WO2006081661A1

WO2006081661A1 - Coal gasification process and apparatus

Info

Publication number: WO2006081661A1
Application number: PCT/CA2006/000134
Authority: WO
Inventors: Andreas V. Tsangaris; Kenneth C. Campbell
Original assignee: Plasco Energy Group Inc.
Priority date: 2005-02-04
Filing date: 2006-02-06
Publication date: 2006-08-10

Abstract

A process is provided that efficiently gasifies coal, using the heat of a first plasma torch configuration, while converting the ash content of the coal to a vitreous slag using a second plasma torch configuration. The process simultaneously uses the controllability of heat provided by the first plasma torch configuration to drive the gasification process, and to ensure that the gas flow and composition from the process remains within acceptable ranges even if the composition of the coal exhibits natural variability. Apparatus suitable for use to conduct the coal gasification process is also provided.

Description

COAL GASIFICATION PROCESS AND APPARATUS

FIELD OF THE INVENTION

This invention relates to the gasification of coal, and in particular to a process and apparatus for the gasification of coal.

BACKGROUND OF THE INVENTION

Coal can typically be gasified with oxygen and steam to produce so-called "synthesis gas" containing carbon monoxide, hydrogen, carbon dioxide, gaseous sulfur compounds and particulates. The gasification step is usually carried out at a temperature in the range of about 65O⁰C to 1200⁰C, either at atmospheric pressure or, more commonly, at a high pressure of from about 20 to about 100 atmospheres.

Synthesis gas is produced according to the Haber Bosch Process, which was developed in 1917. This process operates on the basic reforming reaction that reacts carbon e.g., coal with steam in a primary reaction to produce hydrogen and carbon monoxide- The hydrogen/carbon monoxide ratio of the synthesis gas varies widely depending on the nature of the coal feed. However, if one mol of methane was reformed with steam, it would produce a synthesis gas which is rich in hydrogen, e.g., three mols of hydrogen and one mol of carbon monoxide, i.e., a hydrogen/carbon monoxide ratio of 3/1. A competing secondary reaction known as the water gas shift reaction also takes place wherein carbon monoxide reacts with steam to form carbon dioxide and additional hydrogen. This water gas shift reaction is a secondary reaction since high temperature and lower pressure favor the primary reaction.

Because coal often contains sulfur compounds, attempts have been made to provide processes for the gasification of coal to produce a clean product fuel gas wherein the sulfur is removed from the product fuel gas prior to its use, e.g., in gas turbines to generate electricity. In addition, gases from the gasification zone may be purified to remove coal dust and fly ash and also many other impurities,, e.g., vaporized ash, alkali, etc. Plasma torch technology has also been employed in coal gasification processes. Plasma torch technology was substantially advanced through the 1960's when new plasma generators were developed to simulate the very high temperature conditions experienced by space vehicles re-entering the Earth's atmosphere. Unlike a combustion burner flame, a plasma arc torch can be operated in the absence of oxygen. A plasma arc torch is created by the electrical dissociation and ionization of a working gas to establish high temperatures at the plasma arc centerline. Commercially-available plasma torches can develop suitably high flame temperatures for sustained periods at the point of application and are available in sizes from about 100 Kw to over 6Mw in output power.

Plasma is a high temperature luminous gas that is at least partially ionized, and is made up of gas atoms, gas ions, and electrons. Plasma can be produced with any gas in this manner. This gives excellent control over chemical reactions in the plasma as the gas might be neutral (for example, argon, helium, neon), reductive (for example, hydrogen, methane, ammonia, carbon monoxide), or oxidative (for example, oxygen, nitrogen, carbon dioxide). In the bulk phase, a plasma is electrically neutral. Thermal plasma can be created by passing a gas through an electric arc. The electric arc will rapidly heat the gas by resistive and radiative heating to a very high temperature within microseconds of passing through the arc. A typical plasma torch consists of an elongated tube through which the working gas is passed, with an electrode centered coaxially within the tube. In one type of such torch, a high direct current voltage is applied across the gap between the end of the center electrode as anode, and an external electrode as cathode. The current flowing through the gas^in the gap between the anode and the cathode causes the formation of an arc of high temperature electromagnetic wave energy that is comprised of ionized gas molecules. Any gas or mixture of gases, including air, can be passed through the plasma torch.

For example, U.S. Patent Nos. 4,141,694 and 4,181,504 describe a process for the gasification of coal in which plasma torches were employed as a bank of long arc columns which devolatilized crushed coal in a matter of milliseconds. Steam was continuously injected to produce carbon-rich gases. The process described in these patents, however, is likely expensive to implement as most of the necessary heat for the process is supplied by the plasma arc.

U.S. Patent No. 4,208,191 describes a process for the production of pipeline gas from goal that employs an additional catalytic process and to gasify coal and produce a synthesis gas containing carbon monoxide, hydrogen, gaseous sulfur compounds, methane and carbon dioxide. Gaseous sulfur compounds and carbon dioxide were removed from the gas in an acid gas removal system, followed by contacting the gas with a reduced iron catalyst at conditions to produce methane, and small amounts of olefins. This was followed by separation of carbon dioxide byproduct and methanation with a nickel catalyst to produce additional methane and to convert olefins to alkanes.

U.S. Patent No. 4,410,336 also describes a process for the production of pipeline gas from coal that requires several independent sequential processes to be employed. Initially, the coal was gasified at a relatively low pressure, typically less than about 5 atmospheres, to produce a raw synthesis gas containing carbon monoxide, hydrogen, carbon dioxide, gaseous sulfur compounds and particulates. The so-produced raw synthesis gas was cooled to a temperature range of about 200⁰C to about 400⁰C and was purified to remove substantially all of the sulfur compounds and particulates contained therein. The clean raw synthesis gas was enriched in a first step by converting the carbon monoxide and hydrogen contained therein to yield a gas containing methane and carbon dioxide. The enriched gas was further enriched in a second step by removing carbon dioxide there from to yield a gas consisting essentially of methane.

U.S. Patent No. 4,472,172 describes the gasification of the crushed coal by way of a free-burning arc discharge that produced a highly reactive carbonaceous fume which was subjected to a second independent steam treatment step. This process, however, produced byproduct ash and did not provide secondarily-useful molten slag.

U.S. Patent No. 4,606,799 describes a process in which the carbonaceous fuel and oxygen-containing gases were first endothermally-reacted and then the reaction products were reacted in a plasma zone. The commercial viability of this process, however, may be compromised by the expense of such a two-stage process.

U.S. Patent No. 5,331,906 describes a coal combuster that comprises a slag exhausting device and maintains a combustion capability in a combustion furnace for coal gasification by exhausting molten slag produced within the furnace without the slag stagnating by including a special slag exit construction. The slag exhausting device was configured in such a way that the cooling of the molten slag being exhausted from the furnace was minimized to prevent the slag from solidifying, and causing other slag to stagnate. This was achieved by way of a disposing the slag exhausting device at the center of the bottom wall of the furnace and providing such exhaust device with particular dimensional characteristics.

U.S. Patent No. 5,486,269 describes the gasification of carbonaceous material in a reactor having a gasification zone and a combustion zone. The gasification zone is described as generally being at super-atmospheric pressure up to 150 bar. The thermal energy which is necessary to maintain the first endothermic reaction is supplied by combustion of a fuel with added oxygen-containing gas. Again, the commercial viability of this process, however, may be compromised by the expense of such a two- stage process.

U.S. Patent No. 6,200,430 describes a process whereby coal was subjected to an electric arc-activated, non-catalytic burner at high pressure in the absence of oxygen. Considerable expense would likely be involved in providing a high pressure reactor with attendant apparatus to provide the high pressure, which may impact the commercial viability of this process.

This background information is provided for the purpose of making known information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention. SUMMARY OF THE INVENTION

An object of the present invention is to provide a coal gasification process and apparatus. In accordance with one aspect of the present invention, there is provided a process for producing synthesis gas and vitreous slag from coal, said process comprising the steps of: passing coal into a gasification zone at a coal input rate; passing oxygen, into said gasification zone at an oxygen input rate; subjecting said coal to the heating effect of a first plasma torch configuration in the presence of the oxygen to provide a first gaseous product and by-product ash; passing the first gaseous product to a reforming zone; adding steam to said first gaseous product at a steam input rate to convert the first gaseous product to a synthesis gas; . , passing said by-product ash into a melting zone; subjecting said by-product ash to heating by a second plasma torch configuration to convert the by-product ash to slag and maintain the slag in a molten condition; exhausting the molten slag from the melting zone, and allowing said molten slag to cool to provide said vitreous slag.

In accordance with another aspect, there is provided an apparatus for producing synthesis gas and vitreous slag from coal by the process of the present invention, said apparatus comprising: a gasification zone; one or more coal input in operative communication with said gasification zone for passing coal into said gasification zone; one or more oxygen inlets in operative communication with said gasification zone for passing oxygen into said gasification zone; a first plasma torch configuration positioned to provide a first plasma discharge into said gasification zone and thereby convert said coal and said oxygen into a gaseous product and by-product ash; a reforming zone in operative communication with said gasification zone whereby the first gaseous product passes from said gasification zone into said reformation zone; one or more steam inlets positioned to add steam into said reformation zone and thereby convert said gaseous product into synthesis gas; a synthesis gas outlet in operative communication with said reforming zone for exhausting said synthesis gas from the reformation zone; a melting zone in operative communication with said gasification zone whereby said by-product slag passes from said gasification zone into said melting zone; a second plasma torch configuration positioned to provide a second plasma discharge towards said melting zone and thereby convert said by-product ash into molten slag, and a slag outlet in operative communication with said melting zone for exhausting said molten slag, wherein the molten slag cools to provide vitreous slag.

In accordance with another aspect of the present invention, there is provided an apparatus for producing synthesis gas and vitreous slag from coal, said apparatus comprising: a refractory-lined reactor vessel; a slag reservoir located at a bottom end of the reactor vessel; an axial synthesis gas outlet associated with the reactor vessel for exhausting said synthesis gasl; a first plasma torch configuration for generating a first plasma discharge, said first plasma torch configuration associated with said reactor vessel and positioned to direct the first plasma discharge into the reaction vessel; a second plasma torch configuration for generating a second plasma discharge, said second plasma torch configuration associated with said reactor vessel and positioned to direct the second plasma discharge towards the slag reservoir; a slag outlet associated with said reactor vessel and positioned to exhaust molten slag from the slag reservoir; one or more coal inlets associated with said reactor vessel and positioned to inject coal into the first plasma discharge; one or more oxygen inlets associated with said reactor vessel and positioned to inject oxygen into the first plasma discharge; and one or more steam inlets associated with said reactor vessel to inject steam into said reactor vessel.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the invention will become more apparent in the following detailed description in which reference is made to the appended drawings wherein:

Figure 1 is a central longitudinal cross-section through a reactor vessel in one embodiment of the present invention;

Figure 2 is a block diagram of reactor controls in one embodiment of the present invention; and

Figure 3 is block diagram of process logic in one embodiment of the present invention.

DETAILED DECRIPTION OF THE INVENTION

The present invention provides for a process for the gasification of coal and an apparatus suitable for use to carry out the process.

The process of the present invention efficiently gasifies coal, while converting the ash content of the coal to a vitreous slag. The process utilises plasma torches to generate high temperature heat to gasify the coal and to melt the coal ash and convert it to a glass-like product with commercial value. In one embodiment of the present invention, the use of plasma torches improves the slag quality and, in conjunction with the input of steam and gaseous oxygen, helps in controlling the gas composition. In another embodiment, the input of power required for the plasma torches is less than the potential power production of the process. In a further embodiment, the power input required for the plasma torches is less than the potential power production of the process is due to the relatively homogeneous quality of the coal feedstock.

The process can further comprise a corrective feedback procedure in which one or more of the flow rate, temperature and composition of the synthesis gas are monitored and corrections made to one or more of the coal input rate, the oxygen input rate, the steam input rate and the amount of power supplied to the plasma torches based on changes in the flow rate, temperature and/or composition of the synthesis gas in order to ensure that these remain within acceptable ranges. In general, the ranges for the flow rate, temperature and/or composition of the synthesis gas are selected to optimise the synthesis gas for a particular downstream application, such as gas turbines for electricity generation, hi one embodiment, the process of the present invention simultaneously uses the controllability of plasma heat to drive the gasification process, and to ensure that the gas flow and composition from the process remains within an acceptable range even if the composition of the coal exhibits natural variability. In another embodiment, the process allows for the total amount of carbon processed per unit time to be held as constant as possible, and utilizes the plasma torches to ensure that the total heat that enters and leaves the reactor vessel per unit time is kept within process limits.

The apparatus of the present invention is of a simple construction and can be utilized without the requirement for pressure equipment, such as compressors.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

As used herein, the term "about" refers to a +/-10% variation from the nominal value. It is to be understood that such a variation is always included in any given value provided herein, whether or not it is specifically referred to.

The term "plasma torch configuration," as used herein, refers to one or more plasma torches. When the plasma torch configuration comprises more than one plasma torch, the plasma torches can be provided in a variety of configurations, for example, in parallel, in series, at opposite sides of the reactor vessel, the same side of the reactor vessel, adjacent to each other either vertically or horizontally, spatially separated from each other, and the like. The plasma torches in the plasma torch configuration can receive power from the same source or from different sources. One or more of the plasma torches in a plasma torch configuration can be moveable.

For the purposes of the present invention, the term "composition of the synthesis gas" refers to the amount of carbon monoxide, carbon dioxide and/or hydrogen in the synthesis gas. Composition of the synthesis gas is generally monitored immediately upon, or shortly after, leaving the reactor vessel, i.e. proximal to the synthesis gas outlet.

Coal Gasification Process

The process for gasification of coal generally comprises the steps of:

- passing coal into a gasification zone where it is subjected to the heating effect of a first plasma torch configuration and oxidation by oxygen to provide a first product comprising gaseous carbon monoxide and methane, and some entrained, fine, solid carbon;

- passing the first product to a reforming zone where steam is added to convert the first product to a synthesis gas comprising carbon monoxide, carbon dioxide, hydrogen and steam; and

- subjecting by-product ash to heating by means of a second plasma torch configuration to maintain the slag in a molten homogenized condition to enable exhausting of the molten slag from the combustion zone.

As noted above, the process can further comprise a corrective feedback procedure in which adjustments are made to one or more of the coal input rate, the oxygen input rate, the steam input rate and the amount of power supplied to the plasma torche configurations based on changes in the flow rate, temperature and/or composition of the synthesis gas. The corrective feedback procedure thus allows the flow rate, temperature and/or composition of the synthesis gas to be maintained within acceptable ranges.

In accordance with one embodiment of the present invention, the coal gasification process comprises a specified sequence of steps that are conducted in a single reactor vessel and converts coal, steam and oxygen to a synthesis gas comprising gaseous carbon monoxide, carbon dioxide, and hydrogen.

hi one embodiment of the present invention, the process further comprises the step of pre-heating one or more of the coal, oxygen and steam prior to adding the respective gasification and reformation zones.

Gasification

In general, the process of the present invention is conducted by feeding coal along with oxygen into a gasification zone within a reactor vessel where the coal is subjected to the heat of a first plasma torch configuration which allows the gasification reaction to take place. Extra oxygen may be injected to initiate or to increase the exothermic reactions that produce carbon monoxide, carbon dioxide and carbon particles. The flow is upwardly and the pulverized coal is entrained in the oxygen and in the preliminary gasification products that are formed in the gasification zone. The exothermic reactions along with the heat provided by the first plasma torch configuration increase the processing temperature. In one embodiment, the processing temperature is between about 1200 ⁰C to about 1400 ⁰C, although lower and higher temperatures are also contemplated. In one embodiment of the present invention, the process employs an average gasification temperature within the reactor vessel is about 1300 ⁰C +/- 100 ⁰C. The heat so produced provides the heat required for the enαothermic reactions that are carried out in the reforming zone.

Coal of varying grades- can be used as the feedstock, including low grade, high sulfur coal. As is known in the art, there are several different types of coal, each displaying different properties resulting from geological history. The degree of coal development is referred to as a coal's "rank." Peat is the layer of vegetable material directly underlying the growing zone of a coal-forming environment. The vegetable material shows very little alternation and contains the roots of living plants. Lignite is geologically very young (less than 40,000 years) and can be soft and fibrous. Lignite generally contains large amounts of moisture (typically around 70%) and has a low energy content (8 - 10 MJ/kg). Black coal ranges from 65-105 million years old to up to 260 million years old and is harder and shinier than lignite and contains less than 3% moisture. The energy content of black coal is up to about 24 - 28 MJ/kg. Anthracite contains virtually no moisture and very low volatile content, so it burns with little or no smoke. Anthracite can have energy contents up to about 32MJ7kg. Peat, lignite, black coal and anthracite are all considered to be "coal feedstock" in the context of the present invention.

In one embodiment of the present invention, the coal is pulverized prior to addition to the reactor vessel, hi general, when pulverized coal is used, it is of an appropriate size to provide the necessary rapid reaction. In one embodiment, the coal is of a particle size of 0.75 inches or smaller. Suitable examples of particle size include, but are not limited to, particle sizes of 30 mesh, or -100 mesh or the size recognized in the coal industry as "Buckwheat No. 1".

hi one embodiment of the present invention, the coal and oxygen are fed via inlets into the lower part of the reactor vessel (i.e. the gasification zone is located in the lower portion of the reactor vessel), hi another embodiment, the oxygen is provided in the form of air, oxygen or oxygen enriched air.

Reformation

The gases which are formed in the gasification zone are treated with steam in the reforming zone. These reactions are mainly endothermic. In one embodiment of the present invention, the temperature is maintained in a range that is high enough to keep the reactions at an appropriate level to minimise pollution production, while being low enough to minimize the energy which is expelled as sensible heat. An added benefit of minimizing the sensible heat in this manner is that the gas chemical heat increases accordingly (gas quality/heating value). Appropriate temperature ranges can readily be determined by the skilled worker. The steam that is added in the reformation step acts to reduce the exit temperature of the synthesis gas. hi one embodiment, the exit temperature of the synthesis gas is reduced to between about 900 ⁰C and about 1200 ⁰C. hi another embodiment, the exit temperature is reduced to an average temperature of about 900 ⁰C +/- 100 ⁰C.

Melting ofBy-Product Ash

Inorganic particles produced in the gasification and reformation reactions melt and fall into the slag pool. Enough time is allowed when the particles are entrained in the slag pool so that volatiles and carbon are removed. As would be appreciated by a worked skilled in the art, the residence time is a function of the particle size. The heat produced by the second plasma torch configuration homogenizes the slag and allows it to be extracted while hot. The plasma torch configuration heats the slag to a temperature between about 1400 ⁰C and about 1800 ⁰C. In one embodiment, to a temperature between about 1400 ⁰C and about 1650 ⁰C. This manipulation of the temperature profiles can help to avoid wasting heat and later water to quench the slag in the bottom of the reactor vessel.

The process of the present invention thus efficiently gasifies coal, while converting the ash content of the coal to a vitreous slag, hi one embodiment, the process uses the high temperature heat that the plasma torches provide to melt the coal ash, and to convert it to a glass-like product with commercial value. In one embodiment, the coal gasification process efficiently melts, homogenizes and exhausts slag from the combustion vessel. In a further embodiment, the heating is achieved by means of a plasma torch.

Corrective Feedback Procedure

The process can further comprise a corrective feedback control procedure which includes the steps of monitoring one or more of the synthesis gas flow rate, the synthesis gas temperature and the synthesis gas composition and correcting, via a simple feedback procedure, one or more of the rate of coal input, the rate of oxygen- input, the rate of steam input and the power to the plasma torch configurations. The feedback control procedure is described in more detail below. In one embodiment, the process of the present invention utilizes controlled amounts of oxygen and steam to produce optimum high quality, stable synthesis gas from coal.

Apparatus

The present invention further provides for an apparatus suitable for carrying out the above-described process. As noted above, the apparatus is of a simple construction and in one embodiment generally comprises

- a refractory-lined reactor vessel having one or more coal inlets, one or more oxygen inlets and one or more steam inlets;

a first plasma torch configuration located within the reactor vessel and disposed such that coal entering the reactor vessel through the coal inlet(s) enters into the path of the plasma discharge of this first plasma torch configuration;

- a slag reservoir;

- a second plasma torch configuration disposed adjacent to the slag reservoir and positioned such that the plasma discharge from the second plasma torch configuration is directed towards the slag reservoir;

- an axial outlet from the slag reservoir to the exterior of the reactor vessel; and

- a synthesis gas outlet.

The reactor vessel can be one of a number of standard reaction vessels known in the art. The reactor vessel can be vertically or horizontally oriented and may include internal components, such as baffles, to promote back mixing and turbulence if desired. The plasma torches in each of the first and second plasma torch configurations can be mounted within the reactor vessel to provide axial, radial, tangential or other promoted flow direction for the plasma gas, with plasma sources providing upward or downward gas flow. One or more inlets are incorporated to allow concurrent, countercurrent, radial, tangential, or other feedstock flow directions. In general, the coal and oxygen inlets are located in close proximity to the first plasma torch configuration. Reactor vessels generally comprise an outlet located near the top of the vessel to enable the reformed product gas to exit the reactor vessel.

Examples of reactor vessels known in the art include entrained flow reactor vessels that can accept feedstock in the form of solids, particulates, slurry, liquids, gases, or a combination thereof. The feedstock is injected through one or more inlets, which are disposed close to the first plasma torch configuration. Product synthesis gas exits the reaction vessel via a gas outlet, while slag exits via a slag outlet. The reactor vessel can have a wide range of length-to-diameter ratios and can be oriented either vertically or horizontally, as long as the slag outlet is disposed at the bottom to enable the slag to be removed by gravity flow. The reactor vessel wall can be lined with refractory material and/or a water jacket can encapsulate the reactor vessel for cooling and/or generation of steam.

Another example of a suitable reactor vessel is a down-fired reactor vessel. In down- fired reactor vessels, the first plasma torch configuration is positioned at the top of the reactor vessel, with the plasma jet directed inwardly and downwardly. One or more feed inlets are disposed adjacent to the first plasma torch configuration, so that as soon as the feedstock enters the reaction vessel it encounters the plasma to begin the process. A plurality of inlets are provided to inject oxygen and steam. The product synthesis gas exits via a gas outlet (disposed in a lower portion of the reaction vessel), while slag drops downwardly through the reactor vessel and exits through the bottom of the vessel via a slag outlet. Again, the interior surfaces of the reactor vessel can be lined with refractory material, and the reactor vessel can be partially covered with a water jacket to produce steam. A plurality of baffles oriented at a slight downward angle can be included if desired to help direct the flow of slag towards the outlet. The angles of these baffles can be varied to optimize this function. Again, different length- to-diameter ratios can be used to vary the size and volume of the reaction vessel.

Selection of an appropriate reaction vessel is within the ordinary skills of a worker in the art.

The refractory material used to line the reactor vessel can be one, or a combination of, conventional refractory materials known in the art which are suitable for use as a vessel for a high temperature, e.g., a temperature of about 1100 ⁰C to 1400 ⁰C, un- pressurized reaction. Examples of such refractory materials include, but are not limited to, high temperature fired ceramics (such as aluminum oxide, aluminum nitride, aluminum silicate, boron nitride, zirconium phosphate), glass ceramics and high alumina brick containing principally, silica, alumina and titania.

A variety of commercially-available plasma torches which can develop suitably high flame temperatures for sustained periods at the point of application can be utilized in the apparatus. In general, such plasma torches are available in sizes from about 100 Kw to over 6 Mw in output power. The plasma torch can employ one, or a combination, of suitable gases. Examples include, but are not limited to; argon, helium, neon, hydrogen, methane, ammonia, carbon monoxide, oxygen, nitrogen, and carbon dioxide, hi one embodiment of the present invention, the first plasma torch configuration is continuously operating so as to produce a temperature in the reactor vessel in excess of about 1100 ⁰C.

The second plasma torch configuration is employed to melt the coal ash. The molten slag, at a temperature of, for example, about 1400 ⁰C to about 1800 ⁰C; is periodically exhausted from the reactor vessel and is thereafter cooled to form a solid slag material. Such slag material may be intended for landfill disposal. Alternatively, the molten slag can be poured into containers to form ingots, bricks tiles or similar construction material. The solid product may further be broken into aggregates for conventional uses.

In one embodiment of the present invention, the first plasma torch configuration is disposed adjacent to, but spaced from, the bottom of the reaction vessel and extending a downward angle towards the core of the reaction vessel. In another embodiment, the second plasma torch configuration is disposed closely adjacent to the bottom of the reaction vessel and extending at an upward angle towards the core of the reaction vessel. In a further embodiment, the one or more oxygen inlets comprise a pair of. oxygen inlets to inject oxygen into the path of the plasma discharge of the first plasma torch configuration. In another embodiment, the one or more oxygen inlets inject oxygen into the path of the plasma discharge of the first plasma torch configuration from below and above. In another embodiment, the one or more steam inlets comprise a pair of steam inlets. In a further embodiment, the one or more steam inlets are disposed above the pulverized coal and oxygen inlets.

In another embodiment, the reactor vessel is a vertically oriented reactor vessel • having longitudinally-spaced-apart, bottom radial and upper, axial outlet ends. When the reactor vessel is a vertically oriented vessel, it generally has a predetermined length which is sufficient to effect the desired heating of the contents of the reactor vessel to a selected equilibrium temperature.

The apparatus may further comprise means for monitoring one or more of synthesis gas flow rate, synthesis gas temperature, synthesis gas composition, coal input rate, oxygen input rate, steam input rate and power supply to the plasma torches in order to provide the necessary information to implement the corrective feedback procedure described below. Various monitoring means are know in the art and can be employed in the apparatus of the present invention. Monitoring of the exit synthesis gas can be achieved, for example, by means of a gas monitor and gas flow meter. The gas monitor is used to determine the hydrogen, carbon monoxide and carbon dioxide content of the synthesis gas. Synthesis gas composition, flow rate and/or temperature are generally measured at a position proximal to the upper gas outlet vent. A plurality of thermocouples can be used to monitor the temperature at critical points around the reactor vessel.

Figure 1 presents an example of an apparatus in accordance with one embodiment of the present invention. One skilled in the are will appreciate that a number of variations can be made to the reactor vessel depicted in Figure 1 without detracting from its suitability to be used to carry out the process of the invention, for example, similarly configures horizontally-oriented reactor vessels could be employed.

As seen in Figure 1, the reactor vessel 10, is a refractory-lined vessel. A pair of vertically-spaced-apart, radial oxygen inlets 12, 14 is provided to admit oxygen to the reactor vessel 10. A first plasma torch 16 is disposed above the oxygen inlet 12, and extends upwardly towards the core 18 of the reactor vessel 10. First plasma torch 16 is longitudinally movable towards and away from the core 18, as shown by the two- ended arrow. A second plasma torch 20 is disposed below the oxygen inlet 14, and extends downwardly towards the core 18 of the reactor vessel 10, and towards a slag reservoir 22. Second plasma torch 18 is both longitudinally movable towards and away from the slag reservoir 22, and slewable as shown by the two-ended arcuate arrow. Slag reservoir 22 leads to a radial outlet 24 from the reactor vessel.

A radial, pulverized coal inlet 26 is provided above first plasma torch 16 to discharge the pulverized coal into the path of the plasma arc of first plasma torch 16. A pair of vertically-spaced-apart, radial steam inlets 28, 30, is provided above the pulverized coal inlet 24. A central, axial gas outlet vent 32 is provided at the upper end 34 of the reactor vessel 10.

Synthesis Gas Composition and Corrective Feedback Procedure

The main components of the synthesis gas as it leaves the reactor vessel are carbon monoxide, carbon dioxide, hydrogen, and steam, with lesser amounts of nitrogen. Much smaller amounts of methane, acetylene and hydrogen sulfide are also present. In one embodiment of the present invention, an example of a baseline composition for the synthesis gas as it exits the reactor vessel is as follows:

CARBON MONOXIDE about 26%

CARBON DIOXIDE about 11.5%

HYDROGEN about 28% STEAM about 31%

The composition of the synthesis gas can be optimized for a specific application (e.g., gas turbines for electricity generation) by adjusting the balance between applied plasma heat, oxygen and steam that is used in the above-described process via a corrective feedback procedure based on the monitored composition, flow rate and/or temperature of the synthesis gas being produced by the process. Thus, the product synthesis gas can be tailored for particular energy conversions (e.g., for specific gas engines or gas turbines) and for the conventional well-known particular grades of coal for best overall conversion efficiency. The corrective feedback procedure included in the process of the present invention employs one or more of the following corrective steps:

- monitoring the flow rate of carbon dioxide and carbon monoxide in the synthesis gas and adjusting the input rate of coal in order to correct the flow rate when it falls outside an acceptable range;

- monitoring the amount of carbon dioxide and carbon monoxide in the synthesis gas and adjusting the input rate of coal in order to correct the amount when it falls outside an acceptable range;

- monitoring the amounts of (a) carbon dioxide and carbon monoxide, and (b) hydrogen in the synthesis gas and adjusting the input rate of oxygen and/or steam in order to correct the amounts of each when they fall outside their respective acceptable ranges;

- monitoring the amounts of carbon dioxide and carbon monoxide in the synthesis gas, the input rate of oxygen and/or steam and the temperature of the synthesis gas and adjusting the power supply to the plasma torches in order to correct the temperature of the synthesis gas when it falls outside an acceptable range.

For example, at high temperatures, such as temperatures in excess of about 1100 ⁰C, the coal is quickly gasified, pyrolyzed, disassociated or oxidized. A substantial amount of the coal is converted to carbon monoxide or carbon dioxide/ depending on the amount of oxygen that is fed into the reactor vessel. Thus, the variable of carbon monoxide content of the synthesis gas can be monitored and the flow of oxygen controlled via corrective feedback so as to preclude the stoichiometric conversion of carbon to carbon dioxide, and the process is so operated to produce mainly carbon monoxide.

In one embodiment of the present invention, the composition and flow of synthesis gas from the reactor vessel is controlled within an acceptable range, e.g., by adjusting one or more of the input rate of coal, the input rate of oxygen, the input rate of steam and the power supply to the torches, as described above. The temperature of the process is controlled at atmospheric pressure toiensure that the coal injected into the reactor vessel encounters as stable an environment as possible. The process embodies corrective adjustment of the previously-defined total amounts of coal, steam and oxygen that are fed into the reactor vessel via the corrective feedback procedure.

In one embodiment of the present invention, the pulverized coal is fed continuously into the reactor vessel at a controlled rate. In a further embodiment, the pulverized coal is fed continuously into the reactor vessel at a rate of between about 1.8 to about 2.8 Ib coal/min, for example, about 2.2 Ib coal/min. One skilled in the art will appreciate, however, that this rate may be adjusted above or below this range in order to take into account the composition of the coal, hi another embodiment of the present invention, the feed rate of the coal is correlated to the feed rate of steam, hi a further embodiment, steam is injected at a rate between about 0.2 and about 0.8 lb/min, for example, about 0.5 lb/min.

As is known in the art, many different grades of coal are available. Even within a single grade, coal is a complex material that exhibits substantial variability. The gasification process of the present invention recognizes such variability and compensates for it in the following manner. The parameters of the synthesis gas, i.e.

/ temperature, flow rate and composition, are monitored at the synthesis gas outlet of the reactor vessel. The above-described inputs of the reactants (coal, steam and/or oxygen) are varied to maintain the parameters of the synthesis gas within an acceptable ranges, which are defined by the end use of the synthesis gas.

In one embodiment of the present invention, the total amounts of coal which enter the reactor vessel per unit time and the vitrified slag which exits the reactor vessel are determined and maintained substantially constant. The amount of carbon in the exit gas stream is estimated from the observed flow rate plus the percent of carbon monoxide and the percent of carbon dioxide. The above-described rate of feed of coal is adjusted to maintain the flow of carbon through the reactor vessel as constant as possible.

The above-described rates of injection of steam and oxygen are adjusted to account for any changes in the rate of feed of coal or changes in the composition of the coal, and to provide the desired synthesis gas composition. Finally, the plasma torch power is adjusted to maintain the gasification temperature constant despite any fluctuations in the composition of the coal and corresponding above-described rates of feed of steam and oxygen.

The present invention also contemplates the substitution of conventional medium pressure steam for the conventional low pressure steam in the process.

One or more of the reactants that are fed into the process (i.e. coal, steam and/or oxygen) can be pre-heated. hi one embodiment of the present invention, feed temperatures for the process inputs are selected in order to take best advantage of waste heat from both the gasification equipment and the electrical generation system, ' in order to optimize system economics.

hi a further embodiment, the process, by employing the corrective feedback procedure, automatically adjusts the gas flow and the gas composition within specified limits as the composition of the coal undergoes its normal variation. As a result, the amount of coal that is gasified will vary with time.

Figure 2 shows one embodiment of reactor controls contemplated by the present invention. Generally speaking, the reactor inputs of coal, steam and oxygen are preheated before they are fed into the reactor vessel 10. Thus water is fed to a first pre-heater 212 via water line 214 and steam at a temperature of about 100 ⁰C is fed into the reactor vessel 10 via steam line 216.

Pulverized coal of a size as previously defined is fed through pulverized coal line 218 to a second pre-heater 220 where it is heated to a temperature in excess of about 100⁰C. Such pre-heated pulverized coal is fed to the reactor vessel 10 via heated coal line 222.

Oxygen is fed through oxygen line 224 to a third pre-heater 226, where it is heated to a temperature in excess of about 100⁰C. Such heated oxygen is fed to the reactor vessel 10 via heated oxygen line 228. The flow rate, the temperature, the percent carbon dioxide, the percent carbon monoxide and the percent hydrogen are all monitored at monitoring line 230.

Plasma heat to the reactor vessel 10 is generated by activating the plasma torches 16 and 18, and schematically enters the reactor vessel 10 via line 232, as input C4.

In one embodiment, the heat for the pre-heaters 212, 220 and 226 can be provided by the heat that is generated from the gasification process.

As noted above, the amounts of coal, oxygen, and steam and the power to the plasma torches are corrected on the basis of monitoring the flow rate of the exit synthesis gas, the exit temperature of the exit synthesis gas and the composition of the exit gas. In accordance with one embodiment of the present invention, this monitoring employs the process logic shown in Figure 3.

The numerical value of the flow rate of carbon monoxide and carbon dioxide in the exit gases via lines 312, 314 is inputted into a first processor 316 along with the numerical value of the rate of feed of coal in line 318 (input Cl). First processor 316 estimates the amount of carbon in the reactor vessel 10 and adjusts the coal feed rate accordingly.

Output from first processor 316, and which provides a measure of the numerical value of the percent carbon monoxide and the percent carbon dioxide (output Cl) is inputted via line 320 to second processor 322 along with the numerical value of the percent hydrogen via line 324, and the numerical values of steam (control input C2) and oxygen (control input C3) via line 326. Second processor 322 estimates new oxygen and steam inputs to achieve the desired gas composition.

Output from second processor 322, i.e., output Cl, output C2 and output C3, are inputted into third processor 328 via line 330 along with an input representative of the numerical value of the exit gas temperature via line 332. Third processor 328 computes new torch power which outputs as torch power (C4) via line 334. The invention will now be described with reference to a specific example. It will be understood that the following example is intended to describe an embodiment of the invention and is not intended to limit the invention in any way.

EXAMPLE

A particular low-rank coal having a high heating value of about 22,360 MJ/metric tonne (about 9600 BTU) was used. The elemental composition thereof was:

C: 53.9%

H: 6.9%

O: 33.4%

N: 1%

S: 5%

Ash 4.3%

The gasification process is operated to provide a synthesis gas which exits the reactor vessel 10 at a temperature of about 900⁰C, has a flow rate (wet) of about 2817 NmVtonne of the above coal, and the following composition:

CARBON MONOXIDE 25.695%

CARBON DIOXIDE 11.524%

HYDROGEN 28.310%

STEAM 31.331%

METHANE 0.854%

ACETYLENE 0.138%

HYDROGEN SULFIDE 0.127%

To achieve such gas composition, the process requires about 560.1 kg of oxygen plus 674.8 kg of steam per average tonne of coal. If the oxygen and coal are not pre- heated, and if the steam is supplied at 100⁰C and 1.01 bar, then the process will require an average of about 521.8MJ of plasma heat (about 193.3 KWh/tonne of electricity to the plasma torch, with normal efficiencies). The amount^'of plasma heat that is required can be reduced if the process inputs are pre-heated. For example, if the oxygen is pre-heated to about 600⁰C, but the steam and coal are unchanged, and then the average plasma torch requirements are reduced to about 96 KWh/tonne. If the oxygen is pre-heated to about 600⁰C, and if the coal is pre-heated to about 55°C, then the torch power can be reduced to about 60 KWh/tonne.

The carbon-containing gases (carbon monoxide and carbon dioxide) are thus measured on exit. This dictates a lower or higher carbon input, as coal, to bring the carbon content to the desired level as designed.

The amounts of the hydrogen and steam are also measured. The amount of the steam may be varied to bring the hydrogen to the desired level while simultaneously adjusting the oxygen level.

The gas temperature is also measured. The power to the first plasma torch configuration(s) is varied to bring the temperature to the desired value.

Although the invention has been described with reference to certain specific embodiments, various modifications thereof will be apparent to those skilled in the art without departing from the spirit and scope of the invention as outlined in the claims appended hereto.

The disclosure of all patents, publications, including published patent applications, and database entries referenced in this specification are specifically incorporated by reference in their entirety to the same extent as if each such individual patent, publication, and database entry were specifically and individually indicated to be incorporated by reference.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for producing synthesis gas and vitreous slag from coal, said process comprising the steps of: passing coal into a gasification zone at a coal input rate; passing oxygen into said gasification zone at an oxygen input rate; subjecting said coal to the heating effect of a first plasma torch configuration in the presence of the oxygen to provide a first gaseous product and by-product ash; passing the first gaseous product to a reforming zone; adding steam to said first gaseous product at a steam input rate to convert the first gaseous product to a synthesis gas; passing said by-product ash into a melting zone; subjecting said by-product ash to heating by a second plasma torch configuration to convert the by-product ash to slag and maintain the slag in a molten condition; exhausting the molten slag from the melting zone, and allowing said molten slag to cool to provide said vitreous slag.

2. The process according to claim 2, wherein the gasification zone, the reformation zone and the melting zone are located within a single reactor vessel and further comprising the step of exhausting said synthesis gas from the reactor vessel.

3. The process according to claim 1 or 2, further comprising a corrective feedback procedure that comprises one or more of the following steps: monitoring the composition of the synthesis gas, monitoring the synthesis gas flow and monitoring the synthesis gas temperature.

4. The process according to claim 3, wherein said corrective feedback procedure further comprises the step of adjusting one or more of the coal input rate, the oxygen input rate and the steam input rate to provide a desired synthesis gas composition.

5. The process according to claim 3, wherein said corrective feedback procedure further comprises the step of adjusting one or more of the coal input rate, the oxygen input rate and the steam input rate to account for a change in the synthesis gas composition.

6. The process according to any one of claims 3 to 5, wherein said corrective feedback procedure further comprises the step of adjusting one or both of the oxygen input rate and the steam input rate to account for a change in the coal input rate.

(

7. The process according to claim 2, further comprising a corrective feedback procedure that consists of the following steps:

(a) measuring the flow rate of carbon monoxide and carbon dioxide in the synthesis gas as it exits the reactor vessel to provide a. measured flow rate;

(b) measuring the coal input rate to provide a measured input rate;

(c) calculating the amount of carbon in the reactor vessel based on the measured flow rate and measured input rate;

(d) adjusting the coal input rate if the calculated amount of carbon in the reactor vessel is outside an acceptable carbon range;

(e) measuring the amount of carbon monoxide and carbon dioxide in the synthesis gas as it exits the reactor vessel to provide a measured gaseous carbon amount;

(f) measuring the amount of hydrogen in the synthesis gas as it exits the reactor vessel to provide a measured hydrogen amount;

(g) measuring the amount of steam added to the reactor vessel to provide a measured steam amount;

(h) measuring the amount of oxygen passed into the reactor vessel to provide a measured oxygen amount; (i) adjusting one or both of the steam input rate and the oxygen input rate if the measured gaseous carbon amount is outside an acceptable gaseous carbon range and/or the measured hydrogen amount is outside an acceptable hydrogen range; (j) measuring the temperature of the synthesis gas as it exits the reactor vessel to provide a measured temperature, and (k) adjusting the power to the first plasma torch configuration if the measured temperature is outside an acceptable temperature range.

8. The process according to any one of claims 1 to 7, wherein the coal is pulverized.

9. The process according to any one of claims 1 to 8, further comprising the step of preheating the coal before passing the coal into the gasification zone.

10. The process according to any one of claims 1 to 9, further comprising the step of preheating the oxygen before passing the oxygen into the gasification zone.

11. The process according to any one of claims 1 to 10, further comprising the step of preheating the steam before adding the steam to the first gaseous product.

12. The process according to any one of claims 1 to 11, further comprising the step of recovering sensible heat.

13. The process according to claim 12, further comprising the step of preheating one or more of the coal, oxygen and steam with the recovered sensible heat.

14. The process according to any one or claims 1 to 13, further comprising the step of monitoring the temperature one or more locations around the reactor vessel.

15. An apparatus for producing synthesis gas and vitreous slag from coal by the process according to claim 1, said apparatus comprising: a gasification zone; one or more coal inputs in operative communication with said gasification zone for passing coal into said gasification zone; one or more oxygen inlets in operative communication with said gasification zone for passing oxygen into said gasification zone; a first plasma torch configuration positioned to provide a first plasma discharge into said gasification zone and thereby convert said coal and said oxygen into a gaseous product and by-product ash; a reforming zone in operative communication with said gasification zone whereby the first gaseous product passes from said gasification zone into said reformation zone; one or more steam inlets positioned to add steam into said reformation zone and thereby convert said gaseous product into synthesis gas; a synthesis gas outlet in operative communication with said reforming zone for exhausting said synthesis gas from the reformation zone; a melting zone in operative communication with said gasification zone whereby said by-product slag passes from said gasification zone into said melting zone; a second plasma torch configuration positioned to provide a second plasma discharge towards said melting zone and thereby convert said by-product ash into molten slag, and a slag, outlet in operative communication with said melting zone for exhausting said molten slag, wherein the molten slag cools to provide vitreous slag.

16. The apparatus according to claim 15, wherein said gasification zone, said reformation zone and said melting zone are located within a single reactor vessel.

17. The apparatus according to claim 15 or 16, further comprising means for adjusting the amounts of one or more of coal, steam and oxygen that are fed into the reactor vessel.

18. The apparatus according to any one of claims 15 to 17, further comprising gas monitoring means for monitoring the synthesis gas.

19. An apparatus for producing synthesis gas ana vitreous slag trom coal^SSltr apparatus comprising: a refractory-lined reactor vessel; a slag reservoir located at a bottom end of the reactor vessel; an axial synthesis gas outlet associated with the reactor vessel for exhausting said synthesis gasl; a first plasma torch configuration for generating a first plasma discharge, said first plasma torch configuration associated with said reactor vessel and positioned to direct the first plasma discharge into the reaction vessel; a second plasma torch configuration for generating a second plasma discharge, said second plasma torch configuration associated with said reactor vessel and positioned to direct the second plasma discharge towards the slag reservoir; a slag outlet associated with said reactor vessel and positioned to exhaust molten slag from the slag reservoir; one or more coal inlet associated with said reactor vessel and positioned to inject coal into the first plasma discharge; one or more oxygen inlets associated with said reactor vessel and positioned to inject oxygen into the first plasma discharge; and one or more steam inlets associated with said reactor vessel to inject steam into said reactor vessel.

20. The apparatus according to claim 19, further comprising means for adjusting the amounts of one or more of coal, steam and oxygen that are fed into the reactor vessel.

21. The apparatus according to claim 19 or 20, further comprising gas monitoring means for monitoring the synthesis gas.

22. The apparatus according to claim 21, wherein the gas monitoring means monitors one or more of the temperature, the flow rate and the composition of the synthesis gas.

23. The apparatus according to claim 21, wnerem tne gas monitoring means- monitors the composition of the synthesis gas.

24. The apparatus according to claim 21, wherein the gas monitoring means comprises a gas flow meter.

25. The apparatus according to any one of claims 21 to 24, wherein the gas monitoring means is located proximal to the axial synthesis gas outlet.

26. The apparatus according to any one of claims 19 to 25, comprising two oxygen inlets.

27. The apparatus according to any one of claims 19 to 26, further comprising preheating means for preheating one or more of the coal, the steam and the oxygen before injection into the reactor vessel.

28. The apparatus according to claim 27, wherein said preheating means comprises a heat exchanger for recovering sensible heat from the gasification process and utilizing the recovered sensible heat to preheat one or more of the coal, the steam and the oxygen.

29. The apparatus according to any one of claims 19 to 28, further comprising means for adjusting power to one or both of the first plasma torch configuration and the second plasma torch configuration.