Application of calcium carbide slag in dry cement production line

Date: 2019-08-19 Views:

The reasonable utilization of calcium carbide slag can increase the profit of enterprises. The calcium carbide slag discharged from the enterprise can be used as limestone raw material for production, and the cement produced can be used to fill the mine downhole, forming a circular economic industrial chain.


1. Comprehensive utilization project of calcium carbide slag solid waste

For many years, a cement factory has been committed to building resource-saving and environment-friendly enterprises. Adhering to the principle of comprehensive utilization of solid waste, it "eats dry and squeeze-clean" solid waste discharged by the upstream enterprises of the chlor-alkali industry chain in this region, so as to turn waste into treasure and completely eliminate the environmental pollution caused by the discharge of calcium carbide residue and other waste residue.At the same time, the product structure can be adjusted to meet the market demand for high performance and high quality cement, which is fully in line with the national industrial policy and environmental policy.

Calcium carbide residue is the waste produced when calcium carbide reacts with water in the generator in the process of producing PVC in chlor-alkali chemical industry to produce acetylene gas.Calcium carbide slag can be used to produce cement, which is the most effective way to dispose calcium carbide slag.However, using calcium carbide slag instead of calcareous raw material to produce cement is quite different from the control parameters of traditional natural calcareous raw material to produce cement.


1.1 characteristics of calcium carbide slag

Calcium carbide residue produced by dry preparation of acetylene has a water content of 4% to 12%. According to the impurities including silicon and iron, the density is 1.5 -- 2.0kg/m3, the volumetric density is 0.5 -- 1.0kg/ m3, and the fineness sieve residue (0.08mm square sieve) is 9% -- 18%, which is white and fine powder, and the specific surface area is 260 -- 350m2/kg.With the decrease of calcium carbide slag particles, its specific surface area is proportional.Due to the main chemical composition of calcium carbide slag Ca(OH)2, when the water content is low, it presents moisture absorption. The calcium carbide slag containing water is sticky and water-retaining. Drying at room temperature will produce a shell protective layer, and the water is not easy to evaporate.

The chemical composition of calcium carbide residue produced by dry preparation of acetylene is shown in table 1.CaO is the main chemical composition of calcium carbide residue, and its content is 68% - 74%.

Table 1: main chemical constituents of calcium carbide slag




1.2 harm of calcium carbide slag

Calcium hydroxide (mass fraction of 90.1%), silicon oxide (mass fraction of 3.5%), alumina (mass fraction of 2.5%), and a small amount of calcium carbonate, iron trioxide, magnesium oxide, titanium dioxide, carbon slag, calcium sulfide and other impurities.Calcium carbide slag is gray and has a pungent odor.Calcium carbide slag has strong alkalinity, large quantity, high transportation cost and secondary pollution.If stacked on the spot, it will often cause serious environmental pollution to the surrounding environment, such as taking up a lot of land for stacking, polluting the water resources near the stacking site, air pollution caused by dust, which is the focus and difficulty of China's clean production and resource recycling.

1.3 advantages analysis of calcium carbide slag cement compared with limestone cement

Because the chemical composition of calcium carbide slag is basically the same as that of limestone, theoretically calcium carbide slag can be used to produce cement.Using calcium carbide slag instead of limestone to produce cement has obvious effect of increasing production and saving energy.

(1) CaO content is up to about 70%, which improves the burnability of raw materials;

(2) the decomposition temperature of Ca(OH)2 in calcium carbide slag is much lower than that of CaCO3 in limestone, and the combustion heat consumption is lower.

(3) the use of calcium carbide slag to reduce the amount of limestone, not only saves the amount of non-renewable resources limestone, to meet the raw material demand of cement production, but also to solve the problem caused by the waste residue pollution for many years, so that waste resources can be used, and improve the ecological environment;

(4) the traditional cement industry not only consumes huge resources and energy, but also causes serious pollution to the environment.The fundamental cause of damage to the environment caused by cement production lies in that non-renewable resources and energy such as limestone and fuel must be adopted to undergo crushing, grinding, calcining, re-crushing and re-grinding. Therefore, resources, energy, exhaust gas, dust and other pollutants will inevitably be consumed in the above-mentioned process.The pollutants discharged by traditional cement enterprises are mainly dust, soot, carbon dioxide, sulfur dioxide, nitrogen oxide, etc., while the emission value of various pollutants decreases obviously after using calcium carbide residue as the main raw material to produce cement.

(5) the amount of calcium carbide slag increases by 1.0%, the amount of limestone decreases by 0.85%, and the amount of sandstone increases by 0.15%. The raw material produced by a factory every month is calculated as 100,000 tons, which can save about 420,000 yuan.

(6) when using limestone as raw material to make cement, the coal consumption of tons of clinker reaches 133 kg/ton;When using calcium carbide slag between 20% and 30%, the coal consumption of tons of clinker can reach 119 kg/ton, each ton of clinker can save 14 kg of raw coal, and the cost of raw coal can be saved about 500,000 yuan per month.


2. Difficulties e​ncountered in actual production and solutions


2.1 difficulties encountered in actual production and solutions

(1) in the process of using calcium carbide slag, the use amount less than 20% has little impact on the preheater system and calcining in the kiln. After the use amount exceeds 20%, the materials in the kiln tail system and the preheater are sticky, which is easy to cause equipment failure.

(2) as the supply of calcium carbide slag continues to increase in upstream enterprises, the raw material into the grinding chute transport capacity is limited, can only meet about 20% of the throughput, which brings difficulties to production.

(3) because calcium carbide slag is light material, it is easy to separate in the production process.


2.2 solutions

(1) through repeated test in production, and according to the amount of carbide slag for upstream enterprises, carbide slag usage gradually increased to 30%, from 10% in the groping and probing into the relevant personnel in the head and tail coal usage and a gradual adjustment ingredients, process design and system running situation and combining with our factory, after a period of groping, found that calcium carbide slag amount 20% - 30%, significantly lower system requires heat, under the condition of invariable in the first coal consumption, tail significantly lower coal consumption, a head, tail coal consumption ratio can be controlled in 45%, 55%, completely relieve the preheater system, all levels of preheater crust serious situation,Ensure the normal calcination of clinker and the normal operation of the system.

(2) in order to solve the increase of calcium carbide slag supply, I plant equipment cannot meet the production needs of the problem, the factory department actively organized personnel on raw material into the grinding chute for renovation, the original serving 300mm*22m chute replaced with 400mm*22m chute, increase the transmission capacity fully meet the production needs.

(3) in order to alleviate the phenomenon of raw material stratification, the homogenized storage location was adjusted to ensure the operation of low storage location as far as possible, so as to provide reasonable space for the uniform distribution of raw material powder in storage and effectively ensure the operation rate of raw material grinding.


3. Summary

Cement industry is the best way for calcium carbide residue to be harmless, large dosage, no residue and resource treatment, and calcium carbide residue production cement is the best way for calcium carbide residue cleaning treatment.Because the decomposition heat of calcium carbide slag is much lower than that of limestone, the coal consumption is greatly reduced and the production cost is reduced.And calcium carbide slag decomposition emissions of water, and limestone decomposition emissions of CO2, will produce greenhouse gases.Therefore using calcium carbide slag to produce cement can realize low carbon emission and low heat consumption.Meanwhile, calcium carbide slag with high content of calcium oxide provides a reliable guarantee for the production of high grade cement.

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