Advantages of Low Air-Ratio Combustion in a Stoker-Type Incinerator

Low air-ratio combustion has become the major subject with enormous attention as a measure to reduce the amount of substances with environment impact from the waste incineration process, and to make the most effective use of energy. However, it has been thought that there would be considerable difficulty in utilizing low air-ratio combustion on the classic grate furnace due to fundamental problems in its process, which treats the wide range and heterogeneity of waste materials. The application of high temperature air combustion technology for enhancing sound combustibility provided solutions to these problems. In practice, a mixture of high-temperature air and flue gas is injected at high velocity from both sides of the furnace walls to form a stable high-temperature zone in the combustion initiation region above the waste. This prevents fluctuations or localized extinguishing of the flame, while heating the waste directly with the flame to promote gasification at the same time. A practical study was conducted at a 105-ton/day municipal solid waste stoker type incineration plant. The test demonstrated that stable low excess-air combustion operation is possible at a combustion air stoichiometry of 1.3 with EGR (Exhaust Gas Recirculation) and high temperature air combustion technology resulting in a 17% decrease in flue gas flow, an energy efficiency improvement of 10%, and more than 50% reduction in NOx emissions when compared with an air stoichiometry of 1.6.