CN1296465C

CN1296465C - Method for treating carbonaceous materials

Info

Publication number: CN1296465C
Application number: CNB038088428A
Authority: CN
Inventors: R·劳埃德
Original assignee: Karalee Research Pty Ltd
Current assignee: Karalee Research Pty Ltd
Priority date: 2002-03-05
Filing date: 2003-03-05
Publication date: 2007-01-24
Anticipated expiration: 2023-03-05
Also published as: EA200401152A1; NO20043674L; WO2003074639A1; AUPS091102A0; CO5611206A2; MXPA04008579A; ZA200407112B; AU2009202202A1; BR0308198A; NZ535220A; AU2003205451A1; PL372337A1; PL205213B1; CN1646669A; UA77769C2; KR20040106285A; EP1483360A4; IL163835A; JP2005519017A; EP1483360A1

Abstract

Process for reducing the amount of sulfur-containing impurities in carbonaceous materials are described. One process comprises contacting the materials with an aqueous solution of hydrofluorosilicic acid in the absence of hydrogen fluoride under conditions wherein at least some of the sulfur-containing impurities react with the hydrofluorosilicic acid to form reaction products and separating the reaction products from the carbonaceous materials. Another process comprises contacting the materials with an aqueous solution of hydrofluorosilicic acid in the absence of hydrogen fluoride under conditions wherein at least some of the sulfur-containing impurities react with the hydrofluorosilicic acid to form reaction products, separating the reaction products and the hydrofluorosilicic acid from the carbonaceous materials and subsequently treating the carbonaceous materials with a fluorine acid solution which comprises an aqueous solution of hydrofluorosilicic acid and hydrogen fluoride. A further process comprises treating the carbonaceous materials with a fluorine acid solution which comprises an aqueous solution of hydrofluorosilicic acid and hydrogen fluoride, separating the carbonaceous materials from the aqueous solution of hydrofluorosilicic acid and hydrogen fluoride, and then contacting the carbonaceous materials with an organic solvent capable of dissolving elemental sulfur.

Description

Method for treating carbonaceous material

Technical Field

The present invention relates to a process for treating carbonaceous material to remove or significantly reduce the amount of non-carbon impurities therein

Background

Us patent 4780112 describes a method of treating carbon to reduce ash therein. The process comprises the use of hydrofluorosilicic acid (H)₂SiF₆) And hydrofluoric acid (HF) aqueous solution, thereby converting metal oxides in the carbon to metal fluorides and/or metal fluorosilicates, which are then separated from the carbon. While the process described in us 4780112 provides effective removal of metal oxides from carbon, the inventors have surprisingly found that when carbon including sulphur-containing impurities is treated by the process of us 4780112,the purified carbon still has sulphur impurities, and the inventors have surprisingly found that residual sulphur is present as elemental sulphur, which is visible in some cases when the carbon is observed under a microscope.

The presence of sulfur in carbon to be used as fuel is undesirable because the combustion of carbon will result in the conversion of sulfur to sulfur oxides. Thus, if release of sulfur oxides into the environment is to be avoided, the exhaust gases from carbon combustion are scrubbed or otherwise substantially removed before being released to the atmosphere.

Accordingly, there is a need for an improved process for treating carbonaceous materials to reduce the amount of non-carbon impurities therein, and in particular for an improved process which removes or at least significantly reduces the amount of sulfur in the carbonaceous material.

The present inventors have surprisingly found that significant reduction in the amount of sulfur-containing impurities in carbonaceous materials can be achieved by a process comprising treating the carbonaceous material with hydrofluorosilicic acid or an organic solvent capable of dissolving elemental sulfur.

Summary of The Invention

According to a first aspect of the present invention there is provided a process for significantly reducing the amount of sulfur-containing impurities in carbonaceous material comprising (a) contacting the carbonaceous material with an aqueous solution of hydrofluorosilicic acid in the absence of hydrogen fluoride to enable at least some of the sulfur-containing impurities to react with the hydrofluorosilicic acid to form reaction products, and (b) separating the reaction products from the contacted carbonaceous material.

According to a second aspectof the present invention there is provided a process for substantially reducing the amount of sulfur-containing impurities in carbonaceous material comprising

(a) Contacting the carbonaceous material with an aqueous solution of hydrofluorosilicic acid in the absence of hydrogen fluoride to react at least some of the sulfur-containing impurities with the hydrofluorosilicic acid to form reaction products;

(b) separating the reaction product and hydrofluorosilicic acid from the contacted carbonaceous material, and thereafter

(c) The separated carbonaceous material is treated with a fluorine acid solution comprising hydrofluorosilicic acid and an aqueous hydrogen fluoride solution.

According to a third aspect of the present invention there is provided a process for significantly reducing the amount of sulfur-containing impurities in carbonaceous material comprising treating carbonaceous material with a solution of hydrofluoric acid comprising hydrofluorosilicic acid and aqueous hydrogen fluoride, separating the hydrofluorosilicic acid and aqueous hydrogen fluoride from the treated carbonaceous material, and contacting the separated carbonaceous material with an organic solvent capable of dissolving elemental sulfur.

The term "carbonaceous material" as used herein is understood to mean a material consisting essentially of elemental carbon. Examples of carbonaceous materials include lignite, coke, brown coal, anthracite, charcoal, carbon dioxide, and the like.

As used herein, unless the context clearly dictates otherwise, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Detailed Description

In the first and second aspects of the invention, the concentration of hydrofluorosilicic acid in the step of contacting the material with an aqueous solution of hydrofluorosilicic acid under conditions such that at least some of the sulfur-containing impurities react with the hydrofluorosilicic acid to form reaction products is in the range of 27% to 37% (w/v or w/w or v/w). The concentration of hydrofluorosilicic acid in the step of contacting the material with an aqueous solution of hydrofluorosilicic acid under conditions such that at least some of the sulfur-containing impurities react with the hydrofluorosilicic acid to form reaction products is generally in the range of 28% to 36%, more typically about 32% (w/v or w/w or v/w). The process is typically carried out at atmospheric pressure, but the pressure may also be above or below atmospheric pressure. The temperature may be in the range of 28-75 ℃. The temperature is generally in the range of 30-70 deg.C, more usually 30-40 deg.C. The reaction time may be in the range of 8-120 minutes. The reaction time is generally from 10 to 100 minutes, more usually from 15 to 30 minutes, and most usually from 12 to 16 minutes. The minimum amount of aqueous hydrofluorosilicic acid used is generally sufficient to allow the mixture with the carbonaceous material to be stirred in the acid. The carbonaceous material is typically mixed with at least twice its weight of aqueous hydrofluorosilicic acid. The aqueous hydrofluorosilicic acid solution is more typically present in an amount of about 70 to 90% by weight of the total weight of the mixture, and more typically about 70 to 80% by weight of the total weight of the mixture.

In step (a) of the process of the first and second embodiments of the invention, a number of metal oxides and some metals present in the carbonaceous material are at least partially converted to the corresponding metal fluorosilicates, with the additional product being water. Examples of metals or metal oxides that are converted to their fluorosilicates are nickel, aluminum, calcium, and mercury and their oxides. The sulfur compounds present are converted to sulfur dioxide and/or sulfur tetrafluoride under the reaction conditions.

After step (a) of the process of the first and second embodiments of the present invention, the relatively pure carbonaceous material is still mixed with the aqueous solution containing the dissolved metal fluorosilicate. The mixture of carbonaceous material and metal fluorosilicate may be suitably filtered or centrifuged to separate the relatively pure carbonaceous material. The relatively pure carbonaceous material after filtration is optionally further treated with an aqueous solution of hydrofluorosilicic acid, typically at a concentration of 32% by weight, to wash out any residual metal fluorosilicates. The remaining carbonaceous material is separated from the aqueous phase and optionally washed to provide a semi-purified carbonaceous material having a lower sulfur and metal content than the starting material. The main impurities present in the semi-purified carbonaceous material at this stage are typically silica and iron sulfide.

The semi-purified carbonaceous material may be further purified to remove other impurities not removed in step (a). The method of the second aspect of the invention thus provides such a process. In the process of the second embodiment, step (c) is generally a process according to U.S. patent 4780112, the disclosure of which is incorporated herein by reference. Similarly, the third embodiment of the process wherein the step of treating the carbonaceous material with a solution of hydrofluoric acid comprising an aqueous solution of hydrofluorosilicic acid and hydrogen fluoride and separating the carbonaceous material from the aqueous solution of hydrofluorosilicic acid and hydrogen fluoride may be a process as described in U.S. patent 4780112.

In step (c) of the method of the second embodiment and the method of the third embodiment, the hydrofluoric acid solution has a composition within the following range: 4% w/w H₂SiF₆、92％w/w H₂O, 4% w/w HF to 35% w/w H₂SiF₆、30％w/w H₂O, 35% w/w HF. In the method of the second embodiment, step (c), and the method of the third embodiment, the hydrofluoric acid solution generally has a composition within the following range: 5% w/w H₂SiF₆、90％w/w H₂O, 5% w/w HF to 34% w/w H₂SiF₆、32％w/w H₂O, 34% w/w HF. The composition of the fluoric acid solution is more typically about 25% w/w H₂SiF₆、50％w/w H₂O, 25% w/w HF. This step can be conveniently carried out in two stages, as described in us patent 4780112. That is, the first stage is suitably carried out in a stirred reactor at a pressure of about 100KPa and a temperature of 40-60 deg.C, and the second stage is suitably carried out in a tubular reactor at a pressure in the range of about 340 KPa and 480KPa and a temperature of 65-80 deg.C,More typically at a temperature of about 70 c. Generally, the temperature is maintained at this value by the heat evolved by the reaction of the silicon oxide in the carbonaceous material with hydrogen fluoride. In step (b)The minimum amount of hydrofluoric acid solution used in step (c) is generally sufficient to allow agitation of the mixture with the carbonaceous material. The carbonaceous material is typically mixed with at least twice its weight in the hydrofluoric acid solution. More typically, the hydrofluoric acid solution is present in an amount of about 70 to about 90 weight percent based on the total weight of the mixture, and more typically about 70 to about 80 weight percent based on the total weight of the mixture.

In step (c) of the process of the second embodiment of thepresent invention and in the process of the third embodiment, after the carbonaceous material is mixed with the aqueous solution of hydrofluorosilicic acid and hydrogen fluoride, the mixture of carbonaceous material and aqueous solution of hydrofluoric acid is suitably ultrasonically agitated as described in U.S. Pat. No. 4780112 to effect any unreacted ferrous sulfide (for HF and SiF)₄Relatively inert) or other denser impurities can be separated from the relatively pure body of carbonaceous material (which is less dense than ferrous sulfide) and the aqueous phase. The purified carbonaceous material may be separated from the aqueous phase, optionally with H₂SiF₆The aqueous solution is washed, separated, dried to remove excess water (about 100-₄Gas and water.

The aqueous solution of fluorine acid separated from the carbonaceous material after contacting the carbonaceous material has SiF therein as compared with the aqueous solution of fluorine acid before contacting the carbonaceous material₄The amount is relatively high and the amount of HF is small, as a result of the following reaction:

if this waste water phase is recycled to the step of contacting with the relatively pure carbonaceous material, it tends to reach SiF₄At the saturation point of (c), at which further reaction produces more SiF₄Will be released in gaseous form. The reactor for contacting the hydrofluoric acid solution with the relatively pure carbonaceous material comprises a reactor capable of reacting SiF₄And (4) a removal device. The waste water from this step is suitably sent to a treatment vessel to allow any excess SiF₄Thereby being discharged. By mixing HF and SiF₄Is fed into a vessel, whereby HF is absorbed and SiF₄To increase the HF concentration in the waste water phase. Exhausted SiF₄Suitably fed to a hydrolysis unit and treated with water to produce H according to the following reaction scheme₂SiF₆And SiO₂：

SiO thus produced₂May be separated from the acid by filtration or any convenient means. The acids formed in this way are suitable for use in step (a) of the processes of the first and second embodiments.

The aqueous streams of hydrofluorosilicic acid, with or without hydrofluoric acid, produced in the various process steps associated with the process of the present invention are preferably sent to an acid still where the streams are combined and distilled. Distilling off water, HF and SiF from the distiller₄More volatile than an azeotropic mixture of 32% w/w aqueous hydrofluorosilicic acid. Water, HF and SiF can be mixed₄Is sent to a dehydration system to remove water, and then the obtained dehydrated HF and SiF₄The gaseous mixture is fed to a reactor containing SiF₄Saturated H₂SiF₆The treatment vessel of the solution separates them.

Water, HF and SiF₄The step of dehydrating the gaseous mixture suitably comprises reacting the gas with a sufficient amount of an anhydrous metal fluoride, such as AlF₃Contacting to absorb all of the water present. Other metal fluorides that may be used include zinc fluoride and ferrous fluoride. In this manner, a substantially anhydrous gas is obtained along with hydrated metal fluorides, which can be separated from the anhydrous gas and heated to regenerate the substantially anhydrous metal fluorides for recycling to the dehydration step.

In one form of the process of the first and second embodiments, the reaction product separated from the carbonaceous material in step (b) is formed from sulfur dioxide and dissolved or suspended H₂SiF₆Metal fluorosilicate of aqueous solution. Gaseous HCl derived from inorganic or organic chlorides in the carbonaceous material may also be present. Suitably, the reaction products are fed to a still where they are heated to release themGaseous HF, SiF₄Water vapor, HCl and sulfur dioxide and concentrates any metal fluorosilicates present to their solubility limit and separates as solids, which are removed from the still for further disposal or regeneration. The gaseous mixture leaving the still is suitably subjected to a dehydration treatment by contacting with anhydrous aluminium fluoride as described above, followed by removal of sulphur dioxide and HCl through an activated carbon filter. The remaining dry and sulfur dioxide free HF and SiF₄To a vessel for treatment of the waste water phase from step (c) of the second scheme process.

In the method of the third aspect, the process further comprises, after the separating step:

washing the carbonaceous material to remove any residual acid; and

the carbonaceous material is optionally dried prior to contacting.

Washing may be performed with water. The drying step may be carried out at a temperature in the range of 100 ℃ to 120 ℃, typically at a temperature of 110 ℃.

In the method of the third embodiment, the organic solvent capable of dissolving elemental sulfur is typically ethanol, benzene, carbon disulfide, diethyl ether or carbon tetrachloride, or a mixture of two or more of these or other suitable solvents for dissolving elemental sulfur. The solvent is typically ethanol. The step of contacting the carbonaceous material with the organic solvent is generally carried out at room temperature and atmospheric pressure, but it is also possible to employ conditions of elevated temperature (e.g., in the range of 30 to 90 ℃) or elevated pressure (e.g., 1.01 to 5atm or 1.2 to 2.5atm), or both. The amount of solvent used is not critical, but the minimum amount actually employed should be an amount sufficient to allow the mixture to be stirred or agitated.

In the process of the third embodiment, the organic solvent is contacted with the carbonaceous material for a time sufficient to dissolve at least a portion of the elemental sulphur present therein after the step of treating the carbonaceous material with the hydrofluoric acid solution. Thereafter, the solvent is suitably separated from the carbonaceous material and treated by distillation for recycling as much as possible. The treated carbonaceous material may also be treated to remove any residual solvent, which may be omitted if the solvent does not include halogen or sulfur atoms. The solvent may be removed by any convenient means such as by blowing or heating (e.g. at a temperature in the range 30-100 ℃, the temperature selected depending on the solvent).

The separation step in the present embodiment may comprise filtration, centrifugation or other suitable separation means.

The process of the present invention provides several advantages over prior processes. In addition to providing a carbonaceous material having a significantly reduced sulfur content as compared to the treated carbonaceous material obtained by the process of U.S. patent 4780112, the process of the present invention is capable of removing or partially removing other undesirable materials such as silica, metal oxides and metal sulfides, metal and inorganic chlorides such as mercury and radioactive elements from the carbonaceous material. For example, if the coal contains about 8 wt% sulfur, the sulfur can be removed to a lower level (e.g., about or less than 2 wt% or about or less than 1 wt% or about or less than 0.5 wt%) by subjecting the coal to one (or more) cycles of the first through third embodiment processes. In particular, the method of the second scheme is more effective in removing inorganic chlorides, mercury and radioactive elements than the method of the U.S. patent 4780112. Furthermore, the process of the present invention can reduce the content of bound oxygen in the carbonaceous material, and when applied to coal, can generally increase its calorific value by 3-4%.

In the first to third aspects, the carbonaceous material may be broken up prior to the treatment step into a particulate form having a particle size of about 4, 3, 2, 1.75, 1.5, 1.25, 1 or 0.75 mm. For example, at least about 80%, 85%, 90% or 95% by weight of the particles are in the range of 5-0.25mm, 4-0.25mm, 3-0.25mm, 2-0.25mm or 1-0.25 mm. Or the carbonaceous material is processed as a feedstock. If the carbonaceous material contains excess moisture, it may be dried (e.g., at 60-120 deg.C or 100-120 deg.C) prior to processing to remove excess moisture. The drying process may be continued, for example, so that the moisture content within the carbonaceous material is in the range of 3-8% w/w, more typically 3-5% w/w. Some coals such as lignite, which have a high water content, typically must be pre-dried prior to processing. Prior to treatment, the carbonaceous material may be air dried (e.g., at 60-120 deg.C or 100-120 deg.C), for example, by passing hot air through the carbonaceous material. The temperature of the hot air used to dry the carbonaceous material is below a temperature that causes combustion of the carbonaceous material.

Brief description of the drawings

FIG. 1 is a schematic block diagram of a carbonaceous material purification and combustion system incorporating the process according to the present invention.

FIG. 2 is a schematic block diagram of a still and associated equipment for treating the aqueous solution or suspension produced in step (a) of the process of the first or second embodiment of the present invention.

FIG. 3 is a schematic block diagram of a system for treating carbonaceous material with a solvent to remove elemental sulfur as part of a process according to a third aspect of the invention.

Best method for carrying out the invention

Fig. 1 illustrates, in block schematic form, a carbonaceous material purification and combustion system 10 incorporating the method of the present invention.

Referring to fig. 1, the system 10 includes a hopper 20 containing impure carbonaceous material that has been broken into particulate form, preferably substantially round particles, and preferably having a particle size of less than 2 mm. Connected to hopper 20 is a feed unit 25 for conveying carbonaceous material from hopper 20 to purification reactor 30.

Purification reactor 30 is positioned to receive carbonaceous material from feed unit 25. The purification reactor 30 is also equipped with a line 24 for about 32% w/w H from the hydrolysis column 32₂SiF₆The aqueous solution is admitted. Purification reactor 30 may be a flow reactor or a stirred or rotating reactor. The purification reactor 30 is typically a rotary drum reactor. The reactor is also provided with a line 26 for introducing carbonaceous material and H₂SiF₆After the aqueous solution has been in contact for a suitable time, it is used to transfer the contents of the reactor 30 to the filter 50. Filter 50 is suitably a belt filter and is equipped with a line 51 for carrying separated liquid away from filter 50 and a conveyor 52 for conveying separated solids from filter 50 to a silica removal reactor 55. Reactor 55 is equipped with a line for feeding HF and H from HF absorber 54₂SiF₆A line 58 for feeding the aqueous solution of hydrofluoric acid and a vent line 59 communicating with the hydrolysis column 32.

The bottom discharge line of reactor 55 is connected via pump 56 and line 57 to a two-stage tubular reactor 65A, 65B, the first stage 65A being capable of being agitated ultrasonically. The end of the reactor 65B flows into the separator 16, and the separator 16 is provided with

discharge lines

66 and 67 near the upper and lower portions, respectively. The upper discharge line 66 is connected to a centrifuge or belt filter 70 that separates the solid carbonaceous material from the aqueous solution. The liquid discharge side of the centrifuge or belt filter 70 is fitted with line 69 leading to HF absorber 54, and the solids discharge side of the centrifuge or belt filter 70 is fed to a mixer and separator system for scrubbing.

The mixer/separator system is made up of three mixing

tanks

71, 73 and 75 and three separators such as centrifuges or belt filters 72, 74 and 76 arranged to enable carbonaceous material to flow in sequence from mixing tank 71 to separator 72, then to mixing tank 73 followed by separator 74, then mixing tank 75 and separator 76. The system is arranged so that the aqueous phase is substantially countercurrent to the solids flow.

The solids outlet of the last separator 76 is connected to a drying system consisting of a mixer 77, a tubular reactor 78 and a solids separator 79. The liquid outlet line of the mixer/separator system is from separator 72 and is coupled to still 80. Separator 79 has a vapor outlet also associated with still 80, still 80 being equipped with a jacketed heater, vapor outlet 81 and a bottom outlet leadingto solids separator 98.

Optionally, a solvent extraction system, as described below with reference to fig. 3, is installed between the solids discharge line of separator 76 and mixer 77, as shown in phantom in fig. 1.

The vapor outlet 81 of the still 80 is connected via a forced draft fan 82 and a mixer 83 to a dehydration reactor 84. The mixer 83 is also provided with a line (not shown) for admitting hot gases. Downstream of the dehydration reactor 84 is a separator 86, the anhydrous gas discharge line 87 of which is connected to the HF absorption column 54. Separator 86 is also connected to a solids transfer line 88, which communicates with a fluoride dryer 89. The fluoride dryer 89 is provided with

water removal lines

91a, 91b and a fluoride supply line 90 for conveying substantially anhydrous metal fluoride from the dryer 89 to the mixer 83.

When the system 10 is in operation, carbonaceous material from the hopper 20 is transported into the reactor 30 via the feed unit 25. The transport of the carbonaceous material through the feed unit 25 is suitably accomplished by a system of multiple disks within a tube or pipe, the disks being about the inner diameter of the tube or pipe, and they beingConnected by a cable so that it can be withdrawn from the pipe or tube. A suitable system is sold under the name "Flveyer" by GPM Australia Pty Ltd of Leichardt, N.Lance. The transport of the carbonaceous material may be continuous or batch-wise. The reactor 30 is also supplied with H from the hydrolysis column 32 via line 24₂SiF₆An aqueous solution. Reactor 30 is typically at a temperature of about 30 c and atmospheric pressure.

Carbonaceous material and H₂SiF₆The aqueous solution is contacted in the reactor 30 for a time sufficient to react and dissolve at least some of any sulfur-containing impurities in the carbonaceousmaterial. The flow reactor can achieve this by controlling the flow rate of the reactant aqueous solution so that it has sufficient residence time in the reactor 30. Alternatively, the process may be carried out in a batch mode, with sufficient residence time for each batch of reaction. Suitable reaction times are generally from 10 to 100 minutes, more typically from 15 to 30 minutes, even more typically from 12 to 16 minutes.

The aqueous acid solution and carbonaceous material from reactor 30 are transferred via line 26 to filter 50 wherein the aqueous phase containing aqueous hydrofluorosilicic acid and dissolved metal fluorosilicates and the like is separated from the semi-purified carbonaceous material. The aqueous phase is fed via line 51 to distillation column 110 (not shown in FIG. 1) where the metal fluorides are separated as described in more detail below with reference to FIG. 2.

The semi-purified carbonaceous material is transferred by conveyor 52 to reactor 55 where it is mixed with an aqueous solution of hydrofluoric acid comprising hydrofluorosilicic acid and an aqueous solution of hydrofluoric acid, and the semi-purified carbonaceous material from reactor 30 is allowed to continue to contact the aqueous solution of hydrofluoric acid for a sufficient time to dissolve at least a portion of any silica in the semi-purified carbonaceous material. Reactor 55 is typically maintained at a pressure in the range of about 100kPa to 135kPa and a temperature of about 70 ℃. The residence time of the carbonaceous material within reactor 55 is generally from 10 to 20 minutes, more typically about 15 minutes.

The mixture of carbonaceous material and aqueous hydrofluoric acid solution exiting reactor 55 is pumped by pump 56 to first stage tubular reactor 65A and thence to second stage 65B. The temperature of the tubular reactors 65A and 65B is generally about 70 ℃ and the pressure is generally from 350 to 500 kPa. In the first stage reactor 65A, the suspension of carbonaceous material in aqueous acid is agitated sufficiently to enable any FeS and other denser species present to be separated off at the separator 16 at the end of the second stage reactor 65B. In the second-stage tubular reactor 65B, the mixture was not subjected to ultrasonic agitation. A slurry of solids rich in FeS is removed from the lower portion of separator 16 via line 67. A slurry of carbonaceous material and aqueous hydrofluorosilicic acid is removed from the upper portion of separator 16 via line 66 and passed to a centrifuge or belt filter 70 where aqueous acid is removed and the remaining carbonaceous material is passed to a scrubber/separator system.

In this system, the carbonaceous material is washed with an aqueous solution of hydrofluorosilicic acid flowing through the system countercurrent to the carbonaceous material. A fresh supply of aqueous hydrofluorosilicic acid is supplied from hydrolysis column 32 to mixing tank 75 where it is mixed with carbonaceous material and separated in separator 76. The aqueous phase is passed from separator 76 to mixing tank 73 where it is mixed with carbonaceous material entering the mixing tank and separated in separator 74. The aqueous phase separated by separator 74 is sent to a mixing tank 71 where it is mixed with carbonaceous material from a centrifuge or belt filter 70. The solids and liquids in the mixing tank 71 are separated in a separator 72, the solids are sent to a mixing tank 73, and the liquids are sent to a still 80. Thus, the solids leaving separator 76 are washed solids and the liquid leaving separator 72 is less pure.

The carbonaceous material leaving the last separator 76 of the series of vessels may enter (optionally via a solvent extraction system) a drying system consisting of a mixer 77 and a steel tube reactor 78. The carbonaceous material entering the mixer 77 is mixed with oxygen-depleted fuel gas and fed into a reactor 78 for calcination in an inert atmosphere, typically at about 310 c, to remove residual hydrofluorosilicic acid from the surface of the carbonaceous material. Hydrofluorosilicic acid is removed as gaseous hydrogen fluoride and silicon tetrafluoride along with vapor and after separation of the gas from the dry solids in separator 79, the gas is sent to still 80. The dried solids exiting separator 79 are purified carbonaceous materials suitable for use as fuel. The system 10 further includes a carbonaceous material storage vessel 93 from which dried carbonaceous material can be fed to a furnace and gas turbine system 95. Optionally, system 10 includes a solvent extraction section, described below with reference to FIG. 3, between separator 79 and vessel 93, as shown in phantom in FIG. 1.

The aqueous phase removed from the centrifuge or belt filter 70 is passed through an HF absorber column 54 into which gases from dryer 84 and separator 86 are passed for HF absorption to produce a hydrofluoric acid solution for supply to the silica removal reactor 55. HF and SiF from a system 100 as shown in FIG. 2 and described in detail below₄Gas is also supplied to the HF absorber 54 via line 53. The gas stream leaving the HF absorber column 54 is passed through a hydrolyser 32 to which sufficient water 36 is added to produce the desired concentration of H₂SiF₆The aqueous solution is used in reactor 30. The silica produced in the hydrolyzer 32 is removed through a bottom outlet.

The aqueous acid solution exiting the scrubber/separator system from separator 72 is sent to a still 80 which is heated to a temperature sufficient to allow the hydrogen fluoride and silicon tetrafluoride gases to be released from the aqueous solution and any metal fluorides present in the aqueous phase to be separated as solids (typically 105 ℃ C. and 110 ℃ C.). It should be appreciated that the pressure differential across fan 82 will affect the pressure and thus the temperature of distiller 80. The separated solids are removed from still 80 via separator 98. Still 80 is typically heated with exhaust gas from gas turbine 85. The vapors from mixer 77 and separator 79 are typically returned to still 80 and provide more heat source.

The gas leaving distiller 80 enters mixer 83 via line 81 and pressure fan 82 where it is passed toWith substantially anhydrous AlF₃And (4) mixing. The mixture enters a tubular dehydration reactor 84 to remove substantially all of the water from the vapor phase, thereby producing substantially anhydrous HF and SiF₄The gaseous mixture is fed from the dehydration reactor 84 via line 87 to the HF absorber 54. Moist AlF produced in the dehydration reactor 84₃Is sent into AlF₃A drier 89 for drying the wet AlF₃And (4) heating. The water vapor produced by this heating step is removed at 91a and 91b to remove substantially anhydrous AlF₃Is recycled via line 90 back to mixer 83. Exhaust gas from the gas turbine 95 is suitably used for the purpose of heating the drier 89.

Figure 2 illustrates in block schematic form a system 100 for treating an aqueous solution or suspension produced in step (a) of the process according to the first or second embodiment of the present invention, including a still and associated equipment.

Referring to FIG. 2, system 100 includes a distiller 110 with a feed line 115 coupled to filter 50 of FIG. 1. Still 110 is also equipped with a jacket heater 112, a vapor outlet 120, and a bottom outlet connected to a level control separator 150. The gas outlet line 120 is connected to a dehydration system 130 via a forced draft fan 125, the gas outlet line of the dehydration system 130 being connected to a pair of activated carbon filters 135, 136, which in turn are connected to a vapor condenser 140. The condenser 140 is provided with a vent line 145 and a drain line 146. Carbon filters 135, 136 are provided with gas outlet lines 138 and 139, respectively, and are connected to vapor supply line 133.

In operation, the aqueous phase exiting reactor 30 and separated from solids in filter 50 as shown in FIG. 1 is fed via line 115 to distiller 110, distiller 110 is heated by jacket heater 112 sufficiently to include HF, SiF₄The temperature at which the gases of sulfur dioxide and water vapor are released from still 110 and exit via line 120. These gases are pressurized by blower 125, typically to a pressure in the range of about 70-140kPa, and enter a dehydration train comprising anhydrous aluminum fluorideSystem 130, as described above with reference to fig. 1. The temperature of the vaporizer 110 depends on the pressure generated by the blower 125, but is typically in the range of 105 ℃ and 110 ℃. In thatIn dewatering system 130, the water vapor is mostly removed and the substantially water-free gas exits the dewatering system and enters one of activated carbon filters 135, 136. As the gas passes through the activated carbon filter, the sulfur dioxide and possibly some other gases such as HCl are adsorbed by the activated carbon, producing HF and SiF₄A gas stream which is removed at outlet line 138 or 139 and fed via line 53 to HF absorber 54 of system 10 as shown in figure 1. The activated carbon filters 135, 136 are suitably used in tandem, with one of the activated carbon filters in operation and in contact with the gas exiting the dehydration system 130, while the other activated carbon filter is deactivated and heated to desorb sulfur dioxide and other adsorbed species such as hydrogen chloride. Heating is effected by steam entering via line 133. The desorbed species are passed from the activated carbon filter (purged in this manner) to the vapor condenser 140, where the vapor is condensed and combined with the SO dissolved therein₂Along with any HCl present, is removed via line 146.

The concentration of the liquid in still 110 becomes higher due to heating and evaporation of gas therefrom, up to the point where the dissolved minerals in the liquid exceed their solubility limit. Inorganic solids accumulated in still 110 can be removed from the still bottom line and passed to a level-controlled separator 150, where the solids are separated from the liquid phase by any suitable means and sent to disposal or to a regeneration unit to recover useful materials therefrom. The separated liquid may be returned to still 110.

Figure 3 schematically illustrates a system 200 for treating semi-purified carbonaceous material with a solvent capable of dissolving elemental sulfur in accordance with a method according to a third aspect of the invention.

Referring to fig. 3, the system 200 includes a processing vessel 210 having a carbonaceous material inlet 215 and a solvent inlet 216, and an outlet line 218 that enables the carbonaceous material and solvent to be sent from the processing vessel 210 to a solid/liquid separator 220. Separator 220 may be any suitable type of separator such as a filter and centrifuge or settling tank. Separator 220 is provided with a solids discharge connected to stripper 230 and a liquid discharge 225 connected to a still (not shown). Stripper 230 is equipped with a heater (not shown), a vapor vent line 237, and a solids outlet line 235.

When the system 200 is in operation, carbonaceous material and solvent, which have been treated with a hydrofluoric acid solution such as that described in U.S. patent 4780112, are added to the treatment vessel 210, mixed and maintained in contact for a time sufficient to dissolve at least a portion of any elemental sulfur present in the carbonaceous material with the solvent. The solvent is typically ethanol, but may be any solvent that dissolves elemental sulfur, or a mixture of such solvents. The process in the process vessel 210 is generally carried out at room temperature and atmospheric pressure. After a suitable contact time, the contents of process vessel 210 are sent via bottom outlet line 218 to separator 220 where the solid phase is separated from the solvent phase. The solid phase is sent to a stripper 230, which is heated to evaporate residual solvent. The heating temperature is suitably at or about the boiling point of the solvent used. After heating for a time sufficient to evaporate substantially all of the residual solvent in the carbonaceous material in stripper 230, the dried carbonaceous material is discharged via discharge line 235 for further processing or use.

The liquid exiting separator 220 and the vapor exiting stripper 230 may enter a solvent still (not shown) that distills off the solvent for recovery or reuse. The other major product in the still is elemental sulphur, which can be removed for disposal or sale.

Examples

Coal samples treated as described in us patent 4780112 were dried and examined under an electron microscope. They can be observed to contain two forms of sulfur: pyrite and elemental sulphur.

High sulfur raw coal samples were treated with about twice their weight of 32% w/w aqueous hydrofluorosilicic acid for 30 minutes at room temperature, then dried and treated with aqueous hydrofluoric acid as described in U.S. Pat. No. 4780112, after solids were separated, they were dried again and examined under an electron microscope. Elemental sulfur was not seen.

Claims

1. A method of reducing the amount of sulfur-containing impurities in a carbonaceous material, comprising:

(a) contactingsaid carbonaceous material with an aqueous solution of hydrofluorosilicic acid in the absence of hydrogen fluoride and a strong mineral acid, at least some of the sulfur-containing impurities reacting with the hydrofluorosilicic acid to form a reaction product and

(b) separating the reaction product from the contacted carbonaceous material.

2. A method of reducing the amount of sulfur-containing impurities in a carbonaceous material, comprising:

(a) contacting the carbonaceous material with an aqueous hydrofluorosilicic acid solution in the absence of hydrogen fluoride, at least some of the sulfur-containing impurities reacting with the hydrofluorosilicic acid to form reaction products;

(b) separating the reaction product and the hydrofluorosilicic acid from the contacted carbonaceous material, thereafter

(c) Treating the separated carbonaceous material with a fluorine acid solution comprising hydrofluorosilicic acid and an aqueous hydrogen fluoride solution.

3. A method of reducing the amount of sulfur-containing impurities in a carbonaceous material, comprising:

treating the carbonaceous material with a fluorine acid solution comprising hydrofluorosilicic acid and aqueous hydrogen fluoride,

separating said aqueous hydrofluorosilicic acid and hydrogen fluoride from said treated carbonaceous material, and then

Contacting the separated carbonaceous material with an organic solvent capable of dissolving elemental sulfur.

4. The process according to claim 1 or 2, wherein the concentration of hydrofluorosilicic acid in step (a) is in the range of 27% -37% (w/v or w/w or v/w).

5. The process according to claim 1 or 2, wherein the concentration of hydrofluorosilicic acid in step (a) is in the range of 28% -36% (w/v or w/w or v/w).

6. The process of claim 1 or 2, wherein the temperature of step (a) is in the range of 28-75 ℃.

7. The process of claim 1 or 2, wherein the temperature of step (a) is in the range of 30-70 ℃.

8. The process of claim 1 or 2, wherein the reaction time of step (a) is in the range of 8 to 120 minutes.

9. The process of claim 1 or 2, wherein the reaction time of step (a) is in the range of 10 to 100 minutes.

10. The process of claim 1 or 2 wherein the carbonaceous material in step (a) is mixed with at least about twice its weight of aqueous hydrofluorosilicic acid solution.

11. The process of claim 1 or 2 wherein said separated carbonaceous material after step (b) is further treated with an aqueous solution of hydrofluorosilicic acid to remove residual metal fluorosilicates.

12. The method of claim 2 or 3, wherein the hydrofluoric acid solution has a composition within the following range: 4% w/w H₂SiF₆、92％w/w H₂O, 4% w/w HF to 35% w/w H₂SiF₆、30％w/w H₂O、35％w/w HF。

13. The method of claim 2 or 3, wherein the hydrofluoric acid solution has a composition within the following range: 5% w/w H₂SiF₆、90％w/w H₂O, 5% w/w HF to 34% w/w H₂SiF₆、32％w/w H₂O、34％w/w HF。

14. The method of claim 2 or 3 wherein the composition of the hydrofluoric acid solution is about 25% w/w H₂SiF₆、50％w/w H₂O、25％w/w HF。

15. The process of claim 2 wherein the carbonaceous material in step (c) is treated with at least about twice its weight in solution in hydrofluoric acid.

16. The process of claim 3 wherein the carbonaceous material in step (a) is treated with at least about twice its weight in solution in hydrofluoric acid.

17. The process of claim 1 wherein step (b) is followed by subjecting the separated carbonaceous material to H₂SiF₆The aqueous solution is washed and the washed carbonaceous material is heated at a temperature in the range of about 250 ℃ to about 400 ℃ to evaporate any residual hydrofluorosilicic acid remaining on the carbonaceous material.

18. The process of claim 3, wherein the organic solvent capable of dissolving elemental sulfur is ethanol, benzene, carbon disulfide, diethyl ether or carbon tetrachloride, or a mixture of two or more of these solvents.

19. The method of claim 3 wherein the step of contacting the carbonaceous material with an organic solvent is conducted at ambient temperature and atmospheric pressure.