CS199706B2 - Method of producing liquid fuel from coal available for the pure combustion - Google Patents

Abstract

A liquid fuel is prepd. from coal by (a) pyrolysing coal at low or moderate temp., to form an oil fraction, a carbonisation prod., and a water fraction, and (b) forming a stable suspension by mixing the oil fraction and the carbonisation prod. from stage (a) with water. The fuel burns without a residue (0.5wt.%) and has a low S content ( 0.5%). The fuel is easily pumped and transported in bulk, and can be adapted or use in conventional oil burners. It is stable without the addn. of a stabiliser. The water produced in the pyrolysis is used in the fuel. Ordinary fuel oils may be mixed with the fuel without risk of sepn.

Description

The invention. relates to a process for producing liquid fuel for clean combustion from low sulfur coal.

Coal as a heat source exists in abundance. However, most coal contains a certain amount of sulfur which, when the coal is burned, enters the air as sulfur dioxide, ie an impurity. Since government regulations restricting the amount of sulfur dioxide that can be discharged into the air are restrictive, an expensive process after coal processing for clean combustion has become necessary. A greater barrier to the use of coal as a fuel source is even the way it is burned. In the past, coal has been combusted in a fixed bed and only in recent years have atomized coal particles been injected into the combustion chamber; coal is not easily used in standard industrial oil burners. The usual approach to the previous problem has been broadened by micronized coal fuel oils, but their stability is low and the oil-coal mixture is easily separated.

Related to this is an earlier process that uses a process for treating and burning a water-in-oil mixture containing pulverized coal using sonic energy to stabilize the slurry and adding limestone to minimize the release of sulfur dioxide present in the slurry during combustion. Methods for using special suspension stabilizers are described in the literature. However, the cost of stabilizers is often quite high, and the cost per kilogram of calories of the end product is often equal to or higher than that of conventional liquid fuel oil.

The present invention relates to a process for the production of low sulfur sulfur-containing liquid fuel from coal which allows combustion on a very regular basis with a minimum release of sulfur dioxide and is stable.

The essence of the process for producing liquid fuel for clean combustion from coal, wherein the coal is first subjected to pyrolysis to form an oil fraction, a coke product and an aqueous fraction and further optionally the oil fraction is sulfur-free and mixed with the coke product in micronized form. . It consists in mixing the oil fraction with water in a weight ratio of 3: 0.5 and separately mixing the micronized coke product with water in a weight ratio of 5: 1.5 and combining the two mixtures with each other, and optionally obtaining the fuel mixed with fuel oil.

According to a preferred embodiment of the invention, an aqueous fraction of pyrolysis is used as a water to mix the oil fraction and the coccyte product as water.

The low-sulfur coal-fired fuel produced according to the invention is in the form of a slurry which is sufficiently stable even without the addition of a stabilizer.

According to the present invention, the stability of the slurry, while reducing the cost of fuel production, is promoted by using the aqueous fraction derived from coal pyrolysis instead of water alone.

The low-sulfur liquid coal combustion fuel produced according to the invention, mixed with conventional fuel oils of conventional quality, is free of separation.

Still other features and advantages of the invention will be apparent from the description of the preferred embodiment.

The low sulfur liquid fuel produced by the process of the present invention, produced from coal, is easily pumped and bulk transported and adapted to conventional oil burners.

The low sulfur content liquid fuel produced by the process of the present invention typically has a ash level in the resulting fuel of less than about 0.5 weight percent and a sulfur fuel level of less than 0.5 weight percent as a result of the processing described below. calculated on the carbon present.

The production of a liquid fuel of the low sulfur content of clean combustion is effected from coal which is subjected to an economically acceptable pyrolysis process at low or medium temperature, that is to say at a pyrolysis temperature in the range of about 371 to 815 ° C.

Pyrolytic treatment of coal at low or medium temperature, which is well known in industrial circles, yields four components:.

(1) the liquid oil fraction, (2) the coke product;

3] aqueous 'fraction' a

4] gaseous byproduct.

The liquid oil fraction comprises normal 'paraffinic hydrocarbons,' aromatics, 'polyaromatics and oxo compounds such as phenols, cresols,' organic 'acids and the like. The composition varies with the 'process' as cracking occurs at high temperature. high-boiling components. Liquid oil is' excellent as a fuel ', however, if some' measures' such as' denitrification and desulfurization are taken, using known methods. Oxygen compounds from the oil fraction greatly increase the suspension stability of the resulting fuel of the present invention and thus are highly desirable compounds.

The coke oven product of the pyrolytic process usually contains the largest part of inorganic sulfur from coal, especially in ash. According to the invention, the ash is usually removed by micronization methods and then the ash and sulfur are separated from the coke product by known methods such as flotation, gravity separation or chemical conversion. The remaining coke product consists mainly of carbon, with which only a very small amount of sulfur remains. By these techniques the ash content can be achieved at a level comparable to fuel oils and the sulfur content within the limits set by environmental regulations. The resulting coke product is suitable in the composition of the invention.

The by-product of the pyrolysis process is a liquid aqueous fraction; Its amount greatly depends on the water content of the coal. The liquid aqueous fraction is usually contaminated with volatile components which are to some degree soluble in the aqueous phase. The use of this aqueous phase therefore usually requires cleaning measures, which increases the cost of conventional operations. However, it has been found that this liquid aqueous fraction is suitable according to the invention.

Pyrolysis procedure. It also provides a by-product gaseous product which typically has a high higher molecular weight hydrocarbon content. This gives a 'high kilogram-calorie' gas that serves as an excellent fuel. Certain amounts of organic sulfur from coal usually accompany gas in the form of hydrogen sulphide, sulfur dioxide, carbonyl sulphide, mercaptan and similar compounds which can be 'extracted' by known methods.

The present invention is directed to mixing coal-derived products by pyrolysis, by 'mixing' a desulfurized liquid oil fraction, a micronized coke product from which ashes and sulfur have been removed as much as possible, and water, which may be an aqueous fraction produced by coal pyrolysis. . The 'resulting' mixture is thoroughly 'mixed' with or without a stabilizing additive and forms a stable suspension that can be 'transported by pipeline' or 'in containers and stored, and _; 'forms a' clean combustion 'fuel with a value of 25'588 to' 31,565 J per kilogram, '' depending on 'the composition.

When the coke product. . obtained from the pyrolysis process is micronized and the ash removed by a conventional method, such as, but not limited to, gravity separation, flotation or 'chemical' methods, the resulting coke product mainly being carbon. In addition, when the coke product is micronized to less than about 0.032 cm, the weight of the micronized and suspended coke product in the. compared to the total weight of the 'liquid fuel suspension of the invention'. may 'vary from 0 to' at least '50%. Advantageously, the high carbon content increases the amount of heat per kilogram of production, reducing the leakage of sulfur dioxide and the presence of water in the resulting fuel, reducing the viscosity of the fuel, increasing the possibility of pumping, e.g. In addition, the addition of water to the coke-oil mixture sharply reduces the formation of soot in the furnace of the steam boiler and also allows a leaner air-fuel mixture. Water and emulsions help to explode the droplets

9 9 7 O 6 fuel, so that a better fuel-air mixture is obtained during combustion. Water also reacts with coal and hydrocarbons to form readily combustible carbon monoxide and hydrogen.

The new low and medium temperature pyrolysis process is industrially economical and has properties that make it possible to maximize either gaseous or liquid coal constituents, providing a coke product with a high surface area with a low amount of volatiles. The relative ratio of the components in the fuel mixture can readily vary over a wide range. For example, the water content can easily be reduced to about 1 to 2% by weight of the fuel blends without damaging the fuel quality, and can also be increased to up to 25% by weight without affecting the flame characteristics only when the burner is properly adjusted. In addition, the coke content may be in any range, even more than 50% by weight of the fuel, and it is observed that a higher coke content affects both stability and viscosity.

The coke product from the pyrolysis process forms a stable suspension much more easily than coal by the pyirolytic coke product having a high surface area due to the micropores formed during the pyrolysis process. As a result, the addition of a stabilizer to the fuel is normally not necessary. However, if greater fuel stability is desired, increased suspension stability can be achieved by the addition of organic or inorganic suspension stabilizers, as will be recognized by those skilled in the art.

In a preferred embodiment of the invention, the coal is subjected to any suitable pyrolytic process carried out at low or medium temperature to give a liquid oil fraction, a coke product, an aqueous fraction and a gaseous by-product.

The resulting coke product, the liquid oil fraction and the aqueous fraction thus form components of the final fuel produced. The components may be mixed in any order and in any ratio as long as the fuel can be combusted, but the preferred embodiment consists of using parts by weight of micronized coke product, relatively ash-free and mixed with 1.5 parts by weight of the aqueous fraction, and weight parts of the oil fraction. when the oil is thoroughly mixed with 0.5 parts by weight of water, and then the two mixtures are mixed by pouring the first mixture into a stirred tank containing the second mixture or using a continuous mixing procedure. Depending on the preferred oil fraction and viscosity of the composition, the relationship between the first and second compositions may be varied to meet the end use requirements. For example, if the viscosity is to be changed, conventional fuel oil may be added, in which case the first mixture is preferred,. mixing its part with a mixture of the second and another part, which would otherwise be the second mixture, but in which the fuel oil is replaced by a pyrolytic oil fraction. Then the respective parts are joined. However, it is also possible to mix the fuel oil into the pyrolytic oil fraction and produce a mixed fuel as described above.

If the oil fraction from the pyrolysis process is viscous and contains a considerable amount of tarry substances, preferably the heavy tarry substances are separated by distillation. For example, using a temperature of about 371 ° C as the boiling point of a fraction, the heavy oil fraction is usually solid at room temperature, but is liquid at the boiling point of water. These tars are thoroughly mixed into hot water to obtain an oil-in-water suspension stable at room temperature. The cold slurry is used to make the mixtures mentioned above, with the proviso that the percentage of the components is adjusted to the tar content in the water at the end with respect to the desired composition.

The resulting fuel may be preheated and combusted as fuel oil. If the treatment is properly done, as will be readily appreciated by one skilled in the art, the combustion is smoke-free with a small excess of air, which minimizes the formation of nitrogen oxides in the flue gas.

If desired, the liquid oil fraction is desulfurized by known methods, such as treatment of hydrogen at elevated temperature. The coke product from the pyrolysis process is micronized, preferably to particles smaller than about 0.032 cm, and the ash with sulfur is removed by known methods such as gravity separation, flotation, or chemical methods, to which removal procedures are not limited. When flotation is used, the particle size of the coke product is equal to or less than the particle size of the ash contained in the coal. The flotation method, where the particle size is less than 0.158 cm, is completely unsatisfactory for most types of coal, and as found to be below 0.032 cm for a large amount of material, to be able to separate ash without too much carbon loss. For most coal grades, it is possible to reduce the weight of the coke product to about 0.5 weight percent or less.

The aqueous fraction, which is likely to be contaminated with a small amount of volatile compounds, need not undergo any purification treatment and can be used as a component of the finally produced fuel without further treatment.

Claims (2)

CLAIMS 1. A process for the production of a liquid fuel for clean combustion from coal, wherein the coal is first subjected to pyrolysis to form an oil fraction, coke product and aqueous fraction, and further optionally oil-free sulfur and blending with the coke product in micromised form to form a stable suspension. The mixture is mixed by mixing the oil fraction with water in a weight ratio of 3: 0.5 and separating the micronized coke product with water in a weight ratio of 5: 1.5 and separating the two mixtures with each other and mixing the fuel with fuel oil. . 2. A process according to claim 1, wherein an aqueous fraction of pyirolysis is used to mix the oil fraction and the coke product.