Optimization of Valves Inspection in Order to Reduce Flaring in a Gas Refinery

Introduction

Gas flaring, the process of burning-off associated gas from wells, hydrocarbon processing plants or refineries, either as a means of disposal or as a safety measure to relieve pressure. It is now recognized as a major environmental problem, contributing an amount of about 150 billion m3 of natural gas is flared around the world, contaminating the environment with about 400 Mt CO2 per year.

Why Flaring Occur in an Oil and Gas Plant?

Regardless of unwanted or wanted shut-down, sweeping gases of piping, need for depressurizing piping and equipment, and bad operation, one of the main sources of flaring is flaring system valves include both relief and non-relief valves. Safety relief valves are usually inspect according to the plant specifications, RBI planning or related codes and standards like NBIC NB-23 Part4, EEMUA 188, API 570/510/576/527/RP 524. Non-relief valves on the hand are not easy to inspect both during operation and shut-downs.

On-stream Inspection of Valve or On-line inspection

There are hundreds valves in one flaring system, so it is not easy to inspect and overhaul all of them during shut-downs. The best idea is to know the amount of leakage each valve has, and sort them. Prioritization according to the 80/20 rule is an effect act in reduction of flaring. It is important to sort hundreds valves in a short time with the least cost. First we need to know how to inspect valves when they are in service. There are some methods for on-stream (in-service) inspecting of valves:

1- Touching

By touching a valve, especially in the gas services, due to the pressure drop on the down stream, the fluid becomes cooler. The more leakage the valve has, the cooler it becomes.

2- Hearing the voice

When there is a leakage in the valve, a sharp voice usually could be heard. Sometimes you need to put your ear on the valve!

3- Ultrasonic Measurement

Although when it comes to UT, inspection of welds cross our minds, it is very useful for measuring flow that transmit through the line. We know that velocity speed depends on the density of a medium, so, by increasing flow, the density of the medium gets bigger and velocity of sound increases.

This method could be conducted in 2 different ways, one is portable and the other is in-line. The portable form is usually used for inspection or random checking of a line and the in line form is usually used as a flow-meter or flow transmitter.

4- Thermographic inspection

Thermography is used when there is thermal gradient in an equipment or in the tiny spaces with different temperature. It uses electromagnetic to differentiate the temperature and shows it in different colors. This method is mostly used for inspection of steam-traps.

Conclusion

Thermography is partially cheaper method than the UT, however is it faster that it. On the other hand, UT is more accurate than thermography and the plan for maintenance of the valves has to be based on the flow leakage sent to the flaring system. It seems initial filtration could be based on the thermography and the final sorting of the nominated valves could be based on the UT method. In the end, 80/20 rule which means by maintenance of 20% of valves, you could reduce 80% of flaring will help you to save cost and time!

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