Caking coals, handling

The fluidized-bed system (Fig. 3) uses finely sized coal particles and the bed exhibits Hquid-like characteristics when a gas flows upward through the bed. Gas flowing through the coal produces turbulent lifting and separation of particles and the result is an expanded bed having greater coal surface area to promote the chemical reaction. These systems, however, have only a limited abiUty to handle caking coals (see Fluidization). 

Handling of caking coals has proved to be a serious obstacle to the development of hydrocarbonization processes and was, in fact, one of the principal factors contributing to the failure of the Coalcon project. However, a number of technologically successful approaches to handling of caking coals have now been demonstrated. The most common approach is through special reactor... 

A. CONN Bob McNeese made a comment on how to handle caking coals. He left it up in the air, I was hoping he would be here this afternoon to talk about it. I don t know whether you are in the position to comment on what he might have said or not. 

Lurgi Fixed bed reactor -1000°C 30atm 12 37 18 32 Production of by-product heavy tar ( 1%) restricts coal to non-caking types. Slagging Gasifier under development by British Gas Corporation to enable the difficult caking coals to be handled... 

Relatively high methane content in the produced gas Production of hydrocarbon liquids, such as tars and oils Limited ability to handle fines Special requirements for handling caking coal... 

At first consideration, there may appear to be little, if any, relationship between the physical and chemical behavior of coal, but in fact the converse is very true. For example, the pore size of coal (which is truly a physical property) is a major factor in determining the chemical reactivity of coal (Walker, 1981). And chemical effects that result in the swelling and caking of coal(s) have a substantial effect on the means by which coal should be handled either prior to or during conversion operations. This is the reason for the study and measurement of these very important properties of coal. 

Sodium Sulfate A single-hearth furnace is used, like that shown in Fig. 23-40g. Sodium chloride and sulfuric acid are charged continuously to the center of the pan and the rotating scrapers gradually work the reacting mass to the periphery, where the sodium sulfate is discharged at 540°C (1,000°F). Pans are 3.3 to 5.5 m (11 to 18 ft) in diameter and can handle 5,500 to 9,000 kg/d (12,000 to 20,000 Ibm/d) of salt. Rotary kilns also are used for this purpose. Such a unit 1.5 m (4.9 ft) in diameter by 6.7 m (22 ft) has a capacity of 22,000 kg/d (48,000 Ibm/d) of salt cake. A pan furnace also is used, for instance, in the Leblanc soda ash process and for making sodium sulfide from sodium sulfate and coal. 

At regular intervals, the gas outlet is mechanically cleaned by a scraper on-line to prevent fouling by caking solids. All coal feeding, ash discharge and outlet cleaning operations are fully automated. They are controlled by hydraulic systems whose operating cycles are appropriately adjusted to the properties of the coals to be handled. 

A related property, which is also an important factor, is the ability of the individual coal particles to retain their initial size during handling and processing. In fluidized-bed processes, attrition and decrepitation of the feed coal may result in unacceptable tines carryover losses. For processes that must withstand high temperatures and blast velocities, only hard and resistant coals are satisfactory feed materials. In addition, the fusibility and caking characteristics are properties of importance to moving bed or fluidized-bed processes. 

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