Syngas Cogeneration / Combined Heat & Power
Syngas, also known as synthesis gas, synthetic gas or producer gas, can be produced from a variety of different materials that contain carbon. These can include biomass (wood gas), plastics, coal, municipal waste or similar materials. Historically town gas was used to provide a gas supply to many residences in Europe and other industrialised countries in the 20th Century. Gas engines utilising syngas as a fuel can be configured in a combined heat and power configuration in order to maximise the efficiency of the system.
Syngas is created by the gasification or pyrolysis of carbonaceous materials. Gasification involves subjecting these materials to high temperatures, in the controlled presence of oxygen with only limited combustion to provide thermal energy to sustain the reaction. Gasification can occur in man-made vessels, or alternatively could be conducted in-situ as in underground coal gasification (UCG). Where the fuel to the gasifier is of recent biological origin, such as wood or organic waste, the gas produced by the gasifier is considered to be a renewable fuel and the power produced by its combustion is renewable. When the fuel to the gasifier is a waste stream, its conversion to power in this manner has the combined benefit of the conversion of this waste into useful products.
Benefits of Syngas Utilisation in Gas Engines
- Generation of renewable power
- Conversion of problematic wastes to useful fuels
- Economical onsite power production and reduced transmission losses
- Reduction in carbon emissions
Synthesis Gas Composition Challenges
The composition of syngas is highly dependent upon the inputs to the gasifier. A number of the components of syngas cause challenges which must be addressed at the outset, including tars, hydrogen levels and moisture. Hydrogen gas is much quicker to burn than methane, which is the normal energy source for gas engines. Under normal circumstances, faster combustion in the engine cylinders would lead to the potential of pre-ignition, knocking and engine backfiring. In order to counter this challenge the engine has a number of technical modifications and the output of the engine is reduced to between 50-70% of its typically natural gas output. (I.e. a 1,063kW engine running on natural gas is comparable to a maximum 730kW engine on synthetic gas).
The following table provides a typical range for the composition of syngases. This will be dependent upon the specific chemical composition of the feedstock to the gasifier
Syngas and Fuel Gas Quality Requirements
A wide range of hydrogen gases can be used in gas engines. However as with all engine fuels, there are specific limits to different components the input fuel gas. Gas contaminants in syngas, most notably tar and humidity, are a key technical challenge to the utilisation of synthetic gases. Please request the special gas technical instruction for fuel gas quality for more information.
Syngas CHP Engine Concept
Varying compositions, as well as calorific values and the combustion behaviour of the gases from synthetic gases processes, put greater demands on engine design. Clarke Energy offers specially modified GE Jenbacher gas engines that make efficient use of these gases for combined generation of heat and electricity. Special features of these engines may include flame arrestors for the prevention of backfiring, special gas mixers to improve gas mixing and to be more robust to dirt. In general, the stable composition of wood gas makes it advantageous as an engine fuel. The high hydrogen content of some syngases however, means the combustion process is very fast, which increases the danger of engine pre-ignition, knocking or engine backfiring. To avoid this risk, GE has created an engine control system that is able to fuel the GE Jenbacher engine with a very lean mixture and, at the same time, react very quickly to variations in the engine load. Some synthetic gases have a high carbon monoxide content, which has a low combustion speed and is very harmful. GE has developed the specific gas engine combustion system that enables burning of the gas efficiently and reliably. Additionally, Clarke Energy & GE offer a safety technology package that allows firm handling of harmful gases such as carbon monoxide. Syngas can be used to create hot water, steam and electricity. The hot water and exhaust gases from the engines are fed into boilers. The resulting steam can be used within other localised industrial processes. Electricity generated by the GE gas engines can either be used on-site or sold to the public grid. Syngas electrical efficiencies of 37% and over can be achieved with Jenbacher gas engines
Advantages Fuelling Gas Engines with Syngas
- Independent power supply
- Reduced energy costs, and greater predictability and stability
- Efficient and economic combined heat and electricity supply
- High electrical efficiency compared to other power generation technology (i.e. steam or gas turbines)
- Best suited for an electrical output range of a few hundred kW up to 20-30MW
- Low gas pressure required
- Alternative disposal of a problem gas while simultaneously harnessing it as an energy source
- Substitute to conventional fuels
- Environmental benefits by greenhouse gas reduction
Clarke Energy has comprehensive experience with gas engine technology and has a large reservoir of knowledge with respect to handling tricky gases such as syngas. About 30 GE Jenbacher gas engines now run on either coke gas or LD converter gas. Underscoring GE’s technical expertise, these units recently reached a combined total of more than 1 million operating hours. In addition, by utilising these ‘free’ waste gases compared to using natural gas for power generation, the GE Jenbacher technology-equipped sites have achieved CO2 savings of about 2 million tonnes since commissioning. If you would like to find out more about how Clarke Energy can help you develop your landfill gas project, please contact your local office for more details.