Superheated steam drying of coal
   Humidity coal after drying can improve combustion efficiency, save energy and reduce pollution. Therefore, many countries have low-quality coal drying humidity, coal stove after drying efficiency increased 10% -15%. Using hot air drying of coal is generally used when direct heating, hot air temperature of 700-900 degrees, the exhaust temperature reaches 60-120 ℃, using drum dryer drying coal, the unit heat consumption is 3100kJ/kg water, the use of fluidized coal bed drying machine drying, the unit heat consumption of 3100-4100kJ/kg water, Australian scholar Foner use superheated steam drying tests carried out on coal, to obtain a very favorable effect, he uses an internal pipe superheated steam fluidized bed drying machine, the drying properties are as follows:
    Heat pipe temperature 140-170 ℃
    Bed temperature 110-127 ℃
    Minimum fluidization velocity 0.57m / s
    Superheated steam temperature of 130-150 ℃
    Steam speed 0.2-0.3m / s
    Coal feed rate of 40-70kg / h
    Productivity 16-28kg / h
    Faber et al compared the hot air drying and steam coal drying. He proved the existence of a turning point in temperature over this temperature superheated steam drying faster than hot air drying, he found that when the temperature exceeds 180 ℃, the steam drying than hot air drying costs reduced by 20%. Faber also successfully activated carbon particles using the superheated steam drying, the moisture content from 50% to 2% Steam into the dryer temperature of 300 ℃, the exhaust gas temperature of 150 ℃, the exhaust air for preheating the feed human activated carbon. Prototype working smoothly, equipment costs than ordinary hot-air drying 40% lower. In order to avoid fire, hot air drying can only be used when the maximum temperature 125 ℃
    Woods and others on 1-13mm coal particles superheated steam drying that when coal with superheated steam drying constant drying stage 6-7 times longer than the hot air drying, heat transfer rate of hot air drying 1.7-2.0 times.
    Concluded with superheated steam drying lignite has the following advantages:
    ① higher energy efficiency, the use of exhaust heat utilization condensation method, the total efficiency of up to 36%;
    ② device can be large-scale (up to 15t / h);
    ③ dryer compact, [heat transfer coefficient up to 200w / (mmK)]
    ④ safe operation;
    ⑤ make dryers and power plants combined, make full use of low-pressure steam condensation latent heat;

 

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