How does Combined Heat and Power (CHP) work??
CHP is a single process during
which there is production of two types of energy, heat and power (usually electrical);
hence the name. The principle behind CHP is an increase in the efficiency of
engines and generators which produce electrical energy. The standard efficiency
of electrical generation in an engine is around about 35%. This is obviously
not very efficient the reason for the low efficiency is that a lot of energy is
rejected as heat. The fundamentals behind the low efficiency are tied very
directly to the second lay of thermodynamics. Where the carnot cycle represents
the theoretical maximum efficiency. As this web page is not a tutorial on
thermodynamics no more explanation shall be given. The easiest and most common
way to increase the efficiency of the process of converting a fuel into useful
energy from a generator or an engine is to capture the heat lost in the process
of producing the electricity. The heat lost in the engine can be split into two
categories, the heat lost in the exhaust gases and the heat lost from the
engine jacket. For recovery of heat from the jacket water is most often used,
to recover heat from the exhaust gases a heat exchanger is used. There are
several types of CHP system, for more information a good reference is http://www.esru.strath.ac.uk/EandE/Web_sites/97-8/chp_sizing_case/index.html
which is a project dedicated to CHP produced by previous members of the energy
systems and environment course.
CHP can be used to provide a
secure and highly efficient method of generating electricity and heat at the
point of use. CHP can typically achieve a reduction in the primary energy usage
of around 35% when compared to traditional heat only boilers. This can mean
substantial economic savings in situations where there is a suitable balance
between heat and power loads. Considerable savings in CO2 production
for the same amount of total energy produced are possible. Savings of around
30% are typical from coal-fired power stations.
CHP installations are dominated by
schemes with an electrical capacity of less that 100 KWe, around 43% of the UK
sites, and sites with electrical capacity of around 100 KWe to 999 KWe make up
around 40% of the total. The number of
sites with CHP in the UK is greater than 1600 with a total installed capacity
of more than 4,801 MWe. In terms of the various sectors around 93.2% of CHP
applications are in the industrial sector with the remaining 6.3% in the
commercial, residential and public sector.