This report reviews the origin of trace elements in coal and their partitioning through coal-fired combustion and gasification processes, and downstream pollution control equipment. The importance of coal utilisation as a source of trace element emissions to the atmosphere is evaluated. Deposition of trace elements onto soils and waters may upset the balance of ecosystems, and some elements may be toxic to plants and animals. Coal combustion is the major global source of mercury and selenium emissions from human activities and is also an important source of antimony, arsenic, cadmium, chromium, lead, nickel, vanadium, and zinc. Limits controlling atmospheric emissions of certain potentially toxic trace elements have been introduced in some countries. Currently little legislation applies directly to emissions from coal utilisation, but it is unlikely that this source will remain exempt from regulation in future. Flue gases exiting a coal-fired boiler or gasifier contain trace elements either bound to particles or as volatile substances in the gas phase. High efficiency electrostatic precipitators or fabric filters can reduce particulate emissions to low concentrations. Wet or dry flue gas desulphurisation systems reduce emissions of volatile elements by concentrating the elements from flue gases in solid or liquid streams. Low temperature scrubbers present in some gasification systems provide an effective method for removal of most trace elements from the gas stream. The installation of pollution control equipment to comply with legislation for particulate and sulphur emissions will thus incidentally reduce the release of trace elements to the atmosphere. The report includes studies of the distribution of trace elements in all output streams from coal-fired power stations, focusing on releases to the atmosphere. An integrated approach to pollution control should ensure that reductions in emissions to the atmosphere do not result in increased pollution from solid or liquid wastes.
Title: Trace elements – emissions from coal combustion and gasification, IEACR/49
Author(s): Lee B Clarke, Dr Lesley Sloss
ISBN: ISBN: 92-9029-204-0
Publication Date: 01/07/1992