JP4587197B2 - Wet flue gas desulfurization method and apparatus - Google Patents

Description

  The present invention relates to a method and apparatus for removing sulfur oxides in exhaust gas discharged from a combustion apparatus such as a boiler, and in particular, a wet flue gas desulfurization method and apparatus suitable for reducing scaling attached to a desulfurization drainage line. It is about.

  As a conventional wet flue gas desulfurization device, for example, in a wet flue gas desulfurization device for coal-fired thermal power generation, a large amount of salt such as chlorine in fuel is dissolved and contained in the desulfurization absorption liquid, and the concentration thereof is adjusted. Keeping it within the specified value was necessary for the sound operation of the desulfurization equipment. Therefore, a system configuration is adopted in which a part of the desulfurization absorption liquid is discharged out of the system as waste water and the salt concentration in the system is reduced.

  Here, a system of a conventional wet flue gas desulfurization apparatus is shown in FIG. Exhaust gas 1 from a boiler or the like is introduced into an absorption tower 4 from an inlet flue 3 and is sprayed from a spray nozzle installed in the spray stage 8 through a spray stage 8 installed in the absorption tower 4. By contacting with the droplets of the contained absorbent, sulfur oxides (hereinafter referred to as SOx) in the exhaust gas 1 together with soot, hydrogen chloride (HCl), hydrogen fluoride (HF) and other acidic gases in the exhaust gas 1 are formed. Absorbed on the droplet surface. The mist accompanying the gas is removed by the mist eliminator 5, and the clean exhaust gas 2 passes through the outlet flue 6, is reheated as necessary, and is discharged from the chimney.

  At this time, the SOx concentration in the inlet exhaust gas 1 of the absorption tower 4 is measured by an inlet SOx meter 41, and the SOx concentration in the outlet exhaust gas 2 of the absorption tower 4 is measured by an outlet SOx meter 42, and desulfurization is performed based on these measured values. A rate is calculated. Limestone 16 that is an SOx absorbent is supplied as limestone slurry into the absorption tower 4 by the limestone slurry pump 17 by the limestone slurry flow control valve 18 in accordance with the amount of SOx absorbed. The absorption liquid is pressurized by the absorption tower circulation pump 7 and supplied to the spray stage 8 in the absorption tower 4. The SOx removed in the absorption tower 4 reacts with calcium in the absorption liquid to become calcium sulfite (including calcium bisulfite) as an intermediate product, and the air supplied from the oxidation air blower 21 to the absorption tower 4 Oxidized to gypsum to give the final product (gypsum). At this time, the oxidized air supplied to the absorption tower 4 is refined by the oxidizing stirrer 26 and supplied, thereby increasing the utilization rate of the oxidized air.

  Thereafter, the absorption liquid slurry is extracted by the extraction pump 9 in accordance with the amount of gypsum produced. A part of the absorption slurry is sent to the pH meter tank 30, and the pH of the absorption solution is adjusted by the pH meter 31 installed in the pH meter tank 30. Is measured. The other absorbing liquid is sent to the gypsum dehydrator equipment 10 and collected as powder gypsum 11. On the other hand, the gypsum filtrate 12 is reused in the system as make-up water for the limestone slurry tank 15 and the like, but a part of the gypsum filtrate 12 is extracted as desulfurization waste water 14 and sent to the waste water treatment facility 50 to prevent concentration of chlorine and the like. .

  In the wastewater treatment facility 50, chemical treatment by adding a chemical 51 or passing an ion-adsorbing resin or the like biologically by fungi so that the concentration of harmful substances contained in the desulfurization wastewater 14 is below the emission standard value. The treatment is performed, and the harmful substance in the desulfurization waste water 14 is removed.

  The system | strain around the gypsum dehydration equipment 10 in the said prior art is shown in FIG. The absorbent slurry extracted from the absorption tower 4 by the extraction pump 9 is supplied to the gypsum dehydrator 61 and is converted into gypsum 11 and gypsum filtrate 12 on the belt filter cloth that is absorbed and filtered by the dehydrator vacuum pump 60. To be separated. Thereafter, the gypsum 11 is washed with gypsum washing water 62 as necessary, dehydrated, and recovered in a powder state. On the other hand, a part of the gypsum filtrate 12 is collected by the filtrate receiver A 63 and discharged to the desulfurization drain pit 65. The gypsum washing water 62 and the remaining gypsum filtrate 12 are collected in the filtrate receiver B 64 and collected in the filtrate pit 66.

A portion of the gypsum filtrate 12 that has entered the desulfurization drainage pit 65 is sent to the wastewater treatment facility 50 by the desulfurization drainage pump 67 in order to keep the concentration of dissolved salts such as chlorine in the desulfurization absorption liquid below a certain value. Treated as desulfurized wastewater, the remainder flows into the adjacent filtrate pit 66. The filtrate pit 66 is supplied with the gypsum filtrate 12 flowing from the desulfurization drain pit 65 and the gypsum washing water 62 from the filtrate receiver B 64, and this water is circulated to the absorption tower 4 and the like again by the filtrate recovery pump 68. Used.
JP 59-66328 A

  In the above prior art, the solubility of gypsum in the gypsum filtrate 12 entering the desulfurization drainage pit 65 is saturated. On the other hand, as shown in FIG. 3, the solubility of gypsum in the liquid has a maximum relationship at about 40 ° C. with respect to the liquid temperature. For this reason, when desulfurization wastewater is sent from the desulfurization drainage pit 65 to the wastewater treatment facility 50 by the desulfurization drainage pump 67, gypsum precipitates due to a difference in solubility of gypsum due to a decrease in wastewater temperature during transfer, and the gypsum is plastered on the inner wall of the pipe. Scaling could stick.

  As described above, when gypsum scaling adheres to the pipe, the cross section of the flow path is blocked, so that the resistance of the pipe increases and an appropriate flow rate cannot be secured.

  The object of the present invention is to solve the above problems, reduce the amount of gypsum scaling to the desulfurization drainage line regardless of operating conditions, and keep the salt concentration in the system within a low specified value with a smaller amount of desulfurization drainage. A wet flue gas desulfurization apparatus and method is provided.

According to the first aspect of the present invention, the exhaust gas discharged from the combustion apparatus and the absorbent containing the calcium component-containing absorbent are brought into contact with each other in the exhaust gas absorption system so that the sulfur oxide in the exhaust gas reacts with the calcium component-containing absorbent. The absorption liquid containing gypsum produced by the above is extracted from the exhaust gas absorption system and separated from the absorption liquid containing gypsum into solid gypsum and filtrate, and a part of the separated filtrate is desulfurized wastewater. In the wet flue gas desulfurization method for discharging the desulfurization waste water comprising a part of the separated filtrate from the treatment system to the outside of the flue gas desulfurization treatment system, desulfurization in the vicinity of the inlet of the desulfurization waste water outside the flue gas desulfurization treatment system Heat the desulfurization wastewater in the flue gas desulfurization treatment system so that the solubility of gypsum in the desulfurization wastewater goes to the maximum direction due to the temperature drop and is higher than the maximum point even if the wastewater temperature drops due to heat dissipation This Which is a wet flue gas desulfurization method according to claim.

  Invention of Claim 2 is the wet flue gas desulfurization method of Claim 1 which heats the liquid temperature of the desulfurization drainage in the vicinity of the inlet of the discharge destination of the said desulfurization drainage to 40 degreeC or more.

The invention according to claim 3 is an absorption tower in which exhaust gas discharged from a combustion apparatus and an absorbent containing a calcium component-containing absorbent are brought into contact with each other to react sulfur oxide in the exhaust gas with the calcium component-containing absorbent, and the absorption The absorption liquid containing gypsum generated in the tower is extracted from the absorption tower and separated from the absorption liquid containing gypsum into solid gypsum and filtrate, and a part of the separated filtrate is discharged as desulfurization drainage. In a wet flue gas desulfurization apparatus comprising a flue gas desulfurization treatment system and a discharge device for discharging the desulfurization waste water from the flue gas desulfurization treatment system to a desulfurization waste water treatment apparatus outside the flue gas desulfurization treatment system,
Even if the liquid temperature of the desulfurization wastewater near the inlet of the desulfurization wastewater treatment system outside the flue gas desulfurization treatment system is lowered due to heat dissipation, the solubility of gypsum in the desulfurization wastewater goes to the maximum direction due to the temperature decrease , the temperature higher than the maximum point As described above, there is provided a wet flue gas desulfurization device provided with a heating means for heating the desulfurization waste water in the flue gas desulfurization device system.

  The invention according to claim 4 is the wet flue gas desulfurization apparatus according to claim 3, wherein the heating means is provided at an inlet or an outlet of the gypsum dehydrator.

  Here, the entrance of the gypsum dewatering machine refers to the line on which the gypsum generated in the absorbing liquid is sent to the gypsum dewatering machine as an absorbing liquid slurry.

  A fifth aspect of the present invention is the wet flue gas desulfurization apparatus according to the third aspect, wherein the heating means is provided at an inlet or an outlet of the exhaust device.

  Here, the discharge device is a device for discharging the desulfurization waste water from the inside of the system to the outside of the system, such as a desulfurization drain pump.

  The invention according to claim 6 is the wet flue gas desulfurization apparatus according to claim 4 or 5, wherein the liquid temperature of the desulfurization drainage near the inlet of the desulfurization drainage treatment apparatus as the discharge destination of the discharge apparatus is heated to 40 ° C. or more.

  Here, the discharge destination of the discharge device refers to a desulfurization wastewater treatment facility or the like as a discharge destination for discharging the desulfurization wastewater. Then, by installing a heating means and adjusting the liquid temperature so that the liquid temperature of the desulfurization wastewater near the inlet is 40 ° C. or higher, the distance between the discharge device and the discharge destination, for example, the wastewater treatment facility (desulfurization equipment) In the drainage line), the solubility of gypsum becomes a local maximum on the side of the wastewater treatment facility at the discharge destination. For this reason, even if the temperature of the desulfurization drainage decreases due to heat radiation, the gypsum scaling adheres to the desulfurization drainage piping because the gypsum solubility in the desulfurization drainage line is reduced compared to the liquid in the system, thereby eliminating supersaturated precipitation. Less.

According to the present invention, since no added diluent desulfurization effluent of a wet flue gas desulfurization system, because it is possible to be less restrained desulfurization effluent amount, to maintain the dissolved salt concentration in the absorption liquid to a low value, wet The flue gas desulfurization unit can be operated stably. In addition, even if the liquid temperature of the desulfurization drain near the discharge destination of the desulfurization drain outside the flue gas desulfurization treatment system is lowered due to heat dissipation, the solubility of gypsum in the desulfurization drain is higher than the temperature toward the maximum direction due to the temperature decrease. In order to heat the desulfurization drainage in the flue gas desulfurization treatment system, the desulfurization drainage line is blocked by scaling of gypsum to the desulfurization drainage line that discharges the desulfurization wastewater from the flue gas desulfurization treatment system to the outside of the flue gas desulfurization treatment system Since this can be prevented, the discharge device can be operated stably.

FIG. 1 shows a wet flue gas desulfurization system as an embodiment of the present invention. In addition, the same code | symbol is attached | subjected to the structure same as the system | strain of the conventional wet flue gas desulfurization apparatus shown in FIG. 4, FIG. The gypsum generated in the absorption liquid in the absorption tower 4 of this figure is sent to the gypsum dehydrator 61 as a slurry by the extraction pump 9. A heater for heating the absorbent slurry to be supplied to the gypsum dewatering device 61 so that the liquid temperature of the desulfurization water at the inlet of the wastewater treatment facility 50 for discharging the desulfurization wastewater exceeds 40 ° C. 69 is installed. Thus, this figure has shown the system | strain which enabled adjustment of the temperature of slurry.

Similarly, FIG. 2 shows a heater 69 for heating the desulfurization waste water at the inlet or the outlet of the desulfurization drain pump 67 so that the liquid temperature of the desulfurization waste water at the inlet of the waste water treatment facility 50 for discharging the desulfurization waste water exceeds 40 ° C. The system of the wet flue gas desulfurization apparatus which installed and enabled it to adjust the temperature of desulfurization waste water is shown.

In FIG. 1, desulfurization wastewater at the inlet of a wastewater treatment facility 50 that discharges desulfurization wastewater by adjusting a heater 69 installed in a line where the gypsum generated in the absorption liquid is extracted and sent to a gypsum dehydrator 61 as a slurry by a pump 9. The liquid temperature is over 40 ° C. As a result, as shown in FIG. 3, even if the temperature of the desulfurization drainage is reduced due to heat dissipation, the wastewater treatment facility 50 side of the desulfurization drainage effluent from the desulfurization drainage pit 65 to the wastewater treatment facility 50 It acts in the direction that maximizes the solubility of gypsum. For this reason, in the desulfurization drainage line, there is no supersaturated precipitation due to the lowering of the gypsum solubility compared with the gypsum solubility of the liquid in the desulfurization drainage pit 65, and the scaling amount of gypsum adhering to the desulfurization drainage pipe can be reduced. .

  Therefore, the flow passage cross section of the desulfurization drainage line is not blocked, so that the operation of the desulfurization drainage pump is not limited. Further, since no dilution water is added to the desulfurization drainage pit 65, it is possible to reduce the amount of desulfurization drainage and to maintain the dissolved salt concentration in the absorbent at a low value.

  In FIG. 1, the heater 69 is installed in a slurry line having a solid concentration of about 20%. Therefore, even if the operating conditions are such that the solubility of gypsum decreases and the gypsum precipitates due to an increase in liquid temperature due to heating. Since the solid gypsum is present in a large amount, most of the precipitate is not deposited on the pipe or the heat transfer pipe of the heater 69, but on the surface of the coexisting solid gypsum. It is also possible to reduce the amount of scaling adhesion to the surface.

Similarly, in FIG. 2, the heater 69 installed at the inlet or outlet of the desulfurization drain pump 67 is adjusted so that the liquid temperature of the desulfurization waste water at the inlet of the waste water treatment facility 50 for discharging the desulfurization waste water exceeds 40 ° C. To. As a result, as shown in FIG. 3, even if the temperature of the desulfurization wastewater is reduced due to heat dissipation, the desulfurization is performed on the drainage treatment facility 50 side of the discharge destination between the heater 69 and the wastewater treatment facility 50. It acts in the direction that maximizes the solubility of gypsum in the drainage. For this reason, in the desulfurization drainage line on the downstream side of the heater 69, the supersaturated precipitation due to the lowering of the gypsum solubility compared with the gypsum solubility of the liquid in the desulfurization drainage pit 65 is eliminated, and the desulfurization on the downstream side of the heater 69 is eliminated. The scaling amount of the gypsum adhering in the drain pipe can be reduced.

  Therefore, the flow passage cross section of the desulfurization drainage line on the downstream side of the heater 69 is not blocked, so that the operation of the desulfurization drainage pump 67 is not limited. Since the heater 69 tends to decrease the solubility of gypsum in the desulfurization waste water, gypsum scaling may adhere to the heater 69 itself. It becomes possible to cope without problems by performing the work. In the wet flue gas desulfurization apparatus shown in FIG. 2 as well as the wet flue gas desulfurization apparatus shown in FIG. It is possible to maintain the dissolved salt concentration therein at a low value.

  INDUSTRIAL APPLICABILITY The present invention can be used in a wet flue gas desulfurization method and apparatus that reduces scaling attached to a desulfurization drainage line.

It is a conceptual diagram which shows the system | strain structure of the wet flue gas desulfurization apparatus of the Example of this invention. It is a conceptual diagram which shows the system | strain structure of the wet flue gas desulfurization apparatus which installed the heater of FIG. 1 in the inlet_port | entrance or exit of a desulfurization drainage pump. It is a figure which shows the relationship of the saturated solubility of gypsum with respect to liquid temperature. It is a figure which shows the system | strain structure of the conventional wet flue gas desulfurization apparatus. It is a figure which shows the system | strain structure of the gypsum dehydrator 61 vicinity of the system | strain of the conventional wet flue gas desulfurization apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Exhaust gas 2 Clean exhaust gas 3 Inlet flue 4 Absorption tower 5 Mist eliminator 6 Outlet flue 7 Absorption tower circulation pump 8 Spray stage 9 Extraction pump 10 Gypsum dehydration equipment 11 Gypsum 12 Gypsum filtrate 13 Limestone slurry tank replenishment water 14 Desulfurization drainage 15 Limestone slurry tank 16 Limestone 17 Limestone slurry pump 18 Limestone slurry flow control valve 21 Oxidizing air blower 26 Oxidizing stirrer 30 pH meter tank 31 pH meter 41 Inlet SOx meter 42 Outlet SOx meter 43 Calculator 50 Wastewater treatment equipment 51 Chemicals 60 Dehydrator vacuum pump 61 Gypsum dewatering machine 62 Gypsum washing water 63 Filtrate receiver A 64 Filtrate receiver B
65 Desulfurization drainage pit 66 Filtrate pit 67 Desulfurization drainage pump 68 Filtration recovery pump 69 Heater 70 Dehydrator supply slurry thermometer 71 Desulfurization drainage thermometer

Claims (5)

Absorption liquid containing gypsum generated by contacting exhaust gas discharged from a combustion device with an absorbent containing a calcium component-containing absorbent in an exhaust gas absorption system and reacting sulfur oxides in the exhaust gas with the calcium component-containing absorbent Is extracted from the exhaust gas absorption system and separated from the absorption liquid containing the gypsum into solid gypsum and filtrate, and the separated filtrate from the flue gas desulfurization treatment system using a part of the separated filtrate as desulfurization drainage. In the wet flue gas desulfurization method for discharging the desulfurization effluent consisting of a part of the exhaust gas outside the flue gas desulfurization treatment system,
Even if the liquid temperature of the desulfurization wastewater near the discharge destination of the desulfurization wastewater outside the flue gas desulfurization treatment system is decreased due to heat dissipation, the solubility of gypsum in the desulfurization wastewater is higher than the maximum point due to the temperature decrease. A wet flue gas desulfurization method, wherein the desulfurization waste water in the flue gas desulfurization treatment system is heated so that the temperature is higher than the temperature.   The wet flue gas desulfurization method according to claim 1, wherein the liquid temperature of the desulfurization drainage near the inlet of the discharge destination of the desulfurization drainage is heated to 40 ° C. or more. It includes an absorption tower in which exhaust gas discharged from a combustion apparatus and an absorbent containing a calcium component-containing absorbent are brought into contact to react sulfur oxide in the exhaust gas with the calcium component-containing absorbent, and gypsum generated in the absorption tower A gypsum dewatering machine that extracts the absorption liquid from the absorption tower and separates the gypsum-containing absorption liquid into solid gypsum and filtrate, a flue gas desulfurization treatment system that uses a part of the separated filtrate as desulfurization drainage, and the exhaust In a wet flue gas desulfurization device equipped with a discharge device that discharges the desulfurization waste water from the smoke desulfurization treatment system to the desulfurization waste water treatment device outside the flue gas desulfurization treatment system
Even if the liquid temperature of the desulfurization wastewater near the inlet of the desulfurization wastewater treatment system outside the flue gas desulfurization treatment system is lowered due to heat dissipation, the solubility of gypsum in the desulfurization wastewater goes to the maximum direction due to the temperature decrease , the temperature higher than the maximum point As described above, a wet flue gas desulfurization apparatus provided with a heating means for heating the desulfurization waste water in the flue gas desulfurization apparatus system.   The wet flue gas desulfurization apparatus according to claim 3, wherein the heating means is provided at an inlet or an outlet of the gypsum dehydrator.   The wet flue gas desulfurization apparatus according to claim 3, wherein the heating unit is provided at an inlet or an outlet of the discharge device.

Images