Device for removing impurities from water-containing gas and impurities removal system

Provided are a filler-integrated cooler having a cooler body with cooling space, gas inlet and outlet and communicated with bottom and top of the cooling space, a cooling pipe in the cooling space between the gas inlet and outlet to make cooling fluid from a cooling-fluid inlet go around in the cooling space and discharge the same through a cooling-fluid outlet and a filler vertically partitioning the cooling space into portions with the gas inlet and outlet, a nozzle arranged above in the cooling space, a drain circulator supplying drain in a drain reservoir at inner bottom of the cooling space through a drain outlet to the nozzles, using a pump, and an alkaline-agent addition unit to add an alkaline agent to drain.

TECHNICAL FIELD

The present disclosure relates to a device and a system for removing impurities in water-containing gas.

BACKGROUND ART

Gas discharged from, for example, a combustor or a reaction device contains impurities to be removed. For example, an oxyfuel combustor has been reviewed as one of techniques for abating emission of carbon dioxide (CO2) which is said to be one of factors for global warming, and attention has been attracted to a coal-fired boiler for oxyfuel combustion of pulverized coal. It has been conceived in the coal-fired boiler that oxygen in lieu of air is used as an oxidizing agent to produce exhaust gas mainly composed of carbon dioxide (CO2) and the exhaust gas with high CO2concentration is compressed and cooled into liquefied carbon dioxide which is then transported by a vessel, a vehicle or other carrier means to a destination for storage thereof in the ground or alternatively the liquefied carbon dioxide increased in pressure is transported through a pipeline to a destination for storage thereof in the ground.

Such exhaust gas from the coal-fired boiler for oxyfuel combustion contains, in addition to carbon dioxide (CO2), impurities derived from coal feedstock such as nitrogen oxides (NOx), sulfur oxides (SOx), mercury (Hg), hydrogen chloride (HCl) and dust. Such impurities require to be removed since the impurities may cause environmental contamination, corrosion and the like and admixture of the impurities may lower a purity degree of carbon dioxide (CO2) discharged.

Among the above-mentioned impurities, sulfur oxides (SOx) may be contacted with and dissolved in water into sulfuric acid (H2SO4) and hydrogen chloride (HCl) may be dissolved in water into hydrochloric acid, so that such water-soluble sulfur oxides and hydrogen chloride as well as dust may be separated through contact with water by, for example, water spraying.

Among the nitrogen oxides (NOx) as the above-mentioned impurities, nitrogen dioxide (NO2) may be contacted with and dissolved in water into nitric acid (HNO3) to become separated. However, the exhaust gas from the coal-fired boiler has less oxygen (O2) so that nitrogen (N2) exists substantially in the form of nitrogen monoxide (NO) which is water-insoluble and thus is unremovable by, for example, water spraying.

Among the above-mentioned sulfuric, hydrochloric and nitric acids, especially sulfuric acid is known to corrode instruments in an exhaust gas treatment device; mercury, which is trace metal, is known to hurt low-temperature aluminum members constituting a heat exchanger. Thus, it is preferable to remove these impurities at early stages. There is also a problem that admixture of the impurities into the exhaust gas lowers a purity degree of the carbon dioxide, which makes troublesome the liquefaction of the carbon dioxide through compression and cooling and thus requires large-sized equipment therefor. Thus, in a coal-fired boiler for oxyfuel combustion or other system where produced is exhaust gas mainly composed of carbon dioxide which in turn is to be disposed, it is extremely important to remove the impurities in the exhaust gas.

Thus, it has been conducted, for example, in the coal-fired boiler for oxyfuel combustion that a spray-column-type, packed-column-type or other so-called wet desulfurizer used in a conventional air-fired boiler or the like is provided to remove sulfur oxides which are especially problematic in corrosivity. Moreover, nitrogen and nitrogen oxides derived from coal feedstock are produced in the exhaust gas from coal-fired boiler for oxyfuel combustion or the like, so that it has been conducted that a catalyst-type or other denitrator is arranged upstream of the desulfurizer to remove nitrogen and nitrogen oxides.

It is known that the provision of the wet desulfurizer as mentioned in the above removes sulfur oxides, hydrogen chloride and dust as well as part of nitrogen oxides and slightly removes mercury, which is inherently low in content. It has been also conceived that if mercury in the exhaust gas is still high in concentration even after the above-mentioned exhaust gas treatment is conducted, a mercury-removing column is arranged to remove the mercury by adsorbent or the like.

An exhaust gas treatment system comprises, for example, a duct with a dust collector and a wet desulfurizer for guidance of exhaust gas from a boiler which in turn burns fuel with combustion gas in the form of a mixture of oxygen-rich gas with circulation exhaust gas, an exhaust gas recirculation duct for guidance of part of the exhaust gas downstream of the dust collector to the boiler and CO2separation means for compression of the exhaust gas downstream of the desulfurizer to separate carbon dioxide, water separated during the compression of the exhaust gas by the CO2separation means being supplied to absorbing liquid used circulatorily in the desulfurizer (see Patent Literature 1).

Patent Literature 2 discloses an exhaust gas treatment system for an oxyfuel combustor with a front impurity removal device and at least one rear impurity removal device. The front impurity removal device comprises a compressor for compression of exhaust gas from the oxyfuel combustor to make water-soluble the impurities in the exhaust gas and a cooler for cooling of the exhaust gas compressed by the compressor to condense water and discharge drain with the impurities dissolved. The or each rear impurity removal device comprises a rear compressor for compression of the exhaust gas at a pressure higher than that in the compressor and a rear cooler and serves for discharging drain.

Patent Literature 3 discloses a carbon dioxide purification device comprising a compressor for elevation in pressure of gaseous carbon dioxide; at least one countercurrent gas/liquid contact device for washing of the gaseous carbon dioxide with water at elevated pressure in the presence of molecular oxygen and, when SO2is to be removed, NOxfor a sufficient time to convert SO2to sulfuric acid and/or NOxto nitric acid; conduit means for feeding of the gaseous carbon dioxide at elevated pressure from the compressor to the or each gas/liquid contact device; and conduit means for recycling of aqueous sulfuric acid solution and/or aqueous nitric acid solution to the or each gas/liquid contact device.

Patent Literature 4 discloses a device for simultaneous treatment of dust collection and desulfurization wherein ash-containing boiler exhaust gas is cooled to or less than 40° C. to condense water in the exhaust gas, using boiler feeding water or boiler combustion air, exhaust gas at an outlet of a desulfurizing absorbing column or one or more kinds of seawater; SOxin the exhaust gas is removed, using desulfurizing absorption liquid which is a slurry of ash and condensed water admixed with lime; and unrequisite ash is separated by an unrequisite ash sedimentation/separation device below an absorption column tank.

Patent Literature 5 discloses a combustion exhaust gas purification system comprising a first process for making gas/liquid countercurrent contact of combustion exhaust gas with an aqueous alkali metal carbonate solution containing at least 0.1 N of alkali metal carbonate, using a leaking tray column, to reduce sulfur oxides and nitrogen oxides in the combustion exhaust gas; a second process for making gas/liquid countercurrent contact of the combustion exhaust gas from the first process containing carbon-rich gas and nitrogen with an aqueous alkali metal hydroxide solution, using a leaking tray column, to convert at least part of the carbon-rich gas in the exhaust gas into alkali metal carbonate to thereby purify the carbon-rich gas; and a regeneration process of the aqueous alkali metal hydroxide solution for reacting the alkali metal carbonate produced as a by-product in the second process with alkaline earth metal hydroxide to produce and separate alkaline earth metal carbonate to thereby withdraw the aqueous alkali metal hydroxide solution.

CITATION LIST

Patent Literature

SUMMARY

Technical Problems

However, in the conventional exhaust gas treatment system as disclosed in Patent Literature 1, the spray-column-type or other wet desulfurizer is provided to remove impurities and especially sulfur oxides (SOx) in exhaust gas, so that disadvantageously the device for removal of impurities becomes extremely large in size and complicated in structure, leading to increase in installation cost.

Thus, a technique has been desired which can remove impurities such as sulfuric oxides in exhaust gas to be guided to a compressor, at low cost, using a simple device.

The disclosure was made in view of the above conventional problems and has its object to provide a device and a system for removing impurities in water-containing gas capable of removing impurities in water-containing gas at high efficiency, using a small-sized device.

Solution to Problems

The disclosure is directed to an impurity removal device for water-containing gas comprising

a filler-integrated cooler having a cooler body with a cooling space, a gas inlet in communication with an inner underside of the cooling space, a gas outlet in communication with an inner upside of the cooling space, a cooling pipe arranged in the cooling space between the gas inlet and outlet for making cooling fluid go around from a cooling fluid inlet through the cooling space to discharge the cooling fluid through a cooling fluid outlet and a filler arranged in the cooling space to partition the cooling space vertically into portions with the gas inlet and outlet, respectively;

nozzles arranged in the inner upside of the cooling space; a drain circulator for pumping drain through a drain outlet arranged at a drain reservoir in an inner bottom of the cooling space to the nozzles for injection of the drain; and

an alkaline agent addition unit for adding an alkaline agent to the drain.

It is preferable that the impurity removal device for the water-containing gas further comprises a pH sensor for detecting a pH of the drain in the drain reservoir and an alkaline agent controller for controlling a supply of the alkaline agent by the alkaline agent addition unit so as to keep a pH value detected by the pH sensor to a set value.

It is preferable that the impurity removal device for the water-containing gas further comprises a level gauge for detecting a level of the drain in the drain reservoir and a level controller for controlling a control valve at the drain outlet so as to keep a level value detected by the level gauge to a set value.

It is preferable in the impurity removal device for the water-containing gas that the gas inlet is connected to a compressor.

It is preferable that the impurity removal device for the water-containing gas further comprises a freezer arranged between the cooling fluid outlet and inlet.

The disclosure is directed to an impurity removal system for water-containing gas comprising, downstream of an impurity removal mechanism for removing impurities in gas from an oxyfuel combustor comprising a plurality of impurity separators with a plurality of compressors and aftercoolers for cooling the gas compressed by the compressors to discharge condensed drain, respectively,

a filler-integrated cooler comprising a cooler body with a cooling space, a gas inlet in communication with an inner downside of the cooling space, a gas outlet in communication with an inner upside of the cooling space, a cooling pipe arranged in the cooling space between the gas inlet and outlet for making cooling fluid go around from a cooling fluid inlet through the cooling space to discharge the cooling fluid through a cooling fluid outlet and a filler arranged in the cooling space to partition the cooling space vertically into portions with the gas inlet and outlet, respectively;

nozzles arranged in the inner upside of the cooling space; a drain circulator for pumping drain through a drain outlet arranged at a drain reservoir in an inner bottom of the cooling space to the nozzles for injection of the drain; a freezer arranged between the cooling fluid outlet and inlet; and an alkalinity-control-agent supply flow passage for supply of the drain in the drain reservoir in the cooler body, as an alkalinity control agent, to at least an upstream side of the aftercooler in a first one of the impurity separators.

Advantageous Effects

An impurity removal device and a system for water-containing gas according to the disclosure can exhibit an excellent effect that impurities in water-containing gas can be removed at high efficiency, using a small-sized device.

DESCRIPTION OF EMBODIMENTS

Embodiments of the disclosure will be described in conjunction with the attached drawings.

FIG. 1is a schematic view showing an embodiment of a device for removing impurities in water-containing gas according to the disclosure in which reference numeral50denotes a filler-integrated cooler. The filler-integrated cooler50comprises a cooler body52with a cooling space51, a gas inlet54in communication with an inner underside of the cooling space51to introduce water-containing gas53, a gas outlet55in communication with an inner upside of the cooling space51, and a cooling pipe59arranged in the cooling space51between the gas inlet and outlet54and55to make cooling fluid57such as sea water or other cooling water introduced through a cooling fluid inlet56go around through the cooling space51to discharge the same through a cooling fluid outlet58. Reference numeral60designates a partition plate which provides a partition between the cooling fluid inlet and outlet56and58. Further, arranged in the cooling space51between the gas inlet and outlet54and55is a filler61vertically partitioning the cooling space51. The filler61comprises, for example, upper and lower pored plates61awith particles61b(Raschig rings) filled therebetween.

Arranged in an inner bottom of the cooling space51is a drain reservoir62, and arranged in the inner upside of the cooling space51are nozzles63. A drain circulator68is arranged to supply drain D from a discharge pipe65connected to the drain outlet64of the drain reservoir62through a pump66and a circulation flow passage67to the nozzles63for injection therethrough.

FIG. 1embodiment shows a case where the filler61is arranged above the cooling pipe59and the nozzles63is arranged above the filler61. The circulation flow passage67is provided with an alkaline agent addition unit70for addition of the alkaline agent69to the drain D flowing through the circulation flow passage67. Usable as the alkaline agent69is, for example, sodium hydroxide (NaOH), ammonia (—NH3), magnesium hydrate (Mg(OH)2) or a large amount of water (H2O) (generally water is weak alkali).

The cooler body52is provided with a level gauge71for detection of a level of the drain D in the drain reservoir62and a level controller73for control of a control valve72in the discharge pipe65so as to keep a level value detected by the level gauge71to a set value.

The cooler body52is further provided with a pH sensor74for detection of a pH of the drain D in the drain reservoir62and an alkaline agent controller76for control of a supply valve75in the alkaline agent addition unit70to control a supply of the alkaline agent69so as to keep a pH value detected by the pH sensor74to a set value.

FIGS. 2aand 2bshow modifications ofFIG. 1embodiment.FIG. 2ashows a case where the cooling pipe59is arranged above the filler61, and the nozzles63is arranged above the cooling pipe59, andFIG. 2bshows a case where the cooling pipe59is arranged within the filler61.

Mode of operation of the embodiment shown inFIGS. 1 and 2will be described.

The cooling pipe59in the filler-integrated cooler50constituting the impurity removal device for the water-containing gas is supplied with the cooling fluid57such as sea water or cooling water to thereby cool the cooling space51, and the drain D in the drain reservoir62at the inner bottom of the cooling space51is supplied by the drain circulator68to the nozzles63at the upside of the cooling space51for injection.

In this case, the level controller73makes control to keep the level of the drain D in the drain reservoir62detected by the level gauge71to the constant value, so that the drain D in the drain reservoir62can be reliably circulated by the drain circulator68for injection.

Then, the water-containing gas53from different combustors, reaction devices or the like and containing water and impurities is introduced into the cooling space51through the gas inlet54of the cooling body52in the filler-integrated cooler50constituting the impurity removal device for water-containing gas. The water-containing gas53introduced into the cooling space51is cooled through heat exchange with the cooling pipe59to make the contained water condensed into drain which drops down to the drain reservoir62. The impurities in the gas free from the water are removed when the gas passes through the filler61. In this case, the drain D has been injected to the filler61through the nozzles63of the drain circulator68and has been added with the alkaline agent69from the alkaline agent addition unit70, so that the gas passing through the filler61is contacted with the drain D to effectively remove the impurities.

Since the pH sensor74is provided to detect the pH of the drain D in the drain reservoir62and the alkaline agent controller76is provided to control the supply valve75in the alkaline agent addition unit70for control of the supply of the alkaline agent69so as to keep the pH value detected by the pH sensor74to the set value, the control to keep high the pH value of the drain D injected by the nozzles63enhances dissolution of the impurities in the drain D to further enhance impurity removal performance. As mentioned in the above, clean gas free from the impurities is discharged through the gas outlet55.

FIG. 3shows a further embodiment of the device for removing impurities in water-containing gas according to the disclosure. This embodiment is a case where the gas inlet54is provided with a compressor77for compression of the water-containing gas53. The cooling fluid outlet58is connected to the cooling fluid inlet56through a circulation flow passage90provided with a freezer78.

As shown inFIG. 3, the water-containing gas53, which has been compressed by the compressor77, is introduced into the cooling space51in the cooler body52so that drain D is separated more from the compressed water-containing gas53than that in the previous embodiment, and the impurities in the gas is effectively removed through contact with the low-temperature drain D. In this case, the impurities in the pressurized gas is accelerated in oxidization so that dissolution of the impurities in the drain D is further enhanced to perform effective removal.

By the provision of the freezer78, the cooling fluid (cooling medium) lowered in temperature by the freezer78is supplied to the cooling pipe59to further cool the water-containing gas53, so that still more drain D is separated from the water-containing gas53and the dissolution of the impurities in the gas to the drain D is further enhanced due to lowness in temperature to perform effective removal.

FIG. 4is a schematic view showing an embodiment of a impurity removal system for water-containing gas in which a filler-integrated cooler according to the disclosure is applied downstream of an impurity removal mechanism100for removing impurities in the gas from the oxyfuel combustor.

InFIG. 4, reference numeral1denotes an oxyfuel combustor comprising, for example, a coal-fired boiler1afor oxyfuel combustion of pulverized coal. Discharged from the oxyfuel combustor1is exhaust gas2(water-containing gas53) mainly composed of carbon dioxide (CO2). For supply and liquefaction of such exhaust gas2from the oxyfuel combustor1to and in a carbon dioxide liquefier3, arranged upstream of the carbon dioxide liquefier3is an impurity removal mechanism100which compresses the exhaust gas2up to a target pressure, i.e., a pressure required for the liquefaction in the carbon dioxide liquefier3or a predetermined pressure approximate to the required pressure, to remove the impurities in the exhaust gas2.

The impurity removal mechanism100comprises a plurality of (three in the embodiment illustrated) impurity separators6a,6band6ccomprising a plurality of compressors4a,4band4cfor compression of the exhaust gas2from the oxyfuel combustor1stepwisely up to the target pressure and aftercoolers5a,5band5c(coolers) for downstream cooling of the exhaust gas2compressed in the respective compressors4a,4band4cto discharge water condensed by the cooling as drains. A cooler arranged between compressors is generally called as intercooler; however, for ease of explanation, all of the coolers in the disclosure are explained as aftercoolers5a,5band5c.

Operations of the impurity separators6a,6band6cfor liquefaction of carbon dioxide under various temperature and pressure conditions were studied to find out that it is preferable inFIG. 4embodiment to increase a pressure of the exhaust gas2up to 2.5 MPa prior to supply of the carbon dioxide2to the carbon dioxide liquefier3. Thus, 2.5 MPa is set as the target pressure. The target pressure may be set at will.

It is not efficient to pressurize the exhaust gas2up to the target pressure of 2.5 MPa all at once by a single compressor4. Thus, in the embodiment, the three compressors4a,4band4care arranged for three-step compressions into 0.75 MPa, 1.5 MPa and 2.5 MPa, thus providing the impurity separators6a,6band6c. The number of the compressors4a,4band4c(the number of the impurity separators6a,6band6c) may be any including 4 or more.

By the impurity removal mechanism100, the impurities in the exhaust gas2can be effectively removed. When a concentration of mercury (Hg) in the carbon dioxide having passed through the impurity removal mechanism100is higher than its target value, a mercury-removing column7may be arranged downstream of the impurity removal mechanism100to remove mercury, using an adsorbent or the like.

Arranged upstream of the carbon dioxide liquefier3(and downstream of the mercury-removing column7) is a dryer8for removal of water in the carbon dioxide to be supplied to the carbon dioxide liquefier3.

In the first impurity separator6aof the impurity removal mechanism100, almost all of the water in the exhaust gas2is discharged as drain D1; in the middle impurity separator6b, drain D2is discharged which is smaller in quantity than the drain D1; and in the last impurity separator6c, drain D3is discharged which is smaller than the drain D2. The drains D1, D2and D3separated by the aftercoolers5a,5band5cand having impurities are usually supplied to a drainage treatment apparatus (not shown) for disposal.

In the aftercoolers5a,5band5c, the exhaust gas2is cooled, usually using sea water. Thus, the exhaust gas2discharged from the last aftercooler5cinFIG. 4embodiment usually has a temperature of around 35° C.

The inventor found it preferable to cool the exhaust gas to be guided to a dryer8arranged downstream of the impurity removal mechanism100to a temperature of around 7° C. for effective drying of the exhaust gas by the dryer8. Lowering in temperature of the exhaust gas to be guided to the dryer8lowers a saturated temperature of water in the dryer8so that dehumidification effect by the dryer8is enhanced, whereby the dryer8can be reduced in size.

To this end, inFIG. 4embodiment, arranged downstream of the impurity removal mechanism100is a filler-integrated cooler50constructed as shown inFIG. 1, and a cooling fluid outlet58is connected to a cooling fluid inlet56through a circulation flow passage90which is provided with a freezer78for cooling of cooling space51to around 7° C.

Drain D is discharged also from the filler-integrated cooler50since the exhaust gas with the temperature of 35° C. from the impurity removal mechanism100is cooled down to 7° C. in the filler-integrated cooler50.

The inventor conducted a test for measurement of a pH of the drain D from the filler-integrated cooler50. As a result, it was found out that the pH of the drain D is continuously 11 or more and does not lower below 11, high pH being constantly indicative. It is conceived that, due to the high pressure of 2.5 MPa in the impurity removal mechanism100, sodium and calcium in the water react with carbon dioxide (CO2) in the exhaust gas to facilitate production of, for example, sodium bicarbonate (CHNaO3) and calcium bicarbonate (Ca(HCO3)2) and the pH of 11 or more is kept due to the action of the high pressure.

Thus, it is found out inFIG. 4embodiment that supplying the drain D of pH 11 or more from the filler-integrated cooler50, as an alkalinity control agent10, to an upstream side of the aftercooler5ain the impurity removal mechanism100substantially enhances impurity removal performance of the impurity removal mechanism100, so that the embodiment is constructed as follows. Since the drain D discharged from the filler-integrated cooler50has the pH of 11 or more, the alkaline agent addition unit70shown inFIG. 4may be omitted.

A drain receiver11is arranged to receive the drain D produced in the filler-integrated cooler50, and an alkalinity-control-agent supply flow passage13is arranged to supply the drain D (the alkalinity control agent10) in the drain receiver11through a pump12to an upstream side of the aftercooler5ain the first impurity separator6a. The alkalinity control agent10is supplied through an alkalinity-control-agent supply flow passage13to a nozzle10′ arranged upstream of the aftercooler5ain the first impurity separator6aand is admixed into the exhaust gas2by the nozzle10′. The nozzle10′ may be arranged at any position between the compressor4aand the aftercooler5a.

Further, arranged upstream of the filler-integrated cooler50is an auxiliary cooler9for cooling of the exhaust gas2. The cooling of the exhaust gas2by the auxiliary cooler9produces drain D4with a pH of 11 or more which is received by a drain receiver14and is joined by a pump15with the alkalinity control agent10downstream of the auxiliary cooler9. The drain D from the filler-integrated cooler50, which has a temperature as low as around 7° C., is guided as cooling medium through an alkalinity-control-agent supply flow passage13to the auxiliary cooler9to cool the exhaust gas2. In the auxiliary cooler9, due to the cooling energy of the drain D, the exhaust gas2with a temperature around 35° C. is effectively cooled to, for example, around 12° C. Thus, the provision of the auxiliary cooler9can reduce a load of the filler-integrated cooler50or reduce in size of the filler-integrated cooler50.

Arranged for the aftercooler5ain the first impurity separator6ais a drain tank16which stores an amount of drain D1from the aftercooler5a. The drain tank16is provided with a level controller17which controls an opening degree of a discharge valve18which in turn is arranged on a drain outlet side (downstream) of the drain tank16so as to always keep a detected level to a constant value. The drain tank16is provided with a drain supply flow passage20through which part of the drain D1in the drain tank16is discharged by a pump19into the alkalinity-control-agent supply flow passage13.

The alkalinity-control-agent supply flow passage13has a supply valve21; the drain supply flow passage20has a mixing valve22; and the drain tank16has a pH sensor23for measurement of a pH in the drain D1. A pH value24detected by the pH sensor23is inputted to a controller25which in turn controls the supply and mixing valves21and22to control a pH concentration of the alkalinity control agent10supplied to the nozzle10′ so as to keep the detected pH value24to a predetermined set value of, for example, pH 5.

Arranged at a gas outlet55of the filler-integrated cooler50is an impurity sensor26for detection of impurities (for example, sulfur oxides and/or nitrogen oxides) in the exhaust gas2, and an impurity value27of nitrogen oxides detected by the impurity sensor26is inputted to the controller25. The controller25serves to control the supply and mixing valves21and22to urgently increase a supply of the alkalinity control agent10when the impurity value27of nitrogen oxides detected by the impurity sensor26exceeds a predetermined set value. The mercury-removing column7is provided with a bypass duct43as well as changeover valves44and45for changeover between flowing and non-flowing states of the exhaust gas2to the mercury-removing column7; when the detected value of mercury by the impurity sensor26exceeds the predetermined value, the changeover valves44and45are changed over by a command from the controller25to cause the exhaust gas2passing through the mercury-removing column7. When sufficient impurity removal effect is attained by the impurity removal mechanism100shown inFIG. 4, the exhaust gas2may be bypassed through a bypass line79to a downstream side of the filler-integrated cooler50, without passing the same through the filler-integrated cooler50. Reference numerals80,81and82denote changeover valves for changeover between flowing and non-flowing states of the exhaust gas2to the filler-integrated cooler50.

Next, mode of operation ofFIG. 4embodiment will be described.

In the impurity removal system for water-containing gas shown inFIG. 4, the exhaust gas2(water-containing gas53) mainly constituted of carbon dioxide resulting from the oxyfuel combustion in the oxyfuel combustor1is guided with a pressure of, for example, 0.1 MPa (one atmosphere of pressure) to the compressor4ain the first impurity separator6aof the impurity removal mechanism100, and is pressurized by the compressor4ato 0.7 MPa. The exhaust gas2pressurized by the compressor4ato 0.7 MPa is supplied to and cooled by the adjacent aftercooler5afrom which plenty of drain D1is discharged owing to the cooling. In this case, effectively removed from the first aftercooler5aare almost all of water-soluble impurities, i.e., sulfur oxides, hydrogen chloride and dust in the exhaust gas2. Specifically, the water-soluble impurities, i.e., sulfur oxides and hydrogen chloride are removed in a high removal ratio together with the plenty of drain D1discharged from the first aftercooler5a.

The exhaust gas2cooled by the aftercooler5ais guided to and pressurized by the compressor4bin the downstream (succeeding) impurity separator6bto 1.5 MPa. The exhaust gas2pressurize to 1.5 MPa is cooled by the adjacent aftercooler5bfrom which drain D2is discharged in an amount smaller than that from the aftercooler5a. And, due to the pressure being elevated by the compressor4b, part of sulfur oxides and hydrogen chloride are also removed in the succeeding aftercooler5btogether with the small amount of drain D2.

The exhaust gas2cooled by the aftercooler5bis guided to and pressurized by the compressor4cin the last impurity separator6cto 2.5 MPa. The exhaust gas2compressed by the compressor4cto 2.5 MPa is cooled by the adjacent aftercooler5cand drain D3is discharged from the aftercooler5cin an amount still smaller than that in the aftercooler5b.

The exhaust gas2is pressurized to 2.5 MPa in the compressor4cof the last impurity separator6c, so that nitrogen monoxide (NO) existing in the exhaust gas2is accelerated in oxidization by the pressurization into water-soluble nitrogen dioxide (NO2). Thus, part of nitrogen dioxide (NO2) is removed together with the drain D3discharged from the aftercooler5c.

Further, the exhaust gas2is introduced into and cooled by the filler-integrated cooler50arranged downstream of the impurity removal mechanism100to around 7° C. to thereby produce drain D which is injected by the drain circulator68through the nozzles63, so that during fluidization of the exhaust gas2through the filler61, nitrogen dioxide (NO2) in the exhaust gas2is effectively removed by contact with the drain D. Thus, nitrogen oxides in the exhaust gas is removed at high removing ratio by the filler-integrated cooler50.

In the above, the drain D produced in the filler-integrated cooler50and stored in the drain receiver11is supplied as the alkalinity control agent10by the pump12through the alkalinity-control-agent supply flow passage13to the auxiliary cooler9for cooling of the exhaust gas2, and then is supplied by the nozzle10′ upstream of the aftercooler5ain the first impurity separator6ato the exhaust gas2. Such supply of the alkalinity control agent10upstream of the aftercooler5afor the exhaust gas2effectively performs removal of especially sulfur oxides, hydrogen chloride and the like in exhaust gas2by the impurity removal mechanism100.

Further, the drain D1from the first aftercooler5aand stored in the drain tank16is supplied to the alkalinity-control-agent supply flow passage13through the drain supply flow passage20for mixing with the alkalinity control agent10. By the supply of the drain D1to the alkalinity control agent10, the alkalinity control agent10diluted to a predetermined pH is supplied to the nozzle10′.

Dissolution of plenty of sulfur oxides in the exhaust gas into the drain D1would substantially lower the pH of the drain D1(into, for example, around pH 1) and make the drain D1into a saturated state, leading to substantial lowering in dissolution of the sulfur oxides in the drain D1and thus lowering in removal effect of sulfur oxides. However, the controller25controls the supply and mixing valves21and22in the supply flow passages13and20, respectively, so as to keep the detected pH value of the drain D1discharged from the first aftercooler5ato a set value, e.g., pH 5, so that the atmosphere of the aftercooler5ais kept to high pH, and thus the impurities are removed with the drain D1at high removal ratio.

The drains D4and D with pH of 11 or more discharged as the alkalinity control agent10from the filler-integrated cooler50and auxiliary cooler9, respectively, and supplied upstream of the aftercooler5acan be ensured in a sufficient amount to keep the pH of the drain D1to a set value of pH 5; and superfluous drains D4and D are discharged from the drain receivers11and14into a drainage treatment apparatus (not shown) for disposal.

The detected impurity value27of sulfur oxides by the impurity sensor26arranged downstream of the aftercooler5cin the last impurity separator6cis inputted to the controller25which in turn performs the control to increase the supply of the alkalinity control agent10through the alkalinity-control-agent supply flow passage13when the detected impurity value27of sulfur oxides exceeds a predetermined set value, so that the impurities at the outlet of filler-integrated cooler50can be prevented from increasing.

The level controller73performs the control to keep constant the level of the drain D in the drain reservoir62detected by the level gauge71, so that the drain D in the drain reservoir62can be reliably circulated by the drain circulator68for injection.

Provision of the alkaline agent controller76to keep a pH of the drain D in the drain reservoir62to a set value can keep constant the pH of the drain D and keep constant the impurity removal effect by the filler-integrated cooler50.

As mentioned in the above, in the impurity removal system for water-containing gas with the filler-integrated cooler50downstream of the impurity removal mechanism100according to the disclosure, in addition to the impurity removal effect by the impurity removal mechanism100, the impurity removal effect is exhibited by the filler-integrated cooler50, so that reliable impurity removal can be attained. Further, by guiding the drain D produced in the filler-integrated cooler50as the alkalinity control agent10to the impurity removal mechanism100, the impurity removal effect by the impurity removal mechanism100can be enhanced without supply of new alkaline agent.

It is to be understood that a device and a system for removing impurities in water-containing gas according to the disclosure is not limited to the above embodiments and that various changes and modifications may be made without departing from the scope of the disclosure.

REFERENCE SIGNS LIST