FI107164B - Method and equipment for purifying product gas from a gasification reactor - Google Patents

Abstract

The object of the invention is a method for purifying a productgas of a gasification reactor of tars and other organic compounds condensing out of the gas while it cools in a fluidized bed reactor acting as cracker. The invention is characterized in that the purification is accomplished in a spouted-bed reactor (1, 15), where the productgas (2) is fed into the reactor (1, 15) from at least one inlet point, beneath the inlet point of the productgas (2) is arranged a bubbling fluidized bed (5) that is maintained by an oxidizing gas (6) fed into the reactor (1, 15) and which forms a first zone, the productgas (2) forms above its inlet point a second or spouted zone, where fluidized particles (9) move along with the spout (8) and where purification is mainly accomplished, and above the spouted zone is arranged a third or equalizing zone,where the fluidized particles (9) are separated from the purified gas (12). An inventive object is even an equipment for carrying out the method.

Description

107164

The present invention relates to a process for the purification of product gas of a gasification reactor from tars and other cooling gas condensable organic compounds in a fluidized bed reactor. The invention also relates to apparatus for applying the method.

10 In many gasification applications, the formation of tar-like impurities is a major problem. Healthy mm. cause clogging of heat exchangers and gas filters and prevent the use of gas in engines.

Catalytic gas purification technology has been the subject of research for several years. According to the prior art, there are three alternative ways of avoiding tar formation and efficient tar decomposition: 1. Tar formation in the carburettor itself is minimized by the use of catalytically active mattress material, high gasification temperature and air distribution of the carburettor. In addition, if sufficiently effective tar disintegration is achieved, the final cleaning can be accomplished by water washing.

2. The tar compounds and ammonia are decomposed in a separate catalyst reactor using a Nikke-based cellular catalyst.

3. The tars are disintegrated in a separate catalyst reactor using lime-based catalyst 25.

In practice, however, the first alternative requires a gasification temperature of more than 900-950 ° C, which is not possible with all fuels. It has also been found that it is difficult to achieve tar concentrations of less than 2-4 g / m 3 in the carburettor itself due to poor contact between the gas and the catalytically active material. Thus, * many secondary applications require separate secondary cracking. According to the applicant's studies, complete degradation of the tar compounds can in principle be achieved with both nickel-based and calcium-based catalysts. However, nickel-based catalysts suffer from the high cost of the material, its toxicity, and the difficulties involved in implementing up-and-down laws. Furthermore, the lifetime of such catalysts is not yet known.

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The use of calcium-based catalysts, i.e. lime and / or dolomite, requires the calcination of calcium carbonate, which can easily be achieved at a gasification pressure (1-5 bar) appropriate for engine and boiler applications at temperatures above 780-850 ° C. In tests performed by the applicant's small test apparatus, complete conversion of tars has been achieved in the JI-5 road bed reactor with a very short residence time (less than 0.5 s) and at a moderate temperature of 850-900 ° C. Solid (in the rros reactor, the contact between tar-containing gas and bed material is ideal, but the reactor is very sensitive to clogging by dust and grinding lime and is therefore unsuitable for industrial use.

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SE 8703816 discloses a solution in which a separate circulating catalyst catalyst is used which has obtained quite good results. However, the circulating mass is large and expensive, and the calcium-containing bed material is ground there; very fast due to the high flow rate (typically about 5 m / s). In practice, this leads to high lime consumption.

U.S. Patent 4,865,625, on the other hand, discloses a nickel catalyst based process wherein the gasifier product gas is introduced into a conventional nickel-containing petimatqriaal fluidized bed cracker used at a relatively low temperature of 20 550-750 ° C to prevent the catalyst from sintering. Based on the applicant's own experiments, when operating at such low temperatures, the catalyst bed readily forms carbon, which over time clogs the catalyst. For this reason, the catalyst has to be practically regenerated. In a conventional fluidized bed cracker used in the US, product gas is passed through a catalyst bed grid (Distributor plate) to the reactor. To avoid clogging the grate, the product gas exiting the carburettor must first be filtered. This, in turn, can be tricky as tars in product gas can clog the filter.

Thus, problems with known techniques include coarse price, nickel-based catalysts, toxicity, as well as the difficulties involved in carrying out equipment shut-downs and calcium-based catalysts, dust formation and catalysts! rapid wear.

In addition to conventional fluidized bed reactors and circulating mass reactors, spouted-bed reactors are also known. However, the limiting use of these is the control of bed material fluidity, which can be achieved with conventional (reactors only at very high gas inlet speeds (generally in the order of 50! M / s) and certain critical dimensions (e.g., bed particle size, taper angle, inlet This effectively limits the application of a spouted-bed type reactor and results in high pressure drop at the inlet pipe. high.

It is an object of the present invention to provide a process for purifying product gas from a gasification reactor from tars and other cooling gas condensable organic compounds in a cracker reactor which solves the above problems and meets the following requirements: a) gas and catalyst contact is efficient; and (c) the process is feasible on an industrial scale and at a sufficiently low cost.

These requirements have now been achieved as set forth in the appended claims.

The process according to the invention is characterized in that the purification takes place in a jet bed reactor in which: - the product gas is fed to the reactor from at least one feed point; wherein the fluidized particles move with the jet and wherein the main purification takes place, and - a third or equilibrium zone is imitated above the jet zone, where the fluidized particles differ from the purified gas.

Thus, in the process according to the invention, the product gas exiting the gasifier is introduced into a secondary cracker reactor, the bottom part of which acts as a spouted-bed and the top part as a particle settling and separation space. The jet bed reactor is a technique known to one of ordinary skill in the art from other applications.

According to a preferred embodiment of the invention, a fourth or fluidized bed zone, which functions as a conventional fluidized bed, is further provided between the jet belt 35 and the equilibrium zone of the cracker reactor.

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The operating temperature required for tar cracking, 700-1200 ° C, preferably 800-1000 ° C, is achieved by adjusting the bubbling fluidized bed feed gas. The bed material in the first and / or fourth zones may comprise limestone, dolomite, sand, or a mixture of at least two of these, depending on the target residual tar level. In addition, it is possible to use some other inert and non-refractory material. Inert materials also achieve a better cracking result than an empty reactor because all bed material surfaces are somewhat active, especially at high temperatures (above 900 ° C).

According to one embodiment of the process according to the invention, the product gas to be purified is introduced into the reactor at a rate of 15-50 m / s, preferably 20-45 m / s. In the equilibrium zone, the gas flow rate is again 0.1-1.2 m / s, preferably 0.3-1.0 m / s. Further, the fluidized bed of the first zone is made to bubble by means of an oxidizing gas which is introduced into the reactor at a velocity of 0.4 to 2.0 m / s, preferably 0.5 to 1.5 m / s. Said oxidizing gas may be air, oxygen, water vapor or a mixture of at least two of these. According to a preferred embodiment of the invention, said oxidizing gas is introduced into the reactor through a grate.

The product gas to be purified by the process of the invention may be the result of, for example, 20 coal, peat, solid biomass or waste-based recycled fuel.

The invention further relates to an apparatus for applying the method according to the invention, characterized in that it comprises: - a conical section on which the spray bed can be tracked, - a first cylindrical section below the conical section, - a grate and at least one oxidizing gas in the middle of the feed connection, - substantially the first cylindrical part, to a product gas of at least one feed tube, tracked in the direction of the reactor shaft, the fluidized bed maintained by the oxidizing gas being provided between the feed tube and the walls of the cylindrical part.

In accordance with a preferred embodiment of the invention, the reactor further comprises a second cylindrical section tracked above the tapered portion.

Thus, in the apparatus of the invention, the product gas to be purified is introduced into the reactor via a feed pipe located in the middle of its lower part, which feed pipe is inserted into a larger outer pipe. The oxidizing gas required for the partial combustion of cracking is led through a grate into the space between the feed pipe and the outer pipe. The pipes are dimensioned such that in this intermediate space used to supply the oxidizing gas, a flow rate (typically 0.5-1.5 m / s) favorable for the operation of the bubbling fluidized bed prevails. The reactor surface height can be adjusted higher or lower according to the desired blade removal rate. At its lowest, the reactor has only a jet zone and an overhead equilibrium space, from which gas-trapped particles return back down.

The reactor top is again dimensioned to act as a jet separator for jet-trapped particles (typically at a flow rate of about 0.3 to 1 m / s). When more bed material is used, the conventional fluidized bed above the jet zone is also formed in the reactor, which promotes tar cracking and allows a longer lag time.

15

According to one embodiment of the invention, the apparatus can also be used in large cracker reactors, whereby there are several feed tubes and they are substantially parallel. Such an application is described in more detail below.

The process and apparatus of the invention provide the following advantages over known reactor solutions: particles in the product gas do not pose problems as in conventional fluidized bed scratchers with oxidizing gas, and fluidization with oxidizing gas stabilizes the operation of the jet so as to achieve ) and different size bedding materials.

Further, the oxidizing gas fluidization also carries some of the pressure loss due to the fluidization of the bed material, which results in lower incoming product gas pressure, which is desirable to prevent feeder and other joint leaks. In addition, the oxidizing gas that is introduced is very efficiently mixed with the product gas, because the bed material thrown upwards by the gas jet returns downwardly into the air stream directly along the walls of the cone to retract it back into the ascending jet.

Advantages of the method and apparatus of the invention are still the suitability of the oxidizable gas fluidized space below the conical top for the removal of spent bed material, if it is necessary to replace the bed material by, for example, poisoning with HCl and lime or agglomeration.

The apparatus according to the invention is illustrated in more detail below with reference to the accompanying drawings, in which: Figure 1 is a side elevational view of the first embodiment of the invention, Figure 2a is a side elevation view of the apparatus 10 and Figure 2b is a cross-sectional view AA.

Figure 1 is a side elevational view of an apparatus according to a first embodiment of the invention. Apparatus 1 comprises a bubbling fluidized bed 5 provided below the feed gas 3 of the product gas 2, the fluidized bed 5 being arranged to bubble by supplying air 6 through the grate 7. The upright particles of bed material 9 formed by the gas jet 8 formed by the product gas 2 return downwardly to the air stream directly along the walls of the cavity 10 in order to trickle again into the upwardly rising jet 8. Above the gas jet 8 there is The figure further shows an outlet channel 13 for the purified gas 12 and a bed material outlet channel 14 for the fluidized bed 5.

Figure 2a is a side view of a portion of the apparatus according to another embodiment of the invention. The apparatus 15 is larger than that shown in Figure 1 and comprises a product gas 2 inlet duct 3, which is divided into a plurality of inlet ducts, of which three sections 3a, 3b and 3c are shown in the cross section shown herein. In addition, the figure shows the air supply 6 through the grate 7 and the bubbling fluidized bed 5.

The solution illustrated in Fig. 2a enables efficient sifting and controlled floating also in a large-scale cracker, where good results are not achieved with only one feed tube. By inserting gas into several smaller tubes placed within the same air-fluidized volume, a large cracker achieves as effective mixing as! pie-35 cracker, and also avoids diving into a feed tube typical of spouted-bed reactors.

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Figure 2b is a cross-sectional view AA of the apparatus shown in Figure 2a. The figure shows the gas supply pipes 3a-3i and illustrates the holes 16 of the grate 7. It will be appreciated that the number of said supply pipes 3 and holes 16 may be more than the figure and that said supply pipes 3 and holes 16 may be arranged as desired.

The apparatus according to the invention has also been tested with a bench-scale size cracker having a top diameter of about 100 mm and connected to a fluidized bed gasifier.

The cracker according to the invention was subjected to a testqa in which the variables were the bed material of the carburettor and the cracker, the amount of bed material and fluidizing air of the cracker and the temperature of the cracker. The results of the experiments are shown in Table 1.

In all the experiments shown in Table 1, the gasification air coefficient and the amount of crack material and fluidization air were kept constant. In Comparative Experiment A, the cracker had no bed and no air was introduced into it, with the temperature of the cracker being lower than in other experiments. In experiments B-E, the tar content of the gas entering the cracker was of the same order (6 g / m3n) as in experiment A. In contrast, in trial F, the tar concentration of the gas entering the cracker was lower because the lime bed of the carburetor.

The results of Table 1 (Test B) show that oxidation in cracker alone reduces the tar content of the gas to about half. When the cracker bed material was replaced with catalytically active limestone (Test D), the tar content at ta-25 was reduced to 1 g / m 3. The effect of the catalyst operating temperature is seen in the results of Experiments C-E. Raising the operating temperature of the cracker at 100 ° C reduced the tar concentration from 2.3 g / m3n to one third. When the tar concentration of the gas was already reduced in the carburettor (Test F, lime bed), the tar concentration in the cracker was reduced to 0.3 g / m3n.

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Table 1. Purification of gas with a cracker according to the invention

Experience Carburetor Cracker Cracker tar tar

Bed material Bed material Temperature (° C) after cracker ______ (g / m3n); A H No Pet 820 6.1 B H H 918 2.8 C H K 877 2.3 D H K 918 1.1 EH K 978 0.7 _F 1 K | K 926 1 0.3 H = sand, K = limestone 5 The cracker according to the invention can thus achieve a fairly good ter-conversion of 85-90%. When the tar content of the product gas in the carburettor was lowered with a replacement bed to the carburettor lime bed, the tar content was fairly close to that achieved with the known Nikke-Li monolithic catalyst.

10 Obviously, the cracker applications of the invention are not limited to the purification of the fluidized bed gasification product gas described in the example, but to the process! can also be applied to the treatment of gases formed, for example, in fixed bed gasifiers or other processes.

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Claims (12)

107164 9 A process for purifying product gas from a gasification reactor from tars and other cooling gas condensable organic compounds in a 5-fluidized bed reactor, characterized in that the purification takes place in a jet bed reactor (1,15), wherein - product gas (2) is fed beneath the feed point of the product gas (2) is a bubbling fluidized bed (5) maintained by the oxidizing gas (6) fed to the reactor (1, 15), which forms a first zone, - the product gas (2) forms a second or jet 9) moves with the jet (8) and where the main purification takes place, and - a third or equilibrium zone is arranged above the jet zone, in which the fluidized particles (9) differ from the purified gas (12). Method according to Claim 1, characterized in that a fourth or "Leu" zone is arranged in the reactor (1, 15) of the jet zone and the equilibrium zone. Process according to claim 1 or 2, characterized in that the product gas (2) to be purified is introduced into the reactor (1, 15) at a rate of 15-50 m / s, preferably 20-45 m / s. ; ; Method according to one of the preceding claims, characterized in that, to make the first zone fluidized bed (5) bubble, the oxidizing gas (6) is introduced into the reactor (1, 15) at a rate of 0.4 to 2.0 m / s, preferably 0 , 5-1.5 m / s. A method according to any one of the preceding claims, characterized in that said oxidizing gas (6) is air, oxygen, water vapor or a mixture of at least two of these. Method according to one of the preceding claims, characterized in that said oxidizing gas (6) is introduced into the reactor (1, 15) via a grate (7). • I V 107164 10 Method according to one of the preceding claims, characterized in that the fluidized particles (9) are limestone, dolomite, sand or a mixture of at least two of these. Process according to one of the preceding claims, characterized in that the temperature of the reactor (1, 15) is 700-1200 ° C, preferably 800-1000 ° C. Method according to one of the preceding claims, characterized in that the velocity of the gas flow in the equilibrium zone is 0.1-1.2 m / s, preferably 0.3-1.0 m / s. Method according to one of the preceding claims, characterized in that the product gas to be purified (2) is the result of the gasification of coal, peat, solid biomass or waste-based recycled fuel. 15 An apparatus for purifying the product gas of a gasification reactor from tars and violent gas condensable organic compounds, the apparatus comprising a cracked fluidized bed reactor having feed inlets to the product gas and a purified gas outlet, characterized in that the reactor (1, 15) comprises a traceable, - below a conical portion, a first cylindrical portion, - a grid (7) and at least one oxidizing gas (6) provided in a first cylindrical portion, - substantially in the center of the first cylindrical portion, the axis of the reactor (1, 15); ; 25 for product gas (2) of at least one feed pipe (3) arranged between the feed pipe (3) and the cylindrical part walls by a fluidized bed (5) maintained by the oxidizing gas (6); Apparatus according to Claim 11, characterized in that there are more than one of said *: feed pipes (3) and that they are substantially parallel. • {c »107164 11