Understanding CHP: Compare energy sources

In order to understand CHP and the efficienct use of energy, it is important to grasp the nature of energy generation: how we get heat and electricity.  

There are two different ways of generating energy: Decentralised Heat and Power using CHP and seperate (centralised) power and (local) heat generation.

Seperate production of heat and power

The largest share of electricity supply presently provided to various customer groups by the public electricity company network is from condensation (steam) power generators.  These condensation power generators transform just a small part of primary energy sources used (brown coal/lignite, mineral coal, heavy heating oil) into electricity.  The average gross efficiency level of such power stations is around 38%. Considering the power station’s own electricity use and the network’s losses during electricity transfer, the level of primary energy produced is actually only 30%.   The remaining two-thirds of primary energy used to generate electricity is released in the form of heat.  This is not only released into the atmosphere in a manner damaging to the environment, but also leads to the warming of natural bodies of water as the cooling water is heated. The warm water needed by the end user must be additionally produced with boilers.

Decentralised Heat & Power

The setup of CHP units makes it possible to utilise the heat by-products of electricity generation directly on site for heating purposes or warming processes.  This eliminates the unnecessary losses in the distribution network and the wasteful heat release into the environment.  The primary energy savings of up to 40% helps not only to conserve resources, but saves the environment with lower CO2 emissions.

 

CHP emissions are much lower

The most important factor here is the primary energy saving of Combinend Heat and power units which proportionally contribute to the reduction of emissions.  The NOx emissions of CHP´s with internal combustion engines certainly must be critically examined.  In contrast to gas firings, high NOx emissions are created with IC engines, since temperature and pressure currents occur on location at a considerably higher level.  Therefore, measures towards reducing emissions according to the district regulations must be met. To this purpose Alfagy offer three systems.

3 way catalyst prevents pollution

For gas Otto cycle engines with an output of up to 240 kW mech., a 3 way catalytic converter provides an environmentally-friendly and economical solution.  It allows a NOx conversion of over 95%, reduces CO and HC and clearly surpasses the limit values set out in the German "TA-Luft".  In a weakly reduced atmosphere just under stoichiometric air: gas ratio (Lambda), nitrogen oxides are broken up into nitrogen and oxygen.  The freed oxygen oxidises the present carbon monoxide and partially-burned hydrocarbons.  The highest conversion rate of all three harmful substances is reached only in a very narrow air quality range at Lambda = 0.99 +/- 0.005.  Our electronic control system performs a dependable summary of all operating parameters such as ignition and Lambda signals and self-regulates large load gaps quickly and effectively.

Lean combustion engines save NOx

The lean combustion engine concept consists of a suitable combination of measures to reduce NOx.  Through a compression of the ignitable gas-air mixture with an exhaust turbo charger, a drastic NOx reduction is achieved through a high excess of air and load pressure, through adjusting the point of ignition, modifying the fuel burning area and suitable reduction of the motor load.  Lean combustion engines are used whenever catalytic converter poisons (sulphur, chlorine and fluoride compounds) are expected in the combustion material (digester gas, sewage treatment gases, biogases,...) and always with turbocharged engines.  To run turbo engines with stoichiometric combustion is possible, but leads to very high thermal stress on the engine especially on the valves and valve seats.  Through this matter higher maintenance costs are effected.  Lean combustion engines, running with natural gas, are usualy supplied with oxidation catalysts to burn CO and HC.