1. technical name

Ultra-low emission technology for grate-rotary kiln pellet flue gas in the steel industry.

2. scope of application

Control of flue gas from grate-rotary kiln pellet.

3. technical content

3.1 technical principle

This technology utilizes the mainstream selective non-catalytic reduction (SNCR) and selective catalytic reduction (SCR) denitrification technologies, combined with the production flue gas temperature characteristics of the grate-rotary kiln, and embeds the denitrification technology into the grate-rotary kiln production process. From the perspective of the entire process, a three-stage denitrification system is set up in combination with the change of flue gas temperature in the production process. The first stage adopts SNCR (850℃~1150℃) denitrification, the second stage adopts high temperature and high dust (320℃~420℃) SCR denitrification, and the third stage adopts low temperature (100℃~180℃) oxidation-assisted semi-dry collaborative denitrification. Semi-dry desulfurization + bag-type dust collector is used for desulfurization. Under high SO2 concentration and low exhaust gas temperature in pellet flue gas, the bed pressure drop, circulating ash amount, solid-gas ratio in the tower and desulfurization efficiency of the circulating fluidized bed (CFB) are optimized and designed, optimal process parameters are determined, and operating guidelines are established. The design of the CFB absorber was optimized through chemical kinetics and flow field mass transfer analysis. At the same time, the design has also been optimized in terms of screening low-temperature filter materials, anti-paste bag measures, and insulation and corrosion prevention of cloth bags.

3.2 main innovations

(1) Embed denitrification technology into the grate-rotary kiln production process. There is no need to heat up the flue gas, no need to consume after-combustion heating energy, and the operating cost is low; there is no problem of corrosion and clogging of the GGH heat exchanger. The whole system is relatively simple, has few equipment, and is easy to operate and maintain. (2) Three-level denitrification is set up to realize automatic adjustment of denitrification temperature and ultra-low NOx emissions. Meet the emission standards during start-up, shut-down and load change processes, and achieve 100% synchronous operation with the main engine. It solves the problem that it is difficult to achieve ultra-low emissions by setting only one stage of denitrification, and it is easy to exceed the standard when load and temperature change. (3) The desulfurization system can realize the simultaneous removal of sulfur dioxide and nitrogen oxides in the flue gas, and can meet the ultra-low emission requirements of pellet flue gas with high SO2 concentration and low exhaust gas temperature.

4. Pollution control or environmental restoration effects

Taking the ultra-low emission project of Qian 'an City Jiujiang Wire Rod Co., Ltd. as an example, the emission concentrations of SO2, NOx and particulate matter in the purified flue gas are ≤20mg/m3, ≤30mg/m3 and ≤5mg/m3 respectively.

5. Technology demonstration

This project has been applied to Qian 'an City Jiujiang Wire Rod Co., Ltd. 1# and 2# Each 2.4 million t/a grate-rotary kiln flue gas desulfurization, denitrification and dust removal ultra-low emission EPC general contract project, each system has a processing scale of 1.2 million m3/h, and the technical route is SNCR denitrification +SCR denitrification +CFB desulfurization. The system can continuously and stably meet ultra-low emission requirements, and all technical and economic indicators meet or even exceed the design indicators.

6. investment estimation

Taking a single unit with an annual pellet output of 2.4 million tons of grate-rotary kiln pellets (processing flue gas capacity of 1.2 million m3/h) as an example, the total investment of the project is 68 million yuan.

7. Prospects for transformation and promotion of technological achievements

As domestic large steel companies vigorously develop high-proportion pellet blast furnace smelting technology, pellet flue gas pollutant emissions will also be greatly increased, and the demand for ultra-low flue gas emissions will also increase accordingly. This technology has broad future application prospects.