Drying of brown coal

Following are some of the key advantages claimed for steam-fluidized bed drying of brown coal ... 

Both direct and indirect dryers are in use for coal drying. Combustion gases or steam may be used as the heating medium. Steam-heated dryers (e.g., drum, tray, and tube dryers) are used mainly for drying of brown coals in the coal briquetting process. Frequently, coal drying is carried out in convection dryers, such as the following ... 

Direct drying of brown coal by recirculating boiler flue gas or its equivalent has become standard practice in Victoria, Australia. It should be noted that significant drying occurs during normal coal grinding and other operations associated with preparation of the feed to a boiler. 

Figure 43.23 shows conceptually the steam-fluidized bed drying (Dampf-Wirbelschicht-Trocknung [DWT]) described by Weiss et al. (1991). Typical operating conditions for drying of brown coal are given below. 

The potential use of supercritical water appears especially attractive for the extraction of brown coals with their high water content, 5Q-70% for Victorian brown coals, thus removing the need for a coal-drying stage. The drying and extraction of these low rank coals would occur in a single process. The purpose of the present study was to investigate the feasibility of the extraction of Australian black and brown coals with supercritical water. The... 

Table 32—Effect of Temperature and Humidity on Dust Particles of Brown Coal in a Moving Air Stream. (Coal Initially Dry). Walthkr and Franks ...

Further research work is necessary to extensively determine the influence of the biomass fuel type used and synergistic effects of brown coal/coal as additive to biomass with respect to Carbon conversion, tar formation and NO, precursor formation. Also, gasification modeling is further optimised and validated with these and more experimental data to describe the basic processes of drying, devolatilisation, partial combustion and gasification. 

Coldry is a recently proposed method that is mainly an evaporative drying process based on brown coal densification. In the process, the coal is sheared and attritioned, which results in particle size reduction and releasing water naturally in the porous coal structure (Moore, 2012). This dispersal of surface and/or physically bound water is then evaporated at or near ambient temperature. The extra benefit of brown coal densification is that some chemically bound water is also removed without the need of high tanperature/pressure. The new structure of a dried coal by this method also reduces the tendency to self-heat. 

Brown coals, like the hard coals, are also defined in terms of their calorific value (see the previous text) and were also recognized as potential fuels. The International System for the classification of brown coals is based on two inherent characteristics which indicate the value of brown coals as fuels (1) the total moisture (ash-free basis) and (2) the yield of tar (daf basis). Thus, the six classes of brown coal based on the ash-free, equilibrium moisture content are divided into groups according to the yield of tar on a dry, ash-free basis (Table 2.14). This system indicates... 

The rotary-tube dryers are used widely for coal drying in brown coal briquetting plants. They are also used for drying of hard coals. These dryers are indirect dryers heated by saturated steam at pressures of 0.15 to 0.55 MPa. This dryer (Figure 43.3) consists of a sloping drum (1), in which the perforated walls... 

The Gaskombinat Schwarze Pumpe (GSP) coal gasification demonstration project in former East Germany consumes 600 t/d (dry basis) of brown coal to produce 1.9 million scf/hr (50,000 Nm /h) of medium-Btu town gas and chemical synthesis gas (49, 50). (Section 5 discusses the GSP coal gasification technology in more detail.)... 

The High Temperature Winkler (HTW) based IGCC is called the KoBra project. The HTW demonstration project at the Goldenberg location in Hiirth, Germany will consume 3,600 t/d (dry basis) of brown coal to generate 355 MW (gross) of electricity. (This demonstration is separate from the HTW synthesis gas project. Section 5 discusses the HTW process in each plant in greater detail.)... 

The object of the research project is to confirm and extend in systematic laboratoiy tests the results thus far obtained with the use of brown coal coke for removing and SO2 from flue gases. It has been proved that brown coal coke is an efficient adsoiber/catalyst for dry flue gas eleaning. 

The moisture content of peat or brown coal that is briquetted for fuel must be reduced to about 15% for satisfactory briquetting. Mechanical or natural means are used because of the cost of thermal drying. Moisture is sometimes desirable. About 8% is necessary for prevention of combustible loss from a chain-grate stoker. 

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