Calcium Carbide Industry Should Control Production Capacity

China's calcium carbideindustry has maintained a relatively rapid growth, with high productivity, continuous upgrading of technology and equipment, and remarkable energy saving and emission reduction results. It has made an important contribution to ensuring stable growth of the national economy and meeting the needs of downstream industries. However, affected by the sharp drop in international oil prices, the slowdown of domestic economic growth and the industry's own development cycle, the production and operation of the calcium carbide industry is in a dilemma, and the contradictions such as excess capacity, high resource dependence and low degree of automation are highlighted.

In order to meet the new requirements of energy saving, emission reduction and safe production under the new normal conditions, the calcium carbide industry should change the development mode of "high input, high consumption and low benefit", rely on technological progress to improve the efficiency of resource and energy utilization, reduce carbon dioxide emissions and achieve green sustainable development. In 2016, the calcium carbide industry suffered unprecedented shocks and pressures under the situation of weak global economy and increasing downward pressure of domestic economy. Prices continued to fall and at one point fell below the 2000 CNY/ton threshold, a new low in eight years. The profit level of enterprises has also dropped dramatically, the loss of the industry has increased, and the number of enterprises with shutdown and semi-shutdown has increased, making it particularly difficult for them to survive. In the second half of the year, driven by the recovery of downstream industries such as PVC, the price of calcium carbide began to rise, and the profit situation of enterprises improved.

However, the price of raw materials of orchid and lime also rose, diluting the efficiency of enterprises. By the end of 2015, according to incomplete statistics of China Calcium Carbide Industry Association, there were 255 domestic calcium carbide production enterprises with a capacity of 45 million tons, almost doubling compared with 2010. The national production of calcium carbide is 26.5 million tons, an increase of 2% over the same period last year, an increase of 11 percentage points lower than that in 2014. The overall starting rate of the industry is less than 60%, which is the lowest in recent years. During the 12th Five Year Plan period, the trend of large-scale calcium carbide enterprises is more and more obvious. In 2015, the production capacity of Xinjiang Tianye Group, the largest domestic producer of calcium carbide, has reached 2.89 million tons, accounting for 6.4% of the total domestic production capacity. In the same year, the top 10 enterprises produced 11.754 million tons of calcium carbide, accounting for 44.4% of the total domestic output. According to statistics, there are 57 enterprises with capacity of 200,000 tons or more in 2015, with a total capacity of 32.4 million tons, accounting for 72% of the country's total capacity. In addition, northwest China has abundant coal reserves, abundant power supply and vast land, and has unique advantages in developing calcium carbide industry. In recent years, the focus of national calcium carbide production has continued to shift to the northwest. During the Twelfth Five-Year Plan period, new production capacity of five provinces and regions, including Xinjiang, Inner Mongolia, Shaanxi, Ningxia and Gansu, totaled more than 1 million tons. In 2015, the total production capacity of calcium carbide in six provinces and autonomous regions exceeded 36 million tons, accounting for more than 80% of the total domestic production capacity of calcium carbide.

The high energy consumption forced industry to save energy, that is calcium carbide production energy consumption mainly includes two parts, one is carbon as raw material for production, the other is the electric energy which produces reaction heat, namely electric furnace power consumption. Among them, the consumption of raw carbon is about 0.6-0.7 tons per ton of calcium carbide. However, in addition to the main reaction of calcium carbide formation, some side reactions will also absorb some heat. The sensible heat carried away by flue gas and calcium carbide from the furnace, and the heat loss of furnace transformers, short grids, electrodes, furnace bodies and other equipment will all lead to the increase of electric power consumption of the furnace. Therefore, the average comprehensive energy consumption of domestic tons of calcium carbide products (converted standard gas output) is higher than that of 1 ton of standard coal, and the electric power consumption of electric furnace is higher than 3200 kWh. Another important reason for high energy consumption in calcium carbide production is the quality of raw materials. In order to maximize economic benefits, some enterprises use low-cost and poor-quality carbon and lime raw materials, which leads to the increase of electric power consumption and comprehensive energy consumption of electric furnaces. For example, the raw coke used by calcium carbide enterprises contains less than 90% carbon, while the raw blue carbon is lower, only about 80%. Some enterprises purchase blue carbon which contains a lot of moisture and needs to be dried before entering the furnace. The quality of lime products is uneven, resulting in more side effects and so on.

At present, all domestic calcium carbide production uses electric smelting process, which is highly dependent on power energy and vulnerable to macro-control. For this reason, enterprises and colleges concerned actively develop new calcium carbide production processes such as oxygen-heat method and regenerative method.

Oxythermal process of calcium carbide production uses carbon-containing raw materials and oxygen-enriched or pure oxygen combustion to provide the heat needed for the reaction of calcium carbide. The ratio of C to C a in raw materials is higher than that in electrometallurgy. The carbon and oxygen input increases the production of carbon monoxide. Its power consumption is mainly used in the oxygen production process, only 750 kWh/t of calcium carbide, and the comprehensive energy consumption has decreased significantly. The process produces a large amount of carbon monoxide by-product, can produce a variety of organic chemical products, and can be coupled with other coal chemical plants to form polygeneration, with remarkable economic benefits.

Regenerative calcium carbide production process uses low-rank fly ash and lime as raw materials, after crushing, mixing and pelletizing, then through regenerative radiant tube rotating bed pyrolysis, high-temperature pellets produced by pyrolysis are fed into sealed calcium carbide furnace, and calcium carbide is produced by reduction reaction in the calcium carbide furnace, while methane gas and oil products are produced by-product. In theory, the electric power consumption and comprehensive energy consumption of the electric furnace of this process ton product are lower than that of the electric smelting process

Closed furnace has obvious advantages of energy saving and safety and environmental protection, which is the mainstream of technology and equipment development in the calcium carbide industry. After introducing 25 000 KVA closed furnace, the industry has developed 27 000 KVA, 33 000 KVA, 40 500 KVA and other types of large closed furnace, and successfully realized industrial application. At present, most of the new calcium carbide projects in China use 40500 kV sealed furnace, and some enterprises have tried to build 6300.