Can your CHP be operated on Renewable Energy?

Interestingly CHP or a Cogeneration plant which is one of the most energy efficient devices developed by man is not a sustainable system. The reason is by definition any equipment operated on fossil fuels do not fall under this category.

That is because the fossil fuels once used will not regenerate naturally for many hundreds of millenniums!

However with the developments in technology fuelled by the high fuel prices, scarcity of fossil fuels and most of all the concern for a better environment and a sustainable world, CHPs (which are simple devices based on commonsense more than anything else) are showing signs of being classified as

Renewable Energy Processes at least for some designs.

This has been made possible in these CHPs because of their capacity to operate on renewable fuels.
The basis of this relatively recent development is as follows;

  • The CHPs are normally designed to be operated on Gasoline (Petrol), Natural Gas, Propane, Sludge Gas, Diesel and Heavy fuel oils.
  • Gaseous fuel can be used in Compression Ignition (“Diesel”) type Engines subject to the use of a little Diesel Fuel initially as “Pilot Oil” (ie. as an ignition process initiator). In contrast the Spark Ignition Engines can be used with straight Natural Gas.
  • Methane which is a naturally occurring gas is a good fuel though the energy content is low compared to the Petroleum based fuels. (The Thermal energy content is approximately 26.73 – 32.7 kj/m3).
  • This gas incidentally is an agent much harmful to the environment because it is a greenhouse gas approximately 20 times more potent than the better known adversary CO2!
  • Decaying of all organic matter results in the production of Methane which is naturally released to the environment along with that produced as a result of human activity.
  • Human activity such as land fills; Sewage Treatment Processes generate Methane gas in sufficient quantities to viably operate Power and Thermal Energy Generating CHPs.

There are a few draw backs;

  • The low energy content of the primary fuel
  • The standard design 4 stroke engine cannot be used as it is.
  • The gas produced in land fills and Sewage treatment plants contain impurities such as Hydrogen Sulphide (H2S) and moisture
  • The H2S gas is detrimental to standard bearing material and also affects “O” rings and Gaskets.

The first drawback is overcome by mixing the Methane with natural gas before injection to the combustion chamber.
The second is over come by employing a larger carburetor or Duel Carburetors.

Natural gas is also used as a back up in this case. The third draw back is tackled by cleaning the fuel gas and drying it before the final injection to the prime mover. The last draw back is countered by the use of special material such as Aluminium in the bearings and bushings and low friction plastics such as PTFE in “O” rings and gaskets.

The residual products of the process are excellent fertilizer while that of combustion is mainly CO2 and Water.
The CHP’s value as an energy conserving machine has been further enhanced by this renewable energy technology.
It is clear the CHPs’ inclusion as a renewable energy device for consideration in the design and evaluation of large buildings for BER is accordingly well justified.