FI89810C - Process for the purification of gasification gas from nitrogen and sulfur compounds and organic pollutants - Google Patents

Description

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Method for cleaning gasification gas from inorganic nitrogen, sulfur compounds and organic pollutants - Förfarande för rening av förgasningsgas frän kväve- och svavelföreningar samt organiciska föroreningar 5

The invention relates to a process for purifying gasification gas from inorganic nitrogen and sulfur compounds as well as organic impurities by contacting it with a catalytic adsorption material. The gas formed in the gasification of solid fuel contains as impurities nitrogen compounds such as ammonia and hydrogen cyanide, as well as sulfur compounds such as hydrogen sulfide and carbonyl sulfide, which in the combustion of the gas form oxides of nitrogen and sulfur harmful to the environment. Organic contaminants such as tars cause problems at various stages of gas use by condensing or forming solid carbon upon decomposition.

In power plants using carbon-20 material such as coal, peat, wood waste or household waste, the best way to save energy is to burn gaseous fuel made from the above materials at an elevated temperature to run a gas and steam turbine. Such a so-called. The fuel consumption 25 of an SME plant is up to about 15% lower than current conventional power plants, while its emissions are reduced to a fraction of the corresponding emissions of current technology. Since the nitrogen and sulfur compounds and organic pollutants contained in the gasification gas of such a plant cause harm both to the environment and to the process machinery of the plant, a cheap and efficient method is required to remove the pollutants from the gasification gas.

In known methods for purifying a gasification gas, the gas is contacted with a catalytic adsorption material. Catalyst materials mentioned in previous patents or generally known to be effective against gaseous gas impurities include:

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1. dolomite and calcareous materials for tar decomposition and desulphurisation, 2. iron oxides for ammonia decomposition and desulphurisation, and 5 3. nickel compounds for tar decomposition.

SE-A-459 584 discloses the refining of a raw gas made from a carbonaceous material by means of a secondary step using a fluidized-bed fluidized bed of catalytic adsorption material, which decomposes the tar and ammonia in the raw gas at a high temperature. As the catalytic adsorption material, a magnesium carbonate-containing material such as dolomite or a similar calcined material is used. The publication thus shows that a catalytic adsorption material such as dolomite is best suited for removing tar and ammonia from the gasification gas. The effectiveness of that material in desulfurization is not discussed further.

DE-A-2 824 534 discloses a process for the purification of hot gases containing hydrogen sulphide and ammonia, in which an iron oxide-containing catalyst is first contacted with a gas to remove hydrogen sulphide and then reduced with a reducing agent to convert iron to a reduced form. . The publication is based on the finding that hydrogen sulfide, which is always present in the gas due to the equilibrium reaction, prevents the decomposition of ammonia by iron oxide-30a. If, instead, a process is performed in which the iron oxide is reduced to iron and the gas is brought into contact with the iron, the ammonia in the gas decomposes into nitrogen and hydrogen. However, the process requires the use of two separate reaction steps and similar equipment and the inclusion of an additional step in the process of reducing the iron oxide with hydrogen gas.

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JP-A-55161837 discloses the decomposition of a high molecular weight polycondensate (e.g. tar) of carbon gas by contacting it with an alkali or alkaline earth metal oxide. The process can be carried out by feeding iron ore with coal into the gases-5 thime, whereby the iron ore is reduced while the coal is gasified.

DD-A-242818 discloses a process for thermocatalytically decomposing hot crude gases 10 containing sulfur compounds and hydrocarbons, the gases being passed through a sulfur-sensitive cracking catalyst bed. The cracking catalyst preferably contains nickel. The conditions are preferably adjusted so that the thermodynamic system of nickel, carbon, hydrogen, oxygen and sulfur produces metallic nickel. This publication therefore discloses that a nickel-containing catalyst decomposes sulfur compounds and hydrocarbons in a gasification gas.

It appears from the foregoing that no mention has been made of any of the 20 materials published so far for a catalytic adsorption material which would be effective simultaneously and in the same process unit against nitrogen compounds, sulfur compounds and organic impurities. On the contrary, it has been found that the removal of both hydrogen sulfide and ammonia from the gasification-25 gas is a very laborious and multi-step process.

Eo. it is an object of the invention to provide an even simpler and less expensive method for purifying gasification gas from inorganic nitrogen and sulfur compounds and organic impurities. More specifically, the aim is to provide a one-step purification process for a gasification gas which also uses a cheap and preferably a naturally occurring or by-product substance as a catalytic adsorption material. These objects have now been achieved by a method which is mainly characterized by what is stated in the characterizing part of claim 1.

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It is thus understood that the gasification gas can be purified from inorganic nitrogen and sulfur compounds as well as organic impurities by contacting it with a catalytic adsorption material comprising a mixture of a metal oxide and an alkali or alkaline earth metal compound of the fourth phase of Group VIII of the Periodic Table. .

Eo. the process according to the invention is suitable for both single- and multi-stage processes in which one or more reactors can be used. However, it is preferred to contact the gasification gas with the catalytic adsorption material in substantially one reaction step, preferably using only one gas purification reactor.

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The gasification gas purification reactor can be, for example, a fixed-bed reactor or a vortex fluidized bed reactor according to the above-mentioned publications SE-459 584 and DE-28 24 534. In addition to the main reactors, after-reactors or gas scrubbers can be used, but 20 eo. in particular, the invention makes it possible to purify the gas substantially in one step. Air and / or oxygen can be fed to the gas purification reactor to provide proper decomposition and adsorption conditions.

According to an embodiment of the invention, the gasification gas is contacted with the catalytic adsorption material at a temperature of 600-1200 ° C, preferably at a temperature of 850-1000 ° C.

As the catalytic adsorption material, a mixture or compound of a metal (Fe, Co, Ni) oxide of the fourth phase of Group VIII of the Periodic Table and an alkali or alkaline earth metal carbonate or oxide is preferably used. In this case, the adsorption material is at least initially in the form of an oxide and possibly a carbonate, but it may deform under absorption conditions, in which case the invention is in fact directed to an oxide / oxide (carbonate) mixture or compound or a mixture or compound derived therefrom. 1 0 5 tea. The mixture may also contain other materials, e.g. sintering inhibitors and diluents, but said components form the actual active part of the adsorption material.

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As the metal oxide of the fourth phase of Group VIII, iron and / or nickel oxide, preferably iron oxide, is preferably used. The alkali or alkaline earth metal carbonate or oxide used is preferably calcium and / or magnesium carbonate or oxide, most preferably calcium oxide. The purification of the gas gas is generally carried out at such a temperature that the alkali or earth metal carbonate used is generally calcined to the corresponding oxide.

The concentrations of the active components of the catalytic adsorption material can vary over a wide range. The content of the Group VIII metal compound of the fourth period may, for example, vary between 1 and 70% by weight and preferably between 1 and 40% by weight. The content of the alkali or alkaline earth metal compound 20 may, for example, vary between 3 and 40% by weight. When concentrate sinter obtained from iron refining is used, the content of the iron compound is typically about 60% by weight and the content of the calcium compound is typically about 6% by weight. In the ferrous soil mineral eel, the concentrations are about 5% by weight (Fe) and about 20% by weight (Ca), respectively.

The material, which combines iron or nickel oxide and calcium oxide, simultaneously affects all the above-mentioned groups of impurities in the gasification gas. Therefore, material 30 can be used in one reactor. The effect is based on the fact that iron or Nikke decomposes ammonia or organic compounds almost completely at high temperatures. The calcium and / or magnesium contained in the catalyst, in turn, adsorbs sulfur considerably better than iron or nickel oxides at high temperature under gasification conditions. Calcium also catalyzes the decomposition reactions of tars and the gasification of carbon accumulating in the catalyst. Eo. the method according to the invention is best suited for use in the so-called gasification combined heat and power (SMEs) plants.

A mixture or compound comprising at least a metal oxide of the fourth period of Group V of the Periodic Table and a carbonate or oxide of an alkali or earth metal can be isolated from the soil in the form of a mineral such as anchor or recovered from products used or formed in metal processing such as concentrate or -10 pins. The mixture or compound can also be prepared separately, e.g. by fusing the prepared oxide mixture or by simply mixing the different metal oxide components together.

The following are a few examples which are intended solely to illustrate the present invention.

Example 1

The experiment was started by pouring the mattress material to be examined, which in this experiment was anchorite, onto a tubular reactor Ari-20 nan with a length of .50 mm and an inner diameter of 25 mm. The tubular reactor was installed inside the furnace elements, sealed and connected to the bypass line, and the tightness of the equipment was checked by pumping a vacuum into it and monitoring the maintenance of the vacuum. After the reactor was warmed to a test temperature of 25 ° C, it was connected to a heated probe mounted in the product gas tube.

In the next step, the suction of the sample gas stream from the carburetor used in the heating plant was started. The settling of the reactor internal temperatures was monitored from a plotter. The temperature of the furnace elements and their height around the reactor were adjusted to achieve the desired temperature profile. The gas flow rate was adjusted according to the desired contact time (0.1-0.5 s).

After stabilization of the reactor operation, a tar sample was taken from the cracked gas. The gas flow was then directed to the bypass line, and two parallel gas samples were taken from the 35 S 9 O 1 ö 7 gas cuvettes. After equalization, sampling was resumed.

At the reaction temperature of said 900 ° C, 75% of the ammonia contained in the gasification gas decomposed. The concentration of tar-like compounds in the gasification gas was initially about 100 g / m3, of which the concentration decreased to 0.1 g / m3. Concentrations of sulfur compounds were not measured, but it is known from the literature that calcium strongly adsorbs sulfur compounds at high temperatures.

Example 2

Example 1 was repeated, but iron concentrate sinter was used as the catalyst material. At a reaction temperature of 15,900 ° C, 90% of the ammonia in the gasification gas decomposed.

The concentration of tar-like compounds in the gasification gas was initially about 100 g / m3, of which the concentration was reduced to 3.6 g / m3 by sintering. Concentrations of sulfur compounds were not measured, but it is known from the literature that calcium 20 adsorbs sulfur compounds at high temperatures.

Claims (5)

A process for the purification of gasification gas from inorganic nitrogen and sulfur compounds and organic impurities by contacting it with a catalytic adsorbent, characterized in that the catalytic adsorbent material used is a mixture or compound of an oxide of a metal from the fourth period of group VIII of the periodic table and a carbonate or oxide of an alkali metal or an alkaline earth metal. 10 Process according to claim 1, characterized in that the gasification gas is contacted with the catalytic adsorption material in essentially a reaction step, preferably only one gas purification reactor is used. 15 Process according to claim 1 or 2, characterized in that the oxide of a metal of the fourth period in group VIII is an oxide of iron and / or nickel, preferably iron oxide. 20 4. A process according to claim 1, 2 or 3, characterized in that the carbonate or oxide of the alkali metal or alkaline earth metal is a carbonate or oxide of calcium and / or magnesium, preferably calcium oxide. 25 Process according to any of the preceding claims, characterized in that the gasification gas is contacted with the catalytic adsorbent material in the temperature 600-1200 ° C.