JP2015193715A - start-up method of sour shift catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a start-up method enabling a shift catalyst to exhibit activity, even in the case of the catalyst having low activity.SOLUTION: The method includes: a first step of circulating heated nitrogen gas through a pre-sulfurized shift catalyst; a second step of gradually introducing a gasification gas into the shift catalyst until reaching a specified gas flow less than the supply amount in the steady operation while gradually decreasing the circulation amount of the nitrogen gas; a third step of continuing the supply of the gasification gas to the shift catalyst at the specified gas flow for a specified time, preferably under an atmospheric pressure of the shift catalyst maintained at about the pressure in the steady operation, with the zero amount of the circulating nitrogen; and a fourth step of increasing the supply amount of the gasification gas to the shift catalyst to the supply amount in the steady operation after the passage of the specified time. Preferably the circulating nitrogen gas includes 50 to 5000 ppmv of hydrogen sulfide and carbonyl sulfide, and the gasification gas includes 50 to 5000 ppmv of hydrogen sulfide and carbonyl sulfide.

Description

  The present invention relates to a sour shift catalyst start-up method, and more particularly to a sour shift catalyst start-up method used in a coal gasification process.

Coal is rich in recoverable reserves and has a low ubiquity in the minable area, so it has the advantage that it can be procured stably at a low price in the future. In addition to the generation of environmental pollutants such as oxides, there is a problem that the proportion of carbon dioxide (CO ₂ ) emissions is higher than other energy sources. Therefore, in recent years, a coal gasification process in which coal is gasified without directly burning it is attracting attention as a technology that can effectively use coal while suppressing environmental load.

The coal gasification process is centered on gasification of coal under air or oxygen atmosphere to generate gasification gas (also called synthesis gas) mainly composed of carbon monoxide (CO) and hydrogen (H ₂ ). By combining with various pre-treatments and post-treatments, it is expected to be used for a wide range of applications such as combined power generation, chemical raw materials such as fuel cells and synthetic liquid fuels, and hydrogen production. For example, Patent Document 1 discloses a combined coal gasification combined power generation facility (IGCC) in which a coal gasification process is applied to combined power generation.

  The coal gasification combined power generation facility is configured to drive a gas turbine with combustion energy of gasified gas generated in a gasification furnace, and further drive a steam turbine with steam obtained from the exhaust heat to perform combined power generation. In particular, in the process of Patent Document 1, before the gasified gas is combusted, the gasified gas is introduced into the shift reactor and water is allowed to act on carbon monoxide in the gasified gas to convert it into hydrogen and carbon dioxide. Furthermore, carbon dioxide is removed from the gasification gas by introducing the carbon dioxide into a decarbonator.

Japanese Patent No. 2870929

  As described above, by introducing the gasification gas into the shift reaction device and the decarbonation device before combustion, it is possible to recover carbon dioxide from the gasification gas extremely efficiently, and further increase the power generation efficiency of the power generation facility. Is possible. By the way, when starting up a shift reactor for treating a gas containing a sulfur compound such as coal gasification gas, heated nitrogen is first added to the shift reactor filled with a presulfided shift catalyst in advance. After circulating and heating the shift catalyst to a predetermined temperature, a method of gradually switching the circulating nitrogen to gasification gas has been used.

  However, at the time of start-up described above and at the subsequent re-start-up, there is a case in which a shift reaction hardly occurs when gasified gas is introduced. The present invention has been made in view of such a conventional problem, and a shift reaction can be developed even with a catalyst having low activity (here, the catalyst refers to the catalyst layer of the entire reactor). It aims to provide a startup method.

  In order to achieve the above object, a start-up method of a shift catalyst provided by the present invention includes a first step of circulating heated nitrogen gas to a presulfided shift catalyst, while gradually reducing the circulation amount of the nitrogen gas. A second step of gradually introducing gasified gas into the shift catalyst until a predetermined gas flow rate less than the supply amount during steady operation is reached, and the gasification gas to the shift catalyst with zero circulation of the nitrogen gas And a fourth step of increasing the supply amount of the gasification gas to the shift catalyst to the supply amount during the steady operation after elapse of the predetermined time; and It is characterized by consisting of.

  According to the present invention, it is possible to develop a shift reaction even with a shift catalyst having low activity.

It is a block flow figure showing coal gasification combined cycle power generation provided with the shift reaction device which can apply the start-up method of the shift catalyst of the present invention suitably. It is a typical flowchart of the shift reaction apparatus of FIG. It is a time chart which shows an example of the start-up method of the shift catalyst of this invention.

  Hereinafter, the start-up method of the shift catalyst of the present invention will be described with specific examples. First, a coal gasification combined power generation facility equipped with a shift reaction apparatus to which the shift catalyst start-up method of the present invention is preferably applied will be described with reference to FIG. The coal gasification combined power generation facility shown in FIG. 1 includes a gasification device 10 that gasifies coal, and a shift reaction device 20 that converts carbon monoxide in the gasification gas generated by the gasification device 10 into carbon dioxide. And the desulfurization / decarboxylation device 30 for separating hydrogen sulfide from the gasification gas discharged from the shift reaction device 20 and carbon dioxide, and the combustion energy of the gasification gas from which hydrogen sulfide and carbon dioxide have been removed. It is mainly composed of a combined power generator 40 that generates power using the power generator.

  Each apparatus will be specifically described with reference to FIG. 2. The gasifier 10 supplies coal supply means (not shown) for supplying coal in a form suitable for gasification, and supplies a gasifying agent. It mainly comprises gasifying agent supply means (not shown) and a gasification furnace (not shown) for gasifying coal. The inside of the gasification furnace is in a high-temperature and high-pressure atmosphere by air or oxygen supplied as a gasifying agent, and slurry-like or fine-powder-like coal is fed into this. The fed coal is discharged from the gasification furnace as a gasification gas composed of carbon monoxide, hydrogen, nitrogen, carbon dioxide and the like by a reaction such as thermal decomposition and partial oxidation. In addition, the ash contained in coal is discharged from the bottom as slag.

The gasification gas discharged from the gasification furnace contains particulate matter such as unburned carbon and impurities. Since these may adversely affect the subsequent processing, it is preferable to remove the gasification gas by providing a removing means such as a filter as needed before sending it to the shift reactor 20. The gasification gas sent to the shift reactor 20 is sent to a shift reactor filled with a shift catalyst after adding a predetermined ratio of steam to the flow rate. In the shift reactor, an aqueous shift reaction represented by the following formula 1 proceeds in the presence of a shift catalyst.
[Formula 1]
CO (g) + H ₂ O (g) = H ₂ (g) + CO ₂ (g)

  Since the aqueous shift reaction shown in the above formula 1 is an exothermic reaction, a low temperature is preferable in terms of chemical equilibrium from the viewpoint of CO conversion, and when the shift reaction is performed in one shift reactor, the outlet gas temperature becomes high. A predetermined reaction rate cannot be obtained. Therefore, in the shift reaction apparatus shown in FIG. 2, three shift reactors of the first shift reactor 22, the second shift reactor 24, and the third shift reactor 26 are provided in series, and heating is performed in the preceding stage. 1st-3rd temperature control means 21,23,25, such as an oven and a heat exchanger, are provided. Thereby, it becomes possible to adjust the inlet gas temperature of each shift reactor to about 200-300 degreeC, As a result, it becomes possible to ensure a predetermined shift reaction rate.

  As the shift catalyst filled in the first to third shift reactors, for example, a catalyst in which a cobalt-molybdenum catalyst is supported on an alumina carrier can be used. This catalyst can satisfactorily perform a shift reaction even in a gas containing a high concentration of sulfur compounds such as coal gasification gas, and a gas shift containing such a high concentration of sulfur compounds is possible. The reaction is sometimes called sour shift.

  After the gasified gas leaving the third shift reactor 26 is cooled to a temperature suitable for supply to the subsequent desulfurization / decarbonation apparatus 30 by cooling means 27 by heat exchange using cooling water as a refrigerant, for example. And sent to the desulfurization / decarbonation apparatus 30. The gas supply line from the cooling means 27 through which the gasified gas cooled by the cooling means 27 flows to the desulfurization / decarbonation apparatus 30 is branched from a recycle line that returns to the primary side of the first temperature adjusting means 21. A compressor 28 is provided in front of this branch point. Thereby, the recycle operation | movement of the 1st-3rd shift reactor mentioned later can be performed now.

The desulfurization / decarbonation apparatus 30 includes a chemical absorption method using a chemical absorption liquid such as an alkanolamine solution, a physical absorption method using a physical absorption liquid represented by Selexol ^TM , and the chemical absorption liquid and the physical absorption liquid. A general processing method such as a combined hybrid method can be used. By performing desulfurization treatment and decarbonation treatment on the gasification gas leaving the shift reaction device 20, hydrogen sulfide and carbon dioxide contained in the gasification gas are efficiently separated to obtain a hydrogen-rich gasification gas. On the other hand, hydrogen sulfide and carbon dioxide can be recovered separately.

  For example, in the case of the physical absorption method, first, the gasification gas exiting the shift reaction apparatus 20 is introduced into a desulfurization tower (not shown), and a large amount of carbon dioxide is discharged from the bottom of the subsequent decarbonation tower. By supplying the contained absorbent and bringing them into countercurrent gas-liquid contact, hydrogen sulfide in the gasified gas is selectively absorbed by the absorbent. Next, the desulfurized gasified gas discharged from the top of the desulfurization tower is led to a decarbonation tower (not shown), and an absorption liquid regenerated in the regenerator described later is supplied to counterflow the gas and liquid. By contacting, carbon dioxide in the gasification gas and part of the remaining hydrogen sulfide are absorbed by the absorption liquid. Thereby, the gasification gas desulfurized and decarboxylated can be taken out from the top of the decarboxylation tower. The absorption liquid containing carbon dioxide and hydrogen sulfide is discharged from the bottom of the desulfurization tower, and this absorption liquid containing carbon dioxide and hydrogen sulfide is sent to a flash drum (not shown), where the absorption liquid The carbon dioxide is recovered by depressurizing the gas and then sent to a regeneration tower (not shown) to recover hydrogen sulfide by heating the absorbent. The recovered carbon dioxide gas is pressurized as necessary, and then used for EOR (Enhanced Oil Recovery) or the like. On the other hand, hydrogen sulfide is sent to a sulfur recovery device.

  The gasified gas desulfurized and decarboxylated by the desulfurization / decarbonation apparatus 30 is then sent to the combined power generation apparatus 40. In the combined power generator 40, the desulfurized and decarboxylated gasified gas is burned in a combustor (not shown) to generate a high-temperature and high-pressure gas. Power is generated by turning a gas turbine (not shown) with the energy of the combustion gas. Further, the combustion gas exiting the gas turbine is sent to an exhaust heat recovery boiler (not shown) where steam is generated. A steam turbine (not shown) is rotated by this steam to generate power.

Next, the start-up method of the shift reaction apparatus 20 will be described with reference to FIG. It is assumed that the shift catalyst charged in the shift reactor 20 is presulfided before start-up. The preliminary sulfidation of the shift catalyst can be performed, for example, by the following method. In the present invention, even if carbonyl sulfide (COS) is used instead of hydrogen sulfide or together with hydrogen sulfide, substantially the same effect can be obtained. Therefore, “hydrogen sulfide” hereinafter is “hydrogen sulfide” unless otherwise specified. And / or “carbonyl sulfide”. Further, as a supply source of hydrogen sulfide, a method of vaporizing / decomposing DMDS, a method of using an H ₂ S cylinder, or the like can be considered. First, heated nitrogen is circulated to the shift reactor filled with the shift catalyst using the above-described recycle line and the compressor 28, and then the temperature of the catalyst is prevented from becoming too high in the circulation system. Carefully add hydrogen and hydrogen sulfide each until a predetermined concentration is reached. When the predetermined hydrogen concentration and hydrogen sulfide concentration are reached, the circulation operation is continued while maintaining the concentration until hydrogen sulfide breakthrough is observed.

  Start-up is performed in accordance with the time chart shown in FIG. 3 for the shift reactor 20 including the shift catalyst presulfided in this manner. More specifically, first, as shown in the first step, the first to third shift reactors 22, 24, 26 filled with the shift catalyst are supplied with nitrogen gas using the above-described recycling line and compressor 28. Circulate. The flow rate for circulating nitrogen is, for example, about 90% of the gas flow rate during steady operation.

At that time, the shift catalyst in each shift reactor is gradually heated using the first temperature adjusting means 21 and, if necessary, the second to third temperature adjusting means 23 and 25, and the inlet gas of the first shift reactor 22. This temperature state is maintained when the temperature reaches about 260 ° C. Note that when the shift catalyst is heated, the rate of change in the inlet gas temperature of the first shift reactor 22 is 60 ° C. or less per hour. Further, during the circulation of the nitrogen gas, the pressure in the system is maintained so that the inlet pressure of the first shift reactor 22 is about 1.5 MPaG, preferably near the pressure during steady operation. The vicinity of the pressure during steady operation refers to a pressure range of about ± 0.5 MPa with respect to the pressure during steady operation. The circulation operation in this state is continued until the catalyst temperature of all shift reactors exceeds the vapor dew point (for example, 180 ° C. or more). This makes it possible to heat the shift catalyst while preventing the methanation reaction due to CO or CO _{2 as} compared with a temperature raising method using gasified gas.

  When oxygen is contained in the circulating nitrogen gas, it is preferable to contain hydrogen sulfide or hydrogen sulfide and hydrogen in the circulating nitrogen gas. The reason is that if oxygen is contained in the circulating nitrogen gas, the catalyst may be oxidized and the activity may be reduced. However, as described above, hydrogen sulfide or hydrogen sulfide and hydrogen coexist, It is because the oxidation of can be prevented. In general, the above requirements can be satisfied by setting the hydrogen sulfide concentration in the circulating nitrogen gas to 50 to 5000 ppmv, more preferably about 5 to 10 vol%.

Next, as shown in the second step, the valve on the recycle line is gradually throttled so that the flow rate of the circulating nitrogen gas is approximately half the circulation flow rate in the first step (the gas flow rate during steady operation). Gradually lower until about 45%). In parallel with this, the first to third shift reactors 22, 24, 26 are supplied with gasification gas from the preceding gasification apparatus 10 until the flow rate reaches, for example, about 45% of the supply amount in steady operation. Introduce gradually. At this time, an amount of gas commensurate with the amount of gasification gas introduced is sent to the subsequent desulfurization / decarboxylation device 30. In addition, when introducing gasification gas, attention is paid so that the rate of change per minute of the gas flow rate is 10 Nm ³ / h or less.

When introducing the gasification gas, it is desirable that hydrogen sulfide is contained in the gasification gas in order to prevent reduction of the catalyst by CO and H _{2 in} the gasification gas. Specifically, hydrogen sulfide is introduced into the gasification gas when the gasification gas is introduced so that the hydrogen sulfide concentration in the gasification gas is 50 to 5000 ppmv.

  Next, as shown in the third step, the operation is continued with the gasification gas supply amount maintained at a flow rate of about 45% in the above-described steady operation. In the initial stage of the third step, the valve on the recycle line is gradually closed, so that the amount of nitrogen circulated is gradually reduced from about the above half to finally become zero. As a result, the concentration of carbon monoxide in the gas passing through the shift catalyst is increased and the SV (Space Velocity) of the catalyst is decreased, so that a shift reaction is likely to occur and the activity of the catalyst can be expressed. In addition, among the shift catalysts, it is possible to promote the shift reaction of other sites by utilizing the shift reaction heat expressed from the site where the shift reaction is likely to occur.

  Furthermore, in the third step, it is preferable that the atmospheric pressure of the shift catalyst is gradually increased and maintained near the pressure during steady operation when the amount of nitrogen circulation becomes zero. Thereby, since SV of a catalyst falls, it will be in the situation where a shift reaction will occur more easily. FIG. 3 shows an example in which the inlet pressure of the first shift reactor 22 is maintained at 2.2 MPaG. The increase in the system pressure may be performed in parallel with the operation of decreasing the nitrogen circulation rate. When gradually increasing the atmospheric pressure of the shift catalyst, the rate of change is preferably set to 0.004 MPa or less per minute.

  In the second and third steps, the gasification gas preferably contains about 50 to 5000 ppmv of hydrogen sulfide. The reason is that it is considered that hydrogen sulfide is adsorbed on the shift catalyst and contributes to the expression of its activity. If the gasified gas from the gasifier 10 does not contain hydrogen sulfide at the above concentration, a hydrogen sulfide gas may be added to the upstream side of the first temperature adjusting means 21 by connecting a hydrogen sulfide cylinder or the like. Good.

Next, as shown in the fourth step, the supply amount of the gasification gas from the gasifier 10 is increased to the gas flow rate during normal operation (that is, 100%). When increasing, it is preferable to operate the gas flow rate so that the rate of change per minute is 5 Nm ³ / h or less. Then, the pressure in the system is increased so that the inlet pressure of the first shift reactor 22 becomes about 2.5 MPaG when the supply amount of the gasification gas is increased until the steady operation.

  By starting up with the above method, it becomes possible to effectively develop the activity of the shift catalyst at a relatively early stage after the start of steady operation. Although it is not known in detail about the reason why the activity of the shift catalyst can be expressed by the above-mentioned method, the inventors contact the pre-sulfided shift catalyst with a gas containing a trace amount of sulfide, so that the catalyst has some structure. It is considered that the change is caused or the oxidation or reduction of the catalyst is prevented.

  The start-up method of the shift catalyst of the present invention has been described with a specific example, but the present invention is not limited to such a specific example, and various modifications can be made without departing from the spirit of the present invention. It should be noted that and alternatives may be included. For example, in the above description, the case where the shift catalyst start-up method of the present invention is applied to an IGCC shift reaction apparatus has been described. However, the present invention is not limited to this, and fuel cells, chemical raw materials, and hydrogen production are used. It can also be suitably used for a shift reactor for a coal gasification process.

[Example]
The shift reactor as shown in FIG. 2 filled with the presulfided topsoe shift catalyst (model number SSK-10) was started up according to the time chart shown in FIG. In the third step, hydrogen sulfide gas was added upstream of the first temperature adjusting means 21 so that the H ₂ S concentration in the gas was 1,000 ppmv. As a result, after the nitrogen gas circulation amount became zero, the activity of the catalyst was quickly developed. The expression of the shift catalyst activity was judged by the temperature trend of the catalyst layer.

[Comparative example]
For comparison, for the same shift reaction apparatus as in the above example filled with the same shift catalyst as in the above example, the second to third steps in FIG. After the nitrogen gas was circulated for 24 hours while maintaining the inlet gas temperature of the 1-shift reactor 22 at 265 ° C., gasification equivalent to the above example was performed at a rate of change of 10 Nm ³ / h per minute in the fourth step. Start-up was performed by reducing the nitrogen gas circulation rate from 90% to zero while introducing gas. As a result, no activity was obtained.

DESCRIPTION OF SYMBOLS 10 Gasifier 20 Shift reactor 21 1st temperature control means 22 1st shift reactor 23 2nd temperature control means 24 2nd shift reactor 25 3rd temperature control means 26 3rd shift reactor 27 Cooling means 28 Compressor 30 Desulfurization / decarbonation equipment 40 Combined power generation equipment

Claims (4)

  A first step of circulating heated nitrogen gas to the presulfided shift catalyst, and a predetermined gas flow rate that is less than the supply amount during steady operation of the gasification gas to the shift catalyst while gradually reducing the circulation amount of the nitrogen gas. A second step of gradually introducing the gas until it reaches a value, and a third step of continuing the supply of the gasification gas to the shift catalyst for a predetermined time while maintaining the predetermined gas flow rate with the amount of nitrogen gas circulated zero. A start-up method for a shift catalyst, comprising a fourth step of increasing the supply amount of gasification gas to the shift catalyst to the supply amount during the steady operation after the predetermined time has elapsed.   2. The start-up method of a shift catalyst according to claim 1, wherein in the third step, the atmospheric pressure of the shift catalyst is increased to and maintained near the pressure during the steady operation.   The nitrogen gas to be circulated contains 50 to 5000 ppmv of hydrogen sulfide and / or carbonyl sulfide, and the gasification gas contains 50 to 5000 ppmv of hydrogen sulfide and / or carbonyl sulfide. The start-up method of the shift catalyst according to claim 1 or 2.   The start-up method for a shift catalyst according to claim 3, wherein the nitrogen gas to be circulated further contains 5 to 10 vol% of hydrogen in total.

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