Patent ID: 12195917

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

The present invention relates to a method for removing ammonia from non-condensable gases of a pulp mill. The ammonia is removed by scrubbing. When considered feasible, the non-condensable gases before scrubbing are referred to as “raw non-condensable gases” and the remainder after the scrubbing is referred to as “clean non-condensable gases”. Herein the term non-condensable gases (raw or clean) refer to such gases that are in a gaseous form at a temperature of 20° C. in a pressure of 1 atm (about 1 bar(a)).

The raw non-condensable gases comprise at least ammonia (NH3). In a preferable embodiment, the raw non-condensable gases further comprise a compound comprising Sulfur. The raw non-condensable gases may comprise ammonia (NH3) and at least one of hydrogen sulfide, methyl mercaptan, dimethyl sulfide, or dimethyl disulfide. In an embodiment, the raw non-condensable gases comprise at least 1000 ppm ammonia (on dry basis). Hereinafter the unit ppm refers to parts per million on mass basis, e.g. milligrams per kilograms. Moreover, when measured on dry basis, water is excluded from the measurement. In an embodiment, the raw non-condensable gases comprise at least 1000 ppm ammonia (on dry basis) and at least 20000 ppm methyl mercaptan.

As indicated in the background, strong odorous gases are produced in sulfate and/or sulfite pulping. Table 1 indicates three typical compositions of strong odorous gases in terms of the main components comprising Sulfur and the main component comprising nitrogen. The strong odorous gases are an example of raw non-condensable gases.

TABLE 1composition of three samples of strong odorous gases.content (ppm)molarsamplesamplesampleCompoundwt123hydrogen sulphideH2S345000081300methyl mercaptanCH3SH4880900110000188300dimethyl sulphide(CH3)2SH642200050000116000dimethyl disulphide(CH3)2S294800300003000turpentineC10H161321900methanolCH3OH32ammoniaNH317200020002000

As known in the art, to remove the odorous compounds, strong odorous gases (i.e. odorous gases) or liquids are burned to oxidize the Sulfur. However, at the same time, the ammonia produces nitrogen oxides NOx, which is harmful to the environment.

It has been found that at least some of the ammonia can be scrubbed off from the raw non-condensable gases by contacting the raw non-condensable gas with a scrubbing solution that is aqueous and to which has been added a compound capable of decreasing the pH of the scrubbing solution. In this way, clean non-condensable gas is produced.

Referring toFIG.1a, raw non-condensable gases110are produced in a pulp mill100. The pulp mill100comprises also the other components shown inFIG.1a. The raw non-condensable gases110are conveyed to a scrubber200for scrubbing. InFIG.1a, the scrubber200comprises a tank210and a scrubbing tower220. Into the scrubber200, an aqueous solution and a compound capable of decreasing the pH of the scrubbing solution are conveyed to form a scrubbing solution130into the scrubber200. In the figures, the term “water” indicates the aqueous solution, which may be substantially pure water, or effluent from a process of the pulp mill. In the figures, the term “acid” indicates the compound capable of decreasing the pH of the scrubbing solution. In this way, the term “acid” refer to any and all compounds capable of forming hydroxonium (i.e. hydronium, H3O+) with water to the scrubbing solution. Such compounds include all kinds of acids, and also gases or solids, such as CO2, that form an acid upon reacting with water.

Different scrubbing solutions may be used in different parts of the scrubber200. A first scrubbing solution130may be arranged in the tank210of the scrubber, while a second scrubbing solution140be arranged to circulate in the scrubbing tower220of the scrubber200. However, same scrubbing solution may be used in different parts of the scrubber.

When the pulp mill100comprises the scrubbing tower220, the pulp mill also comprises a circulation221configured to convey scrubbing solution (inFIG.1athe solution140) to an upper part of the scrubbing tower220, wherein the scrubbing solution is sprayed to form droplets of the scrubbing solution. The circulation221comprises a first pump222for the purpose. In the scrubbing tower220, the non-condensable gas, which is being scrubbed, contacts the droplets of the scrubbing solution. It has been found that scrubbing at least in a scrubbing tower220is particularly efficient.

As the scrubbing solution, i.e. as one or both of the first130and the second140scrubbing solutions, an aqueous and acidic solution may be used. In the scrubber200, the raw non-condensable gas110is contacted with the scrubbing solution130,140.

Because the scrubbing solution130,140is aqueous, it comprises water (H2O), of which a part naturally forms hydroxonium (i.e. hydronium, H3O+) and hydroxide (OH−). When ammonia (NH3) reacts with water, ammonium (NH4+) and hydroxide (OH−) is produced. In order to enhance the production of ammonium (NH4+), the compound capable of forming hydroxonium with water (“acid” in the figures) is added to the scrubbing solution130,140. Preferably, the scrubbing solution is acidic. Preferable pH values will be given below. When the scrubbing solution130,140comprises an acid, the scrubbing solution130,140comprises also anions (i.e. negative ions, hereinafter denoted by A−) other than hydroxide (OH−). These anions (A−) are the result of the acid (or more generally, the compound capable of forming hydroxonium with water) giving its proton(s) to the hydroxonium in water.

As a result of scrubbing, clean non-condensable gas120is produced. As indicated above, the scrubbing solution130,140comprises the anions (A−) of the acid of the scrubbing solution130,140, and ammonium (NH4+) formed from the ammonia (NH3) of the raw non-condensable gas110. The anions (A−) and the ammonium are collectable from the scrubber200in the form of foul condensate150. Examples of the anions (A−) will be detailed below.

As for the acid of the scrubbing solution130,140, it has been found that acids comprising a reactive nonmetal atom are particularly effective. Reactive nonmetal atoms are Hydrogen (H), Carbon (C), Nitrogen (N), Oxygen (O), Fluorine (F), Phosphorous (P), Sulfur (S), Chlorine (CI), Selenium (Se), Bromine (Br), and Iodine (I). Naturally, water is not considered as an acid, even if it comprises both hydrogen and oxide. Examples of such acids include aqueous solutions of sulfuric acid (H2SO4), nitric acid (HNO3), carbon dioxide (CO2), and hydrochloric acid (HCl). As an example, sulfuric acid in aqueous solution forms the anions HSO4−and/or SO42−and nitric acid in aqueous solution forms the anion NO3−. These anions have been and will be denoted by (A−). Therefore, in a preferable embodiment, the scrubbing solution130,140comprises hydroxonium (H3O+) and an anion (A−) other than hydroxide (OH−), the anion (A−) comprising an atom selected from a group consisting of Carbon (C), Nitrogen (N), Fluorine (F), Phosphorous (P), Sulfur (S), Chlorine (Cl), Selenium (Se), Bromine (Br), and Iodine (I). Preferably, the acid does not comprise a metal atom from the first group of the periodic table of elements, including Lithium (Li), Sodium (Na), and Potassium (K).

As for the scrubbing solution130,140, preferable an aqueous solution of sulfuric acid (H2SO4), an aqueous solution of nitric acid (HNO3), an aqueous solution of carbon dioxide (CO2), and/or an aqueous solution of hydrochloric acid (HCl) is used. Thus, by the aforementioned reaction, an ammonium salt solution is formed to the scrubbing solution130,140. Corresponding to these acids, respectively, the ammonium salt may be ammonium sulfate ((NH4)2SO4), ammonium nitrate (NH4NO3), ammonium carbonate ((NH4)2CO3), or ammonium chloride (NH4Cl). In the aqueous scrubbing solution, these salts are in the form of ammonia (NH4+) and the anion (A−), wherein the anion is (A−) in these cases, respectively, is sulfate (SO42−), nitrate (NO3−), carbonate (CO32−), or chloride (Cl−). Typically sulfuric acid is naturally available from the pulp mill100, whereby more preferably, an aqueous solution of sulfuric acid (H2SO4) is used as the scrubbing solution130,140, i.e. as at least one of the first130and the second140scrubbing solution. It is noted that because of the reaction, in this case, aqueous ammonium sulfate ((NH4)2SO4) is produced as the result of the reaction, and the ions of ammonium sulfate become part of the scrubbing solution130,140. Moreover, other impurities of the raw non-condensable gas may dissolve or otherwise remain within the scrubbing solution130,140. Thus, the scrubbing solution may comprise further compounds than the acid and the water. These ions and/or impurities may be removed in the form of the foul condensate150. This applies to other aqueous acids used as the scrubbing solution, too, mutatis mutandis.

It has been found that the formation of the anion (A−) other than hydroxide (OH−) as the reaction product of the acid and the ammonia of the raw non-condensable gas110is most effective at a pH of about 5. Moreover, it has been found that when pH is less than 3, hydrocarbons of the raw non-condensable gas start to polymerize, which may block nozzles and/or pipelines of the scrubber200. Therefore, the pH is preferably at least 3. In addition, the scrubbing solution's capability of capturing ammonia to the scrubbing solution is significantly lowered if the pH is more than 7.5. Therefore, in an embodiment, the scrubbing solution130,140has a pH from 3 to 7.5, preferably from 4 to 6, and most preferably from 4.5 to 5.5. This applies in particular, when an aqueous solution of sulfuric acid (H2SO4) is used as the scrubbing solution130,140.

The pH of the scrubbing solution130,140can be measured and controlled based on measurements. Thus, an embodiment comprises measuring a pH of the scrubbing solution130,140and controlling a pH of the scrubbing solution130,140based on the measured pH value by adding at least one of (i) the aqueous solution, which may be substantially pure water, or effluent from a process of the pulp mill (“water”) and (ii) the compound capable of forming hydroxonium with water (“acid”). In particular, a flow of the compound capable of decreasing a pH of the scrubbing solution (“acid”) into the scrubber200can be controlled. For example, if the measured pH of the scrubbing solution130,140is more than a first threshold, acid can be added to the scrubbing solution in order to lower the pH of the scrubbing solution. Moreover, if the measured pH of the scrubbing solution130,140is less than a second threshold, water can be added to the scrubbing solution. Typically, the ammonia as such tends to increase the pH of the scrubbing solution130,140during operation, whereby acid (or other compound capable of forming hydroxonium with water) needs to be added to the process. The first threshold may be e.g. 8, 7, 6, or 5.5 (in the pH scale). The second threshold may be e.g. 3 or 4 (in the pH scale).

Preferably, if an acid is added to the scrubbing solution, a pH of the acid (“acid”) that is added to the scrubbing solution130,140is less than 4. Thus, the pH of the scrubbing solution can be decreased down to 4, and moreover, an excess amount of the acid is not needed for controlling the pH. More preferably, the pH of the acid that is added to the scrubbing solution130,140is less than 3. The amount of added water and added acid may be selected such that the level of the scrubbing solution in the scrubber remains at proper level, and such that the pH of the scrubbing solution is within the aforementioned limits. For these reasons, the scrubber200comprises an inlet205configured to let in the compound capable of decreasing pH of the scrubbing solution of the scrubber200, such as an acid.

In order to keep the pH of the scrubbing solution at a proper level, an embodiment of the pulp mill100comprises a pH sensor230configured to determine the pH of the scrubbing solution130,140. As indicated inFIGS.1band1c, the pH may be measured from the foul condensate150. Even if not shown, the pH could be measured by a sensor230arranged within the scrubber200. The measured value of pH is then used to control a second pump240configured to feed the acid to the scrubber200. For example, if the measured pH is more than the first threshold, the flow of acid (or other compound capable of decreasing pH) into the scrubber200is increased e.g. by using the second pump240, as indicated above. For example, if the measured pH is less than the second threshold, the flow of water into the scrubber200is increased, as indicated above. The pulp mill100may comprise a controller242configured to control the second pump240as detailed above. As an alternative to the second pump240, a valve may be used, provided that the acid (or other compound capable of decreasing pH) is stored under pressure. Thus, by opening the valve, the pressure drives the acid to the scrubber200. The pressure may be hydrostatic, when the acid is stored at a higher vertical level. The pressure may be a pressure of the gas, if the compound capable of decreasing pH (“acid”) is gaseous. As an alternative or in addition, the pressure may be generated by a pump.

Referring toFIG.1a, constituents of the first scrubbing solution130may be conveyed to the tank210of the scrubber200through a single line. Referring toFIG.1b, constituents of the first scrubbing solution130may be conveyed to the tank210of the scrubber200through separate lines.

As a result of the scrubbing, the clean non-condensable gas120comprises less ammonia that the raw non-condensable gas110. A content of ammonia of the clean non-condensable gas120may be e.g. at most half of a content of ammonia of the raw non-condensable gas110. A content of ammonia of the clean non-condensable gas120may be e.g. less than 1000 ppm or less than 500 ppm. It has been found that at least by using sulfuric acid in the scrubbing solution130,140such that the pH of the scrubbing solution is about 5, nearly 90% of ammonia can be scrubbed off from the raw non-condensable gas.

As indicated in the background, typically the raw non-condensable gas110comprises a compound or compounds comprising Sulfur. Moreover, also these compounds are odorous, and they may be transformed to less odorous oxides by combustion. Therefore, and with reference toFIG.1c, in an embodiment, at least some of the clean non-condensable gas120is conveyed to a furnace310, in which the clean non-condensable gas120is burnt. As depicted inFIG.1c, also air or other oxygen containing gas is fed to the furnace310.

In particular, the furnace310may be a furnace of a kiln or boiler of the pulp mill100. The kiln or the boiler may be configured to produce or recover cooking chemicals of the pulp process. Examples include lime kiln and chemical recovery boiler. In order to enhance combustion, also other fuel (“fuel”) may be supplied into the furnace310.

Preferably the heat produced by burning the clean non-condensable gas120is recovered by a heat exchanger320. In this way, the furnace310may be a furnace of a boiler300. In general, a boiler300is configured to heat and boil water to produce steam. The heat recovered in the heat exchanger320may be utilized as needed. One preferable way is to superheat steam in the heat exchanger320, which in this case is a superheater of the boiler, and operate a steam turbine with the steam. Furthermore a generator can may be connected to the steam turbine to form electricity.

By burning at least the clean non-condensable gas120in the furnace310, flue gas is produced. As detailed above, the flue gas may comprise Sulfur oxides (SOx), at least when the raw non-condensable gas110comprises a compound comprising Sulfur and a separate incinerator is used. In case the clean non-condensable gas is burnt in a chemical recovery boiler, the ash of the boiler may absorb the sulfur and/or sulfur oxides. The Sulfur oxides may be removed from flue gas as known in the art.

Even ifFIGS.1aand1bshow the raw non-condensable gas110as a whole, its components may be conveyed in separate lines to the scrubber200. With reference toFIG.1c, an embodiment of a pulp mill comprises at least one, preferably all, of an evaporator area955, a digester area965, and a stripper970. Typically a part of off gas from the stripper970, i.e. stripper off gas, is condensed in a condenser975. The condenser975, if used, may be considered to be comprised by the stripper970. Typically, the stripper off gas comprises methanol, and the methanol may be condensed. However, a part of the stripper off gas is non-condensable and may form part of the raw non-condensable gases as discussed above. Each one of these (955,965,970,975) may comprise a collector990for collecting the resulting gas and/or liquid. One or more evaporators are arranged at the evaporator area955. The evaporator(s) of the evaporator area955are configured to dry a solution comprising cooking chemicals of the pulp mill. Examples of such solutions include black liquor and brown liquor. One or more digesters are arranged at the digester area965. The digester(s) of the digester area are configured to cook raw materials of paper pulp. The stripper970is typically configured to strip foul condensates resulting from evaporator(s) (i.e. from the evaporator area955) and/or digester(s) (i.e. from the digester area965), as indicated by the dashed arrows inFIG.1c. The gas from the evaporator area955can be conveyed to the stripper via the digester area965and vice versa, as indicated inFIG.1c.

A first part110aof the raw non-condensable gas110may be conveyed from the evaporator area955to the scrubber200through a first pipeline. A second part110bof the raw non-condensable gas110may be conveyed from the digester area965to the scrubber200through a second pipeline. A third part110cof the raw non-condensable gas110may be conveyed from the stripper970or the condenser975to the scrubber200through a third pipeline. In general, a collector990of the pulp mill is configured to collect raw non-condensable gas110(i.e.110aand/or110band/or110c), and a pipeline or pipelines is/are configured to convey the raw non-condensable gas, or parts of the raw non-condensable gas, to the scrubber200.

FIG.1calso shows a preferable way of handling the foul condensate150, which comes from the scrubber200as a result of the scrubbing. An embodiment of the method comprises conveying foul condensate150from the scrubber200to the stripper970. In the stripper970, the foul condensate is cleaned to form clean condensate160. The clean condensate160comprises the ammonium salt of the foul condensate150. More specifically, the clean condensate160comprises ammonia ions (NH4+). In a preferable embodiment, the clean condensate160comprises ammonium sulfate, which is a result of the ammonia reacting with sulfuric acid. The clean condensate160is conveyed to pulp bleaching area410, where pulp is bleached. The clean condensate is used in a bleaching solution in the pulp bleaching area410and the bleaching process. As a result of bleaching bleached pulp is produced as the main product, and bleaching effluent170as a side product. As indicated inFIG.1c, the bleaching effluent170comprises ammonia. The bleaching effluent170is conveyed to a waste water treatment area420. In the waste water treatment area420, waste water of the pulp process is being purified.

In prior art, waste water purification requires urea as a purification chemical. However, it has been found that in the present invention, nitrogen is being supplied to the waste water treatment process and waste water treatment area420in the form of the ammonium (NH4+) of the bleaching effluent170. Thus, it has been found that by removing ammonia from the CNCG as detailed above, the ammonium thus formed can be utilized in waste water treatment. Thus, an embodiment comprises purifying water by utilizing ammonium (NH4+) of the scrubbing solution130,140. More preferably, the water is purified without addition of any other nitrogen-containing compound. More preferably, the water is purified without addition of urea (OC(NH2)2).

A corresponding pulp mill comprises a waste water treatment area420and a pipeline for conveying a part of foul condensate150from the scrubber200to the waste water treatment area420. The part of the foul condensate150that is conveyed to the waste water treatment area420comprises ammonia in an aqueous solution. Preferably, the pulp mill comprises a stripper970and a pipeline for conveying foul condensate150from the scrubber200to the stripper970. The pulp mill ofFIG.1cfurther comprises a pulp bleaching area410and a pipeline for conveying clean condensate160from the stripper970to the pulp bleaching area410. The pulp mill ofFIG.1cfurther comprises a waste water treatment area420and a pipeline for conveying bleaching effluent170from the pulp bleaching area410to the waste water treatment area420.

What has been said above about burning the clean CNCG120is applicable in other embodiments, in particular those ofFIGS.2ato4b. What has been said above about handling the foul condensate150is applicable in the other embodiments, in particular those ofFIGS.2ato4b.

In the embodiment ofFIGS.1aand1b, the second scrubbing solution140circulating in the scrubbing tower220may be aqueous. However, the compound capable of decreasing pH needs not be added to the second scrubbing solution140, even if it is added to the first scrubbing solution130. In a similar manner, the compound capable of decreasing pH needs not be added to the first scrubbing solution130, even if it is added to the second scrubbing solution140.

With reference toFIG.4a, the scrubber200needs not comprise a scrubbing tower220. In the embodiment ofFIG.4a, the raw non-condensable gas110is conveyed through a bath comprising the scrubbing solution130,140. The bath may be arranged in a tank210of a scrubber200. Acid and water may be added to the tank210, as depicted inFIG.4a. However, with reference toFIG.4b, the scrubber200needs not comprise a tank210. InFIG.4b, the scrubber400only comprises the scrubbing tower220. The scrubbing solution140is circulated by a first pump222and sprayed onto the non-condensable gases to be cleaned. Acid and water may be added to the circulation of the scrubbing solution, as depicted inFIG.4b.

FIGS.2aand2bshow an embodiment, wherein only one and the same scrubbing solution is used as the (first) scrubbing solution130both in the tank210and in the scrubbing tower220. Referring toFIG.2a, water and acid may be fed to the tank210in order to form the scrubbing solution130into the tank210. The pulp mill100comprises a circulation221configured to convey scrubbing solution to an upper part of the scrubbing tower220, wherein the scrubbing solution is sprayed to form droplets of the scrubbing solution130. In the scrubbing tower220, the non-condensable gas, which is being scrubbed, contacts the droplets of the scrubbing solution130. The droplets may be formed by a nozzle or nozzles (not shown) of the scrubbing tower220. The first pump222is used to circulate the scrubbing solution to the upper part of the scrubbing tower220.

InFIG.2a, the first pump222receives the scrubbing solution130from the tank210. InFIG.2b, the first pump222receives the scrubbing solution130from the tank210, but before the scrubbing solution is conveyed to the scrubbing tower220, some acid, and optionally some water, may be added thereto. To form the scrubbing solution130, the water may be added to the tank210and/or to the circulation221. To form the scrubbing solution, the acid may be added to the tank210and/or to the circulation221.

Using a scrubbing tower220has been found beneficial, since the droplets of the scrubbing solution have a high surface area, whereby the reaction efficiency between the ammonia and the hydroxonium of the scrubbing solution is increased. A tank210may be, but need not be, used in addition. Thus, an embodiment of the method comprises, spraying the scrubbing solution to form droplets of the scrubbing solution in the scrubber, and contacting the non-condensable gas comprising ammonia with the droplets of the scrubbing solution. Herein the non-condensable gas may be partially cleaned, since the system may comprise the tank210before the scrubbing tower220. Moreover in an embodiment of a pulp mill, the scrubber200comprises the circulation221, i.e. a circulation for the scrubbing solution, which is, in use, a circulation of the scrubbing solution. In the circulation221, the scrubbing solution is configured to be sprayed to form droplets of the scrubbing solution130. Moreover, in the scrubber200, the non-condensable gas comprising ammonia is configured to contact the droplets of the scrubbing solution. Also here, the non-condensable gas comprising ammonia may be partly cleaned in the tank210before the tower220.

In order to control the pH, in the embodiments ofFIGS.2aand2b, a sensor230is configured to determine the pH of the scrubbing solution130. The pH may be determined e.g. from the circulation221, as inFIG.2b. In the alternative or in addition, the pH may be measured from the foul condensate150(as inFIG.2a). In the alternative or in addition, the pH may be measured from the tank210and/or from the scrubbing tower220(not shown). The measured pH value may be utilized as detailed above. For example, the controller242may control the second pump240as detailed above.

Referring toFIG.3, the circulation221of the scrubbing tower220may be separated from the scrubbing solution of the tank221. In this embodiment, the pulp mill comprises the circulation221, which is configured to convey second scrubbing solution140to the upper part of the scrubbing tower220, wherein the second scrubbing solution140is sprayed to form droplets of the second scrubbing solution140. In the scrubbing tower220, the non-condensable gas, which is being scrubbed, contacts the droplets of the second scrubbing solution140. The droplets may be formed by a nozzle or nozzles (not shown) of the scrubbing tower220. The first pump222is used to circulate the second scrubbing solution140to the upper part of the scrubbing tower220. InFIG.3, the compound capable of decreasing pH is added to the second scrubbing solution140, which is aqueous. Acid needs not be added to the first scrubbing solution130, which is arranged in the tank210, but may be added, as indicated inFIG.3.

InFIG.3, the first pump222receives some of the second scrubbing solution140from a lower part of the scrubbing tower220. InFIG.3, the first pump222receives some of the second scrubbing solution140from the lower part of the scrubbing tower220, but before the second scrubbing solution140is conveyed to the scrubbing tower220, some acid, and optionally some water, may be added thereto. In addition, the foul condensate150may be removed from a lower part of the scrubbing tower220. In the alternative, the foul condensate may be let to flow to the tank210. The foul condensate150may be used as indicated above or as indicated in connection withFIG.1c.

InFIG.3, the second scrubbing solution140of the circulation221is aqueous and preferably acidic, as detailed above. Moreover, a first scrubbing solution130is utilized in the tank210. Preferably, the first scrubbing solution130is aqueous. However, the first scrubbing solution130need not be acidic. However, also the first scrubbing solution130may be acidic. A secondary foul condensate152may be let out from the tank210and drained or processed as needed. The secondary foul condensate152may be used as indicated above or as indicated in connection withFIG.1cfor the foul condensate150. The foul condensate150ofFIG.3may be utilized as indicated in connection withFIG.1c.

As detailed inFIG.4a, the scrubber200needs not comprise the circulation221of theFIGS.1ato3. Thus, inFIG.4a, the scrubber200comprises the tank210, but not the scrubbing tower220. In use, the tank210is filled to a proper level with the scrubbing liquid130, which is aqueous and preferably acidic as detailed above. The raw non-condensable gas110is conveyed to a lower part of the scrubber200, whereby bubbles of the raw non-condensable gas are formed within the scrubber solution130that is arranged in the scrubber200. Thus, the raw non-condensable gas110reacts with the scrubbing solution130as detailed above. As a result, clean non-condensable gas120can be collected from an upper part of the scrubber200and, if feasible, processed as detailed above. The processing preferably includes at least combustion, as shown inFIG.4a, and optionally also sulfur removal, as detailed above. The foul condensate150may be used as indicated above or as indicated in connection withFIG.1c. However, as detailed above, in a preferable embodiment, the scrubbing solution130,140is sprayed onto the non-condensable gases to be scrubbed.

As detailed inFIG.4b, the scrubber200need not comprise the tank210of theFIGS.1ato4a. Thus, scrubber200ofFIG.4bcomprises the scrubbing tower220and the circulation221, but does not comprise the tank210. The circulation221is configured to convey scrubbing solution130to an upper part of the scrubbing tower220, wherein the scrubbing solution is sprayed to form droplets of the scrubbing solution. The circulation221comprises a first pump222for the purpose. In the scrubbing tower220, the non-condensable gas, which is being scrubbed, contacts the droplets of the scrubbing solution. InFIG.4b, the first pump222receives some of the scrubbing solution130from a lower part of the scrubbing tower220. InFIG.4b, the first pump222receives some of the scrubbing solution130from the lower part of the scrubbing tower220, but before the scrubbing solution130is conveyed to the scrubbing tower220, some acid, and optionally some water, may be added thereto. In addition, the foul condensate150may be removed from a lower part of the scrubbing tower220. The foul condensate150may be used as indicated above or as indicated in connection withFIG.1c. Clean non-condensable gas120can be collected from an upper part of the scrubber200and, if feasible, processed as detailed above. The processing preferably includes at least combustion, as shown inFIG.4b, and optionally also sulfur removal, as discussed above.