On April 12, the reporter learned from the China Chlor-Alkali Industry Association that after the joint efforts of the entire industry, the current comprehensive utilization rate of domestic carbide slag has reached 100%. Among them, the production of cement is the best way, and it is also the most important comprehensive utilization method of calcium carbide slag in the chlor-alkali industry. It has been widely used. At the same time, other calcium carbide slag comprehensive utilization processes provide good supplements for the treatment of calcium carbide slag, and the technology for reducing carbide slag from the source is also constantly developing.
Calcium carbide slag is a by-product of hydrolysis reaction produced during the production of polyvinyl chloride (PVC) by the calcium carbide process. It belongs to industrial waste and its main component is calcium hydroxide. Due to the rapid development of calcium carbide process PVC in recent years, the vast majority of new expansion projects have adopted the calcium carbide process and produced a large amount of calcium carbide slag. If calcium carbide slurry is not properly treated, it will occupy a large amount of land for accumulation, landfill, and pollute the soil and water bodies. Therefore, the Ministry of Environmental Protection has early included calcium carbide slag in Class II general industrial solid waste for treatment and recycling. .
As of 2012, there are more than 100 PVC production companies in China, with a total output of 13.18 million tons, of which calcium carbide method PVC production is approximately 9.81 million tons. According to the emission factor of 1.78 (dry basis) for carbide slag production, the amount of carbide slag produced in China in 2012 was approximately 17.57 million tons.
In view of the comprehensive utilization of carbide slag, domestic companies have made many attempts and made significant progress. The most significant way of using calcium carbide slag is to produce building materials. Cement production has the potential to consume a large amount of calcium carbide slag. In the calcium carbide process PVC production enterprises with a relatively large amount of carbide slag production, the use of waste residue to produce cement is currently the best way for the comprehensive utilization of carbide slag.
The comprehensive utilization of cement made from calcium carbide slag has many advantages. First, it can replace limestone raw materials by a large proportion, reducing the consumption of limestone resources and carbon dioxide emissions (1.28 tons of limestone resources per ton of cement, and 0.56 tons of carbon dioxide emissions can be reduced at the same time); It can significantly reduce the cost of raw material purchases and reduce energy consumption (cement production with lower clinker heat consumption than limestone). Third, the production process is becoming more mature, advanced, and has obvious competitive advantages, which will help eliminate backward production in the cement industry. Process.
At present, the use of calcium carbide slag for cement not only achieves "wet grinding and dry burning", but also achieves "dry grinding and dry burning" (ie, new dry process cement production technology). It has been successfully applied to some enterprises, and some of the technical and economic indicators are better than others. Limestone is currently used as the raw material for the same level of new dry cement production lines, and the replacement rate of limestone can reach over 80%. Compared to the wet acetylene process, the dry acetylene production plant calcium carbide slag does not require slag slurry treatment, resulting in a higher yield of acetylene and lower carbide carbide slag processing costs. To a certain extent, it reduces the cost of calcium carbide slag treatment from the source and increases the efficiency of the enterprise. .
The use of calcium carbide slag to produce fly ash non-fired brick technology has also been successfully applied in many domestic chlor-alkali enterprises. The product has high strength and durability, and no sintering is required during the production process, which can save a lot of energy, and also achieve good environmental and economic benefits. There are fly ash autoclaved standard bricks produced by chlor-alkali enterprises with fly ash, carbide slag, and a small amount of gypsum. The strength can reach 20 megapascals to 30 megapascals. The products have been widely used due to their advantages of low cost and good efficiency. . However, this method has a low added value and cannot use a large amount of carbide slag.
In addition, calcium carbide slag has been used to control air pollution and wastewater pollution. The most typical is the application of desulphurization (solid sulfur) in coal-fired industrial boilers, in which chlor-alkali enterprises use calcium carbide slag instead of lime desulphurization, and the desulfurization efficiency can reach as high as 98%. Carbide slag can also replace chlorine to absorb chlorine and handle accidental chlorine. Calcium carbide slag can be used as a neutralizer and precipitator to treat zinc wastewater containing chemical fiber and wastewater containing arsenic, fluorine and chromium in electroplating wastewater containing sulfuric acid.
Calcium carbide slag can also produce chemical products with an added value, including the production of calcium carbonate products, calcium chloride, soda ash, potassium chlorate and propylene oxide, ethylene oxide, and chloroform. At present, a chlor-alkali company in Shandong uses calcium carbide slag as a by-product for the production of its 2 million tons/year soda ash, and the company's calcium carbide slag for potassium chlorate production technology has also produced good economic benefits.
It is understood that due to the further increase in domestic calcium carbide process PVC production and demand for calcium carbide in the next few years, the state has also introduced some new supporting measures in the application of calcium carbide slag. Including: The newly-built, rebuilt or expanded calcium carbide method PVC project must be matched with the construction of calcium carbide slag to produce cement and other carbide slag comprehensive utilization devices. The carbide slag production cement device must have a single production scale of 2,000 tons/day and above; the use of calcium carbide slag to produce cement The enterprises can enjoy the preferential taxation policies for comprehensive utilization of national resources after being certified by the national circular economy competent department; calcium carbide slag cement enterprises continue to enjoy preferential policies for tax reduction and exemption of comprehensive utilization of resources, and at the same time, research will further strengthen the comprehensive utilization of calcium carbide waste slag. , financial and land support measures.
The relevant person of the chlor-alkali association stated that with various policy guidance and technological progress, the treatment of calcium carbide slag will shift to a more economical and rational way in the future.
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