JP2010017699A - Desulfurization method and device of exhaust gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a desulfurization method and a device of exhaust gas by which sulfur dioxide can inexpensively and highly efficiently be recovered. <P>SOLUTION: The exhaust gas is brought into two-stage contact with an absorption liquid to perform an absorption. The absorption of the exhaust gas at the downstream side assures high desulfurization effect since the saturation degree of the absorbing liquid is low. On the other hand, in the absorption of the exhaust gas at the upperstream side, since the absorption liquid used at the downstream side is used and is made in contact with the exhaust gas of a high concentration of sulfur oxides, the saturation degree of the absorbing liquid becomes high, and the absorbing liquid is evaporated and concentrated by the contact with the high-temperature and low-humidity exhaust gas to drastically increase the saturation degree of the sulfur oxides of the concentrate, thereby drastically reducing the amount of energy to be used for evaporation and concentration in regeneration. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a gas desulfurization method for removing sulfur oxides such as sulfur dioxide contained in various gases, a desulfurization apparatus using this method, and the like.

  The exhaust gas discharged from various industries and daily life often contains sulfur oxides such as sulfur dioxide. In particular, a large amount of sulfur oxides such as sulfur dioxide are contained in the combustion gas obtained by burning coal, heavy oil, etc. as fuel, and exhaust gas from a sintering plant, sulfuric acid plant, refining plant, garbage incinerator, etc., and must be removed. Until now, many flue gas desulfurization methods using calcium compounds represented by the limestone-gypsum method as an absorbent have already been put to practical use. However, a large amount of gypsum has been generated, which is sufficient due to quality and demand. In many cases, it is thrown away as waste.

  A sodium sulfite circulation method that converts sulfur oxides in exhaust gas into sulfuric acid was developed as a method that can use the sulfur generated in the desulfurization process as a resource. However, a large amount of absorption liquid is evaporated by heating from low concentration to decomposition. Since the method of concentrating and regenerating is used, the energy consumption is high, and it is also necessary to partially remove sodium sulfate produced by oxidation, so the running cost is high. An electrolysis method using an ion exchange membrane has also been studied as an absorption and regeneration method that can convert sulfur dioxide into sulfuric acid and recover it for recycling. high. Therefore, there is a demand for an exhaust gas desulfurization method that is easy to operate, inexpensive, and capable of recovering sulfur dioxide.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an exhaust gas desulfurization method and apparatus capable of recovering sulfur dioxide at low cost and high efficiency.

Means to solve the problem

  According to the first aspect of the present invention, after bringing the absorbing liquid containing soluble metal ions into contact with the exhaust gas downstream of the exhaust gas stream containing sulfur oxide, a part of the contact absorbed liquid is removed from the exhaust gas. The exhaust gas desulfurization method is characterized in that it is sent to the upstream of the flow and again brought into contact with the moisture-unsaturated exhaust gas, and the re-contacted liquid is discharged from the absorber and used for regeneration of the absorbed liquid. Examples of the soluble metal ion include sodium and potassium. Usually, in order to consider the absorption efficiency, the absorbing solution containing these ions must be sent in large quantities to the absorption tower and operated with a low absorption saturation. However, the lower the saturation of the solution when regenerating such an absorbing solution, the lower the amount of sulfur dioxide that can be released with respect to the input heat, resulting in lower regeneration efficiency and higher cost. The present invention further absorbs sulfur oxide by contacting a part of the liquid absorbed downstream of the flue gas with the moisture-unsaturated exhaust gas on the upstream side, and the liquid is concentrated by evaporation, so that the sulfur oxide in the liquid As a result, it is possible to significantly increase the saturation of the battery, greatly increase the efficiency of the regeneration process, and significantly reduce the regeneration cost. The technical point of the present invention is that the absorption process is divided into two stages, upstream and downstream of the exhaust gas, and different absorption liquids are used. In contact with the saturated exhaust gas, the sulfur oxide is absorbed again and the liquid is evaporated and concentrated, and the concentrated absorbed liquid is sent to the regeneration process. In actual operation, a part of the absorption liquid is circulated upstream of the exhaust gas, that is, a part of the liquid that has been absorbed by re-contact with the moisture unsaturated exhaust gas is also sent to the inlet of the exhaust gas upstream absorption liquid and circulated. It doesn't matter.

  The invention according to claim 2 recovers the absorption capacity of the absorbed liquid by heating the re-contacted liquid upstream of the exhaust gas described in claim 1 with a heat source and releasing the sulfur oxide as gaseous sulfur dioxide from the liquid. The method for regenerating an absorbed liquid according to claim 1, wherein: Absorbing solutions of soluble metal ions such as sodium and potassium can be evaporated and decomposed at temperatures around 100 ° C, so they are easier to operate because they handle fluids compared to high-temperature pyrolysis of solids, and have lower capital investment and running costs. It is. In a regeneration process in which evaporation is regenerated using thermal energy, energy consumption during regeneration is mainly in the heat source for evaporation, so it is important to reduce the steam for evaporation. In the two-stage absorption of the present invention, the absorption downstream of the exhaust gas has a low degree of saturation of the absorption liquid, and the desulfurization effect can be secured, whereas the absorption upstream of the exhaust gas uses the absorption liquid already absorbed downstream. In addition, since it is in contact with exhaust gas with a high sulfur oxide concentration, the saturation of the absorbing solution is also increased, and at the same time, the absorbing solution is evaporated and concentrated by contact with the exhaust gas with high temperature and low humidity, and the oxidized solution is oxidized with sulfur. Since the concentration of substances and the saturation of absorption are greatly increased, the amount of energy used for evaporation and concentration during regeneration can be greatly reduced. The evaporator can save energy by using a multi-effect system or an exhaust vapor compression reuse system.

  According to the third aspect of the present invention, in the regeneration process of the absorbed liquid upstream of the exhaust gas described in the first and second aspects, the liquid to be regenerated is precipitated, filtered or centrifuged before entering the evaporator. Or a desulfurization absorbing liquid regeneration method, wherein solids are removed using a combination thereof, and then sent to an evaporator. Exhaust gas, especially coal-fired smoke, contains a lot of dust such as ash and is transferred to the absorption liquid in the absorption process, so the solid matter of ash mixed in the absorption liquid is removed using a precipitation or filtration process. As a result, it is possible to avoid wear of the apparatus during the evaporation regeneration process.

  The invention described in claim 4 is a process of evaporating and regenerating the absorbed liquid described in claim 2, wherein all or a part of the concentrated slurry obtained by evaporation is drawn out and sent to a solid-liquid separator for solid-liquid separation. The liquid obtained in this way is returned to the evaporation process and evaporated again, and the concentrated solid obtained by the solid-liquid separator is dissolved in water or a circulating liquid of the absorption liquid and then returned to the absorption process as a regenerated absorption liquid. The exhaust gas desulfurization method is characterized by being recycled. In the evaporation and concentration step, the absorption liquid is concentrated, and at the same time, bisulfite ions are decomposed into sulfur dioxide and discharged as a gas, the pH of the liquid rises, and the sodium sulfite concentration increases and precipitates. If the precipitated sodium sulfite crystal is removed from the liquid and the liquid is further evaporated, the liquid can be continuously regenerated. Centrifugation, filtration, precipitation, etc. can be used as a solid-liquid separation method, but centrifugation is desirable because it is efficient and suitable for continuous operation.

  According to the fifth aspect of the present invention, in the regeneration process of the absorbed liquid described in the fourth aspect, a part of the liquid obtained by the solid-liquid separator for solid-liquid separation of the concentrated slurry is drawn out and discarded or ion exchanged. This is a method for regenerating an absorbed liquid, characterized in that soluble metal ions are recovered by electrolysis using a membrane and recycled, and at the same time the remaining liquid is discarded. At the same time that chlorine is contained in coal and other fuels, sulfite ions are oxidized and become sulfate ions during the desulfurization process, which accumulates and corrodes the equipment and must be removed. The operation of recovering sulfur dioxide and sodium sulfite and then discharging and discarding it can reduce the loss of sodium and sulfite ions. Furthermore, if a method of recovering sodium by electrolysis using an ion exchange membrane is employed, the amount of sodium loss can be further reduced.

  The invention described in claim 6 is a method for preventing oxidation of sulfite ions in an absorbing solution, comprising adding phenolphthalein or a compound having the substance as a basic structure to the absorbing solution as an antioxidant. Oxygen is contained in the exhaust gas, and sulfite ions in the absorbing solution are oxidized to sulfuric acid. Since sulfuric acid cannot be pyrolyzed at low temperatures, it cannot be recovered as sulfur dioxide, and it accumulates in the liquid and adversely affects the absorption performance, so it must be removed. Therefore, if the oxidation of sulfurous acid can be suppressed, these problems can be reduced. Phenolphthalein and a compound having this as a basic structure have the effect of inhibiting oxidation, and therefore, addition to the absorbing solution can inhibit oxidation. Phenolphthalein may be added alone or in combination with other oxidation inhibitors.

  The invention according to claim 7 includes at least an exhaust gas inlet and an exhaust port, an absorption liquid inlet near the exhaust gas inlet, an absorbed liquid outlet of the absorption liquid, an absorption liquid inlet near the exhaust gas outlet, and the An absorption liquid absorption port near the exhaust gas, and the absorption liquid inlet side close to the exhaust gas inlet is connected to the absorbed liquid discharge side close to the exhaust gas discharge and absorbs the absorption liquid close to the exhaust gas inlet. The exhaust port of the spent liquid is an exhaust gas desulfurization absorption device characterized by being connected to the inlet side of the solid-liquid separator of the absorbed liquid in the regeneration step or the inlet side of the evaporator. With this device, exhaust gas from the boiler is sent into the absorber from the inlet of the exhaust gas, contacted with the absorbing liquid to remove sulfur oxides, discharged from the outlet of the absorber, sent to the chimney, and diffused Can be realized. The downstream absorbed liquid that has already been in contact with the exhaust gas downstream of the exhaust gas and passed through the desulfurization absorption process is introduced from the absorption liquid inlet near the exhaust gas inlet to the upstream side of the absorber, and further the sulfur oxide upstream of the exhaust gas After absorption and concentration of the absorption liquid, it can be discharged from the absorbed liquid discharge port of the absorption liquid close to the exhaust gas inlet and sent to the regeneration process. With the configuration of this apparatus, it is possible to simultaneously realize absorption of a high desulfurization rate downstream of exhaust gas, absorption of a high saturation of absorption liquid upstream of exhaust gas, and concentration of absorbed liquid. The absorption liquid inlet and outlet of the absorber are classified according to the flow of exhaust gas and the nature of the absorption liquid, but multiple mechanical ports with the same function are arranged as inlets or outlets to achieve the same function. May be.

  As shown in FIG. 1, the absorption device may use a structure in which one absorption tower and an exhaust gas inlet passage are provided with a concentration stage capable of distributing the absorption liquid, or may be a device in which two independent absorption towers are connected. Further, it may be an absorption device that is configured by a double cylinder and separates exhaust gas into exhaust gas upstream absorption and exhaust gas downstream absorption in the inner circle and the inner / outer circle passage, respectively. Further, in order to promote the separation of the absorbed liquid and the exhaust gas on the upstream side, a gas-liquid separation mechanism may be installed in the absorption device so that the exhaust gas passes through the gas-liquid separation mechanism before entering the downstream absorption portion. .

  Although only the absorbed liquid upstream of the exhaust gas is desired as the absorbed liquid for regeneration to be sent to the regeneration process, if the liquid other than the absorbed liquid is mixed and supplied to the regeneration process, the regeneration efficiency decreases. There is no hindrance to the execution. In addition, it is desirable to supply only the absorbed liquid downstream of the exhaust gas as the absorbing liquid to be fed to the inlet of the absorbing liquid close to the exhaust gas inlet. However, if the liquid other than the absorbed liquid is mixed and supplied, the efficiency is improved. Although it is reduced, there is no problem in the execution of the present invention.

The invention's effect

  According to the present invention, the sulfur oxide contained in the exhaust gas is efficiently absorbed and removed, and at the same time, the absorption contribution contributed from the improvement of the absorption saturation of the absorbed liquid by the re-contact with the moisture unsaturated exhaust gas and the evaporation capability thereof. By concentrating the liquid, it becomes possible to greatly reduce the energy consumption in the regeneration process. Furthermore, it is possible to realize an efficient and stable operation.

  EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not restrict | limited by this Example.

  FIG. 1 shows an example of a process flow process diagram of a processing method according to an embodiment of the present invention. The moisture-unsaturated exhaust gas 1 enters from the absorber inlet 2 and comes into contact with the upstream absorbent 3a to realize the absorption of sulfur oxides and the concentration of the absorbent. The exhaust gas that has passed through the absorption and concentration is separated from the absorption liquid, enters the packed bed of the absorption tower 5, contacts with the downstream absorption liquid 6, further desulfurizes, and then desulfurized exhaust gas 8 from the discharge port 7 of the absorber. Are discharged to the chimney. The absorbed liquid that has absorbed in the downstream of the exhaust gas is drawn out from the downstream absorbed liquid outlet 34b1 of the absorption device by the pump 32, and is mixed with the regenerated absorbent 25 obtained in the regeneration process as the downstream absorbed circulation liquid 3b, and absorbed downstream. The liquid 6 is sent from the exhaust gas downstream absorption liquid inlet 34a into the absorption device to perform desulfurization. A part of the downstream absorbed liquid is used as the upstream absorbent 3a, drawn from the downstream absorbed liquid outlet 34b2 by the pump 33, sent from the absorbent inlet 35a close to the exhaust gas inlet, and further, the water-unsaturated exhaust gas upstream of the exhaust gas. At the same time, it absorbs sulfur oxides, and after being concentrated, is discharged as an upstream absorbed liquid 4 from the upstream absorbed liquid discharge port 35b on the upstream side of the desulfurization apparatus, enters the swirling solid-liquid separator 9, and is exhausted. Separate solids such as ash inside. The supernatant desulfurization liquid 10 obtained in this solid-liquid separation step is sent to an evaporator 11 and heated and evaporated by steam (not shown in the figure), and the sulfur dioxide gas and water vapor 12 are sent to a cooler 13. The water vapor is condensed and separated, the sulfur dioxide gas 14 is sent to the sulfuric acid production process, the condensate 15 containing sulfur dioxide is sent to the heating device 16, the dissolved sulfur dioxide is vaporized, and the desorbed gas of the sulfur dioxide gas. Return to the cooler as 17. The liquid is concentrated in the evaporator 11 and sent to the centrifuge 19 as an evaporation slurry 18 to separate the crystallized solids. The resulting centrifuge 20 is returned to the evaporator 11 and again sulfur dioxide in the liquid. Is released as a gas. The solid material 21 obtained by the centrifuge is sent to the sodium sulfite dissolving device 22 and dissolved by the water 23. Further, the sodium carbonate 24 is added and dissolved, and the regenerated absorbent 25 is used for absorption. The separated solid matter 26 obtained in the swirling solid-liquid separator 9 of the upstream absorbed liquid 4 is sent to the dissolution separator 27, dissolved in the condensed water 28, separated and discharged from the ash 29, and the dissolved supernatant 30 is Send to dissolution device 22. In order to remove chlorine and sulfate ions from the system, a part of the liquid discharged from the centrifuge 19 is discharged as a chlorine removing discharge liquid 31 and is discarded or electrolyzed (not shown in the figure). The liquid containing chlorine and sulfate ions is sent to the wastewater treatment process.

  The process flow of desulfurization is basically the same as that of the first embodiment, except that a part of the upstream absorbed liquid 4 shown in FIG. 1 is connected to the inlet of the upstream absorbent liquid pump 33 and circulated. You may circulate using another pump.

    The process flow of the desulfurization is basically the same as that of the first embodiment, and the difference is that an upstream is obtained by installing a filtration device between the swirling solid-liquid separator 9 of the upstream absorbed liquid 4 shown in FIG. The absorbed liquid 4 is separated by a swirl flow separator into a solid substance with a high specific gravity and then put into a filter (not shown in FIG. 1), and further, a solid substance with a low specific gravity is separated and sent to the evaporator 11. .

It is a figure which shows the example of the process flow of the processing method which concerns on embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Unsaturated exhaust gas 2 Exhaust gas inlet 3a Upstream absorption liquid 3b Downstream absorption circulating liquid 4 Upstream absorbed liquid 5 Absorption tower 6 Downstream absorption liquid 7 Absorption apparatus exhaust gas outlet 8 Desulfurized exhaust gas 9 Swirling solid liquid Separation apparatus 10 Supernatant liquid 11 of upstream absorbed liquid 11 Evaporating apparatus 12 Evaporating gas 13 Cooler 14 Sulfur dioxide gas 15 Condensed liquid 16 Heating apparatus 17 Desorbed gas 18 Evaporating slurry 19 Centrifuge 20 Centrifugal liquid 21 Sodium sulfite crystal 22 Dissolution Apparatus 23 Water 24 Sodium carbonate 25 Regenerated absorbent 26 Upstream absorbed liquid separation solid 27 Dissolving separator 28 Condensed water 29 Ash solid 30 Dissolved supernatant 31 Chlorine removal discharge 32 Downstream circulation pump 33 Upstream absorption pump 34a Downstream Absorbing liquid inlet 34b1, 34b2 Absorbed liquid outlet 35a Absorbed liquid inlet 35b Absorbed upstream 35b Outlet

Claims (7)

After contacting an absorption liquid containing soluble metal ions with the exhaust gas downstream of the exhaust gas stream containing sulfur oxide, a part of the contact-absorbed liquid is sent upstream of the exhaust gas stream, and the moisture again. A method for desulfurizing exhaust gas, wherein the exhaust gas is brought into contact with unsaturated exhaust gas, and the re-contacted liquid is discharged from the absorption device and used for regeneration of the absorbed liquid. The absorbed liquid according to claim 1, wherein the re-contacted liquid upstream of the exhaust gas is heated by a heat source, and sulfur oxide is released from the liquid as gaseous sulfur dioxide to recover the absorption capacity of the absorbed liquid. Liquid regeneration method. In the process of regenerating the absorbed liquid upstream of the exhaust gas described in claim 1 and claim 2, the liquid to be regenerated is solidified using precipitation, filtration, centrifugation, or a combination thereof before entering the evaporator. A method for regenerating a desulfurized absorbent, which comprises removing an object and then sending it to an evaporator. In the process of evaporating and regenerating the absorbed liquid described in claim 2, all or part of the concentrated slurry obtained by evaporation is drawn out and sent to a solid-liquid separator, and the liquid obtained by solid-liquid separation is subjected to the evaporation process. It is returned and evaporated again, and the concentrated solid obtained by the solid-liquid separator is dissolved in water or a circulating solution of absorption liquid, and then returned to the absorption process as a regenerated absorption liquid for recycling. To desulfurize exhaust gas. In the regeneration process of absorbed liquid described in claim 4, a part of the liquid obtained by a solid-liquid separator for solid-liquid separation of the concentrated slurry is drawn out and discarded, or soluble metal is obtained by electrolysis using an ion exchange membrane. A method for regenerating an absorbed liquid, wherein the remaining liquid is discarded at the same time as ions are collected and recycled. A method for preventing oxidation of sulfite ions in an absorbing solution, comprising adding phenolphthalein or a compound having the substance as a basic structure to the absorbing solution as an antioxidant. At least an exhaust gas inlet and outlet, an absorption liquid inlet near the exhaust gas inlet, an absorption liquid outlet of the absorption liquid, an absorption liquid inlet near the exhaust gas outlet and an absorption liquid outlet of the absorption liquid The absorption liquid inlet side near the exhaust gas inlet is connected to the absorbed liquid discharge side near the exhaust gas outlet, and the absorbed liquid outlet near the exhaust gas inlet is used for the regeneration process. A desulfurization absorption apparatus for exhaust gas, which is connected to an inlet side of a solid-liquid separation apparatus for an absorbed liquid or an inlet side of an evaporation apparatus.

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