GB2030593A - Gasifying Coal - Google Patents

Abstract

A method of obtaining carbon monoxide and hydrogen gases by adding to crushed coal from which the volatiles have already been removed a catalyst material selected from the group of materials consisting of barium and strontium prior to steam gasification. It has been found that these materials increase the rate of reaction of a coal char substantially.

Description

SPECIFICATION Coal Gasification Method This invention relates to methods of coal gasification, i.e. to the production of carbon monoxide and hydrogen from carbon containing coal.

It is well known that hydrogen and carbon dioxide can be produced by reacting carbon-containing coal with steam under pressure. It is also known to use catalysts in this process. For example an article entitled "Catalysts of Coal Gasification at Elevated Pressure" appearing in a book entitled "Coal Gasification" published by the American Chemical Society, Washington, D.C., in 1974, pp 1 79-202 discusses a number of possible catalysts. In a Table appearing at page 186, barium oxide and strontium oxide are shown as being used as a catalyst, but it is stated that they only slightly improve the gasification rate of coal.

According to the present invention; there is provided a method of coal gasification which comprises reacting steam and crushed coal from which volatile materials have been removed to produce carbon monoxide and hydrogen, the said reaction being carried out in the presence of a catalyst comprising barium or strontium.

In accordance with the preferred method of this invention, carbon monoxide and hydrogen gases are obtained from a carbon containing coal in the following manner. The coal is initially crushed to a size suitable for a coal gasification operation. The volatile materials are removed from the crushed coal thereby to form a crushed coal char. Alternatively, the volatile materials may be removed before crushing the coal. A catalyst material selected from the group of materials consisting of barium and strontium is now added to the crushed coal char. These materials are then subjected to coal gasification operation in which the crushed coal char is subjected to high pressure steam so that the carbon of the crushed coal char reacts therewith to form carbon monoxide and hydrogen.Having either barium or strontium, or both, present during the coal gasification operation, significantly increases the rate of gasification.

Specific embodiments of the invention will now be described, in the following examples.

In order to show the method of this invention, two coals are selected as representative of various coals. A first coal is Pittsburgh Seam coal which upon analysis is 84% carbon and 5.9% ash. A second coal selected is North Dakota coal which has a carbon content of 79% and an ash content of 9.1%. The Pittsburgh Seam coal is a coal of higher rank than the North Dakota coal in that it has more carbon available therein. The coals are crushed to a size suitable for a coal gasification operation. A suitable size is a size in the range from 10 to 500 um.

The volatile materials of the coals are then removed therefrom in a destructive distillation process in which the coals are heated in an inert atmosphere or in vacuum to a temperature in the range of 400 to 9000C. This heating action drives the volatile materials out of the coals leaving therebehind a crushed coal char. Manners of removing volatile material from coal are well known in the art and no further explanation thereof will be undertaken herein. For example, ordinary coking operation to produce coak is a method of driving volatiles from a coal.

In accordance with the teachings of our invention, barium and/or strontium is added to the crushed coal char prior to the coal gasification operation. The barium and/or strontium may be added as oxides, or in other suitable forms, such as nitrates, acetates or hydroxides, preferentially by impregnation from an aqueous solution or slurry. The catalyst should by thoroughly mixed with the crushed coal or coal char so that it is available to carry out its catalytic function. Preferably 3-12 weight percent of the catalyst should be added in order to secure the best effects (based on the total weight of the material).

After the catalyst material has been added to the crushed coal and mixed therewith, the crushed coal char and catalyst are subjected to a coal gasification operation in which the crushed coal char is subjected to high pressure steam. The high pressure steam acts on the carbon of the coal so that the carbon reacts therewith to form carbon monoxide and hydrogen. Having the barium and/or strontium present enhances the rate of gasification, as will be pointed out hereinbelow.

When the catalyst is added, the coal more rapidly converts its carbon to carbon monoxide and hydrogen in the presence of steam than is obtainable when no catalyst is present. The rate of increase is significant, as will be demonstrated subsequently. In order to demonstrate the significant improvement of the rate of gasification, two types of char of widely different intrinsic activity were tested. These chars were derived from a Pittsburgh seam coal and a North Dakota coal. Steam gasification rates of chars derived from these coals were measured as is, and with additions of calcium, strontium and barium. The data on Ca are included in Table 1 for comparison to illustrate clearly that Sr and Ba are much superior compared to Ca, a known gasification catalyst.

The rate of gasification was measured at a pressure of 20 Torr H2O. The listed data include the catalyst loading in atom percent and weight percent, the gasification rate at 8500C, an apparent activation energy describing the temperature dependence of the rate, and a specific surface area measured by the adsorption of CO2 In accordance with the established BET method. The rate of gasification is given in micrograms per square meter per minute. The rate unit will not be used behind each of these numbers, but it will be understood that this is the rate.

As the data in Table 1 show, when tested by itself, char derived from Pittsburgh seam coal had a gasification rate of 1.0, while addition of Sr and Ba increased the rate by orders of magnitude. In comparison, the rates for 0.3 atom percent of Ca, Sr and Ba added to pure graphite (1.0, 2.2 and 3.4 weight percent, respectively) are 3, 38 and 149, respectively. Again, the improvement by Sr and Ba over Ca is considerable. The improvement in gasification can also be expressed in terms of an equivalent temperature at which a catalyzed gasification rate equals that of pure graphite at 85O0C.

Thus, in the case of graphite, temperatures can be lowered to 760, 721 and 6620C upon addition of 0.3 atom percent of Ca, Sr and Ba, respectively, to achieve the same gasification rate measured on pure graphite at 85O0C.

Table 1 Catalysis of Char Gasification by Ca, Sr and Ba Apparent Coal and Rate at Activation Surface Additive Burn-Off 850 OC Energy Area atom % (wt. %J Percent yg/(m2min) kcal/mol m2/g Pittsburgh Seam Coal Asis 0--70 1.0 66-85 370 0.3 Ca (1.0) 0-22 2.5 69 115 9 2.3 68 133 0.9 Ca (3.0) 0-31 4.5 61 234 18 -5.9 61 234 0.9 Sr (6.6) 2-31 32 85 258 18 33 89 270 0.6 Ba (6.8) 0-30 16 70 236 27 16 72 253 0.9 Ba (10.3) 4 82 65 77 31 198 73 90 North Dakota Coal As is 0--40 19 60 545 37 19 62 577 0.9 Sr (6.6) 0-32 36 66 406 34 135 77 458 0.9 Ba (10.3) 16 208 62 355 36 1250 85 363 It is important to note that the catalysts employed here are resistant to sulfur poisoning to a certain degree. This fact is exemplified by the data in Table 2. Thus, carbons containing Ba show in the presence of H2S significantly higher gasification rates than untreated chars. Moreover, the sulfur poisoning is, in part, reversible. When carbon samples which have been partly deactivated by sulfur are subsequently treated in sulfur-free atmosphere, it is found that the catalytic effect of Ba is, in part, recovered. Thus, these rates show considerable improvement over those restarted by H2S, and over the uncatalyzed rates.

Table 2 Effect of 0.4 Torr H2S on the Steam Gasification Rates of Carbons at 8500C With and Without 0.9 atom % (10.3 wt%) Ba Rates Given in g/(m2min) Pittsburgh North Dakota Graphite Seam Char Char Without H2S a) Without Ba 0.25 1.0 19.2 b) With Ba 149 139 1250 With H2S a) Without Ba 0.15 - 9.8 b)WithBa 0.93 18.6 19.3 After H2S Treatment a) Without Ba 0.25 13.2 b) With Ba 67.0 35.0 31.9

Claims (5)

Claims

1. A method of coal gasification which comprises reacting steam and crushed coal from which volatile materials have been removed to produce carbon monoxide and hydrogen, the said reaction being carried out in the presence of a catalyst comprising barium or strontium.

2. A method according to Claim 1 wherein the said crushed coal is prepared for reaction by crushing coal to a size suitable for a coal gasification operation; removing the volatile materials from said crushed coal to form a crushed coal char; and adding the catalyst material to said crushed coal char.

3. A method according to Claim 1 wherein the said crushed coal is prepared for reaction by removing the volatile materials from said coal to form a coal char; crushing said coal char to a size suitable for a coal gasification operation; and adding the catalyst material to said crushed coal char.

4. A method according to any one of Claims 1 to 3 wherein the catalyst material is present in an amount of from 3 to 12% by weight, based on the weight of the material subjected to the reaction with steam.

5. A method of coal gasification substantially as hereinbefore described and as illustrated (other than by way of comparison) in the Examples.