Gas-liquid contacting apparatus

Abstract: A gas-liquid contacting apparatus in which spray nozzles for spraying slurry solution upward are arranged in a tower body through which gas passes, wherein the material of a spray nozzle is one of polyether urethane rubber having a JIS-A hardness of 50 to 100 or polyethylene having an average molecular weight of 1,000,000 to 4,000,000.

Description: FIELD OF THE INVENTION AND RELATED ART STATEMENT The present invention relates to a gas-liquid contacting apparatus used for a wet type exhaust gas desulfurizer or the like and, more particularly, to a gas-liquid contacting apparatus that improves wear resistance of spray nozzle without using expensive materials and achieves high reliability and greater economy. In recent years, wet type exhaust gas desulfurizers have been widely used, in which absorbent slurry absorbs sulfur dioxide in exhaust gas to remove it. In the desulfurizer of this type, it is important to efficiently bring absorbent slurry into contact with exhaust gas. For this reason, the applicant has proposed a gas-liquid contacting apparatus which achieves improved gas-liquid contact efficiency, reduced necessary volume, and simplified construction by configuring the apparatus so that slurry solution is sprayed upward in the tower body in which the gas flows, as disclosed in Japanese Utility Model Provisional Publication No. 59-53828 (No. 53828/1984). FIG. 3 shows a typical exhaust gas desulfurizer (principal portion only) using this gas-liquid contacting apparatus. This exhaust gas desulfurizer is formed at the bottom of an absorption tower 1. The exhaust gas desulfurizer includes a tank 2 to which absorbent slurry S composed of, for example, limestone is supplied from a slurry supply system (not shown), a circulating pump 4 which sends the slurry in the tank 2 to a tower body 3 formed at the upper part of the absorption tower 1 to bring the slurry into contact with exhaust gas, and a stirrer 7 which is supported on the ceiling of the tank 2 by means of a rotation shaft 5 and is rotated in the slurry by a motor 6. Ducts 8 and 9 which constitutes an inlet or an outlet for exhaust gas are provided at the upper part of the tower body 3 of the absorption tower 1 and at the upper end of the tank 2, respectively, so that exhaust gas flows in the tower body 3 through the space over the liquid surface of the tank 2. A header pipe 10 connected to the discharge side of the circulating pump 4 is disposed in the tower body 3. On this header pipe 10, a plurality of spray nozzles 11 are formed to spray absorbent slurry S upward in a liquid column form. This provides a gas-liquid contacting apparatus in which absorbent slurry S is efficiently brought into contact with exhaust gas. Although several header pipes 10 are provided in the gas-liquid contacting apparatus for the above-mentioned desulfurizer, these pipes are not always arranged in the same plane. The liquid inlet portion of the conventional spray nozzle 11 is of a shape having acute corner. Further, when the liquid column of absorbent slurry S has a height not more than 1 m and the gypsum in absorbent slurry has a concentration not more than 15%, FRP (fiber reinforced plastic) is used as the material for the conventional spray nozzle 11. Under severer conditions, a metallic material having high hardness and wear resistance or a ceramic material such as alumina, zirconia, tungsten carbide, or silicon carbide is normally used. In this apparatus, untreated exhaust gas is introduced through, for example, the duct 8, brought into contact with the absorbent slurry S sprayed from the spray nozzles 11 by means of the circulating pump 4 to absorb and remove sulfur dioxide gas in the untreated exhaust gas, and discharged through the duct 9 as treated exhaust gas. The absorbent slurry S, which is sprayed from the spray nozzles 11 and flows down while absorbing sulfur dioxide gas, comes in contact with many bubbles produced by the air supplying means (not shown) while being stirred by the stirrer 7 in the tank 2 and is oxidized, being taken out as gypsum (by-product). At this time, the absorbent slurry S sprayed from the spray nozzles 11 spouts upward in a liquid column form, is scattered at the top of spout, and falls. The falling absorbent slurry S and the spouting absorbent slurry S collide with each other to form fine particles. Therefore, this absorption tower has a large gas-liquid contact area per unit volume, though having a simple construction, as compared with the filling type absorption tower. Also, the exhaust gas is effectively caught in the flow by the spout of absorbent slurry S in the vicinity of the nozzle, so that the absorbent slurry and the exhaust gas are mixed effectively, resulting in high gas-liquid contact efficiency. This provides a low-volume, simple absorption tower 1 which purifies exhaust gas with high SO X removal efficiency. Further, the liquid column height of absorbent slurry S sprayed from the spray nozzles 11 can be adjusted by setting the discharge pressure of the circulating pump 4. Therefore, the gas-liquid contact efficiency and in turn the SO X removal efficiency can be changed effectively. In the above-described conventional gas-liquid contacting apparatus, the material cost, manufacture cost, and assembly cost of spray nozzle 11 are so high to prevent the reduction in reliability due to wear etc., depending on the conditions such as a great column height of absorbent slurry S or a high concentration of gypsum in absorbent slurry S that the economy is impaired. When the liquid column of absorbent slurry S has a height exceeding 1 m or the gypsum in absorbent slurry S has a concentration exceeding 15%, an expensive material such as a metallic material having high hardness and wear resistance or a ceramic material is normally used, leading to high material cost and manufacture cost. Especially when corrosion resistance is required, a ceramic material must be used, and a special attaching structure is needed to assure shock resistance. In the desulfurizer for a coal burning boiler etc., solid materials such as calcium sulfite, calcium sulfate (gypsum), and fly ash (coal ash) of reaction product and sand particles in coal exist in the absorbent slurry S in the steady operation. These solid materials pass through the spray nozzle 11 more violently as the liquid column height is higher. Therefore, FRP having low wear resistance wears away in a short period of time. Also, in the desulfurizer for a coal burning boiler etc., chlorine ions exist in the absorbent slurry S, so that corrosion such as pitting or deposit attack occurs in stainless steels, depending on the chloride ion concentration. As a material which withstands such corrosion, nickel-base alloys or titanium-base alloys are available, but such alloys are expensive though having lower hardness and poorer wear resistance than stainless steels. When high wear resistance and corrosion resistance are required, ceramics have so far been used as a material for the spray nozzle 11. However, ceramics are difficult to mold, so that their manufacture cost is high. Moreover, ceramics have poor shock resistance and are heavy, so that they are easily broken when the spray nozzle 11 is being attached to the header pipe 10. Also, the ceramic spray nozzle must have a special structure such that shock does not transmit to the support structure of the spray nozzle. Accordingly, an object of the present invention is to provide a gas-liquid contacting apparatus having spray nozzles which have high wear resistance, corrosion resistance, and shock resistance, light in weight, and inexpensive, and achieving high reliability and great economy. Recently, in discharging exhaust gas from a thermal electric power plant or the like, an exhaust gas desulfurizer is installed to prevent environmental pollution by removing SO 2 in exhaust gas. In the conventional exhaust gas desulfurizer, a SO 2 absorbent such as lime slurry is allowed to flow down in an absorption tower which is filled with a filler such as grit, and exhaust gas is introduced into the absorption tower so as to flow in the countercurrent direction or the concurrent direction with respect to the lime slurry. The SO 2 gas in exhaust gas is dissolved in the lime slurry to form SO 2 ions, and reacts with Ca ions existing in the lime slurry to yield CaSO 4 . By removing this CaSO 4 , SO 2 in exhaust gas is removed. However, in the above-described conventional exhaust gas desulfurizer, the yielded CaSO 4 often deposits on the filler such as grit in the absorption tower. For this reason, the absorption capacity of the absorbent decreases, and the flow resistance of exhaust gas increases, resulting in decrease in desulfurizing performance. The removal of the yielded CaSO 4 from the filler requires much time and manpower. Therefore, there has been a demand for developing a gas-liquid contacting apparatus for absorbent slurry and exhaust gas in place of the filling type absorption tower which is filled with grit or other fillers. In order to realize such a spray type absorption tower, the following problems must be solved. First, the nozzle for spraying absorbent slurry must be made of a material having high wear resistance because the absorbent slurry is highly abrasive. A nozzle made of a metal such as steels, stainless steels, or aluminum wears out excessively, so that it is difficult to use practically. SUMMARY OF THE INVENTION To achieve the object of the present invention, the gas-liquid contacting apparatus of the present invention, in which spray nozzles for spraying slurry solution upward are arranged in a tower body through which gas passes, is characterized in that the material of the spray nozzle is polyether urethane rubber having a JIS (Japanese Industrial Standard) - hardness of 50 to 100 or polyethylene having an average molecular weight of 1,000,000 to 4,000,000. When the material of the spray nozzle is polyether urethane rubber having a JIS-A hardness of 50 to 100 or polyethylene having an average molecular weight of 1,000,000 to 4,000,000, a lightweight, inexpensive spray nozzle with high wear resistance, corrosion resistance, and shock resistance can be provided. The reason why polyether urethane rubber having a JIS-A hardness of 50 to 100 has high wear resistance is probably because this material has energy absorption effect due to rubber elasticity. The reason why polyethylene having an average molecular weight of 1,000,000 to 4,000,000 has high wear resistance is probably because the material has high mechanical properties and high frictional resistance. When the material of the spray nozzle is polyether urethane rubber having a JIS-A hardness of 50 to 100 or ultra-high-molecular-weight polyethylene having an average molecular weight of 1,000,000 to 4,000,000, a lightweight, inexpensive spray nozzle with high corrosion resistance and shock resistance is provided because of the characteristics of the material itself. At the same time, high wear resistance can be obtained. Therefore, the spray nozzle used in the present invention has a simple support structure (can be attached directly), and is easy to install and easy to mold, though having reliability as high as that of the ceramic spray nozzle in terms of wear resistance and corrosion resistance, which achieves great economy and significantly improved reliability of the gas-liquid contacting apparatus. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side sectional view showing the principal portion of a gas-liquid contacting apparatus; FIG. 2 is a view for illustrating the principal portion of an exhaust gas desulfurizer using a gas-liquid contacting apparatus; FIG. 3 is a view for illustrating the principal portion of an exhaust gas desulfurizer using a conventional gas-liquid contacting apparatus. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The gas-liquid contacting apparatus of the present invention will be described below by explaining specific embodiments. One embodiment of the gas-liquid contacting apparatus in accordance with the present invention will be described below with reference to the drawings. First, a desulfurizer using a gas-liquid contacting apparatus is described with reference to FIGS. 1 and 2. The desulfurizer of this embodiment is characterized by the shape of its spray nozzle 20, and the other configurations are the same as those of the conventional desulfurizer shown in FIG. 3, so that the same reference numerals are applied to the same elements, and the description of the elements is omitted. As shown in FIG. 2, a plurality of spray nozzles 20 of a cylindrical shape are vertically disposed by being attached to the top of a header pipe 10 in a tower body 3. As shown in FIG. 1, the liquid inlet portion 21 on the base side of the nozzle is of a bell shape having a radius of curvature R of 0.2 times or more of the liquid discharge port diameter d (usually about 50 mm). In this case, the spray nozzle 20 is made of FRP. In the above-described desulfurizer, untreated exhaust gas is introduced through, for example, the duct 8, brought into contact with the absorbent slurry S sprayed from the spray nozzles 20 by means of the circulating pump 4 to absorb and remove sulfur dioxide gas in the untreated exhaust gas, and discharged through the duct 9 as treated exhaust gas, which provides a low-volume, simple absorption tower 1 which purifies exhaust gas with SO X removal efficiency as high as that of the conventional desulfurizer. At this time, because the liquid inlet portion 21 (refer to FIG. 1) of the spray nozzle is of a bell shape having a radius of curvature R of 0.2 times or more of the liquid discharge port diameter d, the flow turbulence of slurry solution S at the liquid inlet port and the discharge port of the spray nozzle 20 is prevented, and wear caused by the generation of bubbles or wear caused by cavitation are inhibited independently of the material of spray nozzle 20. Therefore, even if an inexpensive, lightweight material with high shock resistance, such as FRP, is used, the wear resistance can be assured, and the economy and reliability of the gas-liquid contacting apparatus and in turn the desulfurizer can be improved. Table 1 described below lists the result of a test in which absorbent slurry S having a 20 wt% gypsum concentration is sprayed from the FRP spray nozzles 20 under the condition where the flow velocity at the discharge port is adjusted to 15 m/s, and the wear condition of the spray nozzle 20 is investigated after continuous operation for six months (sample: No. 2 to 8). Table 1 also lists the result of a test performed with conventional spray nozzles under the same conditions (sample: No. 1) for comparison. In this embodiment in which the liquid inlet portion 21 of the spray nozzle is of a bell shape having a radius of curvature R of 0.2 times or more of the liquid discharge port diameter, there is little difference in depth of wear between the liquid inlet portion and the liquid discharge port, the average depth of wear being about 12 mm. Contrarily, the spray nozzle of the conventional shape wears severely as a whole, the depth of wear being about 15 to 16 mm. The wear is especially high in the vicinity of the liquid inlet portion, and holes are found in the spray nozzle of 20 mm wall thickness. Sample No. Radius of curvature of expanded portion at liquid inlet of spray nozzle Ratio of radius of curvature to diameter of liquid discharge port of nozzle Wear observation result after continuous 6 month test 1 <0.5 <0.01 Severely worn, depth of wear is 15-16 mm, 2 through holes near inlet portion 2 10 0.2 Worn evenly from inlet portion to discharge port, depth of wear is about 11-13 mm 3 20 0.4 - ditto - 4 30 0.6 - ditto - 5 40 0.8 - ditto - 6 50 1.0 - ditto - 7 75 1.5 - ditto - 8 100 2.0 - ditto - Next, a desulfurizer using a gas-liquid contacting apparatus according to the invention will be described. In the desulfurizer of this embodiment, the material of the spray nozzle 20 is polyether urethane rubber having a JIS-A hardness of 50 to 100 or ultra-high-molecular-weight polyethylene having an average molecular weight of 1,000,000 to 4,000,000. Other configurations of the machine is the same as those of the desulfurizer of the first embodiment. If the material is selected in such a manner, a lightweight, inexpensive spray nozzle with high corrosion resistance and shock resistance is provided because of the characteristics of the material itself. At the same time, high wear resistance can be obtained as shown by the test result listed in Table 2 below. Therefore, there is provided a spray nozzle which has a simple support structure (can be attached directly), and is easy to install and easy to mold, though having reliability as high as that of the ceramic spray nozzle in terms of wear resistance and corrosion resistance. Thereupon, the desulfurizer of the invention achieves effects of attaining great economy and significantly improving the reliability thereof. Table 2 described below lists the result of a test in which absorbent slurry is sprayed from the spray nozzles 20 of the above material under the same condition as the test in Table 1 and the wear condition of the spray nozzle 20 is investigated after continuous operation for six months (sample: No. 1 to 10). For both polyether urethane rubber and ultra-high-molecular-weight polyethylene, the depth of wear is 0.2 mm or less, which demonstrates significant improvement in wear resistance. Comparing Table 2 with Table 1, it is evident that polyether urethane rubber having a JIS-A hardness of 50 to 100 or ultra-high-molecular-weight polyethylene having an average molecular weight of 1,000,000 to 4,000,000 has higher corrosion resistance and shock resistance than FRP. Sample No. Material Ratio of expanded portion at liquid inlet to liquid discharge port diameter of 50 mm Wear observation result after continuous 6 month test 1 Ultra-high-molecular -weight polyethylene (average molecular weight: 1,000,000) 0.4 No abnormal wear,depth of wear is not larger than 0.2 mm 2 Ultra-high-molecular -weight polyethylene (average molecular weight: 3,000,000) 0.2 - ditto - 3 Ultra-high-molecular -weight polyethylene (average molecular weight: 3,000,000) 0.4 - ditto - 4 Ultra-high-molecular -weight polyethylene (average molecular weight: 3,000,000) 1.0 - ditto - 5 Ultra-high-molecular -weight polyethylene (average molecular weight: 4,000,000) 0.4 - ditto - 6 Polyether urethane rubber (JIS-A hardness:50°) 0.4 - ditto - 7 Polyether urethane rubber (JIS-A hardness:80°) 0.2 - ditto - 8 Polyether urethane rubber (JIS-A hardness:80°) 0.4 - ditto - 9 Polyether urethane rubber (JIS-A hardness:80°) 1.0 - ditto - 10 Polyether urethane rubber (JIS-A hardness:100°) 0.4 - ditto - The application of gas-liquid contacting apparatus of the present invention is not limited to an absorption tower in a wet type exhaust gas desulfurizer of tank oxidation type as described above, and it is apparent that the apparatus can be used in various fields having a process in which there is a need for effectively bringing gas into contact with slurry solution. Also, even when the apparatus is used for an absorption tower in a wet type exhaust gas desulfurizer, various types of apparatuses are available. For example, the apparatus can be applied to a simplified desulfurizer of a stack built-in type, in which the stack and the absorption tower are integrated, to enhance the economy and reliability thereof.

Claims: A gas-liquid contacting apparatus in which spray nozzles (20) for spraying slurry solution upward are arranged in a tower body (3) through which gas passes, characterized in that the material of a spray nozzle is one of polyether urethane rubber having a JIS-A hardness of 50 to 100 or polyethylene having an average molecular weight of 1,000,000 to 4,000,000.

Inventors: HASEGAWA SHIGEO, ISHIHARA MAKIICHI, IWASHITA KOUICHIRO, KANESHIGE KANAME, KITA YUKIO, OZAKI JUNJI, SUNADA TAKAKAZU, TAKASHINA TORU C O HIROSHIMA R, UKAWA NAOHIKO C O HIROSHIMA R, YAMASHITA KOUSUKE, HASEGAWA, SHIGEO, ISHIHARA, MAKIICHI, IWASHITA, KOUICHIRO, KANESHIGE, KANAME, KITA, YUKIO, OZAKI, JUNJI, SUNADA, TAKAKAZU, TAKASHINA, TORU, UKAWA, NAOHIKO, YAMASHITA, KOUSUKE, Hasegawa, Shigeo, Hiroshima R&amp;D Center, ISHIHARA, MAKIICHI, C/O MITSUBISHI JUKOGYO K.K., IWASHITA, KOUICHIRO, C/O MITSUBISHI JUKOGYO K.K., Kaneshige, Kaname, c/o Ohji Rubber &amp; Chem. Co.,Ltd, KITA, YUKIO, C/O MITSUBISHI JUKOGYO K.K., Ozaki, Junji, c/o Ohji Rubber &amp; Chemicals Co., Ltd, Takashina, Toru,c/o Hiroshima R&amp;D Center, Ukawa, Naohiko,c/o Hiroshima R&amp;D Center, Yamashita, Kousuke c/o Ryomei Engineering Co., Ltd
Applicants: MITSUBISHI HEAVY IND LTD, OHJI RUBBER & CHEM, MITSUBISHI JUKOGYO KABUSHIKI KAISHA, OHJI RUBBER & CHEMICALS CO., LTD.
Application year: 1995
Main classification: B01D53
IPC codes: B01D53, B05B15, B01J19, B01J10