ongc, hazira plant achieving reduced flaring through control valves

ONGC, HAZIRA PLANT

ACHIEVING REDUCED FLARING THROUGH CONTROL VALVES

2

Introduction

Control Valve and Characteristics

ANSI Standard

Problems, Investigation & Solution

Achieving reduced Flaring through Control Valves

Conclusion

Reduced Flaring through Control Valves

Introduction - I

• Flaring is a concern both to the public and

government .

• Flaring is an environmental concern with

regards to global warming and acid deposition.

• Flaring is also a very important safety measure

at natural gas facilities as it safely disposes of

gas during emergencies, power failures,

equipment failures or other "upsets" in the

processing.


Introduction - II

•However if during normal operations the flare

control valve is not properly closed then it is

possible that some gas may pass through it.

This state of valve is called passing. Under such

a situation we are losing unprocessed gas to

atmosphere.

Umbhrat

Daman

Mumbai

Vasai

Hazira

Vadodara

N

ArabianSea

PannaaMukta

Tapti

36”42”


Introduction - III

•ONGC Hazira Plant is

situated on the

western shore of India

and spread over an

area of 6.25 square

kilometers. It

processes around

46MMSCMD of sour

gas and 5500 Mf of

sour condensate

everyday


Introduction - IV•With the increased focus on the effects of

climate change on the environment, paper

highlights efforts of ONGC Hazira Plant for

reducing the carbon footprint and abating

greenhouse gases brought on by plant upsets

and how flare control valve 37-PV-1220 of unit

train 37 pertaining to Gas Sweetening Unit was

modified to achieve zero flaring. The

modification was done within the parameters of

defined ANSI standards related to control

valves.


• The control valve is a critical link in the process

control chain in any plant. They can be used for

regulating flow or for regulating and relieving

pressure.

• The flare valve PV-1220 is a 14 inches, 600

Class Globe Type valve having equal

percentage characteristics.


Control Valve Characteristic

•FLOW CHARACTERISTIC

The relationship between Valve capacity and

valve travel is known as the flow characteristic

of the valve. Valves can have quick opening,

linear, equal percentage flow characteristics.


Control Valve Characteristic•A linear flow characteristic is one that has a

flow rate directly proportional to valve travel.

•An equal percentage flow characteristic is one

in which a flow rate change is proportional to

the flow rate just prior to the change in valve

position. Equal increments of valve travel result

in equal percentage changes to the existing

flow rate.


Flow Characteristics


Equal Percentage Characteristics• The change in flow rate observed regarding

travel will be relatively small when the valve

plug is near its seat and relatively high when

the valve plug is nearly wide open. Therefore, a

valve with an inherent equal-percentage flow

characteristic provides precise throttling control

through the lower portion of the travel range

and rapidly increasing capacity as the valve

plug nears the wide-open position.

Reduced Flaring through Control Valves Characterizing Control

Valves• The purpose of characterizing control valves is

to allow for relatively uniform control stability

over the expected operating range.

• The selection of valve body material and trim

material is typically based on pressure,

temperature, and corrosive and erosive

properties of the liquid. Typical materials that

one can cast into a valve are carbon and

stainless steel, Monel, Hastelloy, iron, and

bronze. Valve seats are an integral part of a

valve. Seat material must be compatible with

the process fluid. Valve seats can be either

metallic or nonmetallic.


ANSIFCI 70-2-1991

• In addition, the amount of valve leakage is

important, and the process and design

requirements dictate how much leakage is

allowable.

•Control valve seats are classified as to and in

accordance with ANSIFCI 70-2-1991 for leakage

(Refer Table).


ANSIFCI 70-2-1991

I -

Valve seat leakage classifications

Leakage class designation Maximum allowable leakage

II 0.5% of rated capacity

III 0.1% of rated capacity

IV 0.01% of rated capacity

V 5x10-12m3/s of water per mm of seat diameter per bar differential (0.0005 ml/min per inch of seat diameter per psi differential)VI Not to exceed certain specified and stringent amounts


Detecting problem of Passing, Investigation and Solution

• There are no direct methods to pinpoint that

flare valve is passing. However the following

methods are used to arrive at a conclusion:

• Increase in flare of the flare header which is

also indicated the flare header meter

• Sweating on pipeline on which valve is installed.


Detecting problem of Passing, Investigation and Solution

•Once the valve is identified, the valve is closed

with hand-wheel and it is confirmed whether

any reduction in reading of flare meter has

occurred.

•Once it is established that valve is passing,

attempts of rectification of problem starts.


Probable failures in Control Valves

So what may go wrong with a control valve and reduce overall performance ?

• Actuator Broken Spring Air leakage (diaphragm, tubing)

• Positioner Linkage Pneumatics (I/P, Relay) Calibration / Performance Loss of air supply

• Trim Wear (plug/seat) Seat leakage Body damage

• Packing Wear Fugitive Emissions Stem Wear/Corrosion


Investigation•A thorough investigation of the problem and its

causes was undertaken. In this application, the

control valve is required to provide tight shut-

off capability. There are actually six different

seat leakage classifications as defined by

ANSI/FCI 70-2-1976.

•Most control valves application provide valve

seat leakage classification as per CLASS IV.

•CLASS IV is also known as METAL TO METAL.

Certain kind of leakage rate is always expected

from a valve with a metal plug and metal seat.

Reduced Flaring through Control Valves Solution

•CLASS VI is known as a SOFT SEAT

classification. SOFT SEAT VALVES are those

where either the plug or seat or both are made

from some kind of composition material such as

Teflon.

• Therefore to provide tight shut off it was

decided to provide a soft seat instead of

metallic one. This would confirm to Class VI of

valve leakage classification Table and would be

improvement over the original valve leakage

Class V.


Shutdown Activities

• To carry out the modification, shutdown of

process unit train was taken. Prior to the unit

train GSU shutdown, tripod with chain pulley

arrangement was made for lifting of the big

control valve. Once shutdown of GSU was

taken, upstream and downstream isolation

valves were completely closed. For safety

reasons, all fluids were drained.


Work done on Control Valve

• First actuator was disengaged and removed and

then valve was dropped from bonnet. The old

stem and plug assembly was taken out. The

orientation of parts, such as gaskets, seat rings,

plugs and actuators was marked for proper re-

assembling.


Internals of Control Valves


Internals of Control Valves - II


View of new Stem & Plug Assembly•A new stem and plug assembly with Teflon

coated seat was installed. The valve was

reassembled. The Line gaskets were also

changed. Stroke check was also done.

•After the valve was taken into service, no

passing was observed from the flare valve.

Thus the modification of having a soft seat

had worked successfully.

•Based upon above experience all flare

valves have been fitted with soft seats.


Results and Conclusions

ACHIEVING REDUCED FLARING THROUGH CONTROL

VALVES

THANKS…

ongc, hazira plant achieving reduced flaring through control valves

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