Noncaking coal

An entrainment system (Fig. 3) uses finely sized coal particles blown into the gas steam prior to entry into the reactor and combustion occurs with the coal particles suspended in the gas phase the entrained system is suitable for both caking and noncaking coals. 

Tai yields of approximately 0.32 m /1 were quoted. Because the scheme used hydrogen, the pyrolysis Hquids generally exhibited lower heteroatom contents than conventional tars derived from coal pyrolysis ia an iaert atmosphere. Process development proceeded through a 270 t/d semiworks plant which was operated successfully on noncaking coals. OperabiUty for caking coals was difficult, however. 

The energy content of the coal can be expressed as the useful heating value (UHV), which is an expression derived from the ash and moisture contents for noncaking coal through the formula... 

All coals undergo chemical changes when heated, but there are certain types of coal that also exhibit physical changes when subjected to the influence of heat. These particular types of coals are generally known as caking coals, whereas the remaining coals are referred to as noncaking coals. 

Noncaking coal coal that does not fuse together or cake when heated but bums freely. 

Sparking fuels fuels that do not yield a coherent cake as residue in the volatile matter determination but evolve gaseous products at a rate sufficient to carry solid particles mechanically out of the crucible when heated at the standard rate usually, all low-rank noncaking coal and lignite may also include those anthracite, semianthracite, and bituminous coals that lose solid particles as described above particles escaping at the higher temperatures may become incandescent and spark as they are emitted (ASTM D-3175). 

This process is a fixed-bed process that gasifies crushed, dried coal at 620 to 760°C, 2.43 to 3.14 MPa, and residence times of about 1 h. The raw product gas exits the gasifier at 370 to 590°C and contains tar, oil, naphtha, phenols, ammonia, sulfides, and fines. Quenching with oil removes tar and oil. Catalytic shifting and scrubbing of the quenched product gas provides a gas that can be methanated to produce substitute natural gas, or the equivalent of pipeline gas. The process is limited to noncaking coals. 

In previously reported experiments we have converted caking coals to noncaking coal char by treating coal of 1/8—1-1/2 in. for 3 hours in static bed (3), coal of 18-100 Tyler mesh size for 5 min. in a fluidized bed (I), and coal of 4-8 Tyler mesh in size for 2 sec. in free fall (2). Nitrogen and carbon dioxide, steam, or a mixture of all three with small amounts of oxygen were used as the heating and treating gas. 

Formed coke is a carbonized coal that has been briquetted and is made from weakly caking coals or even from noncaking coals that may have been rejected as coals suitable for coke production. The formed coke may also be used in place of lump coke in certain operations. 

Cylindrical or conical metal sheets (skirt) The simple and robust standard design for noncaking coals is the so-called Bosman s skirt, which is a fixed metal cylinder as shown in Figure 6.36. The coal distribution can be supported by a hanging cone or cone ring. The space outside the coal-filled skirt is filled with product gas that streams toward the gas outlet [188,189]. 

Coal and Coke Gasification, An important process for the gasification of coal and coke is the Lurgi process, used in South Africa at the coal to oil plant and also used in Europe. This process requires the use of coke or a noncaking coal and oxygen the product gas usually is high in methane. The reaction... 

---