Abstract: In view of the existing environmental pollution problems of Minqing building ceramics industry, the paper mainly explores the selection of desulphurization process and desulphurization agent of cold gas and explores the first demonstration project of wet gas desulphurization for small gas furnace. On the basis of practice, Industry gas desulfurization effective way to reduce emissions.
[Key words] gas, wet desulfurization, cyclone, reduction, demonstration project, research and practice
SO2 is an acidic gas, easy to form acid rain in the atmosphere, threatening the ecological environment and public health. SO2 has become the primary pollutant in the air pollution. According to the national guideline of "energy conservation and emission reduction", the total amount of SO2 emission in the atmosphere will be controlled with the total goal of reducing the nationwide SO2 emissions by 10% during the "Eleventh Five-year" period.
Minqing County, Fuzhou City, rich soil resources, building ceramics industry has become the county's pillar industries. Minqing County Building Ceramic industry gas converter to convert gas to fuel. That is, coal is converted into crude gas by using raw materials of coal, and most of the sulfur components in the coal are converted into sulfides (H2S and SO2) simultaneously. Sulfide emissions after combustion in the form of SO2 will pollute the atmosphere. According to the survey, there are 47 building ceramics enterprises in Minqing County, with annual coal consumption of 695,300 tons and SO2 production of 14,300 tons / year.
1 Minqing building ceramics industry pollution status
According to the requirements of pollution reduction targets in Fuzhou, Minqing County Environmental Protection Agency organized the preparation of "Minqing County, building ceramics industry comprehensive pollution control plan," Minqing County, SO2 emission reduction target of 70%, both by 14300 tons / year, Cut to 4291.5 tons / year. Ceramic production process, including material drying and ceramic tile firing two parts, most of the drying process has been used coal pulverized coal-water slurry as a fuel, coal-water slurry coal enterprises accounted for 25% of total coal consumption. -30%. Spray drying is direct contact drying. Due to its smaller particle size and larger specific surface area, its adsorption performance is close to that of activated carbon powder, so the emission of SO2 in this stage is less. Tile firing process, the main use of coal gas as fuel. Minqing built ceramic industry is small-scale investment, the main use of small gas furnace, the existing 47 building ceramics enterprises, 33 use single-stage gas furnace, 14 double-stage furnace. Two-stage furnaces use bituminous coal as raw material. Among the enterprises that use single-stage furnaces, four employ anthracite coal and the other 27 use bituminous coal. Sampling and testing of the raw coal components show that the sulfur content of raw coal is about 0.5-3.5% (calculated as 2%). The existing 47 companies consume 533,000 tons of coal a year, 70-75% of which are used for the production of cold gas, which will result in an output of about 20.07 million tons of ceramic tiles. In the conversion process, most of the sulfides are present in the gas in the form of H2S, which is oxidized and released as SO2 during the firing process (see Tables 1 and 2). Therefore, the gas desulfurization process can not only effectively remove the sulfur compounds in the gas and recover the sulfur, but also can make the gas more clean and help improve the product quality. In order to achieve a win-win goal. In accordance with the above ideas in this paper, focus on the wet gas desulfurization conversion, increase desulfurization tower equipment, thereby reducing the final emissions of S02.
2 desulfurization emission reduction process choice
Gas is divided into two types of hot gas and cold gas, the corresponding desulfurization methods are also divided into two kinds of dry desulfurization and wet desulfurization. Ceramic production mainly uses cold gas, the desulfurization methods are divided into wet desulfurization and dry desulfurization. In particular, the introduction of national energy-saving emission reduction guidelines, the desulfurization of gas increasingly valued by the corporate community. This article focuses on cold gas desulfurization process selection and wet desulfurization process. From the analysis of investment cost of desulfurization system construction, the dry desulfurization and wet desulfurization equipment investment is basically the same, but the dry desulfurization need to regenerate activated carbon and other absorbent filler, and the adsorbent filler is easy to saturation, replacement operation cumbersome; Second, the replacement of the filler process Need to desulfurization system parking emptying, after the replacement also needs system replacement. In particular, the packing has great resistance, and the air is easy to remain during the replacement process. The residual oxygen in the air easily causes exothermic reaction with H2 in the reformed gas, which poses a potential safety hazard. Therefore, the choice of wet desulfurization process more secure.
With the development of ammonia industry, wet desulfurization process is maturing. In view of the fact that the existing building ceramics enterprises in Minqing County generally adopt the small-scale gas furnace, the conversion gas per hour is about 6500-7500m3 / h. Domestic similar desulfurization technology survey results show that the current collection of tunnel kiln exhaust mostly sulfur dioxide, although the exhaust gas desulfurization can achieve the emission reduction targets, due to large gas handling, investment and operating costs are relatively high, and does not help its Improve the quality of products, the relevant benefits are not obvious.
The demonstration project takes the desulphurization route of the process, that is, a new purifying device of the desulfurization tower for the new swirling plate of cold gas after pressurization of the existing gas station [2]. Adopt NaOH and Na2CO3 as desulfurizing absorption liquid to remove acid H2S and a few SO2 and some organic sulfur components in the gas. Because the process gas volume is only 1/3 of the tail gas volume, the investment and operation cost are more economical. The wet desulfurization process is equivalent to the secondary purifying of the gas, effectively reducing tar and other impurities in the gas and reducing the gas temperature. Conducive to product quality and system safety, is conducive to production.
3 wet desulfurizer choice and desulfurization process design
The choice of desulfurization agent is the key, select the appropriate desulfurization agent in order to achieve the removal of hydrogen sulfide in the conversion gas. Desulfurizer varieties, dosage, dosing costs, absorption effect, the final product are all related to the selection of the key factors desulfurization.
This demonstration project to take three sets of desulfurization agent to experiment. The first solution is the use of Na2CO3 and Ca (OH) 2 dual-alkali desulfurization; the second one is the use of Na2CO3 and FeCl3 as the desulfurization agent; the third one is the use of Na2CO3 as the desulfurization agent and the addition of the 888 desulfurization catalyst.
Experimental summary of three programs:
1. Adopting the first solution, the Na2CO3 in the desulfurizing agent has a good absorption effect on the acid gas such as hydrogen sulfide and a small amount of sulfur dioxide in the conversion gas, and Ca (OH) 2 is added to reduce the alkalinity of the circulating liquid after absorption, Although the whole process has a good desulfurization effect on the conversion gas, the sulfide produced by the desulfurization is hard to be removed by calcium ion precipitation and the continuous operation of the system can not be guaranteed.
2. The second option is to use Na2CO3 and FeCl3 as desulfurizer. Na2CO3 in the desulfurizing agent has a good absorption effect on the sulfide in the conversion gas, and NaOH is added to reduce the alkalinity of the circulating liquid after absorption. Absorption of sulfide is expected to precipitate in the form of Fe2S3 and FeS down, FeCl3 as an absorbent can effectively remove sulfide desulfurization by-product Na2S2O3. Therefore, it is a viable option if it is a transitional measure.
3. The third option is to use Na2CO3 as a desulfurizer, while adding 888 desulfurization catalyst. In the first and second schemes, it has been concluded that Na2CO3 has a good absorption effect on the conversion gas sulphide, and NaOH is added to reduce the alkalinity of the circulating liquid after absorption (mixed alkali ratio: NaOH0.08mo1 / LNa2CO3 is 0.16mo1 / L ). 888 desulfurization catalyst is based on cobalt phthalocyanine sulfonate metal organic compounds as the main catalyst [3,4]. Analysis of its specific process principle, Na2CO3 as the alkali source of the wet oxidation desulfurization is essentially a process associated with the oxidation reaction. The H2S in the gas phase is absorbed by the desulfurization solution first, then the neutralization reaction with Na2CO3 occurs, and the NaHS reaction product is oxidized to generate elemental sulfur. As the conversion gas also contains HCN, CO2, O2 and other components, the chemical reaction occurred in the desulfurization process is actually much more complicated. The sulfide is then liberated as elemental sulfur through the 888 desulfurization catalyst and aeration by blast air, and the sulfur is finally recovered.
In addition to being able to remove inorganic sulfides efficiently, some of the organic sulfides (RSH, COS) can be removed by the wet oxidation of some catalysts. The basic reaction is as follows:
Catalytic chemical absorption of sulfides:
The reaction of H2S with Na2CO3 and the oxidation of NaHS are the same as the other liquid-phase catalytic reactions. However, the reaction of NaHS with (X-1) S to form Na2SX under the catalysis of 888 is unique to 888. Due to the formation of Na2SX, the sulfur originally deposited on the desulphurization tower packing is rapidly involved in the chemical reaction of NaHS and is converted into Na2SX, which makes the deposited sulfur loose and plays a role of clearing the tower and reducing the plugging tower.
4 wet desulfurization demonstration project practice summary
The selection of three enterprises in Minqing as a pilot project for desulphurization and emission reduction of gas pollutants has now been fully completed. In August 2007, Fuzhou Environmental Monitoring Station was commissioned to carry out the completion acceptance monitoring (in accordance with the national recommended monitoring method). From the monitoring results, the gas H2S concentration in the desulfurization tower is 550-800mg / m3, the H2S concentration after the desulfurization is less than 20mg / m3, the desulfurization efficiency reaches More than 90%, has reached the design goals.
Summary demonstration engineering practice, the desulfurization process has the following characteristics:
1. Desulfurization system can effectively remove the gas of H2S and SO2 and organic sulfur, thereby reducing the sulfur content of gas, both to reduce the impact of sulfide on the quality of tunnel kiln and tile products, but also to achieve emission reduction purposes, is environmentally friendly Emission reduction technology.
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