Coal reactions

Coal reactions, which on heating are important to the production of coke and synthetic fuels, are compHcated by its stmcture. 

The amount of residue recovered from the other two fractions is almost the same as that recovered from the whole-coal reaction, suggesting that the combined phenol and residual solvent end up... 

Figure 3.6 shows the equilibrium characteristics for the C-02-H20 reaction system. To favor production of CO and H2 from coal, reactions 3.9 and 3.10 should be carried out at a comparatively low pressure and low temperature. However, during actual production, synthesis of chemicals usually occur at high pressures of CO and H2, and therefore, the gasifier should be operated at high pressure and high temperature to obtain high process efficiency. 

An enormous amount of work both at bench scale and at pilot plant scale have been conducted to study the production of liquid and gaseous hydrocarbons from coal. Since most of the analytical methods are either very time consuming or very specialized, almost all the data available on the coal liquefaction process are based on distillation data or on the assumption that all products which are not insoluble solids are converted. It is known that products of liquefaction vary based on coal, reaction conditions, and media of reaction hence, conversion and yield may be based on very different products. 

In ihe coaling reaction, each 3 moles of iron or zinc liberates 4 moles of hydrogen ion. However, in the pickling reaction, 8 moles of hydrogen ion arc consumed. Thus, the pH at the metal interface rises, and insoluble tertiary ferrous phosphate and zinc phosphate crystallize on the iron surface. The coaling closest to the meta interface is largely iron phosphate, while that farther away is rich in zinc phosphate. 

Figure 3 Literature discrepancies in drag coefficient, in mass transfer for CFB due to meso-scale structures and in char reaction rate coefficient. For the drag coefficients, curves are adapted from Wang et al. (2010) for the mass transfer, curves are adapted from Dong et al. (2008a) for the coal reaction, different symbols refer to different coal data.

A second class of radicals of relevance to coal reactions are those that may form a new aromatic ring upon rupture of a single bond (or conversely these radicals may be formed by radical addition to a polyaromatic molecule). An example of... 

To begin the exploration of actual reaction pathways in complex pyrolyses of aromatic substances, we have carried out a detailed experimental and theoretical analysis of the liquid-phase pyrolysis of bibenzyl. This pyrolysis system has been studied by others (44,45,46), and the general kinetic features of this reaction system are now rather well agreed on. Complete details of this work will appear elsewhere (38a) and a few implications of this work of particular relevance to coal reactions will be discussed here. 

Presumably the hydrogen entering a reactor or charged into an autoclave could be relatively clean and dry, represented by a point in the lower lefthand comer of the reactor zone (or if accompanied by steam, somewhere on the left side of the square). As the reaction proceeded, the reactor gas would become relatively wet (from the balance of the coal reactions or from water in the coal) and loaded with H2S as the H2 was consumed, and would be represented by points near the upper righthand comer of the reactor zone. The area of the reactor zone would stay the same (6x6 log units) but the position of the reactor zone will shift with temperature since the two equilibrium constants are functions of temperature. Note that at 527°C (Figure 3), the reactor zone is almost entirely in the pyrrhotite FellS12 zone Note that at 427°C (Figure 4) the reactor zone is... 

Data for the weight increase are lacking in cases where the product was not isolated. This is not easy to accomplish when the solvent is insoluble in water. This lack is unfortunate in the case of cresote oil and benzaldehyde. Here the large negative value for percent depolymerization means the residue weighed more than the maf coal charged. This is evidence of solvent-coal reaction. 

The decision to employ decal in as a solvent was made to circumvent difficulties in handling small quantities of coal and catalyst in a large autoclave and to facilitate separation of solvent and coal reaction products. In some respects this was an unfortunate choice. Some reaction with decal in occurred, so accurate measurement of Hp consumption by reaction with coal was not possible. Further, both coal and depolymerized coal were virtually insoluble in this solvent so the hoped for advantage of solvent solubility anticipated for depolymerized coal may have been lost. 

Investigators Coal Reaction Order Activation Energy (kcal/mole) Frequency Factor (min ) Reference ... 

If the iron- and tin-based catalyst Indeed acts to inhibit radical propagation reactions then two major consequences of this effect can be tested in coal reactions. Firstly, and most importantly, the rate of the thermally Induced breakdown of the coal should be reduced in the initial minutes of the coal reaction. This has recently been demonstrated when iron catalysts were used in a series of short residence time studies ( v l2 minutes to temperature then autoclave quenched). The results, summarized in Table 2, show that the conversion of acid washed coal after rapid heating to 450 C had a conversion of 55% (daf coal) while the conversion of acid washed coal that had been re-exchanged with 240 mmol of iron kg (dry coal) had a conversion of only 46%. A similar trend was found for the reaction of as mined coal (39% conversion) and the same coal that had been treated with a solution of iron(II) acetate (300 mmol kg dry coal) and had a conversion of 33%. It is interesting to note that the natural Inorganics of the as-mlned coal had a very strong inherent activity to slow the rate of thermal decomposition. 

Suppose the oxygen gas fed to the reactor and the oxygen in the coal combine with all the hydrogen in the coal (Reaction 3) and with some of the carbon (Reaction 2), and the remainder of the carbon is consumed in Reaction 1. Taking a basis of 1.00 kg coal fed to the reactor and letting o equal the moles of O2 fed, draw and label a flowchart. Then derive expressions for the molar flow rates of the four outlet gas species in terms of hq. (Partial solution h2 = 51,5 - no.)... 

Smoot, L. D., and P. J. Smith, Modeling pulverized-coal reaction processes, in Pulverized-Coal Combustion and Gasification, L. D. Smoot and D. T. Pratt, eds., Plenum, New York (1979). 

Consumption of alkali metal in the reduction step increases monotonically with time, suggestive of a reagent decomposition reaction. In contrast, the alkali metal consumption in the n-butyllithium-hexane-coal reaction reaches a plateau value of about 4 meq/g of coal. 

Attempts to increase pyrite removal by increasing the reaction time met with limited success under our standard conditions because reaction of the ferric ion with the coal matrix depleted the ferric ion that was needed for extraction of the pyrite. Thus, for example, increasing the coal reaction time from 2 to 12 hrs only increased pyritic sulfur removal from 60 to 80% for Pittsburgh coal. Similar results were obtained for the other three coals. The only alternatives were to increase the amount of leach solution or to use a continuous or semi-continuous (multiple-batch) reactor. A multiple-batch mode was chosen because it was a simple laboratory procedure and at the same time it could approximate conditions encountered in a commercial plant. A 1-hr-per-batch leach time was used because our 2 hr results indicated that in the early stages of removal the rate begins to decrease after 1 hr, and six leaches (or batches) per run were used to assure that any pyrite that could be removed in a reasonable amount of time was removed. The progress of removal was monitored by analyzing the sulfate content in each spent leach solution elemental sulfur was not removed until all the leaches were completed. Table VII shows pyrite extraction as a function of successive leaches as followed by sulfate analysis of the leach solution. Note that the major portion of pyritic sulfur is removed in the first two leaches or 2 hrs, followed by lesser amounts in... 

It is generally known that, in coal, reactions 1 and 2 proceed at a lower temperature, probably because hydrogen from the decomposing coal matrix aids the reaction ... 

In the conversion of coal to gaseous compounds, many reactions are occurring in series and parallel. All the reactions shown in the methane reforming section (Reactions 2.1—2.10) play a role in the gasification process. The important additional coal reactions are shown in Reactions 2.17—2.20. Reaction 2.17 is the partial combustion of coal to form carbon monoxide. Reaction 2.18 is the heterogeneous steam gasification to form carbon monoxide and hydrogen. Reaction 2.19 is the complete oxidation of carbon, while Reaction 2.20 is the methanation of coal. 

Plasmas, which are often produced by exposing a gas stream to an electric arc, are capable of generating tanperatmes in excess of 10,000°C (18,000 F) and can be onployed to study coal reactions, although there is some doubt in regard to the accurate determination of temperatme and residence time. Generally, when coal is heated rapidly to tonperatmes above 1250°C (2280 F), the onitted volatiles are cracked to yield lower hydrocarbons, which, if conditions are favorable, will consist mainly of acetylene. Such conditions involve reaction times of only a few milliseconds coupled with... 

Gasification may be enhanced by the catalytic properties of the melt used. Molten salts, which are generally less corrosive and have lower melting points than molten metals, can strongly catalyze the steam-coal reaction and lead to very high conversion efficiencies. 

On the basis of the thermal chemistry of coal (Chapters 13 and 16), many primary products of coal reactions are high-molecular weight species, often aromatic in nature, that bear some relation to the carbon skeletal of coal. The secondary products (i.e., products formed by decomposition of the primary products) of the thermal decomposition of coal are lower molecular weight species but are less related to the carbon species in the original coal as the secondary reaction conditions become more severe (higher temperatures and/or longer reaction times) (Xu and Tomita, 1987). 

Wall, T Liu, G., Wu, H Roberts, D Benfell, K Gupta, S., Lucas, J and Harris, D. (2002) The effects of pressure on coal reactions during pulverised coal combustion and gasification. Progress in Energy and Combustion Science, 28 (5), 405-433. 

The principal gasification reaction (7.26) is highly endothermic. The heat requirements for this reaction are met by the carefully controlled partial burning of coal (reaction 7.28). 

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