Natural Gas Compressor

[sloeffle]

Was in WV riding SXS this past weekend and we came across this natural gas compressor (we think). At first we thought it was broken but a friend of mine thinks it's a hit and miss engine. I didn't realize those were still widely used. There was a gas pipe on the other side, so I was little hesitant on walking over there. The side I took the video from looks to be where the radiator is at.

We also came across an old Cat 777C dump truck. The engine was still in it, all of the wiring etc was missing.

 

[Tonty]

The “hit and miss” engines are still used some in this area to run oil derricks. Most of them here would be Fairbanks and Morse diesel powered, I think. I have an uncle who worked on those types of oil wells, and he has one at his place that he fires every now and then for nostalgia.

 

[ABMax24]

Pumpjacks around here still use the Arrow single cylinder engines, they are not hit and miss but are low speed, 300-800rpm. Can here them popping along for miles out in the bush. Beauty of those engines is they run on just about any gaseous fuel, so a small amount of fuel gas from the wellhead is all that is needed to power the pumpjacks.

In terms of gas compression though, that compressor in the video is tiny. I was working at a site 2 day ago that ran 4 Waukesha 7044 engines coupled to 4 cylinder Ariel compressors. 1440hp per unit. That site moves 53 million cuft of gas per day. I worked at another plant that ran 2 solar gas turbines for gas compression, 22,000hp a piece.

The biggest I've ever seen was a 25,000hp turbine powering a compressor, that was on a deepcut unit that compresses the gas, then expands it in a refrigeration cycle to cool the gas to -150f, to condense the light products like ethane to allow them to be separated off. The turbo expander in that plant generates 5000hp alone when the gas is expanded.

 

[sloeffle]

Pumpjacks around here still use the Arrow single cylinder engines, they are not hit and miss but are low speed, 300-800rpm. Can here them popping along for miles out in the bush. Beauty of those engines is they run on just about any gaseous fuel, so a small amount of fuel gas from the wellhead is all that is needed to power the pumpjacks.

From what we could tell, it looked to be a horizontal cylinder too ?? There were two four - six ( as a guess ) inch gas lines running down the hill.

In terms of gas compression though, that compressor in the video is tiny. I was working at a site 2 day ago that ran 4 Waukesha 7044 engines coupled to 4 cylinder Ariel compressors. 1440hp per unit. That site moves 53 million cuft of gas per day. I worked at another plant that ran 2 solar gas turbines for gas compression, 22,000hp a piece.

Coincidentally, Ariel compressors are built about twenty minutes from my house in Mt Vernon OH. Rolls Royce, and then Siemens had a factory in Mt Vernon also that built natural gas compressors too but it shut down a few years ago.

The biggest I've ever seen was a 25,000hp turbine powering a compressor, that was on a deepcut unit that compresses the gas, then expands it in a refrigeration cycle to cool the gas to -150f, to condense the light products like ethane to allow them to be separated off. The turbo expander in that plant generates 5000hp alone when the gas is expanded.

Can you explain what a natural gas compressor does, or point me to a article ? Very interesting stuff.

 

[peakbagger]

Natural gas is moved around the country in high pressure gas lines, the higher the pressure the more gas that can be pumped through a pipe. Natural Gas formations may coming out of the ground at very low pressure so its pressure needs to be raised to whatever pressure the pipeline its discharging to. Natural Gas has friction when its running through a pipeline so every so many miles, the pipeline will have a compressor station to bring the pressure back up to compensate for the pressure lost in friction. The compressors are very similar to air compressors, they can be reciprocating or rotary. The big difference is if there is leak around an air compressor, its just wasting a bit of air while a leak around a natural gas compressor is fire or explosion hazard. The compressors can be either driven by electricity or a natural gas driven engine or turbine. Natural gas is lot cheaper and its already right there but its another ignition source. Electric is far less of an ignition source and the electricity is more expensive. Most gas utilities distribute gas at very low pressures, fine for house but not so good for big equipment like big turbocharged or direct injection engines or gas turbines. This equipment takes the low pressure street gas and raises it up to the required pressure for the equipment. It also needs to be built explosion proof. A project I am working on has to buy one of these and its $750,000 and the size of cube van.

There is big gas line that runs through our town that goes from Quebec to South Portland Maine. They were in a rush to build it and did not put in compressor stations in the US portion of the pipeline. Its pumped up to 1400 psi at the border and ends up at 400 psi at the other end. They could pump a lot more gas through the line if they put in compressor stations. New England is alwayss complaining about not enough gas line capacity but when the pipeline owners go out looking for someone to put in the compressor stations no one is willing to pony up for it.

 

[ABMax24]

From what we could tell, it looked to be a horizontal cylinder too ?? There were two four - six ( as a guess ) inch gas lines running down the hill.


Coincidentally, Ariel compressors are built about twenty minutes from my house in Mt Vernon OH. Rolls Royce, and then Siemens had a factory in Mt Vernon also that built natural gas compressors too but it shut down a few years ago.




Can you explain what a natural gas compressor does, or point me to a article ? Very interesting stuff.

Ariel compressors are the gold standard around here for reciprocating gas compression, if your in North America and use natural gas the odds are it went through at least one Ariel compressor along the way. Pretty cool they are built that close to you.

As has already been mentioned, in the most basic sense a natural gas compressor is like an air compressor that is completely sealed. Suck in gas at low pressure, compress the gas in one or more stages, and discharge it. Again as already been said this is done for gas transmission.

Gas compression is also needed for gas processing, I work in the upstream and midstream side of the industry, basically anywhere from the well to the long distance transmission line. Generally you don't have an oil well or a gas well, usually it's a combination of both with water, it's the proportions that change and denote the naming. A well will produce hydrocarbons ranging from wax or bitumen all the way to methane, with thousands of products in between.

Raw "natural gas" is the same way. Usually you will have from C1 to C4 (number of carbon atoms in the hydrogen carbon chain) in the mix. Quite often there are even traces of heavier C5+ compounds. When a gas is compressed these heavier molecules tend to condense into a liquid where they can be separated out. Generally it's possible to extract the majority of molecules heavier than C3, and even a good portion of the C3 with compression alone. The remaining C3 (propane and it's isomers that are sold as LPG) are more valuable than the methane, and there is financial advantages to separating this remaining propane out. In this case refrigeration is used to help condense out the propane, ironically using a compressor pumping propane in a sealed loop as the refrigerant, chilling the process gas to around -15c allowing the propane to condense and be separated out.

This leaves C1-C2 gas behind. C2 is ethane and it's isomers. Ethane again is more valuable than the methane, so there is advantages to stripping this out. It's also for safety of the consumer, natural gas usually runs about 1000 btu/cuft, leaving lots of ethane or propane in the gas increases this btu rating considerably, burning hotter and can even run a risk of overheating natural gas appliances. Again this is stripped out by compressing the gas and also cooling it, either with a separate refrigeration loop or the process gas itself, except this time the gas has to be cooled much lower to drop out the ethane. In a big plant this refrigeration step takes lots of energy, and a big compressor to run it.

 

[ABMax24]

I should have just posted this video. It pretty much explains the basics.

Smaller compressors less than 5000hp are often reciprocating types, but the large turbine powered ones are often screw or centrifugal type. But I've even seen small screw compressors on Chevy V8s.

What's not talked about enough is sizing, that is a science in itself, ensuring the compressor cylinders are sized for the hp moving them.

 

[brenndatomu]

Ethane again is more valuable than the methane, so there is advantages to stripping this out. It's also for safety of the consumer, natural gas usually runs about 1000 btu/cuft, leaving lots of ethane or propane in the gas increases this btu rating considerably, burning hotter and can even run a risk of overheating natural gas appliances

Now this, I did not know.

Years ago our shop class went to tour a gas booster station...they had one of the engines tore down for rebuild, it was a 4 cylinder of displacement that I do not recall (large!) but I do recall that something like 6-800 RPM was wide open. It was about the size of a room and we were able to walk into the crankcase and stand up in the cylinders. They gave us a couple of the piston rings to hang on the wall back at school...they were big enough to use a small hula hoops (way too heavy though)
They had 2-3 of these engines at this particular station...I can't even remember where it was anymore...down a dirt road and back in some holler, I do know that.

 

[ABMax24]

Now this, I did not know.

Years ago our shop class went to tour a gas booster station...they had one of the engines tore down for rebuild, it was a 4 cylinder of displacement that I do not recall (large!) but I do recall that something like 6-800 RPM was wide open. It was about the size of a room and we were able to walk into the crankcase and stand up in the cylinders. They gave us a couple of the piston rings to hang on the wall back at school...they were big enough to use a small hula hoops (way too heavy though)
They had 2-3 of these engines at this particular station...I can't even remember where it was anymore...down a dirt road and back in some holler, I do know that.

I've never had the opportunity to see the old engines like that, by time I started in the industry 14 years ago they were all shut in or replaced with more modern equipment.

The operating rpm hasn't increased much though, a 7044 maxes out at 1200rpm to make 1900hp (I had it wrong at 1440hp earlier). High rpm is a killer though for longevity, these engines go 4 years between overhauls and essentially run non-stop at full load for that time, speeding them up would likely shorten that interval. They even go 4000 hrs (almost a year) on an oil change, although they do hold 190 gallons of oil.

 

[peakbagger]

Ariel compressors are the gold standard around here for reciprocating gas compression, if your in North America and use natural gas the odds are it went through at least one Ariel compressor along the way. Pretty cool they are built that close to you.

As has already been mentioned, in the most basic sense a natural gas compressor is like an air compressor that is completely sealed. Suck in gas at low pressure, compress the gas in one or more stages, and discharge it. Again as already been said this is done for gas transmission.

Gas compression is also needed for gas processing, I work in the upstream and midstream side of the industry, basically anywhere from the well to the long distance transmission line. Generally you don't have an oil well or a gas well, usually it's a combination of both with water, it's the proportions that change and denote the naming. A well will produce hydrocarbons ranging from wax or bitumen all the way to methane, with thousands of products in between.

Raw "natural gas" is the same way. Usually you will have from C1 to C4 (number of carbon atoms in the hydrogen carbon chain) in the mix. Quite often there are even traces of heavier C5+ compounds. When a gas is compressed these heavier molecules tend to condense into a liquid where they can be separated out. Generally it's possible to extract the majority of molecules heavier than C3, and even a good portion of the C3 with compression alone. The remaining C3 (propane and it's isomers that are sold as LPG) are more valuable than the methane, and there is financial advantages to separating this remaining propane out. In this case refrigeration is used to help condense out the propane, ironically using a compressor pumping propane in a sealed loop as the refrigerant, chilling the process gas to around -15c allowing the propane to condense and be separated out.

This leaves C1-C2 gas behind. C2 is ethane and it's isomers. Ethane again is more valuable than the methane, so there is advantages to stripping this out. It's also for safety of the consumer, natural gas usually runs about 1000 btu/cuft, leaving lots of ethane or propane in the gas increases this btu rating considerably, burning hotter and can even run a risk of overheating natural gas appliances. Again this is stripped out by compressing the gas and also cooling it, either with a separate refrigeration loop or the process gas itself, except this time the gas has to be cooled much lower to drop out the ethane. In a big plant this refrigeration step takes lots of energy, and a big compressor to run it.

Thanks for the info on the processing side, something I never spent a lot of time on. The company I worked for was developing a small gas turbine package equipped with an Eliot microturbine to burn flare gas for auxiliary power units for small gas platform monitoring wells. I ran into something called gas hydrate formations that could form in pipelines but didnt spend much time on what needed to be done to deal with them before the company decided to abandon the project.

For my last employer I had to go through lots of calculations to make sure we avoided a potentially destructive shut down of a experimental natural gas compressor that we were asked to develop a test procedure for. There was some oddball transient pressure pulse that could form on shutdown of gas compressors that could damage them if not handled properly. It was long ago enough that I dont remember the details except that it was a PITA set of calculations. I also never got to see the compressor plant that supplied the CNG for the gas turbine our firm helped get installed in Mass, there were no gas lines nearby so the plant runs on several truck loads of CNG every day. Oil carryover from the compressors at the supply plant was a problem initially until they modified the plant.

When we did performance tests on big power plants near the mexican border we always needed to take many gas samples of the inlet gas during the test as the Mexican sourced gas could be highly variable composition, it usually had a higher btu content. I think the issue was propane and ethane making it into the pipeline.

 

[ABMax24]

Thanks for the info on the processing side, something I never spent a lot of time on. The company I worked for was developing a small gas turbine package equipped with an Eliot microturbine to burn flare gas for auxiliary power units for small gas platform monitoring wells. I ran into something called gas hydrate formations that could form in pipelines but didnt spend much time on what needed to be done to deal with them before the company decided to abandon the project.

For my last employer I had to go through lots of calculations to make sure we avoided a potentially destructive shut down of a experimental natural gas compressor that we were asked to develop a test procedure for. There was some oddball transient pressure pulse that could form on shutdown of gas compressors that could damage them if not handled properly. It was long ago enough that I dont remember the details except that it was a PITA set of calculations. I also never got to see the compressor plant that supplied the CNG for the gas turbine our firm helped get installed in Mass, there were no gas lines nearby so the plant runs on several truck loads of CNG every day. Oil carryover from the compressors at the supply plant was a problem initially until they modified the plant.

When we did performance tests on big power plants near the mexican border we always needed to take many gas samples of the inlet gas during the test as the Mexican sourced gas could be highly variable composition, it usually had a higher btu content. I think the issue was propane and ethane making it into the pipeline.

Hydrate formation is a major issue in upstream oil and gas too. The simple (but not simple to implement) solution is to remove all the water from the gas stream. Upon entering a facility the gas, oil, water mix enters the inlet seperator where the 3 fractions are roughly separated based on density. The gas then goes through the compressors, after which it is sent through a dehydration (dehy) unit. A dehy unit is simply a vertical column (sometimes called a contactor tower) where the gas stream flows upward and glycol rains down from the top and glycols affinity for water strips the water from the gas stream. The glycol is regenerated in a boiler for use again.

A very similar process is used to strip CO2 and H2S from the gas stream, except using amines instead of glycol.

These two steps remove the majority of the water from the gas stream, in a deepcut facility where the ethane is stripped from the gas the water content must be much lower due to the low temperatures involved. In this case large towers full of desiccant beads are used after the dehy process, where the gas flows through the towers reducing water content further. Generally these system are built in multiples of 3 towers, one is processing gas, another has hot gas flowing through it to regenerate the beads, this gas becomes saturated with water and is sent back upstream if the dehy. And the third tower is being cooled back down readying it to handle process gas again.

As you can imagine these desiccant towers and deepcut units are large and complex units and are only built at the large processing plants prior to the gas entering the large transmission lines.

Most of the facilities I work at are upstream of the final processing plants, so in this case a small amount of methanol is injected at the end of the process to prevent hydrate formation in the pipelines.

As far as gas composition, most of the modern engines have controls to handle variability in fuels, at least to some degree. One issue I have heard of is when a gas stream has a significant portion of CO2. Inevitably it often leads to some level of derating of the engine to adjust for the lower levels of fuel and oxygen being delivered to the cylinders.