final report for industrial training done at mukwano industries

8/10/2019 Final Report For Industrial Training Done At Mukwano Industries

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INDUSTRIAL TRAINING REPORT DONE AT MUKWANO

INDUSTRIES UGANDA LIMITED, INDUSTRIAL AREA

KAMPALA (UGANDA)

PREPARED BY

ORTEGA IAN

SUPERVISED BY: MR.HENRY LUBA

.


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KYAMBOGO UNIVERSITY

FACULTY OF ENGINEERING

DEPARTMENT OF MECHANICAL AND PRODUCTION

PROGRAMME: BACHELOR OF ENGINEERING IN

MECHANICAL AND MANUFACTURING ENGINEERING

TOPIC: INDUSTRIAL TRAINING DONE AT MUKWANO GROUP

NAME: ORTEGA IAN

REG NO: 11/U/11049/EMD/PD

A REPORT SUBMITTED IN PARTIAL FULFILMENT OF THE

REQUIREMENT FOR THE AWARD OF BACHELORS DEGGREE IN

MECHANICAL AND MANUFACTURING ENGINEERING AT

KYAMBOGO UNIVERSITY

2012/2013

June 4th

- August 4th

2013


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DECLARATION

I sincerely declare that:

1. I am the sole writer of this report

2. The details of training and experience contain in this report describe my involvement as a

trainee in the field of Mechanical and Manufacturing Engineering at Mukwano Group and

Mukwano Industries (U) Ltd.

3. All the information contains in this report is certain and correct to the knowledge of the

author.

Signature: ___________________________________

Name: ORTEGA IAN

Reg. No: 11/U/11049/EMD/PD

Date: 19thAugust 2009

For Company Supervisor: ___________________________________

For University Supervisor: __________________________________


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Acknowledgments

First and foremost, I thank the Management and the entire staff of Mukwano Group for

according me the opportunity to train with such a big company. The lifetime skills ingrained in

me will never be forgotten. I thank my university Supervisor, Mr. Sseku Charles for the

guidance and great service offered.

My special thanks go to my parents for the guidance and discipline instilled in me. I cant forget

to thank my mentor, Andrew Mwenda for teaching me about life. And to the Almighty God,

nothing beats your love. To everyone I may have missed out, accept my appreciation.

Namaste.


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Report Summary

The report covers the events, skills attained and lessons learned during my Industrial training at

Mukwano Group and Mukwano Industries (U) Ltd. The internship program was undertaken in

the manufacturing division covering a period of two (2) months from 4th June 2013 to 4th

August 2013.


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TABLE OF CONTENTS

Declaration .................................................................................................................................................. 3

Acknowledgements .................................................................................................................................. 4

Report Summary .................................................................................................................................. 5

Table of Contents ......................................................................................................................................... 6

Introduction .............................................................................................................................................. 7

BOILERS ............................................................................................................................................... 10

Soap Plant17

Production of Vegetable Oil.21

Beverages..25

Plastics.26

Utilities (Pumps, Heat Exchangers, valves, Chillers).............................................................................3 9

Challenges.61

Recommendations..61

Conclusion...61

References...62


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INTRODUCTION

Background

Brief-History of Mukwano

The Mukwano Group of Companies is the leading manufacturer of Fast Moving Consumer

Goods (FMCG) in the Great Lakes region, producing a wide range of market leader brands in

soaps, edible cooking oils and fats, detergents, beverages, personal care products and plastics.

Having pioneered Ugandas economic resurgence in the late 1980s and early 1990s, the Group

has proudly attained unparalleled regional reputation for uncompromised quality and

affordability of its products. Today, Mukwano products can be found in almost every household

in Eastern and Central Africa where they have been warmly embraced by loyal customers.

The Mukwano Group continues to steadily diversify into other business interests such as

agriculture, estate development and supply and logistics with commitment towards responsibleinvestment and national development.

Mukwano Vision Statement To become the supplier of choice for Fast Moving Consumer

Goods in East and Central Africa

Mukwano Mission To ensure timely delivery of quality, affordable products to our customers

in East and Central Africa


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The Company Organization Structure is as follows:


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Aims and Objectives For Industrial Training

1. To broaden my knowledge as far as mechanical and manufacturing systems and processes are

concerned.

2. To gain practical hands-on skills in partial fulfillment to my Mechanical and Manufacturingdegree.

3. To acquire insight in project progress from the planning phase to completion.

4. To get exposure to organization policy and culture.

5. To gain an understanding of company structure and hierarchy.


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BOILER SECTION

Design and operation

A boiler is an enclosed vessel that provides a means for combustion heat to be transferred into

water until it becomes heated water or steam. The hot water or steam under pressure is thenusable for transferring the heat for the steam requirements of Mukwano Industries and for power

generation.

Combustion boilers are designed to use the chemical energy in fuel to raise the energy content of

water so that it can be used for heating and power applications. Many fossil and non-fossil fuels

are fired in boilers, but the most common types of fuel include coal, oil and natural gas.

Previously, Mukwano had oil fired boilers but due to the high cost of operation, it has focused on

only wood-husk fired boilers. During the combustion process, oxygen reacts with carbon,

hydrogen and other elements in the fuel to produce a flame and hot combustion gases. As these

gases are drawn through the boiler, they cool as heat is transferred to water. Eventually the gasesflow through a stack and into the atmosphere. As long as fuel and air are both available to

continue the combustion process, heat will be generated.

Boilers are manufactured depending on the characteristics of the fuel, the specified heating

output, and the required emission controls.

Components of a boil er system

The main components in a boiler system are boiler feedwater heaters, deaerators, feed pump,

economiser, superheater, attemperator, steam system, condenser and condensate pump. In

addition, there are sets of controls to monitor water and steam flow, fuel flow, airflow and

chemical treatment additions.

More broadly speaking, the boiler system comprises a feedwater system, steam system and fuels

system. The feedwater system provides water to the boiler and regulates it automatically to meet

the steam demand. Various valves provide access for maintenance and repair.


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The stem system collects and controls the steam produced in the boiler. Steam is directed

through a piping system to the point of use. Throughout the system, steam pressure is regulated

using valves and checked with steam pressure gauges. The fuel system includes all equipment

used to provide fuel to generate the necessary heat. The equipment required in the fuel system

depends on the type of fuel used in the system.

Feedwater system

The water supplied to the boiler, which is converted into steam, is called feedwater. The two

sources of feedwater are condensate or condensed steam returned from the process and makeup

water (treated raw water) which must come from outside the boiler room and plant processes.

Feedwater heater

Boiler efficiency is improved by the extraction of waste heat from spent steam to preheat the

boiler feedwater. Heaters are shell and tube heat exchangers with the feedwater on the tube side

(inside) and steam on the shell side (outside). The heater closest to the boiler receives the hottest

steam. The condensed steam is recovered in the heater drains and pumped forward to the heater

immediately upstream, where its heat value is combined with that of the steam for that heater.

Ultimately the condensate is returned to the condensate storage tank or condenser hotwell.

Deaerators

Feedwater often has oxygen dissolved in it at objectionable levels, which comes from air in-

leakage from the condenser, pump seals, or from the condensate itself. The oxygen is

mechanically removed in a deaerator. Dearators function on the principle that oxygen is

decreasingly soluble as the temperature is raised. This is done by passing a stream of steamthrough the feedwater. Deaerators are generally a combination of spray and tray type. One

problem with the control of deaerators is ensuring sufficient temperature difference between the

incoming water temperature and the stripping steam. If the temperature is too close, not enough

steam will be available to strip the oxygen from the make-up water.

Economisers

Economisers are the last stage of the feedwater system. They are designed to extract heat value

from exhaust gases to heat the steam still further and improve the efficiency of the boiler. They

are simple finned tube heat exchangers. Not all boilers have economizers. Usually they are found

only on water tube boilers using fossil fuel as an energy conservation measure.

A feedwater economiser reduces steam boiler fuel requirements by transferring heat from the

flue gas to incoming feedwater. By recovering waste heat, an economiser can often reduce fuel

requirements by 5 per cent to 10 per cent and pay for itself in less than two years.


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A feedwater economiser is appropriate when insufficient heat transfer surface exists within the

boiler to remove combustion heat. Boilers that exceed 100 boiler hp, operating at pressures

exceeding 75 psig or above, and those that are significantly loaded all year long are excellent

candidates for economiser retrofit.

Steam system

Steam and mud drums

A boiler system consists of a steam drum and a mud drum. The steam drum is the upper drum of

a watertube boiler where the separation of water and steam occurs. Feedwater enters the boiler

steam drum from the economizers or from the feedwater heater train if there is no economiser.

The colder feedwater helps create the circulation in the boiler.

The steam outlet line normally takes off from this drum to a lower drum by a set of riser and

downcomer tubes. The lower drum, called the mud drum, is a tank at the bottom of the boiler

that equalizes distribution of water to the generating tubes and collects solids such as salts

formed from hardness and silica or corrosion products carried into the boiler.

In the circulation process, the colder water, which is outside the heat transfer area, sinks and

enters the mud drum. The water is heated in the heat transfer tubes to form steam. The steam-

water mixture is less dense than water and rises in the riser tubes to the steam drum. The steam

drum contains internal elements for feedwater entry, chemical injection, blowdown removal,

level control, and steam-water separation. The steam bubbles disengage from the boiler water in

the riser tubes and steam flows out from the top of the drum through steam separators.

Boi ler tubes

Boiler tubes are usually fabricated from high-strength carbon steel. The tubes are welded to form

a continuous sheet or wall of tubes. Often more than one bank of tubes is used, with the bank

closest to the heat sources providing the greatest share of heat transfer. They will also tend to be

the most susceptible to failure due to flow problems or corrosion/ deposition problems.

Superheaters

The purpose of the superheater is to remove all moisture content from the steam by raising the

temperature of the steam above its saturation point. The steam leaving the boiler is saturated, that

is, it is in equilibrium with liquid water at the boiler pressure (temperature).

The superheater adds energy to the exit steam of the boiler. It can be a single bank or multiple

banks or tubes either in a horizontal or vertical arrangement that is suspended in the convective

or radiation zone of the boiler. The added energy raises the temperature and heat content of the

steam above saturation point.


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In the case of turbines, excessive moisture in the steam above saturation point. In the case of

turbines, excessive moisture in the steam can adversely affect the efficiency and integrity of the

turbine. Super-heated steam has a larger specific volume as the amount of superheat increases.

This necessitates larger diameter pipelines to carry the same amount of steam. Due to

temperatures, higher alloy steel is used. It is important that the steam is of high purity and low

moisture content so that non-volatile substances do not build up in the superheater.

Attemperators

Attemperation is the primary means for controlling the degree of superheat in a superheated

boiler.

Attemperation is the process of partially de-superheating steam by the controlled injection of

water into the superheated steam flow. The degree of superheat will depend on the steam load

and the heat available, given the design of the superheater. The degree of superheat of the final

exiting steam is generally not subject to wide variation because of the design of the downstreamprocesses. In order to achieve the proper control of superheat temperature an attemperator is

used.

A direct contact attempaerator injects a stream of high purity water into the superheated steam. It

is usually located at the exit of the superheater, but may be placed in an intermediate position.

Usually, boiler feedwater is sued for attemperation. The water must be free of non-volatile solids

to prevent objectionable buildup of solids in the main steam tubes and on turbine blades.

Since attemperator water comes from the boiler feedwater, provision for it has to be made in

calculating flows. The calculation is based on heat balance. The total enthalpy (heat content) of

the final superheat steam must be the mass weighted sum of the enthalpies of the initial superheat

steam and the attemperation water.

Condensate systems

Although not a part of the boiler per se, condensate is usually returned to the boiler as part of the

feedwater. Accordingly, one must take into account the amount and quality of the condensate

when calculating boiler treatment parameters. In a complex steam distribution system there will

be several components. These will include heat exchangers, process equipment, flash tanks, and

storage tanks. Heat exchangers are the places in the system where steam is used to heat a process

or air by indirect contact. Shell and tube exchangers are the usual design, with steam usually onthe shell side. The steam enters as superheated or saturated and may leave as superheated,

saturated, or as liquid water, depending on the initial steam conditions and the design load of the

exchanger.

Process equipment includes turbines whether used for HVAC equipment, air compressors, or

turbine pumps. Condensate tanks and pumps are major points for oxygen to enter the condensate


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system and cause corrosion. These points should be monitored closely for pH and oxygen ingress

and proper condensate treatment applied.

Fuel system

Fuel feed systems play a critical role in the performance of boilers. Their primary functionsinclude transferring the fuel into the boiler and distributing the fuel within the boiler to promote

uniform and complete combustion. The type of fuel influences the operational features of a fuel

system

The fuel feed system forms the most significant component of the boiler system.

Feed system for gaseous fuels

Gaseous fuels are relatively easy to transport and handle. Any pressure difference will cause gas

to flow, and most gaseous fuels mix easily with air. Because on-site storage of gaseous fuel is

typically not feasible, boilers must be connected to a fuel source such as a natural gas pipeline.Flow of gaseous fuels to a boiler can be precisely controlled using a variety of control systems.

These systems generally include automatic valves that meter gas flow through a burner and into

the boiler based on steam or hot water demand.

The purpose of the burner is to increase the stability of the flame over a wide range of flow rates

by creating a favourable condition for fuel ignition and establishing aerodynamic conditions that

ensure good mixing between the primary combustion air and the fuel. Burners are the central

elements of an effective combustion system.

Other elements of their design and application include equipment for fuel preparation and air-

fuel distribution as well as a comprehensive system of combustion controls. Like gaseous fuels,

liquid fuels are also relatively easy to transport and handle by using pumps and piping networks

that link the boiler to a fuel supply such as a fuel oil storage tank. To promote complete

combustion, liquid fuels must be atomized to allow through mixing with combustion air.

Atomisation by air, steam, or pressure produces tiny droplets that burn more like gas than liquid.

Control of boilers that burns liquid fuels can also be accomplished using a variety of control

systems that meter fuel flow.

Feed system for soli d fuels

Solid fuels are much more difficult to handle than gaseous and liquid fuels. Preparing the fuel forcombustion is generally necessary and may involve techniques such as crushing or shredding.

Before combustion can occur, the individual fuels particles must be transported from a storage

area to the boiler.


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Mechanical devices such as conveyors, augers, hoppers, slide gates, vibrators, and blowers are

often used for this purpose. The method selected depends primarily on the size of the individual

fuels particles and the properties and characteristics of the fuel.

Stokers are commonly used to feed solid fuel particles such as crushed coal, TDF, MSW, wood

chips, and other forms of biomass into boilers. Mechanical stokers evolved from the hand-firedboiler era and now include sophisticated electromechanical components that respond rapidly to

changes in steam demand.

The design of these components provides good turndown and fuel-handling capability. In this

context, turndown is defined as the ratio of maximum fuel flow to minimum fuel flow.

In the case of pulverized coal boilers, which burn very fine particles of coal, the stoker is not

used. Coal in this form can be transported along with the primary combustion air through pipes

that are connected to specially designed burners.

A burner is defined as a devices or group of devices for the introduction of fuel and air into a

furnace at the required velocities, turbulence, and concentration to maintain ignition and

combustion of fuel with in the furnace. Burners for gaseous fuels are less complex than those for

liquid or solid fuels because mixing of gas and combustion air is relatively simple compared to

atomizing liquid fuels or dispersing solid fuel particles.

The ability of a burner to mix combustion air with fuel is a measure of its performance. A good

burner mixes well and liberates a maximum amount of heat from the fuel. The best burners are

engineered to liberate the maximum amount of heat from the fuel and limit the amount of

pollutants such as CO, NOx, and PM that are released. Burners with these capabilities are now

used routinely in boilers that must comply with mandated emission limitations.

Mukwano Industries Boilers


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Cocomax is a high-efficiency packaged smoke tube boiler designed to use crushed wood husks

as fuel. It can achieve an unmatched efficiency of 81%.

Product Features

Low cost heating

Bubbling bed combustion to enhance output and efficiency

Wood-husk fired boiler

Provided with unique combustor to prevent fuel from falling below the grate

Specially designed chromium grate bar to protect smoke tubes from abrasion

Fuel feeding can be mechanized as per customer requirement

Operating Range

Capacities:In the range of 2 to 5 TPH

Pressure:In the range of 10.54 to 17.5 kg/cm2(g)

Firing fuels:Wood husk

Efficiency:Overall efficiency of 81 % (+/-2%)

Boiler System Failures

1. Dearator cracking: This is due to poorly treated water which causes corrosion at welds

and heat-affected zones near the welds.

2. Feedwater Line Erosion: This is due to high velocity water.

3. Economizer tubes

4. Faults due to over-heating

5. Failures due to corrosion.


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SOAP PLANT

In the soap plant, manufacture of soaps at Mukwano Industries takes place. Below is a process

flow diagram of soap-making.

Process Description

The process starts off from the mixing of sodium silicate, china clay and salt. These are then

taken in a mixing tank in the required quantity and mixed thoroughly into a homogenous mass.

The basic raw materials of soap making are thus; oil (containing FFA greater than 10%), caustic

soda, steam, salt and scarp soap.

1. Crutcher

-The crutcher is a vertical mixer used in the semi-boiled batch saponification, for

the neutralization of fatty acids with caustic soda and for the neutral fats

saponification.

-The crutcher is also used to add additives such as caoline, silicate and to color the

laundry soap in the drying plant.

-Another use of the crutcher is the synthetic detergent soaps base production.

-The crutcher can operate either at atmospheric pressure of pressurized.

-The crutcher is provided with a vertical mixing worm placed inside a containing

tube which assures a strong mixing of the material to be processed.


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-The worm directs the fluent ascendant movement of the material to be processed

inside the containing tube and the fluent descendent movement outside the

containing tube.

2. The Dryer

Here, the continuous drying of the laundry soap takes place.

Neat Soap Filtration

The liquid soap is pumped through the soap filter into the service tank.

Neat Soap Heating

The liquid soap is fed by the feeding pump into the heat exchanger where

it is heated at 80 to 90 degrees centigrade.

Drying


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The heated liquid soap is atomized inside of the atomizer. The vapors

liberated inside (ones preformed inside heat exchanger and the ones

flashed off) are sucked away by the vacuum system. Soap that is sprayed

on the wall of the atomizer is, at this point dry, cold and solid. The spray

dryer chamber is at a pressure of 5-6mm of Hg. It is scrapped off the wall

by action of rotary scrappers. Scrapped soap falls on the worms of the

plodder and is extruded out in form of pellets or continuous bar.

Soap Fines Separation and Recovery

The vapors containing the soap dusts formed during spraying, are

conveyed out of the atomizer through the cyclones where they are

separated from the dusts which falls on the bottom of cyclones and is

recovered.

Vapours CondensationThe vapors are condensed inside barometric condenser. The vacuum pump

produces and maintains the vacuum degree inside the plant by removing

all uncondensables.


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Plodding and Extrusion

The dried soap is then forced out by a twin-worm plodder through a

perforated plate. The soap, coming out through the perforated plate is cut

into small pieces by a rotating knife cutter. The pieces are finally extruded

in the form of a bar through the nozzle plate of the specified dimensions.

Packing

Here, stamping, wrapping and packing takesplace which completes the

soap process.

Main Task Carried Out In the Soap Plant

1. Pump diagnosis and repair

2. Valve replacements

3. Replacement of Gaskets4. Repair of conveyors

5. Preventive Maintenance

6. Breakdown Maintenance

7. Compressor fault-finding and maintenance

8. Repairs done on wrapping and sealing machines


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PRODUCTION OF VEGETABLE OIL

At Mukwano Industries, the main section to do with Production of Vegetable Oil is AK Oils and

Fats (AKOF).

Extraction

Oil is extracted from beans, grains, seeds, nuts, and fruits. The raw materials are received at the

facility and stored before initial processing. The type of storage depends on the raw material,

(e.g. soybeans are stored in grain elevators). The raw materials are prepared using a variety of

processes, including cleaning, drying, crushing, conditioning, and pressing. Beans are processed


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into flakes so that the oil cells are exposed, facilitating oil extraction, and fruits are pressed to

extract oil.

Oil extraction can be performed mechanically (e.g. by boiling fruits and pressing seeds and nuts)or in combination with the use of solvents. During solvent extraction, hexane is used to wash the

processed raw materials, typically in a countercurrent extractor.

Refinement

The crude oil is refined to remove undesired impurities such as gums, free fatty acids (FFA),

traces of metals, coloring components, and volatile components. During refining, the FFA are

removed to the level of less than 0.1 percent in the refined oil either by chemical or physical

refining. Where appropriate, preference should be given to physical rather than chemical refining

of crude oil as the bleaching earth used in this process has a lower environmental impact.

Conversely, chemical refining results in a better product quality in terms of lower FFA levels,

longer shelf life, and a more reliable process

Chemical Refi ning

Conventional chemical refining involves degumming for the removal of phospholipids,

neutralization for the removal of FFA, and bleaching for decolorization and deodorization. Water

is added during degumming to hydrate any gums present and the mixture is then centrifuged for


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separation. Non-hydratable gums are removed using phosphoric or citric acid before water is

added and separation takes place in a centrifuge. During degumming, caustic soda is added to the

oil, which has been preheated to between 75oC and 110oC to saponify the FFA. This process

gives rise to two main outputs, namely semirefined oil and soap stock. The soap stock is

removed by precipitation followed by sedimentation or centrifugation and may be further

processed into acid oils by splitting. The soap stock is heated to between 70oC and 100oC and

reacts with sulfuric acid to reform the fatty acids. The resulting by-products can be sold to the

paints and cosmetics sector, as well as to the animal feed industry. The neutralized oil is

bleached to remove coloring matter and other minor constituents.

Physical Refi ning

Physical refining is a more simple process in which the crude oil is degummed and bleached, and

then steam stripped to remove FFA, odor, and VOCs all in one step. A physical pretreatment can

be used to achieve a low phospholipid content by degumming and using bleaching earth.

Following this, FFA can be stripped from the physically pretreated oil using steam in a vacuumat temperatures of around 250oC and refined by the oil flowing over a series of trays

countercurrent to the flow of the stripping steam. Previous neutralization stages are not necessary

because the neutralization and deodorization are combined. A scrubber is then used to condense

the greater part of the fat from the vapors as a water-free product.

Other Modifications

1. Hydrogenation

Most installations carry out hydrogenation to produce fats with superior retention

qualities and higher melting points. Hydrogenation is usually carried out bydispersing hydrogen gas in the oil in the presence of a finely divided nickel

catalyst supported on diatomaceous earth. The resultant hydrogenated fats are

filtered to remove the hydrogenation catalyst, subjected to a light earth bleach,

and deodorized before they can be used for edible purposes. After hardening, the

oil is mixed with an aqueous solution to produce an emulsion. The emulsified

mixture is then pasteurized, cooled, and crystallized to obtain the final product.

2. Interestification

Interestification involves the separation of triglycerides into fatty acids and

glycerol followed by recombination. The reaction is carried out using phosphoricor citric acid with a catalyst, typically sodium methoxide. Interestification

modifies the functional properties of the treated oil and may be carried out after

neutralization or deodorization.


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Deodorization

During deodorization, the bleached oil is steam-distilled at low pressure to remove volatile

impurities, including undesirable odors and flavors. Volatile components are removed from the

feedstock using steam in a process that may last from 15 minutes to 5 hours. The vapors from the

deodorizer contain air, water vapor, fatty acids, and other variables. Before entering the vessel,the vapors pass through a scrubber and a scrubbing liquid is sprayed in the vapor stream. Fatty

acids and volatiles partly condense on the scrubbing droplets or alternatively on the packing

material. This process produces the fully refined, edible oils and fats.

Filmatics

This is the final process to the processing of vegetable oil and it simply involves the use of

electro-mechanical machines to fill the ready cooking oil in their respective containers ready for

consumption.

Tasks In This Section

1. Repairing pumps in the physical and chemical refinery

2. Stopping leakages on steam, water and air lines

3. Preventive maintenance of various equipment in the refineries

4. Repairing of filmatic machines during break-down.


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BEVERAGES

This is the section where Aqua Sipi water is made from. Currently, the company uses a fully

automated plant to process its water. From the borehole area, water is stored in water reservoirs

awaiting transportation.

Water is loaded onto trucks and transported to the beverages plant. The water goes through the

filtration stage passing through the sand filter (removing 50 micron particle sizes) to the carbon

filter. The main use of the carbon filter is to remove smell, dechlorinate the water, and absorb

dust.

The water is then sent to the UV system filter before its sent for the ozonation process. This

process is carried out by the ozone generator which has a high electrical discharge. The ozone

reacts with the water and kills bacteria. The advantage of which, is that it never produces any by-

products and has a half-life period of 28 minutes thus helps to preserve the water.

Once the ozonation is done, water is bottled and filled, and shrink sealing tunneling takes place.

The final process involves cartooning, and palletizing the read drinking mineral water.

How The Bottles Get to The Line

The pet-jar bottles are fed onto the bottle feed conveyor. Thereafter, they go through bottle

rinsing. The washed bottles are then made available for filling. Bottle rinsing is done using a

combination of steam and the UV system.

Tasks Handled In the Section

1. Replacement of moulds in the cap making and bottle making machines.

2. Working on faults on the stretch blow moulding machines.

3. Chiller and compressor breakdown maintenance.


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PLASTICS SECTION

The plastics section of the Mukwano Group is at AK Plastics. Plastic products at this section are

formed through a manufacturing process known as Plastic Blow Molding.

Plastic Blow Molding

These processes represent the most popular way of producing hollow products such as bottles,

drums, and other vessels out of thermoplastic materials. This modern industrial technology has

evolved from the ancient art of glass blowing.

Among the many types of resins used are:

various densities of polyethylene

polyethylene terephthalate polypropylene

polyvinyl chloride

thermoplastic elastomers

polystyrene

fluoropolymers, and many others

The principle process is extrusion blow molding. Others include injection blow molding,

biaxial stretch blow molding, and co-extrusion blow molding.

All of which utilize elements of either extrusion or injection, or both. All of the processes sharedistinct production stages:

plasticizing or the melting of resin

Parison production which refers to most blow molding operations; or preform production when

referring to biaxial stretch blow molding

Inflation and cooling phases in the mold

Ejection from the mold

A fifth stage required in extrusion blow molding involves trimming the final product.

Process Operation

The same blowing technique is common to all the process variations and is accomplished

through either a blow pin, needle, stuffer, or a core rod.


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The process begins with applications of heat and pressure to create the melt. The melt is then

processed through a reciprocating screw and ram assembly that pushes the material through a die

to produce the parison.This production of the parison may be continuous or intermittent and is

similar to the injection molding process. The reciprocal screw, which heats and moves the resin,

has feed, compression, and metering zones. Once the proper amount of melt is available, a

ramming action delivers the material to the die and forms the parison. In the case where very

large parisons need to be formed, an accumulator type of machine is used. This is reservoir

system, which allows a melt delivery rate independent of the screw and ramming sequences.

In the continuous extrusion form of blow molding. The screw does not reciprocate, but continues

turning and thus continuously delivers melt to the head and die assemblies, forming a continuous

parison. Most extruder head and die assemblies are known as the cross head type which divert

the flow of the resin from horizontal to vertical. Crossheads may either be center-feed or side-

feed. The center-feed design produces a uniform flow downward around the tip of conical core

or mandrel and results in a straight flow all around the mandrel. Side-feed assemblies force the

resin around the perimeter of the mandrel and then extruded through the die as a parison with

varying wall thickness. To control the parisons temperature and wall thickness, aprogrammer

is used.

While the intermittent extrusion system is able to produce a wide range of products, the

continuous system uses several process variations that widen the product range even further.

These include the shuttle or reciprocating blow molding system and the rotary wheel blow

molding system.

The shuttle system uses multiple molds and so requires multiple parisons. To accomplish this a

manifold is used to distribute the melt to several dies at once as the parisons arrive at the moldsblow position. A cutting device separates the required portion of the continuous parison, a blow

pin or needle is inserted in the parison and with a jet of air the product is blown into shape. For

high volume production, 20 or more split molds can be mounted on a horizontal turntable or

vertical rotary wheel for continuous molding.

Injection blow molding utilizes elements of conventional thermoplastic injection molding. This

is more economical than the extrusion process and generally is used for large production

quantities of smaller containers of less than liter size. Basically, the systems include an injection

station, a blow station, and a strip or eject station.


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Plastics Formation Explained

Plastics can be subdivided into three main categories, thermoplastics, thermosets and elastomers.

Thermoplasticsmelt and flow when heated and solidify as they cool. On subsequent re-heating

they regain the ability to flow. This means they can be reprocessed and hence recycled by re-

melting them. Thermoplastics are used to make consumer items such as drinks containers, carrier

bags and buckets. Thermosetsmaterials decompose before they can melt, therefore, they cannot

be reprocessed in the same way as thermoplastics. An Elastomer is a material that, at room

temperature, can be stretched repeatedly to at least twice its original length, and upon immediate

release of the stretch, will return with force to its approximate original length.Which means, to

put it in laymans terms, its rubbery!

Injection Molding Machinery

The basic parts of an injection molding machine are:

3. Injection Unit

4. Machine Base with Hydraulics

5. Control Unit and Control Cabinet

6. Clamping Unit with Mould

The Injection Unit

The first aim of the plastication stage is to produce a homogeneous melt for the next stage where

the material enters the mould. A second important function of the injection unit is the actual

injection into the mould. Here, it is important that injection speeds are reproducible as slight

changes can cause variations in the end product.


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There are two different injection units available. There is the Piston (plunger) injection unit

which is being phased out. The other one, which is used world-wide and at Mukwano is theReciprocating Screw Piston injection unit.

In the screw piston injection unit, the material is plasticized and dosed simultaneously as

previously described. The design of a plasticising screw has several advantages over a piston

type mainly in the ability to produce a homogeneous melt as a result of mixing. The flow of the

material is also improved as shear from the screw lowers the viscosity of the material. The long

residence times present in the piston type machines are eliminated allowing heat sensitive

materials such as PVC to be processed. The screw is also easier to purge and less prone to

degradation or material hang-ups.

Important parameters for these screws are:

1. The diameter of the screw and the ratio of the diameter to the length

2. Shot Capacity: This is the amount of material required to fill a moulding tool.

3. Plasticizing Capacity: This is the maximum rate at which the injection unit can deliver

polymer melt.


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The Feeding Hopper

Material is placed in the hopper prior to plastication. It must be designed to avoid material

bridging in the throat and to let gravity feed the material. Material hold up spots must be

avoided. Additives, especially when they are different weights to the polymer, may tend to

accumulate and be fed inconsistently. This can lead to variations in melt quality. The hopper maycontain magnets to collect metal contamination, which must be prevented from entering the feed

system. It may also contain grids to prevent large particulates from entering and blocking the

feeding system, especially important if using recyclate materials. Keeping the feed system cool is

also important, if material begins to melt in the throat of the feeding system it may stick to the

sides of the throat and in extreme cases block the machine completely.

The Injection Cylinder

Once the material has passed through the hopper, it enters the injection barrel. The barrel will

consist of a number of separately controlled heating zones as can be seen. The heat is generatedfrom conduction of heat from the cylinder and also the heat generated by the shearing action of

the screw on the material feedstock. Polymers are not particularly good conductors of heat;

therefore the polymer thickness in any section of the screw tends to be kept low. The amount of

shear is material dependent, mainly viscosity related and controlled by the machine screw back

and back pressure.


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Non-Return Valve

Many materials require the use of a valve with a check ring to be fitted to the end of the screw to

prevent backflow. They also help to ensure that a constant cavity pressure is maintained. The

most important design consideration is that they should avoid flow restrictions or hold up of the

melt flow.

Non-return valves are more prone to wear than other components, so it must be ensured that

suitably toughened materials are used in manufacture.

The Nozzle

The nozzle provides the connection between the injection cylinder and the mould tool. Its job is

to convey the material with minimal pressure or heat change. There are two common types of

nozzle.

-Open Nozzle

-Nozzle shut-off Valve

Clamping Units

The clamping units of injection machines are described and rated separately to the injection unit.

The clamping units are required to enable mounting and holding of the two mould halves. They

must also provide sufficient clamping force during injection and cooling to enable effective

moulding. The mould halves must also open and close accurately and smoothly to enable part

injection and begin the next process cycle. Injection machines can be run by hydraulics, a

hydraulic and toggle combination or by electrical power. The clamping units on injectionmoulding machines use hydraulic force.

Figure below shows a clamping unit. The stationary platen is attached to the machine with four

tie rods connecting it to the movable platen. The clamp ram moves the moving platen until it

reaches the stationary platen and the pressure begins to build up. The ejectors are fitted onto the

moving platen and can be activated once the tool is opened and the moving platen retracted.


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Differential Piston System

For the opening and closing movements of the mould tool a minimal volume of oil is required.

The oil volume required from the pump results from the differential surface and stroke of the

piston (approx. 7% of the clamping cylinder volume). The rest of the oil flows through the

borings in the main piston as a result of the piston stroke.

When opening with increased opening force (high pressure opening) the control piston closes the

main piston. The main piston and opening piston now open the mould with 50 bar pressure.

When the injection unit is in the vertical position and braking is selected, the borings in the

main piston are closed shortly before the end of the opening motion, This ensures an exact

positioning of the movable platens in their lower-most end position. Sinkage of the movable

platern on an idle machine is also avoided.

Mould Weights

Each machine will have a maximum permitted mould weight for the movable mould halves.

These values should not be exceeded for any reason as production problems and premature wear

would be the result.


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Mould Clamping Force

The mould clamping force must be set high enough to prevent flash. This is caused by the

swelling of the mould under the compound force during initial injection resulting in the

compound coming out of the mould cavity. The mould clamping force required depends on the

size of the moulded component surface projected onto the parting plane, and on the internalmould pressure.

The type of clamp and the clamping force are the main specifications of a clamping unit.

However, there are other design features which also need consideration. These are:

Maximum daylight

Space between tie bars

Clamp stroke

Clamp speed

Knockout stroke.

Injection Mould Tooling Basics

An injection mould tool has two major purposes:

It is the cavity into which the molten plastic is injected

The surface of the tool acts as a heat exchanger (as the injected material solidifies with contact)

Injection mould designs differ depending on the type of material and component being moulded.

Mould tool design and component design are equally important considerations for success.

After parts are injection moulded they must be ejected. A variety of mechanisms can be

employed such as ejector pins, sleeves, plates or rings. The design standard for injection mould

tools is the two-plate design.


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The Feed System

The feed system accommodates the molten polymer coming from the barrel and guides it into the

mould cavity. Its configuration, dimensions and connection with the moulding greatly affect the

mould filling process and subsequently, the quality of the product. A design that is based

primarily on economic viewpoints, (rapid solidification and short cycles) is mostly incompatible

with quality demands. The two main areas that need to be considered are the runner system and

the gate.


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Ejection Systems

After a component has solidified and cooled down, it needs to be removed from the mouldcavity. Ideally, this is done by gravity and the part falls to the floor. However, some components

with design features such as undercuts, adhesion or internal stresses may have to be removed

from the mould manually or by robots.

Ejection equipment is usually actuated mechanically by the opening stroke of the moulding

machine. If this simple arrangement is insufficient, ejection can be performed pneumatically or

hydraulically.

The ejector system is normally housed in the movable mould half. Mould opening causes the

mechanically actuated ejector system to move towards the parting line and to eject the moulding.

The result of this procedure is that the moulding stays on or in the movable mould half. This can

be achieved by undercuts or by letting the moulding shrink onto a core. Taper and surface

treatment should prevent too much adhesion.


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Venting

Another design aspect of tooling is the need to provide vents for compressed air and gases to

escape during moulding. Trapped air and gases can cause a variety of moulding defects such as:

1. short shots (incomplete filling of the mould)

2. scorching or burning

3. shrinkage (often seen as ripples or depressions in finished parts)

4.

in extreme cases volatile gases may cause etching on the mould surface.

Process Control Systems

The control system is there to ensure repeatability during moulding operation. It monitors both

the hydraulic system and the process parameters such as temperature, injection speed, screw

retraction speed and injection and back pressure. The ability to control the process has a direct


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impact on final part quality, part to part consistency and economy. The nature of the control

system may vary from a simple relay switch to a complex microprocessor system with closed-

loop control.

The major mechanical control components include:

1. The Pump: The hydraulic pump generally draws the hydraulic fluid from the supply

reservoir and delivers it to the pump outlet.

2. The Motor: Hydraulic motors transform the hydraulic energy supplied by the pumps

back into a mechanically- utilized working force with a rotary motion.

3. The Cylinder:The cylinder (located behind the injection unit) is charged with hydraulic

fluid through valves in the base and the head. Through this, a motion is transferred

through the piston surface of the working cylinder to the pistons connecting rod.

4. Di rectional Valves: The function of directional valves is to block different hydraulic

lines from one another or to open them, and to continually create alternating line

connections. In this manner, the effective direction of pressures and volume flows isinfluenced, and the starting, stopping and the direction of motion of the consumer

(cylinder or hydraulic) motor are thus controlled.

5.

Pressure Valves:Pressure control valves have the primary task of limiting pressure in the

system and thus protecting individual components and lines from rupturing or

overloading. The valve opens when a predetermined pressure is reached and conveys the

pumps excess delivery flow back into the tank.

6. F low Regulator Valves:The task of the flow-regulator valve is to influence volume flow

by changing the diameter of the valve governor, and thus to control the speeds of

cylinders and hydraulic motors.

7.

Check Valves: Non-return valves have the task of blocking the volume flow in one

direction and allowing free-flow in the opposite direction. The blockage should provide

completely leakproof sealing. Balls or cones are used primarily as sealing elements.

8. Receivers: Hydropneumatic receivers have the task of collecting and storing hydraulic

energy, and then releasing it on demand. This type of receiver is used in conjunction with

injection moulding machines with very rapid injection (with accumulator). Here, a high

volume flow which can be partially accessed from the receiver is required periodically

for brief intervals. The benefits in the application of a hydropneumatic receiver are in the

use of relatively small pumps, drive motors and oil reservoirs. The working principle of a

receiver is that it is virtually impossible to compress the hydraulic fluid. If it isnevertheless to be stored under pressure, a gas is utilized, in this case nitrogen. The gas is

compressed in a pressure reservoir by the hydraulic fluid and decompresses as needed

through the release of fluid. In order to ensure that the gas does not mix with the

hydraulic fluid, the pressure reservoir is divided into two chambers by an elastic

separation wall (membrane).


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Tasks Handled At The Plastics Section

1. Mould Replacements

2. Trouble shooting of faults on the injection moulding machines

3. Preventive Maintenance

4.

Machining jobs in the Workshop at Plastics

UTILITIES

There is machinery and equipment, that is required for the successful running of a plant and it

includes:

1. Pumps

2. Compressors

3.

Chillers

4. Heat Exhangers

5. Valves

PUMPS

A pump is a device that moves fluids (liquids or gases), or sometimes slurries, by mechanical

action.

Classification of Pumps

All pumps may be divided into two major categories: (1) dynamic, in which energy is

continuously added to increase the fluid velocities within the machine


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to values greater than those occurring at the discharge so subsequent velocity reduction within or

beyond the pump produces a pressure increase, and (2) displacement, in which energy is

periodically added by application of force to one or more movable boundaries of any desired

number of enclosed, fluid-containing volumes, resulting in a direct increase in pressure up to the

value required to move the fluid through valves or ports into the discharge line.


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Pump Priming

Centrifugal pumps usually are completely filled with the liquid to be pumped before starting.

When so filled with liquid, the pump is said to be primed. Pumps have been developed to start

with air in the casing and then be primed. This procedure is unusual with low-specific-speed

pumps but is sometimes done with propeller pumps. In many installations, the pump is at a lower

elevation than the supply and remains primed at all times. This is customary for pumps of high

specific speed and all pumps requiring a positive suction head to avoid cavitation.


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Pumps operated with a suction lift may be primed in any of several ways. A relatively

inexpensive method is to install a special type of check valve, called a foot valve, on the inlet end

of the suction pipe and prime the pump by filling the system with liquid from any available

source. Foot valves cause undesirable frictional loss and may leak enough to require priming

before each starting of the pump. A better method is to close a valve in the discharge line and

prime by evacuating air from the highest point of the pump casing.

Many types of vacuum pumps are available for this service. A priming chamber is a tank that

holds enough liquid to keep the pump submerged until pumping action can be initiated. Self-

priming pumps usually incorporate some form of priming chamber in the pump casing.

The Commonest Pumps At Mukwano

1. Gear Pump

This is the simplest of rotary positive displacement pumps. It consists of two meshed

gears that rotate in a closely fitted casing. The tooth spaces trap fluid and force it aroundthe outer boundary. The fluid does not travel back on the meshed part, because the teeth

mesh closely in the centre.

2. Screw Pump

A Screw pump is a more complicated type of rotary pump that uses two or three screws

with opposing threade.g., one screw turns clockwise and the other counterclockwise.

The screws are mounted on parallel shafts that have gears that mesh so the shafts turn

together and everything stays in place. The screws turn on the shafts and drive fluid

through the pump. As with other forms of rotary pumps, the clearance between moving

parts and the pump's casing is minimal.

3. Plunger Pump

Plunger pumps are reciprocating positive displacement pumps. These consist of a

cylinder with a reciprocating plunger. The suction and discharge valves are mounted in

the head of the cylinder. In the suction stroke the plunger retracts and the suction valves

open causing suction of fluid into the cylinder. In the forward stroke the plunger pushes

the liquid out of the discharge valve. Efficiency and common problems: With only one

cylinder in plunger pumps, the fluid flow varies between maximum flow when the

plunger moves through the middle positions, and zero flow when the plunger is at the end

positions. A lot of energy is wasted when the fluid is accelerated in the piping system.

Vibration and water hammer may be a serious problem.

4. Centrifugal Pump

A centrifugal pump is a rotodynamic pump that uses a rotating impeller to increase the

pressure and flow rate of a fluid. Centrifugal pumps are the most common type of pump

used to move liquids through a piping system. The fluid enters the pump impeller along


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or near to the rotating axis and is accelerated by the impeller, flowing radially outward or

axially into a diffuser or volute chamber, from where it exits into the downstream piping

system. Centrifugal pumps are typically used for large discharge through smaller heads.

Centrifugal pumps are most often associated with the radial-flow type.

Centrifugal Pump Packing

Packing is used in the stuffing box of a centrifugal pump to control the leakage of the pumped

liquid out, or the leakage of air in,where the shaft passes through the casing. This basic form of a

seal can be applied in light- to medium-duty services and to those liquids that prove difficult for

mechanical seals.

How To Install A Packing

To install continuous coil packing, perform the following steps:

1. Loosen and remove the gland from the stuffing box.

2. Using a packing puller, begin to remove the old packing rings.


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3. Remove the split lantern ring (if present) and then continue removing the packing with the

puller.

4. After the packing has been removed, check the sleeve for scoring and nicks. If the shaft sleeve

or shaft cannot be cleaned up, it must be replaced. Check the size of the stuffing box bore and the

shaft sleeve or shaft diameter to determine which size packing should be used.

5. After the size of the packing has been determined, wrap the packing tightly around a mandrel,

which should be the same size as the pump shaft or sleeve. The number of coils should be

sufficient to fill the stuffing box. Cut the packing along one side to form the individual rings.

6. Before beginning the assembly of any packing material,be sure to read all the instructions

from the manufacturer. Assemble the split packing rings on the pump. Each ring should be

sealed individually with the split ends staggered 90 and the gland tightened to seal and fully

compress the ring. Be sure the lantern ring is reinstalled correctly at the flush connection. Then

back off the gland and retighten it, but only finger-tight. The exception to this procedure is thatTFE packing should be installed one ring at a time, but not seated because TFE packings have

high thermal expansion.

7. Allow excess leakage during break-in to avoid the possibility of rapid expansion of the

packing, which could score the shaft sleeve or shaft so that leakage could not be controlled.

8. Leakage should be generous upon startup. If the packing begins to overheat at startup, stop the

pump and loosen the packing until leakage is obtained. Restart only if the packing is leaking.

Packing Troubles, Causes and Cures


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Water Hammering

Waterhammer is a very destructive force that exists in any pumping installation where the rate of

flow changes abruptly for various reasons.

Diagnostic Chart For Centrifugal pump Troubles

Pump Installation

The following factors are taken into consideration during pump installation:


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1. Pump Location: Working space must be checked to assure adequate accessibility for

maintenance. Pumps should be located as close as practicable to the source of liquid

supply. Whenever possible, the pump centerline should be placed below the level of the

liquid in the suction reservoir.

2. Foundation

3.

Alignment

4.

Grouting: The purpose of grouting is to prevent lateral shifting of the baseplate, toincrease the mass to reduce vibration, and to fill in irregularities in the foundation.

5. Doweling of Pump and Driver: When the pump handles hot liquids, doweling of both the

pump and its driver should be delayed until the unit has been operated. A final recheck of

alignment with the coupling bolts removed and with the pump and driver at operating

temperature is advisable before doweling.

Large pumps handling hot liquids are usually doweled near the coupling end, allowing

the pump to expand from that end out. Sometimes the other end is provided with a key

and a keyway in the casing foot and the baseplate.

Piping

Suction Piping: The suction piping should be as direct and short as possible. If a long suction

line is required, the pipe size should be increased to reduce frictional losses. (The exception to

this recommendation is in the case of boiler-feed pumps, where difficulties may arise during


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transient conditions of load change if the suction piping volume is excessive. This is a special

and complex subject, and the manufacturer should be consulted.)

Discharge Piping:Generally both a check valve and a gate valve are installed in thdischarge

line. The check valve is placed between the pump and the gate valve and protects the pump from

reverse flow in the event of unexpected driver failure or from reverse flow from anotheroperating pump. The gate valve is used when priming the pump or when shutting it down for

inspection and repairs. Manually operated valves that are difficult to reach should be fitted with a

sprocket rim wheel and chain. In many cases, discharge gate valves are motorized and can be

operated by remote control.

Pump Operation

Pumps are generally selected for a given capacity and total head when operating at rated speed.

These characteristics are referred to as rated conditions of service and, with few exceptions,

represent those conditions at or near which the pump will operate the greatest part of the time.

Positive displacement pumps cannot operate at any greater flows than rated except by increasing

their speed, nor can they operate at lower flows except by reducing their operating speed or

bypassing some of the flow back to the source of supply.

On the other hand, centrifugal pumps can operate over a wide range of capacities, from near zero

flow to well beyond the rated capacity. Because a centrifugal pump will always operate at the

intersection of its head-capacity and system-head curves, the pump operating capacity may be

altered either by throttling the pump discharge (hence altering the system-head curve) or by

varying the pump speed (changing the pump head capacity curve).This makes the centrifugal

pump very flexible in a wide range of service and applications that require the pump to operate at

capacities and heads differing considerably from the rated conditions. There are, however, some

limitations imposed upon such operation by hydraulic, mechanical, or thermodynamic

considerations.

Priming

With very few exceptions, no centrifugal pump should ever be started until it is fully primed; that

is, until it has been filled with the liquid pumped and all the air contained in the pump has been

allowed to escape. The exceptions involve self-priming pumps and some special large-capacity,

low-head, and low-speed installations where it is not practical to prime the pump prior to

starting; the priming takes place almost simultaneously with the starting in these cases.


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Reciprocating pumps of the piston or plunger type are in principle self-priming. However, if

quick starting is required, priming connections should be piped to a supply above the pump.

Positive displacement pumps of the rotating type, such as rotary or screw pumps, have clearances

that allow the liquid in the pump to drain back to the suction. When pumping low-viscosity

liquids, the pump may completely dry out when it is idle. In such cases a foot valve may be usedto help keep the pump primed. Alternately, a vacuum device may be used to prime the pump.

When handling liquids of higher viscosity, foot valves are usually not required because liquid is

retained in the clearances and acts as a seal when the pump is restarted. However, before the

initial start of a rotating positive displacement pump, some of the liquid to be pumped should be

introduced through the discharge side of the pump to wet the rotating element.

How To Start A Pump

Assuming that the pump in question is motor-driven, that its shutoff power does not exceed the

safe motor power, and that it is to be started against a closed gate valve, the starting procedure isas follows:

1. Prime the pump, opening the suction valve, closing the drains, and so on, to prepare the pump

for operation.

2. Open the valve in the cooling supply to the bearings, where applicable.

3. Open the valve in the cooling supply if the seal chambers are liquid-cooled.

4. Open the valve in the sealing liquid supply if the pump is so fitted.

5. Open the warm-up valve of a pump handling hot liquids if the pump is not normally kept atoperating temperature. When the pump is warmed up, close the valve.

6. Open the valve in the recirculating line if the pump should not be operated against dead

shutoff.

7. Start the motor.

8. Open the discharge valve slowly.

9. For pumps equipped with mechanical seals, check for seal leakage: there should be none.

10. For pump with shelf packing, observe the leakage from the stuffing boxes and adjust the

sealing liquid valve for proper flow to ensure the lubrication of the packing. If the packing is

new, do not tighten up on the gland immediately, but let the packing run in before reducing the

leakage through the stuffing boxes.

11. Check the general mechanical operation of the pump and motor.


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12. Close the valve in the recirculating line when there is sufficient flow through the pump to

prevent overheating.

If the pump is to be started against a closed check valve with the discharge gate valve open, the

steps are the same, except that the discharge gate valve is opened some time before the motor is

started.

In certain cases, cooling to the bearings and flush liquid to the mechanical seals or to the packing

seal cages is provided by the pump. This, of course, eliminates the need for the steps listed for

the cooling and sealing supply.

How To Stop A Pump

Just as in starting a pump, the stopping procedure depends upon the type and service of the

pump. Generally, the steps followed to stop a pump that can operate against a closed gate valve

are

1. Open the valve in the recirculating line.

2. Close the gate valve.

3. Stop the motor.

4. Open the warm-up valve if the pump is to be kept at operating temperature.

5. Close the valve in the cooling supply to the bearings and seal chambers.

6. If the sealing liquid supply is not required while the pump is idle, close the valve in this supply

line.

7. Close the suction valve, open the drain valves, and so on, as required by the particular

installation or if the pump is to be opened up for inspection.

If the pump is of a type that does not permit operation against a closed gate valve, steps 2 and 3

are reversed.

Most of the steps listed for starting and stopping centrifugal pumps are equally applicable to

positive displacement pumps. There are, however, two notable exceptions:

1. Never operate a positive displacement pump against a closed discharge. If the gate valve on

the discharge must be closed, always start the pump with the recirculation bypass valve open.

2. Always open the steam cylinder drain cocks of a steam reciprocating pump before starting, to

allow condensate to escape and to prevent damage to the cylinder heads.


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Maintenance Of Pumps

Because of the wide variation in pump types, sizes, designs, and materials of construction, these

comments on maintenance are restricted to those types of pumps most commonly encountered.

The manufacturers instruction books must be carefully studied before any attempt is made to

service a particular pump.

The following is taken into consideration for maintenance:

1. Daily Observation of Pump Maintenance

When operators are on constant duty, hourly and daily inspections should be made and

any irregularities in the operation of a pump should be recorded and reported

immediately. This applies particularly to changes in sound of a running pump, abrupt

changes in bearing temperatures, and seal chamber leakage. A check of pressure gages

and of flowmeters, if installed, and vibration should be made routinely during the day. If

recording instruments are provided, a daily check should be made to determine whetherthe current capacity, pressure, power consumption or vibration level indicates that further

inspection is required. If these readings are taken electronically, trending charts should be

produced to allow observation of changes as a function of time. Certain trends may allow

for scheduled outages to address deterioration of specific performance values.

2. Semiannual Inspection

The following should be done at least every six months:

1. For pumps equipped with shaft packing, the free movement of stuffing box glands

should be checked, gland bolts should be cleaned and lubricated, and the packing should

be inspected to determine whether it requires replacement.

2. The pump and driver alignment should be checked and corrected if necessary.3. Housings for oil-lubricated bearings should be drained, flushed, and refilled with fresh

oil.

4. Grease-lubricated bearings should be checked to see that they contain the correct

amount of grease and that it is still of suitable consistency.

3. Annual Inspection

A very thorough inspection should be performed once a year. In addition to the

semiannual procedure, the following items should be considered:

1. Vibration trends should be reviewed. If the pump is trending toward unacceptable

vibration levels,

a. The bearings should be removed, cleaned, and examined for flaws and wear.

b. The bearing housings should be carefully cleaned.

c. Rolling element bearings should be examined for scratches and wear.

d. Immediately after cleaning, rolling element bearings that are considered acceptable for

reinstallation should be coated with oil or grease. Note: If there is any sign of damage, or

if the bearings were damaged during removal, they should be replaced with new bearings

of the correct size and type per the manufacturers instruction book.


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e. The assembled rotoror major rotor components if the rotor is not assembled of

shrink-fit componentsshould be checked for balance prior to reassembly in the pump.

2. For pumps equipped with shaft packing, the packing should be removed and the shaft

sleevesor shaft, if no sleeves are usedshould be examined for wear.

3. For pumps equipped with mechanical seals, if the seals were indicating signs of

leaking, they should be removed and returned to the seal manufacturer for inspection,

possible bench testing, and refurbishment.

4. When coupling halves are disconnected for an alignment check, the vertical shaft

movement of a pump with sleeve (journal) bearings should be checked at both ends with

packing or seals removed. Any movement exceeding 150% of the original design

clearance should be investigated to determine the cause. Endplay allowed by the bearings

should also be checked. If it exceeds that recommended by the manufacturer, the cause

should be determined and corrected.

5. All auxiliary piping, such as drains, sealing water piping, and cooling water piping,

should be checked and flushed, as necessary. Auxiliary coolers should also be flushedand cleaned.

6. Pump equipped with stuffing boxes should be repacked, and the pump and driver

should be realigned and reconnected.

7. All instruments and flow-metering devices should be recalibrated, whenever feasible,

andwhenever possiblethe pump should be tested to determine whether proper

performance is being obtained. If internal repairs are made, the pump should again be

tested after completion of the repairs.

Complete Overhaul

It is difficult to make general rules about the frequency of complete pump overhauls as it

depends on the pump service, the pump construction and materials, the liquid handled, and the

economic evaluation of overhaul costs versus the cost of power losses resulting from increased

clearances or of unscheduled downtime. Some pumps on very severe service may need a

complete overhaul monthly, whereas other applications require overhauls only every two to four

years or even less frequently.

A pump should not be opened for inspection unless either factual or circumstantial evidence

indicates that overhaul is necessary. Factual evidence implies that the pump performance has

fallen off significantly or that the noise or driver load indicates trouble.

Circumstantial evidence refers to past experience with the pump in question or with similar

equipment on similar service. In order to ensure rapid restoration to service in the event of an

unexpected overhaul, an adequate store of spare parts should be maintained at all times.

Diagnosis Of Pump Problems


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Pump operating problems may be either hydraulic or mechanical. In the first category, a pump

may fail to deliver liquid, it may deliver an insufficient capacity or develop insufficient pressure,

or it may lose its prime after starting. In the second category, it may consume excessive power,

or symptoms of mechanical difficulties may develop at the seal chambers or at the bearings, or

vibration, noise, or breakage of some pump parts may occur.


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Common Pump Problems

1. Suction Problems

1. Insufficient suction pressure

2. Partial loss of prime

3. Cavitation4. Lift too high

5. Leaking suction at foot valve

6. Acceleration head requirement too high

2. System Problems

7. System shocks

8. Poorly supported piping, abrupt turns in piping, pipe too small, piping misaligned

9. Air in liquid

10. Overpressure or overspeed

11. Dirty liquid

12. Dirty environment

13. Water hammer

3. Mechanical Problems

14. Valves broken or badly worn

15. Packing worn

16. Obstruction under valve

17. Main bearings loose

18. Bearings worn19. Oil level low

20. Plunger loose

21. Main bearings tight

22. Ventilation inadequate

23. Belts too tight

24. Driver misaligned

25. Condensation

26. Seals worn

27. Oil level too high

28. Pump not level and rigid29. Packing loose

30. Corrosion

31. Valve binding

32. Valve spring broken

33. Cylinder plug loose

34. O-ring seal damaged


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CHILLERS

Chillers are typical refrigerant equipment that uses heat transfer between two different fluids to

achieve desired temperatures. Chillers are air-cooled or water-cooled, depending on the capacity

of the refrigeration system as well as the operating conditions of the system. The three primary

components of a chiller are condensers, compressors, and evaporators.

How A Chiller Operates:

1. Refrigerant flows over evaporator tube bundle and evaporates, removing heat energy

from the fluid.

2. The refrigerant vapor is drawn out of the evaporator by a compressor that pumps the

vapor to the condenser.

3. The refrigerant condenses on the condenser cooling coils giving its heat energy to the

cooling fluid; the condensed refrigerant heads back to the evaporator.

Key Components of A Chiller

Evaporator

Chillers produce chilled water in the evaporator where cold refrigerant flows over the evaporator

tube bundle. The refrigerant evaporates (changes into vapor) as the heat is transferred from the

water to the refrigerant. The chilled water is then pumped, via the chilled-water distribution

system to the manufacturing plants air-handling units.


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The chilled water passes through coils in the air-handler to remove heat from the air used in

various equipment. The warm water (warmed by the heat transferred from the plant machinery)

returns to the evaporator and the cycle starts over.

Compressor

This works on the principle of the refrigeration cycle. Vaporized refrigerant leaves the

evaporator and travels to the compressor where it is mechanically compressed, and changed into

a high-pressure, high-temperature vapor. Upon leaving the compressor, the refrigerant enters the

condenser side of the chiller.

Condenser

Inside the water-cooled condenser, hot refrigerant flows around the tubes containing the

condenser-loop water. The heat transfers to the water, causing the refrigerant to condense into

liquid form. The condenser water is pumped from the condenser bundle to the cooling tower

where heat is transferred from the water to the atmosphere. The liquid refrigerant then travels to

the expansion valve.

Expansion Valve

The refrigerant flows into the evaporator through the expansion valve or metering device. This

valve controls the rate of cooling. Once through the valve, the refrigerant expands to a lower

pressure and a much lower temperature. It flows around the evaporator tubes, absorbing the heat

of the chilled water thats been returned from the air handlers, completing the refrigeration cycle.

HEAT EXCHANGERS

The word exchanger really applies to all types of equipment in which heat is exchanged but is

often used specially to denote equipment in which heat is exchanged between two process

streams. Exchangers in which a process fluid is heated or cooled by a plant service stream are

referred to as heatsers and coolers. If the process stream is vaporized the exchanger is called a

vaporizer if the the stream is essentially completely vaporized: called a reboiled if associated

with a distillation column: and evaporator if used to concentrate a solution.

If the process fluid is condensed the exchanger is called a condenser. The term fired exchanger isused for exchangers heated by combustion gases, such as boiler. In heat exchanger the heat

transfer between the fluid takes place through a separating wall. The wall may a solid wall or

interface.

Heat exchangers are classified basing on the following:

1. Transfer Process (Direct or Indirect)


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2. Surface Compactness

3. Construction (Tubular, Plate)

4. Flow Arrangement

5. Transfer mechanisms

Figure 1: U-tube Heat Exchanger

Figure 2: Plate Heat Exchanger


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The common heat-exchanger at Mukwano is the Gasketed-plate heat exchanger.It consists of

a series of corrugated alloy material channel plates, bounded by elastomeric gaskets are hung off

and guided by longitudinal carrying bars, then compressed by large-diameter tightening bolts

between two pressure retaining frame plates (cover plates). For these heat-exchangers, common

repairs rotate around gasket replacements due to over-heating. They rarely break-down.

VALVES

By definition, valves are mechanical devices specifically designed to direct, start, stop, mix, or

regulate the flow, pressure, or temperature of a process fluid. Valves can be designed to handle

either liquid or gas applications.

Valve Classification According to Function

By the nature of their design and function in handling process fluids, valves can be categorizedinto three areas: onoff valves, which handle the function of blocking the flow or allowing it to

pass; nonreturn valves, which only allow flow to travel in one direction; and throttling valves,

which allow for regulation of the flow at any point between fully open to fully closed.

One confusing aspect of defining valves by function is that specific valve-body designssuch as

globe, gate, plug, ball, butterfly, and pinch stylesmay fit into one, two, or all three


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classifications. For example, a plug valve may be used for onoff service, or with the addition of

actuation may be used as a throttling control valve.

Another example is the globe-style body, which, depending on its internal design, may be an on

off, nonreturn, or throttling valve.


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References

1. Company Equipment and Machinery Manuals

2. Pump Hand-book by Igor J. Karassik

3. Engineering Maintenance, A Modern Approach by B. Dhillon

4.

Maitra, G.M.; and Prasad, L.V. 1985. Handbook of Mechanical Design, pp. 89-108.McGraw Hill, New Delhi, India.

5. The Art Of Soap Making by Alexander Watt

6. Plastics Machinery and Technology and Ian Willsburg

7. Company Engineers, Machine Operators and Documents