Combustion processes can produce small quantities of various organic and chemical compounds which may include gases of unburned hydrocarbons (UHC). These compounds often occur alongside particle and carbon monoxide emissions and, therefore, tend to be associated with poorly controlled combustion or inadequate maintenance. However, under normal circumstances, the emissions levels of these compounds are not considered a major concern.
In CHP schemes that incorporate the combustion of by-product or waste fuels, there may be other compounds such as dioxins, furans, heavy metals etc. in the exhaust gases. Most plants of this type are regulated under the EP Regulations as incineration installations, and often incorporate techniques for cleaning exhaust gases before discharge to atmosphere.