JP2011194286A - Boiler plant - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase a removal rate of mercury in exhaust gas without using a venturi scrubber.SOLUTION: Soot in exhaust gas generated by combustion of coal with oxygen-rich combustion gas is collected by a dust collector 5; sulfur oxides in the exhaust gas discharged from the dust collector 5 is removed by a wet type desulfurization apparatus 15; halogen or a halogen compound is added into the exhaust gas discharged from the wet desulfurization apparatus by an addition apparatus 37; the mercury in the exhaust gas discharged from the addition apparatus 37 is reacted with halogen or the halogen compound by a mercury oxidizing apparatus 39 to be thereby oxidized into mercury oxide easily soluble in water; moisture in the exhaust gas discharged from the mercury oxidizing apparatus 39 is condensed by a mercury removal apparatus; and the mercury oxide is absorbed in at least the condensate and is removed from the exhaust gas.

Description

  The present invention relates to a boiler plant, and more particularly to a technique for removing mercury from exhaust gas of an oxyfuel boiler that burns coal with an oxygen-rich combustion gas.

  For example, in Patent Document 1, nitrogen oxides in exhaust gas generated by oxygen combustion of coal are removed by a denitration device, dust in the exhaust gas is collected by a dust collector, and sulfur oxides in the exhaust gas are desulfurized. There has been proposed a boiler plant that removes moisture and water vapor in exhaust gas with a drying device, cools the exhaust gas, and recovers carbon dioxide in the exhaust gas. Further, when coal is oxygen-burned, the flame temperature becomes high, so that oxygen is diluted with the recovered carbon dioxide to generate combustion gas, thereby suppressing the flame temperature from becoming high. However, the technique described in Patent Document 1 does not consider removing mercury in the exhaust gas.

On the other hand, Patent Document 2 proposes a technique for removing mercury oxide (Hg ²⁺ ) contained in exhaust gas generated by air combustion of coal by using a desulfurization absorbent in a wet desulfurization apparatus and removing it from the exhaust gas. . In particular, according to this document, mercury oxide (Hg ²⁺ ) absorbed by a wet desulfurization apparatus is reduced to metallic mercury (Hg ⁰ ) having low solubility by a reducing substance in the absorption liquid for desulfurization, and is regenerated into exhaust gas. Since it is released, the exhaust gas discharged from the wet desulfurization unit is introduced into the oxidation unit filled with mercury oxidation catalyst, and the re-released metal mercury is oxidized to mercury oxide that is easily soluble in water, and then absorbed into the absorption liquid of Venturi scrubber. It is made to remove from exhaust gas.

JP-A-5-231609 JP 2008-302345 A

  However, a venturi scrubber like Patent Document 2 increases the flow rate of exhaust gas by narrowing the exhaust gas flow path, and jets the absorption liquid into the venturi section where the flow speed has been increased, thereby making the absorption liquid finer by the high-speed gas flow. Since this increases the possibility of contact between the liquid and mercury oxide, in order to increase the mercury removal rate, there is a problem that the pressure loss is large because the speed of the exhaust gas in the venturi section must be increased.

  The problem to be solved by the present invention is to improve the removal rate of mercury in exhaust gas without using a venturi scrubber.

  In order to solve the above problems, a boiler plant according to the present invention includes an oxyfuel boiler that burns coal with an oxygen-rich combustion gas, and a dust collector that collects dust in exhaust gas discharged from the boiler. , A wet desulfurization device that removes sulfur oxides in the exhaust gas discharged from the dust collector, an addition device that adds a halogen or a halogen compound to the exhaust gas discharged from the wet desulfurization device, and in the exhaust gas discharged from the addition device A mercury oxidation device with a catalyst layer that oxidizes mercury by reacting with mercury or halogen compounds, and condensing moisture in the exhaust gas discharged from the mercury oxidation device, and at least condensate absorbs the mercury oxide and removes it from the exhaust gas And a carbon dioxide recovery device that recovers carbon dioxide in exhaust gas discharged from the mercury removal device.

  According to this, since the mercury metal in the exhaust gas is oxidized and converted to mercury oxide that is easily soluble in water on the upstream side of the mercury removal device, the mercury removal device condenses the moisture in the exhaust gas and converts it into this condensed water. Since mercury oxide can be absorbed and removed from the exhaust gas, the removal rate of mercury in the exhaust gas can be improved without using a venturi scrubber with a large pressure loss. Further, since the metallic mercury is oxidized on the downstream side of the wet desulfurization apparatus, it is possible to remove the metallic mercury that is reduced and re-released after being absorbed by the wet desulfurization apparatus. In addition, since the flame temperature becomes high when oxygen is burned to coal, for example, the exhaust gas downstream of the dust collector is branched to dilute the oxygen supplied from the oxygen supply device to generate combustion gas. Coal can be burned with gas.

  Further, the mercury removing device can be constituted by a compression device that compresses the exhaust gas and a cooling device that cools the exhaust gas compressed by the compression device and condenses moisture in the exhaust gas.

  Further, a wet desulfurization apparatus can be used as the mercury removal apparatus. That is, another wet desulfurization device is arranged downstream of the mercury oxidation device, the desulfurization absorbing liquid of this wet desulfurization device and the exhaust gas are brought into contact, and the exhaust gas is mixed with the condensed water of the moisture in the exhaust gas and the absorbing solution for desulfurization. It can absorb mercury oxide and remove it from exhaust gas. In this case, if there is a large amount of sulfur oxide absorbed in the desulfurization absorbent, the concentration of sulfurous acid in the desulfurization absorbent increases and mercury oxide is reduced and re-released. It is preferable to remove the sulfur oxide with a wet desulfurization apparatus in front of the mercury oxidation apparatus so that the amount of sulfur oxide absorbed is within a range in which the reduction of mercury oxide is suppressed.

  On the other hand, if the temperature of the exhaust gas discharged from the wet desulfurization device is low and the water vapor in the exhaust gas becomes saturated, condensation tends to occur in the catalyst layer of the mercury oxidation device at the latter stage of the wet desulfurization device, and the performance and durability of the catalyst are reduced. There is a risk of reduction. In this case, it is preferable to heat the exhaust gas discharged from the wet desulfurization device upstream of the mercury oxidation device to a temperature exceeding the saturation temperature of the water vapor and introduce the heated exhaust gas into the mercury oxidation device.

  In addition, if unreacted halogen or halogen compounds are discharged from the mercury oxidizer, the piping and equipment on the downstream side may corrode, so the mercury concentration or halogen concentration in the exhaust gas discharged from the mercury oxidizer will be reduced. Based on this, it is preferable to adjust the addition amount of halogen or halogen compound to suppress discharge of unreacted halogen or halogen compound from the mercury oxidation apparatus.

  According to the present invention, the removal rate of mercury in exhaust gas can be improved without using a venturi scrubber.

It is the schematic of the boiler plant of Embodiment 1 of this invention. It is the schematic of the wet desulfurization apparatus of FIG. FIG. 5 is a schematic view of a modification of the boiler plant of the first embodiment. It is the schematic of the boiler plant of Embodiment 2 of this invention.

Hereinafter, the present invention will be described based on embodiments.
(Embodiment 1)
As shown in FIG. 1, the boiler plant according to the first embodiment is provided with an oxyfuel boiler 1 that burns coal with a combustion gas containing rich oxygen. Steam generated by burning coal in the boiler 1 is supplied to a steam turbine (not shown) to drive the steam turbine.

  The exhaust gas discharged from the boiler 1 is guided to the air heater 3 that heats the circulating exhaust gas by exchanging heat with the circulating exhaust gas for diluting oxygen used for combustion. The exhaust gas discharged from the air heater 3 is guided to a dust collector 5 that collects dust in the exhaust gas. A distributor 6 for branching the exhaust gas is provided in the exhaust gas passage on the downstream side of the dust collector 5. An exhaust gas circulation line 7 through which the branched circulating exhaust gas flows is connected to the distributor 6. The exhaust gas circulation line 7 is provided with a circulation fan 9. The exhaust gas circulation line 7 is connected to the exhaust gas mixer 11 via the air heater 3. The exhaust gas mixer 11 mixes circulating exhaust gas with coal mixed in the oxygen mixer 13, for example, a mixture of pulverized coal and oxygen, to dilute oxygen to generate combustion gas.

  The remaining exhaust gas discharged from the dust collector 5 and from which the circulating exhaust gas is branched is led to a wet desulfurization device 15 that removes sulfur oxides in the exhaust gas. As shown in FIG. 2, the wet desulfurization apparatus 15 is, for example, a vertical cylindrical wet desulfurization apparatus 15 that introduces exhaust gas from an inlet duct 17 on the bottom side and exhausts exhaust gas from an outlet duct 19 on the top side. It is like that. In the wet desulfurization apparatus 15, a nozzle 23 for spraying the desulfurization absorbing liquid 21 to the exhaust gas is provided. A circulation pump 25 that circulates the desulfurization absorbing liquid 21 to the nozzle 23 is connected to the nozzle 23 so that the desulfurization absorbing liquid 21 stored at the bottom of the wet desulfurization apparatus 15 is circulated. Oxidation air is supplied to the position where the desulfurization absorbing liquid 21 of the wet desulfurization apparatus 15 is stored, and the product generated by the reaction between the sulfur oxide and the desulfurization absorbing liquid 21 is oxidized. . The exhaust gas discharged from the wet desulfurization device 15 is guided to a carbon dioxide recovery device 27 that recovers carbon dioxide in the exhaust gas.

  Next, the characteristic configuration of the first embodiment will be described. A heat exchanger 33 for heating the exhaust gas discharged from the wet desulfurization device 15 is provided on the downstream side of the wet desulfurization device 15. In the heat exchanger 33, a hot water channel 34 through which hot water flows is provided. The hot water flow path 34 guides the hot water to a heat exchanger 35 provided between the air heater 3 and the dust collector 5, and converts the hot water heated by the exhaust gas flowing through the heat exchanger 35 into the heat exchanger 33. Is supposed to lead to.

The exhaust gas discharged from the heat exchanger 33 is guided to an adding device 37 for adding halogen or a halogen compound, for example, chlorine. The adding device 37 is provided with an adjusting device for adjusting the amount of chlorine not shown. The exhaust gas discharged from the adding device 37 is guided to a mercury oxidation device 39 having a catalyst layer that reacts metallic mercury and chlorine in the exhaust gas to oxidize metallic mercury into mercury oxide. The catalyst layer for oxidizing mercury has, for example, at least one of TiO ₂ , SiO ₂ , ZrO ₂ , Al ₂ O ₃ and zeolite as a carrier, and Pt, Ru, Rh, Pd, Ir, Of V, W, Mo, Ni, Co, Fe, Cr, Cu and Mn, those carrying at least one as an active ingredient can be used.

  The exhaust gas discharged from the mercury oxidation device 39 passes through a detection device 41 that detects the concentration of metallic mercury in the exhaust gas and is guided to the carbon dioxide recovery device 27. The detection device 41 is connected to an adjustment device (not shown) of the addition device 37 and adjusts the addition amount of chlorine based on the detected metal mercury concentration. The carbon dioxide recovery device 27 includes a compression device 43, a cooling device 45 to which the exhaust gas discharged from the compression device 43 is guided, and a compression device 47 to which the exhaust gas discharged from the cooling device 45 is guided. The compressor 43 compresses the introduced exhaust gas. The cooling device 45 cools the exhaust gas compressed by the compression device 43 to condense moisture in the exhaust gas, and allows the condensed water to absorb mercury oxide in the exhaust gas. The compression device 47 further compresses the exhaust gas that has passed through the cooling device 45 to liquefy and collect carbon dioxide.

  Operation | movement of the boiler plant of Embodiment 1 comprised in this way is demonstrated. The mixture of coal and oxygen mixed in the oxygen mixer 13 is introduced into the exhaust gas mixer 11 and mixed with the circulating exhaust gas supplied from the circulating exhaust gas line 7. Thereby, oxygen is diluted with circulating exhaust gas, and combustion gas is produced | generated. The amount of circulating exhaust gas for diluting oxygen is adjusted, for example, to a range in which the flame temperature in the boiler 1 becomes the flame temperature when coal is air-burned, and for example, 70 to 80% of exhaust gas is circulated to dilute oxygen. .

  The exhaust gas discharged from the boiler 1 heats the circulating exhaust gas introduced into the air heater 3 and flowing through the exhaust gas circulation line 7 by heat exchange. The exhaust gas discharged from the air heater 3, for example, having a temperature lowered to 160 ° C. to 200 ° C., is introduced into the dust collector 5 to remove the dust in the exhaust gas. The exhaust gas discharged from the dust collector 5 is introduced into the wet desulfurization device 15 after the circulation exhaust gas is branched by the distributor 6. The exhaust gas introduced into the wet desulfurization apparatus 15 is sprayed with the desulfurization absorbing liquid 21 from the nozzle 23. For example, when a calcium carbonate aqueous solution is used as the desulfurization absorbing liquid 21, sulfur oxides, for example, sulfur dioxide, in the exhaust gas are absorbed by the desulfurization absorbing liquid 21 and converted into sulfurous acid. Thereby, sulfur dioxide in the exhaust gas is removed. The sulfurous acid in the desulfurizing absorbent 21 reacts with the calcium carbonate in the desulfurizing absorbent 21 and is converted to calcium sulfite. This calcium sulfite accumulates at the bottom of the wet desulfurization device 15 together with the desulfurization absorbent 21, and is oxidized by the oxidizing air supplied to the bottom to be converted into calcium sulfate. Calcium sulfate is discharged from an outlet (not shown) of the wet desulfurization device 15.

  Next, the characteristic operation of the first embodiment will be described. In the wet desulfurization device 15, for example, the exhaust gas cooled to 70 ° C. is heated to a temperature exceeding the saturation temperature of water vapor in the exhaust gas by heat exchange with the hot water flowing through the heat exchanger 33. Thereby, it can suppress that dew condensation arises in the catalyst layer of mercury oxidation device 39. The hot water flowing through the heat exchanger 33 is circulated through the hot water flow path 34 and led to the heat exchanger 35, where it is heated by heat exchange with the exhaust gas. At this time, the exhaust gas discharged from the heat exchanger 35 by heat exchange with the hot metal is lowered to 90 to 130 ° C., for example.

Chlorine is added to the exhaust gas discharged from the heat exchanger 33 by the adding device 37. The exhaust gas to which chlorine is added is converted into mercury oxide that is easily dissolved in water by oxidizing metallic mercury in the exhaust gas with chlorine in the presence of the catalyst layer of the mercury oxidizer 39. At this time, metallic mercury re-released from the wet desulfurization apparatus 15 is also converted into mercury oxide. The exhaust gas discharged from the mercury oxidation device 39 passes through the detection device 41, so that the metal mercury concentration in the exhaust gas is detected. Based on this detection value, the addition amount of chlorine is adjusted so that the metal mercury concentration in the exhaust gas discharged from the mercury oxidation device 39 is, for example, 0.2 μg / m ³ N or less. As a result, it is possible to suppress the addition of excess chlorine, so that unreacted chlorine discharged from the mercury oxidation device 39 can be reduced, and piping and devices on the downstream side of the mercury oxidation device 39 are corroded by chlorine. Can be suppressed.

  The exhaust gas that has passed through the detection device 41 is introduced into the compression device 43 of the carbon dioxide recovery device 27 and compressed so as to have a predetermined pressure. The compressed exhaust gas is introduced into the cooling device 45 and cooled to a temperature at which moisture in the exhaust gas is condensed. At this time, since mercury oxide in the exhaust gas is easily dissolved in water, it is absorbed by the condensed water and removed from the exhaust gas. The exhaust gas discharged from the cooling device 45 is further compressed by the compression device 47, and carbon dioxide in the exhaust gas is liquefied. In this case, if necessary, a cooling device can be provided to promote liquefaction of carbon dioxide. Thereby, the carbon dioxide of the exhaust gas discharged | emitted from a boiler plant can be reduced. In addition, the condensed water which absorbed mercury oxide is discharged | emitted from the cooling device 45, and is processed suitably.

  Further, by absorbing the mercury oxide in the exhaust gas introduced into the cooling device 45 into the condensed water, for example, mercury adhering to the cooling device 45 is reduced, and corrosion of the cooling device 45 due to mercury can be suppressed. That is, when the cooling device 45 is formed of a metal corroded by metal mercury, for example, an aluminum alloy, mercury adheres to the aluminum alloy and amalgamates to corrode the aluminum alloy. By making it absorb, it can suppress that aluminum adheres to an aluminum alloy and corrodes.

  In addition, it can be set as the structure which arrange | positions a denitration apparatus between the boiler 1 and the air heater 3, and removes the sulfur oxide in waste gas.

  In addition, when coal containing chlorine is burned, chlorine is contained in the exhaust gas, and metal mercury can be converted into mercury oxide by this chlorine. However, as in the first embodiment, the mercury oxidation device 39 is provided downstream of the wet desulfurization device 15. Since chlorine in the exhaust gas is removed by the wet desulfurization device 15, it is preferable to add chlorine to the exhaust gas discharged from the wet desulfurization device 15 as in the first embodiment.

  Moreover, the halogen added from the addition apparatus 37 is not limited to chlorine, Bromine etc. can be added to waste gas. Further, a halogen compound that can oxidize metallic mercury to mercury oxide, such as hydrogen halide, can be added to the exhaust gas.

In addition, the detection device 41 detects the metal mercury concentration in the exhaust gas. Instead, the detection device 41 detects the chlorine concentration in the exhaust gas, and based on the detected chlorine concentration, the addition amount of chlorine in the addition device 37 is detected. Can be adjusted. In this case, the relationship between the chlorine concentration in the exhaust gas and the mercury oxidation characteristics is measured in advance, and the chlorine concentration at which the metal mercury concentration in the exhaust gas discharged from the mercury oxidizer 39 is 0.2 μg / m ³ N or less is obtained. It can be set as the structure which adjusts the addition amount of chlorine based on the calculated | required chlorine concentration and the detected chlorine concentration.

  Moreover, it can replace with the structure which branches the waste gas discharged | emitted from the dust collector 5, and can be set as the structure which branches the waste gas discharged | emitted from the wet desulfurization apparatus 15. FIG.

  Moreover, the position of the heat exchanger 35 is not limited to the position of Embodiment 1, For example, as shown in FIG. 3, it is the upstream of the wet desulfurization apparatus 15, and is downstream of the distributor 6 (exhaust gas branch part). Can be placed on the side.

  Thus, according to the first embodiment, moisture in the exhaust gas discharged from the mercury oxidation device 39 can be condensed, and the condensed water can absorb the mercury oxide in the exhaust gas and remove it from the exhaust gas. In particular, since the metallic mercury is converted into mercury oxide which is easily dissolved in water on the upstream side of the carbon dioxide recovery device 27, the compression device 43 and the cooling device 45 of the carbon dioxide recovery device 27 can be used as a mercury removal device, and pressure loss The mercury removal rate can be improved without using a large venturi scrubber.

(Embodiment 2)
The boiler plant of Embodiment 2 is demonstrated using FIG. The difference between the second embodiment and the first embodiment is that a wet desulfurization device 51 different from the wet desulfurization device 15 is arranged at the rear stage of the mercury oxidation device 39. Since other configurations are the same as those of the first embodiment, the same reference numerals are given and description thereof is omitted.

  The latter-stage wet desulfurization apparatus 51 sprays and contacts the exhaust gas with the desulfurization absorption liquid, and absorbs the condensed water and mercury oxide in the exhaust gas into the desulfurization absorption liquid. In other words, the condensed water of the moisture in the exhaust gas is absorbed by the desulfurization absorption liquid to become a mixed liquid of the desulfurization absorption liquid and the condensed water, and the mercury oxide in the exhaust gas is absorbed into this mixed liquid and the mercury oxide is removed from the exhaust gas. Is done.

  According to this, since the wet desulfurization apparatus 51 can be used as the mercury removing apparatus, the removal rate of mercury in the exhaust gas can be improved without using a venturi scrubber having a large pressure loss. That is, in one wet desulfurization apparatus, mercury oxide absorbed in the desulfurization absorbing liquid is reduced to metallic mercury and re-released by sulfurous acid generated by absorbing sulfur oxide, so the mercury removal rate is poor. In particular, in the case of oxyfuel combustion in which exhaust gas is circulated, the amount of metal mercury re-released from the wet desulfurization device increases due to moisture in the exhaust gas and the moisture concentration of the exhaust gas becoming higher and the temperature of the wet desulfurization device rising. . Therefore, most of the sulfur oxides in the exhaust gas are removed by the wet desulfurization device 15 at the front stage of the mercury oxidation device 39, and the sulfur oxide concentration absorbed by the absorbent for desulfurization of the wet desulfurization device 51 at the rear stage of the mercury oxidation device 39. By reducing this, the phenomenon that mercury oxide absorbed by the wet desulfurization apparatus 51 is released again can be suppressed, and the wet desulfurization apparatus can be used for the mercury removal apparatus.

  The wet desulfurization apparatus 51 can use a wet desulfurization apparatus having the same configuration as the wet desulfurization apparatus 15.

1 Boiler 5 Dust Collector 15 Wet Desulfurizer
27 Carbon Dioxide Recovery Device 33 Heat Exchanger 37 Addition Device 39 Mercury Oxidation Device 41 Detection Device 43 Compression Device 45 Cooling Device 51 Wet Desulfurization Device

Claims (5)

  An oxyfuel boiler that burns coal with an oxygen-rich combustion gas, a dust collector that collects soot in exhaust gas discharged from the boiler, and sulfur oxidation in the exhaust gas discharged from the dust collector A wet desulfurization apparatus for removing substances, an addition apparatus for adding halogen or a halogen compound to the exhaust gas discharged from the wet desulfurization apparatus, and a reaction of mercury in the exhaust gas discharged from the addition apparatus with the halogen or the halogen compound A mercury oxidation apparatus including a catalyst layer that oxidizes the mercury, a mercury removal apparatus that condenses moisture in exhaust gas discharged from the mercury oxidation apparatus, absorbs mercury oxide in at least condensed water, and removes the mercury from the exhaust gas; and the mercury A boiler plant comprising a carbon dioxide recovery device that recovers carbon dioxide in exhaust gas discharged from a removal device. In the boiler plant according to claim 1,
The mercury removing device includes a compression device that compresses exhaust gas, and a cooling device that cools the exhaust gas compressed by the compression device and condenses moisture in the exhaust gas, and mercury oxide is condensed into the condensed water condensed by the cooling device. Boiler plant characterized by absorbing and removing from exhaust gas. In the boiler plant according to claim 1,
The mercury removal device is another wet desulfurization device provided separately from the wet desulfurization device, and the other wet desulfurization device is configured to contact the desulfurization absorption liquid and the exhaust gas, and to condense the water in the exhaust gas and desulfurization. A boiler plant characterized in that mercury oxide is absorbed into a mixed liquid of the absorbing liquid and removed from the exhaust gas. In the boiler plant according to any one of claims 1 to 3,
A boiler plant characterized in that a heating device for heating the exhaust gas is provided upstream of the mercury oxidation device, and the exhaust gas heated by the heating device is introduced into the mercury oxidation device. In the boiler plant according to any one of claims 1 to 4,
A detection device for detecting mercury concentration or halogen concentration in exhaust gas discharged from the mercury oxidation device, and an adjustment device for adjusting the addition amount of the halogen or the halogen compound based on a detection value of the detection device. A boiler plant characterized by that.

Images