Masaaki Nishino

Advantages of Low Air-Ratio Combustion in a Stoker-Type Incinerator (With High Temperature Air Combustion Technology)

Measures such as low air-ratio combustion have become the subject of a great deal of attention with a view to reducing the amount of environment impacting substances from the waste incineration process, and also to making the most effective use of energy. However, it has been understood there would be considerable difficulty utilizing low air-ratio combustion on the classic grate furnace due to fundamental problems in its process resulting from the wide range and heterogeneity of waste materials. The application of high-temperature air combustion technology for enhancing sound combustibility could provide 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 at the same time heating the waste directly with the flame to promote gasification. A practical study was conducted at a 105 t/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.