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Compressors are heart of natural gas

production

By Norm Shade Published: August 6, 2014 2:30PM

With the development of the Utica Shale, more and more natural gas compressors are appearingon the Eastern Ohio landscape. Gas compressors have always beenpart of Ohios oil and gas

production, however, the size of the Utica play requires more and larger compressors than everbefore.

Raw natural gas is commonly collected from a group of adjacent wells and, after processing atthe collection point to remove water and natural gas condensate, it is pipelined to a gasprocessing plant. After further processing to remove salable liquid hydrocarbons (ethane,propane, butane, etc.), the natural gas is then delivered into the interstate pipeline grid, whichtakes it to commercial, industrial and residential customers.

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Natural gas compressors are literally the heart of natural gas production. Shale gas wells tend toproduce at very high pressures and flow rates initially, but they decline rapidly to a lower levelthat is sustained for many years. As the pressure declines, gas compressors must be deployed toboost the gas pressure high enough to push it through pipelines to market. Just as the heart isvital to collecting and pumping blood throughout the body, a gas compressor collects natural gas

from underground wells and pumps it to market.

Gas compressors are prevalent throughout the interstate pipeline grid and in gas processingplants, strategically located in a limited number of centralized plants. But upstream of thoseplants are many more gathering compressors, located at or near the actual wells that produce

gas from deep underground. Gathering compressors typically sit out in the open, not housed inbuildings. They pull gas from individual or a group of wells and boost the pressure to push it intoa gathering pipeline that leads to various types of processing facilities.

Most natural gas compressors are reciprocating (i.e., piston-type) compressors, driven byreciprocating engines that use natural gas fuel. Much larger than the average 110 to 150

horsepower automobile engine or even a 450 horsepower semi-truck engine, turbochargedcompressor engines are typically more than 1000 to as high as 4500 horsepower or even larger.Engine exhaust is quieted by a large industrial muffler, and to meet environmental regulatoryrequirements, exhaust is treated with a catalytic convertor, just as automotive engines are.

Large industrial gas compressors have two to six cylinders with internal pistons and checkvalves. Connected into a pipeline, a compressor draws gas in at a low pressure and delivers it outagain at a higher pressure to move it through the pipeline system. Depending on the needs of theparticular gathering system, the cylinders on a compressor may be configured to operate inparallel or in series (called staging). Most gas gathering compressors are configured in two- orthree-stages.

The compression process naturally causes the gas to heat up, so cooling is required before itenters the next stage for further compression or before continuing on into the pipeline. This isaccomplished with large air cooled heat exchangers. Similar in principal to the radiators in carsand trucks, the heat exchangers also cool the engine and compressor.

The engine, compressor and heat exchanger are mounted on one or more welded I-beam skidsthat allow the packaged compressor syst

The compression process naturally causes the gas to heat up, so cooling is required before itenters the next stage for further compression or before continuing on into the pipeline. This isaccomplished with large air cooled heat exchangers. Similar in principal to the radiators in carsand trucks, the heat exchangers also cool the engine and compressor.

The engine, compressor and heat exchanger are mounted on one or more welded I-beam skidsthat allow the packaged compressor system to be built in a factory and transported to a field siteon one or more large trucks. The skid also provides a platform for mounting accessory itemssuch as gas separators that remove small amounts of liquid from the gas, pulsation bottles thatsmooth out the pressure waves from the compressor, controls, and other equipment.

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Most compressor packages are built in the Southwestern states, however, Youngstown, Ohiopackager, Dearing Compressor & Pump Co., has enjoyed major growth with the development ofthe Marcellus and now the Utica Shale. Another Ohio company, Ariel Corporation in MountVernon, manufactures the majority of the large reciprocating gas compressors used throughoutthe world.

Most large compressor packages are mounted on concrete slabs. Some are housed insidebuildings, but most gathering compressors operate out in the open. Gas gathering compressorsoperate around the clock, often running more than 8400 hours a year. To put that figure inperspective, driving an automobile 15,000 miles a year at an average speed of 50 mph takes only300 hours.

A typical new Utica Shale gathering compressor has the capacity to deliver as much as $50,000of natural gas each day, make high reliability extremely important. Computerized controlsoperate and monitor the engine and compressor, keeping the system operating reliably orautomatically shutting it off if maintenance is required or a problem occurs. Satellite or cellular

links allow operators to remotely monitor the compressors, and mechanics are automaticallycalled out when unscheduled maintenance is needed. With annual maintenance and majoroverhauls every 4 or 6 years, these large compressor packages typically last for more than 20years.

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