A method for removing ammonia from non-condensable gases from a pulp making apparatus

Abstract

This application relates to a method for removing ammonia (NH3) from a gas generated from a pulping apparatus (100). The method includes generating an untreated non-condensable gas containing ammonia (NH3) in the pulping apparatus (100) and transferring at least some of the untreated non-condensable gas to a scrubber (200) containing an aqueous washing solution (130, 140). The method includes adding a compound capable of lowering the pH of the washing solution to the washing solution (130, 140), and in the scrubber (200), contacting the untreated non-condensable gas with the washing solution (130, 140) to react the ammonia (NH3) in the untreated non-condensable gas with the washing solution to generate a clean non-condensable gas and ammonium (NH4). + This application also relates to a pulping apparatus, including devices for performing the method.

Description

Technical Field

[0001] This invention relates to the treatment of odorous gases. Specifically, it relates to the treatment of odorous gases generated in the pulping process. It also relates to reducing NOx emissions from pulping equipment. This invention relates to such a system. Background Technology

[0002] In chemical pulping, wood is treated with cooking liquor to hydrolyze lignin. Pulping processes include sulfite and sulfate processes. Several organic odor compounds are formed during these processes, such as ammonia, rosin, methanol, hydrogen sulfide, methanethiol, dimethyl sulfide, and dimethyl disulfide. These compounds contribute to the unpleasant odors emitted from chemical pulping equipment. These gases are formed at several stages of the chemical pulping process, such as in the cooking unit and waste liquor evaporation. The most common method for removing odor compounds is to collect the odor gases from various sources and burn them in lime kilns, chemical recovery boilers, or separate incinerators. The purpose of combustion is to oxidize sulfur-containing substances into sulfur dioxide and / or sulfur trioxide. Simultaneously, the ammonia produced during the combustion of these substances forms nitrogen oxides (NOx).

[0003] In chemical pulping, vapors containing these odorous compounds are released into, for example, waste liquid evaporation zones, such as black liquor, where the compounds can be distilled and condensed into condensate. Some compounds are non-condensable. Non-condensable gases (NCGs) can burn together with other odorous gas streams from the equipment.

[0004] Odor gases are generally classified into strong odorous gases (LVHC, high concentration at low volume) and dilute odorous gases (HVLC, low concentration at high volume). Dilute odorous gases are sometimes referred to as DNCG (dilute non-condensable gases). Dilute gases are typically collected from the unpressurized portion of the pulping process. They are collected from containers and units in fiber production lines, evaporation equipment, tall oil equipment, and causticizing equipment. Dilute odorous gases contain the same components as strong odorous gases, but they also contain so much air that their concentration is significantly lower.

[0005] Strong-odor gases are typically collected from pressurized sections of the pulping process. These gases primarily originate from cooking equipment, evaporation equipment, stripping equipment, sludge condensate tanks, and pressurized cooking liquor tanks. Strong-odor gases can be classified according to their source. CNCG refers to concentrated non-condensable gases collected from processes outside the stripper (e.g., evaporator and / or cooking areas). SOG refers to stripper tail gas collected from the stripper. SOG can be condensed to obtain methanol. This invention particularly relates to the combustion of strong-odor gases and / or their condensates (i.e., contaminated methanol).

[0006] The purpose of burning odorous gases or contaminated methanol is to oxidize sulfur compounds contained in the gas or liquid, thereby forming compounds with less odor, such as sulfur dioxide and / or sulfur trioxide. Therefore, combustion occurs in the presence of excess air. However, it has been noted that under such conditions, ammonia tends to react with oxygen in the excess air, forming nitrogen oxides (NOx). However, for environmental reasons, NOx levels should be kept low. In most countries, maximum permissible NOx levels are stipulated.

[0007] In the prior art, low NOx emissions are achieved through staged combustion. In the first stage, only a substoichiometric amount of air is used, which reduces NOx formation. For example, a method and burner for burning odorous gases with low NOx emissions are disclosed in document WO2019 / 122510.

[0008] One object of the present invention is to provide a simple method for treating odorous gases containing ammonia, wherein the combustion of the odorous gases can be carried out in a conventional boiler without producing excessive NOx emissions. Summary of the Invention

[0009] It has been found that, in existing technologies, most of the NOx generated by burning odorous gases is formed during the combustion of ammonia in the odorous gas. Furthermore, it has been found that washing the odorous gas before combustion can remove most of the ammonia. Therefore, washed odorous gas contains less ammonia than untreated raw odorous gas, resulting in significantly lower NOx production from its combustion compared to the combustion of raw odorous gas. It has been found that washing can be performed by contacting the untreated odorous gas with a washing solution containing a compound (e.g., an acid) that lowers the pH of the washing solution. The washed odorous gas can then be burned.

[0010] Brief description of the attached figures

[0011] Figure 1a A method for removing ammonia from gas produced by a pulping plant is shown.

[0012] Figure 1b The formation of the washing solution and the control of its pH are shown.

[0013] Figure 1c The method for removing ammonia and sulfur from gases produced by a pulping plant and for treating contaminated condensate is shown.

[0014] Figure 2a A method for removing ammonia from gas produced by a pulping plant is shown, wherein the same washing solution is used in both the tank and the washing tower.

[0015] Figure 2b The pH of the washing solution was controlled.

[0016] Figure 3 A method for removing ammonia and sulfur from gases produced by a pulping plant is shown, wherein ammonia is removed in a scrubbing tower of a scrubber, which also includes a tank.

[0017] Figure 4a A method for removing ammonia and sulfur from gases produced by a pulping plant is shown, wherein ammonia is removed in a tank.

[0018] Figure 4b A method for removing ammonia and sulfur from gases produced by a pulping plant is shown, wherein ammonia is removed in a scrubbing tower.

[0019] Detailed Description of the Invention This invention relates to a method for removing ammonia from non-condensable gases in a pulping apparatus. Ammonia is removed by washing. Where deemed feasible, the non-condensable gas before washing is referred to as “raw non-condensable gases,” and the remaining portion after washing is referred to as “clean non-condensable gases.” In this document, the term non-condensable gas (raw or clean) refers to a gas in gaseous form at a temperature of 20°C and a pressure of 1 atmosphere (approximately 1 bar(a)).

[0020] The untreated non-condensable gas contains at least ammonia (NH3). In a preferred embodiment, the untreated non-condensable gas also includes sulfur-containing compounds. The untreated non-condensable gas may include ammonia (NH3) and at least one of hydrogen sulfide, methanethiol, dimethyl sulfide, or dimethyl disulfide. In one embodiment, the untreated non-condensable gas contains at least 1000 ppm of ammonia (on a dry basis). Hereinafter, ppm refers to parts per million based on mass, such as milligrams per kilogram. Furthermore, when measured on a dry basis, water is not included in the measurement. In one embodiment, the untreated non-condensable gas contains at least 1000 ppm of ammonia (on a dry basis) and at least 20000 ppm of methanethiol.

[0021] As noted in the background section, strong-odor gases are produced during sulfate and / or sulfite pulping. Table 1 shows three typical compositions of strong-odor gases, whose main components include sulfur and nitrogen. Strong-odor gases are an example of untreated, non-condensable gases.

[0022] Table 1: Composition of three samples of strong odor gas.

[0023]

[0024] As is known in the art, to remove odor compounds, strong odor gases (i.e., odorous gases) or liquids are burned to oxidize sulfur. However, ammonia simultaneously produces nitrogen oxides (NOx), which are harmful to the environment.

[0025] It has been found that at least some ammonia can be washed away from untreated non-condensable gas by contacting it with a washing solution that is aqueous and has a compound added to it to lower the pH of the washing solution. This produces clean non-condensable gas.

[0026] refer to Figure 1a Untreated non-condensable gas 110 is generated in the pulping apparatus 100. The pulping apparatus 100 also includes... Figure 1a Other components are shown. Untreated non-condensable gas 110 is fed to scrubber 200 for washing. Figure 1a In this design, scrubber 200 includes tank 210 and scrubbing tower 220. An aqueous solution and a compound capable of lowering the pH of the scrubbing solution are supplied to scrubber 200 to form scrubbing solution 130 within scrubber 200. In the figure, the term "water" refers to the aqueous solution, which can be substantially pure water or an effluent from a pulping process. In the figure, the term "acid" refers to a compound capable of lowering the pH of the scrubbing solution. In this way, the term "acid" refers to any and all compounds entering the scrubbing solution capable of forming hydrated hydrogen ions (i.e., hydrated hydrogen, H3O) with water. + Compounds of this type include all kinds of acids, as well as gases or solids that react with water to form acids, such as CO2.

[0027] Different washing solutions can be used in different parts of the scrubber 200. A first washing solution 130 can be placed in the tank 210 of the scrubber, while a second washing solution 140 is configured to circulate in the scrubbing tower 220 of the scrubber 200. However, the same washing solution can be used in different parts of the scrubber.

[0028] When the pulping apparatus 100 includes a washing tower 220, the pulping apparatus also includes a circulation 221 configured to discharge the washing solution (in...) Figure 1a The washing solution (140) is fed to the upper part of the scrubbing tower 220, where it is sprayed to form droplets. For this purpose, the circulation 221 includes a first pump 222. In the scrubbing tower 220, the non-condensable gas to be scrubbed comes into contact with the droplets of the washing solution. It has been found that scrubbing, at least in the scrubbing tower 220, is particularly effective.

[0029] As the washing solution, namely, as one or both of the first washing solution 130 and the second washing solution 140, both aqueous and acidic solutions can be used. In the scrubber 200, the untreated non-condensable gas 110 comes into contact with the washing solutions 130 and 140.

[0030] Because washing solutions 130 and 140 are aqueous, containing water (H2O), a portion of which naturally forms hydrated hydrogen ions (i.e., hydrated hydrogen, H3O). + ) and hydroxide ions (OH) - When ammonia (NH3) reacts with water, it produces ammonium (NH4). + ) and hydroxide ions (OH) - In order to increase ammonium (NH4) + The generation of hydride ions (acids in the figure) involves adding compounds capable of forming hydrated hydrogen ions with water to washing solutions 130 and 140. Preferably, the washing solutions are acidic. Preferred pH values ​​will be given below. When washing solutions 130 and 140 contain acids, they also contain hydroxyl radicals (OH-). - Anions other than ) (i.e., negative ions, hereinafter referred to as A) - (Represented). These anions (A) - A hydride ion is the result of an acid (or more generally, a compound that can form a hydrated hydrogen ion with water) giving its proton to a hydrated hydrogen ion in water.

[0031] As a result of washing, a clean, non-condensable gas 120 is produced. As described above, washing solutions 130 and 140 contain the anions (A+) of the acids in washing solutions 130 and 140. - ) and ammonium (NH4) formed from untreated non-condensable gas 110 ammonia (NH3). + Anion (A) - Ammonium and ions can be collected from scrubber 200 as turbid condensate 150. The following details the process of collecting anions (A...). - Examples of ).

[0032] Regarding the acids used to wash solutions of 130 and 140, acids containing reactive nonmetallic atoms have been found to be particularly effective. Reactive nonmetallic atoms are hydrogen (H), carbon (C), nitrogen (N), oxygen (O), fluorine (F), phosphorus (P), sulfur (S), chlorine (Cl), selenium (Se), bromine (Br), and iodine (I). Naturally, water is not considered an acid, even though it contains hydrogen and oxygen. Examples of such acids include aqueous solutions of sulfuric acid (H₂SO₄), nitric acid (HNO₃), carbon dioxide (CO₂), and hydrochloric acid (HCl). For example, sulfuric acid in aqueous solutions forms the anion HSO₄. - and / or SO4 2-Nitric acid in aqueous solution forms anion NO3. - These anions have been and will be used with (A) - Therefore, in a preferred embodiment, the washing solutions 130 and 140 contain hydrated hydrogen ions (H3O). + ) and the removal of hydroxide ions (OH) - Anions other than ) (A - The anion (A) - The acid contains atoms selected from carbon (C), nitrogen (N), fluorine (F), phosphorus (P), sulfur (S), chlorine (Cl), selenium (Se), bromine (Br), and iodine (I). Preferably, the acid does not contain metal atoms from Group 1 of the periodic table, such as lithium (Li), sodium (Na), and potassium (K).

[0033] For washing solutions 130 and 140, aqueous solutions of sulfuric acid (H₂SO₄), nitric acid (HNO₃), carbon dioxide (CO₂), and / or hydrochloric acid (HCl) are preferably used. Therefore, through the above reaction, an ammonium salt solution is formed in washing solutions 130 and 140. Corresponding to these acids, the ammonium salt can be ammonium sulfate ((NH₄)₂SO₄), ammonium nitrate (NH₄NO₃), ammonium carbonate ((NH₄)₂CO₃), or ammonium chloride (NH₄Cl). In the aqueous washing solution, these salts are in the form of ammonia (NH₄)₂SO₄. + ) and anion (A - It exists in the form of anion (A) in these cases. - ) are sulfate (SO4) 2- ), nitrate (NO3) - ), carbonate (CO3) 2- ) or chloride ions (Cl - Sulfuric acid is typically obtained naturally from the pulping equipment 100; therefore, more preferably, an aqueous solution of sulfuric acid (H₂SO₄) is used as washing solutions 130 and 140, i.e., as at least one of the first washing solution 130 and the second washing solution 140. It is noteworthy that, due to this reaction, an aqueous solution of ammonium sulfate ((NH₄)₂SO₄) is produced as a result of the reaction, and ammonium sulfate ions become part of washing solutions 130 and 140. Furthermore, other impurities of untreated non-condensable gases may dissolve or otherwise remain in washing solutions 130 and 140. Therefore, the washing solutions may contain compounds other than acid and water. These ions and / or impurities can be removed in the form of turbid condensate 150. This also applies to aqueous solutions of other acids used as washing solutions, with necessary adjustments made.

[0034] It has been found that the reaction product of ammonia, an acid, and untreated non-condensable gas 110, is free of hydroxide ions (OH-). -Anions other than ) (A - The formation of [ammonia] is most effective at a pH of approximately 5. Furthermore, it has been found that when the pH is less than 3, untreated non-condensable hydrocarbons begin to polymerize, which may clog the nozzles and / or lines of the scrubber 200. Therefore, the pH is preferably at least 3. Additionally, if the pH is greater than 7.5, the ability of the scrubbing solution to capture ammonia is significantly reduced. Therefore, in one embodiment, the pH of the scrubbing solutions 130 and 140 is 3 to 7.5, preferably 4 to 6, and most preferably 4.5 to 5.5. This is particularly suitable when an aqueous solution of sulfuric acid (H2SO4) is used as scrubbing solutions 130 and 140.

[0035] The pH of washing solutions 130 and 140 can be measured and controlled based on measurements. Therefore, one embodiment includes measuring the pH of washing solutions 130 and 140 and controlling the pH of washing solutions 130 and 140 based on the measured pH value by adding at least one of the following: (i) an aqueous solution, which may be substantially pure water or an effluent from a pulping equipment process (“water”); and (ii) a compound capable of forming hydrated hydrogen ions with water (“acid”). Specifically, the flow rate of the compound (“acid”) capable of lowering the pH of the washing solution into the scrubber 200 can be controlled. For example, if the measured pH of washing solutions 130 and 140 is greater than a first threshold, an acid can be added to the washing solution to lower the pH of the washing solution. Furthermore, if the measured pH of washing solutions 130 and 140 is less than a second threshold, water can be added to the washing solution. Typically, ammonia itself tends to increase the pH of washing solutions 130 and 140 during operation, thus necessitating the addition of an acid (or other compound capable of forming hydrated hydrogen ions with water) to the process. The first threshold can be, for example, 8, 7, 6, or 5.5 (within the pH scale). The second threshold can be, for example, 3 or 4 (within the pH scale).

[0036] Preferably, if an acid is added to the washing solution, the pH of the acid (“acid”) added to the washing solutions 130 and 140 is less than 4. Therefore, the pH of the washing solution can be lowered to 4, and controlling the pH does not require an excessive amount of acid. More preferably, the pH of the acid added to the washing solutions 130 and 140 is less than 3. The amount of water and acid added can be selected such that the level of the washing solution in the washer is maintained at an appropriate level, and that the pH of the washing solution is within the aforementioned limits. For these reasons, the washer 200 includes an inlet 205 configured to allow a compound (e.g., an acid) capable of lowering the pH of the washing solution in the washer 200 to enter.

[0037] To maintain the pH of the washing solution at an appropriate level, an embodiment of the pulping apparatus 100 includes a pH sensor 230 configured to determine the pH of the washing solutions 130 and 140. Figure 1b and 1c As shown, pH can be measured from the sludge condensate 150. Even if not shown, pH can be measured by a sensor 230 located within the scrubber 200. The measured pH value is then used to control a second pump 240, which is configured to feed acid into the scrubber 200. For example, if the measured pH is greater than a first threshold, the flow rate of acid (or other compounds capable of lowering pH) entering the scrubber 200 is increased, for example, by using the second pump 240, as described above. For example, if the measured pH is less than a second threshold, the flow rate of water entering the scrubber 200 is increased, as shown above. The pulping apparatus 100 may include a controller 242 configured to control the second pump 240, as detailed above. As an alternative to the second pump 240, a valve can be used, provided that the acid (or other compounds capable of lowering pH) is stored under pressure. Thus, by opening the valve, pressure drives the acid into the scrubber 200. When the acid is stored at a higher vertical height, the pressure may be hydrostatic pressure. If the compound that can lower the pH (“acid”) is gaseous, then the pressure can be the pressure of the gas. Alternatively or additionally, the pressure can be generated by a pump.

[0038] refer to Figure 1a The components of the first washing solution 130 can be delivered to tank 210 of the washer 200 via a single pipeline. (Reference) Figure 1b The components of the first washing solution 130 can be delivered to the tank 210 of the washer 200 via a separate pipeline.

[0039] As a result of washing, the cleaned non-condensable gas 120 contains less ammonia than the untreated non-condensable gas 110. The ammonia content of the cleaned non-condensable gas 120 can be, for example, at most half the ammonia content of the untreated non-condensable gas 110. The ammonia content of the cleaned non-condensable gas 120 can be, for example, less than 1000 ppm or less than 500 ppm. It has been found that nearly 90% of the ammonia can be washed away from the untreated non-condensable gas by using sulfuric acid in the washing solutions 130 and 140, such that the pH of the washing solution is about 5.

[0040] As noted in the background section, untreated non-condensable gases 110 typically comprise one or more sulfur-containing compounds. Furthermore, these compounds are also odorous and can be converted into less odorous oxides through combustion. Therefore, and referring to... Figure 1cIn one embodiment, at least some clean, non-condensable gas 120 is fed to a combustion furnace 310, where the clean, non-condensable gas 120 is combusted. Figure 1c As shown, air or other oxygen-containing gases are also fed into the combustion furnace 310.

[0041] Specifically, the combustion furnace 310 can be a kiln or boiler of the pulping equipment 100. The kiln or boiler can be configured for producing or recycling cooking chemicals from the pulping process. Examples include lime kilns and chemical recovery boilers. To enhance combustion, other fuels (“fuels”) can also be supplied to the combustion furnace 310.

[0042] Preferably, the heat generated by burning the clean, non-condensable gas 120 is recovered by the heat exchanger 320. Thus, the combustion furnace 310 can be the combustion furnace of the boiler 300. Typically, the boiler 300 is configured to heat water and boil it to generate steam. The heat recovered in the heat exchanger 320 can be utilized as needed. A preferred approach is to superheat the steam in the heat exchanger 320, in which case the heat exchanger 320 acts as a superheater for the boiler, and the steam is used to operate a steam turbine. Furthermore, a generator can be connected to the steam turbine to generate electricity.

[0043] Flue gas is produced by burning at least a clean, non-condensable gas 120 in a combustion furnace 310. As detailed above, the flue gas may contain sulfur oxides (SOx) at least when the untreated non-condensable gas 110 contains sulfur compounds and a separate incinerator is used. If the clean non-condensable gas is burned in a chemical recovery boiler, the boiler ash may absorb sulfur and / or sulfur oxides. As is known in the art, sulfur oxides can be removed from the flue gas.

[0044] even though Figure 1a and 1b The image shows an untreated, non-condensable gas 110 as a whole, whose components can be delivered to the scrubber 200 in separate lines. (Reference) Figure 1cThe pulping apparatus embodiment includes at least one, preferably all, of an evaporator zone 955, a digester zone 965, and a stripper 970. Typically, a portion of the tail gas from the stripper 970, i.e., the stripper tail gas, is condensed in a condenser 975. The condenser 975 (if used) can be considered as consisting of the stripper 970. Typically, the stripper tail gas contains methanol, and the methanol can be condensed. However, a portion of the stripper tail gas is non-condensable and can form a portion of untreated non-condensable gases as described above. Each of these (955, 965, 970, 975) may include a collector 990 for collecting the resulting gases and / or liquids. One or more evaporators are arranged in the evaporator zone 955. The evaporators in the evaporator zone 955 are configured for drying a solution containing the digesting chemicals of the pulping apparatus. Examples of such solutions include black liquor and brown liquor. One or more digesters are arranged in the digester zone 965. The digesters in the digester section are configured for cooking pulp raw materials. For example... Figure 1c As indicated by the dashed arrow, stripper 970 is typically configured to strip foul condensate produced by the evaporator (i.e., from evaporator zone 955) and / or the cooker (i.e., from cooker zone 965). Gas from evaporator zone 955 can be fed through cooker zone 965 to the stripping tower, and vice versa, as shown in the image. Figure 1c As shown.

[0045] A first portion 110a of untreated non-condensable gas 110 can be conveyed from evaporator zone 955 to scrubber 200 via a first line. A second portion 110b of untreated non-condensable gas 110 can be conveyed from digester zone 965 to scrubber 200 via a second line. A third portion 110c of untreated non-condensable gas 110 can be conveyed from stripper 970 or condenser 975 to scrubber 200 via a third line. Typically, collector 990 of the pulping apparatus is configured to collect untreated non-condensable gas 110 (i.e., 110a and / or 110b and / or 110c), and one or more lines are configured to convey untreated non-condensable gas, or a portion of untreated non-condensable gas, to scrubber 200.

[0046] Figure 1c A preferred method for treating contaminated condensate 150, which is the result of washing, is also shown. One embodiment of the method includes conveying the contaminated condensate 150 from the scrubber 200 to a stripper 970. In the stripper 970, the contaminated condensate is cleaned to form clean condensate 160. Clean condensate 160 contains an ammonium salt of the contaminated condensate 150. More specifically, clean condensate 160 contains ammonia ions (NH4+). +In a preferred embodiment, the cleaning condensate 160 comprises ammonium sulfate, which is the result of the reaction of ammonia and sulfuric acid. The cleaning condensate 160 is conveyed to the pulp bleaching zone 410, where the pulp is bleached. The cleaning condensate is used in the pulp bleaching zone 410 and in the bleaching solution during the bleaching process. As a result of bleaching, bleached pulp is produced as the main product, and bleached effluent 170 is produced as a byproduct. Figure 1c As shown, the bleaching effluent 170 contains ammonia. The bleaching effluent 170 is conveyed to a wastewater treatment area 420. In the wastewater treatment area 420, wastewater from the pulping process is purified.

[0047] In existing technologies, wastewater purification requires urea as a purification chemical. However, it has been found that in this invention, nitrogen is used in the bleaching effluent as ammonium (NH4) at a concentration of 170%. + The ammonium (NH4) is supplied to the wastewater treatment process and wastewater treatment area 420 in the form of ammonia removal from CNCG as described above. Therefore, it has been found that the ammonium formed by removing ammonia from CNCG as described above can be used for wastewater treatment. Thus, one embodiment includes using ammonium (NH4) in washing solutions 130 and 140. + The water is purified by adding urea (OC(NH2)2). More preferably, the water is purified without adding any other nitrogen-containing compounds. More preferably, the water is purified without adding urea (OC(NH2)2).

[0048] The corresponding pulping equipment includes a wastewater treatment zone 420 and piping for conveying a portion of the turbid condensate 150 from the scrubber 200 to the wastewater treatment zone 420. The portion of turbid condensate 150 conveyed to the wastewater treatment zone 420 includes ammonia in an aqueous solution. Preferably, the pulping equipment includes a stripper 970 and piping for conveying the turbid condensate 150 from the scrubber 200 to the stripper 970. Figure 1c The pulping equipment also includes a pulp bleaching zone 410 and pipelines for conveying clean condensate 160 from stripper 970 to pulp bleaching zone 410. Figure 1c The pulping equipment also includes a wastewater treatment zone 420 and pipelines for conveying bleached effluent 170 from the pulp bleaching zone 410 to the wastewater treatment zone 420.

[0049] The above information regarding CNCG 120 for combustion cleanliness also applies to other implementation schemes, especially... Figures 2a to 4b Those. The above content regarding the treatment of turbid condensate 150 also applies to other implementation schemes, especially Figures 2a to 4b Those.

[0050] exist Figure 1a and 1bIn one embodiment, the second washing solution 140 circulating in the washing tower 220 can be aqueous. However, it is not necessary to add a pH-lowering compound to the second washing solution 140, even if it is added to the first washing solution 130. Similarly, it is not necessary to add a pH-lowering compound to the first washing solution 130, even if it is added to the second washing solution 140.

[0051] refer to Figure 4a The scrubber 200 does not need to include the scrubbing tower 220. Figure 4a In one embodiment, untreated non-condensable gas 110 is conveyed through a bath containing washing solutions 130 and 140. This bath may be arranged in tank 210 of the scrubber 200. Figure 4a As shown, acid and water can be added to tank 210. However, reference Figure 4b Washer 200 does not need to include tank 210. Figure 4b In this configuration, scrubber 400 comprises only scrubbing tower 220. Scrubbing solution 140 is circulated by a first pump 222 and sprayed onto the non-condensable gas to be cleaned. Acid and water can be added to the circulating scrubbing solution, such as... Figure 4b As shown.

[0052] Figure 2a and 2b One embodiment is shown in which only one and the same washing solution is used as (first) washing solution 130 in tank 210 and washing tower 220. Reference Figure 2a Water and acid can be fed into tank 210 to form a washing solution 130 in tank 210. The pulping apparatus 100 includes a circulation 221 configured to deliver the washing solution to the upper part of a washing tower 220, where the washing solution is sprayed to form droplets of washing solution 130. In the washing tower 220, the non-condensable gases being washed come into contact with the droplets of washing solution 130. The droplets may be formed by one or more nozzles (not shown) of the washing tower 220. A first pump 222 is used to circulate the washing solution to the upper part of the washing tower 220.

[0053] exist Figure 2a In the process, the first pump 222 receives washing solution 130 from tank 210. Figure 2b In this process, the first pump 222 receives the washing solution 130 from tank 210, but before the washing solution is conveyed to the washing tower 220, some acid and optionally some water may be added to it. To form the washing solution 130, water may be added to tank 210 and / or circulation 221. To form the washing solution, acid may be added to tank 210 and / or circulation 221.

[0054] It has been found advantageous to use a scrubbing tower 220 because the droplets of the scrubbing solution have a high surface area, thereby increasing the reaction efficiency between ammonia and hydrated hydrogen ions of the scrubbing solution. A separate tank 210 can be used, but is not necessary. Therefore, one embodiment of the method includes spraying the scrubbing solution to form droplets of the scrubbing solution in the scrubber, and contacting a non-condensable gas containing ammonia with the droplets of the scrubbing solution. The non-condensable gas can be partially cleaned because the system can include a tank 210 prior to the scrubbing tower 220. Furthermore, in one embodiment of the pulping apparatus, the scrubber 200 includes a circulation 221, i.e., a circulation of the scrubbing solution, which is used for the circulation of the scrubbing solution. In circulation 221, the scrubbing solution is configured to be sprayed to form droplets of scrubbing solution 130. Furthermore, in the scrubber 200, a non-condensable gas containing ammonia is configured to contact the droplets of the scrubbing solution. Again, here, the non-condensable gas containing ammonia can be partially cleaned in the tank 210 prior to the tower 220.

[0055] In order to control pH, Figure 2a and 2b In the illustrated embodiment, sensor 230 is configured to determine the pH of washing solution 130. The pH can be determined, for example, from cycle 221, such as... Figure 2b As shown. Alternatively or additionally, pH can be measured from the turbid condensate 150 (e.g., Figure 2a (As shown in the diagram). Alternatively or additionally, pH may be measured from tank 210 and / or from scrubbing tower 220 (not shown). The measured pH value may be used, as detailed above. For example, controller 242 may control a second pump 240, as detailed above.

[0056] refer to Figure 3 The circulation 221 of the scrubbing tower 220 can be separated from the scrubbing solution in tank 221. In this embodiment, the pulping equipment includes circulation 221 configured to deliver a second scrubbing solution 140 to the upper part of the scrubbing tower 220, wherein the second scrubbing solution 140 is sprayed to form droplets of the second scrubbing solution 140. In the scrubbing tower 220, the non-condensable gas being scrubbed comes into contact with the droplets of the second scrubbing solution 140. The droplets may be formed by one or more nozzles (not shown) of the scrubbing tower 220. A first pump 222 is used to circulate the second scrubbing solution 140 to the upper part of the scrubbing tower 220. Figure 3 In this process, a compound capable of lowering the pH is added to the aqueous second washing solution 140. It is not necessary to add acid to the first washing solution 130 arranged in tank 210, but it can be added, such as... Figure 3 As shown.

[0057] exist Figure 3 In this process, the first pump 222 receives some of the second washing solution 140 from the lower part of the washing tower 220. Figure 3In this process, the first pump 222 receives some of the second washing solution 140 from the lower part of the washing tower 220, but before conveying the second washing solution 140 to the washing tower 220, some acid and optionally some water may be added to it. Furthermore, turbid condensate 150 can be removed from the lower part of the washing tower 220. Alternatively, the turbid condensate can be allowed to flow to tank 210. The turbid condensate 150 can be as shown above or in combination with... Figure 1c Use it as shown.

[0058] exist Figure 3 In this process, the second washing solution 140 in circulation 221 is aqueous and preferably acidic, as detailed above. Furthermore, the first washing solution 130 is used in tank 210. Preferably, the first washing solution 130 is aqueous. However, the first washing solution 130 does not necessarily have to be acidic. However, the first washing solution 130 can also be acidic. Secondary turbid condensate 152 can be discharged from tank 210 and disposed of or treated as needed. The secondary turbid condensate 152 can be as shown above or in combination with... Figure 1c Used for contaminated condensate 150 as shown. Figure 3 The condensate 150 can be combined as follows Figure 1c As shown in the diagram.

[0059] like Figure 4a As detailed in the description, the washer 200 does not need to include... Figures 1a to 3 The loop 221. Therefore, in Figure 4a In this design, the scrubber 200 includes a tank 210 but not a scrubbing tower 220. In use, the tank 210 is filled to a suitable level with a scrubbing solution 130, which is aqueous and preferably acidic, as detailed above. Untreated non-condensable gas 110 is conveyed to the lower part of the scrubber 200, thereby forming bubbles of untreated non-condensable gas within the scrubbing solution 130 disposed in the scrubber 200. Therefore, the untreated non-condensable gas 110 reacts with the scrubbing solution 130, as detailed above. As a result, clean non-condensable gas 120 can be collected from the upper part of the scrubber 200 and, if feasible, processed as described above. This processing preferably includes at least combustion, such as... Figure 4a As shown, and optionally also includes sulfur removal, as described above. The contaminated condensate 150 can be as shown above or in combination with... Figure 1c It is used as shown. However, as detailed above, in a preferred embodiment, the washing solution 130, 140 is sprayed onto the non-condensable gas to be washed.

[0060] like Figure 4b As detailed in the description, the washer 200 does not need to include... Figures 1a to 4a Can 210. Therefore. Figure 4bThe scrubber 200 includes a scrubbing tower 220 and a circulation system 221, but does not include a tank 210. The circulation system 221 is configured to deliver a scrubbing solution 130 to the upper part of the scrubbing tower 220, where the scrubbing solution is sprayed to form droplets of the scrubbing solution. For this purpose, the circulation system 221 includes a first pump 222. In the scrubbing tower 220, the non-condensable gas being scrubbed comes into contact with the droplets of the scrubbing solution. Figure 4b In this process, the first pump 222 receives some washing solution 130 from the lower part of the washing tower 220. Figure 4b In this process, the first pump 222 receives some washing solution 130 from the lower part of the scrubbing tower 220, but before the washing solution 130 is conveyed to the scrubbing tower 220, some acid and optionally some water may be added to it. Furthermore, turbid condensate 150 can be removed from the lower part of the scrubbing tower 220. The turbid condensate 150 may be as shown above or as combined with... Figure 1c Used as shown. The clean, non-condensable gas 120 can be collected from the top of the scrubber 200 and, if feasible, treated as described above. This treatment preferably includes at least combustion, such as... Figure 4b As shown, and optionally also includes sulfur removal, as described above.

Claims

1. A method for removing NH3 from gas generated by a pulping apparatus, the method comprising: - An untreated non-condensable gas containing NH3 is generated in a pulping apparatus. This untreated non-condensable gas comprises at least one sulfur-containing compound, specifically hydrogen sulfide, methanethiol, dimethyl sulfide, and dimethyl disulfide. - Transfer at least some of the untreated non-condensable gases to a scrubber containing an aqueous washing solution. In the scrubber, untreated non-condensable gas is brought into contact with a scrubbing solution, causing the NH3 in the untreated non-condensable gas to react with the scrubbing solution to produce clean non-condensable gas and NH4. + , - Add a compound that can lower the pH of the washing solution. - Measure the pH of the washing solution, and - The pH of the washing solution is controlled by adjusting the flow rate of compounds that can lower the pH of the washing solution into the washer, based on the measured pH value. - In the washer, the washing solution is sprayed to form droplets of the washing solution, and - To bring non-condensable gases containing ammonia into contact with droplets of the washing solution; Its features Compounds that can lower the pH of a washing solution include H₂SO₄, and - The pH of the washing solution is 4.5-5.

5.

2. The method according to claim 1, comprising: - Determine that the measured pH value exceeds a first threshold, and - Add acid to the washing solution.

3. The method according to claim 2, wherein - The pH of the acid is less than 4.

4. The method according to claim 2 or 3, wherein - The first threshold is 5.

5.

5. The method according to claim 1 or 2, wherein - Untreated non-condensable gases contain at least 1000 ppm of NH3, and - Untreated non-condensable gases have a higher ammonia content than clean non-condensable gases.

6. The method according to claim 5, wherein - The ammonia content of clean, non-condensable gases is less than 1000 ppm.

7. The method according to claim 1 or 2, wherein - Untreated noncondensable gases contain at least 20,000 ppm of methanethiol on a dry basis.

8. The method according to claim 7, wherein - Untreated noncondensable gases contain at least 1,000 ppm of ammonia and at least 20,000 ppm of methanethiol on a dry basis.

9. The method according to claim 1 or 2, comprising: - To deliver at least some clean, non-condensable gases to the combustion furnace, and - Combustion of at least some clean, non-condensable gases in a combustion furnace.

10. The method of claim 9, comprising: In the combustion furnace, in addition to clean, non-condensable gases, other fuels are also burned.

11. The method of claim 10, comprising: - Heat is recovered from the combustion furnace by using a heat exchanger.

12. The method of claim 11, comprising: - Use recovered heat to run steam turbines.

13. The method according to claim 1 or 2, comprising: - Utilizing the NH4 in the washing solution + To purify the water.

14. The method of claim 13, comprising: - Transports contaminated condensate from the scrubber to the stripper. - Stripping the contaminated condensate to produce clean condensate. - The cleaned condensate is then transported to the pulp bleaching area. - Clean condensate is used in the pulp bleaching zone to bleach the pulp, producing bleached pulp and bleached effluent. - Transporting the bleach effluent to the wastewater treatment area, and - The wastewater in the wastewater treatment area is purified using bleach effluent, in which... - Bleach effluent contains NH4 + .

15. The method of claim 13, comprising: - Purify water without adding urea.

16. The method of claim 14, comprising: - Purify water without adding urea.

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