JP4594239B2 - Gas purification system and gas purification method - Google Patents

Description

  The present invention relates to a gas purification system including a process for purifying generated gas, and also relates to a purification method.

  The use of gas generated by coal gasification, that is, coal gas, as a fuel for gas turbines and fuel cells has been studied. When using coal gas for a gas turbine or a fuel cell, it is required to reduce the corrosive sulfur compound contained in the coal gas to a concentration of 1 ppm or less. For this reason, studies have been conducted to reduce the sulfur compound of coal gas (see, for example, Patent Document 1). Patent Document 1 describes that coal gas is cooled, dedusted, and desulfurized and used as fuel gas for a fuel cell.

  The sulfur compound removal method includes a humidity treatment method and a dry treatment method using a desulfurizing agent such as an adsorbent and a catalyst. As the desulfurizing agent, a zinc oxide-based desulfurizing agent is mainly used, and it is known to have high adsorption performance at a high temperature of about 350 ° C. Moreover, although it is hardly used for desulfurization of coal gas, synthetic zeolite is known as a desulfurization agent for hydrocarbon gas such as natural gas (for example, see Patent Document 2).

Japanese Patent No. 3108079 (Claim 2) JP 10-237473 A (summary)

  When a zinc oxide-based desulfurizing agent is used, it is necessary to supply oxygen and burn the sulfur during the regeneration process. When the sulfur content is combusted, sulfur dioxide is generated, and this gas remains in the regenerated desulfurizing agent, resulting in a problem that the sulfur adsorbing capacity of the regenerated desulfurizing agent is lowered. In addition, when a zinc oxide-based desulfurizing agent is used, since this desulfurizing agent has excellent adsorption performance at a high temperature of about 350 ° C., a heat exchanger is often installed in the desulfurizing tower. However, there is a problem that the desulfurization agent replacement work becomes complicated.

  An object of the present invention is to provide a gas purification system and a gas purification method capable of removing sulfur in a gas at a low temperature and regenerating the desulfurizing agent without burning.

  The present invention comprises a wet desulfurization apparatus and a dry desulfurization apparatus as gas desulfurization apparatuses, and then a purified gas purified by the wet desulfurization apparatus is then processed by a dry desulfurization apparatus having a desulfurization catalyst made of synthetic zeolite. In the purification system.

  The present invention also lies in a gas purification method in which a gas is subjected to a wet desulfurization treatment and thereafter a dry desulfurization treatment is performed using a desulfurization catalyst made of synthetic zeolite.

  In the present invention, a plurality of types of synthetic zeolites having different removal functions are used, and the gas is first treated with a synthetic zeolite having an excellent water removal capability, such as 3A, and then a synthetic zeolite having an excellent sulfur compound removal capability, such as 4A and 5A. It is desirable to use it for dry desulfurization treatment. Further, it is desirable to lower the temperature of the gas to 0 to 10 ° C. before performing dry desulfurization.

  According to the present invention, a sulfur compound contained in a gas can be removed at a low temperature. Moreover, since synthetic zeolite is used, it can be regenerated without burning.

  Hereinafter, although embodiment of this invention is described, this invention is not limited to embodiment shown below.

  FIG. 1 shows a first embodiment of a coal gasification system according to the present invention. The coal gasification system according to the present embodiment includes a coal supply system including coal hoppers 1A and 1B, an oxygen production apparatus 2, a gasification furnace 3, a heat recovery device 4, a filter 5, a cleaning tower 6, and an absorption unit. The tower 7, the regeneration tower 8, the sulfur content recovery device 9, and the precision desulfurization towers 11A and 11B are the main components.

  The process flow of this coal gasification system will be described. The coal 10 is pulverized into pulverized coal having an average particle size of about 40 μm suitable for gasification, supplied to the coal hopper 1A, and then supplied to the coal hopper 1B maintained at a pressure higher than the pressure of the gasification furnace 3. . Although not shown, the oxygen production apparatus 2 includes an air separation tower, a nitrogen compressor, and an oxygen compressor, and separates air into nitrogen and oxygen 1001. Oxygen 1001 is compressed by an oxygen compressor, supplied to a gasification furnace together with pulverized coal, and used as an oxidizing agent for gasifying the coal. The separated nitrogen 1003A and 1003B are compressed by a nitrogen compressor and then used as a carrier gas for conveying pulverized coal to the gasification furnace 3 or a regeneration gas for regenerating synthetic zeolite.

  In the gasification furnace 3, a gasification reaction of coal is caused by a fuel 1002 composed of pulverized coal and oxygen 1001 as an oxidant, and a combustible product gas 1101 mainly composed of hydrogen and carbon monoxide is generated. Since the gasification furnace 3 is at a high temperature of about 1600 ° C., the ash contained in the coal is melted, taken out from the lower part of the gasification furnace 3, crushed by water cooling, and slag which is a glassy solid. It becomes. The product gas 1101 has a high temperature of about 1000 ° C. and is cooled to a temperature of about 400 ° C. by the heat recovery device 4 such as an exhaust heat recovery boiler.

  Since the product gas 1101 contains impurities such as sulfur and halogen in addition to unburned char, first, solids such as char are collected by a dry dust removal system including the filter 5. The dust removal system includes a cyclone and a filter 5 (not shown). The recovered char is re-supplied to the gasification furnace 3 to melt ash into slag, and the unreacted carbon is gasified.

  The coal gas after dedusting contains fine solids that could not be removed by the dedusting system, and impurities such as ammonia, carbonyl sulfide, and hydrogen sulfide generated from nitrogen and sulfur contained in the coal. It is. Fine solids may cause clogging or wear of various devices installed downstream, and ammonia and sulfur compounds generate harmful gases such as nitrogen oxides and sulfur oxides when gas is burned. Need to be removed. Fine solids are removed by washing the gas in the washing tower 6 with water. By cooling the gas to a temperature of about 110 ° C. in the washing tower 6, ammonia in the coal gas is also absorbed and removed by the water. After washing in coal gas, carbonyl sulfide is removed using a carbonyl sulfide converter (not shown). As the carbonyl sulfide converter, a reactor in which carbonyl sulfide is reacted with moisture using a catalyst to convert to hydrogen sulfide can be used. As a result, most of the sulfur compounds in the coal gas become hydrogen sulfide. Next, the hydrogen sulfide is removed by the absorption tower 7. A hydrogen sulfide absorption liquid, which is an amine compound, circulates in the absorption tower 7, and hydrogen sulfide is absorbed by passing coal gas, and the concentration of the sulfur compound in the gas is reduced to about 10 ppm.

  The hydrogen sulfide absorbing liquid composed of an amine compound circulating in the absorption tower 7 becomes a rich liquid 1201 containing hydrogen sulfide and carbon dioxide, and after being recovered by the heat exchanger 23, becomes a rich liquid 1202. It is thrown into the upper part of the regeneration tower 8. In the regeneration tower 8, steam is supplied from a reboiler (not shown) installed in the lower part, and comes into contact with the rich liquid 1202 supplied from the upper part to separate hydrogen sulfide and carbon dioxide in the rich liquid. The lean liquid from which hydrogen sulfide and carbon dioxide have been removed from the rich liquid is withdrawn as a lean liquid 1203 from the lower part of the regeneration tower 8 and is introduced into the upper part of the absorption tower 7 via the heat exchanger 23.

  On the other hand, the acidic gas 1211 mainly consisting of water vapor, carbon dioxide and hydrogen sulfide extracted from the upper part of the regeneration tower 8 is sent to the sulfur content recovery device 9, where the sulfur content is burned and recovered as gypsum, The remaining gas 1212 is discharged out of the system as exhaust gas 100.

  The refined gas 1106 refined by treating the coal gas in the absorption tower 7 becomes the refined gas 1108 via the heat exchangers 22 and 21, and is supplied to one of the precision desulfurization towers 11A and 11B. The reason why two precision desulfurization towers are installed in FIG. 1 is that when the desulfurization treatment is performed on the one hand, the regeneration treatment is performed on the other hand.

  A case where the purified gas 1108 is sent to the precision desulfurization tower 11A will be described as an example. The purified gas 1108 is sent as the purified gas 1109A to the precision desulfurization tower 11A through the valve 51. In the precision desulfurization tower 11 </ b> A, sulfur-containing gases such as hydrogen sulfide and carbonyl sulfide are removed by synthetic zeolite to become clean purified gas 1110 </ b> A and fuel 101 through the valve 53. This fuel is used as fuel for fuel cells and the like.

  When the desulfurization treatment is performed in the precision desulfurization tower 11A, the precision desulfurization tower 11B performs a process of regenerating the desulfurization agent. In the precision desulfurization tower 11B, the purified gas 1109B has already been supplied and the desulfurization process has already been performed. In the regeneration process, the regeneration gas 1302 stored in the regeneration gas storage tank 12 is supplied to the precision desulfurization tower 11B through the valve 62. Thereby, hydrogen sulfide and carbonyl sulfide adsorbed on the synthetic zeolite are desorbed. Regenerated exhaust gas 1110B containing hydrogen sulfide and carbonyl sulfide is discharged out of the system as exhaust gas 102 via valve 64. Note that the regeneration gas storage tank 12 stores the regeneration gas 1301 whose pressure has been increased by the regeneration gas compressor 13. Examples of the regeneration gas include dry air and dry nitrogen.

  According to the coal gasification system of this embodiment, the sulfur component which is an impurity in coal gas can be removed to a molecular sieve with high precision.

  In the precision desulfurization towers 11A and 11B, synthetic zeolite is used as a desulfurization agent. Synthetic zeolite has molecular selectivity in which components that can be adsorbed are determined by the size and polarizability of molecules in the gas. The adsorption capacity of molecules is in the order of water> hydrogen sulfide> sulfur dioxide> carbonyl sulfide> carbon dioxide, and adsorbs hydrogen sulfide and carbonyl sulfide, but also has the property of adsorbing moisture and carbon dioxide at the same time. These adsorption capacities vary depending on the type of synthetic zeolite.

  In the present invention, it is desirable to use 3A, 4A and 5A as the synthetic zeolite. 3A synthetic zeolite is excellent in the adsorption performance of molecules having an effective diameter of 0.3 nm or less, such as moisture, ammonia and helium. The synthetic zeolite 4A is excellent in adsorbing molecules having an effective diameter of 0.4 nm or less, such as hydrogen sulfide, carbonyl sulfide, and carbon dioxide, but also adsorbs moisture and ammonia that can be adsorbed by 3A. 5A zeolite is excellent in adsorbing molecules having an effective diameter of 0.5 nm or less, such as n-paraffin and n-olefin, but also adsorbs molecules that can be adsorbed by 4A.

  The purified gas after treatment in the absorption tower 7 usually contains several percent of carbon dioxide and about 10 ppm of sulfur compounds. Thus, it is considered difficult to remove a sulfur compound of several ppm order by synthetic zeolite with a gas containing several percent of carbon dioxide, and a zinc oxide-based desulfurizing agent has been conventionally used. However, in the course of reaching the present invention, it was confirmed that even if several percent of carbon dioxide was contained, a sulfur compound in the order of several ppm could be removed by synthetic zeolite.

  In removing sulfur compounds with synthetic zeolite, it is desirable to stack a plurality of synthetic zeolites having different adsorption capacities in multiple stages, or to install a plurality of desulfurization towers filled with synthetic zeolite in series. Then, moisture is first removed using a synthetic zeolite such as 3A having excellent moisture adsorption ability, and then sulfur compound removal treatment is performed using a synthetic zeolite such as 4A and 5A having excellent sulfur compound adsorption ability. It is desirable to do.

  FIG. 2 shows a precision desulfurization tower 11 having a configuration in which different types of synthetic zeolite are installed in two stages. Synthetic zeolite 110 having excellent water removal capability such as 3A is disposed at the inlet portion where purified gas 1109 from absorption tower 7 flows, and sulfur compound removal capability such as 4A and 5A is disposed at the outlet portion of purified gas 1110. An excellent synthetic zeolite 120 is arranged. By comprising in this way, the refined gas which flowed into the precision desulfurization tower is dried and isolate | separated into a sulfur component and a water | moisture content, Therefore There exists an effect that the sulfur compound removal performance by the latter synthetic zeolite improves.

  FIG. 7 shows the sulfur adsorption ability when coal gas containing several percent of carbon dioxide and several tens of ppm of hydrogen sulfide is desulfurized using synthetic zeolite 5A. If the amount of carbon dioxide is large, the ability to adsorb sulfur content decreases, but if the amount of carbon dioxide is within a range of several percent, the sulfur content can be adsorbed and removed by synthetic zeolite.

  In the present invention, when the desulfurization treatment is performed in the precision desulfurization tower, the temperature of the coal gas is preferably lowered to about 0 to 10 ° C. Lowering the temperature of the coal gas reduces the amount of moisture in the gas and has the effect of increasing the subsequent desulfurization performance with synthetic zeolite. FIG. 6 shows the relationship between the temperature of the coal refined gas by the absorption tower and the sulfur adsorption capacity by the synthetic zeolite 5A. When the coal gas temperature is in the range of 0 to 10 ° C., the sulfur adsorption capacity is high. I understand that.

  FIG. 3 shows a coal gasification system according to a second embodiment of the present invention. FIG. 3 differs from FIG. 1 in that nitrogen 1310 obtained by the oxygen production apparatus 2 is used as the gas used for regeneration of the desulfurization agent in the precision desulfurization towers 11A and 11B.

  In the coal gasifier system equipped with the oxygen production apparatus 2, oxygen 1001 necessary for the combustion of coal is produced from air, and as a by-product, nitrogen is produced in an amount nearly four times that of oxygen. Since this nitrogen is produced by a deep-layer cooling method, it is dry and is a suitable condition for regenerating a synthetic zeolite adsorbed with impurities. Since the desulfurization treatment with the synthetic zeolite is performed by physically adsorbing the sulfur content, the adsorbed sulfur content can be easily desorbed by flowing nitrogen gas.

  According to the second embodiment, dry nitrogen, which is a by-product of the oxygen production apparatus provided in the coal gasification system, can be used as a regeneration gas for the synthetic zeolite. Therefore, the system efficiency of the coal gasification system The effect is that can be increased. In this embodiment, nitrogen gas produced as a by-product by an oxygen production apparatus, which is unique to a coal gasification system, is used as regeneration gas.

  However, the nitrogen produced by the oxygen production apparatus is also used for transporting coal, backwashing the filter, etc., and cannot be used unconditionally only for regeneration of the desulfurization agent. Increasing the capacity of the oxygen production system makes it possible to use nitrogen for regeneration regardless of other nitrogen utilization conditions, but oxygen is left over, resulting in higher system production costs and operational costs. Not right.

  Therefore, it is desirable to operate the nitrogen produced by the oxygen production apparatus as shown in FIG. FIG. 4 shows the nitrogen supply amount (ratio to the rated capacity) in the upper stage, and the time course of the ratio of the adsorption quantity to the adsorption capacity of the synthetic zeolite, which is a precision desulfurization catalyst, in the lower stage. In the upper nitrogen supply amount, there are a nitrogen amount for a coal supply system that is always used at a rating and a nitrogen amount for preventing the pressure detection end from being blocked. Apart from this, there is a nitrogen amount for backwashing used to eliminate clogging of the filter that collects char contained in the coal gas, and the coal is supplied from the coal hopper 1003A to the coal supply hopper 1003B. There is an amount of nitrogen supplied to the lock hopper for use. The use time interval of nitrogen used to prevent clogging of the filter or supply to the lock hopper is irregular.

  On the other hand, the adsorption amount in precision desulfurization can be calculated from the gas amount of the purified gas 1106 from the absorption tower 7 and the sulfur content in the gas. These vary depending on the concentration of sulfur in the coal to be input and the amount of input coal. If there is almost no sulfur concentration at the exit of the precision desulfurization towers 11A and 11B, the product of the flow rate of the refined gas 1106 and the sulfur concentration in the gas can estimate the sulfur content adsorbed in the precision desulfurization towers 11A and 11B. It can be estimated whether it is necessary to regenerate the precision desulfurization towers 11A and 11B in the period of time. Therefore, the precise desulfurization adsorption amount at the lower limit of regeneration indicated by LL in FIG. 4 and the upper limit of regeneration indicated by UL (Usually, this is a safety factor, so UL is a value of 100% or less.) Set. Since the time a when the precise desulfurization adsorption amount reaches LL is a time required for the amount of nitrogen supplied to the lock hopper, the regeneration cannot be performed immediately. Therefore, operation is performed so that the total amount of necessary nitrogen does not exceed the amount of nitrogen that can be supplied by starting regeneration from time zone b in which the lock hopper supply nitrogen is zero and there is no other irregular amount of nitrogen usage. .

  According to the operation of the nitrogen gas shown in FIG. 4, dry nitrogen, which is a byproduct of the oxygen production apparatus, can be efficiently used as a regeneration gas, so that the system efficiency of the coal gasification system can be increased. .

  A third embodiment of the present invention will be described with reference to FIG. 5 is different from FIG. 1 in that the absorption tower is omitted and the coal gas 1104 discharged from the washing tower 6 is directly supplied to the precision desulfurization towers 11A and 11B. The coal gas 1104 exiting the washing tower contains a sulfur compound and contains several times the amount of carbon dioxide. The temperature of the coal gas 1104 is about 40 ° C. With such a sulfur compound and carbon dioxide content, desulfurization treatment with synthetic zeolite is possible. Therefore, the washed coal gas is cooled by the heat exchangers 22 and 21, cooled to a temperature of 0 to 10 ° C. suitable for desulfurization treatment with synthetic zeolite, and supplied to the precision desulfurization tower 11A or 11B. As described above, it is desirable to provide a plurality of synthetic zeolites having different adsorption capacities in a multistage in the precision desulfurization tower. According to this embodiment, the system configuration of the coal gasification system can be simplified.

  According to the third embodiment, a coal gas refining method can be proposed in which coal gas is washed with water, cooled, and then subjected to dry desulfurization treatment with a desulfurization catalyst made of synthetic zeolite.

  In the above embodiment, the target gas is described as a coal gasification gas. However, as long as the gas contains a sulfur compound, it is not applicable only to coal gas. Needless to say, the gas can be applied to a gas, and it is obvious that a gas having a lower carbon dioxide content requires less desulfurization agent for desulfurization.

The system block diagram which showed the coal gasification system by 1st embodiment of this invention. The schematic block diagram of the precision desulfurization tower by one Example of this invention. The system block diagram which showed the coal gasification system by 2nd embodiment of this invention. The figure which shows the nitrogen gas operation example in the coal gasification system of this invention. The system block diagram which showed the coal gasification system by 3rd embodiment of this invention. The figure which showed the correlation with the sulfur content adsorption capacity of synthetic zeolite, and coal gas temperature. The figure which shows the sulfur adsorption capacity of a synthetic zeolite with respect to the coal gas containing a carbon dioxide and a sulfur compound.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 2 ... Oxygen production apparatus, 3 ... Gasification furnace, 4 ... Heat recovery device, 5 ... Filter, 6 ... Cleaning tower, 7 ... Absorption tower, 8 ... Regeneration tower, 9 ... Sulfur recovery apparatus, 10 ... Coal, 11 ... Precision Desulfurization tower, 11A ... precision desulfurization tower, 11B ... precision desulfurization tower, 12 ... regeneration gas storage tank, 13 ... regeneration gas compressor, 21 ... heat exchanger, 22 ... heat exchanger, 23 ... heat recovery heat exchanger, 1101 ... Product gas, 1106 ... purified gas.

Claims (7)

A dry desulfurization apparatus comprising a wet desulfurization apparatus and a dry desulfurization apparatus for removing sulfur compounds contained in a gas, wherein a trace amount of sulfur compounds contained in the purified gas purified by the wet desulfurization apparatus is filled with a desulfurization catalyst made of synthetic zeolite. A gas purification system for processing with an apparatus,
The gas purification system characterized in that the synthetic zeolite charged in the dry desulfurization apparatus is 3A, 4A and / or 5A . 2. The gas purification system according to claim 1 , wherein the dry desulfurization apparatus includes a desulfurization tower in which the desulfurization catalyst is disposed in a plurality of stages, and a synthetic zeolite having an excellent water removal capability is disposed at an inlet portion of the desulfurization tower. The synthetic zeolite having excellent sulfur compound removal ability is disposed at the outlet portion, the synthetic zeolite disposed at the inlet portion of the desulfurization tower is 3A, and the synthetic zeolite disposed at the outlet portion is 4A and / or 5A. A gas purification system characterized by that. A wet desulfurization apparatus and a dry desulfurization apparatus for removing sulfur compounds contained in the generated gas, and a desulfurization catalyst made of synthetic zeolite for converting a trace amount of sulfur compounds contained in the purified gas purified by the wet desulfurization apparatus. A gas purification system comprising a cooling device that is treated with a dry desulfurization apparatus and that recovers and cools the purified gas treated with the wet desulfurization apparatus between the wet desulfurization apparatus and the dry desulfurization apparatus,
The gas purification system, wherein the cooling device is a cooling device having a function of cooling the purified gas to a temperature range of 0 to 10 ° C. 4. The gas purification system according to claim 3 , wherein the dry desulfurization apparatus includes a desulfurization tower in which the desulfurization catalyst is arranged in a plurality of stages, and a synthetic zeolite having an excellent water removal capability is disposed at an inlet portion of the desulfurization tower. The synthetic zeolite having excellent sulfur compound removal ability is disposed at the outlet portion, the synthetic zeolite disposed at the inlet portion of the desulfurization tower is 3A, and the synthetic zeolite disposed at the outlet portion is 4A and / or 5A. gas purification system, characterized in that there. A desulfurization comprising a synthetic zeolite as the desulfurization device, comprising: a washing tower for washing solids contained in the generated gas with water; and a desulfurization device for removing sulfur compounds contained in the gas after washing in the washing tower. A dry desulfurization apparatus filled with a catalyst; and a cooling apparatus that heat-recovers and cools the gas washed in the washing tower on the upstream side of the dry desulfurization apparatus, and the gas cooled by the cooling apparatus A gas purification system for processing in the dry desulfurization apparatus,
The gas refining system, wherein the cooling device is a cooling device having a function of cooling the coal-producing gas to a temperature range of 0 to 10 ° C. 6. The gas purification system according to claim 5 , wherein the dry desulfurization apparatus is provided with a desulfurization tower in which the desulfurization catalyst is disposed in a plurality of stages, and a synthetic zeolite having an excellent water removal capability is disposed at an inlet portion of the desulfurization tower. A synthetic zeolite having an excellent ability to remove sulfur compounds is disposed at the outlet portion, the synthetic zeolite disposed at the inlet portion of the desulfurization tower is 3A, and the synthetic zeolite disposed at the outlet portion is 4A and / or 5A. gas purification system, characterized in that there. In the gas purification method in which the generated gas is contacted with a desulfurization catalyst to remove sulfur compounds, the product gas is subjected to wet desulfurization treatment, and then dry desulfurization treatment is performed with a desulfurization catalyst made of synthetic zeolite. The gas purification method is characterized in that after the purified gas obtained by the wet desulfurization treatment is subjected to heat exchange and cooled to a temperature of 0 to 10 ° C., the dry desulfurization treatment is performed.

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