

consists of following device like solenoids valves, air compressor, air filter regulator, Rota

meter, bourdon tube, and pressure switch etc. atmosphere air with various impurities

admitted and compressed through air compressor and send to an air receiver, then to the

system.


other associated paraphernalia. When the pressure in compressor exceeds 7kg/cm2, it

1

NITROGEN PLANT AUTOMATION USING PLC AND SCADA


adsorbed by the CMS (carbon molecular sieve) and nitrogen is separated. The first tank


both tank equalize the pressure. Nitrogen generated in first tank pass to the storage tank,


the operation repeated in the second tank. Both tanks operate simultaneously one after

another with an interval of 58 second. So that process is continued and nitrogen storage

tank is filled as required. A nitrogen storage tank is installed after nitrogen surge vessel

for storage of nitrogen gas at pressure of 5.0 kg/cm 2. Two manual valves are provided at

inlet and outlet of tank. The plant is made to trip, by high pressure switch, when pressure

of gas in the tank goes up to 5.0kg/cm2.

1.2 Motivation

The motivation of our project is to design a nitrogen plant and the automation process

in the plant is through the PLC and SCADA operation.

1.3 Objectives

The objectives of our project are:

1. Extracting nitrogen gas from atmosphere

2. Separating the impurities from nitrogen gas using carbon molecular sieves (CMS)

technique.

3. Controlling the plant using PLC and SCADA.

4. Analyzing the content of oxygen in the surge vessel using oxygen analyzer

5. Store the nitrogen gas in the air receiver tank.

Dept of AEI - RCET Akkikavu 2


1.4 Scope of the project

The scope of the project is of extracting nitrogen gas from atmosphere by a system

that consist of following devices like solenoid valves, air compressor, air filter regulator,

rotameter, bourdon tube, pressure switch etc. and the impurities are adsorbed by CMS

(carbon molecular sieve) and nitrogen gas is separated and send to an air receiver tank.

1.5 Report organisation

The report is organized as follows: chapter 1 includes the introduction part which

include background of our project, motivation, objectives and scope of our project. Chapter

2 includes the literature survey part it includes the technologies for the proper operation

of the plant. Chapter 3 describes the block diagram hardware and software descriptions.

Chapter 4 is the result and discussion part it includes results and interference, advantages,

disadvantages, limitations and future scope in our project. Chapter 5 is the conclusion

part.


Chapter 2

LITERATURE SURVEY

2.1 Design for dynamic performance: air separation

unit

Dynamic performance of a plant has led to systemic analysis of the interaction between

design and control. Dynamic optimization provides a useful framework for the assessment

of control performance limitations. It presents an approach toward identifying the de-

sign characteristics of air separation plants that limit agility. Optimization problem was

formulated as a two tiered approach-steady state optimization was followed by dynamic

optimization. Disadvantage-A base case design is specified and limits to control perfor-

mance in response to variations in electricity price and production demand identified via

optimization in a two-tiered approach.

4


2.2 Nitrogen generation by pressure swing

adsorption

PSA can be cost effective method of onsite nitrogen generation for wide range of purity

and flow requirements. Process includes separations of nitrogen and oxygen from air, takes

place in an absorber vessel filled with CMS. The nitrogen PSA plant is controlled by PLC.

It has significance for the bulk removal of carbon dioxide from direct reduction top gases.

Advantages-low nitrogen product cost, highest reliability, easy turn down and maintenance.

2.3 Reactions and separations - producing nitrogen

via PSA

Multiple nitrogen technologies and supply modes now exist to meet a range of specifi-

cation. Onsite nitrogen generators and PSA membrane systems can be more cost effective

than traditional cryogenic distillate/ stored liquid nitrogen. The principles of different

methods are described with schematic diagram.Adsorption & other technology for air sep-

aration continue to advance as more efficient, highly packaged & compact gas generators

are developed.

2.4 A review of air separation technology & their

integration with energy conservation process

This paper describes the process for separating industrial gases from air and notes

economic & other limits for each process. Non – cryogenic industrial gas processes includes

adsorption process, chemical process, polymeric membrane and iron transport membrane



(ITM) technology. The detailed explanation of cryogenic processing with descriptions

about compression cycles, pumped liquid cycles and low and elevated pressure cycles are

included in this paper.

2.5 Stability analysis of a process swing adsorption

process

The general frame work is that of a pressure swing adsorption (PSA) on beds of zeolite

beads. The studies on PSA process to improve its performance are described here. And

the system under consideration was designed to produce oxygen from air. In this paper,

stability during cyclic gas flow description & adsorption in a porous column, as encountered

during PSA was investigated.


Chapter 3

DESIGN CONSIDERATIONS

3.1 Block diagram

The main blocks of PSA nitrogen generator includes air compressor, air receiver tank,

pressure switch, two towers, surge vessel, oxygen analyzer and nitrogen storage tank. Ni-

trogen is produces from the air taken from the atmosphere.

Figure 3.1: Block diagram of proposed system

7


3.1.1 Air compressor

An air compressor is a device that converts power (usually from an electric motor, a

diesel engine or a gasoline engine) into kinetic energy by compressing and pressurizing air,

which, on command, can be released in quick bursts. There are numerous methods of air

compression, divided into either positive-displacement or negative-displacement types.

Positive-displacement air compressors work by forcing air into a chamber whose volume

is reduced to compress the air. Piston-type air compressors use this principle by pumping

air into an air chamber and reducing the volume by the constant motion of pistons. They

use one-way valves to guide air into a chamber, where the air is compressed. Rotary screw

compressors also use positive-displacement compression by matching two helical screws

that, when turned, guide air into a chamber, whose volume is reduced as the screws

turned. Vane compressors use a slotted rotor with varied blade placement to guide air

into a chamber and compress the volume.

Negative-displacement air compressors include centrifugal compressors. These compres-

sors use centrifugal force generated by a spinning impeller to accelerate and then decelerate

captured air, which pressurizes it.

Figure 3.2: Reciprocating air compressor



Conventional air compressors are used in several different applications:

• To supply high-pressure clean air to fill gas cylinders

• To supply moderate-pressure clean air to a submerged surface supplied diver

• To supply moderate-pressure clean air for driving some office and school building

pneumatic HVAC control system valves

• To supply a large amount of moderate-pressure air to power pneumatic tools, such

as jackhammers

• For filling tires

• To produce large volumes of moderate-pressure air for large-scale industrial processes

(such as oxidation for petroleum coking or cement plant bag house purge systems).

Most air compressors are either reciprocating piston type, rotary vane or rotary screw.

There are two main types of air compressor’s pumps: oil-lubed and oil-less. The oil-less

system has more technical development, but is more expensive, louder and lasts for less

time than oil-lubed pumps. The oil-less system also delivers air of better quality.

3.1.2 Air receiver tank

Air receivers are tanks used for compressed air storage and are recommended to be in

all compressed air systems. Using air receivers of unsound or questionable construction

can be very dangerous

Air receivers serve several important purposes:

• Decrease wear and tear on the compression module, capacity control system and

motor by reducing excessive compressor cycling.

• Eliminate pulsations from the discharge line.

• Separate some of the moisture, oil and solid particles that might be present in the

air.



Figure 3.3: Air receiver tank

• The compressor or that may be carried over from the after cooler.

• Help reduce dew point and temperature spikes that follow regeneration.

• Offer additional storage capacity made to compensate for surges in compressed air

usage.

• Contribute to reduced energy costs by minimizing electric demand charges associated

with excessive starting of the compressor motor.

3.1.3 Pressure switch

A pressure switch is a form of switch that closes an electrical contact when a certain

set pressure has been reached on its input. The switch may be designed to make contact

either on pressure rise or on pressure fall.

Fluid pressure switch

A pressure switch for sensing fluid pressure contains a capsule, bellows, Bourdon tube,

diaphragm or piston element that deforms or displaces proportionally to the applied pres-

sure. The resulting motion is applied, either directly or through amplifying levers, to a

set of switch contacts. Since pressure may be changing slowly and contacts should operate



quickly, some kind of over-center mechanism such as a miniature snap-action switch is

used to ensure quick operation of the contacts. One sensitive type of pressure switch uses

mercury switches mounted on a Bourdon tube; the shifting weight of the mercury provides

a useful over-center characteristic.

The pressure switch may be adjustable, by moving the contacts or adjusting tension

in a counterbalance spring. Industrial pressure switches may have a calibrated scale and

pointer to show the set point of the switch. A pressure switch will have a differential range

around its set point in which small changes of pressure do not change the state of the

contacts. Some types allow adjustment of the differential. ]

The pressure-sensing element of a pressure switch may be arranged to respond to the

difference of two pressures. Such switches are useful when the difference is significant, for

example, to detect a clogged filter in a water supply system. The switches must be designed

to respond only to the difference and not to false-operate for changes in the common mode

pressure.

The contacts of the pressure switch may be rated a few tenths of an ampere to around 15

amperes, with smaller ratings found on more sensitive switches. Often a pressure switch

will operate a relay or other control device, but some types can directly control small

electric motors or other loads.

Since the internal parts of the switch are exposed to the process fluid, they must be

chosen to balance strength and life expectancy against compatibility with process fluids.

For example, rubber diaphragms are commonly used in contact with water, but would

quickly degrade if used in a system containing mineral oil.

Switches designed for use in hazardous areas with flammable gas have enclosure to

prevent an arc at the contacts from igniting the surrounding gas. Switch enclosures may

also be required to be weatherproof, corrosion resistant, or submersible.

An electronic pressure switch incorporates some variety of pressure transducer (strain



gauge, capacitive element, or other) and an internal circuit to compare the measured

pressure to a set point. Such devices may provide improved repeatability, accuracy and

precision over a mechanical switch.

Pneumatic pressure switch

Uses of pneumatic pressure switches include:

• Switch a household well water pump automatically when water is drawn from the

pressure tank.

• Switching off an electrically driven gas compressor when a set pressure is achieved in

the reservoir

• Switching off a gas compressor, whenever there is no feed in the suction stage.

• In-cell charge control in a battery

• Switching on/off an alarm light in the cockpit of an aircraft if cabin pressure (based

on altitude) is critically low.

• Air filled hoses that activate switches when vehicles drive over them. Common for

counting traffic and at gas stations.

Hydraulic pressure switch

Hydraulic pressure switches have various uses in automobiles, for example:

• To switch on a warning light if engine oil pressure falls below a safe level

• In dust control systems (bag filter), a pressure switch is mounted on the header which

will raise an alarm when air pressure in the header is less than necessary to gain or

decline energy beyond the set value.

• To control automatic transmission torque converter lock-up



3.1.4 Tower-1 & Tower-2 or PSA Unit

There are 2 towers filled with special grade carbon molecular sieves (CMS) to absorb

o2, co2 & moisture present in the air. At the bottom of each tower a perforated plate is

welded to hold the activated alumina & CMS. Just above the plate, ceramic balls are put

to as a holding bed for activated alumina. Lumina are used to remove the moisture of the

air entering the CMS. The dry air is also tapped to operate the actuators and valves.

Above the alumina, the CMS is filled up to the straight portion of tower. A perfo-

rated plate on the top prevents CMS from flowing out by the wire mesh. A 50mm thick

loose coconut fiber is packed in the top above CMS to fix the absorbing bed. The upper

perforated plate compresses absorbent fill to avoid undesired void. The coconut fiber is

squeezed together when the cover is tightened. Cycle time of PSA unit is 1 minute + 1

minute.

Each tower has air inlet valve (v1 & v2) bottom, gas outlet valve (v7 & v8) at top and

exhaust outlet valve (v3 & v4) at bottom. Besides these, a valve v6 is for equalization at

the top and a valve v5 after exhaust valve (v3 & v4) at the bottom. The air inlet line

from air receiver has a global valve v9 to control the flow of air, so that the pressure in the

absorbing tower goes up to 7.0kg/cm2g maximum.

3.1.5 Nitrogen surge vessel

Nitrogen from PSA unit will have varying purity in 1 minute cycle time. This surge

vessel gives nitrogen at constant pressure with a constant average purity. For analyzing

oxygen percentage in the nitrogen gas, one needle valve for sampling is provided in this

vessel.

In surge vessel, 1 NRV is fitted in reverse direction through which some of nitrogen gas

goes back to PSA towers during the pressurization cycle.



3.1.6 Oxygen analyser

An online oxygen analyzer continuously monitoring oxygen percentage in surge vessel.

Whenever oxygen percentage goes above the set valve, vent valve open. For more details

please refer percentage oxygen analyzer manual.

Method of analysis

The Nucon solid state oxygen analyzer model 4326 utilizes a unique micro-fuel cell to

electro chemical measure the concentration of oxygen in a gas stream. The cell has an

absolute zero and produces a linear output from the low level through 25% oxygen. No

zero gas is normally required and the instrument may be calibrated with air. However

where calibration gas is available, it is recommended for use. The instrument can be used

continuously online in the range 0-25%

Micro-fuel cell

The micro-fuel cell is sealed electrochemical transducer with no electrolyte to change

or electrodes to clean. When the cell reaches the end of its useful life (6 months minimum)

it is merely thrown away and replaces, as one would replace a battery in a flashlight. The

transducer housing located inside the instrument. To change the cell, open the bottom

screw on cover by hand and let it drop. The cell is now exposed. A typical microbial fuel

cell consists of anode and cathode compartments separated by a cat ion (positively charged

ion) specific membrane. In the anode compartment, fuel is oxidized by microorganisms,

generating CO2, electrons and protons. Electrons are transferred to the cathode com-

partment through an external electric circuit, while protons are transferred to the cathode

compartment through the membrane. Electrons and protons are consumed in the cathode

compartment, combining with oxygen to form water.



More broadly, there are two types of microbial fuel cell: mediator and mediator-less

microbial fuel cells.

Controls and operation

Gases used for calibration from cylinder or pipeline should be at pressure between 0.1

and 2.0kg/cm2 and should be clean dry.

1. Flow control needle valve:

It is located on I.H.S inside the instrument and used to set flow through the

analyzer, recommended flow is between 200 and 400 ml/min. to approach the needle

valve loosen the top nut on front panel. The front plate mounted on hinges at bottom

will come down. This expose the inside back. The adjustment can be done with the

instrument mounted on the panel.

2. Range selection:

Toggle switch on the panel are used to calibrate with all 0-25.0 position and used

at this position with sample.

3. Output:

Output is on Digital Display.

4. Recorded terminals:

These are provided at the back where a 0-1V D.C recorded can be connected for

permanent record or output.

5. Sensitivity/span/calibration:

It is by means of the Dial Setting on Turn potentiometer. An increase in reading

means higher sensitivity.

6. Alarm:

terminal strip. A few second delays is provided in action to avoid Chattering

Relay also a small positive feedback/ hysteresis is provided for the same purpose.



7. Pressure reduction and/or regulation:

We recommend that the sample pressure be reduced at the sample point to be-

tween 0.1 and 2.0kg/cm2. If the magnitude of the sample pressure does not exceed

25 psig and is reasonably stable, a sample throttle valve will be satisfactory. If, on

the other hand, the pressure is in excess of 25 psig or vacillates over wide range, a

regulator should be employed.

8. Shut off valve:

This is shut/open valve located inside front plate above the flow control needle

valve and is accessible on lowering the front plate, as in the case flow control needle

valve. It has two positions:

• CLOSE-The flow through system is closed.

• OPEN-The oxygen cell comes in flow path.

OPEN is CCW and Shut is CW.

9. Vent line instalation:

Whenever possible, we recommend that the analyzer be allowed to vent directly

to the atmosphere. If the vent line is required, the following conditions apply to the

installation:

• The vent line must constructed of 1/8” or 14” tubing (or equivalent),so that no

back pressure from restricted flow is experiences by micro fuel cell.

• The vent line must be terminated in area that experiences no more than normal

barometric pressure changes.

• The vent line must be installed so that water and dirt cannot accumulated in

it.

10. Normal working/sample start-up:

Check the inlet and outlet Blocking Nuts are removed from the Gas inlet parts

at the back open shut off Valve. Connect inlet gas. Adjust flow control valve so that



the sample gas flow is between 200 and 400 ml/min. Now the Oxygen Transducer

comes put main on. Wait for reading to stabilize. Take reading.

11. Calibration:

This is recommended only periodically e.g. once in two months.

There are two ways on calibration:

• By using atmosphere Oxygen. The level of oxygen in atmosphere is 20.9%sum-

mers or winters, India or abroad. Since the Galvanic Cell is linear up-to this

range and beyond, this property is used for calibration. Compressed air is sent

through the span port, selection valve is set to let air pass through the cell at

200 ml/min. (adjust by needle valve) and once reading is stable, adjust the span

Potentiometer on front panel to get a readout 20.9.

• By using a standard i.e a gas with known oxygen concentration. In this case

connect standard cylinder to inlet port at back of instrument, set flow control

valve on front panel to let standard pass. . . 200 to 400 ml/min.., place selec-

tion valve to OPERATE, allow to stabilize, adjust span potentiometer to read

whatever. . . . . . .the standard contains.

After calibration changes span gas with sample, flush for 5 minutes, allow to

stabilize, take reading.

12. Precuation:

• Cell should not be subjected to pass 10% atmosphere. The outlet port at back

of instrument should be open(no blocking/blanking nut should be there) when

inlet gas is connected. No flow would result in his were to happen but the

pressure would be transmitted to cell which is not desirable.

• When not in use (no gas flowing) atmosphere Oxygen can diffuse through the

outlet and reduce cell life. So place gas shut off valve to CLOSE position. If the

instrument is not in use for prolonged time for transportation of for storage, it



is recommended that the flow control valve be closed (close wise however do not

over tight as this can damage control valve seat) and the inlet and outlet parts

are blanked by means of blanking nut (standard 1/8” Nut with Rubber washer

for sealing)

• If gases used are not clean or dry appropriate filters/dryers before inlet to ana-

lyzer.

• If gases used are at high pressure use pressure Regulator with metal diaphragm

to reduce pressure. A working pressure between 0.1 and 2.0kg/cm2.

3.1.7 Nitrogen storage tank

A nitrogen storage tank is installed after the nitrogen surge vessel for storage of nitrogen

gas at pressure of 5.0kg/cm2g. Two numbers manual valves are provided at inlet and outlet

of tank. The plant is made to trip, by high pressure switch, when pressure of gas in tank

goes up-to 5.0kg/cm2g.

3.2 Hardware discription

3.2.1 Pre-filter & air inlet header

Incoming compressed air at 7.0kg/cm2g pressure from your compressed air system

passes through the pre-filter and enters the PSA unit via inlet header. In case of low air

pressure the low pressure switch will trip the PSA system and give audio-visual alarm.

3.2.2 Vent valve

This vent valve is a compressed air operated 3-way valve. Without compressed air

signal, its bottom port will be open to atmosphere and the gas initially of low purity will



go to atmosphere through this valve. This valve closes its bottom port when compressed

air signal will be available through solenoid valve and then nitrogen gas will go into the

intermediate storage tank.

3.2.3 Pressure Holding Valve (PHV)

A pressure holding valve is provided after the Rota-meter to maintain 5.5kg/cm2g

pressure in surge vessel. The setting of pressure holding valve can changed by adjusting

the provided at the top.

3.2.4 Solenoid valve

A solenoid valve is an electro-mechanical valve for use with liquid or gas. The valve is

controlled by an electric current through a solenoid: in the case of a two- port valve the

flow is switched on or off; in the case of a three-port valve, the outflow is switched between

the two outlet ports. Multiple solenoid valves can be together on a manifold.

Solenoid valves are the most frequently used control elements in fluidics. Their tasks

are to shut-off, release, dose, distribute or mix fluids. They are found in many application

areas. Solenoid offers fast and safe switching, high reliability, long service life, good medium

compatibility of the materials used, low control power and compact design.

Besides the plunger-type actuator which is used most frequently, pivoted-armature

actuator and rocker actuator are also used.

A solenoid valve has two main parts: the solenoid and the valve. The solenoid converts

electrical energy into mechanical energy which, in turn, open or close the valve mechani-

cally. A direct acting valve has only a small flow circuit, shown within section E of this

diagram (this section is mentioned below as a pilot valve). This diaphragm piloted valve

multiplies this small flow by using it to control the flow through a much larger orifice



Solenoid valves may use metal seals or rubber seals, and may also have electrical inter-

faces to allow for easy control. A spring may be used to hold the valve opened or closed

while the valve is not activated.

The diagram below shows the design of a basic valve. At the top figure is the valve

in its closed state. The water under pressure enters at A. B is an elastic diaphragm and

above it is a weak spring pushing it down. The function of this spring is irrelevant for now

as the valve would stay closed even without it. The diaphragm has a pinhole through its

center which allows very small amount of water to flow through it. This water fills the

cavity C on the other side of the diaphragm so that pressure is equal on both sides of the

diaphragm; however the compressed spring supplies a net downward force. The spring is

weak and is only able to close the inlet because water pressure is equalized on both sides

of the diaphragm.

In the previous configuration the small conduit D was blocked by a pin which is the

armature of the solenoid E and which is pushed down by a spring. If the solenoid is

activated by drawing the pin upwards via magnetic force from the solenoid current, the

water in chamber C will drop and the incoming pressure will lift the diaphragm thus

opening the main valve. Water now flows directly from A to F.

When the solenoid is again deactivated and the conduit D is closed again, the spring

need very little force to push the diaphragm down again and the main valve closes. In

practice there is often no separate spring, the elastomeric diaphragm is mounded so that

it function as its own spring, preferring to be in the closed shape.

When the solenoid is again deactivated and the conduit D is closed again, the spring

need very little force to push the diaphragm down again and the main valve closes. In

practice there is often no separate spring, the elastomeric diaphragm is mounded so that

it function as its own spring, preferring to be in the closed shape.From this explanation it

can be seen that this type of valve relies on a differential of pressure between input and



Figure 3.4: Solenoid valve

output as the pressure at the input must always be greater than the pressure at the output

for it to work. Should the pressure at the output, for any reason, rise above that of the

input then the valve would open regardless of the state of the solenoid and pivot valve.



3.2.5 Bourdon

The Bourdon pressure gauge uses the principle that a flattened tube tends to change

to be straightened or large circular cross-section when pressurized. Although this change

in cross-section may be hardly noticeable, and thus involving moderate stresses within

the elastic range tube into a C shape or even a helix, such that the entire tube tends to

straighten out or uncoil, elastically, as it is pressurized. Eugene Bourdon patented his gauge

in France in 1849, and it was wildly adopted because of its superior sensitivity, linearity,

and accuracy; Edward Ashcroft purchased Bourdon’s American patent rights in 1852 and

became a major manufacturer of gauges. Also in 1849, Bernard Schaeffer in Magdeburg,

Germany patented a successful diaphragm (see below) pressure gauge, which together

with the bourdon gauges, revolutionized pressure measurement in industry. But in 1875

after Bourdon’s patents expired, his company Schaeffer and Bubenberg also manufactured

Bourdon tube gauges.

In practice, a flattened thin-wall, closed-end tube is connected at the hollow end to

a fixed pipe contained the fluid pressure to be measured. As the pressure increases, the

closed end moves in an arc, and this motion is converted into the rotation of a (segment of

a) gear by a connecting link that is usually adjustable. A small- diameter pinion gear is on

the pointer shaft, so the motion is magnified further by the gear ratio. The positioning of

the indicator card behind the pointer, the initial pointer shaft position shaft position, the

linkage length and initial position, all provide means to calibrate the pointer to indicate

the desired range of pressure for variations in the behavior of the Bourdon tube itself.

Differential pressure can be measured by gauges containing two different Bourdon tubes,

with connecting linkages.

Bourdon tubes measure gauge pressure, relative to ambient atmospheric pressure, as

opposed to absolute pressure; vacuum is sensed as a reverse motion. Some aneroid barom-

eters use Bourdon tubes closed at ends (but most use diaphragms or capsules, see below).



Figure 3.5: Bourdon

When the measured pressure is rapidly pulsing, such as when the gauge is near a recip-

rocating pump, an orifice restriction in the connecting pipe is frequently used to avoid

unnecessary wear on the gears and provide an average reading; when the whole gauge is

subjected to mechanical vibration, the entire case including the pointer and indicator card

can be filled with an oil or glycerin. Tapping on the face of the gauge is not recommended

as it will tend to falsify actual readings thus has no effect on the actual reading of pressure.

Typically high-quality modern gauges provide an accuracy of +2% or -2% of span and a

special high- precision gauge can be as accurate as 0.1% of full scale.

In the following illusions the transparent cover faces of the pictured combination pres-

sure and vacuum gauge and has been removed and the mechanism removed from the case.

This particular gauge is a combination vacuum and pressure gauge used for automotive

diagnosis:



• The left side of the face, used for measuring manifold vacuum, is calibrated in cen-

timeters on its inner scale and inches of mercury on its outer scale.

• The right portion of the face is used to measure fuel pump pressure and is calibrated

in fraction of 1kg/cm2 on its inner scale and pounds per square inch on its outer

scale.

3.2.6 Rotameter

A rotameter is a device that measures the flow rate of liquid or gas in a closed tube. It

belongs to a class of meters called variable area meters, which measure flow rate by allowing

the cross-sectional area the fluid travels through to vary, causing some measurable effect.

Rotameter are popular because they have linear scales, a relatively large measurement

ranges, and low pressure drop, and are simple to install and maintain. Rotameter are a

subset of meters called variable area flow meters that measure the flow rate by allowing the

fluid to travel through a tapered tube where the cross-sectional area of the tube gradually

becomes greater as the fluid travels through the tube. The flow rate inside the rotameter

is measured using a float that is lifted by the fluid flow based on the buoyancy and velocity

of the fluid opposing gravity pulling the float down. For gasses the float responds to the

velocity alone, buoyancy is negligible.

The float moves up and down inside the rotameter’s tapered tube proportionally to the

flow rate of the fluid. It reaches a constant position once the fluid and gravitational forces

have equalized. Changes in the flow rate cause rotameter’s flow to change position inside

the tube. Since the float position is based on gravity it is important that all rotameters

be mounted vertically and oriented with the widest end of the taper at the top. It is also

important that if there is no flow the float will sink to the bottom of the rotameter due to

its own weight.

The operator reads the flow from a graduated scale on the side of the rotameter, which



has been calibrated to a specific fluid with a known specific gravity. Specific gravity or the

weight of the fluid has a great impact on the rotameter’s accuracy and reliability. All of

global Water’s rotameters have been calibrated using water as the standard fluid with a

specific gravity of 1.0.

Figure 3.6: Rotameter

Rotameters can be calibrated for other fluids by understanding the basic operating

principles. Rotameter accuracy is determined by the accuracy of pressure, temperature,

and flow control during the initial calibration. Any change in the density and weight of

the float will have impacts on the rotameter’s flow reading. Additionally any changes

that would affect the fluid such as pressure or temperature will also have an effect on the

rotameter’s accuracy. Given this, rotameter should be calibrated yearly to connect for any

changes in the system that may have occurred.



3.2.7 Pressure switch

A pressure switch is a form of switch that makes electrical contact when a certain set

pressure has been reached on its input. This is used to provide on/off switching from a

pneumatic or hydraulic source. The switch may be designed to make contact either on

pressure rise or on pressure fall.

Generally, a pressure switch is included in any type of equipment that includes com-

ponents that generate some type of pressure during operation. The pressure may relate

to electrical current, the flow of natural gas or liquids, or the creation of steam. With

each application, the pressure switch will include components that monitor the amount of

pressure generated, as long as the pressure remains within acceptable levels, the pressure

switch serves as an easy way to monitor activity. However, most switches will sound some

sort of alarm when the level of pressure begins to exceed what is considered a safe range.

Designs for the pressure switch vary, based on the type of action that is required. When

manual intervention is desired, the pressure switch is often constructed as a toggle switch.

This design allows for easy operation when an alarm sounds and there is a need to either

activate a venting process or immediately shut-down the machinery. For switches that

are configured to work in conjunction with computer technology, a micro switch design is

common. The micro switches receives commands from the computer program once a safety

shut-down or a pressure release is determined to be the next logical step in the sequence.

Since the inception of the pressure switch, the device has proven to be an ideal means of

preventing a number of injuries that could result from an overload or explosion. Just about

every piece of machinery that employs the use of compressors will include a pressure switch

at key phases as part of the safety requirements for operation of the equipment. While

automated switches have become more popular in recent years, manual pressure switches

are still often installed as a backup that can be utilized in the event of an electrical failure.



Figure 3.7: Pressure switch

Pneumatic:

Uses of pneumatic pressure switches include:

• Switching off an electrically driven gas compressor when a set pressure is achieved in

the reservoir.

• Switching off a gas compressor, whenever there is no feed in the suction stage.

• In-cell charge control in a battery.

• Switching on/off an alarm light in the cockpit of an aircraft if cabin pressure (based

on altitude) is critically low.

Hydraulic:

Hydraulic pressure switches have various uses in automobiles, for example:

• To switch on a warning light if engine oil pressure falls below a safe level.



• To switch on brake lights automatically by detecting a rise in pressure in hydraulic

brake pipes.

• In dust control system (bag filters), pressure switch is mounted on the header which

will raise an alarm when air pressure in the header is less than necessary to gain or

decline energy beyond the set value.

Setting of switching points

Set-up

A pressure source and a master gauge of accuracy better than 0.5% is required to set

the actuating point. In the case of Differential Pressure switches connect the pressure

source to the high pressure port and leave the low pressure port vented to atmosphere.

Switching point should preferably lie in the mid 50% of the adjustable range span. Arkings

provided on the range scale are for guidance only. To set switching points precisely use a

master Pressure Gauge. The switching point can be set, either for in pressure or in rise in

pressure by rotating the Range Adjusting screw. Remove the instrument cover. Unscrew

and remove the lock plate, which prevents the movement of the Range screw.

Now proceed with the setting of the switching points as below:

Fixed on-off differntial models:

• Rotate the range adjustment screw clockwise to increase the switching point. Rotat-

ing anti-clockwise will decrease the switching point.

• After setting, re-fix the locking device back in position to prevent unauthorized ad-

justment of the set point.

3.2.8 Air filter regulator

A Pressure Regulator is a value that automatically cuts off the flow of a liquid or gas at

a certain pressure. Regulators are used to allow high-pressure fluid supply lines or tanks

to be reduced to safe and/or usable pressure for various applications.



Gas pressure regulators are used to regulate the gas pressure and are not appropriate

for measuring flow rates. Flow meters, Rotameters or Mass Flow Controllers should be

used to accurately regulate gas flow rates.

Operation

A pressure regulator’s primary function is to match the flow of gas through the regulator

to the demand for gas placed upon the system. If the load flow decrease, then the regulator

flow must decrease also. If the load flow increases, then the regulator flow must increase

in order to keep the controlled pressure from decreasing due to a shortage of gas in the

pressure system.

A pressure regulator includes a restricting element, a loading element, and a measuring

element:

• The restricting element is a type of valve. It can be a globe valve, butterfly valve,

poppet valve, or any other type of valve that is capable of operating as a variable

restriction to the flow.

• The loading element applies the needed force to the restricting element. It can be

any number of things such as a weight, a spring, piston actuator, or more commonly

the diaphragm actuator in combination with a spring.

• When the actuator is forced against an expansion desk, the force is distributed among

he pressure walls. This allows the gas to flow at the proper rate and not to be

continually vaporized and diluted.

• The measuring element determines when the inlet flow is equal to the outlet flow.

The diaphragm is often used as a measuring element because it can also serve as a

combine element.

In the pictured single-stage regulator, a diaphragm is used with a poppet valve to regulate

pressure. As pressure in the upper chamber increases, the diaphragm is pushed upward,



Figure 3.8: Pressure regulator

causing the poppet to reduce flow, bring the pressure back down. By adjusting the top

screw, the downward pressure on the diaphragm can be increased, requiring more pressure

in the upper chamber to maintain equilibrium. In this way, the outlet pressure of the

regulator is controlled.

Applications

• Water pressure reduction

Often, water enters water-using appliances at fluctuating pressure, especially in

remote locations, and industrial settings. This pressure often needs to be kept within

a range avoid damage to appliances, or accidents involving burst pipes/conduits. A

single-stage regulator is sufficient in accuracy due to the high error tolerance of most

such appliances.

• Oxy-fuel welding and cutting

Oxy-fuel welding and cutting processes require gases at specific pressure, and

regulators will generally be used to reduce the high pressure of storage cylinder to

those usable for cutting and welding. Oxy-gas regulators usually have two stages:



The first stage of the regulator releases the gas at a constant rate from the cylinder

despite the pressure in the cylinder becoming less as the gas is released. The second

stage of the regulator controls the pressure reduction from the intermediate pressure

to low pressure. It is constant flow. The valve assembly has two pressure gauges, one

indicating cylinder pressure, and the other indicating hose pressure.

• Propane/lp gas

All propane and LP gas applications require the use of a regulator. Because

pressure in propane tanks can fluctuate significantly, regulators must be present to

deliver a steady flow pressure to downstream appliances. These regulators normally

compensate for tank pressure between 30-200 psig and commonly deliver 11 inches

water column (0.4 psig) for residential applications and 35 inches of water column (1.3

psig) for industrial applications. Propane regulators differ in size and shape, delivery

pressure and adjust-ability but are uniform in their purpose to deliver a constant

outlet pressure for downstream requirement. As is the case in all regulators, outlet

pressure is lower than inlet pressure.

3.2.9 Three way vent valve

3 way vent valve after nitrogen surge vessel is a pneumatic operated 3 way valve.

With no instrument air signal, its bottom port is open to atmosphere. Thus when the gas

generator is started the gas ,initially of low purity will be vented to atmosphere through this

3 way valve. This valve closes its bottom port when it gets compressed air through solenoid

valve and then nitrogen gas starts going to storage tank. In case of any abnormality in the

plant, 3 way vent valve bottom port will open automatically and the gas will be vented to

atmosphere.



Figure 3.9: Three way vent valve

3.3 Software description

3.3.1 Programmable Logic Controller (PLC)

A programmable logical controller (PLC) is an industrially hardened computer-based

unit that performs discrete or continuous control functions in a variety of processing plant

and factory environments. Originally indented as relay replacement equipment for the

automotive industry, the PLC can now be found in some part of virtually every part of

industry imaginable.



3.3.2 Why PLC is used instead of relay

Relay based system has:

• Low reliability due to electro-mechanical components.

• Complex and tedious wiring.

• Higher maintenance and modification cost.

• Higher down time.

• Occupies larger space.

• No support for Batch Processing.

3.3.3 Advantages of PLC

• High speed manufacturing.

• Fast switching.

• Less power consumption.

• Comparatively low cost for large systems.

• Ability for batch production.

• Reusability.

• Easy troubleshooting and modification.

3.3.4 Some procedures of PLC

• Allen Bradely.

• Siemens.

• Omron.

• Milsubishi.

• General Electric Fanuc.

• Messung.



3.3.5 PLC block diagram

Figure 3.10: Block diagram of PLC

• Input Module

Inputs are defined as real world signals giving the controller real-time status of

process variables. These signals can be analog or digital, low or high frequency,

maintained or momentary.

• Output Devices

There are devices which are used to indicate or work by using processor output.

The output devices are given below.

1. Pilot lamp.

2. Annunciator.

3. Solenoid valve.



4. MCC.

5. Relay coil.

Most I/O systems are modular in nature that is a system can be arranged by use

of modules that contain multiples of I/O point.

• Central Processor Unit (CPU) The central processor unit (CPU) or central

control unit (CCU) which is a real time processor performs tasks necessary to fulfil

the PLC function. Among these tasks are scanning, I/O bus traffic control, program

execution, peripheral and external device communication, special function or data

handling execution and self-diagnostics.

The CPU use TTL (Transistor-Transistor Logic), CORE (ferric core), CMOS

(Complementary Metal Oxide Silicon) or VLSI (Very Large System Integration).

Here TTL is faster (faster scan time), CORE require no battery, CMOS is more

compact and require low power level and VLSI is both more powerful and more

flexible.

Normally CPU is off microprocessor based or micro controlled type.

• Memory Unit

The memory unit of the PLC serves several functions. It is the library where the

application program is stored. It is also where the PLC‘s executive program function

as the operating system of the PLC. It is the program that interprets, manages and

executes the user‘s application program. Finally the memory unit is the part of the

programmable controllers where process data from the input modules and control

data for the output modules are temporarily stored as data tables.

Memory can be volatile or non-volatile. Volatile memory is erased when power is

removed, so always battery backup is provided.

The basic programmable controller memory is the word. A word is a collection of

4, 8, 16 or 32 bits that is used to transfer data about PLC. As word length increases,



more information can be stored in memory.

• Power Supply

The power supply drives the I/O logic signals, the central processor unit, the

memory unit and some peripheral devices. It is necessary to protect the solid state

devices from most high voltage line spikes. So the power supply converts power line

voltage to those required by the solid state components.

• Programmer Unit (Hand Held)

The programmer unit provides an inference between the PLC and the user during

program development, start up and troubleshooting. The instruction to be performed

during each scan are coded and inserted into memory with the programmer.

• Communication Interface

This is the PLC‘s window to outside world. The function of communication

inference is programming, monitoring the PLC and its activities. Varies Series Com-

munication protocols used are

–>RS-232

–>RS-422

–>RS-485

3.3.6 Different types of PLCs

There are two types of PLCs:

1. Fixed I/O PLC.

2. Modular I/O PLC.

3.3.7 Programming documentation

The following techniques can be used for PLC programming applications.



1. Develop detailed I/O list, this list should be used extensively. Starting without it

will cause confusion and error resulting from inevitable changes.

2. Develop a detailed descriptive operational sequence of events.

3. Develop electrical schematic or ladder diagram for sequential control.

4. Develop piping and instrumentation drawings for process control (also logic diagram).

5. Translate the diagram (step 3 & 4) to programmable controller language.

6. Enter the program code using memory map.

7. Debug the program at the programmer‘s ability.

8. Save and document the program.

9. Enter and debug the program at the field.

10. Re document and reproduce the final program

3.3.8 PLC installation

Installation of programmable controller system is not a difficult or mysterious proce-

dure, but the following general rules will save time and trouble for the systems designer

or installer. Safety rules and practice governing proper use of electrical control equipment

in general should be observed. These include correct grounding techniques, placement of

disconnect devices, proper selection of wire gauge, fusing and logical of the device.

Programmable logic controller requires sequential execution with a scan starting with

task 1 and proceeding through task 4.

PLC is designed to operate in real time control environment.

PLCs are designed to operate near the equipment they are meant to control.

PLC must be maintainable by plant electrician or instrument technician.

PLCs are more flexible.



3.3.9 Ladder diagram

Ladder diagram is a special schematic representation of the hardware and its connection

has been developed that makes combination of the hardware and event sequence descrip-

tion. It is an outgrowth of early controllers that operated from ac lines and used relays as

the primary switching elements.

3.3.10 Control relays

Relays can be used for much more than just an energy level translator. An example

is given below: When we push push-button (PB1), the relay (RL1) operates which close

Figure 3.11: Example for control relay

the valve/switch so that motor gets voltage to work. Here the switch is of normally open

type. That is if there is no signal, the switch is open.Special symbols used for represent

the various circuit element in a ladder diagram is shown below.

Control relay coil

A control relay coil is represented by a circle identified by CR and associated identifying

number as shown below.



Figure 3.12: Symbol Control relay

Figure 3.13: Symbol CR1 (NO) and CR1 (NC)

Time delay relay

In this type of delay, the contacts do not active until a specified time delay has occurred.

This coil is still indicated by a circle, but with the designation of TR to indicate timer

delay. The contacts are shown below. The above figure is the type of on-delay timer

Figure 3.14: Symbol Time relay

Figure 3.15: symbol TR1 (NO) and TR1(NC)

relay. When the coil is energized, the contacts are not energized until the time delay has



lapsed. The other type of time delay relay is off-delay timer relay, in which the contacts

engage when the coil is energized. But when the coil de-energized, the contacs are not

de-energized until the time delay has lapsed.

Motors

The symbol for motor is a circle with designation of M followed by a number as shown

in figure. The control system treats this circle as the actual motor, although in fact, this

Figure 3.16: Symbol Motor

may be a motor start system. This is also used to represent the ‘fact’ of motor.

Solenoids

Figure 3.17: Symbol SOL1

The solenoid symbol is shown in figure. Of course, the symbol itself tells nothing of

what function the solenoid plays in the process.



Light

Figure 3.18: Symbol Light

The light symbol is shown in above figure is used to give operator information about the

state of system. The color of light is indicated by a capital letter in a circle; for example,

R stands for Red, G stands for Green, A for Amber and B for Blue.

Switches

One of the primary input elements in a discrete state control system is a switch. The

switch may be normally open (NO) or normally closed (NC) and may be activated from

many sources. Different types of switches/symbols are given below.

1. Push Button Switches

Figure 3.19: Symbol PB1 (NO) and PB1 (NC)

These switches are typically used for operator input, such as to stop and/or to

start a system.

2. Limit Switches

These switches are used to detect physical motions limit within the process.



Figure 3.20: Symbol LS1 (NO) and LS1 (NC)

3. Pressure Limit Switches

Figure 3.21: Symbol PS1 (NO) and PS1 (NC)

3.3.11 Features of ALLEN BRADLEY’S SLC 503

The SLC processors offer a wide range of choices in memory, I/O capacity, instruction

set, and communication ports to allow you to tailor a control system to your exact appli-

cation requirements. These products have a strong reliability history covering hundreds of

thousands of installations in a broad range of applications.

SLC 5/03 processors let you configure modular controllers of up to 4096 inputs plus

4096 outputs and a memory of 8K, 16K, or 32K words. In addition, they have a second

built-in communication port—an RS-232-C port that can be configured for ASCII or DF1

protocol, and can be configured for connection to a 1761-NET-AIC converter to provide

access to a DH-485 network. SLC 5/03 processors provide bit-instruction execution times

of 0.44 ms and an overall system throughput of up to 10 times faster than competitive

processors. Additional capabilities include: floating-point math, online programming and

run-time editing, flash memory upgrades, built-in key-switch, and a built-in real-time clock

and calendar.



Adventages of SLC 5/03

• Simple and affordable processors with broad capabilities to address applications such

as material handling, HVAC control, assembly operations, small process control, and

SCADA applications.

• Advanced instruction set based on PLC-5 mid-size processors

• SLC 5/03 processor have communication ports (Ethernet, DH+, DH-485, or RS-232-

C) that can initiate communication.

Addressing syntax

1. SLC 5/03 I/O files

F: ss.www/bb

F File type:

I = Input

O = Output

ss I/O slot number: 0 – 30 decimal

Www (optional)I/O word number expansion: 0 – 255 decimal

bb(optional)Bit offset within word: 0 – 15 decimal

When input slot is 0: 0 – 23 decimal

Example: I: 22.254/13

2. SLC 5/03 Binary Files: Optional Syntax

Fnnn/bbbb

F File type

B = Binary

nnn(optional)File number: 3, 9 – 255 decimal

For direct driver communication, the default file number 3 is used if the file

number



is absent.

bbbb Bit offset from start of file: 0 – 4095 decimal

Example: B3/3999

3. SLC 5/03 Timers, Counter, and Control Files

Fnnn:eee.MNE/bb

F File type:

T = Timer

C = Counter

R = Control

nnn (optional) File number: Timer: 4, 9 – 255 decimal

Counter: 5, 9 – 255 decimal

Control: 6, 9 – 255 decimal

For direct driver communication, timer, counter, and control file types use the

default file number if the file number is absent. The default numbers are 4 (timer),

5 (counter), and 6 (control).

eee Element number: 0 – 255 decimal

MNE Member mnemonic (see mnemonic tables

Starting on page D-30)

Bb (optional) Bit number: 0 – 15 decimal

Applies to analog members only. Example: R67:123.EN

4. SLC 5/03(Enhanced) I/O files

F: ss.www/bb

F File type:

I = Input

O = Output

ss I/O slot number: 0 – 30 decimal



www(optional)I/O word number expansion: 0 – 255 decimal

bb(optional)Bit offset within word: 0 – 15 decimal

When input slot is 0: 0 – 23 decimal

Example: I:22.254/13

3.3.12 RS Logix500

The RSLogixTM family of IEC-1131-compliant ladder logic programming packages helps

you maximize performance, save project development time, and improve productivity. This

family of products has been developed to operate on Microsoft R© Windows R© operating sys-

tems. Supporting the Allen-Bradley SLCTM 500 and MicroLogixTM families of processors,

RSLogixTM 500 was the first PLC programming software to offer unbeatable productivity

with an industry-leading user interface.

3.3.13 Benefits

RSLogix programming packages are compatible with programs created with Rockwell

Software’s DOS-based programming packages for the SLC 500 and MicroLogix families of

processors, making program maintenance across hardware platforms convenient and easy.

In addition, RSLogix 500 benefits include:

1. Ladder

Edit several rungs simultaneously and/or program using symbols that are not yet

assigned addresses to using the Program Editor.

2. Cross-Reference information

Move to any rung or instruction that need by clicking on the cross-referenced item

using the online Cross-Reference. View cross reference information simultaneously

with your control program online or on a project.

3. Drag-and-Drop editing



Add addresses to instructions by dragging them from the Data Table Monitor,

Database Files, or the Address/Symbols Picker to the desired instruction, or quickly

move instructions within a project or from one project to another, or move data table

elements from one data file to another.

4. Diagnostics

Locate problem areas in your application using Advanced Diagnostics. Locate and

replace addresses and description text easily using Search and Replace. Examine the

status of data table elements simultaneously with the Custom Display Monitor.

5. Dependable Communications

Rockwell Software’s RSLinx provides quick and accurate setup, and auto-

detection and configuration of communication parameters.

6. Database editing

Build and classify groups of symbols using the Symbol Group Editor. Assign

addresses or symbols to ladder instructions using the Symbol Picker.

7. Reporting

Let’s preview every detail of your data before sending it to a printer.

8. Compatibility

RSLogix provides compatibility with Rockwell Software’s popular MS-DOS pro-

gramming products: A.I. Series PLC-500 and MicroLogix 1000, and APS for SLC

500 and MPS for MicroLogix 1000,A.I series PLC-5 and 6200 series PLC-5.

9. Interoperability

Satisfy all of your application needs with Rockwell Software’s completely inter-

operable solutions.



3.3.14 RS-Linx

RSLinx ClassicTM is the most widely installed communication server in automation to-

day. RSLinx Classic provides plant-floor device connectivity for a wide variety of Rockwell

Software applications such as RSLogixTM 5/500/5000 and RSView32. RSLinx Classic also

provides open interfaces for third-party HMI, data collection and analysis packages, as well

as custom client-applications. RSLinx Classic supports multiple software applications

3.3.15 RS Emulate 500

RSLogix Emulate 500 is Microsoft Windows-based software package that emulate one

or more PLC-5, SLC 500 processors respectively. RSLogix Emulate scans the ladder logic

like an actual processor.

3.3.16 Supervisory Control And Data Acquistion (SCADA)

SCADA is the technology that enables a user to collect data from one or more distant

facilities and/or send control instructions to those facilities. SCADA makes it unnecessary

for an operator to be assigned to stay at or to visit, remote locations in the normal oper-

ation of that remote facilities. SCADA is an acronym of Supervisory Control And Data

Acquisition. Even though the distance is the main factor in this facility, it does not appear

in this acronym. A SCADA system allows an operator, in a location, central to a widely

distributed process such as an oil or gas field, pipe line system, or hydroelectric generating

complex, to make set point changes on distant process controllers, to open or close valve

or switches, to monitor alarms, and to gather measurement information.

When the process become very large (hundreds or even thousands of kilometers from

one end to another), the benefits in terms of reduced cost of routine visit is of great

importance.



3.3.17 Elements of SCADA system

At the center is the operators, who access the system, by means of an operator interface

device, which is sometimes called an operator I/O. The operator output is usually a CRT

(VDU, Video display unit) and its input is computer keyboard, track balls etc. MTU is a

system controller which almost always a computer. So it can read from RTU and control

even though the operator is not there. RTU can respond MTU through cable or radio.

Each RTU have the capability to understand message, read message, direct the message

and shutdown. Because of the complexity, most RTUs are computer based technology.

In the same way MTU scans RTU, RTU scans sensors, actuators that are wired into it.

This scanning rate is higher than MTU scanning rate. The electrical power required for

both actuators and sensors is usually supplied by RTU only. In some cases there may be a

UPS to ensure that utility power failures do not result in process or safety upsets. SCADA

technology is best applied to process that are spread over large areas, are relatively simple

to control and monitor, and require frequent, regular, or immediate intervention. Every

technology has some applications for which it suits exactly, other applications for which

suits marginally, and a group of applications for which it should not be used

3.3.18 SCADA implementation

It is implemented using the Software Rockwell Automation‘s RS View 32 for the

SCADA, and associated communication tool RSLinx.

3.3.19 Communication in SCADA

The justification for installing SCADA is usually based on the remoteness of a site and

the difficulty or cost of manning it. In some cases, it is dangerous, unhealthy or unpleasant

for a person to be at the site. Communication plays a vital role in the operation of a



SCADA system. There are several means by which electronic machines can talk among

themselves.

1. Communication Access

Depending on the purpose of conversion, the speed requirements, and the ma-

chine‘s status relative to each other, different access methods may be used. The

communication requirements both determine and are controlled by the communica-

tions protocol selected. The communications method used by most SCADA systems

is called master slave‘. In a master slave arrangement, only one machine (the master,

MTU in this case) is capable of initiating communication. The MTU calls one RTU,

gives instructions, asks for information updates, and orders the RTU to respond.

The MTU then listens for the answer. The RTU answers as soon as the MTU has

finished talking, then stops talking and listens for more orders. The MTU moves to

the second RTU and goes through the same procedure.

2. Modem and Protocols

The MTU and RTU have the ability to formulate a signal that contains the

intelligence that must be sent. They also have the ability to interface with the

medium. This interfacing function is performed by equipment called Modem‘which

stands for modulator-and-demodulator. In telecommunication terminology, the MTU

and RTU are called as data terminal equipment‘(DTE) and modem is called as data

communication equipment‘(DCE). This interface is shown below. While transferring

Figure 3.22: Modems and Protocols

binary sequences from MTU to RTU and vice-versa, they should be bound to certain



rules to send the data, clock signal and address of the RTU, the schemes used for

communication. To ensure efficient transfer of data between the MTU and RTU,

they must use the same protocols. Detailed and standard protocols are developed

with the seven layer ISO-OSI communication model. The lower two layers, namely,

physical and data link layers, are sufficient for most SCADA systems.

3. Radio Communication

Radio communication used for SCADA is somewhat more complex than the wire

communication. Depending on the ability of a communication system, they are clas-

sified as Simplex, Half duplex and Full duplex systems. Simplex systems are those

which can transfer the information only in one direction. Commercial broadcasting

radio is an example of this category. But for supervisory control applications, the

data must move in both the directions. In half duplex systems, both the stations

communicating with each other will be having both transmitter and receiver associ-

ated with them, but they have only one communication path or link. Because of this

single communication path, only one station can transmit at any time and the other

station will be in receiving mode during this time. After this is over, if it is required,

the second station can transmit, while the first station is in receiving mode.

In full duplex systems, there exist two communication paths. Both the stations

will be capable of transmitting and receiving, at any time. Path study is an important

aspect in radio communication. Because the communication is line of sight, the

detailed path study with the help of topographical maps is essential, especially to

see whether there are any hills lying between the transmitter and receiver, and to

change the locations of transmitter or receiver accordingly.

Transmitter power, antenna gain, losses as functions of distance and other similar

things have to be treated to think about the need of repeater and its location. The

last but not the least aspect is to consider the solar disturbance. The only way to



minimize these disturbances is to design for a high signal to noise ratios.

4. Satellite Communication

Geosynchronous communication satellites are gaining their popularity in recent

years, to make use of them for SCADA applications. But for very large systems

such as pipelines and electrical transmission lines, especially in remote and poorly

developed areas, this may be the most cost-effective method.

Its principle is simple. Each of the RTUs and the MTU has access to an antenna

that is pointed at a satellite that stays over the same spot (geosynchronous). The

satellite acts as a radio repeater, receiving data from one station and sending it to

the others.

3.3.20 Applications

SCADA has the application in the field of Real-Time control, Advisory applications,

accounting and grade of data and in automatic control also. These are discussed below.

1. Real-Time Applications

A real time control system is one that introduces no time delay or dead time

between receiving a process measurement and outputting a control signal. But in

practice, nearly all control systems will introduce some time delay. So, the control

systems that introduce an amount of time-delay without any measurable effect are

usually called real-time control systems. SCADA can not be categorized as real-time‘.

But MTU scans each RTU on a periodic basis to observe the status of different control

points and pass the necessary commands for their control.

2. Automatic Control

SCADA can result in automatic control of process. This statement may appear

somewhat confusing to somebody who thinks that SCADA must be automatic be-

cause it involves a highly sophisticated computers and other equipment. To clear



this doubt it may be worth to recall that it is supervisory control’ only. Operator is

responsible to do any type of control at any time, but not the computer.

But at present, the increased reliability of communication networks and increased

speed and power of MTU computers have encouraged system designers to shift toward

automatic control. Otherwise SCADA is manual only.

3. Advisory Applications

It is another category of applications gaining appreciation in the recent years. It

was observed that almost all control applications with SCADA systems require the

presence and intervention of operator at one or the other stage, even if it is thought

to be completely automatic.

In advisory applications, the system gathers data from many locations over a

wide geographical area, integrating it, and making it digestible by the operator and

presents it as advice. The required control action is taken by operator only. So,

these applications are partly automatic and partly manual also. For example, in the

application of pipeline leak detection, the MTU may warn the operator that there

is a leak probably. But, if the operator knows that the meters are being calibrated

that day, the decision may be made not to shut in the line.

3.4 Flowchart

Flow-chart diagrammatic is shown in the figure: 3.23. This Flow-chart gives the entire

idea for the working principle of the automation. Initially the process starts from the air

receiver tank. when pressure in the air receiver tank is exceeds 7kg/cm2 the valve v9 opens

and it starts operation. The PSA process cycle consists of 2key mechanisms:

• Adsorption

• Desorption



Figure 3.23: Flow chart

When first tank 1works for 40 seconds the second one regenerates. At this time ad-

sorption takes place for tank 1 and the valves v1, v4 and v7 were open. simultaneously all

other valves get closed for the process to take place. Nitrogen generated in first tank pass



to the surge vessel for a temporary storage. Within another 10 seconds both tank equalize

the pressure with valves v5 and v6 were open. Next 40 seconds adsorption take place

for tank 2 and at this time first tank generated and the impurities gets released through

the silencer. Nitrogen generated in tank 2 reaches the storage tank through v2, v3 and

v8. Next 10 seconds both tank equalize the pressure similarly as above. This operation

alternatively repeated in both tanks. After the process of storing in the surge vessel it gets

transferred to the main storage tank. but in between the surge vessel and storage tank

there is a special device known as the oxygen analyzer for analysis of oxygen contend in

the purified product. When the amount of oxygen is less than o.7% ,it reaches the storage

tank. Otherwise it is vented back to air. Then from storage tank it is used for further uses.

3.5 Specification of equipments

1. AIR LINE DUST FILTER:

• Type: coalescing filter

• Model: AO80G

• Outlet oil and dust content: 0.5 ppm

2. PSA TOWER:

• Size: 500[U+1DB2] X 1200 ww

• MOC: SS-316L

• Op. pressure: 7.0 kg/cm2g

• Type: composite bed

– Bottom: alumina balls-35lt/tower

– Top: CMS Bed – 225lt/tower

• N2 generation capacity: 50 NM3/ hr. , 99.5% purity

3. PSA Valves:



• Make: Rotex

• Type: angle, double acting pneumatic on/off design

• Size: 25 NB

• MOC: SS 316 L valves

• Quantity: 8 Nos.

4. N2 SURGE VESSEL:

• Size: 1100 [U+1DB2] x 1200 ww

• Op. pressure: 7.0 kg/cm2g

• MOC: SS 316 L

5. NITROGEN ROTAMETER

• Make: flow star

• End connection: 25 NB

• Op. pressure: 7 kg/cm2g

• Range: 7.0-70.0 NM3/hr.

6. THREE WAY VENT VALVE:

• Type: 3 way ball valve

• Size: 25 NB

• MOC: SS 316 L

• Actuator: PD- 60, Elomatic

7. AIR SOLENOID VALVE:

• Make: Rotex

• Type: 4”, 5 port , Namur- 8 Nos

• Type:4”, 3 port-4Nos

• Type:4”, 2 way – 1 No

• Voltage: 220 V AC

• Air pressure: 7 kg/cm2g



8. LOW PRESSURE SWITCH AT AIR INLET:

• Make: switzer

• Model: GH-901-2D

• Range: 0-7 kg/cm2g

9. PLC FOR PSA VALVES OPERATION:

• Make: SIEMENS PLC – LOGO

• Model: logo – 230 RC

• Voltage: 220 volts

10. OXYGEN ANALYZER:

• Make: MVS (H)

• Oxygen range: 0-100

• Model: OMPC-D-001

• Sensor type: Electrochemical


Chapter 4

RESULTS AND DISCUSSIONS

4.1 Experimental setup


other associated paraphernalia. When the pressure in compressor exceeds 7 kg/cm2, it


adsorbed by the CMS (carbon molecular sieve) and nitrogen is separated.The first tank


both tank equalize the pressure. Nitrogen generated in first tank pass to the storage tank,


the operation repeated in the second tank. Both tanks operate simultaneously one after

another with an interval of 58 second. So that process is continued and nitrogen storage

tank is filled as required. A nitrogen storage tank is installed after nitrogen surge vessel

for storage of nitrogen gas at pressure of 5.0 kg/cm 2. Two manual valves are provided at

inlet and outlet of tank.The plant is made to trip, by high pressure switch, when pressure

of gas in the tank goes up to 5.0kg/cm2.

57


4.2 Results and inference

1. Adsorption and other technologies for air separation continue to advance as more

efficient, highly packaged, and compact gas generators are developed.

2. Increased power efficiency in PSA nitrogen generators is being driven both by process

improvements and enhanced adsorption materials.

3. Virtually any industry can benefit from nitrogen’s unique properties to improve

yields, optimize performance, project product quality and make operations safer.

4. Nitrogen is valued both as a gas for its inert properties and as a liquid for cooling &

freezing.

4.3 Advantages

1. Nitrogen generators are efficient in continuous nitrogen supply.

2. The plant is secure and reliable.

3. Easy to operate by using PSA technology.

4. Reduce storage cost.

5. Minimize support and maintenance.

6. Nitrogen purity is high.

4.4 Disadvantages

1. The oxygen content increases when explosion occurs in the storage tank.

2. Time delay depends on the proper working of oxygen analyzer.



4.5 Limitations

• The plant is working until the storage tank is full. When the tank is full, process is

stop.

4.6 Future scope

• Increase the purity of nitrogen up to 99.9%.


Chapter 5

CONCLUSION

As per the project “Nitrogen plant automation using PLC & SCADA” highlights the

process of manufacture and quantity control with the automation process in the industry.

Nitrogen is valued both as a gas for its inert properties and as a liquid for cooling &

freezing. Virtually any industry can benefit from nitrogen’s unique properties to improve

yields, optimize performance, project product quality and make operations safer.

Adsorption and other technologies for air separation continue to advance as more ef-

ficient, highly packaged, and compact gas generators are developed. Increased power ef-

ficiency in PSA nitrogen generators is being driven both by process improvements and

enhanced adsorption materials. Nitrogen users will benefit from these advances as they

evaluate supply options for nitrogen facilities and manage increased demand at existing

plants

60

Bibliography

[1] Svetlana Ivanova, Robert Lewis,” Producing Nitrogen via Pressure Swing Adsorption-

Reactions and Separations”.

[2] “Memo 3 preliminary design of nitrogen processes: PSA and Membrane systems”

CARNEGIE MELLONUNIVERSITY CHEMICAL ENGINEERING DEPARTMENT.

Retrieved 9 January 2012.

[3] http://en.wikipedia.org/wiki/nitrogen_generator

[4] http://www.nitrogengenerators.com/ecom.asp?pg=psa-nitrogen-generators

[5] Nitrogen generation by PSA, http:// www.linde.com http://www.linde.com

61

http://en.wikipedia.org/wiki/nitrogen_generator

http://www.nitrogengenerators.com/ecom.asp?pg=psa-nitrogen-generators

http://www.linde.com

Appendix A

LADDER DIAGRAM

62

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