JPH0114274B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to liquid extraction of coal, and more particularly to control of certain aspects of extraction conditions to facilitate separation of undissolved particles from coal extract and increase extraction yield. The technique of dissolving coal in a liquid extractant, usually a coal tar fraction, e.g. a heavy aromatic oil such as anthracene oil or a highly aromatic petroleum fraction, is a well-established technology. . Considerable research has been conducted into this technology in countries with domestic coal reserves, especially since the impending energy gap has become public knowledge. If coal is hydrogenated, there is no great difficulty in achieving a high extraction rate of about 80-90% of coal into oil, but without hydrogenation, such a high yield would be difficult due to repolymerization of the dissolved coal. rate is more difficult to achieve. For the process to be economically viable, it is important to obtain high extraction yields. It is generally desirable to separate the undissolved materials and reduce the ash and sulfur content before further processing of the coal extract. These insoluble materials consist primarily of minerals (ash) and especially certain insoluble carbonaceous substances known as fusain. However, considerable difficulties have been experienced in the separation of this substance, and various methods have been proposed, including perturbation, solubility reduction precipitation, centrifugation, and gravity sedimentation. I believe that the best compromise between the two is overlaw. It has already been disclosed in British Patent No.
It is proposed in the specification of No. 1090556. The viscosity of coal extract or coal extract varies considerably with extraction time. The inventors have
No. 1492739 states that the viscosity of the coal extract is not necessarily the best criterion for determining the extraction time;
The excess cake is constant and the specific resistance is low.
By adjusting the dissolution (digestion) conditions to have
For the first time, we have disclosed that it is possible to improve the situation. This generally has a more important effect on ease of filtration than the viscosity of the coal extract. The inventors have now determined that good control over the entire extraction process is extremely important for rapid filtration. It has now been found that in the case of continuous coal extraction operations, which are invariably employed in large-scale industrial implementation, there are very significant variations in the residence time in the coal extraction reactor (dissolver). . This is illustrated by the attached FIG. 1 which clearly illustrates the residence time distribution for a nominal residence time of 173 minutes. It is important to note that there is a peak of extraction at approximately 60 minutes. FIG. 1 shows the results of a test in which a radioactive tracer was injected into a pilot plant digester charge. It was confirmed that overcake resistance has a strong time dependence; the shorter the residence time, the greater the overcake resistance, and the longer the residence time, the lower the overcake resistance. Ta. Unfortunately, in nonhydrogenative melting (cooking), the reduction in cake resistance occurs at least in part due to polymerization of the dissolved coal component species, and this polymerization reduces yield. This information is illustrated in Table 1 and FIG. Figure 2 shows hydrogenated anthracene oil as a hydrogen donor solvent and Annesley coal in a 1:3 coal:solvent ratio.
Figure 2 shows the effect of dissolution (cooking) time on yield and overcaking resistance when used at a temperature of 430°C. The yields shown in Figure 2 were determined by standard methods of quinoline solubility, and Figure 2 shows that the highest yields are achieved almost instantaneously. During the first few minutes of extraction, all extractable coal material is converted into a gel-like material that retains its insoluble coal and ash content, and this gel-like material is soluble in the quinoline, but is free from any solvent present. Some are theorized to be insoluble. As the extraction proceeds, the gel-like material gradually dissolves and it can be theorized that under normal conditions essentially all of the soluble coal will be dissolved after about 30-60 minutes.
This theory is supported by experimental results showing that the yield of overcake (ie, material not dissolved in the solvent) approaches a nadir at about 60 minutes and shows a fairly smooth downward slope. Such a theory also explains, at least in part, the high overcake resistance of short residence times since gel-like particles can deform under stress applied to the overcake and thus inhibit flow.

Table 1 Referring again to Figure 1, widening the residence time produces a short residence time material with very high cake resistance and a longer residence time material with low cake resistance. Short residence time components with high cake resistance tend to dominate overoperation. This can be demonstrated by comparing the overcaking resistance obtained in the case of coal extracts made from the same coal in similar operations but from different operating systems, namely continuous flow extraction operations and batch extraction operations. It is proven that Batch extract of Beynon coal (400℃, 60
The resistance (residence time in minutes) was 53×10 ¹⁰ mKg ⁻¹ and at 430° C. the resistance decreased to 0.4×10 ¹⁰ mKg ⁻¹ (see Table 1). However, a continuous dissolver for a nominal residence time of 60 minutes
Using the same coal, oil, etc., except at 410°C to 420°C, gave an overcake resistance of 60×10 ¹⁰ mKg under the same flow conditions. High volatile content coal from Ansley Coal Pit (CRC702, volatile content 34%, ash content 3
This difference was even more obvious in another experiment using %). This coal is 20×10 ¹⁰ mKg ^-1 and 90×10 ¹⁰ Kg ^-1 under otherwise identical melting and overconditioning conditions in batch and continuous operations.
gave cake resistance. The inventors have concluded that the spread of residence time is the decisive factor in achieving low overcake resistance and therefore rapid overflow. This spread could be avoided if the reactor used plug flow for extraction, but this is inherently difficult to achieve in the large scale reactors in which industrial coal extraction plants operate. It is. This invention involves dissolving coal in a continuous operation using an aromatic solvent oil under conditions where the solvent oil is liquid, and then separating substantially all the undissolved material from the resulting melt into the solvent. In a process for the continuous production of coal extract by creating a liquid of extracted coal material, the plug with respect to the contact time by using at least two stirred dissolvers arranged in series. Characterized by flowing coal from one melter to another in flow-like conditions, thereby reducing short residence time materials with high overcake resistance and maintaining liquid permeability of the filter cake. The present invention provides a continuous method for producing coal extracts. Preferably from 3 to 10 stirred dissolvers in series are used, more preferably from 4 to 7, especially 5 stirred dissolvers in series. Although it is convenient for the dissolvers to all be of the same size, so that the same conditions are obtained in each dissolver, this does not necessarily have to be the case, and each individual design may be different for some or all of the dissolvers. Sizes and/or conditions may also be used. The use of multiple stirred dissolvers in series gives a flow very similar to the plug flow in a single dissolver. The actual number of dissolvers depends on economics,
In particular, there are transfers to the material being processed and the cost of invested capital. Each melt is increased with respect to the previous dissolver until the extra extraction cost required by increasing the number of dissolvers equals the cost savings in excess, i.e. the excess cost savings is commensurate with the cost of the increased dissolver. It is economically possible to increase the number of dissolvers by considering the number of dissolvers. Dissolver selection and agitation methods are common chemical engineering design matters. For example, it is convenient to theoretically configure multiple melters within one melter enclosure, thereby minimizing the costs associated with maintaining elevated temperatures and pressures. In theory, a turbulent dissolver would produce a plug flow and sufficient mixing, but this is not achieved in practice and agitation is necessary. It is important that sufficient agitation occurs during dissolution. If this is insufficient, the progress will be much slower. This is explained in Table 2 below. In this Table 2, the same dissolver was used and the same dissolution conditions were used without stirring and with stirring.

[Table] Charcoal/Hydrogenated Ant
None 84 42.3
Spiral Oil In the process of this invention, the solvent oil is preferably a coal tar fraction or a highly aromatic petroleum fraction or a hydrogen donor solvent, these classes of solvents being well known in the art. The coal is preferably high-grade or low-grade bituminous coal, but the present invention can also be applied to other coals such as lignite. The dissolution (reaction) conditions are selected within those known in the industry, taking into account overcaking resistance and extraction yield. It is to be understood that the process of this invention can be carried out in the presence or absence of free gaseous hydrogen. Although this invention is not to be limited by any theory presented herein, it is believed that the initial and primary action of the hydrogen is to hydrogenate the solvent oil, which then transfers the hydrogen to the coal material. It is therefore believed that the experiments underlying this invention demonstrate its applicability to both hydro- and non-hydro-extraction of coal. Generally, in the temperature range of 350°C to 450°C, higher temperatures require shorter residence times. To illustrate this invention, the best coking Beynon coal was extracted in anthracene oil at 430°C with a residence time of 20 minutes and passed at 200°C and 138 KNm ^-2 . Using different numbers of identical dissolvers in series and otherwise using the same conditions, the overrate for the number of extractions is expressed as the cumulative flow rate (weight) versus time (minutes) using a logarithmic scale. I plotted (3rd
figure). The numbers attached to the curves in Figure 3 indicate the number of dissolvers. For example, the cumulative flow rate (weight) of the liquid after 10 minutes for each number of dissolvers (simply written as the flow rate after 10 minutes) is as follows. be.

[Table] Significant improvements are made using two dissolvers compared to one dissolver, and additional improvements are
It is observed that with more than 10 dissolvers there is little expectation. In non-hydrogenated systems, the extraction yield depends on the dissolution time;
Longer dissolution times cause polymerization of the dissolved coal, reducing yield. Therefore, increasing the residence time reduces the extraction yield due to the formation of repolymerization products. By using several stirred dissolvers almost plug flow can be achieved, increasing the extraction yield. Extraction yield is of considerable importance to the overall economics of a coal melting operation, and even small improvements are worth the effort. Repolymerization of the coal component is relatively slow when using higher grade coals (of Table 1) or hydrogen donors, and repolymerization of the coal is relatively rapid when lower grade coals are dissolved. Thus, the use of several stirred dissolvers according to the invention has the additional benefit of increasing the extraction yield, especially when using lower grade coals. It therefore follows that a mere increase in the number of melters according to the present invention will result in a significant and unexpected increase in overspeed, and that the overall output of a coal extraction plant can be increased or that the size of the overvessel can be reduced. shown. The additional benefit of increased extraction yield also results from this invention.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between the time from tracer injection and the tracer concentration in the effluent stream in a test in which radioactive tracer was injected into the pilot plant dissolver charge, and Figure 2 is a graph showing the yield and overcake resistance. Fig. 3 is a graph showing the relationship between dissolution time (minutes) and extraction rate [cumulative amount of liquid flowing out (weight)] when the number of extractors is changed. .

Claims (1)

[Claims] 1. Dissolving coal in a continuous operation using an aromatic solvent oil under conditions where the solvent oil is liquid, and then removing substantially all of the undissolved material from the resulting melt. A method for continuously producing a coal extract by separately producing a liquid of extracted coal material in a solvent, comprising at least two
By using several stirred dissolvers,
Flowing coal from one melter to another in a plug flow-like manner with respect to contact time, thereby reducing short residence time materials with high overcake resistance and maintaining liquid permeability of the filter cake. A continuous method for producing a coal extract characterized by: 2. A continuous method for producing a coal extract according to claim 1, using 3 to 10 stirred dissolvers installed in series. 3. Continuous production of coal extract according to claim 2, using from 4 to 7 stirred dissolvers installed in series. 4 Any one of claims 1 to 3 in which the melting is carried out at a temperature within the range of 350°C to 450°C.
Continuous production of coal extracts as described in Section. 5. A continuous method of coal extract according to any one of claims 1 to 4, wherein the solvent oil is a coal tar fraction, a highly aromatic petroleum fraction, or a hydrogen donor solvent oil. Manufacturing method. 6. The continuous method for producing a coal extract according to claim 5, wherein the solvent oil is anthracene oil or hydrogenated anthracene oil.