FI91129B - Device for desulfurization by wet method and circulation tank - Google Patents

Description

91129

Wet desulphurisation device and recycling tank

Divided by application 850 681 5

The invention relates to the desulfurization of wet type flue gas. More specifically, the invention relates to a recycle tank for an apparatus for desulfurizing an exhaust gas for a wet process, into which the apparatus enters an absorption slurry into which the sulfur oxide compound of the exhaust gas is absorbed to form calcium sulfite. The invention also relates to an apparatus for desulfurizing an exhaust gas for a wet process, which apparatus comprises arc cooling means, dust removal means, means for absorbing and removing the sulfur oxide compound and defrosting means. Hereinafter, sulfur oxides are commonly labeled S0X.

The wet type of flue gas desulphurisation device now used in practice is mainly a device using a calcium absorber, and gypsum is obtained as a by-product. It is a device that operates according to the limestone-gypsum process (or the lime-gypsum process) and uses limestone, quicklime or slaked lime as an absorbent. Figure 8 shows a conventional apparatus for flue gas desulphurisation using limestone as an absorbent, with gypsum as a by-product. Exhaust gas 1 from a boiler or the like is led to a dust removal tower 2, where it is cooled, dust is removed and sulfur is partially removed. The resulting gas is then led to an absorption tower 3, where it is brought into contact with the circulating slurry 30, the frost is removed in a defroster 4 and discharged from the absorption tower. On the other hand, the limestone slurry 20 is fed as an absorption slurry by means of a limestone slurry pump 21 to a recycle tank 5 and an absorption tower, from which it is then fed by a recirculation pump 7 to SOx and then returned to the recycling tank and reused by recycling. After absorption, the sludge is fed by means of the absorption tower lowering pump 8 to the recirculation tank 6 of the dust removal tower 2 and further contacted with the exhaust gas in the dust removal tower, whereby SOX in the exhaust gas is removed and thus the amount of unreacted limestone in the sludge is reduced. The resulting slurry is fed to a by-product recovery system, i.e. to the feed tank 10 of the oxidation tower 12, where the unreacted limestone is converted to calcium sulfite by adding sulfuric acid and the pH of the slurry is adjusted to suit the oxidation. The pH-adjusted slurry is fed to the tower of the oxidation tower 12 by a feed pump 11, where the calcium sulfite is oxidized to gypsum by air and then passed through a channel 13 to a thickener 14 where it is concentrated. The resulting gypsum slurry is dewatered with a centrifugal separator 17 to obtain a gypsum-20 powder 18. The filtered water from the thickener 14 and the centrifugal separator 17 is recycled and reused.

However, according to such prior art device, the absorption tower and the dust removal tower are separate and an unreacted limestone neutralization device is required, which unreacted limestone is in the slurry leaving the absorption system (tank, pump, etc. for sulfuric acid) and a calcium sulfite oxidizer; thus, such disadvantages have arisen that the surface area of the system increases and the equipment becomes complex. There is still a need for equipment for unreacted limestone (excess limestone) and added sulfuric acid.

For the above reasons, there has been a need for a compact desulfurization device that does not require equipment for these chemicals, which simplifies equipment 35 and requires a small surface area.

Il 91129 3

The device according to the invention and the recycling tank for the desulphurisation of wet-type flue gas eliminate the above-mentioned disadvantages of the prior art, so that there are no special means for the absorption tower and the means for neutralization and oxidation can be omitted.

The recycling tank according to the invention is characterized in that the recycling tank comprises at least one lower mixing means for mixing the absorbent slurry, at least one upper mixing means above the lower mixing means for mixing the absorbent slurry, means for supplying air to the absorbent slurry and means for discharging or removing the treated absorbent slurry. Preferred embodiments of the recycling according to the invention are also set out in claims 2 to 5. The device according to the invention is characterized in that all said means are arranged inside a single absorption tower and that the device is provided with a recycling tank comprising at least one lower mixing device. 20 for mixing the absorbent slurry, at least one upper mixing means for mixing the absorbent slurry located above the lower mixing means, means for supplying air to the absorbent slurry and means for removing or circulating the treated absorbent slurry to said device.

Figure 1 shows an apparatus for desulfurizing a wet type flue gas as an embodiment of the present invention.

Figures 2-5 each show drawings illustrating an apparatus for desulfurizing a wet type flue gas 30 in other embodiments of the present invention.

Fig. 6 is a side view showing an implementation of arranging the mixer inside the sludge circulating tank of the dust removal section and the location of the air supply pipe.

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Figure 7 shows a cross-section of the plane of the above arrangement.

Fig. 8 is a drawing illustrating a flow chart of a conventional apparatus for desulfurizing wet-type flue gas.

The present invention will be described in more detail with reference to the accompanying drawings.

Figure 1 shows, as described above, a view of an apparatus for desulfurizing a wet type flue gas, as an embodiment of the present invention. In this figure, the device comprises a vertical cylindrical tower body 50; a dust extraction portion 34 and an absorption portion 35 formed in the lower portion and the upper portion within the tower body 50, respectively; a dust tank 36 to a dust extraction part, which tank 15 is in the bottom part of the tower frame; mixing equipment 32 inside the recycling tank 36; an air supply pipe 30 having some holes for supplying air to the liquid surface of the recirculation tank 36 of the dust extraction section; a screen 31 for oxidation, which screen is above the air supply pipe 30; a pump device 37 and spraying means 22 for supplying and spraying the absorbent liquid into the recirculation tank 36 of the dust removing part, into the dust removing part 34; a port 45 for supplying the exhaust gas 1 located in the dust extraction section 34; piping 39A for supplying a portion of the absorbent liquid 25 to the absorbent liquid recycle tank 38, the dust removal section 36 to the recycle tank; a spray apparatus 22 for an absorbent liquid disposed in the absorbent portion 35; a collector 33 for the absorbent liquid located below the spray apparatus 22; 30 an absorbent liquid recycling tank 38, and this absorbent liquid is collected in a collector 3 and circulated through a downcomer 40; a pump 39 for supplying absorbent liquid from inside the tank 38 to the spraying apparatus 22 in the absorption section 35; a mixing apparatus 43 disposed within the recirculation tank 38 of the absorption section; apparatus for feeding absorbent (CaCO 3) 91129 5 to the recycling tank 38 of the absorption section; an outlet 46 for the exhaust gas located at the top of the tower frame; a defroster 4 disposed between the spray device 22 in the absorption section 35 and the outlet 5 of the discharge section 46; and a line 13 for removing the gypsum-containing liquid from the dust removal section of the recycle tank 36, the pump 37 and the line 13.

Exhaust gas 1 from a boiler or the like is led to a dust extraction section 34 through an exhaust gas outlet 45 10 in the lower part of the absorption tower, where it is dedusted, cooled and partially desulfurized.

The resulting gas rises through the collector of the absorbent liquid 33 and the diffusion plate 49 and is passed to the absorbent section 35 in an absorption tower, where the SO 2 contained in the exhaust gas is absorbed and the calcium absorbent (CaCO 3, Ca (OH) 2) is removed.

CaO). The resulting exhaust gas is dehumidified with a defroster 4 and discharged through an outlet at the top of the absorption tower. On the other hand, the absorbent (CaCO 3, etc.) slurry is fed to the tank 38 of the absorbent portion 35, where the slurry is mixed by a mixer 43, then fed to the absorbent portion 35 by a recirculation pump 39 to remove SOx in the exhaust gas, collected by a collector 33, returned to a recycle tank 5 25 by. Such a collector is implemented in the form of U-shaped collection containers (trough shape or semicircular tube shape) in cross-section and arranged knee-like in several layers, as described in JP Patent Application No. Sho 58-126363 / 1983, which is incorporated herein by reference. filed (U.S. Patent Application No. 51,065, Jan. 16, 1984). The collector may consist of several water collection devices such as a funnel. A portion of the above slurry is removed via line 39A to the dust removal section of the recycle tank 36 in an amount corresponding to the amount of absorbent slurry (CaCO 3) fed. The sludge fed to the recycle tank 36 of the dedusting section 6 is mixed in the tank by a mixer 32 and recirculated by a pump 37 to the dedusting section 34, where it is brought into contact with the exhaust gas, whereby the reacting limestone contained in the slurry is used. Further, air is supplied through an air supply pipe 30 located above the recirculation tank 36 of the dust extraction section and further above the air supply pipe 30 there is a screen 31 for oxidation, in which screen the recirculation liquid of the dust extraction section (i.e. the recirculation liquid 10 absorbed in the SO 2 tower). and whose pH has been lowered) is effectively contacted with air, whereby the calcium sulfite formed during the absorption of SO 2 gas is oxidized to gypsum. The resulting gypsum-containing slurry is removed by a dust removal section recirculation pump 37 to a thickener and a centrifugal separator, whereby the gypsum is concentrated and separated, and finally the gypsum is recovered in powder form with 10% or less water. As the above oxidation screen 31, any type of screen that promotes contact efficiency between calcium sulfite (slurry) and air can be used, such as those consisting of a metal mesh, filler, etc. Such a metal mesh, filler, etc. can be formed or coated with metals that act as oxidation catalysts.

In order to recover good quality gypsum, it is necessary to reduce the concentration of unreacted limestone in the slurry after the sludge has entered the dust removal recycle tank into the thickener, and also to complete the oxidation of calcium sulfite in the dust removal recycle tank 36. It has been found that these conditions select the pH of the slurry appropriately in the recycle tank of the dust extraction section, the capacity of the tank and the amount of air supplied for oxidation.

In the blocked embodiment in Figure 1, a method of flowing air 35 per liquid surface of the recirculation tank is used as the oxidation air supply pipe 30, taking the scale

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91129 7, but as illustrated in Figure 2, a method may also be used in which the air supply pipe 30 is immersed in the liquid in the tank and air is supplied thereto. According to this method, since the recycle liquid is in contact with the air in the tank, the oxidation rate increases, making it possible to reduce the amount of oxidation air. Further, as illustrated in Fig. 6, the air supply pipe 30 and the oxidation screen 31 can each be immersed in the liquid of the recirculation tank. According to such a construction, the oxidation screen 10 31 prevents the air injected into the liquid from rising, whereby it is possible to keep the contact time of the air with the recirculation liquid sufficient. Further, in this case, when the oxidation screen is in many layers, its efficiency can be improved.

In the present invention, as an air supply device located in the recirculation tank of the dust extraction section, in addition to a barrel 30 having holes as shown in Fig. 1, those shown in Fig. 6 or Fig. 7 are used, the air supply nozzles 30A to 30G being arranged in mixers 32A to 32D. proximity accordingly. It is preferred that such nozzles 30A to 30G be arranged to face the blades of the agitators 32A to 32D so that the supplied air could collide with the blades, be finely divided, and disperse in the liquid. When 25 such devices are used, the mixing of the slurry and the fine distribution and dispersion of the supplied air are achieved at the same time, whereby it is possible to achieve the oxidation of calcium sulfite uniformly and with high efficiency. In Figure 6, a stirrer 32E located below the air supply nozzle 30G prevents the pump 37 from causing air cavitation.

With respect to the agitators 32A to 32D, in addition to those arranged in a radial position in the recycle tank 36 (i.e., directed to its center), as shown in these figures 35, the agitators can be positioned obliquely so that the flow formed by agitation can form an eddy current. Further, when the air supply pipe is fixed along the axis of the agitators and air is supplied along the axis behind the rotating blade of the agitators, then the efficiency of the gas-liquid contact is further improved. It has been found that with respect to a rotating blade, propeller-type ones are more desirable than wing-type ones.

The embodiments described in Figures 1, 2 and 3 relate to an apparatus in which the recycle tank 38 of the absorbent part is located separately outside the absorption tower. However, as illustrated in Fig. 4, when the lower part of the tower is divided into two parts by a partition wall 42, the dust removal section recycling tank 36 and the absorbent section recycling tank 38 may be in the same tower to make the device compact, in addition to the above efficiency. In Fig. 41, the number 41 refers to a sludge downcomer.

The above embodiments in which the dust in the exhaust gas is removed only with a slurry containing absorbent are called dust mixing systems, but the dust separation system illustrated in Fig. 5 can also be used.

The device shown in Figure 5 comprises the following parts: a vertically arranged, cylindrical tower structure 50; a dust extraction portion 34 and an absorption portion 35 formed in the lower space 25, and in the upper space of the tower body, respectively; a recycling tank 36 for the dust extraction section; formed in the bottom portion of the tower frame 50; a tube 51 for supplying water to the recycling tank 36 of the dust extraction section; a pump device 37 and a spray device 22 for supplying and spraying water 30 into the recirculation tank 36 of the dust extraction part, into the dust extraction part 34; a port 45 for supplying an exhaust gas located in the dust extraction section 34; a spray apparatus 22 for the absorption liquid attached to the absorption section 35; a collector 33 for the absorbent liquid, located under the spray device 35; defroster 4A located below the collector 33; a recycling tank 38 for the absorbent liquid, for receiving the liquid collected by the collector 33; a pump device 39 for an absorbent liquid recycle liquid tank 38, an absorbent liquid spray apparatus 22; mixing equipment 32 5 located in the recirculation tank 38 of the absorption section; an air supply device to or into the surface of the liquid inside the recirculation tank 38 of the absorption section; a tube 52 for supplying the absorbent slurry to the recycle tank 38 of the absorption section; an outlet 46 for the exhaust gas, at the top of the tower frame; and an apparatus 10 for removing the gypsum-containing slurry from the recirculation tank 38 of the absorption section.

As shown in the drawing, the liquid recirculation systems of the dust removal section 34 and the absorbent section 35 are separated by a partition 42 and water is recirculated to the dust removal section 34 to remove and cool dust, while the absorbent slurry is fed to the absorption section 35 and air is fed to the top of the recycle tank 38. The frost (or dust) in the exhaust gas is taken by the defroster 4A.

In the device of Figure 5, the partition 42 can be replaced by a horizontal screen with which the tank is divided into upper and lower parts. An air supply pipe and a pipe for removing gypsum-containing liquid are provided in the upper part, whereby the pH of the upper part is made lower, while a pipe for supplying absorbent slurry and a pipe for circulating the absorbent slurry to the absorption part is provided in the lower part.

According to the above embodiment, high efficiencies in SOx absorption and calcium sulfite oxidation are obtained.

30 Example

An example of exhaust gas treatment was performed using the apparatus shown in Figure 1 for desulfurizing a wet type gas.

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The test conditions are as follows:

Gas content: 3 000 Nm3 / h, SO2 content: 1 000 ppm, desulphurisation percentage: 90 or higher, dust concentration at the inlet: 200 mg / Nm3, dust concentration at the outlet: 5 15 mg / Nm3 or lower.

The test results were as follows:

Gas volume: 3,000 Nm3 / h, SO2 content: 1,000 ppm, desulphurisation percentage: 98, dust concentration at inlet: 200 mg / Nm3, dust concentration at exit: 7 mg / Nm3, percentage of lime-10 scale: 0 , 01%, amount of sulfuric acid used: 0 kg / h, purity of gypsum formed as a by - product: 96.3%.

According to the device of the present invention, a tank for supplying absorbent liquid to the oxidation tower and devices around the oxidation tower can be omitted and thus made compact and since limestone and sulfuric acid equipment is not required, nor an air compressor to supply air to the oxidation tower, but a fan can be used instead. use. Furthermore, since the dust extraction part, the absorption part, and the recycling tank of the dust extraction part are kept in one tower, the transport loss in the supply of gases from one tower to another through the piping can be reduced. When the exhaust gas is fed to the absorption section and passed through the collector and diffusion plate after cooling in the dust extraction section, the material used to build the collector and diffusion plate need not be heat-resistant and can be inexpensive.

Claims (4)

91129 11 A recycling tank (36) for a device for removing sulfur from an exhaust gas by a wet process, the device receiving an absorption slurry into which the sulfur oxide compound of the exhaust gas is absorbed to form calcium sulphite, characterized in that the recycling tank (36) includes at least one lower vane mixer (32E) for mixing the absorbent slurry, at least one upper mixing means (32A, 32B) located above the lower mixing means for mixing the absorbent slurry, means (30A-30G) adapted to supply air to the suction side of the upper mixing device (32A-32D) absorboin-15 to the sludge, and means (37) for removing the treated absorboin sludge or recycling it to said device. Recirculating tank according to claim 1, characterized in that it comprises a plurality of upper mixing devices (32A to 32D) spaced a certain circumferential distance apart and at least one lower mixing device on the opposite side of the circulation pump (37). A recirculation tank according to claim 1, characterized in that the air supply device (30A to 30G) is located on the shaft of the vane mixers of the upper mixing device (32A to 32D). An apparatus for desulfurizing an exhaust gas for a wet process, the apparatus comprising gas cooling means, dust removal means (34), means for absorbing and removing sulfur oxide compound and defrosting means (4), characterized in that all said means are located in a single absorption tower (50). and that the apparatus is provided with a recirculation tank (36) including at least one lower mixing means (32E) for mixing the absorbent slurry, at least one upper mixing means (32A, 32B) located above the lower mixing means 12 for mixing the absorbent slurry, means (30) for supplying air to the absorbent slurry, and means (37) for removing the treated absorbent slurry 5 or recycling it to said device. 91129 13