GB2180849A

GB2180849A - Producing clean gas containing hydrogen and carbon monoxide

Info

Publication number: GB2180849A
Application number: GB08622866A
Authority: GB
Inventors: Sven Santen; Lars Bentell
Original assignee: SKF Steel Engineering AB
Current assignee: SKF Steel Engineering AB
Priority date: 1985-09-25
Filing date: 1986-09-23
Publication date: 1987-04-08
Also published as: SE457355B; ATA256086A; AT396366B; IT8621793A0; AU589997B2; FI863726A0; CA1309589C; BE905480A; AU6258286A; IT1213497B; GB2180849B; DE3631015A1; JPS6274993A; FR2587717B1; FI863726A; SE8504439D0; IL80027A0; SE8504439L; JP2509192B2; BR8701328A

Abstract

In a method of producing a gas containing carbon monoxide and hydrogen, in which method the gas does not need to be subjected to energy-consuming and costly scrubbing steps before being used as reduction gas, combustion gas or synthesis gas, the gas is produced from material containing carbon and/or hydrocarbon and oxidant and is supplied to a reaction chamber (2) simultaneously with a gas heated by plasma generator (at 3), in order to crack the hydrocarbon in the gas. The gas may be passed through a limestone or dolomite filling to the remove sulphur therefrom. <IMAGE>

Description

SPECIFICATION A method of producing a clean gas containing carbon monoxide and hydrogen The present invention relates to a method of producing a gas containing carbon monoxide and hydrogen, permitting the use of commercially known technology and utilizing any form of starting material containing carbon and/or hydrocarbon, according to which the gas does not need to be subjected to energy-consuming and costly scrubbing steps before being used as reduction gas, combustion gas or synthesis gas.

In processes utilizing combustion to supply energy, and in processes utilizing starting materials other than dried coke, such as bituminous coal, peat and the like, a gas is obtained which contains H20 and hydrocarbon as well as CO+H2.

Normally a maximum CO2+H2O content of about 10% in the gas is aimed at, while at the same time the content of heavy hydrocarbons should be as close to 0% as possible.

In traditional gasification processes using oxygen gas (air) and steam, where gas and carbonaceous material move in counter-flow, it is possible to make extremely good use of the heat but, due to the low reaction temperature, this gas will contain large amounts of tar. Furthermore, a residual product is obtained in the form of ash, which is difficult to dispose of in a manner not detrimental to the environment. Considerable advantages can be gained by increasing the reaction temperature in the combustion stage so that the ash melts, and by increasing the process pressure. The solidified slag drawn off is extremely resistant to leaching and the production per unit volume of the reactor is increased.Furthermore, the excess oxygen can be kept at a reasonable level for reduction processes, i.e. less of the carbon monoxide formed need be combusted to CO2 to cover thermal losses, for instance. However, the problem of tar still remains, and the gas therefore cannot be used directly as the reduction gas, for instance.

The principal object of the present invention is thus to achieve a method which will permit the use of any form of starting material containing carbon and/or hydrocarbon for the gas generation, while also utilizing commercially known technology, in which the gas does not need to be subjected to energy-consuming and costly scrubbing steps before being used as reduction gas, combustion gas or synthesis gas.

The principal object is achieved by the method according to the present invention in which the gas produced from material containing carbon and/or hydrocarbon and oxidant is supplied to a supplementary reaction chamber simultaneously with a gas heated by plasma generator, in order to crack the hydrocarbon in the gas.

It has been found that by supplying a hot gas, heated by plasma generator and thus having extremely high energy density, a thermal disintegration of the hydrcarbon in the gas from the gasifier is obtained, as well as the reaction with H2O, 02 and/or CO2 in the gas to form H2 and CO. Due to the high energy density in the gas supplied, a comparatively small volume of gas is required, which thus makes the process possible.

The gas can be produced by means of pyrolysis or partial combustion of material containing carbon and/or hydrocarbon, such as peat, pit coal, anthracite, or forest waste. If coke-oven gas derived from pyrolysis of pit coal is to be used there will be other contaminants as well as hydrocarbons. A great advantage with the invention is that these will also be cracked in the supplementary reaction chamber.

According to one embodiment of the invention, after passing the supplementary reaction chamber, the gas is conducted through a limestone or dolomite filling to remove sulphur. The limestone or dolomite used for said sulphur purification will also act as catalyst in cracking hydrocarbon and in the reaction with oxidant. This enables the electrical energy consumption to be correspondingly lowered in the supplementary reaction chamber.

According to another embodiment of the invention the content of CO2+H20 in the gas from the supplementary reaction chamber is controlled to below 5%.

Additional advantages and features of the invention will be revealed in the following detailed description with reference to the accompanying drawing showing schematically the flowchart for a gas-producing process according to the present invention connected to a subsequent reduction process.

A crude gas is produced in a gasifier or coke oven designated 1. The crude gas generated is supplied to a supplementary reaction chamber 2. At least one plasma generator 3 is arranged in conjunction with the supplementary reaction chamber, for the supply of a hot gas having high energy density. The hydrocarbon in the crude gas is cracked in the supplementary reaction chamber and reacts to form CO+H2. Finely divided coke or H20 may be introduced through lances 4 in the supplementary reaction chamber, to adjust the hydrogen/carbon ratio.

After this the gas is subjected to sulphur purification in the shaft 5 which contains a filling 6 of limestone or dolomite supplied through a gastight sluice arrangement 7 and consumed filling is withdrawn at the bottom of the shaft through a gastight sluice arrangement 8. Any hydrocarbons remaining in the gas are also catalytically cracked in the limestone or dolomite filling. This can be utilized to reduce the electric energy consumed in the plasma generator 3 used for thermal disintegration of the hydrocarbon content.

The gas purified in this way and containing substantially only H2+CO and a small quantity of H20+CO2, can then be transported to a chamber 9 to be controlled with respect to temperature and composition before entering a shaft furnace 10 for reduction of oxidic material.

The gas produced is supplied through an inlet 12 at the bottom of the shaft furnace 10 and is caused to flow in counter-flow with the material containing metal oxide. The partially consumed gas containing impurities and dust is withdrawn through an outlet 13 and cleaned in a scrubber 14.

The cleaned, partially consumed gas can then be used for other purposes, as indicated by the filter 15. If necessary, some of the gas can be recirculated in the process via pipes 16, 16a, 1 6b and may be used, for instance, in the mixing chamber 9 to control the temperature and composition of the gas to be introduced into the shaft. Part of the recirculated gas may also be used in the plasma generator in conjunction with the supplementary reaction chamber.

The invention is further illustrated by the following example.

Example 10 ton forest waste containing 30% water and the following composition C H O N S Ash 51 6,2 42 0,2 0,5 0,5% is introduced at the top of a counter-flow gasifier per hour while an oxidant is introduced at the bottom of the gasifier in the form of air heated to 1000 C. The air added is 3700 Nm3. The composition of the top gas will be CO CO2 H2 H20 N2 CH4 25,8 9,8 41,1 4,8 15,8 2,9% At the same time a tar sample is withdrawn which indicates that the gas contains 3,2 gram tar/Nm3.

The temperature of the gas leaving is 550 C and its volume is approximately 17200 Nm3. The gas is now supplied to a supplementary reaction chamber and heated using air heated in plasma generators. The quantity of air required is only about 2100 Nm3. With the aid of the plasma generator the temperature of the gas entering is increased to 1250"C, with a consumption of approximately 8,7 MWh electric energy.

The methane and tar contents are thus removed from the heated pyrolysis gas and the gas leaving the chamber will have the following composition CO CO2 H2 H20 N2 28,6 4,8 29,6 13,6 23,4 The quantity of gas leaving will be approximately 19900 Nm3.

Claims

1. A method of producing a gas containing carbon monoxide and hydrogen which gas is substantially free from tar and is suitable for use as reduction gas, combustion gas or synthesis gas, comprising producing a gas from an oxidant and material containing carbon and/or hydrocarbon and supplying the gas to a reaction chamber simultaneously with gas heated by plasma generator, such that hydrocarbon in the gas is cracked.

2. A method according to claim 1, wherein after passing the supplementary reaction chamber, the gas is conducted through a-limestone or dolomite filling to remove sulphur, such that any remaining hydrocarbon is cracked and reaction with the oxidation occurs.

3. A method according to claims 1 or claim 2, wherein finely divided coke and/or water is injected into the supplementary reaction chamber.

4. A method according to any of claims 1 to 3, wherein the content of CO2+H2O in the gas from the supplementary reaction chamber is controlled to below 5%.

5. A method according to claim 1 and substantially as hereinbefore described with reference to the Example.