Circulating fluidized bed boiler system for achieving low nitrogen oxide discharge

Abstract

The invention discloses a circulating fluidized bed boiler system for achieving low nitrogen oxide discharge. The circulating fluidized bed boiler system comprises a boiler, a cyclone separator, a dust remover and an induced draft fan which are sequentially connected. The circulating fluidized bed boiler system further comprises a primary air supply system and a secondary air supply system. A flue gas recirculation pipe is guided out of the rear portion of the induced draft fan and connected with the primary air supply system and the secondary air supply system in parallel. The secondary air supply system comprises a secondary air fan, a secondary air pipe, a plurality of secondary air vertical pipes arranged on the outer sides of a front wall and a rear wall of the boiler and secondary air nozzles, wherein the secondary air nozzles are arranged on a water cooling wall, connected with the secondary air vertical pipes and arranged in a dilute phase area of the boiler in a layered manner. According to the circulating fluidized bed boiler system, part of flue gas is mixed into primary air, the fluidization characteristic of a dense phase area during low-load running is improved, part of flue gas is mixed into secondary air, the air speed of the secondary air nozzles can be increased easily, a local high-temperature area is avoided, and generated NOx is reduced. By means of the secondary air arrangement manner of the system, the disturbance function of the flue gas in a hearth is increased, fuel is combusted fully, and the generated NOx is reduced.

Description

technical field [0001] The invention belongs to the technical field of boiler combustion, and in particular relates to a circulating fluidized bed boiler system for realizing low nitrogen oxide discharge. Background technique [0002] In the nitrogen oxides produced during boiler combustion, NO accounts for more than 90%, and nitrogen dioxide accounts for 5%-10%. The production mechanism is generally divided into the following three types: (1) Thermal type: During combustion, nitrogen in the air is Oxidation, with the increase of the reaction temperature T, the reaction rate follows an exponential law. When T<1500°C, the amount of NO produced is very small, and when T>1500°C, the reaction rate increases for every 100°C increase in T. 6-7 times larger; (2) Instantaneous reaction type: CH free radicals generated by pyrolysis of hydrocarbons in fuel volatiles can react with nitrogen in the air to form HCN and N, and then react with oxygen to form at an extremely fast sp...

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Problems solved by technology

However, due to the unique low-temperature combustion and secondary air graded layout of circulating fluidized bed boiler combustion technology, the nitrogen oxide generation is lower than that of ordinary pulverized coal boilers using the same fuel. It can meet the requirements of the boiler for the secondary air volume, but the secondary air has a poor disturbance effect on the flue gas in the furnace, which is not conducive to the full combustion of fuel in the furnace

[0004] In order to reduce the formation of nitrogen oxides, it is often used to reduce the excess air coefficient of combustion and reduce the peak temperature of boiler combustion, but this will affect the full combustion of fuel in the boiler, and the oxygen concentration in the boiler is too low (below 3%), which will increase the chemical Heat loss from incomplete combustion increases the carbon content of fly ash and reduces the combustion efficiency of the boiler

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