GB2160219A

GB2160219A - Carbon gasification

Info

Publication number: GB2160219A
Application number: GB08427969A
Authority: GB
Inventors: Sven Santen; Kari Trog
Original assignee: SKF Steel Engineering AB
Current assignee: SKF Steel Engineering AB
Priority date: 1984-06-14
Filing date: 1984-11-05
Publication date: 1985-12-18
Also published as: JPS614788A; IT1177078B; ES538141A0; AU577071B2; YU45682B; NO844797L; GB8427969D0; SE8403190D0; FR2565993A1; SE8403190L; NZ210165A; KR860000354A; ES8602099A1; SE453750B; GB2160219B; CN85101040A; AU3525484A; YU202084A; IN162480B; BR8406068A

Abstract

The present invention relates to generating a hot gas consisting primarily of CO and H2 from a carbonaceous starting material which, in pulverulent form, together with oxidizing agent and optionally also a slag-former, is introduced into a gasification chamber, where it is combusted and partially gasified. The resultant gas mixture is then introduced into a shaft containing a bed of solid carbonaceous lump material. The physical thermal content of the mixture emerging from the gasification chamber is used in the coke bed to reduce the content of carbon dioxide and/or water in the gas. The gas generating process is controlled so that the gas leaving has a temperature and a composition suitable for a following process step.

Description

SPECIFICATION Carbon gasification The present invention relates to a process for generating a hot gas consisting primarily of CO and H2 from a carbonaceous starting material which, in pulverulent form, with the aid of a carrier gas, together with oxidizing agent and optionally also a slag-former, is introduced into a gasification chamber, said starting material in said chamber being partially combusted and at least partially gasified.

Reduction or combustion gas based on a content of carbon monoxide and hydrogen is currently generated using several types of processes, which operate in accordance with a variety of entirely different principles, and all of which have certain drawbacks. The energy required is usually generated by combustion of a carbonaceous starting material injected into an empty chamber with oxidizing agent.

To cover the energy requirement in the process a certain amount of the CO and H2 formed must be combusted to CO2 and H2O, and this results in the gas having higher contents of carbon dioxide and water than desired.

Consequently, the gas generated in known carbon gasification processes must be relieved of a part of its carbon dioxide content and this means that the gas must first be cooled before being heated again. In other processes such a low temperature is used that tar and phenols are formed. The gas must therefore be washed and then reheated if it is to be used in subsequent process steps.

Against the background of the above, the prime object of the present invention is to effect a process for generating a hot reduction or combustion gas consisting primarily of carbon monoxide and hydrogen, said process permitting control of the temperature and composition of the emerging gas, as well as the process offering optimal utilization of energy.

This and other objects are achieved with the proces according to the present invention, in which the starting material is partially combusted and at least partially gasified in a gasification chamber, after which the resultant mixture is introduced into a shaft containing a bed of solid carbonaceous lump material; the physical thermal content of the mixture emerging from the gasification chamber is used in the bed of solid carbonaceous lump material to reduce the content of carbon dioxide and water in the gas, and the gas generating process is controlled so that the gas leaving has a temperature and a composition suitable for the following process step.

Preferably the solid carbonaceous lump material is coke.

The oxidizing agent may consist of 2 CO2, H2O, air or various arbitrary mixtures thereof.

According to one embodiment of the invention the energy required is generated in the gasification chamber by supplying an excess of air and/or oxygen gas with a maximum of ca.20% H20 which reacts exothermically or autothermically with a part of the carbonaceous starting material.

According to a second embodiment of the invention external thermal energy is supplied to the gasification chamber. This external thermal energy may be supplied by means of a gas heated in plasma generators, the gas being selected from a group consisting of 02, H20, air and recycled gas containing CO + H2 + CO2 + H20, or mixtures of two or more components from the group.

According to another embodiment of the invention the transport gas consists of the oxidizing agent.

According to a further embodiment of the invention water vapour for introducing material and/or for use as carrier gas is partially or wholly generated with the aid of coolant heated in a pressurized cooling system in water-cooled parts of the installation and/or by making use of the physical heat in the gas generated.

According to a further embodiment of the invention the physical thermal content of the gas mixture emerging from the gasification chamber is used to convert gas injected into the coke bed, and containing carbon dioxide and/or water, to carbon monoxide and hydrogen.

According to a further embodiment of the invention the entire gas generating proces is controlled by analyzing the oxygen potential in the gas mixture before and/or after the coke-filled shaft.

According to a further embodiment of the invention the slag is fed separately out of the gasification chamber and the coke-filled shaft.

Alternatively all the slag may be removed from the shaft.

According to a further embodiment of the invention sulphur acceptors are injected in pulverulent form into the gasification chamber and/or in lump form into the coke shaft.

According to yet another embodiment of the invention the material injected into the gasification chamber is given a rotary motion produce a slag layer protecting the inner walls of the gasification chamber.

Additional features, advantages and embodiments of the invention will be revealed in the following detailed description.

The process is of course not limited to only one gasification chamber per shaft. On the contrary, several gasification chambers are preferably arranged in connection with one coke-filled shaft.

There are considerable advantages in performing the majority of the gasification reactions in a gasification chamber and then completing the reactions in a coke bed.

One advantage is that gasification can be performed at a high temperature which shall always be above the melting point of the slag, and generally above ca 1 400'C, after which the physical thermal content of the gas can be utilized in the subsequent shaft to perform the carburizing reactions which are discontinued at about 1 000 C.

As intimated above, the excess heat in the gas can be used in several ways. For instance, a relatively high content of carbon dioxide is permitted in the gas generated in the gasification chamber, and this is then converted to carbon monoxide in the coke bed, utilizing the physical thermal content of the gas.

The advantage of working with increased CO2 content in the gasification stage is that the resultant higher oxygen potential gives higher reaction speed between the fuel and the oxidizing agent and at the same time, the process is caused to operate further from the limit where soot deposits occur.

Another, or supplementary method of exploiting the surplus heat is to inject carbon dioxide and/or water into the coke bed. This can be achieved, for instance, by utilizing a partially spent recycled gas with a high content of carbon dioxide and water.

The coke bed fulfils a number of important functions, as indicated above, and as will be described in more detail below.

The coke bed collects any coke particles and slag drops accompanying the gas mixture from the gasification chamber. These particles and drops will then be returned to the process as the coke in the coke bed is spent. The fuel is thus used extremely efficiently.

The coke bed also functions as a heat store, equalizing any variations in the heat supplied in the gasification chamber. It also acts as carbon store, equalizing any variations, in the quantity of carbonaceous material supplied in relation to the quantity of oxidizing agent supplied. This in turn gives reduced risk of explosion, in practice entirely eliminating this risk, even should pure oxygen be added without an equivalent quantity of carbonaceous material being supplied to the gasification chamber. The risk of explosion is otherwise an extremely serious problem.

The fuel or the carbonaceoous starting material is supplied in finely distributed form. If it consists of pulverulent, solid material this may be injected with the aid of water vapour, for instance, according to the preferred embodiment of the invention.

The carbonaceous starting material may be selected from a group consisting of oil, coal, coke, charcoal, gas, peat, saw-dust and various mixtures thereof. This offers considerable economic advantages over the known gasification processes, all of which are limited with respect to the choice of starting material. To a great extent the coke consumption is kept low since the oxidizing agent is forced to react with the carbonaceous material in the gasification chamber before it reaches the hot, and thus reactive, coke.

If only combustion is utilized to generate the heat required for the reactions, a limitation is caused by the thermal balance of the reactions, which results in a relatively high carbon dioxide content. This has previously meant that carbon dioxide must be subsequently removed from the gas in a separate process stage. However, in the process according to the invention, this involves no problem. When oxygen is used as oxidizing agent with the addition of H2O, autothermic conditions will occur if ca.20% water is added, i.e. the reactions continue but no excess energy is generated. If thermal energy is supplied externally, excess energy is obtained which, according to the above, can be used in the following coke bed.Electric energy can thus be used, preferably by the use of plasma generators in which a carrier gas is heated to a considerable temperature upon passage through an electric arc generated between electrodes in the plasma generated. In the preferred embodiment, the carrier gas used is oxygen and water vapour. However, water vapour, a mixture of H20 and oxygen, pure oxygen or even air may be used as carrier gas.

The supply of external energy enables the use of a spent reducing gas containing high contents of carbon dioxide and water as oxidizing agent.

According to a preferred embodiment, the process can be controlled by recording the content of CO2 or 0? partial pressure in the gas generated, immediately after the gasification chamber, prior to entering the coke bed and/or in the gas outlet after the coke bed.

The analysis immediately after the gasification chamber is preferably utilized to control the ratio between carbonaceous material fed in and oxidizing agent, and possibly also the temperature of the gas leaving, whereas the analysis of the gas after the coke bed is used to control the quantity of CO2 and/or H20 fed into the coke bed. A final gas can thus be produced having the composition and temperature desired for the process following, which may be a sponge-iron proces, for instance, while at the same time almost optimal energy consumption is achieved.

In view of the high temperatures used in the process, at least parts of the shaft, and the entire gasification chamber with its burners, must be water-cooled. Arranging the cooling system to operate under pressure, preferably in the vicinity of 5-6 bar overpressure, enables the heated coolant to be used to generate steam which can then be used as carrier and/or transport gas. Heat losses from the cooling system can thus be utilized.

The gasification chamber shall preferably have substantially circular inner walls. According to the invention the flows of gas and material introduced into the gasification chamber can then be given a rotatory motion. Slag particles will then be separated off and form a protective layer on the inner walls of the gasification chamber. The thickness of this slag deposit is determined by the thermal balance between thermal energy removed to the cooling casing and thermal energy supplied to the slag surface by convection and radiation. Excess slag runs out through a slag overflow which may be arranged separately for the gasification chamber, or may be combined with the slag overflow for the shaft.

Slag-formers and/or sulphur acceptors in finely divided form, may be injected into the gasification chamber together with the carbonaceous material or separately from it and/or they may be introduced together with the solid carbonaceous material in lump form in the shaft, thus forming a part of the coke bed.

To achieve rapid and efficient mixing between the hot gas generated in the plasma generator and the pulverulent, carbon-carrying fuel supplied, the hot gas is introduced through the orifice of the plasma generator into the gasification chamber. This is achieved by the carrier gas being given a rotary motion during its passage through the plasma generator, the pulverulent fuel having been given a rotary motion prior to entering the gasification chamber, and/or by the plasma generator and/or supply means for carbonaceous fuel being arranged to open tangentially into the gasification chamber. This will cause the hot gas to expand upon entering the gasification chamber and this turbulence will provide an extremely short mixing space.

The invention will now be described more fully with reference to the accompanying drawing showing one embodiment of an installation for performing the process according to the invention.

The figure shows a gasification plant having a gasification chamber 1, and a shaft 2 filled with coke 3.

The gasification chamber 1 has an outer, water-cooled casing 4 and a refractory lining 5 and is preferably essentially cylindrical. Several gasification chambers are preferably arranged in connection with one shaft.

The shaft 2 has a lower slag outlet 6 and an upper gas outlet 7. Coke in lump form is supplied to the shaft through a gas-tight supply means 8 at the top of the shaft. The gasification chamber 1 leads into the lower part of the shaft, from whence the gas passes up through the coke bed and out through the gas outlet. In the embodiment shown the slag outlet 6 is common for both gasification chamber and shaft.

Associated with the gasification chamber is at least one burner consisting, in the embodiment shown, of a plasma generator 9. The plasma generator is connected to the gasification chamber via a valve means 1 0. Oxidizing agent is introduced into the plasma generator through a supply pipe 11. The oxidizing agent may comprise a carrier gas which is led through the plasma generator or a separate carrier gas may be used. The hot, turbulent gas generated in the plasma generator, is introduced into the gasification chamber through the opening 1 2 of the plasma generator.The carbonaceous fuel, preferably in pulverulent form, is introduced with the aid of a transport gas through a supply pipe 1 3 into an annular gap 14 arranged concentrically around the plasma generator, and/or lance 1 5 which may also be used with advantage for the supply of any additive, such as slagformer.

Lances 16, 1 7 are also arranged in the shaft for the supply, if necessary, of additional oxidizing agent, such as H20 or CO2, to exploit the physical surplus heat in the gas. This also allows for control of the temperature and composition of the gas.

At the end of the gasification chamber close to the coke bed, a first sensing device 1 8 is arranged and a second sensing device 1 9 is arranged in the gas outlet 7 from the shaft for measuring temperature and/or analyzing the gas. These two sensing devices enable control of the process by regulation of the external energy supplied and/or by variation in the flows of material supplied.

The figure shows only one embodiment of a plant for performing the process according to the invention and many other solutions are feasible. For example, the plasma generators or burners may be arranged tangentially on the periphery of the gasification chamber so as to produce a circulating flow in the gasification chamber. Furthermore, to facilitate slag separation, the gasification chamber may be vertical, or the gasification chamber and shaft may have separate slag outlets.

Claims

1. A method for generating a hot gas consisting primarily of CO and H2 from a carbonaceous starting material, in which starting material in pulverulent form, together with oxidizing agent and optionally also a slagformer, is introduced into a gasification chamber with the aid of a transport gas, the starting material being partially combusted and at least partially gasified in the gasification chamber, the resultant mixture is introduced into a shaft containing a bed of solid carbonaceous lump material, wherein the physical thermal content of the mixture emerging from the gasification chamber is used in the bed of lump material to reduce the content of carbon dioxide and water in the gas, and wherein the gas generating process is controlled so that the gas leaving the shaft has a temperature and a composition suitable for use in a following process step.

2. A method according to claim 1, wherein the oxidizing agent is 02, H2O, CO2 or air or mixtures thereof.

3. A method according to claim 1 or claim 2, wherein the energy required is generated in the chamber by supplying an excess of air and/or oxygen gas with a maximum of ca.20% H20 which reacts exothermically or autothermically with a part of the carbonaceous starting material.

4. A method according to claim 1 or claim 2, wherein external thermal energy is supplied to the gasification chamber.

5. A method according to claim 4, wherein the external thermal energy is supplied by means of a carrier gas heated in a plasma generator.

6. A method according to claim 5, wherein the carrier gas is selected from a group consisting of 02, H2O, air, recycled gas containing CO + H2 + CO2 + H2O, or mixtures of two or more components from this group.

7. A method according to any one of claims 1 to 6, wherein the transport gas consists of the oxidizing agent.

8. A method according to any one of claims 1 to 6, wherein recycled gas is used to inject pulverulent, carbonaceous starting material.

9. A method according to any one of claims 1 to 8, wherein water vapour optionally used for introducing material and/or as carrier gas is partially or wholly generated with the aid of coolant heated in a pressurized cooling system in water-cooled parts of the installation.

1 0. A method according to any one of claims 5 to 9, wherein the hot carrier gas emerging from the plasma generator is given a rotary movement before being introduced into the gasification chamber and the pulverulent carbonaceous fuel is introduced concentri cally around the hot gas flowing into the gasification charnber.

11. A method according to any one of claims 1 to 1 0, wherein the physical thermal content of the gas emerging from the gasification chamber is used to convert gas injected externally into the coke bed, and containing carbon dioxide and/or water, to carbon monoxide and hydrogen.

1 2. A method according to any one of claims 1 to 11, wherein the gas-generating process is controlled by analyzing the carbon dioxide content or oxygen potential in the gas mixture before and/or after the coke-filled shaft.

1 3. A method according to any one of claims 1 to 12, wherein the slag is fed separately out of the gasification chamber and the coke-filled shaft.

14. A method according to any one of claims 1 to 12, wherein the slap from the gasification chamber is fed to the shaft, from whence all the slag is then removed.

1 5. A method according to any one of claims 1 to 14, wherein sulphur acceptors are injected in pulverulent form into the gasification chamber and/or in lump form into the coke shaft.

1 6. A method according to any one of claims 1 to 15, wherein the material in the gasification chamber is given a rotary movement to produce a slag layer protecting the inner walls of the gasification chamber. 1 7. A method for generating gas from a carbonaceous starting material according to claim 1 and substantially as herein described with reference to the drawings.