Brief introduction of zinc oxide desulfurization at home and abroad
In China, Shuikoushan Mining Bureau and Zhongnan Mining and Metallurgy Research Institute studied the topic of "desulfurization of zinc oxide fume and comprehensive utilization of desulfurization by-products" in the early 1980s, and established an industrial test device with a flue gas volume of 8000Nm/h, but it was not applied in industry because some key technical problems were not solved. From 2000 to 2002, China Yunnan Copper Group Company and Guangxi Laibin Smelter established zinc oxide desulfurization industrial devices, but failed to put them into operation. In recent years, some lead-zinc smelting enterprises in China have successively established industrial devices for zinc oxide desulfurization, but they have all failed.
Abroad, Japan, South Korea, Germany and the United States all have industrial applications, but some foreign enterprises have higher requirements on the grade and impurities of ZnO dust (for example, the ZnO desulfurization project of Sachibin company in Germany requires that ZnO dust contain Pb)
In 2002, Professor Tong Zhiquan of Xiangtan University presided over the research and development of low-grade zinc oxide fume desulfurization and sulfur and zinc resource recovery technology. From 2004 to 2006, three sets of flue gas desulfurization systems were successfully put into operation in Guangzhou Huali Company.
In 2009, Professor Tong Zhiquan entrusted this world-leading and unique zinc oxide desulfurization technology to Sichuan Qingyuan Environmental Engineering Co., Ltd. for engineering practice. The company has been successfully applied to flue gas desulfurization projects of Yunnan Jinding Zinc Industry Co., Ltd. and Zinc Industry Branch of Western Mining Co., Ltd., and the projects are running normally at present, with no scaling and blockage. Adopting the new oxidation desulfurization technology, a leading technology, can not only treat waste with waste, but also create certain economic benefits for enterprises.
Brief introduction of zinc oxide desulfurization technology
Zinc oxide desulfurization technology is to add water to powder containing ZnO or desulfurization residue washing liquid returned from the process to make suspension, which reacts with SO2 in flue gas in an absorption device to remove SO2 mainly in the form of zinc sulfite (zinc bisulfite and zinc sulfate). Zinc sulfate, electrolytic zinc and sulfuric acid (or liquid sulfur dioxide) can be produced by air oxidation, thermal decomposition or acid decomposition of absorbed by-product zinc sulfite.
1, desulfurization mechanism
The newly prepared ZnO slurry reacts with SO2 in flue gas in the absorption tower as follows:
ZnO+SO2+5/2H2O = = znso 3 5/2H2O↓( 1)
At this time, the desulfurization rate is high. The solubility of the product ZnSO 3.5/2H2O is small, and most of it enters the precipitation in solid state.
With the progress of absorption, there is less and less ZnO in the slurry. When SO2 in the flue gas is relatively excessive, the following desulfurization reactions will occur (at this time, the desulfurization rate will decrease and soluble Zn(HSO3)2 will be generated):
Zinc oxide+sulfur dioxide +H2O = = zinc nitrate
At the same time, ZnSO3+SO2+H2O==Zn(HSO3)2 (3) appeared.
In addition, due to the presence of oxygen in the flue gas, the following side reactions will occur during the absorption process:
Zinc sulfate+1/2 O2 = = zinc sulfate (4)
Zinc (nitric acid)+oxygen = = zinc sulfate+sulfuric acid (5)
Under good absorption equipment and suitable operating conditions, the absorption efficiency is over 95%.
2. Process flow
(1)ZnO absorption-air oxidation process According to the property that Zn(HSO3)2 and ZnSO3 in the solution can be oxidized by oxygen in the air, the desulfurization slurry is oxidized by air, so that both Zn(HSO3)2 and ZnSO 3.5/2H2O in the slurry are oxidized into ZnSO4. After purification, zinc sulfate solution can be used to electrolyze metallic zinc, or concentrate and crystallize to produce qualified zinc sulfate heptahydrate or monohydrate.
(2) The adsorption-thermal decomposition process of ZnO controls that the adsorption products of ZnO mainly enter the sediments in the form of ZnSO 3.5/2 H2O. After liquid-solid separation, the precipitate and zinc concentrate are sent to a fluidized bed furnace or separately decomposed in a rotary kiln to generate high-concentration SO2 for acid production and regeneration of ZnO. The regenerated zinc oxide can be recycled for flue gas desulfurization and can also be used to produce zinc sulfate or electrolytic zinc products.
(3)ZnO absorption-acid decomposition process utilizes the property that ZnSO3 _ 3 _ 3 is easily decomposed by acid, and decomposes ZnO absorption products with acid or acidic solution (such as zinc electrolysis waste liquid) to generate 10%~ 15% SO2 gas for acid production; The decomposed zinc sulfate solution is purified and sent to electrolytic zinc.
Advantages of zinc oxide desulfurization
1. Treatment of desulfurization products (zinc sulfite, etc.). Less investment can be combined with the production process of lead-zinc smelter, that is, some original production equipment (such as zinc concentrate fluidized roasting furnace, SO2 acid production system, zinc sulfate solution purification, electrolysis system, etc.). ) can be used as the recovery equipment of desulfurization by-products. Therefore, compared with other desulfurization methods, this method has less investment and embodies the characteristics of adapting to conditions.
2. Low operating cost. After using the intermediate product of lead-zinc smelting process-ZnO fume as desulfurizer to remove SO2, zinc in desulfurizer and sulfur in flue gas are converted into by-products, thus realizing the comprehensive utilization of sulfur and zinc resources. Compared with other desulfurization methods, this method saves the cost of desulfurizer (in other desulfurization methods, the cost of desulfurizer accounts for more than 60% of the total operating cost), and only needs power, maintenance, wages and other expenses. Therefore, the operation cost of zinc oxide desulfurization is low.
3. No secondary pollution. Because both zinc and SO2 are recovered, there is no secondary pollution problem in this method, which is often found in many other desulfurization methods. For example, if NaOH or Na2CO3 is used for desulfurization, if the desulfurization product Na2SO3 is directly discharged, it will not only consume alkali but also fail to recover sulfur from flue gas, and because the discharged Na2SO3 is reductive, it will increase the COD of environmental water and cause secondary pollution; If the desulfurization solution containing Na2SO3 is discharged after wastewater treatment, the treatment cost will be greatly increased.
Application example
From 2004 to 2006, Guangzhou Huali Company successfully put into operation three sets of zinc oxide flue gas desulfurization systems, all of which were provided by Professor Tong Zhiquan. The relevant information of the three sets of devices is as follows:
1. Basic parameters
Flue gas quantity (m/h), flue gas temperature (℃) and SO2 concentration (mg/Nm)
Barium sulfate calcining rotary kiln 35000 180 7000 ~ 8500
Lithopone calcination rotary kiln 75000180 ~190 3000 ~ 4000
10t/h heavy oil boiler 32000180 ~190 2500 ~ 3000
The above three sets of zinc oxide dust desulfurization projects were successfully put into operation in August 2004, August 2005 and March 2006 respectively.
2. Process flow
The above three sets of ZnO flue gas desulfurization projects all adopt the process of "low-priced zinc oxide slurry absorption-air oxidation-zinc sulfate production", as shown in the following figure (sorry for not uploading the picture):
3. Desulfurization agent
Zinc oxide dust for desulfurization is purchased from small lead-zinc smelting enterprises all over the country, and contains 40% ~ 50% zinc oxide and high impurities such as lead, arsenic, iron and copper.
4. Desulfurization rate
The flue gas volume of the first set of barium sulfate calcination rotary kiln is 35,000 m/h, the average concentration of SO2 before desulfurization is 7592mg/m, and the average concentration of SO2 after desulfurization is 358mg/m, and the desulfurization efficiency is 96.73%.
5. Oxidation efficiency of zinc sulfite
The air oxidation rate of zinc sulfite, the desulfurization product, is more than or equal to 96%, and the zinc sulfate solution, the oxidation product, is used as the raw material for producing lithopone, a chemical pigment.
6. Economic and environmental benefits
This project not only eliminates SO2 pollution, but also recycles SO2 from flue gas into chemical products, which has good economic benefits. The annual economic benefit of the above 1 and two sets of desulfurization systems is 177438+0438+00000 yuan. The annual emission of SO2 is less than 27 17 tons, which has obvious environmental benefits and has an important contribution to reducing air pollution in Guangzhou.