Application of SDS dry desulfurization in coke oven flue gas treatment

As the environmental protection emission requirements become more and more stringent, the efforts of enterprises to control pollution are also increasing, and the control of coke oven flue gas is also receiving more and more attention. During the production process of coke ovens, waste gas containing harmful substances such as dust, SO2, NOx, etc. will be produced, which will pollute the environment. In order to reduce the emissions of harmful substances such as SO2 and NOx in the coke oven flue gas, to meet environmental protection requirements, and to better improve the quality of the atmospheric environment, many advanced methods have been applied to practical projects. Studies have found that SCR denitration technology has good sulfur resistance in low temperature environments, and the flue gas denitration rate reaches over 85%. Jin Hui et al. [2] applied SCR technology to a project of Jiangsu Yizhou Coal Coking Co., Ltd., and overcome the problem that coke oven flue gas cannot be processed at low temperatures. Wang Yan et al. [3] believe that coke oven flue gas treatment should effectively integrate the three aspects of source control, low-nitrogen combustion, and end purification, and pay attention to it.

After purification by the desulfurization, denitrification and dust removal process, the coke oven flue gas emission concentration reaches SO2 ≤ 30 mg/m3, NOx ≤ 150 mg/m3, and dust concentration ≤ 15 mg/m3, meeting the GB 16171—2012 《Coking Chemical Industry Pollutant Emission Standard》， and can meet the requirements of ultra-low emission standards.

1. Coke oven flue gas desulfurization and denitration process

1.1 Process flow

The coke oven flue gas is respectively led from the underground machine side and coke side flue, switched and merged by the bypass flue gas pipeline valve and the newly added inlet pipeline valve, and then enters the flue gas main pipe. At the same time, an efficient desulfurizer (particle size of 20-25 μm) is sprayed into the total flue through the SDS dry deacidification injection and uniform distribution device and is heated and activated in the flue. After full contact with the gas, physical and chemical reactions occur. Acidic substances such as SO2 in the flue gas are absorbed and purified. The absorbed and dried powder-containing flue gas enters the bag filter for further desulfurization reaction and soot purification. The flue gas after desulfurization and dust removal is denitrified and purified in the SCR denitration reactor. The NOx in the flue gas and the NH3 sprayed from the ammonia injection grid are fully mixed in the static mixer, and in the SCR reactor under the action of the medium and low temperature catalyst It chemically reacts with NH3 to generate N2 and H2O, so as to achieve the purpose of removing NOx in the flue gas. The net flue gas is drawn by a booster fan and discharged into the atmosphere through the outlet flue to the original coke oven chimney. The flue gas temperature of the returned coke oven chimney meets the hot standby temperature requirements of the coke oven, which can ensure that the hot pull force of the coke oven chimney remains normal under the accident state.

1.2 Comprehensive utilization of by-products

 The desulfurizer for SDS dry desulfurization is a high-efficiency composite desulfurizer. Due to the small amount of overspray in the SDS process, compared with other desulfurization methods, this program has few desulfurization by-products. The proportion of Na2SO4 in the by-products is very high, which is convenient for comprehensive utilization. The by-products are dry powdered materials, in which the mass of Na2SO4 accounts for about 80% to 90% of the total mass, and the mass of Na2CO3 accounts for about 10% to 20% of the total mass. Coke oven desulfurization by-products can be used as raw materials for the production of mine tailings curing agents, and can also be used in the following fields: blending into cement, so that the hydration product calcium sulfoaluminate is generated faster, and the rate of hydration and hardening of cement is accelerated; Used as a substitute for soda ash in the glass industry; used as a cooking agent in the manufacture of sulphate pulp in the paper industry; used as a raw material for the manufacture of sodium sulfide, sodium silicate and other chemical products in the chemical industry; used in the textile industry for blending Vinylon spinning coagulant; can also be used in non-ferrous metallurgy, leather and other aspects. The renewed waste catalyst of the denitration system is recycled by the catalyst manufacturer.

2. Process technology

Commonly used coke oven flue gas desulfurization and denitrification methods mainly include SDS dry desulfurization + medium and low temperature SCR denitrification, SDA(Na) semi-dry desulfurization + medium and low temperature SCR denitrification, SDA(Ca) semi-dry desulfurization + GGH- medium and low temperature SCR denitrification And activated carbon dry desulfurization and denitrification process.

2.1 SDS dry desulfurization process

The high-efficiency desulfurizer (particle size 20~25 μm) is sprayed into the flue through the SDS dry deacidification spray and uniform distribution device and is activated by heating in the flue. Its specific surface area increases rapidly. The background is developed by the waste incineration industry. HCl removal dry process system, the main component of the by-product is NaCl, which can be recycled as raw material and then used to produce soda ash. After that, the SDS dry deacidification technology developed rapidly in Europe, and its supporting spray system was in full contact with the flue gas, and physical and chemical reactions occurred, and the SO2 and other acidic substances in the flue gas were absorbed and purified. The development of this technology and the grinding system have been developed one after another. At present, in the European market, this process is mainly used for deacidification of waste incinerator tail gas. However, this technology has achieved great success in other industries including coking, glass manufacturing, coal-fired power plants, hazardous waste incinerators, diesel power generation, biomass power generation, and cement. Good application effect.

The advantages of SDS dry desulfurization + medium and low temperature SCR denitrification process are high desulfurization and denitrification efficiency, no temperature drop, no water operation, low investment, small floor space, few by-products, low power consumption, no corrosion, simple equipment, easy Operation and maintenance, small amount of desulfurization by-products, high sodium sulfate content, etc.; the disadvantage is that a small amount of desulfurization by-products will be produced, which needs to be comprehensively utilized.

2.2 SDA semi-dry desulfurization process (including Na method and Ca method)

The spin spray drying (SDA) desulfurization technology was developed by the Danish Niro company in the early 1970s. The desulfurization process is to prepare Ca(OH)2 slurry or Na2CO3 solution with a solid content of 20%~25% by adding CaO or Na2CO3 with water, and spraying the solution into 30~80μm droplets through the high-speed rotation of the atomizer into the absorption tower. Inside, the Ca(OH)2 slurry or Na2CO3 solution mist (absorbent) in the tower quickly absorbs SO2 in the flue gas to achieve the purpose of removing SO2 and other acidic media. At the same time, the heat of the coke oven flue gas instantly dries the droplets sprayed into the tower, turning it into a powdery dry solid, which is captured by the bag filter.

The desulfurization process is simple, and the absorption tower is an empty tower structure. The advantages of SDA(Na) semi-dry desulfurization + medium and low temperature SCR denitrification are high desulfurization efficiency, no waste water generation, low water consumption, low power consumption, and no corrosion; the disadvantages are that the desulfurizer is easy to crystallize, difficult to maintain, and difficult to recycle by-products. . The advantages of the SDA(Ca) semi-dry desulfurization + GGH- medium and low temperature SCR denitration process are that the desulfurization efficiency is medium, no waste water is produced, low water consumption, low power consumption, and no corrosion; the disadvantage is that it covers a large area and reduces the flue gas temperature first. After rising, the energy consumption is high, and the by-products are difficult to use.

2.3 Activated carbon dry desulfurization and denitrification process

Based on the principle of physical-chemical adsorption, activated carbon adsorbs SO2, H2O and O2 in the flue gas and then catalyzes the reaction to produce sulfuric acid, which then migrates to the micropores for storage. The NOx in the flue gas is catalyzed by activated carbon and sprayed. The ammonia in the flue gas undergoes a reduction reaction to generate N2 and H2O. Activated carbon releases active adsorption sites through the regeneration system to continue to adsorb SO2, and the SO2 containing flue gas discharged from the regeneration system enters the by-product recovery system, and SO2 can be processed into a variety of sulfurized products.

Activated carbon will be worn and chemically consumed during the regeneration process, so new activated carbon needs to be replenished regularly, and the worn-out activated carbon powder can be returned to the coal blending section for reuse.

The dry activated carbon desulfurization and denitrification process uses the adsorption of activated carbon to adsorb SO2, particulate matter and NOx in the flue gas, so as to achieve the purpose of simultaneous desulfurization, denitrification and dust removal. The disadvantage is that the flue gas temperature needs to be lowered to below 150 ℃; the by-products of desulfurization contain sulfuric acid while producing polluted wastewater, which requires a large one-time investment and high operating costs.

In summary, no matter from the advanced nature of process technology (desulfurization and denitrification efficiency), or from the practicality of process technology, floor space, investment cost, waste water, by-product utilization, etc., comprehensive analysis and comparison, SDS dry desulfurization The medium and low temperature SCR denitrification process is the most suitable process technology for coke oven flue gas purification. Its configuration is reasonable and the control level has reached the international advanced level, which can ensure the long-term, safe, stable and continuous operation of the desulfurization and denitrification system.

3. Process principle

3.1 SDS process principle

SDS dry deacidification spray technology is to spray high-efficiency desulfurization agent (particle size 20-25 μm) uniformly in the pipeline. The desulfurization agent is activated by heating in the pipeline, and the specific surface area increases rapidly. Physical and chemical reactions, acidic substances such as SO2 in the flue gas are absorbed and purified.

The main chemical reactions are:

2NaHCO3 +SO2+1/2O2 → Na2SO4 +2CO2+H2O

2NaHCO3 +SO3 → Na2SO4 +2CO2+H2O

Its main reaction with other acidic substances (such as SO3, etc.) is:

NaHCO3 +HCl → NaCl +CO2+H2O

NaHCO3 +HF → NaF +CO2+H2O

4. Process characteristics

4.1 Technical characteristics of SDS desulfurization process

The SDS desulfurization process has good adjustment characteristics. The operation and shutdown of the desulfurization device does not affect the continuous operation of the coke oven. The load range of the desulfurization system is coordinated with the load range of the coke oven to ensure the reliable and stable continuous operation of the desulfurization system. The technical characteristics of the process are as follows:

(1) The system is simple and easy to operate and maintain;

(2) Less one-time investment and small floor space;

(3) Low operating cost;

(4) Fully dry system without water;

(5) High desulfurization efficiency;

(6) Reasonable desulfurizing agent uniform distribution device;

(7) The flexibility is very high, and it can be adjusted according to the emission index requirements at any time;

(8) It has a good removal effect on acidic substances;

(9) Strong adaptability to the working conditions of the coke oven;

(10) The amount of by-products is small, and the purity of sodium sulfate is high, which is convenient for recycling;

(11) The system is equipped with a quick switching device for the accident channel, once a failure does not affect the normal production of the coke oven.

5. The composition of the desulfurization and denitration process system

The coke oven flue gas desulfurization and denitration system consists of the following parts:

(1) SDS desulfurization agent dosing and uniform distribution device (key equipment is considered as spare);

(2) Dust removal equipment and auxiliary equipment;

(3) Denitration reactor system and auxiliary equipment;

(4) Public auxiliary equipment of desulfurization and denitrification system, including nitrogen supply system, circulating water supply, etc.;

(5) Instrumentation, communication, power supply and distribution, online monitoring, fire protection and control systems, etc.

With the increasingly stringent requirements of environmental protection laws and regulations, Perlman's process based on the principle of dry deacidification of baking soda developed in combination with advanced processes in Europe and the United States has been applied more and more. The dry method using sodium bicarbonate as the adsorbent adsorbs and removes various pollutants contained in the flue gas. Its purification effect can be compared with other known methods, such as the spray adsorption method using lime milk as the adsorbent. Dry flue gas purification can be used not only in coal power plants, hazardous waste treatment, municipal waste or alternative fuel incineration plants, but also in industrial furnaces in glass, cement, metallurgy and other industries. Dry flue gas purification can economically remove gases containing acidic substances, such as SO2, HCI, etc., and meet the national standard for flue gas emission. In recent years, the baking soda dry desulfurization and deacidification grinding machine developed by our company has served many environmental protection companies across the country, and successfully completed flue gas desulfurization renovation projects for many iron and steel group owners across the country, thereby achieving desulfurization, deacidification and flue gas purification. Today, our company and a Hubei Environmental Protection Technology Co., Ltd. cooperated with the grinding and pulverizing system for the hot blast furnace flue gas desulfurization transformation project of a Tianjin United Special Steel Co., Ltd. The equipment has been completed, contributing to the realization of a more beautiful blue sky and white clouds. strength.