Sulphur deposition in gas pipelines 2

[Adam01]

We operate a gas fired power station. A mix of gas converted PF fired boilers and CCGT's, some HRSG's with supplementary firing. We have had problems with sulphur blocking pressure regulating valves on the GT skids. The problem is intermittent, supporting the theory that the formation is a consequence of temp and pressure. It also seems to be forming only where there is a pressure change like an obstruction or regulating valve. Has anyone else experienced the same problem. If so were you able to address it through operational changes to T and P?

Adam01

 

[hacksaw]

you must be using pilot operated valves

transmitter based control loops will be less prone to that sort of problem.


the more difficult problem is the sulfur accumulation. you need to contact your gas supplier and get the low down on the cause (improperly operated h2s removal eq).

 

[Adam01]

The gas is within specification as fas as sulphur is concerned.

We regulate with pilot operated valves as you suspected. The sulphur can accumulate to significant quantities but we see it mostly at the first unit off the main. It has caused a trip of this unit to liquid fuel (back-up fuel) when the strainer was blocked with it. Apart from that occasion we have not seen it continue to build-up. There is a light dusting of it in the entire pipeline and at the regulating valves of the other units.

There is a theory that it re-entrains itself when the temperature or pressure changes. I'd be interested to hear of anyone that may have done any testing to determine if it is possible to cause it to form. The aim would be to form it where it can be controlled and then removed from the gas system.

We also have a complicating issue. The gas compressors, some 850 km away are reciprocating units. These are lubricated with a mineral oil. The compressors were over-lubricated and the pipeline filled with oil. Being the biggest user we receive the highest flow, and most of the oil. The oil causes many problems as the pipeline was not built to handle liquids. However the oil also mixes with the sulphur to form a paste. The oil prevents the sulphur from re-entraining in the gas, so as the oil builds up so does the S.

The oil also changes the Dew point so now we have large quantities of S and an "off design" dew point. I am concerned that the S can now come through in "slugs" significantly higher than the GT manufacturers limit and we do not know if the dew point controls (+20 Deg C of superheat) are adequate.

Adam01

 

[rjouan]

Oil and gas journal have been approaching the subject called S8 threatens natural gas operation written by A B Chesnoy. You can do research on the web with S8 or Andre Bernard Chesnoy.

GE had similar problems on some of their gas turbines and issued an IAD service letter where they were advising to heat up the gas before injecting in in gas turbine engine to avoid fuel regulating valve blockage with sulfur.

Increasing gas temperature is a spending but it is minimized because the utility efficiency should increase.

 

[hacksaw]

preheat won't eliminate your problems unless you vaporize the sulfur or cause it to react. both would be undesireable.

you've got a definite mech. problem. sounds like you need to identify the scope of work needed to correct it and to start assigning costs/benefits to the changes.

 

[TingaTangaBob]

Have you solved this problem since the post Adam1? I am currently facing similar problems. thanks

 

[oxilume]

Sulfur Problems,

In 1994, when I worked for a large water treatment and process side treatment chemical company, I injected an oxygen scavenger into a crude tower to reduce corrosion.

The unexpected result is that sulfur in raw products decreased dramatically.

One of my other customers was a NG company. Their pipeline was accidentally struck by a backhoe during excavation of a telephone line. Since, the NG in the pipeline had more than 10 ppm of H2S, OSHA requirements were going to make this pipeline repair job quite expensive. I suggested using the oxygen scavenger.

The O2 scavenger was injected about 30 miles upstream. It worked. The H2S levels dropped to below 10 ppm.

Consequently, this led to two patents. Many of the R&D people who got involved later, could not believe that the results were real, primarly due to the chemistry. About a year later, I injected the O2 scavenger down hole into an oil well to eliminate corrosion. It stopped corrosion dead in its track. Also, the sucker rod did not part in the usual 90 to 120 days. Paraffin wax deposition on the sucker rod was inhibited.

With respect to your problem of sulfur buildup on the surface of equipment and consequently fouling the equipment, you need to investigate with the NG company to determine if any of the chemicals have been changed. Corrosion inhibitors are injected throughout the pipeline route and not just at the compressor station.

Ask if they are injecting an O2 scavenger? Be specific about requesting the MSDS and the Product Data Sheet.

If you need very detailed information, please let me know.

 

[Adam01]

Thanks all for the responses, We had an acceleration of the sulphur deposition in one GT supply and were forced to take the unit offline and blow out the gas line. When we inspected the internals with a camera it was clear that the S was worst after the regulating valve. The regulated pressure was set differently to all the other GT's. This was raised by 200 kPa to 2400 kPa and the unit put back into service with a cleaned line. We have inspected it twice now over 1 month and have found no significant build-up. We will continue to inspect. I will advise progress.

On the issue of corrosion inhibitors, We have never asked the question. The gas is conditioned and treated at the well head some 900 km away and delivered by a pipeline carrier to us. It is dry and HC free when it enters the pipe. On this basis I do not think the gas is treated by the carrier after it enters the pipeline. However I will ask. It may well be treated at the well head as you say but we find that the gas supplier (not the carrier)is not cooperative and answers questions through their lawyers.

Thanks again for the responses I will follow-up.

 

[oxilume]

Adam01,

If you have any other questions or problems regarding sulfur please don't hesitate to ask. I have a library full of sulfur documents from the research I conducted in the mid 90's.

Todd

http://www.oxilume.com

 

[mb44]

Adam,

Where is your power station?

I am aware of compresosr oil being supplied into main gas lines from faulty or not correctly operated gas compressors. I doubt if you will ever get the gas supplier to admit this is there fault, if they did they would have to install equipment for every end user and they won't want to do that.

There are ultra high efficeincy filter coalescers avaialble that can be installed and will remove this lube oil to 30 parts per billion....(I didnt belive this figure either but its correct)

If you don't do something about the lube oil it will eventually cause you problems if it gets to the GT

If you want more information on this just ask. I am investigating a similar problem for a large power station in the UK. We have done three others previously.

MB

 

[Adam01]

Power station is in Australia. There has been some movement on the issue by the gas supplier and I believe they are putting a coalescing filter in the line close to discharge of the compressors. I am not sure of the filter element rating, but will find out. They did admit to over lubricating the pistons and have reduced the lube rate. However there remains the problem of oil in the downstream 900km of gas line.

Sounds like a common problem if you have done installations in 4 stations? By the way, were there any issues with sulphur?

We are considering installation of coalescing filters in the gas lines before the GT's, so information on the filters you used would be most useful if you can direct me to it.

Much appreciative Adam01