Gaseous Waste Fuel
A number of activities, for example landfill, sewage treatment and some industrial processes, produce gaseous waste fuels.
In many cases, the gases are produced on a continuous basis and are available for use in a packaged CHP unit, although their composition and quality will usually vary. In the past, such gases have often been allowed to escape into the air, or have been flared, but it is now realised that this can cause significant damage to the environment, and their use as fuel is encouraged.
The waste gases from landfill sites and sewage plants and those from coal mining activities are usually methane-based, often with small quantities of other hydrocarbons and larger proportions of inert gases. These gases can sometimes contain compounds of chlorine and other contaminants such as water and will require some filtration or treatment before they can be used. CHP packages based on gas engines can operate on these fuels, although the engine design must be configured for the particular fuel. Consistency of supply and composition are key issues. The nature of these fuel sources is such that heat loads may or may not be present. Sewage treatment plants, for example, have a readily available heat load, whereas landfill sites seldom do.
Gases from industrial processes may also be suitable for packaged CHP units, although fuel composition can sometimes render the gas unsuitable for use in an engine. Fuel composition is determined by the nature of the process in which the gases are produced. Any sulphur in the gas will result in the production of sulphur dioxide in the exhaust, which is potentially corrosive as well as being environmentally damaging. Some gases may need to be filtered and dried prior to use. In all cases, the CHP package must be selected for use with the particular fuel envisaged. Consistency of supply is also an important issue.
In some chemical processes, gas turbines can provide a convenient and economic way of disposing of solvents.
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