According to different reducers, the direct reducing process can be divided into two categories: gas based and coal based.
       Gas based direct reducing process was popular in Middle East, South America and other areas with abundant resources, where the steel industry developed rapidly with electric stove with short process.  The represent process is Midrex, a vertical stove method, HYL, reacting pot method and fluid state method. Coal based direct reduced process distributes in South Africa, India, New Zealand and other areas with limited gas resources but abundant high-quality iron resources and coal resources. The represent processes are SL-RN method and Krupp method.
       Considering energy reserves and rational utilization in China, we can not offer enough natural gas for metallurgical industry, even there is gas that can be used, the cost is too high. To produce a ton of direct reduced steel (sponge iron) needs 400-500 m3 of natural gas or 1600 m3 of coal gas, but the cost of natural gas is 600-750 Yuan, the cost of coal gas is RMB1600 Yuan. So the gas based direct reduced process is unacceptable. We use tunnel oven process, rotary oven process and inverted flame oven process, all these are coal based reduced process.
       Inverted flame oven developed relatively early in our country, its characteristics are as follow: little investment, going into operation fast, low cost, flexible scale, operating simply and low requirement of raw materials, but its product quality is bad and unstable, production efficiency is low, energy consumption is high, labor intensity is high, the operating environment is bad, the environment is seriously polluted, equipments are lag, all operation are artificial. Because its little investment, some small companies also use it, but our country does not recommend to use it.
        Tunnel oven process is reliable with little investment, instant effect, low cost and consumption, low requirement of raw materials, flexible scale. The products are of high grade and steady, operation is simple, equipments run steadily, and fill factor is high ( generally above 30% ). But the labor intensity is high and the degree of mechanization is lower. A dozen companies use this process at home. It is the ripe and reliable process which used most.
       Characteristics of rotary oven process: The degree of mechanization is relatively high, labor intensity is relatively low, the cost is high, the investment is high, it is easy to be hitched, the quality is low, differentiation rate is high, requirement of raw material and reducers is strict, production efficiency is low, thermal efficiency is low, and fill factor is low ( generally 10%-20% ). Several companies use this process at home, but failed.

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