Coal heating

The CO2 Acceptor process, also developed under AGA/DOE sponsorship, by the ConsoHdation Coal Co., uses steam to gasify lignitic coal. Heat is supphed by the exothermic reaction between CO2 and calciaed dolomite [17069-72-6]. The dolomite is calciaed ia a separate fluidized bed. This process operates ia a 40 t/d pilot plant, but there are no plans for commercialization as of this writing. 

A coherent plastic layer from a few mm to 2—3 cm thick separates the semicoke and coke from the unfused coal in the coke oven. Coking properties are assessed in Russia and some other countries by a measurement of the thickness of this plastic layer. A standardized test widely used in eastern Europe is the best known of this type (6) and involves a penetrometer used to measure the thickness of the plastic layer in a column of coal heated from the bottom. The various standard tests give results that are similar but do not give close correlations with each other. 

These products, called by-products of coal, include coal gas, coal oil, coal tar, coal tar pitch, coal tar resins and coke Coal gas is obtd by destructive distillation of bituminous coal heated to high temps in fire-clay or silica retorts, or in special by-product ovens. The gas is used in domestic industrial heating lighting and as a source of coal-tar, ammonia, benzene, toluene, xyline and related items (Refs 1,2,8,10 11)... 

When coal is heated in a vacuum, the plastic range is generally reduced substantially, perhaps because of the rapid evaporation of the bituminous hydrocarbons that are reputedly responsible for the fluidity of the plastic coal. Heating coal to the plastic range followed by rapid cooling yields coal with a lower softening point (if plasticized a second time), and this has been ascribed to the presence of liquid in the coal that arose from the first heating. 

Fluidity degree of plasticity exhibited by a sample of coal heated in the absence of air under controlled conditions (ASTM D-1812 ASTM D-2639). 

Free-swelling index measure of the agglomerating tendency of coal heated to 800°C (1470°F) in a crucible. Coals with a high index are referred to as coking coals, those with a low index are referred to as free-burning coal. 

Tires are a good fuel for several reasons. Tires contain about 15,000 Btu s per pound (about 300,000 Btu s per tire). Coal heating values range from 6,000 to 13,500 Btu s per pound. Further, they are compact, have a consistent composition, and contain a low moisture content. Also, many components of tires, such as sulfur and nitrogen, compare favorably to coal in percent makeup. Table 1-2 compares composition of tires to that of midwest coal.4 Table 1-3 compares composition of various types of tires.5 Most trace metal levels in tires are equivalent to the levels in coal zinc and cobalt are higher in tires.6 Figure 1-1 shows trace metal level of whole tires compared to bituminous coal.6... 

When we produce synthetic liquid fuel, such as Fischer-Tropsch (FT, diesel) oil from coal, heat is necessary for the coal gasification process to produce synthetic gas (syn gas, CO+HJ and additional hydrogen is necessary to adjust the hydrogen content in the syn gas for the subsequent FT synthesis... 

Figure 1. EPR spectra of coal, coal-naphthalene-h8 and coal-naphthalene-d8 heated at 400°C a. unheated coal b. coal heated for 30 min c. coal heated for 10 h d. coal heated with naphthalene-d8 for 10 h e. coal heated with naphthalene-...

Figure 4. The g-factors of Illinois No. 6 coal heated for the same periods of time under different conditions Set 1,0, coal heated in sealed tubes Set 2, coal heated with naphthalene-d8 Set 3, , coal heated with naphthalene-h8 Set 4, A,...

Figure 2. Typical pressure TGA thermograms of Wyoming coal heated at 50 C/min and 500 psig H2 ...

The kinetic parameters for four different coals heated under H2 pressure are presented in Table II. A reaction order equal 2.3 to 2.9 was observed for the primary hydropyrolysis peaks. A high reaction order was obtained for the secondary reaction peak under hydrogen pressure. The kinetic parameters for four different coals heated under No atmosphere compared with data presented in the literature (6,10-12) are listed in Table III. 

Figure 2. Pyrolysis product distributions from bituminous coal heated to different peak temperatures. (%) H20 and H2S (O) H20, H2S, CO, and C02 (X) H20, H2S, CO, C02, and all hydrocarbon gases (T) total weight loss, i.e., H20, H2S, CO, C02, all HC gases, tar, and liquids. Pressure = 1 atm (helium). Heating rate = 1000°C/sec. (14)...

ESR g values for West Virginia (Ireland Mine) hvAb coal heat-treated at four different temperatures are shown graphically in Figure 9. The points connected by the dashed lines represent the results of measurements made on neat samples after heat treatment. The general shape of this curve has been established for other coals (8, 15). The point for the sample heat-treated at 450 C falls considerably below the free electron value similar results for other coals have been attributed to the formation of sigma radicals during heat treatment (8). Three experiments were conducted to show that this observed g value was an apparent and not a true value. 

To establish the true relationship between ESR g values and coal heat treatment, samples of Ireland Mine coal diluted with potassium bromide were heat-treated at different temperatures. The results, represented by the open circles in Figure 9, show that the g value is... 

Preparation of blast furnace coke involves the heating of metallurgical coal to 1,000-1,100°C in the absence of air in a battery of refractory brick-lined coke ovens. This is referred to as the by-product coke plant from the association of by-product recovery with coke formation. The coal charge is heated until all of the volatile matter has been vaporized and pyrolysis is complete, a process which takes 16-24 hr. The residual lumps of coke, still hot, are then pushed out of the oven through a quenching shower of water and into a rail car for final shipment. About 700 kg of coke plus a number of volatile products are recovered from each tonne of metallurgical coal heated. More details on the coking process itself are available [40]. 

A large volume of work has been reported on rapid devolatilization of coal (heating rates approximating process conditions (21,22). Recently, the effects of coal minerals on the rapid pyrolysis of a bituminous coal were reported by Franklin, et al ( 23). They found that only the calcium minerals affected the pyrolysis products. Addition of CaCO3 reduced the tar, hydrocarbon gas and liquid yields by 20-30%. The calcium minerals also altered the oxygen release mechanism from the coal. Franklin, et al. attribute these effects to CaCOj reduction to CaO, which acts as a solid base catalyst for a keto-enol isomerization reaction that produces the observed CO and H2O. 

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