ACHIEVING REDUCED FLARING THROUGH CONTROL VALVES ONGC, HAZIRA PLANT SYNERGY WITH NATURE

Achieving reduced Flaring through Control Valves Introduction Control Valve and Characteristics ANSI Standard Problems, Investigation & Solution Conclusion 2

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.

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 N Vadodara Hazira Umbhrat Arabian Sea Daman Tapti 36” 42” Pannaa Mumbai Mukta Vasai

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

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.

Reduced Flaring through Control Valves Results and Conclusions 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.

ACHIEVING REDUCED FLARING THROUGH CONTROL VALVES THANKS…