EA029238B1 - Process and apparatus for the gasification of solids - Google Patents

Abstract

In the gasification of carbonaceous solids with oxygen and/or steam, the solids are at least partly converted to CO and Hin a first process step. In a second process step, a stream containing water is separated from the product mixture obtained. The stream containing water finally is subjected to water purification in a third process step. The water purification is effected such that three streams (31, 36, 37) with different degrees of purity are obtained, at least one of which is recirculated in the process.

Description

The invention relates to a method and apparatus for gasifying carbon-containing solids, wherein in the first step the solids are converted into CO and H ₂ at least partially during the gasification process, and the steam containing water is separated in the second step of the method and in the third step of the method obtained in the second step, the water-containing steam is subjected to a water treatment process.

Gasification is a chemical-physical process in which at least part of the solid is converted into a gaseous final product. The gaseous end product is a mixture that consists mainly of carbon monoxide (CO) and hydrogen (H ₂ ). At the same time many reactions take place, which until now were not fully known.

The actual gasification occurs due to the exothermic combustion of solids. The products of this reaction can then react with solids and additionally introduced steam or with each other. With the exception of the combustion reaction, all the main reactions are equilibrium reactions, so the transformation can also go in the opposite direction. At relatively high temperatures during coal gasification (from 600 to 1600 ° C), the composition of the gaseous product is usually close to equilibrium.

In principle, three different types of solidification gasification methods are known: gasification in a fluidized bed, gasification in a fixed bed formed by solids, and finally gasification in a gas-flow reactor.

Regardless of how the gasification reaction proceeds, the synthesis gas produced in it from CO and H ₂ must then be purified. Since steam is required as a reactant during the reaction, and water is one of the possible reaction products, water, among other things, must be removed from the gas stream.

Impurities, such as solids, ammonia, phenols, etc., are also contained in the effluent water stream, so the water stream must be cleaned.

Such a method is known, for example, from ΌΕ 4107109 C1. Solid fuels are gasified at pressures in the range from 10 to 100 bar using an oxygen-containing and steam-gasifying medium to produce raw gas. The raw gas coming out of the gasification process is cooled to temperatures from 20 to 200 ° C, whereby a condensate rich in water is obtained. The condensate is separated and at least partially evaporated, while the condensate steam and the brine containing salt are removed separately. The brine-containing brine is burned, the condensate steam is partially added to the cleaned raw gas.

ΌΕ 3515484 describes that the condensate produced by the stepwise cooling of a gaseous product is cooled in a flushing and cooling device into which circulating water is supplied, whereby the halogens are largely flushed out. Used wash water, which has a temperature of from 120 to 220 ° C, expands to a lower pressure, whereby a vapor and liquid phase is obtained. The evaporation, which is practically free of halogens, is removed, the main part of the liquid phase is fed back into the washing and cooling device, and the residual liquid phase is fed for recycling.

ΌΕ 3207779 A1 describes that condensate obtained from syngas expands and is supplied to a separation device, from which the condensate phase, largely consisting of water, is removed. The condensate phase is cooled by direct contact with the colder gas before it is used to cool the raw gas stream. The heated, steam-containing cooling gas is fed to the combustion and is used, for example, to heat the reactor.

ΌΌ 147679 describes the recirculation of a stream consisting mainly of water, which originates from hydroclone, in which a stream rich in solids is separated from a stream poor in solids. The flow from the upper drain, poor in solids, is mixed into the initial flow of the gasifier and serves as the source of the required vapor in the reaction. The bottom stream, rich in solids, is distilled at atmospheric pressure for further purification.

OB 2198744 A finally describes the gasification of coal in a fixed bed, in which, after the gases are separated, the stream of waste water is sent to an evaporation device. From there, the gaseous component is recycled to the reactor as a gasification medium.

Recycling water flow, which partially contains significant amounts of solids, is otherwise known from completely different processes. For example, I8 5586510 describes the production of cement in a rotary kiln, and the sludge that is produced in the production of cement is recycled into a rotary kiln, sprayed and burned there.

All methods have in common that large quantities of wastewater cannot be further used in the process. Therefore, costly subsequent sewage treatment is necessary for the treatment of the stream or streams so that the disposal regulations comply with environmental standards.

Therefore, the aim of the invention is to reduce the production of waste water during the gasification of solids.

According to the invention, this objective is solved by a method with the characteristics of claim 1. The carbon-containing solid is gasified and at least partially converted to carbon monoxide and hydrogen in the presence of oxygen and steam. Then the generated gas mixture is fed to

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a separating device in which the liquid fractions are separated from the gas fractions, whereby a stream of so-called raw gas and a stream containing water are obtained. The liquid stream containing water is finally subjected to water treatment.

According to the invention, the water treatment is carried out in such a way that three streams with different degrees of purity are obtained. The first stream has the highest degree of purity, consists almost entirely of water and has the following composition:

Table 1. Compounds contained in the first stream

pH 7-8 Total iron (Fe) mcg / l <200, preferably <20 Total Copper (C) mcg / l <30, preferably <3 Total amount of silica (δΐθ ₂ ) mcg / l <200, preferably <20 The total amount of sodium (Ka) mcg / l <100, preferably <10 Organic components (chemical oxygen consumption, abbreviated) mcg / l <2000, preferably <200 Electrical conductivity µS / cm <0.2-2, preferably <2 Oxygen (O ₂ ) mcg / l 50-1000, preferably 50250

Thus, such a stream is suitable for use in steam generation. If the flow does not reach these limit values, then the first flow can be used as cooling water inside the plant. The second stream has an average degree of purity.

Table 2. Compounds contained in the second stream

Organic components (chemical oxygen consumption, abbreviated COO) mg / l 100 - 10,000 Organic components (biochemical oxygen demand, abbreviated) mg / l 10 - 1000 Ammonium Nitrogen (abbreviated as ΝΗ4-Ν) mg / l 5 - 500 Nitrate nitrogen (abbreviated as 3-Ν) mg / l 5 - 1000 Phosphate phosphorus (abbreviated as X-R) mg / l 2 - 100 The total content of suspended substances (abbreviated T88) mg / l 5 - 1000

Total solute content mg / l 100-25,000 (abbreviated Τϋ8)

The third stream has the lowest degree of purity and has a high solids content.

Table 3. The compounds contained in the third stream

Organic compounds % by weight 5-80 Nitrogen and / or phosphorus-containing compounds % by weight 15 Metal hydroxides % by weight 5 - 15

The procedure according to the invention involves the recycling of each of these three streams. The water stream, which has the highest degree of purity, is supplied to the water inlet of the steam generator; water flow, which has an average degree of purity, is fed to the further processing of the ash obtained in the gasification reactor; and / or a stream of water that has the lowest degree of purity and is rich in solids is sent back to the gasification reactor.

It is particularly preferred when all three streams are recycled to the gasification plant itself. The amount of wastewater obtained in the process, thus not only can be significantly reduced, but can be completely reduced to zero.

At the same time, medium and lowest purity streams can also be recycled together to the gasification zone, whereby particularly high use of the contained organic compounds can be made.

Partially, the purity of the first stream does not reach the purity required to generate steam. At the same pH value, it then has a composition in which the individual components are present in a concentration three times or partially even six times higher than the concentration indicated in Table. 1. A stream with this composition can be used as a stream of cooling water at any point in the process without evaporating the cooling water or it can be added to the cooling tower of the gasification plant.

In one preferred aspect of the invention, the stream with the least degree of purity is separated by decantation in the first step. You can still reduce the water content, for example by evaporation. In the second step, the remaining flow is then fed to the reverse osmosis unit. Reverse osmosis is a physical process for concentrating substances dissolved in liquids, in which the natural process of osmosis is reversed by pressure. The medium in which the concentration of a particular substance must be reduced is separated from the medium in which the concentration is to be increased by means of a semi-permeable membrane. In this case, the concentration of solids in the incoming

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water flow should be reduced, and increased in the outgoing stream with the least degree of purity. The medium in which the concentration must be increased is subjected to a pressure that must be higher than the pressure that is obtained by the osmotic requirement for leveling the concentrations. This leads to particle migration against the direction of propagation. In this process, the resulting purified first stream is preferably again subjected to a second reverse osmosis to obtain the stream with the highest and the stream with an average degree of purity.

Medium purity portions of the stream can also be obtained through an ion exchange unit located upstream of the reverse osmosis device. Two partial streams with an average degree of purity from the ion exchange unit and the reverse osmosis unit are then mixed.

Before the separation of the three streams and / or between the separation of the stream with the lowest degree of purity, the water content of which lies below 80 wt.%, Preferably below 50 wt.% And particularly preferably below 30 wt.%, Further steps may be provided by reverse osmosis. cleaning, such as denitrification, nitrification and / or removal of organic compounds.

Denitrification refers to the conversion of nitrogen bound to nitrate (ΝΟ ₃ ^- ) into molecular nitrogen ( ₂ ) by heterotrophic and some autotrophic bacteria that are attached to the membrane. In this process, which serves to generate bacterium energy, various oxidizable substances (electron donors), such as organic substances, hydrogen, hydrogen sulfide (H ₂ §) and molecular hydrogen, are oxidized with nitrate as an oxidizing agent (oxidizing agent) in the absence of molecular oxygen ( Ο2) (oxygen-free conditions).

Nitrification refers to bacterial oxidation of ammonia (ΝΗ ₃ ) to nitrate ( ₃ ). It consists of two related partial processes: in the first part, ammonia is oxidized to nitrite, in the second partial process, it is oxidized to nitrate.

The removal of organic compounds is preferably carried out by anaerobic treatment with bacteria in an oxygen-free environment. In addition, it was found advantageous to use steam generated in the steam generation process inside the steam supply system for the gasification process, for example, to preheat the raw materials, for example, in the distillation process, and / or use steam to generate electrical energy, for example, to bring turbine action. In this way, the water requirement of the process can be reduced.

First of all, when gasification is carried out in a fixed bed reactor, the ash obtained there should be washed. For this purpose, according to the improvement of the invention, a stream of water with an average degree of purity is used.

When gasified in a fixed bed, this ash is produced by the reaction of carbon-containing substances, such as coal or biomass, and falls through the grate provided in the bottom area of the fixed bed. For the further transportation of ash, water is introduced and, thus, the ash is washed out.

In the gasification method, which is carried out in the fluidized bed, it was found particularly advantageous to recycle the stream with an average degree of purity to the reactor.

For gasification in a stream, it is recommended to mix the stream with an average degree of purity or to the raw materials fed to the reactor as sludge and / or after rapid cooling to the sludge / wastewater stream.

In addition, it may be necessary to subject the stream of water, which has the highest degree of purity, and / or that stream of water, which has an average degree of purity, to further purification before being recirculated to a steam generating device or further processing the ash. Such further purification ensures significant recycling of wastewater streams even when when a large amount of impurities is introduced into the process with the solid raw material used.

Possible further purification processes can be chemical processes, such as the Fenton reaction (oxidation of organic substrates with hydrogen peroxide in an acidic environment, catalyzed by iron salts), ozonation (sterilization by introducing ozone), using activated carbon (as an adsorbent) and / or adding calcium hydroxide ( to reduce water hardness by ion exchange). It is also possible to use precipitating or coagulating agents. In addition, separators and / or wastewater treatment plants can be used.

One preferred aspect of the invention further provides that solids are gasified in a fixed bed.

During gasification in a fixed bed, it was found advantageous to introduce a stream of water, which has the lowest degree of purity, over a fixed bed, and the stream is injected as finely distributed as possible.

When a gasification reactor is used in the stream, it is possible to supply the stream of water with the lowest degree of purity directly through the feed pipes to the burner flame. In a fluid bed reactor, spraying over the fluid bed should also be taken into account. When fuel in gasification in a stream is supplied as sludge, it is recommended to mix the stream to this sludge before entering the reactor area.

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As a solid, on the one hand, coal can be used. Coal gasification processes have been used for decades. On the other hand, biomass can also serve as a source material, whereby renewable raw materials can be converted to synthesis gas. First of all, during the gasification of biomass, the above described method may be of interest, since the main amount of unburned material is discharged by the flow of water.

In addition, the invention proposes an installation for the gasification of a carbon-containing solid with signs of claim 9. Accordingly, the installation contains a gasification reactor in which solids are at least partially converted into carbon monoxide and hydrogen, a separation device in which the raw gas is separated from the liquid water stream, and a device for purifying water, in which the aqueous liquid stream obtained in the separation device cleared. When water purification water flow is divided into three streams with varying degrees of purity. Through the first pipeline, a stream of water that is of the highest degree of purity is supplied to the water inlet pipe of the steam generation device; through the second pipeline this stream of water, which has an average degree of purity, is fed to the device for further processing of ash from the gasification reactor; and / or through the third pipeline that flow of water that has the lowest degree of purity, is sent back to the gasification reactor.

Preferably, the device for separating the gas fraction from the liquid stream is made in the form of a condenser or in the form of a droplet separator. The design in the form of a condenser has the advantage that at the same time the gas flow is further cooled. When a droplet separator is used, the gas stream may already be pre-cooled and the thermal energy collected during cooling may be used elsewhere.

The installation according to the invention preferably also includes a device for cooling the gas between the gasification reactor and the separation device, which is recommended primarily when the gas-liquid separator is designed as a droplet separator and, thus, the cooling must be carried out in some other place.

In addition, the installation according to the invention preferably includes a device for extracting ammonia between the separation device and the device for treating ash.

In the separation of gas and liquid, the liquid stream obtained from the gas cooling device is further separated by decantation, with resins, oils, phenols and ammonia (ΝΗ ₃ ) being largely separated.

Further purification of water can be carried out downstream by the process of "fenosolvan" (РПсио8о1уи®). In the "phenosolvan" process, phenol-containing water is thoroughly mixed with phenosolvan (commercial name of diisopropyl ether) in a multistage extractor in accordance with the principle of a separator mixer. After the subsequent phase separation, most of the phenols are present in the solvent. This process is repeated several times, with the phenol-containing water and the solvent being sent in countercurrent. The solvent is separated from the phenols by distillation and flows back to the extractor to wash out the phenols.

After the process of "fenosolvan" the LF process can be carried out (SNSPISHB-BGERSR®). In this process, acid gases and ammonia are removed from the condensate of the process "phenosolvan" by selective distillation.

Due to this plant design, especially in connection with the increasingly restrictive requirements for environmental protection, investment costs and operating costs can be markedly reduced, since costly purification of waste water to be disposed of can be completely or partially excluded. By introducing a stream containing most of the solids back into the gasification process, the separation of solids from water can be eliminated using an energy-intensive drying operation.

When an average purity water stream is used to flush out the ash, you can save on the cost of additional fresh water and the cost of further purifying water with an average degree of purity.

Other features, advantages and possible uses of the invention may also be taken from the following description of an exemplary embodiment and drawings. All features described or illustrated form the subject matter of the invention by themselves or in any combination, regardless of their inclusion in the claims or their reciprocal references.

In the pictures

FIG. 1 shows a flow chart of a conventional gasification process followed by treatment of waste water according to the prior art;

FIG. 2 shows a flow chart of a method according to the invention.

In the conventional method, as shown in FIG. 1, solids are introduced into the gasification reactor 10 through conduit 1, and oxygen is introduced through conduit 2. Steam is supplied through these conduits or another pipe not shown. Through the pipeline 14, the gas mixture formed by the reaction is supplied from the reactor 10 to the gas cooling device 20. This device has cooled 4 029238

waiting for gas, the raw synthesis gas is withdrawn through line 21. Through line 22, the resulting liquid stream is supplied to the gas-liquid separator 23. From there it is introduced into the device 25 for extracting ammonia through the pipe 24. A process can be provided between the gas-liquid separator 23 and the device 25 for extracting ammonia "phenosolvan" (not shown in Fig. 1).

From the ammonia recovery unit 25, the liquid stream containing water is transferred to the water treatment unit 30 via conduit 26. From the water treatment unit, the wastewater, on the one hand, is discharged through conduit 31 and, if possible, treated so that the wastewater can be disposed of. Through conduit 32, a stream is withdrawn that contains most of the solid particles and is therefore also called a sludge stream.

A stream containing solids is fed to the dryer 33, in which the contained water is evaporated by supplying energy and released into the atmosphere. The dried sludge can then, for example, be delivered to a landfill site.

From the gasification reactor 10, in particular, if gasification takes place in a fixed bed, the ash is discharged through pipe 11 and fed to the device 12 for further processing of the ash. Flowing ash is then discharged through line 13.

In this method, water obtained from the wastewater treatment device is disposed of as wastewater, but not recycled to the process. Instead, fresh water is introduced at some point in the process.

FIG. 2 shows the configuration of the method according to the invention in the form of a flow chart, the solids to be gasified are also fed to the gasification reactor 10 through line 1, and oxygen is supplied through line 2. From the gasification reactor 10, ash is removed through line 11 and fed to the device 12 for further ash treatment. From this device for the further processing of ash, the ash is then discharged through line 13.

In the shown embodiment, the gasifier 10 is designed as a fixed bed reactor and includes a mainly cylindrical vertical reactor with an outer water jacket. Coal or biomass is fed from above through a sluice into a solid distributor inside the reactor, whereby a fixed bed is formed that rests on a rotating grate located in the lower region of the reactor 10. Oxygen and steam are also introduced from this lower region. Due to the rising hot gases, used coal or biomass is dried at the top of the gasifier 10, and desorption of physically adsorbed gases occurs. Below the drying zone is the reaction zone, in the upper part of which the degassing of coal or biomass takes place. Inside the reaction zone, degassing is followed by the actual gasification of coal or biomass in accordance with the Budua reaction. In the next, lowest zone, the combustion of coal or biomass occurs, as well as the reaction of formation of water gas and the reaction of conversion of water gas. The resulting gas falls through the grate and is discharged from there. Hot gases that are directed in countercurrent to coal or biomass falling from above are discharged through an exhaust pipe located above the fixed bed.

Through pipe 14, the gas mixture obtained by the gasification reaction is discharged from reactor 10 and fed to the refrigerator 20. As a result of cooling, crude synthesis gas is obtained, which is discharged through pipe 21. Through pipe 22, a liquid stream containing water flows into the gas-liquid separator (separator device) 23. It is also possible that the separation of gas and liquid is caused solely by condensation in the gas cooler 20.

From the gas-liquid separator 23, which can be designed as a condenser or droplet separator, the resulting liquid stream is recycled to the device 25 for the extraction of ammonia through the pipe 24. A process of "phenosolvan" can be provided between the gas-liquid separator 23 and the device 25 for the extraction of ammonia (Fig. 2 not shown). From the ammonia extraction unit 25, the conduit 26 then leads to the water treatment unit 30. The water stream obtained there is divided into three streams. The stream that has the highest degree of purity is fed through conduit 31 to a not shown steam generator. The steam produced there can then be used as a coolant in the current gasification method, for example, to heat the raw materials, or used to generate energy in a turbine. In principle, it also seems possible to feed water as coolant into the cooling circuit. It may be necessary to skip this stream, not shown.

The stream with an average degree of purity through the pipeline 37 is sent for further processing 12 ashes and serves there as a fluidizing agent. Thus, the introduction of make-up water can be completely excluded. Perhaps, it may also be provided further purification 38 of the water for flow in the pipeline 37.

Through conduit 36, the stream that contains most of the solids is finally transported back to gasification. When reactor 10 is designed as a fixed bed reactor, it is recommended that the stream containing solids be sprayed onto the fixed bed from above. In this way, a lot of energy consuming and therefore costly drying of solids can be avoided. In addition, valuable products still contained in it can thus be fed to gasification.

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With this method it is possible to ensure the gasification of solids, in which no waste water is obtained.

Reference List 1, 2 Pipeline

10 gasification reactor

11 pipeline

12 further processing of ash 13, 14 pipeline

20 refrigerator 21, pipeline 22

23 separating device

24 pipeline

25 ammonia recovery

26 pipeline

30 subsequent water treatment 31, 32 pipeline 33 drying solids 34-37 pipeline 38 subsequent processing water 40 pipeline

Claims (8)

CLAIM 1. The method of gasification of solid carbon-containing substances, comprising the following stages: the first stage is at least partial conversion of solid carbon-containing substances into CO and H ₂ to produce a gas stream containing steam; the second stage is the separation from the resulting gas stream of a liquid stream containing water; and the third stage - water purification of the stream containing water obtained in the previous stage, characterized in that during water purification the stream containing water is divided into three streams with varying degrees of purity, the first stream of water, which has the highest degree of purity, is directed to the production couple, the second stream of water, which has an average degree of purity, is directed to leaching the resulting ash from the gasification reactor or into a special device for treating the ash as a fluidizing agent, followed by the formation in it of sludge withdrawn from the system, the third stream of water, which has the lowest degree of purity, is recycled to the gasification reactor for solids. 2. The method according to claim 1, characterized in that the third stream of water is separated by decantation, and then the first and second streams of water obtained by the method of reverse osmosis. 3. The method according to one of the preceding paragraphs, characterized in that the steam generated in the steam generator, is used to ensure the gasification process with steam and / or for the generation of electrical energy. 4. The method according to one of the preceding paragraphs, characterized in that the first stream of water, which has the highest degree of purity, and / or the second stream of water, which has an average degree of purity, is subjected to further purification before recirculation. 5. The method according to one of the preceding paragraphs, characterized in that the gasification of solids is carried out in a fixed bed. 6. The method according to claim 5, characterized in that the third stream of water, which has the lowest degree of purity, is sprayed into the solidification gasification reactor over a fixed bed. 7. Installation for gasification of solid carbon-containing substances by the method according to any of the preceding paragraphs, containing the gasification reactor (10), which provides at least partial conversion of solid carbon-containing substances into CO and H ₂ to produce a gas stream containing steam, a separation device (20), in which the separation from the raw synthesis gas obtained in the process of said gasification is provided, a liquid stream containing water, and a water treatment device (30), in which the resulting a stream containing water, characterized in that the water treatment device (30) is arranged to divide the stream containing water into three streams with varying degrees of purity and the water treatment device (30) through the pipeline (31) for the stream having the highest degree of purity, connected to a steam generation device and through a pipe (37) for a stream having an average degree of purity, to a device (12) for treating ash, including liquefying ash and turning it into sludge, or to a reactor (10) for washing out ash from a solidification gasification reactor thing STV and through the pipeline (36) with the reactor (10) gasification. - 6 029238 8. Installation according to claim 7, characterized in that the separation device (20) is a condenser or droplet separator.