ongc, hazira plant achieving reduced flaring through control valves
TRANSCRIPT
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.
Reduced Flaring through Control Valves
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”
Reduced Flaring through Control Valves
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
Reduced Flaring through Control Valves
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.
Reduced Flaring through 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.
Reduced Flaring through Control Valves
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.
Reduced Flaring through Control Valves
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.
Reduced Flaring through Control Valves
Flow Characteristics
Reduced Flaring through Control Valves
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.
Reduced Flaring through Control Valves
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).
Reduced Flaring through Control Valves
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
Reduced Flaring through Control Valves
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.
Reduced Flaring through Control Valves
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.
Reduced Flaring through Control Valves
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
Reduced Flaring through Control Valves
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.
Reduced Flaring through Control Valves
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.
Reduced Flaring through Control Valves
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.
Reduced Flaring through Control Valves
Internals of Control Valves
Reduced Flaring through Control Valves
Internals of Control Valves - II
Reduced Flaring through Control Valves
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.
Reduced Flaring through Control Valves
Results and Conclusions
ACHIEVING REDUCED FLARING THROUGH CONTROL
VALVES
THANKS…