Low-nitrogen combustion technique based on circulating fluidized bed boiler

Abstract

The invention discloses a low-nitrogen combustion technique based on circulating fluidized bed boiler. The circulating fluidized bed boiler comprises a boiler body, a cyclone separator, a deduster, an induced draft fan, a primary air supply system and a secondary air supply system which are connected in sequence. A smoke recirculation pipe is drawn out behind the induced draft fan. The primary air supply system and the secondary air supply system are connected to the smoke recirculation pipe in parallel. A burn-out chamber is arranged at an outlet of the cyclone separator. The low-nitrogen combustion technique based on the circulating fluidized bed boiler comprises the following steps that pulverized coal enters the boiler body under the action of primary air, specifically, the amount of smoke recirculation air in the primary air accounts for 8-10% the total air amount of the primary amount, and the amount of the primary air accounts for 40-45% of the total air amount; secondary air is introduced into the boiler body through the secondary air supply system, specifically, the amount of smoke recirculation air in the secondary air accounts for 12-14% the total air amount of the secondary air; fine flying ash enters the burn-out chamber; and over fire air is introduced into the burn-out chamber. According to the low-nitrogen combustion technique based on the circulating fluidized bed boiler, the burn-out chamber is arranged at the outlet of the separator, and part of smoke is mixed into the primary air and the secondary air, so that generation of NOx is reduced.

Description

technical field [0001] The invention belongs to the technical field of boiler combustion, and in particular relates to a low-nitrogen combustion process based on a circulating fluidized bed boiler. 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 speed. I...

AI Technical Summary

Problems solved by technology

The circulating fluidized bed boiler has the remarkable characteristics of low nitrogen oxide emissions. The main reason is that the combustion temperature is low, only 850-1000 ℃, so the thermal NO x The second is that the solid bed material in the furnace has a great influence on NO along the height of the furnace. x The third is that circulating fluidized bed boilers are generally designed in a graded air supply mode, so that the dense phase area is in a reducing atmosphere, but although the traditional layout of secondary air inlet ducts can meet the requirements of the boiler for secondary air volume, However, the disturbance effect of the secondary air on the flue gas in the furnace is poor, which is not conducive to the full combustion of fuel in the furnace, and there is still room for improvement of circulating fluidized bed boilers

[0005] 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

Images