Engine-driven compressor suppliers for gas turbines and reciprocating engines are constantly challenged to improve efficiency while also complying with regulations on emission limits set by the U.S. Environmental Protection Agency (EPA). Striving for both increased efficiency and decreased emissions can be seen as conflicting objectives.
For example, high gas turbine efficiency can be achieved when combustion temperature increases. This leads to the formation of nitrogen oxides (NOx) and other harmful pollutants. However, lowering the combustion temperature to avoid NOx formation may lead to carbon monoxide (CO) and other potentially toxic agents. Many companies need a strategic solution to meet the regulations and gain efficiency with gas compressor technology.
Some companies lean toward replacing aging reciprocating engine compressors with the most efficient and low-emission gas turbine-driven compressors available. This trend was prompted by stricter EPA emission requirements, along with high natural gas demands that require long-lasting engine performance.
To minimize emission rates to comply with standards set by the EPA, several pollutant control methods for existing gas compressors have been developed by original equipment manufacturers (OEMs) as well as research and development companies. These innovative technologies include:
- Selective catalytic reduction
- Installation of catalyst on the exhaust duct
- Steam or water injection
- Lean pre-mixed (LPM) combustion technology
- Selection of the fuel gas
- Hydrogen as a fuel supplement source
Crafting the Right Solution
Most gas turbine manufacturers are now using LPM technology through the solutions mentioned above to gain higher efficiencies and lower emissions. One LPM technology solution alone may not adequately reduce emissions depending on the specific compressor station’s variance in operating modes. Implementing a combination of emissions reductions measures, such as installing a catalyst on the exhaust duct and utilizing hydrogen as a supplement to fuel gas, should be considered to fit needs of the company implementing the new technology.
The selection of the fuel gas source is just one variance that can be critical when it comes to identifying a solution to minimize emissions, as the engine performance is strongly tied to the fuel type used. The heating value of the fuel gas is also important to consider, as it controls the amount of heat produced during the combustion process and contributes to greenhouse gas emissions. Failure to operate gas compressors within the planned specifications, as well as not taking these two factors into account, can cause a system to fall short of the EPA’s emission targets.
Looking to the future, one alternative fuel source — a supplement to regular fuel gas — to minimize emissions and environmental impact is the use of hydrogen, an alternative energy source that has traditionally been used in power plants. Intentionally adding hydrogen to the fuel gas, at certain proportions, may help reduce the emissions and reduce the operating costs of the stations. However, because of hydrogen’s high combustion temperature, hydrogen-fueled gas compressors are still in development but could be a viable solution moving forward.
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