Method for reducing recovery boiler emissions

Abstract

The present invention relates to a method for reducing emissions from a recovery boiler, the method comprising the steps of spraying black liquor into a boiler furnace, burning the sprayed black liquor in the boiler furnace, generating steam by cooling flue gas of the burned black liquor through a heat exchanger, removing particles from the cooled flue gas using at least one electrostatic precipitator, passing the flue gas through at least one baghouse filter, further removing particles from the flue gas using bags in the at least one baghouse, and reducing flue gas emissions with an SCR catalytic process.

Description

[Technical Field]

[0001] FIELD OF THE INVENTION The present invention relates to a method for reducing emissions from recovery boiler flue gases, particularly from kraft recovery boilers in pulp manufacturing plants. [Background technology]

[0002] Emissions of boilers generating electricity and / or steam, in accordance with official regulations, e.g. NO X There is a demand to reduce emissions. Future regulations will gradually require even lower emission limits, so low NO X Boiler design and combustion air control are insufficient. Emission levels required for kraft recovery boilers have been less stringent than for power boilers because the chemical and other characteristics of their flue gases differ from those of power boilers. Furthermore, as better emission control technologies are developed for recovery boilers, they will likely be adopted to comply with official emission limits, even though this may incur additional investment and operating costs. Further reductions in airborne emissions of other harmful particles and gases are also desirable.

[0003] The "Best Available Techniques (BAT) Reference Document for the Production of Pulp, Paper and Board" published by the European Commission in 2015 describes the available technologies for controlling emissions from recovery boilers in pulp mills. Valmet Oy's publication "Recovery Boiler SCR - A Challenge and an Opportunity in Retrofit Cases" provides a NOx reduction strategy for recovery boilers. X Further solutions to how emissions can be reduced are described.

[0004] US8211391, US8480984, and US8808652 are electric boiler NO. XNO by SCR (selective catalytic reduction) and SNCR (selective non-catalytic reduction) to reduce emissions X The redemption method is described.

[0005] Publications US5585081, US20190118126, and US10071340 disclose integrated baghouse filtering and SCR processes. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] US8211391 [Patent Document 2] US8480984 [Patent Document 3] US8808652 [Patent Document 4] US5585081 [Patent Document 5] US20190118126 [Patent Document 6] US10071340 [Non-patent literature]

[0007] [Non-Patent Document 1] "Best Available Techniques (BAT) Reference Document for the Production of Pulp, Paper and Board", European Commission Publishing, 2015 [Non-patent document 2] "Recovery Boiler SCR - A Challenge and an Opportunity in Retrofit Cases", published by Valmet Oy [Non-patent document 3] "Paastomittausten Kasikirja Osa 1 (Handbook of emission measurements part 1)", VTT Publishing, June 2007 [Non-patent document 4] "Paastomittausten Kasikirja Osa 2 (Handbook of emission measurements part 2)", VTT Publishing, April 2004 Summary of the Invention [Means for solving the problem]

[0008] The invention is defined by the features of the independent claims. Some particular embodiments are defined in the dependent claims.

[0009] According to a first aspect of the present invention, there is provided a method for reducing emissions from a recovery boiler, the method comprising the steps of spraying black liquor into a boiler furnace, combusting the sprayed black liquor in the boiler furnace, generating steam by cooling a flue gas of the combusted black liquor through a heat exchanger, and removing particles from the cooled flue gas using at least one electrostatic precipitator. The method further comprises passing the flue gas after electrostatic precipitator through at least one baghouse filter, removing particles from the flue gas in the at least one baghouse filter, and reducing emissions of flue gas having a temperature of 180°C or greater that has passed through the bags of the at least one baghouse filter in a catalytic process by selective catalytic reduction (SCR). [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram of an exemplary recovery boiler process in accordance with at least some embodiments of this invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] Detailed Description of the Drawings Figure 1 is a schematic diagram of an exemplary recovery boiler process along with surrounding components. Evaporator 2 processes black liquor discharged from a pulp mill's pulp production process and dries the liquor to a desired dry solids content. The dried black liquor is sprayed into the furnace of recovery boiler 1 for combustion and recovery of recycled chemicals. Economizer 3 is a heat exchanger that heats feedwater and cools flue gases to recovery boiler outlet temperatures.

[0012] The flue gas contains ash particles, most of which are filtered in at least one electrostatic precipitator (ESP) 4. The flue gas is then directed from the ESP 4 to a baghouse 5 for filtering out the remaining particles. The ESP 4 is most effective at filtering out the smallest particles, which can create an overly dense particle layer on the filter bags in the baghouse 5. The NOx of the cleaned flue gas that has passed through the filter bags in the baghouse 5 is then filtered out. X The components are reduced in a catalytic SCR process, which can take place in the baghouse or in a separate SCR unit 6. Before going to the chimney 8, the residual thermal energy of the flue gas is recovered by at least one heat exchanger 7.

[0013] Additive A is injected into the flue gas before ESP 4, or at least before baghouse 5, to reduce the SO X The additive A reacts with the components. Additive A can include, for example, calcium hydroxide, or more preferably, sodium bicarbonate. Such additives and their resulting reaction products are the same chemicals that are recycled within the pulp mill. Additive A, sodium bicarbonate, can be produced in the pulp mill from available sodium carbonate, carbon dioxide, and water. Since all of the additive injected can be reused within the pulp mill, the amount of additive injected can be greater than required without additional cost. This reduces the amount of SO XThe economics of emission reduction are improved. The excess additive ensures that combustion instabilities can be accommodated. Furthermore, the injected additive has a particle size distribution that is larger than or different from the recovery boiler ash, which helps to clean the baghouse filter. The reaction products are returned to the evaporator 2 and are therefore mixed with the atomized black liquor. The SO of the flue gas is X When the content is reduced to a sufficiently low level, the ash dust accumulating on the filter bags in the baghouse 5 does not contain significant amounts of sticky components, thereby allowing for continuous NO production by the SCR process. X Emissions reduction is possible. The baghouse also ensures that particulate plumes from occasional ESP 4 failures are constantly filtered out and do not contaminate the catalytic surfaces of the SCR process. Additional or supplemental ammonia and / or urea can be injected into the flue gas stream before the baghouse 5, or at least before the separate SCR unit 6. [Example]

[0014] An object of the embodiments is to overcome at least some of the problems described above and provide a method for reducing recovery boiler emissions. The method includes burning atomized black liquor in a boiler furnace, generating steam by cooling flue gas from the combusted black liquor flowing through a heat exchanger, and removing particles from the cooled flue gas with at least one electrostatic precipitator. Another object of the embodiments is to achieve reliable emissions reduction of kraft recovery boiler flue gases without compromising the efficiency of power generation. Surprisingly, it has been found that a method comprising spraying black liquor into a boiler furnace, burning the sprayed black liquor in the boiler furnace, generating steam by cooling the combusted black liquor flue gas through a heat exchanger, removing particles from the cooled flue gas with at least one electrostatic precipitator, passing the flue gas through at least one baghouse filter, further removing particles from the flue gas with bags in the at least one baghouse, and reducing flue gas emissions with an SCR catalytic process reduces recovery boiler emissions and improves recovery boiler energy efficiency.

[0015] Detailed Description An embodiment of the present invention describes a method for reducing emissions from a recovery boiler, the method comprising spraying black liquor into a boiler furnace, combusting the sprayed black liquor in the boiler furnace, generating steam by cooling a flue gas of the combusted black liquor through a heat exchanger, removing particles from the cooled flue gas using at least one electrostatic precipitator, passing the flue gas through at least one baghouse filter, further removing particles from the flue gas using bags in the at least one baghouse, and reducing flue gas emissions with a catalytic process using selective catalytic reduction (SCR).

[0016] Power boilers use baghouse filters downstream of electrostatic precipitators (ESPs) to minimize particulate emissions. Kraft recovery boilers have historically not used baghouse filters, primarily due to their unique dust characteristics. Kraft recovery boiler ash is extremely fine and has a very narrow particle size distribution. Typically, 95% of the particles by mass have a diameter of 1.0 μm ± 0.5 μm. On average, the fine particles leaving the boiler have a diameter of 1 micrometer (1.0 μm). Dust removal in baghouse filters is based on the formation of a dust cake on the bag, but small, uniform particle sizes can result in a cake that is too dense. A dense cake on a baghouse filter can excessively increase pressure drop, for example, due to excessive pressure through the filter fabric caused by the cake density and / or excessive flue gas pressure drop caused by the resistance offered by the clean filter and cake layer. Furthermore, the dense cake, which is made up of small particles of uniform size, tends to crumble easily, resulting in dust that is difficult to remove from the system. X Emissions have also limited the use of baghouse filters because sticky compounds in the dust can cause dust particles to adhere to each other and to the bag. The sticky particle layer can grow too thick, obstructing flow and not come off reliably even when reverse flow cleaning cycles are attempted. Therefore, recovery boilers (RBs) have used ESPs rather than baghouses.

[0017] ESP is not a fully reliable method for particle removal. It cannot guarantee continuous particle removal in the RB environment and occasionally experiences performance degradation, i.e., not all particles are continuously removed. This can be due to, for example, sudden changes in the combustion process, incomplete combustion, or operational problems. When performance degradation occurs, the amount of dust particles in the flue gas after ESP increases significantly, causing clogging of the SCR catalyst bed. Because recovery boilers are usually operated continuously at full capacity, cleaning the SCR catalyst bed or replacing the catalyst during operation is not a simple task. For power boilers, which often operate at fluctuating power levels or discontinuously, maintenance and inspection work is much easier.

[0018] In one embodiment, the temperature of the flue gases directed to the SCR catalytic process is increased to above 180°C, preferably above 250°C, especially above 300°C when the ammonia slip increases above a predetermined value, and is reduced when the ammonia slip decreases below a lower predetermined value. For example, for demonstration purposes, the temperature may be increased to above 4 or 4.5 mg / Nm 3 or when it reaches 5 mg / Nm 3 By increasing the temperature when the temperature exceeds 5000kJ / s, the ammonia slip is reduced to a maximum value of 5mg / Nm2 at 6% standard O2. 3 The amount of ammonia slip is a measure of how much ammonia can be injected into the flue gas, e.g., a maximum allowable level of 5 mg / Nm 3 If the amount of ammonia slip is too high, such as exceeding 0.05, the ammonia injected into the flue gas is reduced, thereby reducing the level of ammonia slip. XIf the reduction in NO is limited, this indicates that the activity of the catalyst is reduced compared to that of a fresh catalyst. To avoid the accumulation of ammonium bisulfate (ABS) on the catalyst surface, the operating temperature of the SCR process should be higher than the dew point of ABS. Preferably, to avoid the accumulation of sodium bisulfate (SBS) on the catalyst surface, the operating temperature of the SCR process should be higher than the dew point of SBS. The accumulated ABS and / or SBS cover the active surface of the catalyst, thus reducing the NOx reduction rate by the catalyst. X The reduction of ABS and / or SBS is prevented. To avoid the accumulation of ABS and / or SBS, the operating temperature should preferably be in the range of 200°C to 250°C, preferably 230°C or 220°C. To optimize power and steam production efficiency, the temperature of the flue gas after the recovery boiler economizer heat exchanger should be close to 200°C according to current best practice. The still-hot flue gas from the SCR process can be effectively utilized for combustion air preheaters or other heating needs of the pulp mill. The temperature of the flue gas leading to the SCR catalytic process is advantageously maintained above 180°C for at least 95% of the recovery boiler's operating time. The typical temperature range for a conventional recovery boiler allows for maximum steam power generation efficiency and minimizes carbon dioxide emissions per unit of energy produced. This temperature range is the typical flue gas temperature after the economizer. Particulates are carefully filtered out and SO is removed from the flue gas. X By ensuring that emissions are sufficiently reduced, temperatures can be kept very low.To maximize heat recovery for heating the combustion air or other processes in the pulp mill, the flue gas should be cooled to the outlet temperature in at least one heat exchange step after the SCR catalytic step.

[0019] In another embodiment, ammonia or urea is injected into the flue gas stream prior to the SCR catalytic step. XFor the reduction of SO, injection of ammonia or urea into the flue gas stream should occur prior to the SCR catalytic step. Thus, in an additional or supplemental embodiment, ammonia, urea, or a mixture thereof can be injected into the stream. Injection of ammonia and / or urea for the SCR step reduces the amount of SO X It is preferably carried out downstream of the reduction step. In one embodiment, the ammonia is injected in the form of ammonia gas, for example, pure ammonia gas or anhydrous ammonia. In another embodiment, the ammonia is injected in the form of an aqueous ammonia solution (ammonia water). The amount of ammonia in the aqueous ammonia solution or ammonia water is not particularly limited. The amount of ammonia present can be up to 50% by weight, including 50% by weight of the ammonia water, for example, 19% or 29% by weight of the ammonia water, preferably 25% by weight, and most preferably 24% by weight.

[0020] In one embodiment, the SCR catalytic process is performed within the bags of a baghouse filter. When the SCR process is performed within the bags of a baghouse, the installation space is significantly reduced. The catalyst can be embedded in the bags or the bag's support structure can be coated with a catalyst. By reducing the number of ESP processes and installing baghouse filters in their locations, it becomes possible to add SCR to an existing recovery boiler without requiring additional, sometimes unavailable, space around the recovery boiler.

[0021] In one embodiment, the removed particles from the flue gas are mixed with virgin black liquor. The removed particles contain valuable chemicals that can be recovered after mixing with the black liquor. Chemicals such as sodium sulfate would otherwise be lost to landfill. Thus, in one embodiment, the environmental impact of a factory or plant that includes a recovery boiler is reduced by reducing the amount of particles removed from the flue gas that are landfilled.

[0022] In another embodiment, the dry solids content of the atomized black liquor is greater than 75 weight percent of the weight of the black liquor. When the dry solids content of the atomized black liquor is greater than 75 weight percent, the SO X The level of sulfur dioxide is sufficiently low, for example, 5 ppm or less, preferably less than 5 ppm. As the solids content of the black liquor increases, the temperature in the furnace increases, which causes more of the sulfur present in the black liquor to bind to sodium sulfate. As the solids content of the black liquor decreases, the temperature in the furnace decreases, which causes the sulfur present in the black liquor to tend to form sulfur dioxide.

[0023] In certain embodiments, the flue gas is cooled in at least one heat exchange step after the SCR catalytic step, where heat is recovered and utilized for power generation, such as electricity production. Cooling the flue gas to an outlet temperature in at least one heat exchange step after the SCR catalytic step allows for maximum heat recovery for combustion air heating or other pulp mill processes.

[0024] By continuously feeding the adsorbent into the flue gas stream, the SO X This ensures that the levels remain low at all times. In a typical recovery boiler, there are occasional SO X Although a peak in emissions is observed, the continuous supply of adsorbent reduces the SO X The amount of SO produced is reduced to substantially zero, i.e., less than 5 ppm, such as 0, 1, 2, 3, or 4 ppm. Thus, in embodiments where the sorbent is continuously fed or continuously injected into the flue gas stream, the amount of SO produced is reduced to substantially zero, i.e., less than 5 ppm, such as 0, 1, 2, 3, or 4 ppm. X The dry solids content is not critical in limiting the amount of SO. Therefore, in one embodiment, the sorbent is continuously injected into the flue gas stream. X The adsorbent for reacting with the gas is preferably a dry powder. The adsorbent should be injected into the flue gas stream before the baghouse filter. More preferably, the adsorbent is a dry powder. XThe injection is done before the ESP step to allow more time for reaction with the gas, which results in reusable material from the collected particles. X Removal of the effluent prevents the formation of layers of ABS, SBS, and sticky particles on the baghouse bags. Because the adsorbent contains materials that are normally circulated in the pulp mill's chemical recovery process, the reaction products can be returned to the chemical circulation, preferably mixed with black liquor.

[0025] Therefore, in one embodiment, the possible SO X To reduce emissions, sorbents are injected into the flue gas stream before the baghouse filter, preferably before the electrostatic precipitator. Because the sorbent has a particle size distribution that is larger or different than the recovery boiler ash, the injected sorbent has the added benefit of cleaning the surface of the baghouse filter.

[0026] The sorbent typically comprises an alkali metal salt, an alkaline earth metal salt, or a mixture thereof. In one embodiment, the sorbent comprises sodium hydroxide, calcium carbonate, sodium carbonate, sodium bicarbonate, and / or sodium sesquicarbonate.

[0027] Selective catalytic reduction (SCR) removes NO from cooler flue gases. X It is possible to reduce emissions significantly. XWhile commercial gas scrubbers are also efficient, their drawback is the toxic liquid effluents. Toxic liquid effluents include liquids containing chlorine, chlorates, nitrates, nitrites, etc., or strong acids, such as ClO2, HCl, and HNO3. The SCR process does not produce harmful by-products. SCR catalytic elements are extremely vulnerable to contaminants that coat the elements and shield the active, porous catalytic surface. For example, the catalytic surface can be shielded or blocked by dust, ammonium sulfate, and / or sodium salts, such as sodium sulfate and sodium carbonate, found and / or formed in the recovery boiler. Blockages can block active sites, preventing reactions at the catalytic surface. Any fault in the ESP, even if it lasts only a few seconds, can result in fouling of the SCR catalytic elements and the loss of their NOx. X The reduction capacity is reduced. Catalyst fouling or poisoning is caused by substances such as CaO, MgO, P, and Na diffusing into and occupying the active sites of the catalyst. Such fouling requires cleaning the fouled catalyst elements with a liquid solution, such as an acid, which is difficult or impossible to perform while the recovery boiler is in continuous operation. Therefore, a reliable method for particle removal is required prior to the SCR catalytic process.

[0028] A method for reducing nitrogen oxide emissions from a kraft recovery boiler in a pulp mill includes burning atomized black liquor in a boiler furnace, cooling the combusted black liquor flue gas flowing through a furnace heat exchanger, and removing particles from the cooled flue gas with at least one electrostatic precipitator. The flue gas from the at least one electrostatic precipitator then flows to at least one baghouse filter, which further removes particles from the flue gas and removes NOx from the flue gas that has flowed through the bags of the at least one baghouse filter. X The compounds are reduced during the SCR catalytic process. The baghouse removes particles that may contaminate the catalytic surfaces of the SCR catalytic process.

[0029] To ensure proper operation of the baghouse and prevent the formation of ammonium bicarbonate (ABS) and sodium bisulfate (SBS), the flue gas SO 2 must be filtered before entering the baghouse. X The level should be low enough. X The level is adjusted according to the dry solids content of the sprayed black liquor. If the dry solids content of the sprayed black liquor is greater than 75 weight percent, the SO X The level is low enough.

[0030] An advantageous range for the temperature of the flue gas entering the SCR process is below the deposition temperature of SBS, about 260°C, and preferably below the deposition temperature of ABS, about 250°C. Suitably, the temperature of the flue gas entering the SCR process is 230°C, typically 220°C. Prior to injecting ammonia for the SCR process, SO X Even if most of the emissions can be removed from the flue gas, ABS still slowly accumulates on the catalyst surface. The accumulated ABS can be vaporized by occasionally raising the flue gas temperature. This temperature should be at least 250°C. In practice, to clean the catalyst surface quickly enough, the temperature should be increased to above 300°C, and more preferably above 350°C. Even so, cleaning at high temperatures should occur much less than 5% of the recovery boiler's operating time. The flue gas warming process leading to the SCR process is activated when the ammonia slip increases and exceeds a predetermined value. When the ammonia slip decreases below a lower predetermined value, the temperature is reduced to the normal operating temperature. The normal operating temperature range may be used for longer periods, exceeding one month depending on the operating conditions. Another means of ensuring catalytic reaction is cleaning, replacing, or, in the case of catalyst poisoning, regenerating the catalyst elements. If cleaning or replacement is required, the SCR process can be bypassed via a bypass line.

[0031] Recovery boiler NO XReducing emissions not only incurs installation and operating costs. X Emission reduction achieved through combustion procedures Low NO X The boiler is significantly more expensive to build than a conventional boiler. X Effective reduction in CO2 allows for significantly cheaper designs of new recovery boilers.

[0032] Therefore, proper operation of the SCR is ensured even at moderate temperatures. Therefore, there should be no need to constantly operate additional duct burners / heaters before the SCR process. The flue gas temperature can be kept at an optimal level in terms of energy efficiency.

[0033] The following table (Table 1) illustrates how emissions are reduced by at least some embodiments of the present invention: Column 1 shows the emissions from the recovery boiler under consideration, Column 2 shows the amount of emissions from the recovery boiler when the flue gas is not treated in accordance with at least some embodiments of the present invention, and Column 3 shows the amount of emissions from the recovery boiler when the flue gas is treated in accordance with at least some embodiments of the present invention.

[0034] [Table 1]

[0035] The measurements in Table 1 were made using FT-IR, except for dust, which was measured using gravimetric measurements. After treatment according to the examples of the present invention, NO X Reductions in dust and particulate matter are measured, and reductions in SO2 are predicted as well. X SO2 and NO contained in X The reduction in emissions can be measured, for example, by gravimetric determination (dust) according to SFS-EN 13284-1, UV fluorescence detection (SO2) according to CEN / Ts 17021:2017, or chemiluminescence detection (NO2) according to SFS-EN 14792. X) can be used to check the reductions in each of the emissions, as well as NH3, for example, as described in the " NH3 may be measured by various means as described in "Handbook of emission measurements part 1," Chapter 5, page 28, JPEG2025541784000003.jpg7134. In this example, NH3 is not an emission whose amount is reduced, but is increased slightly by the injection of NH3 into the flue gas. Its presence can be measured, for example, by chemiluminescence. Measurements are typically performed continuously in pulp mills, but also periodically (usually annually) by external consultants for environmental monitoring. Methods for both continuous and periodic measurements are described in "Measurements for Continuous and Periodic Measurements," published in June 2007 by VTT. JPEG2025541784000004.jpg7134 (Handbook of emission measurements part 1) and " This is described in detail in both "JPEG2025541784000005.jpg7134 (Handbook of emission measurements part 2)".

[0036] It is to be understood that the disclosed embodiments of the invention are not limited to the particular structures, process steps, or materials disclosed herein, but extend to equivalents thereof that would be recognized by those skilled in the art. It is also to be understood that the terminology used herein is used only for the purpose of describing particular embodiments, and is not intended to be limiting.

[0037] Throughout this specification, a reference to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with that embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrase "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. For example, when a numerical value is referred to using terms such as about or substantially, the exact numerical value is also disclosed.

[0038] As used herein, a plurality of items, structural elements, components, and / or materials may be presented in a common list for convenience. However, these lists should be construed as though each element of the list were each identified as a separate and unique element. Accordingly, the individual elements of such lists should not be construed as de facto equivalents to other elements of the same list solely based on their presentation in a common grouping, unless otherwise indicated. Furthermore, various embodiments and examples of the present invention may be referred to herein, along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives should not be construed as de facto equivalents of each other, but rather as separate and autonomous manifestations of the present invention.

[0039] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided, such as example lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. However, one skilled in the art will recognize that the invention may be practiced without one or more of such specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

[0040] While the foregoing examples illustrate the principles of the present invention in one or more particular applications, it will be apparent to those skilled in the art that many changes in form, application, and details of implementation can be made without the exercise of the inventive faculty and without departing from the principles and concepts of the present invention. Accordingly, it is not intended that the present invention be limited except as by the claims set forth below.

[0041] In this document, the verbs "to comprise" and "to include" are used as open limitations which neither exclude nor require the presence of any unrecited features. Features recited in the dependent claims may be freely combined with one another unless expressly stated otherwise. Furthermore, it is to be understood that the use of "a" or "an", i.e., the singular, does not exclude a plurality throughout this document.

Claims

1. 1. A method for reducing emissions from a recovery boiler, comprising: spraying black liquor into a boiler furnace; burning the atomized black liquor in the boiler furnace; generating steam by cooling the combusted black liquor flue gas through a heat exchanger; removing particles from the cooled flue gas using at least one electrostatic precipitator; passing the flue gas through at least one baghouse filter; further removing particles from the flue gas using bags in the at least one baghouse; The NO of the flue gas is removed by the SCR catalytic process. Ｘ reducing emissions; A method comprising:

2. 2. The method according to claim 1, wherein the temperature of the flue gases led to the SCR catalytic step is at least 180°C, preferably at least 250°C, in particular at least 300°C.

3. The method according to claim 1 or 2, wherein the operating temperature of the SCR process is in the range of 200°C to 250°C, preferably 230°C or 220°C.

4. 4. The method of any of claims 1 to 3, wherein ammonia, or urea, or a mixture thereof is injected into the flue gas stream prior to the SCR catalytic step.

5. 5. The method according to any of claims 1 to 4, wherein ammonia is injected into the flue gas stream prior to the SCR catalytic step, the ammonia being in the form of ammonia gas, preferably pure ammonia gas or anhydrous ammonia.

6. 5. The method of any one of claims 1 to 4, wherein ammonia is injected into the flue gas stream prior to the SCR catalytic step, the ammonia being in the form of an aqueous ammonia solution.

7. 7. The method of any of claims 1 to 6, wherein the SCR catalytic step is carried out in an SCR catalyst bed.

8. 8. The method of any of claims 1 to 7, wherein the SCR catalytic process is carried out within the bag of the baghouse.

9. 9. The method of claim 1, wherein the SCR catalytic process is carried out both in the SCR catalyst bed and in the bags of the baghouse.

10. 10. The method of any of claims 1 to 9, wherein the removed particles from the flue gas are mixed with virgin black liquor.

11. 11. The method of any of claims 1 to 10, wherein the dry solids content of the atomized black liquor is greater than 75 weight percent.

12. 12. The method according to any of the preceding claims, wherein the flue gas is cooled after the SCR catalytic step in at least one heat exchange step.

13. SO Ｘ 13. The method of any preceding claim, wherein an adsorbent is injected into the flue gas stream before the electrostatic precipitator, or at least before the baghouse, to reduce emissions.

14. 14. The method of any of claims 1 to 13, wherein the adsorbent comprises sodium hydroxide, and / or calcium carbonate, and / or sodium carbonate, and / or sodium bicarbonate, and / or sodium sesquicarbonate.

15. 15. The method of any of claims 1 to 14, wherein the sorbent is injected continuously into the flue gas stream.

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