WO2007012151A1

WO2007012151A1 - A method of converting coal into fuels

Info

Publication number: WO2007012151A1
Application number: PCT/BG2006/000004
Authority: WO
Inventors: Chavdar Angelov Angelov
Original assignee: Chavdar Angelov Angelov
Priority date: 2005-07-29
Filing date: 2006-01-17
Publication date: 2007-02-01
Also published as: UA79216C2; EA200600431A1; EP1996679A1; EA008269B1; BG109247A

Abstract

The method is applicable to chemical and petrochemical industries for the production of synthesis gas. The method includes the preparation of the water-coal mixture and its gasification in two stages. The first stage (2) takes place in a vertical counter-flow pipe heat-exchanger (3) on a gasification column, and the second in a heating reactor (8) with production o synthesis gas and solid residues . A stage of catalytic conversion of the synthesis gas into motor fuels follows. The vapor-gas-coal mixture in the heat-exchanger (3) is subject to an action by modulated high-frequency fields in the frequency range from 1 MHz to 50 MHz at modulation frequencies in the range from 1 KHz to 200 KHz. In the reactor (8) , the vapor-gas-coal mixture is subject to the action of plasma from single-electrode high-frequency discharges at temperature 600-800° C.

Description

A METHOD OF CONVERTING COAL INTO FUELS

FIELD OF APPLICATION

The invention relates to a method for thermal and thermochemical conversion of coal into synthesis gas, applicable to the chemical and petrochemical industries for the production of synthesis gas, which is a raw material for obtaining various types of chemical products and synthetic motor fuels.

PRIOR STATE OF THE ART

A method of converting solid fuel is known, said method including saturation of the coal with hydrogen at high temperatures (above 400 ⁰C) and pressure from 50 to 300 atm with following separation into liquid and solid intermediate products. Subsequently, the liquid products are subject to hydrogenation refinement with the following production of components of high- octane petrol, diesel fuel, propellant and gas-turbine fuel, phenols, nitrogen hydroxides and other products [Chulkov, V. V., Motor Fuels: Resources, Quality, Substitutes. Moscow, 1998].

A disadvantage of this known method as well as of all known methods for obtaining fuels from coal by means of hydrogenation is the necessity of using considerable quantities of hydrogen. The hydrogen volume needed for this purpose is more than three times greater than the volume of the fuels obtained. This factor restrains the wide-spread implementation of similar producing technologies.

It is also known a method of obtaining motor fuels from coal by means of its conversion into synthesis gas (a mixture of CO + H₂) with the subsequent conversion of said synthesis gas into motor fuels [Setterfield, Ch., Practical Course of Heterogeneous Catalysis. Moscow, Mir, 1984, 362 p.]

In this method, the mixture of hydrogen and carbon monoxide, necessary for the production, is obtained by treating the coal with water vapor and oxygen.

It is also known a method for thermal conversion of solid fuel, including preliminary mixing of ground coal with a gaseous oxydizer and subsequent gasification by feeding it into a zone with electric arc with the purpose that the speed vector of the so described mixture has a component parallel to the arc axis. In this process, the average temperature of the synthesis gas is maintained at a level of 1,200 - 1,700 ⁰C by regulating the power of the electric arc. Water vapor and oxygen in the ratio: water vapor 15 - 45 %, and oxygen 85 - 55 %, are used as an oxydizer in the method presented [FR2491490]. Using oxygen as an oxydizer leads to ballasting the synthesis gas with carbon dioxide that is a product from the interaction between carbon and oxygen, and moreover, to obtain oxygen also requires a special installation. AU this leads to additional, energy consumption as the synthesis gas should be purified,, and obtaining and storing oxygen in the required volume results in increased energy consumption.

Maintaining the temperature of the synthesis gas obtained at the expense of regulating the electric arc power is low-efficient, non-reliable and complex as the release of heat in the reactor occurs at the expense of both the coal combustion in oxygen environment and the energy released by the electric arc, and at the same time only one source of heat emission is regulated, namely the electric arc.

The disadvantages described diminish significantly the values of technical and cost-effective parameters and complicate the process as a whole.

A method of converting coal into synthesis gas is known; said method including coal preparation in the form of colloidal-dispersion fuel system with average surface size of the particles of the dispersion phase not larger than 1 μm, gasification of the obtained fuel mixture in a single stage in a reactor with pipes placed vertically, into which the fuel mixture mentioned is fed, and at that the temperature of the heat-transfer medium in the space between the pipes in the reactor being maintained within the range of 400 - 1,000 ⁰C, and the temperature in the pipes in the range of 200 - 800 ⁰C [RU2190661]. A disadvantage of this method is its low energy efficiency in the process of producing the synthesis gas because: - the preparation of the colloidal-dispersion fuel system is accompanied by grinding not only the organic component of the coal, but also its mineral component, to average surface size of the particles of the dispersion phase not larger than 1 μm, which increases considerably the energy consumption for their grinding;

- the independent heating of the heat-transfer medium, fed into the space between the pipes in the reactor, up to 1,000⁰C in the presence of hot air cooling the synthesis gas after the pipe cooler leads to excessive consumption of energy for pre-heating of the dispersion fuel system;

- using a forward-flow pipe cooler for cooling the synthesis gas, instead of a counter-flow one, is also considered inefficient.

The recommended temperature range of gasification from 200 to 800 ⁰C does not ensure efficient development of the process when using low-reaction coal, for instance, anthracite.

In addition, for non-determinate mass ratio between coal and water in the prepared dispersion-colloidal fuel system it, is not possible to determine the energy consumption in the production of the synthesis gas.

A thermal plasma method of converting coal into synthesis gas is also known, where said method includes preparation, thermal treatment and gasification of coal by the use of plasma in a plasmoreactor, said gasification process being performed in three stages, two of which being conducted in pipe heat-exchangers, and the third final stage is performed immediately in the volume of the plasmoreactor, simultaneously with the process of high-temperature pyrolysis in the presence of a reagent. The preparation of the coal is carried out through its dispergation in methanol water, to which surface-active substances - alkylamides - are added, and the coal suspension obtained at the first stage of gasification is heated in pipes to 200 - 300 ⁰C in the flow of flue gases exhausting from the gasification column and fed into the space between the pipes of the reactor, and before the second gasification stage, said coal suspension is heated to 900 - 1,100 ⁰C in the flow of synthesis gas discharged from the plasmoreactor. Water vapor is used as a reagent in high-temparature pyrolysis, which is injected in the reaction zone with the help of plasma sources. The synthesis gas obtained in the plasmoreactor is cooled and purified from impurities in a centrifugal-barbotage apparatus by using atmosphere air and water, the atmosphere air being used subsequently with a part of the synthesis gas in the combustion device of the gasification column, and the water being fed to the dispergating device for preparation of the coal suspension [RU2047650].

A disadvantage of this method is the complexity of the technological process, which is realized in three stages with preliminary heating-up of the water- coal suspension up to 200 - 300 ⁰C, with simultaneous burning of a part of the synthesis gas and using the synthesis gas discharged from the plasmoreactor, heated up to temperature 2,200 - 2,700 ⁰C. For the purposes of preliminary heating-up and realizing the first and second stages of gasification in the temparature range of 900 - 1,100 ⁰C it is sufficient to use the heat accumulated in the synthesis gas discharged from the plasmoreactor.

The consumption of energy for production of synthesis gas according to this method is also increased, which is connected with the introduction of vapor-gas- coal suspension, consisting of carbon oxide, carbon dioxide, hydrogen, water vapors and non-reacted coal particles, in the plasmoreactor. Water vapors are used in the plasmoreactor as a reagent, which leads to additional ballasting of the gaseous products from the gasification with water vapor and simple hydrocarbons being formed at high temperatures within 2,200 - 2,700 ⁰C.

The scheme, applied in this method for the interaction of plasma jets of the vapor with jets of the mixture being gasified and for the organization of returning the non-reacted organic coal particles to the reaction zone for their complete conversion into gas, applies to the same extend also to the solid mineral coal particles that do not react with the vapor phase, which results in their accumulation in the high-temparature zone of the plasmoreactor. Due to high temperatures and prolonged stay in the plasmoreactor, metal oxides participating in the mineral composition of the coal melt and this creates a possibility for chemical interaction with carbon, resulting in the formation of metals, their carbides and carbon oxides, for which a considerable part of the energy is consumed, and which, as a whole, diminishes the caloricity of the synthesis gas at the expense of its saturation with carbon oxides.

The method for producing synthesis gas from a water-coal suspension is the closest to the present invention [RU2233312], said method including the preparation and gasification of the water-coal suspension, said gasification being realized in two stages, the first of which is carried out in a vertical counter-flow pipe heat-exchanger on the gasification column, and the second in a reactor for heating by means of an ultrahigh-frequency emission (UHF-reactor). In this method, the preparation of the water-coal suspension is achieved through dispergation of the coal in water phase to sizes of the solid-phase particles from 10 to 30 μm with mass concentration of the organic component of coal in the water- coal suspension from 32 % to 48 %. At the first gasification stage, the water-coal suspension obtained is directed to the heat-exchanger on the gasification column under pressure of 0.5 - 10 MPa, where it is heated up to temperature 500 - 700 ⁰C and until a vapor-gas-coal suspension is formed. Further on, this suspension is directed into a vapor-jet mill for grinding the particles of the solid phase to a fine dispersion state of 1 - 3 μm. The vapor-gas-coal suspension, ground to the preset size, is fed to the second gasification stage, i. e. into a reactor for heating, for example - the UHF-reactor, where it is heated to temperature 700 - 1,500 ⁰C in order to produce a synthesis gas. The synthesis gas obtained is cooled in the heat- exchanger on the gasification column with the aid of the water-coal suspension entering the heat-exchanger and purified from the ballast substances by means of water used for preparing the water-coal suspension.

In contrast to the method described in the patent [RU2190661], here the process of gasification conducted is realized in two stages, instead of three, which enables simplifying the technology for producing a synthesis gas. In addition, the process of preparing the water-coal suspension is realized by grinding the coal introduced initially through dispergation in water phase in order to separate the bound organic and mineral particles of the coal (down to a size of solid phase particles within 10 - 30 μm), which permits avoiding the fragmentation of the most solid and hard-dispergating mineral coal particles to the size of the fine dispersion fraction, less than 1 μm, considerably diminishing in such a way the energy consumption in the preparation of the water-coal suspension.

At that, the mass concentration of the organic part of coal in the water-coal suspension represents 32 % - 48 %, which provides low values of the viscosity of the water-coal suspension even for a size of the coal particles within 10 - 30 μm, and as a result of this the efficiency of the process of producing synthesis gas is increased.

At the first gasification stage, the water-coal suspension obtained under pressure 0.5 — 10 MPa is heated in a heat-exchanger up to temperature 500 - 700 ⁰C, at which a vapor-gas-coal suspension is formed. The so realized gasification process takes place in a more intensive way as compared to the gasification performed at atmospheric pressure.

Using a vapor-jet mill is not connected with additional consumption of energy for grinding because the energy used in it is accumulated in the overheated vapor-gas-coal suspension in the form of increased pressure (0.5 - 10 MPa) and inincreased temperature 500 - 700 ⁰C. It should be noted that additional grinding is applied mostly to porous particles from the coke residue of the organic component of the coal because this occurs both at the collision of particles into one another and as a result of the difference between the pressure inside the particles themselves and the pressure in the working chamber of the mill. Particles participating in the mineral composition of the coal are ground additionally to a considerably lesser extent as they practically lack any porousity. The second gasification stage takes place in an UHF-reactor, in which direct heating of the whole reacting mass of the vapor-gas-coal suspension up to temperatures 700 - 1500 ⁰C is realized under the effect of an ultrahigh-frequency electromagnetic emission. As a result of this effect, at the expense of the absorption of UHF-energy, the process of gasification of the vapor-gas-coal suspension is accompanied by further dispergation of the solid particles, which leads to intensification of the gasification process and to more complete use of carbon.

A disadvantage of this method, which is a prototype, is the realization of the process within such a high-temparature range, which leads to an increase in the energy consumption, diminishment of the economical efficiency of the process, and partial melting of the mineral components of coal and soot formation.

Other disadvantages of the method are the low intensity of the process of producing synthesis gas and the technical complexity of introducing an UHF- emission inside the reactor by means of waveguides.

The task of the invention consists in creating a method of converting coal into fuels with increased efficiency of the process of producing synthesis gas from a high- viscosity water-coal fuel.

TECHNICAL ESSENCE OF THE INVENTION

This task is solved by creating a method of converting coal into fuels, which includes preparation of a water-coal mixture and its gasification in two stages. The first of them takes place in a vertical counter-flow pipe heat-exchanger on a gasification column, and the second in a heating reactor with production of synthesis gas and solid residues. A stage of catalytic conversion of the synthesis gas in motor fuels follows. It is characteristic that the vapor-gas-coal mixture in the heat-exchanger is subject to the action of modulated high-frequency fields in the frequency range from 1 MHz to 50 MHz at modulation frequencies in the range from 1 KHz to 200 KHz. In the reactor the vapor-gas-coal mixture is subject to the action of plasma from single-electrode high-frequency discharges at temperature 600 - 800 ⁰C. The synthesis gas obtained is subject to electrochemical purification from the compounds of sulphur and nitrogen, purification from chemical impurities, compressed and subject to conversion with the help of a polyfunctionaL catalyst, containing oxides of iron, zinc and molybdenum in combination with a carrier, namely aluminium, its oxides and aluminium phosphate.

It is possible to perform the gasification process of the vapor-gas-coal mixture in the reactor in the presence of catalysts for the vapor conversion of carbon, which are deposited upon the thermoinsulating coating of the internal walls of the reactor.

An advantage of the invention is that the method of converting of coal into fuels is characterized by increased efficiency of the process of producing synthesis gas from high-viscosity water-coal fuel.

DESCRIPTION OF THE ACCOMPANYING FIGURES

The invention is explained in more details by means of an exemplary embodiment of the installation realizing the method of converting coal into fuels, which is shown in the figure representing a scheme of said installation.

EXEMPLARY EMBODIMENT

AND OPERATION OF THE INVENTION

The installation in the figure is a possible embodiment realizing the method. In contrast to the prototype, the vapor-gas-coal mixture is fed by means of a pump 1 into a vertical counter-flow pipe heat-exchanger 2 on the gasification column 3 and treated additionally by means of high-frequency electromagnetic fields. Transferring high-frequency energy into the vapor-gas-coal mixture is carried out by metal rods 4, which are covered entirely with dielectric materials (for instance, ceramics, quartz) 5. These metal rods 4 are connected to a high- frequency generator 6 that provides in working regime the transfer of high- frequency power into the vapor-gas-coal mixture at carrier frequency 1 - 50 MHz and modulation frequency 1- 200 KHz. Intensive absorption of high-frequency power by the vapor-gas-coal mixture takes place in the frequency range indicated. In such a way, controlling the gasification process of the water-coal fuel is realized by changing the temperature of the process, and moreover, intensification in mixing the treated fuel is achieved by means of modulated high-frequency electromagnetic waves.

The second stage of the method is connected with an additional process of gasification of the vapor-gas-coal mixture being fed through pipelines 7 into the reactor 8, in which the internal walls are covered with a special material on the basis of refractory coating, having not only low heat conductivity and low heat capacity, but also catalyzing properties in the reactor for the vapor conversion of carbon into synthesis gas. Using such a material being a catalyst permits accelerating the process of carbon gasification at relatively low temperatures (up to 400 ⁰C), which under equal other conditions makes it possible to increase 1.5 to 2 times the productivity of the installation for synthesis-gas production.

Moreover, additional treatment of the vapor-gas-coal mixture is accomplished in the reactor by means of a strongly non-equilibrium plasma being created by single-electrode high-frequency discharges generated by electrodes specially made in the form of a blade 9 inside the generator, irrespective of the chemical composition of the vapor-gas-coal mixture and the thermal regime.

Transferring the UHF-energy to the electrodes described above is performed by high-frequency generators 10. They operate at frequency 1 - 40 MHz and modulation frequency 0.5 - 50 KHz.

At that, in the reactor, the vapor-gas-coal mixture is subject to action by both the plasma from single-electrode discharges and the high-frequency electromagnetic fields, which causes the occurrence of fullerenes and fullerites increasing the quantity of synthesis gas obtained from the mixture treated.

The distinguishing features of the invention are: - Using high-frequency energy the both stages of producing synthesis gas from a vapor-gas-coal mixture;

- Using strongly non-equilibrium plasma from a single-electrode high- frequency discharge in the second stage of producing synthesis gas from a vapor- gas-coal mixture;

- Using a coating on the internal walls of the reactor, made of a refractory material featuring not only resistance to chemical and mechanical actions exerted by the vapor-gas-coal mixture, but also strong catalyzing properties for the vapor conversion of carbon;

- Converting the synthesis gas into synthetic motor fuels takes place in the presence of a polyfunctional catalyst containing oxides of iron, zinc and molybdenum, aluminium, its oxides and aluminium phosphate.

The realization of the method proposed, as compared to the prototype, involves a number of original technological approaches and design solutions for the technological processes that consist in the following:

- Inside the reaction gasification column (3), activation of the process of synthesis-gas production is achieved by means of modelled high-frequency fields, which permits lowering the temperature of the process to 500 - 800 ⁰C.

- In the reactor 8, an action upon the vapor-gas-coal mixture is exerted by plasma from single-electrode high-frequency discharges with subsequent formation of fullerene-like compounds, which, as a whole, intensifies the process of gasification of the mixture treated.

- The internal walls of the reactor 8 are lined with a material that possesses not only thermoinsulating, but also catalyzing properties, which permits increasing the intensivity of the process of producing synthesis gas from the vapor-gas-coal mixture and shortening in such a way the time for treatment of the vapor-gas-coal mixture in the reactor.

The process of gasification of the vapor-gas-coal mixture is realized in the following way: The prepared watercoal mixture with particles with size no larger than 30 μm is fed by means of a pump 1 at pressure 0.1 - 3.0 MPa into a vertical counter-flow pipe heat-exchanger 2 on the gasification column 3. In the gasification column 3 the water-coal mixture is heated to 200 - 400 ⁰C and until a vapor-gas-coal suspension is formed, said suspension being treated by means of modulated high-frequency fields. Transferring the UHF-power is performed through metal rods 4 covered with dielectric material 5. Said metal rods are coupled directly to the high-frequency generators 6 that operate at carrier frequency 1 - 50 MHz and modulation frequency 1 — 200 KHz.

The process of gasification, which takes place at the expense of the absorption of electromagnetic energy, starts in the central part of the reactor and is run most intensively in the upper part of the reactor at temperatures 500 - 700 ⁰C.

The partially gasified vapor-gas-coal suspension is fed along the pipelines 7 into the reactor 8 through a static mixer 11, where, under the action of the high- frequency fields and the plasma from single-electrode discharges, the vapor-gas- coal mixture is heated to temperature 500 - 800 ⁰C. The internal walls of the reactor 8 are lined with a thermoinsulating coating, on the external surface of which a layer of catalyst used in the vapor conversion of carbon is deposited.

The synthesis gas obtained in the reactor 8, along with the ballast substances, is introduced in the space between the pipes of the gasification column 3, where the water-coal mixture entering the pipe part of the heat- exchanger 2 is used as a coolant. After passing through the heat-exchanger, the synthesis gas is fed to a purification device 12, for instance, a centrifugal- barbotage apparatus, in which, as a result of the direct contact with cooling water, the synthesis gas is cooled to the temperature of the environment and releases the ballast substances of the gasification products (water vapor, coal ash particles, hydrogen sulphide, carbon dioxide, etc.). The purified synthesis gas is compressed by a compressor and fed through pipelines to the customers. The purified water is fed to the pipeline for circulating water. Ash residues from the gasification are discharged from the lower part of the gasification column and directed for further conversion. The mass ratio between water and the organic part of the solid phase of the water-coal mixture is determined from the condition that the water content should exceed with 10 - 20 % the quantity of water which is needed according to the stoichiometric equation of the gasification reaction of carbon with the water vapor, and depends on the carbon content in coal [RU2233312]. For mass ratio of the carbon in coal within 0.96 - 0.6, the mass concentration of coal in the water- coal mixture is approximately 32 - 48 %.

The synthesis gas obtained is directed for electrochemical and plasma- chemical treatment at temperature about 600 ⁰C for maximum removal of the compounds of sulphur and nitrogen. Then the synthesis gas is cooled, purified from chemical impurities, compressed and directed into a reactor for synthesis of hydrocarbons at temperature 300 ⁰C and pressure 3 MPa. The synthesis of liquid hydrocarbons takes place in the presence of a polyfunctional catalyst containing oxides of iron, zinc and molybdenum in combination with a carrier, namely aluminium, its oxides and aluminium phosphate. The total quantity of the synthetic fuels produced is 190 g/nm³ of synthesis gas for 90-percent conversion of the carbon oxides.

Claims

PATENT CLAIMS

1. A method of converting coal into fuels, including the preparation of a water-coal mixture and its gasification in two stages, where the first of them takes place in a vertical counter-flow pipe heat-exchanger on a gasification column, and the second in a heating reactor with production of synthesis gas and solid residues, as well as a stage of catalytic conversion of the synthesis gas into motor fuels, characterized by the fact that the vapor-gas-coal mixture in the heat-exchanger is subject to an action by modulated high-frequency fields in the frequency range from 1 MHz to 50 MHz at modulation frequencies in the range from 1 KHz to 200 KHz, and in the reactor the vapor-gas-coal mixture is subject to the action of plasma from single-electrode high-frequency discharges at temperature 600 - 800 ⁰C, and the synthesis gas obtained is subject to electrochemical purification from the compounds of sulphur and nitrogen, purification from chemical impurities, compressed and subject to conversion with the help of a polyfunctional catalyst containing oxides of iron, zinc and molybdenum in combination with a carrier, namely aluminium, its oxides and aluminium phosphate.

2. A method according to claim 1, characterized by the fact that the process of gasification of the vapor-gas-coal mixture in the reactor is performed in the presence of catalysts for the vapor conversion of carbon, which are deposited upon the thermoinsulating coating of the internal walls of the reactor.