ESET-212 Lecture 6: ESET212-draft
Document Summary
Definition: draft is the difference in pressure between two points that causes air or gases to flow. The primary purpose of a draft system on a boiler is to supply sufficient air to complete the combustion process and remove products of combustion. To burn fuel completely, sufficient quantities of air with pressures high enough to overcome the resistance caused by breeching, dampers, baffles, tube passes, economizers, and superheaters are required. Approximately 15 lb of air is required to burn 1 lb of fuel. Natural draft is produced by a chimney alone, without mechanical means. It is caused by the difference in weight between the column of hot gas inside the chimney and a column of cold outside air of the same height and cross section. Forced draft is used when the fan or blower located in front of the boiler setting forces (pushes) air into the furnace.
