Developers of distributed generating systems have two primary power sources to choose from: gas engines and gas turbines. Both have been proven in thousands of cogeneration (combined heat and power or CHP) installations around the world. Electric utilities, hospitals, universities, district heating, seawater desalting, food processing, textiles, petrochemical refining, chemical processing, pharmaceuticals, pulp and paper, and general manufacturing all use gas engines and turbines in CHP applications. Both technologies have steadily improved in terms of efficiency, reliability, emissions performance, and operating costs over the years. Both gas turbines and gas engines have distinct characteristics, and we provide the distinction between the two to meet the needs of the customer.
Gas Turbine
A gas turbine is an engine that is powered by the pressure of burning compressed air and fuel. A gas turbine, or power plant’s brain, is a combustion engine that converts liquid fuels, particularly natural gas, into mechanical energy. This energy drives a generator, which generates electricity. A fuel-air mixture is heated to extremely high temperatures within the gas turbine. As a result, the turbine blades spin quickly. Gas turbines power aircraft, trains, and ships, as well as electrical generators, pumps, gas compressors, and tanks.
Gas Engine
The gas engine is a type of engine that is powered by the production, expansion, or combustion of gas. Gas engines are mass-produced and inexpensive, whereas central power plants are a one-of-a-kind technology. Several gas engines are interconnected to form generating sets in a power plant setting. Every engine, however, is linked to a shaft, which is linked to an electric generator. The sets are available in standard sizes ranging from 5 to 20 MW. The gas engine contributes significantly to CO2 reduction through high-efficiency operation with natural gas and city gas, as well as low-calorie gases generated in gasification melting furnaces.
Gas Turbine VS Gas Engine
Several factors are used to describe the difference between a gas turbine and a gas engine. Various factors, such as those mentioned above, are considered when selecting a gas turbine or a gas engine for a specific application. The following factors highlight the primary distinctions between a gas turbine and a gas engine.
Cogeneration Energy Ratio
- The energy ratio of cogeneration in a gas turbine is composed of electricity (33%), steam (50%), and loss (20 percent).
- The energy ratio of cogeneration in a gas engine is composed of electricity (49%), steam (15%), hot water (13%), low-temperature water (10%), and loss (13 percent).
Heat Type Required
- The majority of the heat in a gas engine comes from steam.
- Hot water and some steam provide the necessary heat in the gas engine.
Cogeneration Total Efficiency
- The gas turbine achieves a total cogeneration efficiency of 80% to 83%.
- The gas engine has a total efficiency of cogeneration ranging from 63.5% to 77%.
Electrical Energy Efficiency (Partial Load)
- The gas turbine has a high electrical efficiency.
- The gas engine has a high electrical efficiency.
Heat Exhaust
- The gas turbine produces a large amount and temperature of exhaust gas.
- The exhaust gas temperature of the gas turbine is low.
Emissions of NOx (O2=15%)
- NOx emissions from a gas turbine range between 15 and 25 ppm.
- NOx emissions from gas engines are around 57 ppm.
Vibration
- The gas turbine has very little vibration.
- The gas turbine vibrates very little.
Machine Dimensions
- Small-scale gas turbine machines are available.
- The gas turbine category includes large-scale machines.
- Start-up Time
The start-up time of a gas turbine is 20 minutes. - The start-up time of a gas engine is 10 minutes.
Interval of Maintenance
- The gas turbine has a very long maintenance interval.
- The gas engine has a very long maintenance interval.
Other Differences
Here are a few more points to consider when deciding between a gas turbine and a steam engine:
- With the introduction of more gas engine products in the larger (more than 3 MWe) size range, improved performance (i.e. higher electrical efficiencies), and increased demand for flexibility, gas turbine suppliers are increasingly under pressure from gas engines.
- Peaking power plants must be able to operate flexibly, often with rapid ramp-up and ramp-down rates. Gas engines are well suited to meet these requirements. Although gas turbines will continue to be used, especially in larger peaking plants, the transition to gas engines is already well underway.
- 30 MWe gas turbines will most likely continue to dominate the market in mid-sized and large industrial sites with electricity and high-temperature steam/heat requirements. Gas engines (100 kWe to 20 MWe) are, however, stealing market share in a variety of other end-use sectors. Gas engines have gained market share at the expense of gas turbines, which are slower to ramp up and ramp down.
Summary
Gas turbines and gas engines have both proven to be useful to users in power generation applications. Each technology is well accepted in the market today and has found favor with users looking for reliable power and thermal alternatives. All of this points to a significant opportunity for gas-fired CHP systems. The time has come for power users and producers in industrial and commercial facilities to investigate the economic potential of CHP using today’s gas engine and turbine technologies.
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