Most power plants these days are powered by combustion process, which produce massive amount of heat. A percentage of heat is harnessed and transformed into electricity, a large percentage of heat is lost into the enviroment. A co-generation power plant re-use the lost energy, which increase the total thermal efficiency of the power plant.
Co-generation (Combined Heat and Power) is a system that uses fuel to simultaneously generate electricity and heat energy. an engine that’s hooked up to a generator and a heat exchanger would be an example of Co-generation, the engine consumes fuel to produce kinetic energy and heat, the kinetic energy then drives the generator to produce electricity, and the heat is harnessed to supply different kinds of application.
Co generation system can increase a combustion power plant’s thermal efficiency from a efficiency of 50 percent to 80 percent (2002 Sim’s). at Skelleftea one of the co generating plant we visited, can achieve up to 85 percent thermal efficiency.
Thermal Chemical Conversion is basically taking pellets of biomass (cellulose), and partially oxidize to produce syn-gass (H2 + CO). a complete combustion of cellulose will give us water and carbon dioxide as the final product, producing the maximum chemical energy stored in the cellulose compound.
normal combustion of cellulose C6H12O6 –> H2O + CO2
In the process of partial oxidation, the limited amount of oxygen is reacted with cellulose, giving an incomplete combustion producing carbon monoxide and Hydrogen gas.
partial Oxidation of cellulose C6H12O6 –>H2 + CO
there are also the common steam treatment gasification, using high temperature water to oxidize carbon or carbon monoxide, However the high temperature requirement makes the process less economical.
2 H2O + C –> 2 H2 + CO2
steam gasification of carbon
H2O + CO –> H2 + CO2
steam gasification of carbon monoxide
for more gasification processes and operation detail, check out the link below:
1. Personal interview with Olov Öhrman on May 15th 2014.
2. Gassification of biomass for syn gas production on May 15th 2014
3. Sims, R. E. (2002). The Brilliance of Bioenergy (pp. 209-210). London: James & James. Retrieved May 17, 2014
4. Ziger Snead (2008) http://www.zigersnead.com/current/blog/post/cogeneration-have-your-electricity-and-heat-it-too/04-04-2008/1041/ Retrieved May 7, 2014
5. Sims, R. E. (2002). The Brilliance of Bioenergy (pp. 146-147). London: James & James. Retrieved May 28, 2014
6. Sadaka, Samy. Gasification. Nevada: Associate Scientist, Center for Sustainable Environmental Technologies, n.d. N. pag. Web. 4 June 2014. http://bioweb.sungrant.org/NR/rdonlyres/F4AE220B-0D98-442C-899F-177CFD725ADD/0/Gasification.pdf