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Combined Heat and Power Engines (CHP)

Internal combustion engines are used extensively for a variety of energy services such as power generation (for example on fishing boats), transport and irrigation. They are also used for Combined Heat and Power (CHP) and Combined Cooling, Heating and Power (CCHP) application to achieve a higher overall efficiency than could be achieved through single generation. Energy services account for around two-thirds of the total greenhouse gas (GHG) emissions in the world; out of total GHG about 40% is from transportation, heat and electricity. Therefore, a considerable reduction in GHG emissions is possible by substituting fossils fuels with new and renewable biofuels produced from biomass conversion such as pyrolysis, gasification or anaerobic digestion.

CHP research at EBRI    

EBRI CHP engine
The CHP engine in the EBRI demonstration power plant

EBRI researchers are working to produce both liquid and gaseous advanced biofuels for CHP applications. Liquid biofuels produced through pyrolysis can be used in internal and external combustion engines and are promising to replace fossil diesel use in compression ignition engines. Gaseous biofuels can either be produced by pyrolysis, gasification or anaerobic digestion and can be used in gas-fired boilers, gas turbines, spark ignition (SI) engines or dual-fuel engines.

Tackling industry issues

One of the main issues with pyrolysis oils is that they are generally corrosive and have a high water and low energy content. For this reason research is being undertaken at EBRI to upgrade pyrolysis oils and modify engine components to adapt internal combustion engines for CHP applications so that they can run on these bio-oils.

Some of the ways to upgrade pyrolysis oils are:

  • Cracking: This process consists of catalytically decomposing long-chain molecules present in the pyrolysis oils and converting them into shorter molecules. In this way, properties such as viscosity and ignition quality are improved.
  • Concentration: This is done through evaporation or distillation. The difficulty lies in possible degradation of pyrolysis oil when it is subjected to temperature treatments.
  • Hydrodeoxygenation: This process consists of adding hydrogen and removing oxygen from the bio-oil components. Reactions involved in this process are activated by oxide catalysts.
  • Blending and emulsification: The blend is usually with biodiesel or fossil diesel, but other alternative fuels like bioethanol are also being studied.
  • Biorefinery: This concept refers to the upgrading of pyrolysis oil to produce commodity chemicals. The concept is analogous to a petroleum refinery, which produces both fuels and chemical products from petroleum.

Other options to upgrade pyrolysis oils and gases are gasification and steam reforming. The latter is a catalytic reaction in which molecules are decomposed into CO, CO2, CH4 and H2 using water as the oxidising agent in order to obtain a H2–rich gas.

Regarding the engine components, some of the modifications involve the use of dual-injection which consists of having one injector for the oil and another injector for diesel or biodiesel. Other modifications include the use of corrosion resistance injectors; this involves adapting the injector materials with more corrosion-resistant materials such as stainless steel. Modification of the fuel supply system, cylinder liners and piston are also required to use pyrolysis oils in the engine.

EBRI researchers tested bio-oils obtained from pyrolysis of sewage sludge and paper industry sludge in stationary diesel engines to assess the engine performance and exhaust emissions. Two engine test beds were used, a three-cylinder Lister Petter indirect injection biodiesel engine test bed and a two-cylinder Lister diesel engine test bed. Pyrolysis oils were then blended with biodiesel in different proportions. The performance of different blends, that is quality of emissions and general operation of the engine, was then assessed.

Based on these initial studies, work is currently being done on optimisation of the pyrolysis reactor parameters and additional units, up-gradation of bio-oils and engine modification to better improve the quality and performance of the biofuels based-CHP operation.

 

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