JP2573681B2 - Purification of raw material gas - Google Patents

Abstract

The invention relates to a process for the refining of a raw gas produced from a carbonaceous material by means of a gasification process, refining taking place in a secondary stage separated from the gasifier. In order to reduce the gas contents of tar in the form of organic compounds condensible at lower temperatures, such as ambient temperatures, and of ammonia, the refining is carried out in a secondary stage being a fast circulating fluidized bed, the bed material of which at least mainly being an active material in the form of a material that is catalytic for tar and ammonia conversion, whereby a catalytic conversion of tar and ammonia contained in the raw gas is obtained. In order to decrease the content of hydrogen chloride in the gas, an active material that also can absorb chloride is used. Fresh catalytic and absorbing material is supplied in an amount sufficient to have the hydrogen chloride present in the raw gas absorbed on the material, a corresponding amount of the material containing absorbed chloride being discharged from the secondary stage.

Description

The present invention relates to a method for purifying a raw material gas generated from a carbonaceous material by means of a gasification process in a second stage separated from the gasification process.

Feed gas produced from various fossil fuels and used as fuel gas is a valuable oil substitute. This is because process requirements make it impossible to directly burn solid fuels (eg burning lime furnaces or converting existing oil fired boilers).

In other types of applications, for example the so-called so-called (power and heat) cogeneration with the use of diesel engines, very high requirements are placed on the gas purity, mainly for tar and dust. Furthermore, there is a demand suppressed during burning in view of environmental NO _X, the discharging compound harm such as SO _X and various chlorinated compounds at a low concentration. The last point mentioned is waste-derived combustion (RD
This is especially true for the gas produced from F). These requirements regarding gas purity can be satisfied by purifying the raw material gas by an appropriate method.

Gasification of the RDF and subsequent purification of the feed gas may be in terms of recovering energy from waste by utilizing the purified gas in existing boilers or in cogeneration in diesel engines and / or boilers. This means that it is an environmentally preferable method.

In addition, the use of source gases is often associated with other technical problems.

At temperatures below 1200 ° C, carbonaceous materials, such as coal,
Tar is always present in the raw gas produced by gasification of peat, bark, wood or RDF, so that hot gas can be used directly or close to the gasifier for combustion. There is a limit. This is a major problem because its ability is limited due to operational hindrance caused by the deposition of tar on equipment and equipment. During the combustion of the hot gases, nitrogen and in some cases sulfur bound in the tar (eg, from peat) and ammonia, H ₂ S (peat) or HCl (from RDF) are further harmful to the environment (each NO _X, SO _X and HCl chlorinated hydrocarbons namely dioxin) cause.

Despite extensive research on the conversion of tar and ammonia, no process has been developed to date that has achieved satisfactory raw material gases on an industrial scale. The traditional way to reduce the tar concentration in the feed gas is by means of a wet scrubber, but the tar removal is inadequate due to the formation of aerosols in the scrubber. Water containing even higher concentrations of organic compounds and ammonia is produced in the manufacturing process. As a result, the water must be cleaned before it is subsequently discharged to the sewer. Even when gasifying RDF, the water generated in the process contains a high concentration of dissolved hydrochloric acid and / or ammonium chloride. Further, when gasifying a high sulfur content fuel such as peat or coal, the raw material gas must be purified to remove hydrogen sulfide.

It is an object of the present invention to provide a method for purifying a raw gas by means which solves the above problems to a considerable extent.

This method is achieved by the method of the present invention having the contents defined in the following claims.

That is, the present invention relates to a method for purifying a source gas containing tar and ammonia, and in particular, a source gas containing significant amounts of hydrogen chloride gas, wherein said gas is a carbonaceous material such as bark, wood, peat, or Produced by means of any gasification process from RDF, a fuel derived from waste, where in the second step a suitable active material (catalytic and also absorbable) such as dolomite is present in the feed gas And the conversion is preferably carried out to such an extent that the residual content is below 500 and 300 mg / Nm ³ respectively. In special cases, the absorption of hydrogen chloride takes place at the same time, reaching almost thermodynamic equilibrium. Said second stage is at least mainly a bed material in the form of an active material, for example dolomite.
ial) and a circulating high-speed fluidized bed (CFB). For this arrangement, it is also possible that the second stage is integrated with any CFB-gasifier and only the primary particle separator or only other types of gasifiers are arranged upstream.

We have found that sufficient conversion of tar and ammonia and, in special cases, simultaneous absorption of hydrogen chloride can be achieved. It first separates the tar-containing gas by heating large fuel particles in the gasification stage,
Next, in a separated second stage, the circulating high-speed fluidized bed is brought into contact with a suitable active material, for example dolomite, with suitable process parameters.

In the case where the carbonaceous raw material is, for example, peat, which contains a considerable amount of sulfur, the absorption of hydrogen sulfide on the contacting and absorbing material naturally occurs.

The amount of active material required in relation to the amount of feed gas is determined by the space velocity required for the catalytic conversion of tar and ammonia, and several parameters such as temperature,
It depends on the gas residence time, the particle size of the active material, the partial pressure of the reactants and the degree of degradation of the active material. If the temperature is low too and / or CO ₂ is too low, tar cause carbon deposition on the transformed active surface leads to Therefore deactivation. If this occurs, the material can be activated by treatment with an oxidizing gas such as air and / or steam. The absorption of HCl (and / or H ₂ S) is limited by the temperature of operation
t) Being so fast that these reactions are almost entirely determined by equilibrium, resulting in the consumption of the active material corresponding to the chloride solids formed (and sulfides in the case of H ₂ S) Will be.

That is, we have found that the absorption of chloride (and in some cases hydrogen sulfide) on active materials such as dolomite is a fast reaction, and that the active material is present in a significantly lower amount with respect to gas flow than catalytic conversion of tar and ammonia. I found out what to do.

Utilizing the second stage in the form of a fast circulating fluidized bed (CFB) has considerable advantageous results.

Such a bed is capable of handling airborne dust from the gasifier, providing a very uniform temperature in the reaction zone and providing a uniform phase contact between the gas and the bed material. Is possible, which means that there is less risk of varying the degree of conversion / absorption. It is also possible to vary the particle size significantly downward if necessary to increase the conversion at a given temperature and space velocity. Corresponding erosion of the floor material also results in increased accessibility of the active surface. Also
The second stage with the advantages designed as CFB is the optional CFB
It can be integrated with a vaporizer, which simply has a primary particle separator or other type of gasifier. When scaled up, relatively small particle sizes can be achieved because the gas flow rate is relatively high and can be maintained up to about 10 m / s, preferably up to 6 m / s.

When the gasifier is a CFB gasifier, it is connected directly after the first dust separation. If the active material is used as a bed material in a CFB gasifier, the second stage is advantageously carried out with the gasifier and, for example, all dust from the second particle separator after the second stage is passed to the gasifier. Alternatively, they can be integrated so as to partially circulate. In this way, the total loss of floor material is also reduced, and the advantage of using only one floor material mold is obtained.

The amount of active material required in the second stage reactor to satisfactorily catalytically convert the tar and ammonia is controlled by the total amount added and by recirculation of the bed material. The conversion required will determine the proper combination of temperature, particle size and amount of active material. Active material consumed for abrasion, deactivation and / or absorption of HCl (and possibly H ₂ S) can be achieved by adding a corresponding amount of fresh active material and / or activated such material. Will be replaced. Gas residence time is controlled by the diameter / height combination above the gas inlet.

In the special case where HCl is present in a considerable amount in the feed gas, the active material floating out in the exhaust gas from the second stage results in improved absorption of said HCl. This is because thermodynamically, at a lower temperature, to a greater extent under conditions where the purified gas is cooled to an essentially lower temperature prior to final dust removal.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings, but the present invention is not limited thereto. The figure schematically illustrates a gasification and gas purification system to illustrate embodiments of the present invention.

In the illustrated system, a carbonaceous feedstock 1 is conveyed to a gasifier 3 which circulates at a high flow rate (CFB).
It is composed of This comprises a reactor 51, a first separator 52
And recirculation means 53 for the bed material separated in said first separator. The bed material is in the form of dolomite mixed with active catalyst and absorbent material, preferably a non-gasified carbonaceous feedstock, charcoal. First separator 52
Is a non-centrifugal mechanical separator, suitably a U-beam separator, consistent with that associated with the CFB boiler described in our European Patent EP 0 103 613, which is incorporated herein by reference.

The hot feed gas 2 produced in the gasifier 3 is withdrawn directly from the first separator 52 and fed directly to the second gas cleaning stage 25 without any additional dust removal. The second stage 25 is designed as a circulating high-speed fluidized bed (CFB) 26 and has the same type of active bed material as the gasifier 3 described above.

The feed gas 2 is supplied to the second stage 25 so that it constitutes a filling gas.

The second stage 25 is designed to have a long and narrow reaction column with an arbitrary cross section (for example, a circle or a square).
The bed material following the vapor gas discharged from the top of the reaction column is for the most part in the first particle separator 27, preferably in a U-beam separator of the same kind as the U-beam separator of the gasifier. Separated, followed by a second separator 28, preferably a cyclone. The material 30 separated in the first particle separator is circulated to the lower part of the circulating bed 26 through a recirculation device. The material 29 separated in the second particle separator 28 is mainly added as a stream 31 to the lower part of the gasifier 3. If necessary, a portion of the material stream 29 can be fed as stream 34 to the lower portion of the circulating bed 26 and / or can be discharged out of the system as stream 43.

To supply fresh catalyst material and absorbent material 14 to the second stage 25, a side feed device 15 arranged at a suitable height is used. The consumed and / or deactivated floor material 35 is discharged by means of a discharge device 36 arranged at the bottom of the second stage 25.

The active material used in the second stage of this embodiment is composed of a calcium-magnesium carbonate-containing material, preferably dolomite having a particle size of less than 2 mm, preferably less than 1 mm, which is Combined to form a fast circulating fluidized bed 26.

The gas flow rate in the upper part of the reaction tower is designed to have a free cross section, and is adjusted so as to be 10 m / s or less, preferably 6 m / s or less.

The flowing gas of the high-speed circulating bed 26 is composed of the raw material gas 2 and the added oxidizing gas 13, for example, air. If necessary, the oxidizing gas 33 can be added to the second stage 25 at one or several suitably higher levels.

The conversion of tar and ammonia contained in the raw material gas 2 and the absorption of chloride contained in the raw material gas are 600
~ 1000 ° C, preferably 700-900 ° C, most preferably 850-9
By means of contact with the catalyst and the absorbent material in the circulating bed 26 at a temperature range of 50 ° C. The required temperature level is maintained by burning the combustible gas components within said second stage 25, which is controlled by adjusting the amount of oxidizing gas streams 13 and 33 added.

The average buoyant density in the reaction tower of the second stage 25 is 20-300 kg / m ³
Range, preferably maintained in the range of 80~250kg / m ^3,
The necessary contact between the passing gas and the active material is obtained. This is the total amount of recycled material and recovered material 30 and 34
This is achieved by adjusting the combination with the flow rate control.

The gas residence time in the reactor is maintained in the range of 0.2 to 20 seconds, preferably 0.5 to 7 seconds, calculated assuming the reactor is empty.

Activation of the deactivated catalyst and absorbent material, if necessary, is accomplished by adding an oxidizing gas 32, such as air, to the material recycled as streams 30 and 34 to the bottom of the circulating bed. The addition amount of the oxidizing gas 32 is controlled so that the activation occurs in the range of 600 to 1000 ° C, preferably in the range of 750 to 900 ° C.

Prior to commencing the above operation, the heating of the second stage 25 including the floor material is performed by means of burning the LP gas 24 therein.

The purified gas stream 4 leaving the second separator 28 of the second stage 25 is withdrawn in the next gas treatment stage from the finely divided bed material and steam emerging from the suspension.

The gas passes through two heat exchangers. 1st heat exchanger
Heat exchange with the oxidizing gas, stream 10, takes place in 37, said gas going to both the gasifier 3 and the second stage 25, in which case the oxidizing gas 11 coming out of the heat exchanger 37 is preferably at a suitable temperature.
Preheated to have 400 ° C. The preheated gas 1
1 is a stream 12 into the gasifier 3 (especially as a filling gas)
And in both streams 13, 32 and 33 into the second stage 25.

In the subsequent second heat exchanger 38, the temperature of the gas 5 is such that it can be further cleaned by further dust removal at 39, for example using a standard woven cloth or cyclone, i.e. preferably 150-300. To ℃. The removal dust 18 is removed from a dust removal stage 39.

As mentioned above, the gas stream 4 contains finely divided active substances that emerge in suspension, which is
Followed by the gas stream coming out of. Special cases, for example RD
When connected to the gasifier of F, the raw material gas 2 from the gasifier contains a considerable amount of HCl. The absorption of HCl on carbonaceous materials, such as dolomite, is due to endotherm and contributes to the increased degree of absorption of residual HCl on suspended and emerging materials by gas cooling in the heat exchangers 37 and 38. I do.

The substantially dust-free gas 7 leaves the dust removal stage 39 and is fed to a scrubber 40 where the dust is removed from moisture and other water-soluble components. In the scrubber 40, humidification of the gas stream 7 and condensation of the vapor take place. (Current)
The conditions also result in precipitation of almost all residual fines and absorption of water-soluble gas components such as NH ₃ , HCl and / or NH ₄ Cl.

The water stream 20 emerging from the scrubber 40 is recirculated by the pump 41, where it is cooled to maintain the temperature of the water 19 recycled to the scrubber 40 in the heat exchanger 42 in the range of 15-20 ° C. . Excess water 21 is discharged from the water circulation system.

The gas 9 leaving the scrubber is pure for industrial use, ie tar, ammonia, dust, HCl and H _2.
It can be considered that S hardly contains S. However, at the outlet temperature here (about 30 ° C.), it is saturated with steam. Depending on the application, to reduce the relative humidity, the gas stream 8 can also be preheated or even passed through a drying stage to reduce its moisture content. The pure gas satisfies the requirements of the engine operation, for example by means of a turbocharged diesel engine, and can be burned without any cleaning of the resulting waste gas.

The scrubber 40 can be omitted for simpler applications, e.g. for heat generation in boilers, so that the purified gas is used directly after the stream 22 from the heat exchange 37 or after the stream 23 from the dust separator 39. I can do it.

In the example, the second stage 25 has been integrated with the gasifier 3 on the basis of CFB technology. The gasifier 3 can be a variety of fuels such as crude bark, peat or waste derived fuel RDF
From which the source gas 2 can be produced. As the bed material in the circulating bed of the gasifier 3, it is convenient to use the same catalyst material and absorption material as in the second stage 25, as described above.

The total pressure drop of the oxidizing gas, for example air, supplied through the production loop is slightly higher than about 1 bar. This requires the use of a compressor 16 to increase the oxidizing gas pressure in stream 9 to the required pressure level in stream 10 for the purposes of this purpose.

Continuation of the front page (72) Inventor Kovalitsk, Vuaklav S-127 40 Sierholmen, Sweden. Butlerholmsglend 85 (72) Inventor Lensfeld, Erik Sweden 611 63 New Chipping. Vietri Siestagen 10 (72) Inventor Valdheim, Lars Sweden S-127 38 Sierholmen. Borg Setlavien 2

Claims (15)

(57) [Claims] 1. A method of purifying a raw material gas used as a fuel produced by a gasification process from a carbonaceous material in a second stage apart from the gasification process, wherein a tar form condensable at a low temperature. In order to reduce the content of organic compounds and ammonia in the gas, the purification is carried out in a second stage in the form of a fast circulating fluidized bed with an upright reactor, the material of said fluidized bed being at least predominantly tar and Containing an active material in the form of a material that catalyzes ammonia conversion,
The active material comprises a magnesium carbonate-calcium carbonate containing material and / or a corresponding calcined product, the particle size of which is
2 mm, the operating temperature of the second stage is maintained in the range of 600-1000 ° C., and the average buoyant density in the reaction tower is 80-250 kg /
m ³ , the gas flow rate in the second stage reactor is less than 10 m / s calculated as empty reactor;
Then, the gas residence time is calculated based on the empty
And maintained within the range of 20 seconds to a concentration of the contact conversion purified gas of tar and ammonia present contact in the gas between the gas and the active material passing through is lower than the respective 500 and 300 mg / Nm ³ A method for purifying a raw material gas, the method comprising: 2. The feed gas contains hydrogen chloride, the active material containing the absorbed chloride is removed intermittently or continuously from the second stage, and a corresponding amount of new active material is passed to the second stage. The method according to claim 1, wherein the feeding is performed intermittently or continuously. 3. The process according to claim 1, wherein the oxidizing gas and / or steam are added simultaneously to the second stage reactor. 4. The method according to claim 1, wherein the operating temperature of the second stage is controlled by the amount of oxygen-containing gas added.
4. The method according to any one of 2 or 3. 5. The method of claim 1 wherein the active material deactivated as a result of carbon deposition or for other reasons is removed intermittently or continuously from the second stage and replaced with an equal amount of fresh and / or activated material. The feature of claim 1
The method according to any one of Items 1 to 4, wherein 6. The deactivated active material removed from the second stage is activated by treatment with an oxidizing gas in another activation stage, and the activated material is returned to the second stage. The method of claim 5. 7. The active material deactivated as a result of carbon deposition or for other reasons is activated by treatment with oxidizing gas and / or steam in a system for recycling the separated fluidized bed material of the second stage. The method according to any one of claims 1 to 6, wherein the method is performed. 8. The process according to claim 6, wherein the activation is carried out at an operating temperature in the range from 600 to 1000 ° C. 9. The process according to claim 6, wherein the operating temperature of the activation is controlled by the amount of oxygen-containing gas added. 10. The process according to claim 1, wherein the feed gas is fed directly from the gasifier to the second stage without any intermediate dust removal. 11. The gasifier comprises a high-speed circulating fluidized bed,
The method according to claim 10, characterized in that the feed gas is supplied directly from the first separator of the gasifier to the second stage. 12. The method according to claim 1, wherein the fluidizing gas in the second stage comprises a source gas and optionally an oxidizing gas. 13. An oxidizing gas which does not constitute a fluidizing gas is supplied to a first stage reactor above the fluidizing gas supply port of the reactor.
Or adding at several positions.
Method according to 12. 14. The hydrogen chloride content in the purified gas exiting the second stage is further reduced by absorption into the catalytic absorbent remaining in the gas after the second stage particle separation,
14. The process as claimed in claim 1, wherein the gas after the step (a) is first cooled to a considerably lower temperature and then a further dust separation is carried out. 15. The feed gas supply system of the second stage is directly connected to a first particle separator of a gasifier having a high-speed circulating fluidized bed, and the circulating fluidized bed material is the same active material as that of the second stage. The dust separated in the second stage is at least partially recycled to the lower part of the gasification reactor and fluidized bed material and optionally gasification coming out of the gasifier with the feed gas The material withdrawn from the bottom of the unit is replaced by the material recycled from the second stage to the gasification reactor together with new catalytic absorbing material added intermittently or continuously to the gas unit. The method according to any one of claims 1 to 14, wherein