MULTI-STAGE CONTACT COMBUSTION METHOD AND APPARATUS EMPLOYING PROCESS INVOLVED

摘要

A process and system for combusting a nitrogen-containing fuel to produce low NO.sub.x levels in the exhaust emissions. A stream of the fuel mixed with air is combusted in two or more fuel-rich zones having catalytic beds. The stoichiometry of the mixture in each zone is controlled for the particular catalytic material employed so that a minimum of NO.sub.x precursors is formed upon combustion in the zones. Additional air is injected into the flow to maintain the predetermined stoichiometry in the downstream zones. The beds of the fuel-rich zones can be comprised of different catalytic materials having different theoretical air proportion at which the NO.sub.x precursors are at a minimum. The beds of the fuel-rich zones can also be comprised of the same catalyst material having different minima at which NO.sub.x precursors are formed at different theoretical air proportions. A final zone combusts the exhaust products at a stoichiometry of at least 100% theoretical air to substantially complete combustion of fuel. Means can be provided for extracting heat from the flow between the combustion zones.