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Why to Produce PVC by Calcium Carbide Method
Limited by the resource endowment of rich coal, poor oil and little gas, calcium carbide method was the main method in China. As of December 2007, calcium carbide method accounted for more than 70% of the total production capacity of PVC in China.
1. Production process
There are two main preparation processes for PVC production, one is calcium carbide process, the main raw materials are calcium carbide, coal and raw salt; the other is ethylene process, the main raw materials are petroleum. In the international market, the production of PVC is mainly based on ethylene method, while in China, due to the resource endowment limitation of rich coal, poor oil and little gas, the production of PVC is mainly based on calcium carbide method. By December 2007, calcium carbide method accounted for more than 70% of the total production capacity of PVC in China.
It is worth noting that in the preparation of PVC by calcium carbide method, hydrogen chloride is used to produce PVC after electrolysis of raw salt, and the remaining sodium is used to produce caustic soda. Therefore, there is a symbiotic relationship between chlorine and alkali, and the balance of chlor-alkali is also an important factor to be considered in the development of the whole industry.
2. Cost analysis
From the point of view of production cost, the cost of the two processes differs greatly in different economic development cycles. Usually, in the stage of high-speed development of international macro-economy, because of high oil price, high production cost of ethylene method and obvious cost advantage of calcium carbide method, once the international economy enters recession, oil price will run at a low level, and the cost advantage of calcium carbide method will disappear because of its high energy consumption, high price of kerosene, electricity and oil transportation, etc. Since 2003, the international oil price has risen sharply, which has increased the cost of vinyl-based PVC, while the production of calcium carbide method has been less affected. This has led to a new upsurge in the construction of domestic calcium carbide-based PVC production facilities, which has greatly expanded the production capacity of calcium carbide-based PVC and posed a great challenge to the production of vinyl-based PVC. Many ethylene-based enterprises are in deficit. Damage margin. However, with the continuous decline of crude oil prices after May 2008, the cost advantage of ethylene process is obvious, and the calcium carbide process producers operate at a slight profit, or even unsustainable.
The cost components of calcium carbide process are mainly composed of calcium carbide cost, hydrogen chloride cost and water and electricity cost. The national standard stipulates that 1 ton of PVC will consume 1.45-1.5 tons of calcium carbide (generally calculated as 1.45, but generally the actual production process will consume more than this proportion, only a few can meet the standard), 0.75-0.85 tons of hydrogen chloride gas (generally calculated as 0.76), about 450-500 kW per ton of electricity consumption, and other projects will be opened. Expenditures, such as packing fee, initiator, dispersant, water fee and management fee, vary with the manufacturer and scale of production. Overall, the cost components of calcium carbide process are about 65-70%, 15% for hydrogen chloride, 6% for electricity and 6% for other manufacturing costs. A notable feature of calcium carbide process is that it consumes a lot of electricity not only in the production of PVC, but also in the preparation of calcium carbide from coke. For example, the production of a ton of calcium carbide requires about 3450 kW h of electricity, 0.6 tons of coke and 0.9 tons of limestone.
The main factors affecting the cost of ethylene process are ethylene consumption, chlorine consumption, power consumption, processing aids, management labor costs and so on. Each ton of PVC produced by ethylene process consumes 0.5 tons of ethylene and 0.65 tons of chlorine, accounting for about 60% of the cost. The cost of ethylene accounts for the main part of the raw material cost, and the price of ethylene has a great influence on the cost of PVC. Although the energy consumption of ethylene process is lower than that of calcium carbide process, its equipment investment is huge, so equipment Depreciation accounts for a large proportion of the cost. The equipment investment is fixed, so the price change of ethylene and vinyl chloride is the main factor of the price change of polyvinyl chloride resin.