Method for regenerating sodium hydroxide by combining spontaneous steam gasification and catalytic reaction of black liquor

Abstract

The invention belongs to the field of pulping and papermaking, and provides a method for regenerating sodium hydroxide through spontaneous steam gasification combined with catalytic reaction of black liquor, which comprises the following steps: S1, uniformly mixing concentrated black liquor with a catalyst to obtain mixed slurry; s2, diesel oil is combusted, and after the temperature in the reaction furnace reaches the first furnace temperature, the mixed slurry is sprayed into the reaction furnace according to the set flow; s3, the air flow is increased at the same time, and when the temperature in the reaction furnace reaches the second furnace temperature, diesel combustion is stopped; s4, controlling the furnace temperature at a third furnace temperature, and carrying out continuous gasification and catalytic reaction for more than 1 hour; and S5, discharging the molten product out of the reaction furnace, dissolving part of the molten product with hot water to generate hydration reaction, and performing alkalization reaction on the other part of the molten product to obtain the sodium hydroxide mixed alkali liquor with the proper causticization rate of 65-80%. According to the method, sodium hydroxide is regenerated in one step through spontaneous vapor gasification and catalytic reaction of the black liquor.

Description

Technical Field

[0001] The invention belongs to the technical field of pulping and papermaking, relates to the field of resource utilization of pulping black liquor, and particularly relates to a method for regenerating sodium hydroxide through spontaneous water vapor gasification and catalytic reaction of black liquor. Background Art

[0002] Currently, the pulp and paper industry still uses the traditional alkaline pulping process. During the pulping process, wood chips are cooked with alkali, resulting in a large amount of dark black cooking waste liquid, known as pulping black liquor. Black liquor contains a large amount of organic matter and sodium, making it a potential source of water pollution. The traditional black liquor treatment method in the pulping industry is to evaporate and concentrate the dilute black liquor to obtain a concentrated black liquor with a solids concentration of 50%-70%. This is then sent to a black liquor incinerator to burn and eliminate the water-polluting organic matter. At the same time, the sodium compounds in the black liquor are converted into molten sodium carbonate solids. The sodium carbonate solids are then dissolved in water to produce a sodium carbonate aqueous solution, which reacts with lime to regenerate sodium hydroxide and is recycled for wood chip cooking.

[0003] The traditional treatment method of pulping black liquor has the following shortcomings: 1) The production process is complex and the production efficiency is low. As mentioned above, the traditional concentration-combustion-lime alkalization process is used to treat black liquor, which has many production links, complex processes and low production efficiency. 2) The process consumes a lot of energy. In the process of treating black liquor, the evaporation and concentration process of dilute black liquor consumes a large amount of heating steam, which consumes a lot of energy. The evaporation energy consumption accounts for 21% of the energy consumption of the entire pulping plant. On the other hand, the black liquor combustion process consumes a certain amount of auxiliary fuel, which increases energy consumption. 3) A large amount of carbon dioxide is emitted. In the traditional alkali recovery reaction, a large amount of lime (20%-30%) is required. The lime used is generally regenerated by calcining the white mud produced during the alkalization reaction. The regenerated lime reaction and fuel combustion emit a large amount of carbon dioxide.

[0004] To improve production efficiency and economic benefits while reducing energy consumption and CO2 emissions, scientists have conducted a variety of research on the resource utilization of black liquor over the past five decades, particularly on black liquor gasification and its applications. These include: 1) Black liquor gasification to hydrogen: Using incomplete combustion of oxygen to gasify black liquor, hydrogen is produced, accounting for 41% of the total gas volume; using externally heated steam to gasify black liquor, hydrogen is produced, accounting for 67.1% of the total gas volume, both of which hold great promise for development. However, large-scale hydrogen production and transportation demand currently lacks, and hydrogen sales are limited, making it premature to pursue large-scale black liquor gasification for hydrogen production. 2) Black liquor gasification to synthesis gas and dimethyl ether (DME): Using black liquor gasification, black liquor is converted into carbon monoxide and hydrogen, which are then used as raw materials to synthesize dimethyl ether. This converts black liquor into high-value-added dimethyl ether liquid fuel while reducing CO2 emissions from the black liquor combustion process. From the 1980s to the first decade of this century, black liquor gasification and its applications were extensively researched, with the construction of several pilot production plants. Production trials for the combined synthesis of dimethyl ether (DME) from black liquor gasification were completed. However, the complex production process and high production equipment requirements resulted in high production costs, making it difficult to maintain normal production, and thus hindered widespread application. 3) Black liquor gasification combined with combustion power generation: Black liquor gasification is used to convert black liquor into a mixed fuel gas of hydrogen, carbon monoxide, and hydrocarbon molecules. The gasified gas then serves as fuel for a circulating power generation system, thereby improving the efficiency of power generation using black liquor as the raw fuel and indirectly reducing CO2 emissions. However, research has found that when air is used as a combustion aid in the black liquor gasification process, the black liquor gasified gas contains a large amount of nitrogen. This increases the compression power consumption of the high-pressure combustion chamber of the gas turbine, resulting in a decrease in the external power supply efficiency of the air-black liquor gasification combined power generation system. Using oxygen as a combustion aid in the black liquor gasification process prevents the presence of significant amounts of nitrogen in the black liquor gasification gas, thereby reducing power consumption by the compressor feeding the high-pressure combustion chamber of the gas turbine. However, the air separation oxygen production process consumes significant amounts of electricity, resulting in a reduced power supply efficiency of the black liquor gasification combined power generation system, to only 28.5%. Therefore, compared to traditional black liquor combustion combined with steam turbine power generation, the power supply efficiency of the oxygen-black liquor gasification combined cycle power generation system is not significantly improved, making it of little practical significance.

[0005] In summary, the hydrogen application market is limited, and the time has not yet come for large-scale black liquor gasification to produce hydrogen. The production cost of co-producing dimethyl ether with black liquor gasification is high, and the efficiency of external power supply from black liquor gasification and co-generation has not been significantly improved, making its application in production meaningless. Therefore, there is an urgent need to conduct theoretical and technical research to identify new black liquor gasification methods and new application paths that meet the needs of modern pulping companies. Summary of the Invention

[0006] To solve the above technical problems, the present invention provides a method for regenerating sodium hydroxide through spontaneous steam gasification of black liquor combined with a catalytic reaction. The new process for spontaneous steam gasification combined with a catalytic reaction and sodium hydroxide regeneration uses caustic soda pulping black liquor as raw material. In a gasification and catalytic reaction furnace, the black liquor is converted into sodium oxide in a single step; then, after hot water dissolution and a small amount of alkalization reaction, a sodium hydroxide mixed alkali liquor with a causticity of 65-80% suitable for wood chip cooking is obtained. Thus, the complex technical problems of traditional black liquor treatment and alkali recovery processes are solved, and the process plays an important role in promoting the improvement of pulping production efficiency and energy conservation and emission reduction, which is beneficial to improving the economic benefits of pulping production enterprises.

[0007] To achieve the above object, the technical solution adopted by the present invention is:

[0008] A method for regenerating sodium hydroxide by spontaneous steam gasification of black liquor combined with catalytic reaction, comprising the following steps:

[0009] S1. Pump the concentrated black liquor into a stirring liquid storage tank, add a catalyst, and mechanically stir and mix uniformly to obtain a mixed slurry of black liquor and catalyst;

[0010] S2. Start the diesel burner and supply air through the variable frequency blower to fully burn the diesel. When the temperature in the reactor reaches the first furnace temperature, use the black liquor sprayer to spray the mixed slurry obtained in step S1 into the reactor at a predetermined flow rate;

[0011] S3. When the mixed slurry is sprayed in, the air flow rate is increased to ensure stable combustion and gasification of the black liquor in the reactor. When the temperature in the reactor reaches the second furnace temperature, the diesel burner is turned off.

[0012] S4. Within the established black liquor flow rate range, the temperature in the reactor is controlled at the third furnace temperature, and the gasification and catalytic reaction are continued for more than 1 hour;

[0013] S5. The molten product accumulated in the inner cavity of the catalytic reaction layer is discharged from the reactor by gravity or vacuum absorption equipment. During the dissolution process in hot water, the sodium oxide in the melt reacts with water molecules to form a majority of sodium hydroxide. A small amount of calcium oxide in the melt also reacts with water molecules to form calcium hydroxide (slaked lime). Finally, the residual sodium carbonate component in the melt dissolves in water and reacts with calcium hydroxide to form a small amount of sodium hydroxide product. Thus, a sodium hydroxide mixed alkali solution with a causticization rate of 65-80% suitable for wood chip cooking is obtained.

[0014] Preferably, the catalyst is solid white mud or lime powder.

[0015] Preferably, the added amount of the catalyst is 2%-5% of the weight of the concentrated black liquor solids.

[0016] Preferably, the flow rate of each kilogram of diesel corresponds to an air flow rate of 28 to 32 cubic meters of air.

[0017] Preferably, the first furnace temperature is about 500°C.

[0018] Preferably, the second furnace temperature is about 650°C.

[0019] Preferably, the increasing of the air flow rate is to increase the air flow rate by 10 to 13 cubic meters of air per kilogram of the concentrated black liquor solids.

[0020] Preferably, in step S4, the furnace temperature is controlled by combining a temperature controller and a variable frequency blower to control the air flow rate according to the furnace temperature, thereby achieving furnace temperature control, and the third furnace temperature is 830-950°C.

[0021] Preferably, the gasification reaction refers to a gasification reaction between the cracking products produced by cracking the concentrated black liquor under high temperature conditions, the water vapor produced by the concentrated black liquor in the high temperature reactor, and the carbon dioxide produced by the combustion of the concentrated black liquor.

[0022] Preferably, the reaction equation of the water vapor generated by the concentrated black liquor in the high-temperature reactor is:

[0023] BL.H2O(l)→BL(s)+H2O(g) (1)

[0024] The reaction equation of the pyrolysis product produced by the pyrolysis of the concentrated black liquor under high temperature conditions is as follows:

[0025] Na-Lignin→Na2CO3+Na-O-C+CO↑+CO2↑+H2O↑+CH3OH↑ (2)

[0026] Cellulose→C+CO↑+CO2↑+H2O↑ (3)

[0027] Na-Acid→Na2CO3+CO↑+H2O↑ (4).

[0028] Preferably, the gasification reaction equation is as follows:

[0029] Na-O-C+H2O(g)→NaOH+CO+H2 (5)

[0030] C+H2O(g)→CO+H2 (6)

[0031] C+CO2→2 CO (7)

[0032] C+2H2→CH4 (8).

[0033] Preferably, the catalytic reaction refers to the sodium carbonate produced by the cracking of concentrated black liquor under high temperature conditions, which generates sodium oxide under the action of a catalyst, and then dissolves in water to generate sodium hydroxide. The equation of the catalytic reaction is as follows:

[0034]

[0035] Preferably, the molten product comprises sodium oxide, sodium carbonate and calcium oxide, and the equation for the composite reaction with water is:

[0036] Na2O+H2O→2NaOH (10)

[0037] CaO+H2O→Ca(OH) (11)

[0038] The equation of the alkalization reaction is:

[0039] Na2CO3+Ca(OH)2→2NaOH+CaCO3(white mud) (12).

[0040] The principles of the present invention are as follows:

[0041] (1) The principle of black liquor cracking to produce sodium carbonate:

[0042] Black liquor contains organic sodium acids (Na-Acid) such as sodium formate and sodium oxalate, which decompose at high temperatures to produce sodium carbonate, carbon monoxide and water.

[0043] (2) Principle of sodium lignin cracking to form carbon-sodium complex:

[0044] During the cracking process of sodium lignin (Na-Lignin) in black liquor, gaseous substances such as carbon monoxide, carbon dioxide and water are decomposed, and only carbonized solids containing carbon elements and inorganic sodium ions are retained in the residual solids. This solid is difficult to dissolve in water, and it is difficult to separate carbon particles and sodium ions by water dissolution. Therefore, the solid product of sodium lignin cracking is defined as a carbon-sodium complex.

[0045] (3) Principle of gasification reaction between high temperature water vapor and carbon sodium complex:

[0046] Based on the principle that charcoal can undergo gasification reaction with high-temperature water vapor, experiments have confirmed that carbon-sodium complex can react with water vapor to produce sodium hydroxide, hydrogen, carbon monoxide and water.

[0047] (4) The principle of white mud or calcium oxide catalyzing the conversion of sodium carbonate into sodium hydroxide:

[0048] White mud is calcium carbonate powder. The principle of calcium carbonate catalyzing the sodium carbonate reaction is that calcium oxide catalyzes the sodium carbonate reaction. Calcium carbonate decomposes under high temperature conditions to produce calcium oxide, while the principle of calcium oxide catalyzing the sodium carbonate reaction is that under high temperature conditions, calcium oxide and sodium carbonate undergo a double decomposition reaction to produce sodium oxide and calcium carbonate products; then, under high temperature conditions, calcium carbonate molecules decompose into calcium oxide and carbon dioxide. The cycle of these two reactions promotes the continuous conversion of sodium carbonate into sodium hydroxide. The reaction equation is expressed as:

[0049] Na2CO3+CaO→Na2O+CaCO3 (13)

[0050] CaCO3→CaO+CO2↑ (14)

[0051] Combining equations (9) and (10), we get the total equation

[0052]

[0053] During the water dissolution stage, the melt (mainly sodium oxide, with a small amount of residual sodium carbonate and calcium oxide) is dissolved in hot water. First, solid sodium oxide reacts with water to form sodium hydroxide. Simultaneously, the added calcium carbonate decomposes at high temperature to form calcium oxide, or the solid catalyst of the originally added calcium oxide powder reacts with water to form slaked lime. Next, the slaked lime generated by the reaction and the residual sodium carbonate that has been dissolved by water undergo an alkalization reaction, generating a small amount of new white mud and adding a portion of sodium hydroxide product, thereby increasing the causticity of the mixed alkali solution to a sodium hydroxide mixed alkali solution with a causticity of 65-80% suitable for wood chip cooking. The reaction equation is expressed as:

[0054] Na2O+H2O→2NaOH (10)

[0055] CaO+H2O→Ca(OH)2 (11)

[0056] Na2CO3+Ca(OH)2→2NaOH+CaCO3(white mud) (12).

[0057] Compared with the prior art, the present invention has the following beneficial effects:

[0058] This invention proposes a novel concept for producing a molten mixture of sodium oxide, calcium oxide, and sodium carbonate from soda pulping black liquor through spontaneous steam vaporization combined with a catalytic reaction. This mixture is then dissolved in hot water and subjected to a minor alkalization reaction to produce a sodium hydroxide solution suitable for wood chip cooking, broadening the application of black liquor gasification. This invention achieves the chemical conversion of black liquor to sodium oxide within a single reactor. Subsequently, through hot water dissolution and a minor alkalization reaction, an alkali liquor with a suitable causticity for wood chip cooking is obtained. This eliminates the three production steps required for traditional black liquor treatment and alkali recovery: black liquor combustion, lime-based alkali recovery, and lime regeneration. This method effectively improves black liquor treatment efficiency, reduces energy consumption during the pulping process, and reduces equipment investment and production costs for pulping companies, ultimately improving their economic benefits. Furthermore, through the catalytic reaction, the causticity of the resulting mixed alkali reaches 65% to 80.7%, meeting the causticity required for wood chip cooking. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 This is a flow chart of a method for regenerating sodium hydroxide by spontaneous steam gasification of black liquor combined with catalytic reaction according to the present invention;

[0060] Figure 2 This is a schematic diagram of the process flow of a device for regenerating sodium hydroxide by spontaneous steam gasification of black liquor combined with catalytic reaction;

[0061] Figure 3 Schematic diagram of the reaction process for preparing sodium hydroxide by spontaneous steam gasification of black liquor combined with catalytic reaction of the present invention;

[0062] Figure 4 Schematic diagram of the reaction mechanism of the present invention in which white mud and calcium oxide catalyze the decomposition of sodium carbonate. DETAILED DESCRIPTION

[0063] In the present invention, unless otherwise specified, the scientific and technical terms used herein have the meanings commonly understood by those skilled in the art.

[0064] The term "black liquor" in this article refers to the use of alkali solution to cook wood chips during the pulping process, which results in a large amount of cooking waste liquid. This waste liquid is dark black in color and contains a large amount of sodium lignin and other organic acid sodium compounds, called black liquor.

[0065] As used herein, the term "strong black liquor" refers to a black liquor concentrate containing approximately 30% to 50% water and 50% to 70% bone dry solids.

[0066] It should be noted here that the different pulping fiber raw materials and cooking processes lead to certain differences in the composition of pulping black liquor. Generally, the absolute dry solids of black liquor contain about 38%-45% sodium lignin, 8%-18% sodium organic acid (including sodium formate, sodium oxalate, sodium phenylpropionate and sodium hexenuronate, etc.), 5%-12% dissolved sugars (including glucose and its oligomers produced by fiber dissolution, and various pentoses produced by hemicellulose hydrolysis) and about 13%-20% fine cellulose, as well as 4%-10% inorganic components (including residual sodium hydroxide, sodium carbonate and sodium chloride, etc.).

[0067] The term "black liquor gasification" herein refers to a chemical reaction process in which black liquor undergoes a cracking reaction at high temperature using methods such as partial combustion gasification with oxygen (or air) and steam gasification to produce a solid mixture of charcoal, sodium carbonate, and sodium hydroxide, and a mixed fuel gas containing hydrogen, carbon monoxide, carbon dioxide, and other hydrocarbon gas molecules.

[0068] The term "spontaneous steam gasification of black liquor" herein refers to a chemical reaction process in which the water content of concentrated black liquor is fully utilized. Under high temperature conditions, the water content in the concentrated black liquor evaporates to generate water vapor. Subsequently, the spontaneously generated water vapor acts as a gasifying agent to promote the gasification reaction of the black liquor to produce charcoal and a carbon-sodium complex, as well as a solid mixture of sodium carbonate and sodium hydroxide. At the same time, a mixed fuel gas containing hydrogen, carbon monoxide and other hydrocarbon gas molecules is generated.

[0069] The term "regenerated sodium hydroxide" herein refers to NaOH generated by converting sodium-containing organic and inorganic substances in black liquor through a special process.

[0070] The term "traditional black liquor alkali recovery" herein refers to the process of concentrating dilute black liquor to a solids content of 50%-70% using a multi-effect concentrating evaporator. The black liquor is then burned at high temperature, converting organic matter in the black liquor into heat energy and melting inorganic matter into a molten material (primarily containing Na2CO3 and Na2S). The molten material is dissolved in water to form green liquor, to which lime milk (Ca(OH)2) is added for a causticizing reaction, producing white liquor (a NaOH+Na2S mixture) and white mud (CaCO3 precipitate). The white mud is then calcined to regenerate quicklime (CaO) for reuse in the causticizing process, achieving calcium oxide recycling.

[0071] The term "white mud" in this article refers to the calcium carbonate precipitate generated by the alkaline reaction between the green liquor (sodium carbonate aqueous solution) produced after the combustion of black liquor and slaked lime during the alkali recovery process of the paper mill. After filtration and separation, a solid in the shape of white mud is obtained, the main component of which is calcium carbonate.

[0072] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0073] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0074] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0075] like Figure 1 As shown, the present invention provides a method for regenerating sodium hydroxide by spontaneous steam gasification of black liquor combined with catalytic reaction, comprising the following steps:

[0076] S1. Pumping concentrated black liquor with a solid content of 50%-70% into a stirring liquid storage tank, adding solid white mud or lime powder as a catalyst at a weight of 2%-5% of the solid content of the concentrated black liquor, and mechanically stirring and mixing to obtain a mixed slurry of black liquor and catalyst.

[0077] S2. Turn on the diesel burner and supply air via a variable frequency blower at a rate of 28 to 32 cubic meters of air per kilogram of diesel flow rate to ensure full combustion of the diesel. When the temperature in the reactor reaches approximately 500° C. (the first furnace temperature), a black liquor sprayer is used to spray the mixed slurry obtained in step S1 into the reactor at a predetermined flow rate.

[0078] It should be noted here that the established flow rate refers to the concentrated black liquor flow rate during treatment, which is determined according to production requirements and furnace size. This is because the actual processing volume of concentrated black liquor is related to the size of the gasifier, and different gasifiers correspond to certain concentrated black liquor flow rates.

[0079] S3. When the mixed slurry is injected, the air flow rate is increased by 10-13 cubic meters of air flow per kilogram of concentrated black liquor solids to ensure stable combustion of the black liquor, increase the combustion and gasification reactions in the reactor, and further increase the furnace temperature. When the temperature in the reactor reaches 650°C (the second furnace temperature), turn off the diesel burner and stop burning diesel.

[0080] S4. Within the established black liquor flow range, the temperature controller and variable frequency blower are combined to control the air flow rate by the furnace temperature, so that the temperature in the reaction furnace rises to 900℃ and is controlled within the range of 830-950℃. The gasification and catalytic reaction in the furnace temperature continues for more than 1 hour.

[0081] It should be noted here that the black liquor undergoes four stages in the reactor: evaporation and drying, high-temperature cracking, gasification and catalytic reaction.

[0082] The first stage is the black liquor evaporation stage: in a high-temperature combustion furnace, concentrated black liquor containing 30%-50% water evaporates and dries to form black liquor solid (commonly known as black ash).

[0083] BL.H2O(l)→BL(s)+H2O(g) (1)

[0084] The second stage is the high-temperature cracking of black liquor: In a high-temperature furnace, the solid black liquor is heated to about 200-400°C, and the sodium lignin (Na-Lignin), organic sodium acid (Na-Acid), and residual cellulose (Cellulose) in the black liquor undergo cracking reactions to produce sodium carbonate and sodium carbonate complexes, as well as volatile gases such as CO, CO2, and CH3OH. The chemical reaction equation for the black liquor pyrolysis stage is:

[0085] Na-Lignin→Na2CO3+Na-O-C+CO↑+CO2↑+H2O↑+CH3OH↑ (2)

[0086] Cellulose→C+CO↑+CO2↑+H2O↑ (3)

[0087] Na-Acid→Na2CO3+CO↑+H2O↑ (4)

[0088] The third stage is the gasification stage: within the high-temperature reactor, the water vapor generated in the first stage reacts with the carbon-oxygen-sodium complex gas produced by the black liquor cracking in the second stage to produce sodium hydroxide, carbon monoxide, and hydrogen. Simultaneously, the charcoal produced by cracking reacts with the water vapor and carbon dioxide produced by combustion, respectively, to produce hydrogen and carbon monoxide. Simultaneously, the hydrogen generated in the gasification stage reacts with the charcoal to produce methane, achieving the goal of gasifying the black liquor to produce synthesis gas. (In this stage, in the absence of a catalyst, the concentrated black liquor undergoes cracking and gasification reactions within the gasification reactor to produce a mixed base of sodium hydroxide and sodium carbonate, with a causticity ranging from 48.6% to 50.7%.) The chemical reaction equation for the black liquor gasification stage is:

[0089] Na-O-C+H2O(g)→NaOH+CO+H2 (5)

[0090] C+H2O(g)→CO+H2 (6)

[0091] C+CO2→2 CO (7)

[0092] C+2H2→CH4 (8)

[0093] The fourth stage is the catalytic reaction stage: under the catalytic action of white mud or calcium oxide, the sodium carbonate is further converted into sodium hydroxide. After dissolution in hot water and additional alkalization reaction, the causticity of the mixed lye is increased to 65%-80.7%.

[0094] Na2CO3+CaO→Na2O+CaCO3 (13)

[0095] CaCO3→CaO+CO2↑ (14)

[0096] Combining equations (13) and (14), we get the total equation:

[0097]

[0098] S5. When the molten product accumulated in the inner cavity of the catalytic reaction layer reaches the discharge height, the molten product is discharged from the reactor by gravity or vacuum absorption equipment. The molten material (mainly sodium oxide, with a small amount of residual sodium carbonate and calcium oxide) dissolves in hot water, and the following three chemical reactions occur: First, the sodium oxide solid reacts with water to form sodium hydroxide; at the same time, the calcium oxide reacts with water to form calcium hydroxide (slaked lime); then, the slaked lime generated by the reaction and the residual sodium carbonate dissolved by water undergo an alkalization reaction, increasing a portion of the sodium hydroxide product and improving the causticity of the mixed alkali solution to a sodium hydroxide mixed alkali solution with a causticity of 65-80% suitable for wood chip cooking; at the same time, a small amount of new white mud is generated. The reaction equation is expressed as:

[0099] Na2O+H2O→2NaOH (10)

[0100] CaO+H2O→Ca(OH)2 (11)

[0101] Na2CO3+Ca(OH)2→2NaOH+CaCO3(white mud) (12)

[0102] The pilot test of producing sodium hydroxide based on spontaneous steam gasification and catalytic reaction of black liquor from caustic soda pulping was successful. Figure 2 As shown, the present invention has constructed a pilot-scale reactor with a height of 4.5 meters and an outer diameter of 1.38 meters. It is equipped with auxiliary equipment such as a black liquor sprayer, a diesel burner, a blower, and an exhaust fan, capable of processing 500 kilograms of concentrated black liquor per hour. The following, combined with examples, further describes in detail the present invention's method for regenerating sodium hydroxide through spontaneous steam gasification of black liquor combined with a catalytic reaction.

[0103] Example 1:

[0104] Weigh 2 kg of white mud catalyst and mix it evenly with 100 kg of concentrated black liquor containing solids. Then, spray it into the reactor when the temperature reaches approximately 500°C. Increase the air flow until the furnace temperature reaches 650°C, then stop burning the fuel. The gasifier temperature is 850°C, spray the concentrated black liquor continuously for 20 minutes, and maintain the reaction temperature at 850°C for 60 minutes. Titration with 0.1 M hydrochloric acid yields a causticity of 67.3% in the resulting sodium hydroxide mixed solution.

[0105] Example 2:

[0106] 3 kg of white mud catalyst was weighed and mixed evenly with 100 kg of concentrated black liquor containing solids. The mixture was then sprayed into the reactor when the temperature reached approximately 500°C. The air flow was increased until the furnace temperature reached 650°C, at which point fuel combustion was stopped. The gasifier temperature was set at 900°C, and the concentrated black liquor was continuously sprayed for 20 minutes. The reaction temperature was maintained at 900°C for 60 minutes. The causticity of the resulting sodium hydroxide mixed solution reached 72.3% by titration with 0.1M hydrochloric acid.

[0107] Example 3:

[0108] Weigh 5 kg of white mud catalyst and mix it evenly with 100 kg of concentrated black liquor containing solids. Then, spray it into the reactor when the temperature reaches approximately 500°C. Increase the air flow until the furnace temperature reaches 850°C, then stop burning the fuel. The gasifier temperature is set at 900°C, spray the concentrated black liquor continuously for 20 minutes, and maintain the reaction temperature at 850°C for 60 minutes. Titration with 0.1 M hydrochloric acid yields a causticity of 80.7% in the resulting sodium hydroxide mixed solution.

[0109] Comparative Example 1:

[0110] In this comparative example, except that no catalyst was added, other parameters were the same as those in Example 1. The causticity of the obtained sodium hydroxide mixed alkali solution reached 48.6% by titration with 0.1 M hydrochloric acid.

[0111] Comparative Example 2:

[0112] In this comparative example, except that 1 kg of catalyst was added, other parameters were the same as those in Example 1. The causticity of the obtained sodium hydroxide mixed alkali solution reached 56.7% by titration with 0.1 M hydrochloric acid.

[0113] Comparative Example 3:

[0114] In this comparative example, except that 7 kg of catalyst was added, other parameters were the same as those in Example 1. The causticity of the obtained sodium hydroxide mixed alkali solution reached 85.1% by titration with 0.1 M hydrochloric acid.

[0115] Titration analysis of the solid products in Examples 1-3 confirmed that the solid products obtained contained both sodium carbonate and sodium hydroxide, with the sodium hydroxide content accounting for 67.3% to 80.7% of the total alkali content. This indicates that when the catalyst dosage ranged from 2% to 5%, the causticity of the sodium hydroxide mixture obtained through spontaneous steam gasification met the causticity required for wood chip cooking.

[0116] By comparing Example 1 with Comparative Example 1, it can be seen that when there is no catalyst, the causticity of the sodium hydroxide mixed alkali obtained through spontaneous water vapor gasification reaction in the gasifier body is only 48.6%, which can be used for cooking wood chips. However, the pulp hardness is relatively high, which affects the pulp quality to a certain extent.

[0117] By comparing Example 1 with Comparative Example 2, it can be seen that when the catalyst dosage is less than 2%, the catalytic reaction effect is poor, and the sodium hydroxide mixed alkali produced after gasification cannot reach a causticity of 65%.

[0118] Comparing Example 1 with Comparative Example 3 shows that when the catalyst dosage exceeds 5%, the catalytic reaction is more effective, and the causticity exceeds 80%, exceeding the causticity required for wood chip cooking and affecting the wood chip cooking effect. More importantly, increasing the amount of white mud and lime powder catalyst increases the viscosity of the concentrated black liquor, seriously affecting the operation of the black liquor spray gun. Therefore, a catalyst dosage of 2%-5% is selected.

[0119] Of course, the present invention may have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art may of course make various corresponding changes and modifications based on the present invention, but these corresponding changes and modifications should all fall within the scope of protection of the claims attached to the present invention.

Claims

1. A method for regenerating sodium hydroxide by spontaneous steam gasification of black liquor combined with catalytic reaction, characterized in that: The following steps are involved: S1. Pump the concentrated black liquor into a stirring liquid storage tank, add a catalyst, and mechanically stir and mix uniformly to obtain a mixed slurry of black liquor and catalyst; S2. Start the diesel burner and supply air through the variable frequency blower to fully burn the diesel. When the temperature in the reactor reaches the first furnace temperature, use the black liquor sprayer to spray the mixed slurry obtained in step S1 into the reactor at a predetermined flow rate; S3. When the mixed slurry is sprayed in, the air flow rate is increased to ensure stable combustion and gasification of the black liquor in the reactor. When the temperature in the reactor reaches the second furnace temperature, the diesel burner is turned off. S4. Within the established black liquor flow rate range, the furnace temperature is controlled at the third furnace temperature, and the gasification and catalytic reaction are continued for more than 1 hour; S5. The molten product is discharged from the reactor, part of the molten product is dissolved in hot water to undergo hydration reaction, and the other part undergoes alkalization reaction to obtain a sodium hydroxide mixed alkali solution with a causticization rate of 65-80% suitable for wood chip cooking.

2. The method for regenerating sodium hydroxide by spontaneous steam gasification of black liquor combined with catalytic reaction according to claim 1, characterized in that: The catalyst is one or more of white mud and lime powder.

3. The method for regenerating sodium hydroxide by spontaneous steam gasification of black liquor combined with catalytic reaction according to claim 1, characterized in that: The added amount of the catalyst is 2%-5% of the weight of the concentrated black liquor fixed material.

4. The method for regenerating sodium hydroxide by spontaneous steam gasification of black liquor combined with catalytic reaction according to claim 1, characterized in that: Each kilogram of the diesel fuel corresponds to an air flow rate of 28 to 32 cubic meters of air.

5. The method for regenerating sodium hydroxide by spontaneous steam gasification of black liquor combined with catalytic reaction according to claim 1, characterized in that: The first furnace temperature is about 500°C.

6. The method for regenerating sodium hydroxide by spontaneous steam gasification of black liquor combined with catalytic reaction according to claim 1, characterized in that: The second furnace temperature is about 650°C.

7. The method for regenerating sodium hydroxide by spontaneous steam gasification of black liquor combined with catalytic reaction according to claim 1, characterized in that: The air flow rate is increased by 10 to 13 cubic meters of air per kilogram of the concentrated black liquor solids.

8. The method for regenerating sodium hydroxide by spontaneous steam gasification of black liquor combined with catalytic reaction according to claim 1, characterized in that: In step S4, the furnace temperature is controlled by combining a temperature controller and a variable frequency blower to control the air flow rate according to the furnace temperature, thereby achieving furnace temperature control. The third furnace temperature is 830-950°C.

9. The method for regenerating sodium hydroxide by spontaneous steam gasification of black liquor combined with catalytic reaction according to claim 2, characterized in that: The gasification reaction refers to the gasification reaction of the cracking products produced by the cracking of the concentrated black liquor under high temperature conditions, the water vapor produced by the concentrated black liquor in the high temperature reactor, and the carbon dioxide produced by the combustion of the concentrated black liquor.

10. The method for regenerating sodium hydroxide by spontaneous steam gasification of black liquor combined with catalytic reaction according to claim 9, characterized in that: The equation for the reaction of the water vapor generated by the concentrated black liquor in the high-temperature reactor is: BL.H2O(l)→BL(s)+H2O(g) (1) The reaction equation of the pyrolysis product produced by the pyrolysis of the concentrated black liquor under high temperature conditions is as follows: Na-Lignin→Na2CO3+Na-O-C+CO↑+CO2↑+H2O↑+CH3OH↑ (2) Cellulose→C+CO↑+CO2↑+H2O↑ (3) Na-Acid→Na2CO3+CO↑+H2O↑ (4).

11. The method for regenerating sodium hydroxide by spontaneous steam gasification of black liquor combined with catalytic reaction according to claim 10, characterized in that: The equation for the gasification reaction is as follows: Na-O-C+H2O(g)→NaOH+CO+H2 (5) C+H2O(g)→CO+H2 (6) C+CO2→2CO (7) C+2H2→CH4 (8).

12. The method for regenerating sodium hydroxide by spontaneous steam gasification of black liquor combined with catalytic reaction according to claim 11, characterized in that: The catalytic reaction refers to the sodium carbonate produced by the cracking of concentrated black liquor under high temperature conditions to generate sodium oxide under the action of a catalyst, which is then dissolved in water to generate sodium hydroxide. The equation of the catalytic reaction is as follows:

13. The method for regenerating sodium hydroxide by spontaneous steam gasification of black liquor combined with catalytic reaction according to claim 12, characterized in that: The molten product includes sodium oxide, sodium carbonate and calcium oxide, and the equation of the hydration reaction is: Na2O+H2O→2NaOH (10) CaO+H2O→Ca(OH)2 (11) The equation of the alkalization reaction is: Na2CO3+Ca(OH)2→2NaOH+CaCO3(white mud) (12).

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