Coal digestion

Solvent solubility has been used to separate coal tar pitch [65] into heptane solubles, heptane insolubles but toluene soluble (asphaltenes), and toluene insolubles (preasphaltenes). The same pitch was separated into acetone-soluble, pyridine-soluble, and pyridine-insoluble fractions [66]. The same pitch, a coal digest, and a low-temperature coal tar were similarly fractionated [67,68]. 

British Coal Corp. is developing a gasoline-from-coal process at a faciUty at Point of Ayr (Scotiand). This process involves treatment with Hquid recycle solvents, digestion at 450—500°C, filtration to separate unconverted residues, and separation into two fractions. The lighter fraction is mildly hydrotreated, and the heavier one is hydrocracked (56). 

Phosphoms determination involves the conversion of phosphoms to soluble phosphate by digesting the coal ash with a mixture of sulfuric, nitric, and hydrofluoric acids (18). Phosphate is precipitated as ammonium phosphomolybdate, which may be reduced to give a blue solution that is determined colorimetricaHy or volumetricaHy (D2795) (18). 

A schematic diagram of the liquid solvent extraction process is illustrated in Figure 1. Where the production of liquid hydrocarbons is the main objective an hydrogenated donor process solvent is used, whereas in the production of needle coke this is not necessary and a coal derived high boiling aromatic solvent may be used (e.g. anthracene oil). An essential economic requirement of the process is that a high extraction yield of the coal is obtained and this will depend upon the coal used and the digestion conditions. 

The extraction yield Of the coal was determined from the concentration of residual solids in the digest and the yield of gas. The solids concentration of the digest was determined from the measurement of the solubility of the digest in quinoline. The addition of quinoline does not precipitate the dissolved coal in the digest and thus the yield of quinoline insolubles can be directly equated to the concentration of solids in the digest (12). 

Digestion 400°C, 60 minute residence time Coal Solvent ratio 1 4... 

Figure 5. Influence of digestion time and temperature on extraction yield. Coal = Beynon solvent = anthracene oil coal solvent ratio = 1 4.

Figure 6. Influence of digestion time on the extraction yield and yield of filter cake. Digestion Annesley coal/hydrogenated solvent prepared at 430°C (— —), yield of filter cake (------------------), extraction yield.

Selection of Solvents. The extraction yield of a low rank coal (Annesley) has been determined after digestion using a selection of solvents (Table II). The results show large variations in solvent power and, in particular, the high extraction yields obtained with hydrogen donor solvents. It is important to differentiate between the ability of a solvent to prevent polymerisation of the dissolved coal by hydrogen transfer, and its ability to retain the dissolved coal in solution. For example, Tetralin is frequently quoted as an... 

For example, Beynon and Cwm coals when digested in anthracene oil give extraction yields of 68% and 47% respectively. This variation can be explained by reference to the maceral composition of the coals. Beynon coal contains a lower concentration of inertinite than the Cwm coal (Table V). In experiments where relatively pure samples of petrographic species were digested in anthracene oil, exinite and vitrinite were shown to be highly soluble, whilst in comparison the inertinite was almost completely insoluble. Similar variations in reactivity of macerals have been reported from studies of solubility in pure organic solvents (1(3). 

Digestion conditions 400°C 60 minute residence time Coal solvent ratio 1 3... 

It has been shown that data from this classification is applicable to large scale digesters and can be used with blends of different coals. 

In a new method for determination of sulfur in coal, the samples are oxidised with an aqueous mixture of permanganate and the peroxoacid. During the digestion, a reflux condenser is essential to prevent loss of water, which could lead to explosively violent oxidation. 

Early expectations of very low emissions and relatively high efficiencies have been met in power plants with each type of fuel cell. Fuel flexibility has been demonstrated using natural gas, propane, landfill gas, anaerobic digester gas, military logistic fuels, and coal gas, greatly expanding market opportunities. Transportation markets worldwide have shown remarkable interest in fuel cells nearly every major vehicle manufacturer in the U.S., Europe, and the Far East is supporting development. 

One of the aims of the work carried out in this laboratory was to investigate the deposition of trace elements on the hydrocracking catalyst. To this end, a continuous laboratory hydrocracker was installed and, to provide feed material for this, a 2-1 autoclave and pressure filter were also installed. It was noticed on the initial runs with the autoclave that the ash level of the filtered extract solution was considerably lower, at 100-200 ppm, than that normally obtained by British Coal, at 500-600 ppm. The reason for this difference was not known, so an investigation was carried out which found that the lower ash levels could be produced by a higher digestion pressure. Table 1 shows some of the results obtained, which have b n previously published (10). Note that throughout all the experiments described in this paper the coals used were Point of Ayr and Calverton, whose analyses are given in Table 2, and that the HAO to coal ratio us was always 2 1. Hence, ash analyses in the coal extract solution are comparable. 

Table 1 shows that as the digestion pressure is increased the extract ash decreases. With Calverton coal the decrease in ash level is less marked, but these results coincide with the use of the second batch of HAO. Point of Ayr coal also shows an increase in ash level with the second batch of HAO. However, by reducing the filtration temperature a low ash level is again observed. Many other similar experiments have been carried out (10.14) using different coals and further combinations of digestion pressure and filtration temperature, and the effect is always confirmed with the requirement that digestion pressure be above about 30 bar. ( timisation is achieved by reducing the filtration temperature where different HAO and coal combinations are us. ... 

In another series of e q>eriments in this laboratory (U), it was found that the particle size of the coal fraction used affected the ash level in the filtered coal extract solution. In these e q>eriments, the coal sample, which is nominally < 200 pm, was divided into different size fractions by sieving, and each fraction digested using the normal procedure. Table 3 shows the results obtained with Point of Ayr and Calverton coals. Note that the Point of Ayr coal was a different batch to that used for the results described previously, with a simil analysis except for ash, which was higher at 19 %. 

The results in Table 5 show a large increase in proportion of Mn and Ti, and increases for Mg and Ca from coal to extract. Fe stays about the same and all the others decrease. Previous work Q) has also shown that the elements which increase in proportion also deposit readily and steadily on the hydrocracking catalyst. Thus, any method which reduces the ash level in the filtered extract solution needs to be, if at all posible, selective towards Mn, Ti, Ca, Mg, and Fe. In the case of digestion pressure, as shown by the results above, most trace elements do not significantly change their proportion as the ash level decreases, except for Mn where the situation becomes worse and Mg where there is some improvement. Liquefaction of different-sized coal fractions has little effect on the distribution of elements in the ash as the overall ash level decreases. However, with the use of HAO with different saturates levels, there is a distinct increase in the levels of Ti with decreasing ash level, but a significant decrease in Mn. 

Several options have been outlined for the reduction of mineral matter to low levels in filtered extract solution. These are mainly applicable to the British Coal process, but have implications for other 2-stage processes. By running the digestion at a pressure above about 30 bar and reducing the filtration temperature as required, low levels of trace elements have been obtained with a series of different coals and HAO solvents. Discarding the fine fraction of the coal from the feed to the digestor will also result in lower levels of trace elements in the extract solution, as will increasing the saturates content of the HAO. However, in the latter case this may also lead to reduced overall conversion. 

You break vials, and consume coals, only to soften your brains still more with the vapours. You also digest alum, salt, orpiment, and altrament you melt metals, build small and large furnaces, and use many vessels nevertheless I am sick of your folly, and you suffocate me with your sulphurous smoke. You would do better to mind your own business, than to dissolve and distil so many absurd substances, and then to pass them through alembics, cucurbits, stills, and pelicans."... 

Anaerobic digestion to methane, on-site combustion, mixing with coal to form solid fuel Direct combustion, can utilize carbon dioxide from industrial flue gas, can grow in municipal waste facilities... 

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