NO116629B - - Google Patents

Description

Process for producing essentially ash-free fuel

with low sulfur content. '

The present invention relates to a method for producing essentially ash-free fuel with a low sulfur content from carbonaceous fuel.

There are known methods for the extraction of carbonaceous fuel, such as bituminous and subbituminous coal, lignite, peat and the like, using solvents under a hydrogen atmosphere. However, due to the poor economics of these processes, they have been limited to the production of highly specialized products such as waxes and other low-volume but high-paying compounds. For various reasons, the economics of these old methods have prevented their use in processing carbonaceous fuel into petrol, diesel oil, lubricating oil, kerosene and other refined solid fuels. The main reason why it has not been possible to commercially use these methods for processing carbon-containing fuel is that the operating costs in these old methods are too high, so that the product cannot compete with cheap types of fuel, such as e.g. residual oil from petroleum. Two of the most important factors that have made the operating costs too high are that it has not been possible to achieve complete dissolution of all potentially present carbonaceous fuel that has been used as starting material for the aforementioned methods, and that it has not been possible to recycle the solvent in the system without special treatment. As a third factor, one can mention that these old methods needed a significant excess of hydrogen.

In contrast to the preceding, the present invention provides a new and economical method which, from naturally occurring carbonaceous fuel, provides fuel with a low content of ash, oxygen and sulphur. This method is cyclical and does not require the supply of solvent after the process has been started.

According to the present invention, a method has thus been provided for the production of substantially ash-free fuel with a low sulfur content from carbonaceous fuel, where a slurry of finely divided carbonaceous fuel is formed in a. aromatic solvent with a boiling point in the range 150 - 750°C, a specific weight of approx. 1.1 and a carbon to hydrogen mole ratio of 1.0:0.9 to 1.0:0.3, at a solvent to solid fuel ratio of 1:1 to 4'-lj°g the slurry is heated to a temperature in the range 370 - 500°C , after which this slurry is kept at said temperature and at an elevated pressure in a discharge zone, the formed discharge is separated from the solid residue, a solvent with a boiling point in the range from 150° to 750°C is recovered from said discharge, and this recovered discharge agent is returned for further treatment of new carbonaceous fuel, characterized by the addition of hydrogen to the slurry fed to the discharge zone, to increase the pressure to at least 35 kg/cm 2 , the slurry is kept in the discharge zone under said hydrogen pressure until the relative viscosity of the discharge rises above 20 and then falls below 10, and in that the solution is then separated from the rest while the relative viscosity of the solution is below 10.

In accordance with the present invention, the above-mentioned advantages are therefore achieved by a significant part of the potentially available fuel fractions in naturally occurring carbonaceous fuel types, such as coal, lignite, peat and the like, being dissolved by using a solvent which is originally produced from the starting material under critical regulated conditions regarding temperature, pressure and atmosphere, together with a very critical operating time, during which the normally insoluble parts of the fuel decompose. This decomposition generally takes place by a depolymerisation of the starting material, into fractions which are soluble in the solvent. By taking into account the critical operating parameters specified in this invention, not only are these naturally occurring types of fuel processed into new fuel with a low content of ash, oxygen and sulphur, but an additional amount of release agent is developed from part of the starting product . More solvent is thus developed than (what is lost purely mechanically in the system.

The drawing illustrates a continuous method of the invention. Here, the starting material is supplied, e.g. Kentucky coal No. 11, which has been painted. by some suitable method it is preferred that the coal is finely ground to approx. 80% passage in a 200 mesh filter, U.S. Standard (0.074 millimeter screen opening)), by means of a conveyor belt or similar, to a tank 1 where it is mixed with a release agent, (made during previous operations) in a ratio of l/l to 4/1 release agent to coal. If it is desirable, the coal release agent suspension in tank 1 can be heated to a suitable temperature, which will drive off any moisture that may be present in the coal.

As the solvent used in the present invention is extracted from the coal that is dissolved, the composition will vary depending on the coal used as starting material. However, a solvent is used in the invention which is highly aromatic, and whose boiling range is from 150° to 750°Cj it will have a specific weight of approx. 1.1, and a carbon to hydrogen molar ratio in the range of 1.0:0.9 to 1.0:0.3. A typical solvent is e.g. a medium oil produced from coal, and with a boiling range of 190° to 300°C. A solvent that has been found particularly useful as a starting solvent is anthracene oil or creosote oil with a boiling range from 220° to /\. 00°C. However, the choice of a special starting release agent is not particularly critical, as fractions from the starting material will be released during operation, which will form significant amounts of release agent. This will mean that you eventually get a larger amount of solvent than you originally started with. Regardless of what the original solvent was, it will thus gradually lose its identity and approach the composition obtained from the solvent formed during the dissolution and depolymerization of the starting material. As a result, the composition of the solvent will be close to that obtained on the washed product, but will have a lower molecular weight, and the relevant composition in each case will be determined by the composition of the particular starting material used. For this reason, the solvent can generally be defined as obtained by previous extraction of carbonaceous fuel in accordance with this invention.

In all cases, the ratio of solvent to coal in the suspension in tank 1 is in the range from l/l to 4A> with a preferred range from l/l to 2.3/1. Ratio between solvent and coal of e.g. O.5/I, gives suspensions that have a tar consistency when the coal is dissolved in the solvent, and this makes it difficult for the solution to move in the system and the whole thing easily stops. If a ratio between solvent and coal greater than 4/l> is used, this has the disadvantage that additional energy and work must be used when the solvent to be recycled in the system is to be separated from the washed coal product. It is therefore obvious that the more solvent you feed into the system, the more you have to recover later, so that the lower the ratio you can use, the better it is. There may, however, be other factors, either economic or purely process-related, which can put this out of consideration, and make it necessary to use a higher ratio between solvent and coal. The viscosity of the different solvent-coal suspensions was measured at 75°c - It should be clear from the following table how advantageous it is to use a ratio between solvent and coal of l/l (ie 50% coal concentration).

As can be seen from the above table, there is a significant increase in the viscosity of the coal/solvent suspension when the coal concentration increases from 50 to 55%. This increase in viscosity means that

greater pressure must be used to feed the suspension through the system,

and furthermore the filtration speed will be greatly reduced.

The suspension that is formed in tank 1 is then lined using a suitable method, e.g. a positive displacement pump 2, to a preheating chamber 3°g then into a dissolution chamber 4> which is heated to keep the suspension at its elevated temperature. It is essential

in accordance with this invention that hydrogen is added to the suspension for preheating chamber 3 or dissolution chamber 4, by a

partial pressure of at least 35 kg/cm . Normally, hydrogen that has been recycled from previous operation will be used at this stage of operation, but it will be. necessary to add additional hydrogen in order to obtain a hydrogen content of at least 70 percent by volume in the gases that are added for the dissolution chamber 4- Although there is no upper critical limit for the hydrogen pressure that can be used, for purely practical reasons it will normally range from 35 to 140 kg/cm 2 , and where one prefers to use 70 kg/cm 2 .

The suspension under hydrogen pressure is heated in the preheating chamber very quickly so that the temperature rises to between 370° and 500°C, and advantageously between 375° and 440°C.

The rudders are dimensioned with regard to diameter and length, so that the suspension current passing through them can be heated to operating temperature as quickly as possible, and experimentally times as low as between 12 and 20 seconds have been achieved. Generally, preheaters will be constructed so that the desired heating rate is achieved at a heat flux that is not greater than 2,712 gram calories/hour/cm of roover surface. In order to achieve good heat transfer, the pipe diameter will normally be chosen so that you will get a turbulent flow of the suspension through the preheater.

The time the suspension stays in the dissolution chamber 4> is

critical for this procedure to be successful. Although the treatment time will vary depending on the particular carbonaceous fuel used, it has been found that the mechanical properties of the solution provide an accurate measure of the suspension's residence time in the dissolution chamber 4* ^ in this respect it has been found that the viscosity of the solution increases with the treatment time in the dissolution chamber 4> after which the viscosity decreases again as the dissolution continues, after which it rises again if the solution is kept for a longer time in the dissolution chamber 4« One of the criteria used to determine when the dissolution process is finished is the relative viscosity of the formed solution. This is the ratio between the viscosity of the solution and the viscosity of the solvent added to the system, and both viscosities are measured at 99°C. Accordingly, the term "relative viscosity" as used herein and in the following claims is limited to and defined as the viscosity at 99°C of the solution formed divided by the viscosity at 99°C of the solvent added to the system, i.e.; Relative viscosity =<L>viscosity of the solution at 99°C ;Viscosity of the solvent at 99°C ;This "relative viscosity" can be used to determine the residence time of the solution in the dissolution chamber 4-By referring to this "relative viscosity", it can it is noted that as the solution progresses, the "relative viscosity" of the solution will first rise to a value of approx. 20, whereby the solution becomes extremely viscous and gel-like. If you use low ratios between solvent and coal, e.g. 0.5/1, then in reality you will get a gel. After the "relative viscosity" has reached a maximum of something above 20, it will begin to decrease to a minimum, after which it rises again to higher values. It has been found critical that the dissolution process should continue until the "relative viscosity" falls ( after first rising) to a value below 10, and that the resulting discharge is separated from the undissolved coal residue so that the "relative viscosity" again rises above 10. Normally, one would allow the "relative viscosity" to drop to less than 5, and advantageously to the range between 1 1/2 and 2. ;It may be noted that as the solution is formed, the starting material will depolymerize in the presence of hydrogen, forming fractions which are soluble in the solvent, and it was observed that while the coal depolymerized during the extraction, then there was a development of hydrogen sulphide, water, carbon dioxide, methane, propane, butane and other higher hydrocarbons which will form part of the atmosphere in the dissolution chamber 4" ;During the depolymerisation of the starting material, hydrogen will be consumed up to a weight equivalent of approx. 2.0$ of the starting material's weight, and under preferred conditions in an amount of 0.5 to 1% of the starting material. When the dissolution process in chamber 4 is finished, the resulting solution is transferred to a filter 5 to separate the coal solution from the undissolved residue (ie mineral compounds). The filter 5 shown in the drawing is a normal rotary pressure filter which is well suited for the discharge of gases and regulation of pressure. Although a rotating filter has been described as being used in connection with this embodiment, this must be understood to mean that other separation devices can also be used, e.g. centrifuges and the like. The gases released from filter 5 are then fed through line 10 to a gas treatment unit 6 in which hydrogen sulphide and carbon dioxide are washed out by a suitable method, e.g. by a solution of caustic soda. The remaining gases can be processed further as desired. The treated gas, which is free of hydrogen sulphide and carbon dioxide, is recycled to the process by feeding new suspension into preheater 3, after it has been supplemented with new hydrogen. Analyzes of the recovered gases show that the total consumption of hydrogen in the system is quite low, and is often no greater than 2$, (based on the weight of the starting material), and often as low as 0.5$. ;The filter cake obtained on filter 5j is taken out for further processing, e.g. to recover more solvent, which will be discussed below. In practice, it would be desirable to process the filter cake, because, in addition to mineral compounds, it can also contain between 40 and 50 percent by weight of solvent, which can be recovered during the distillation. This dried filter cake often contains approx. 50$ of carbon, and when burned, it can give 3900 kg-calories per kg. Further processing of the filter cake is particularly important, as the mineral compounds in the carbon and the absorbed solvent can constitute . from 10 to 20$ of the total amount of suspension supplied to the system. In cases where the filter cake consists of 40 to 50$ of solvent, then the amount of recoverable solvent will constitute between 5 and 15$ of the original amount of solvent that was supplied to the system. If the filter cake is therefore processed for the recovery of the release agent, this can be recycled back into the system for the production of new coal suspension to be fed into the system. The filtrate from filter 5 is then pumped at a temperature of between 270° and 430°C through suitable nozzles into a simple vacuum atomization evaporator 7 to remove the main amount of solvent. In accordance with common practice, the evaporator will be equipped with a device that will remove any liquid that may have entered the vapor, and also suitable heating devices will be placed on the outside of the evaporator to compensate for heat loss. The atomized solvent from evaporator 7 can be fed through a distillation room 8, or it can be recycled directly into the system again. The amount of solvent that is recovered for recycling will usually make up between 85 and 100$ of the amount of solvent that was originally introduced into the system. The recycled release agent can come entirely from the evaporator, or it can be a mixture of release agent from the evaporator and release agent obtained during the preparation of the filter cake. It is to be understood that the recovery of the solvent can be carried out by a wide range of methods, such as e.g. by a film evaporator, and so that other devices can also be used if this is desired. The remaining product from evaporator 7, which is liquid at this point, can be used as such, or it can be pumped onto a continuously rotating steel belt 15, where it cools and solidifies. The hardened product is very brittle and breaks into flakes when it falls from the belt. Other methods can also be used to recover the product, e.g. atomization cooling or the like, or if it is desirable, the product can be kept in a liquid state and used as such. The resulting spurious product recovered from the evaporator 7 is a hydrocarbon material that bears little resemblance to the starting material that was added to the system. As with the filter cake, a significant amount of recoverable solvent remains in the product, and this can amount from 15 to 60$. The composition and properties of the mentioned product appear in the following table, where the corresponding properties and the corresponding composition of Kentucky coal no. 11 are also set up. ; As can be seen from the above analysis, the carbon percentage has increased, while the sulfur and oxygen percentages are significantly lower. ;The melting point of this product is very strongly dependent on the amount of volatile compounds that remain in the product. If e.g. a product with approx. 39$ volatile compounds and a softening point of 180°C had been treated to give 50$ volatile compounds, then its melting point would have dropped to about 130°C. The viscosity-temperature curves for this product are very steep and mean that they can be liquefied as well as atomized in a normal heating system, which usually uses other types of fuel, such as e.g. residual oils. It has been found that by heating the products of the invention to a temperature of between 240° and 350°C, they become sufficiently liquid that they can be used for e.g. fuel. The economy of the invention makes its products competitive with residual oils and other types of fuel for many purposes, such as e.g. application in gas turbines, locomotives and the like. The following examples will describe the nature of the invention in more detail, and in what way it can be used in practice. ;Example 1;Kentucky coal No. 11 of composition as stated above,;was dissolved in a solvent, which had been recovered from previous extraction (in accordance with the present invention) under the following conditions: ;Operating conditions:; ; The charcoal/solvent suspension was heated over the course of 12 to 20 seconds to a reaction temperature of approx. 410°C, and the dissolution was continued until the "relative viscosity" of the solution rose, and then decreased to 3.43. The solution was then filtered at this "relative viscosity," and the filtrate was treated to separate the solvent from the product. The resulting product had the following analysis: ; ; Example 2; Also in this example, Kentucky coal No. 11 was dissolved in a solvent obtained from previous extractions (in accordance with this invention) with the following conditions: Operating conditions: The procedure was the same as in Example 1, but solutions were continued until the "relative viscosity" of the solution rose and then fell to 4*57• The solution was then filtered from the undissolved carbon residue, and then the solvent was separated from the product. A product with the following properties was obtained;

/ U 'l

For the sake of comparison, the properties for the products from examples 1 and 2, as well as the corresponding properties for Kentucky coal no. 11, have been listed below:

To further compare the product from example 1 with the starting coal, 500 gram samples of each were coked in a laboratory retort to a final temperature of approx. 750°C. Data regarding coking of the two samples is set out below.

Claims (5)

1. Method for producing essentially ash-free fuel with a low sulfur content from carbonaceous fuel, where a slurry of a finely divided carbonaceous fuel is formed in an aromatic solvent with a boiling point in the range 150 - 750°C, a specific weight of approx. 1.1 and a carbon to hydrogen mole ratio from 1.0:0.9 to 1.0:0.3, at a solvent to solid fuel ratio of 1:1 to 4;lj° g the slurry is heated to a temperature in the range 370° - 500°C, after which this slurry is kept at said temperature and at an elevated pressure in a discharge zone, the formed discharge is separated from the solid residue, a solvent with a boiling point in the range from 150° to 750°C is recovered from said discharge, and this recovered discharge agent is returned for further treatment of new carbonaceous fuel, characterized in that hydrogen is added to the slurry fed to the discharge zone, to increase the pressure to at least 35 kg/cm 2 , the slurry is kept in the discharge zone under said hydrogen pressure until the relative viscosity of the discharge rises above 20 and then falls below 10, and in that the solution is then separated from the rest while the relative viscosity of the solution is below 10..., 2. The method according to claim 1, characterized in that the solvent with a boiling point between I5O <0> and 750 C after separation of the undissolved residue is recovered from the liquid extract by distillation, and in that a solid fuel is recovered from the the remaining allowance when it cools down. 3- Method according to claim 1 or 2, characterized in that the slurry is kept in said temperature range under said hydrogen pressure until the total solvent, with a boiling point in the range I5O <0> - 750°C, in the slurry is increased by dissolved parts of said fuel to a quantity of at least 130$ of the original amount of solvent introduced into the process, and that at least 90$ of the original amount of solvent introduced into the process is recovered. 4. Method according to any one of claims 1-3" characterized in that the slurry is fed to an extended treatment zone, and that the temperature of the slurry is raised until it is 375° - 440°C as the slurry is fed through said extended zone, hydrogen is added to the slurry before it reaches its maximum temperature, and by which further treatment is carried out. 5. Method according to any one of the claims 1 - 4> characterized in that the slurry, for separation of the undissolved residue, is kept in the solution zone in said temperature range under said hydrogen pressure until the relative viscosity of the solution falls below 4> in particular to 11/2 to 2, after which the solution is separated from the undissolved residue while its relative viscosity is at said value.