CN1190254C - Deep treatment method of waste gas desulfurization by using sea water - Google Patents

Abstract

A method comprising removing acidic components contained in waste gas by using a system comprising (a) a gas-liquid contact device consisting of an absorption tower, which is equipped with at least one orifice plate inside, and at the top, bottom of the absorption tower or top and bottom with at least one packing, (b) means for feeding seawater into an absorption tower, (c) means for oxidizing seawater after gas-liquid contact, and (d) mixing and oxidizing said seawater with Equipment for mixing uncontacted seawater so that exhaust gas containing acidic components is brought into gas-liquid contact with seawater.

Description

Advanced treatment method for exhaust gas desulfurization with seawater

The invention relates to a method for removing acidic components in waste gas by seawater wet method, especially removing acidic components discharged from boilers or various heating furnaces and acidic components in waste gas containing sulfurous acid gas.

At present, for example, when heavy oil, coal, etc. are burned in combustion equipment such as boilers or various types of heating furnaces, because the fuel contains sulfur components, the sulfur components combine with oxygen in the air during combustion to form sulfur oxides, which Finally contained in the combustion exhaust gas. Such sulfur oxides are carried by gas from the source of generation to areas thousands of kilometers away, producing various phenomena such as acid rain or acid fog, polluting air, water, soil, etc. over a wide area and exerting harmful effects on human health.

However, with growing international interest in global environmental issues, various global-scale measures have been explored. In Japan, effective boiler combustion technology has been realized with the progress made in exhaust gas desulfurization or denitrification technology, etc. Essentially 100% pollution prevention measures can now be taken at the source of production. For example, as a method for wet removal of acidic components such as sulfur oxides contained in gas, a packed tower without an overflow weir and a downcomer, a spray tower, a bubble cap tower, an orifice tower or a The grid column is used to contact the gas to be treated with the alkali treatment solution in countercurrent. In other words, it can be said that the desulfurization treatment technology for environmental protection has reached an almost perfect stage. For example, desulfurization efficiencies of 90-99% have been achieved and applied industrially. However, since calcium hydroxide, calcium carbonate, sodium hydroxide, magnesium hydroxide and the like are used as the alkali treatment solution, there is a problem that, in addition to higher cost, waste solution must be treated, solid matter must be treated, and the like. Therefore, there are problems of complicating the method and high construction and operation costs. Therefore, as a method of treating exhaust gas with seawater, the present inventors developed a method of using a method without an overflow weir and a downcomer in JP-A-11-290643 (Method for treating acidic components in exhaust gas with seawater). Orifice tower or grid tower is a method of wet treatment of waste gas. However, this method is not adequate in the low Ug (low superficial gas velocity) region.

As explained above, not only in industrialized countries but also in developing countries, such a method of removing acidic components from waste gas is sought, and new technologies are developed to simplify the method, make the equipment more compact and significantly reduce the construction and operation costs. In particular, such a reliable method is sought, which is often required in the case of deep processing of all areas including low Ug areas.

Therefore, the object of the present invention is to develop a simplified method in a more compact plant and at a significantly reduced construction cost and operating cost, taking into account international needs, under a wide range of areas including low Ug and low L/G areas A new technology capable of highly removing acid components contained in exhaust gas such as sulfurous acid gas (sulfate gas).

According to the present invention, there is provided a method for removing sulfur oxides contained in waste gas comprising the use of a system comprising (a) a gas-liquid contacting device consisting of an absorption tower having at least one Orifice plate, filling the top, bottom or top and bottom of an absorption tower with at least one packing material, (b) an apparatus for feeding seawater into an absorption tower, (c) an apparatus for oxidizing seawater after gas-liquid contact , and (d) an apparatus for mixing uncontacted seawater with the above-mentioned seawater after mixing and oxidation, whereby exhaust gas containing acidic components comes into gas-liquid contact with seawater.

According to the present invention, there is also provided a wet process for removing sulfur oxides contained in waste gas in such a gas-liquid contacting plant, said gas-liquid contacting plant comprising an absorption tower having a diameter of at least 500 mm , the tower is equipped with at least one free space ratio Fc of orifice plate of 0.25-0.5 and at least one packing height of 0.5-4 meters of packing, the method includes sending such a quantity of seawater so that the flow rate of seawater from the top of the tower The ratio L/G of L (kg/ ^m2 ·hour) to the gas flow rate G (kg/ ^m2 ·hour) to be treated is at least 3.6 and the flow rate L of seawater is 1×10 ⁴ to 25×10 ⁴ kg/m ² hours; and such an amount of process gas is fed in that from the bottom of the gas-liquid contacting device, the superficial gas velocity Ug in the device is in the range of 0-2 Ugm (meters per second):

In the case of using an orifice or grid column without weirs and downcomers, the column includes at least one orifice and the density of the process gas ρ _G (kg/ ^m3 ) and the density of seawater ρ _L (1030 kg/ ^m3 ) ratio ρ _G /ρ _L is at least 0.838×10 ^-3 , $\mathrm{Ugm}=49.1{4\mathrm{Fc}}^{0.7}{({\mathrm{\ρ}}_G/{\mathrm{\ρ}}_L{x10}^3)}^{-0.5}\&Center\; Dot;{(L/G)}^{-1/3}\·\sqrt{g\&Center\; Dot;L}.$ In the formula, L is the capillary constant g is the gravitational acceleration (m/s ² ) and σ is the surface tension of sea water (kg/s ² ), so that the gas to be treated is in countercurrent gas-liquid contact with the sea water.

The present invention will be better understood from the following description with reference to the accompanying drawings, in which:

1 is a schematic diagram illustrating the relationship between the liquid flow rate L and the superficial gas velocity Ug processed in the operating region of the method of the present invention, wherein regions A and B represent Japanese Examined Patent Publication (Gazette) No.51-31036 and No. 60-18206, and area C indicates the operation area of JP-A-11-290643. The operating region of the present invention is that Ug is greater than 0 but not greater than 2×Ugm, and the flow velocity of the treated liquid in Fig. 1 is greater than 1×10 ⁴ (kg/m ² ·hour), L/G=3.6 and flow velocity 25×10 The area enclosed by the line of ⁴ (kg/ ^m2 ·h).

Fig. 2 is a treatment system diagram centered on the equipment for removing acidic components in wastewater by using seawater in the present invention, that is, the gas-liquid contact equipment.

Fig. 3 is an embodiment of an absorption plant composed of a combination of perforated plate towers or grid plate towers and packed towers without overflow weirs and downcomers in the case of treating boiler exhaust gas with the method of the present invention.

Fig. 4 is another embodiment of the absorption equipment composed of an orifice tower without overflow weir and downcomer or a combination of grid tower and packed tower under the situation of treating boiler exhaust gas with the method of the present invention.

According to the present invention, as shown in Fig. 2, since the combination of the orifice tower or grid tower and packing without overflow weir and downcomer is used, so in the whole process, in order to absorb the gas and adjust the pH value of the absorption liquid, Possibility to operate from small liquid/gas ratios to large liquid/gas ratios without using any chemicals at all, using alkalis contained in spent cooling seawater or used in power plants, factories, etc. The waste seawater can remove the required acidic components. Note that the orifice or grid without weir and downcomer here refers to the orifice or grid with a free space ratio Fc of 0.25-0.5, preferably 0.3-0.4. In the present invention, by using a gas-liquid contacting device comprising at least one such orifice or grid in combination with a packing having a packing height of at least 0.5 m, preferably 0.5-4 m, it is possible to use seawater or waste Seawater is used to remove acidic components such as sulfurous acid gas contained in the exhaust gas. In addition, since seawater after gas-liquid contact renders components absorbed therein harmless by supplying air and oxidation by the seawater treatment system, there is no problem of marine pollution at all.

The invention is not limited in the mechanistic context below, but now the chemistry of the seawater desulfurization process of the invention is illustrated when the acidic component is sulfurous acid gas (SO ₂ ).

That is, sulfurous acid gas (SO ₂ ) contained in exhaust gas is absorbed in seawater, and then it is converted into bisulfite ion as shown in formula (1):

(1)

The bisulfite ion thus generated is converted to sulfate ion by aeration oxidation as shown in formula (2):

(2)

Then, hydrogen ions generated by the reaction formula (2) are reacted with carbonate ions or bicarbonate ions contained in seawater, and thus are neutralized as shown in the reaction formulas (3) and (4):

(3)

(4)

According to the present invention, the sulfurous acid gas eventually turns into sulfate ions, which are then dissolved in seawater. It is said that the sulfur content in the ocean is as high as 10 ¹⁵ tons. This corresponds to about 2300 mg/L sulfate ion. The concentration of harmless sulfate ions contained in the treated seawater effluent at the end of the process only increases by about a few mg/l, so the increase in sulfur content in the sea is minimal.

Part of the sulfur from sulfur oxides produced in modern industry from the use of fossil fuels circulates naturally through the atmosphere and by returning to the soil or ocean in the form of acid rain. Different from this, the method of the present invention for removing acidic components in gas is an environmentally friendly technology. According to the method of the present invention, it is possible to use this method to recycle sulfur into the sea for simple and effective protection against such dangers as acid rain, air pollution and the like.

As explained above, the present invention successfully employs a gas-liquid contacting apparatus internally equipped with an absorption tower having at least one orifice plate and at least one packing with a height of at least 0.5 m, preferably 0.5-4 m fillers (such as Raschig rings, pole rings (Polerings), Terralets, interlock saddles, etc.), and seawater is introduced from the top of the gas-liquid contact equipment, so as to be in countercurrent gas-liquid contact with the gas to be treated and to utilize the gas in seawater The alkali effectively and deeply removes the contained sulfur oxides in the exhaust gas.

Note that the technology for treating exhaust gas using an orifice column or grid column without an overflow weir and downcomer (such as a "Moretana" column) is described in Japanese Examined Patent Publication (Gazette) No. 51-31036 and No. 60-18208 ( or US3892837 and 3941572), but the inventors found that the shown operating areas A and B (see Figure 1) are not suitable for treating waste gas with seawater. The ratio L/G of the above mentioned JP-A-11-290643 to the gas flow rate G supplied to the tower and the flow rate L of the seawater should be at least 3.6, preferably 7-25 and the superficial gas velocity Ug and process liquid flow rate through the "Moretana" tower L should be in the relationship determined by region C of Fig. 1, ie at a requirement from greater than 3.43L ^{- 0.0807} ·Ugm to 8 (m/s). However, outside this region, especially when Ug is too low, there is a problem that the gas-liquid contact efficiency drops rapidly, which makes removal of acidic components impossible. However, according to the present invention, by utilizing an absorption plant consisting of a combination of a "Moretana" tower and a packed tower, the desired gas-liquid absorption can be efficiently performed even in the region D of Fig. 1, thereby enabling efficient desulfurization treatment become possible.

Seawater contains about 110-130 mg/L alkali (calculated as _CaCO3 ). The present invention utilizes seawater highly efficiently, and seawater can be easily obtained in large quantities in areas close to the sea. According to the present invention, for example, in the case of a power station that uses seawater near the ocean as cooling water, it is possible to reuse the seawater that would have been returned to the ocean after cooling to treat the exhaust gas of the boiler and remove the of sulfur oxides. Furthermore, according to the present invention, even in the case of a plant producing magnesium hydroxide from seawater or a pulp and paper mill using seawater, it is possible to reuse the waste seawater that had to be reprocessed before being returned to the sea, and it is possible to use the above-mentioned gas -Liquid equipment to treat acid waste gas and waste sea water.

According to the present invention, after oxidation of a sulfur-absorbing acidic liquid containing bisulfite ions (which becomes a source of COD (i.e. chemical oxygen demand)) with air in an aerated oxidation vessel and at the pH of the mixed seawater by decarburization After recovery, the sulfur-absorbing liquid is discharged into the sea; therefore, it is possible to discharge the seawater into the sea and restore the quality of the seawater without using any chemicals.

The present invention is now illustrated in further detail by the following examples, which are by no means limited thereto.

Example 1

Fig. 3 shows an embodiment of the present process flow, wherein the boiler waste gas is treated by the method of the present invention.

The combustion exhaust gas containing about 1000ppm sulfur oxides discharged by the boiler 1 is sent into the electric precipitator 2 so as to remove dust, and then the exhaust gas is passed through an orifice plate with a free space ratio FC of 0.3 and with 2 meters of packing for processing (i.e. Ring-type packing, the gas-liquid contacting device 3 of the packing part with dimensions 100×78×32 mmH), is then discharged from the tower to atmosphere as gas effluent. In the gas-liquid contact device 3, the waste gas is sent in from the bottom of the tower, and the seawater pumped from the ocean is sent in from the top of the gas-liquid contact device 3, so that the sea water and the waste gas are countercurrently contacted in the device 3, absorbed and removed Sulfur oxides contained in exhaust gas. Acidic waste seawater containing bisulfite ions is discharged from the bottom of the plant as a liquid effluent and is oxidized with air in the air oxidation vessel 4 to oxidize the sulfite ions and decarbonize the gaseous effluent to restore the seawater pH, and then discharge the seawater into the sea. When the liquid-gas ratio L/G is 5-10, Ug is 1-2 m/s and the concentration of sulfur oxide in the gas to be treated is 10-100ppm, the removal rate is 90-99%.

Example 2

Fig. 4 is another embodiment of treating boiler exhaust gas by the method of the present invention, which shows a flowchart corresponding to an embodiment of the treatment for maintaining a high desulfurization rate under low load operation of the boiler.

The combustion exhaust gas containing about 800ppm of sulfur oxides discharged by the boiler 1 is sent into the electric precipitator 2 to remove dust, and then the exhaust gas is equipped with two orifice plates with a free space ratio Fc of 0.3 and 1.5 meters of packing (i.e. annular packing , Dimensions: 100×78×32 mm) for the gas-liquid contacting device 3 of the packing part to be treated, and then discharged into the atmosphere. In the gas-liquid contact device 3, the exhaust gas is fed from the bottom of the device, and the seawater pumped from the ocean is fed in from the top, so that the sea water and the exhaust gas are in countercurrent contact in the device 3, and the sulfur oxides contained in the exhaust gas are absorbed. and remove. Acidic waste seawater containing bisulfite ions is discharged from the bottom of the equipment as a liquid effluent, oxidized and decarbonized with air in the air oxidation vessel 4, and the pH of the seawater is restored, and then the seawater is discharged into the sea as a liquid effluent . At seawater flow rate L (5×10 ⁴ kg/m ² ·hour), Ug is 0.25, 0.5, 1, 1.5 and 2 m/s and the concentration of sulfur oxides in the gas to be treated is 5, 10, 17, 25 and 60ppm, the removal rates were 99.4%, 98.7%, 97.9%, 96.9% and 92.5%.

As described above, according to the present invention, it is possible to use seawater to treat sulfur oxides contained in the exhaust gas deeply and effectively, although in the past this area could not be treated with the "Moretana" tower, that is, the low Ug area, and it is possible to use simple The method is environmentally friendly with compact equipment and low cost.

Claims (3)

1. A method for removing sulfur oxides contained in waste gas, the method comprising: (a) introducing raw seawater and waste gas into a gas-liquid contacting device consisting of an absorption tower, the absorption tower is internally equipped with at least one orifice plate and at least one packing material, thereby realizing countercurrent contact treatment of waste gas-seawater, (b) mixing seawater from the gas-liquid contacting facility with raw seawater and air in the oxidation facility, (c) then oxidize the _SO2 absorbed in the seawater, thereby discharging the oxidized seawater into the sea without the use of chemicals, Wherein, seawater is introduced into the gas-liquid contacting apparatus from the top of the absorption tower in such an amount that the ratio of the seawater flow rate L (kg/ ^m2 ·hour) to the gas flow rate G (kg/ ^m2 ·hour) to be treated is L/G is at least 3.6 and the flow rate L of seawater is 1×10 ⁴ to 25×10 ⁴ kg/m ² ·hour, the gas-liquid contacting equipment includes an absorption tower with a diameter of at least 500 mm, which is equipped with At least one orifice plate with a free space ratio Fc of 0.25-0.5 and at least one packing with a packing height of 0.5-4 meters; Liquid contact equipment such that the superficial gas velocity Ug in the equipment is in the range of less than 2 Ugm (m/s); When using an orifice column or a grid column consisting of at least one orifice plate without overflow weirs and downcomers and dealing with the density of gas ρ _G (kg/ ^m3 ) and seawater density ρ _L (kg/ ^m3 ) When the ratio ρ _G /ρ _L is at least 0.838×10 ^-3 : $\mathrm{<span\; class="notranslate">\; Ugm</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 49.14</span>}\mathrm{<span\; class="notranslate">\; f</span>}{\mathrm{<span\; class="notranslate">\; c</span>}}^{\mathrm{<span\; class="notranslate">\; 0.7</span>}}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; G</span>}}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; \&times;</span>{\mathrm{<span\; class="notranslate">\; 10</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span>}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 0.5</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; G</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; \&CenterDot;</span>\sqrt{\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; L</span>}}$ In the formula: L is the capillary constant g is the acceleration due to gravity (m/s ² ), and σ is the surface tension of sea water (kg/s ² ). 2. The method of claim 1, wherein the free space ratio _Fc is 0.3-0.4 and the ratio L/G is 7-25. 3. The method of claim 1, wherein the exhaust gas is from a boiler.