CN111287011A - A method for comprehensive recycling and utilization of pulping waste liquid - Google Patents

Abstract

The invention discloses a method for comprehensive recycling and utilization of pulping waste liquor. First, dilute black liquor is extracted from pulping and cooking liquor, then the dilute black liquor is pretreated, and finally the pretreated pulp is treated by a mixed-flow indirect evaporation method. The dilute black liquor is evaporated and concentrated; then it is burned in a jet furnace, the high temperature flue gas generated by the combustion of the organic matter in the black liquor rises in the furnace, and the inorganic matter melts from the chute below the combustion furnace into the dissolving tank, and dissolves in the dilute white liquor or The green liquor is formed in the water, and the components of the green liquor include Na ₂ CO ₃ and Na ₂ S; the green liquor formed by dissolving the inorganic melt in dilute white liquor or water is subjected to the causticization reaction; finally, the products produced by the causticization reaction of the green liquor are for recycling. The invention solves the problems of serious pollution and difficult treatment of pulp and papermaking wastewater existing in the prior art.

Description

A method for comprehensive recycling and utilization of pulping waste liquid

technical field

The invention belongs to the technical field of waste liquid treatment, and in particular relates to a method for comprehensive recycling and utilization of pulping waste liquid.

Background technique

The pulp and paper industry is a traditional large water user and one of the important sources of water pollution. With the development of economy, enterprises are increasingly faced with the problem of water shortage and raw material shortage. On the other hand, water pollution is becoming more and more serious. At present, the discharge of wastewater and COD from the pulp and paper industry in China ranks first in the discharge of various industries in my country. Therefore, in order to prevent the pollutants in the pulp and paper waste liquid from causing damage to my country's environment, the pulp and paper waste liquid Processing has become an essential link.

The pulping waste liquor refers to the cooking waste liquor produced by chemical pulping and the waste water produced in the pulp washing and bleaching process. my country's pulping method is mainly based on alkaline cooking, and its solids can be divided into inorganic and organic substances. It is the residual chemicals in the cooking waste liquid, as well as the metal salt base that is combined with the organic matter in the pulping raw material, and the inorganic components brought by the pulping raw material itself, such as silicon compounds; the organic matter mainly includes the pulping raw material in the cooking process. Degradation products, leachables, etc., such as lignin, cellulose, hemicellulose, starch, resin, pigment and organic acid, etc. The purpose of pulp washing is to maximize the extraction of black liquor and improve the recovery rate of chemicals. A small amount of washing water is brown-black and has a high concentration of organic pollutants. Bleaching is carried out in a multi-stage process and uses different bleaching agents. This section is the main source of wastewater discharged from the factory, which is toxic and difficult to handle.

The discharge of waste liquid into rivers not only seriously affects the pollution of water sources, but also causes a lot of waste of resources. How to eliminate the pollution of pulp and papermaking wastewater and make use of the precious resources in the wastewater is a work of great social significance and economic value, which should be paid attention to.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a method for comprehensive recycling and utilization of pulping waste liquid, which solves the problems of serious pollution and difficult treatment of pulping and papermaking waste water in the prior art.

The technical scheme adopted in the present invention is, a method for comprehensive recycling and utilization of pulping waste liquid, which is specifically implemented according to the following steps:

Step 1. Extract the dilute black liquor from the pulping and cooking liquor, then pretreat the dilute black liquor, and finally adopt the mixed-flow indirect evaporation method to evaporate and concentrate the pretreated dilute black liquor;

Step 2. The black liquor concentrated in step 1 is burned in a jet furnace. The high-temperature flue gas generated by the combustion of the organic matter in the black liquor rises in the furnace, and the inorganic matter melts from the chute below the combustion furnace into the dissolving tank, and dissolves. Form green liquor in dilute white liquor or water, and the components of green liquor include Na ₂ CO ₃ and Na ₂ S;

Step 3, causticizing the green liquor formed by the inorganic melt dissolved in dilute white liquor or water;

Step 4: Recycling the product produced by the causticization reaction of the green liquor.

The present invention is also characterized in that,

The dilute black liquor extracted in step 1 is composed of 70% combustible organic matter and 30% inorganic matter. The inorganic matter includes the residual chemicals in the cooking waste liquor, such as NaOH, Na ₂ S, and the raw materials for pulping. The metal salt base of organic compounds and the inorganic components brought by the pulping raw material itself.

In step 1, the pretreatment of the dilute black liquor includes slag removal, oxidation and silicon removal. The slag removal is to remove the fine fibers and various residues contained in the black liquor; the oxidation is to oxidize Na ₂ S in the black liquor to stable Na ₂ SO ₄ and Na ₂ S ₂ O ₃ , the specific reaction is: 2Na ₂ S+2O ₂ +H ₂ O=Na ₂ S ₂ O ₃ +2NaOH, Na ₂ S+2O ₂ =Na ₂ SO ₄ ; Using the bauxite desilicon method, an appropriate amount of bauxite is added to the black liquor before combustion, and the sodium aluminate formed during the combustion process reacts with sodium silicate in the green liquor to form a sodium aluminosilicate complex precipitate. and removed.

In step 1, the pretreated dilute black liquor is evaporated and concentrated, specifically: firstly adopting mixed-flow heating, during the heating process, the concentration of water vaporization escapes is concentrated to 45% to 48%, and then the waste heat of flue gas is used to heat and concentrate to the concentration value 50% to 65%.

Step 2 is implemented according to the following steps:

Step 2.1, the first stage: when the black liquor entering the furnace is further dried to a concentration of 85% under the action of the hot furnace gas, black ash is formed, and the SO ₂ , SO ₃ and CO ₂ contained in the flue gas and the black liquor The active alkali and organically bound sodium react chemically; the free NaOH and most of Na ₂ S in the black liquor are transformed into Na ₂ CO ₃ , Na ₂ SO ₃ , Na ₂ SO ₄ and Na ₂ S ₂ O ₃ ;

Step 2.2, the second stage: the last remaining water of the black ash is gradually evaporated. When the temperature rises rapidly to 350℃～450℃, the organic matter is rapidly decomposed into CH ₃ OH, CH ₃ COOH, CH ₃ SH, H ₂ S , phenol, low molecular aldehyde acid and complex structure of alkyl sulfide organic gas, and mixed with the secondary air and tertiary air entering the furnace, gas-phase combustion occurs to generate SO ₂ , SO ₃ , CO, H ₂ O, H ₂ S gas; a part of the organic matter is carbonized and becomes elemental carbon for the reduction of mirabilite; in addition, the sodium compound formed by combining with the organic matter also undergoes a decomposition reaction to generate Na ₂ CO ₃ ;

In order to fully burn the black ash under reducing conditions, the air entering the furnace needs to be preheated to 140-150 °C, the primary air is added in the reduction area of the combustion furnace, and the secondary air is added above the reduction area and near the injection inlet of the black liquor, three times. The air is added above the black liquor spray gun. The air volume distribution ratio of the primary, secondary and tertiary air is roughly 50:20:30, the primary air pressure is 0.8~1.2KPa, and the secondary and tertiary air pressure is 1.5~3KPa.

Step 2.3, the third stage: the inorganic matter is melted at high temperature, and then mirabilite is added at the same time.

Step 3 is implemented according to the following steps:

Step 3.1, clarify the green liquor in the dissolving tank, remove the insoluble impurity green mud, then wash and precipitate the remaining crude green mud to recover the green liquor entrained in the green mud;

Step 3.2, the clarified green liquor and the green liquor entrained in the green mud are digested, the specific reaction is CaO+H ₂ O=Ca(OH) ₂ , and the feeding time is controlled at 60-130min, in order to further improve the causticizing efficiency , CaO needs to be ground, and the particle size is controlled to 3-4 μm;

Step 3.3. The initial causticized emulsion formed after lime digestion enters the separator, and after removing the undigested lime residue, it is sent to the continuous causticizer system for causticization. The specific reaction is Ca(OH) ₂ +Na ₂ CO ₃ = CaCO ₃ ↓+2NaOH;

Step 3.4, the concentrated white liquor from the continuous causticizer system is sent to the white liquor clarifier to remove the white mud in the white liquor;

Step 3.5. After further filtration treatment, the clarified white liquor is sent to the concentrated white liquor tank, and then sent to the cooking section. The white mud from the white liquor filtration equipment is sent to the white mud scrubber for dilution, washing and mixing with hot water. Afterwards, dilute white liquor and white mud emulsion are obtained;

In step 3.6, the dilute white liquor and white mud emulsion are sent to the centrifuge system for processing, part of the dilute white liquor is recovered again, and the white mud is sent to the white mud treatment system.

Step 4 is implemented according to the following steps:

Step 4.1, after the lime mud from the causticization section of the step 3 is sent into the calciner, evaporate and dry under the effect of high temperature furnace gas and form granular white mud;

Step 4.2. The dried white mud is further preheated to 600°C, and CaCO ₃ begins to decompose; then the white mud is heated to 825° C. At this time, CaCO ₃ begins to decompose rapidly, that is, it enters the calcination section to generate recyclable CaO. The reaction is: CaCO ₃ =CaO+CO ₂ ↑.

The beneficial effect of the present invention is that, in a method for comprehensive recycling and utilization of pulping waste liquor, dilute black liquor is extracted from pulping and cooking liquor, undergoes pretreatment stages such as slag removal, oxidation, and silicon removal, and then passes through plate type falling film evaporation. It is evaporated and concentrated in the device, and the soap is removed to recover the tall oil, and then sent to the jet furnace for combustion. Finally, the caustic soda is recovered through the causticization of the green liquor, and the slaked lime used in the causticization stage is recycled, so as to complete the recovery of the black liquor of the papermaking waste liquor. use. The optimized process for recycling and utilizing pulping waste liquid provided by the present invention has a more refined process, and through the optimized process, the defects such as heavy pollution, low recovery efficiency and low safety factor of traditional papermaking waste liquid in the treatment and recycling are effectively eliminated, and the The purpose of reducing production costs and recycling chemicals.

Description of drawings

Fig. 1 is a flow chart of a method for comprehensive recycling and utilization of pulping waste liquid according to the present invention.

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

A method for comprehensive recycling and utilization of pulping waste liquid of the present invention, the flowchart is shown in Figure 1, and is specifically implemented according to the following steps:

Step 1. Extract the dilute black liquor from the pulping and cooking liquor, then pretreat the dilute black liquor, and finally adopt the mixed-flow indirect evaporation method to evaporate and concentrate the pretreated dilute black liquor;

The dilute black liquor extracted in step 1 is composed of 70% combustible organic matter and 30% inorganic matter. The inorganic matter includes the residual chemicals in the cooking waste liquor, such as NaOH, Na ₂ S, and the raw materials for pulping. The metal salt base of organic compounds and the inorganic components brought by the pulping raw material itself.

In step 1, the pretreatment of the dilute black liquor includes slag removal, oxidation and silicon removal. The slag removal is to remove the fine fibers and various residues contained in the black liquor; the oxidation is to oxidize Na ₂ S in the black liquor to stable Na ₂ SO ₄ and Na ₂ S ₂ O ₃ , the specific reaction is: 2Na ₂ S+2O ₂ +H ₂ O=Na ₂ S ₂ O ₃ +2NaOH, Na ₂ S+2O ₂ =Na ₂ SO ₄ ; Using the bauxite desilicon method, an appropriate amount of bauxite is added to the black liquor before combustion, and the sodium aluminate formed during the combustion process reacts with sodium silicate in the green liquor to form a sodium aluminosilicate complex precipitate. and removed.

In step 1, the pretreated dilute black liquor is evaporated and concentrated, specifically: firstly adopting mixed-flow heating, during the heating process, the concentration of water vaporization escapes is concentrated to 45% to 48%, and then the waste heat of flue gas is used to heat and concentrate to the concentration value 50% to 65%.

Step 2. The black liquor concentrated in step 1 is burned in a jet furnace. The high-temperature flue gas generated by the combustion of the organic matter in the black liquor rises in the furnace, and the inorganic matter melts from the chute below the combustion furnace into the dissolving tank, and dissolves. Form green liquor in dilute white liquor or water, and the components of green liquor include Na ₂ CO ₃ and Na ₂ S;

Step 2 is implemented according to the following steps:

Step 2.1, the first stage: when the black liquor entering the furnace is further dried to a concentration of 85% under the action of the hot furnace gas, black ash is formed, and the SO ₂ , SO ₃ and CO ₂ contained in the flue gas and the black liquor The active alkali and organically bound sodium react chemically; the free NaOH and most of Na ₂ S in the black liquor are transformed into Na ₂ CO ₃ , Na ₂ SO ₃ , Na ₂ SO ₄ and Na ₂ S ₂ O ₃ ;

Step 2.2, the second stage: the last remaining water of the black ash is gradually evaporated. When the temperature rises rapidly to 350℃～450℃, the organic matter is rapidly decomposed into CH ₃ OH, CH ₃ COOH, CH ₃ SH, H ₂ S , phenol, low molecular aldehyde acid and complex structure of alkyl sulfide organic gas, and mixed with the secondary air and tertiary air entering the furnace, gas-phase combustion occurs to generate SO ₂ , SO ₃ , CO, H ₂ O, H ₂ S gas; a part of the organic matter is carbonized and becomes elemental carbon for the reduction of mirabilite; in addition, the sodium compound formed by combining with the organic matter also undergoes a decomposition reaction to generate Na ₂ CO ₃ ;

In order to fully burn the black ash under reducing conditions, the air entering the furnace needs to be preheated to 140-150 °C, the primary air is added in the reduction area of the combustion furnace, and the secondary air is added above the reduction area and near the injection inlet of the black liquor, three times. The air is added above the black liquor spray gun. The air volume distribution ratio of the primary, secondary and tertiary air is roughly 50:20:30, the primary air pressure is 0.8~1.2KPa, and the secondary and tertiary air pressure is 1.5~3KPa.

Step 2.3, the third stage: the inorganic matter is melted at high temperature, and then mirabilite is added at the same time.

Step 3, causticizing the green liquor formed by the inorganic melt dissolved in dilute white liquor or water;

Step 3 is implemented according to the following steps:

Step 3.1, clarify the green liquor in the dissolving tank, remove the insoluble impurity green mud, then wash and precipitate the remaining crude green mud to recover the green liquor entrained in the green mud;

Step 3.2, the clarified green liquor and the green liquor entrained in the green mud are digested, the specific reaction is CaO+H ₂ O=Ca(OH) ₂ , and the feeding time is controlled at 60-130min, in order to further improve the causticizing efficiency , CaO needs to be ground, and the particle size is controlled to 3-4 μm;

Step 3.3. The initial causticized emulsion formed after lime digestion enters the separator, and after removing the undigested lime residue, it is sent to the continuous causticizer system for causticization. The specific reaction is Ca(OH) ₂ +Na ₂ CO ₃ = CaCO ₃ ↓+2NaOH;

Step 3.4, the concentrated white liquor from the continuous causticizer system is sent to the white liquor clarifier to remove the white mud in the white liquor;

Step 3.5. After further filtration treatment, the clarified white liquor is sent to the concentrated white liquor tank, and then sent to the cooking section. The white mud from the white liquor filtration equipment is sent to the white mud scrubber for dilution, washing and mixing with hot water. Afterwards, dilute white liquor and white mud emulsion are obtained;

In step 3.6, the dilute white liquor and white mud emulsion are sent to the centrifuge system for processing, part of the dilute white liquor is recovered again, and the white mud is sent to the white mud treatment system.

Step 4. Recycling the product produced by the green liquor causticization reaction is implemented according to the following steps:

Step 4.1, after the lime mud from the causticization section of the step 3 is sent into the calciner, evaporate and dry under the effect of high temperature furnace gas and form granular white mud;

Step 4.2. The dried white mud is further preheated to 600°C, and CaCO ₃ begins to decompose; then the white mud is heated to 825° C. At this time, CaCO ₃ begins to decompose rapidly, that is, it enters the calcination section to generate recyclable CaO. The reaction is: CaCO ₃ =CaO+CO ₂ ↑.

Example 1

A method for comprehensive recycling and utilization of pulping waste liquid of the present invention, the flowchart is shown in Figure 1, and is specifically implemented according to the following steps:

Step 1. Extract the dilute black liquor from the pulping and cooking liquor, then pretreat the dilute black liquor, and finally adopt the mixed-flow indirect evaporation method to evaporate and concentrate the pretreated dilute black liquor;

The dilute black liquor extracted in step 1 is composed of 70% combustible organic matter and 30% inorganic matter. The inorganic matter includes the residual chemicals in the cooking waste liquor, such as NaOH, Na ₂ S, and the raw materials for pulping. The metal salt base of organic compounds and the inorganic components brought by the pulping raw material itself.

In step 1, the pretreatment of the dilute black liquor includes slag removal, oxidation and silicon removal. The slag removal is to remove the fine fibers and various residues contained in the black liquor; the oxidation is to oxidize Na ₂ S in the black liquor to stable Na ₂ SO ₄ and Na ₂ S ₂ O ₃ , the specific reaction is: 2Na ₂ S+2O ₂ +H ₂ O=Na ₂ S ₂ O ₃ +2NaOH, Na ₂ S+2O ₂ =Na ₂ SO ₄ ; Using the bauxite desilicon method, an appropriate amount of bauxite is added to the black liquor before combustion, and the sodium aluminate formed during the combustion process reacts with sodium silicate in the green liquor to form a sodium aluminosilicate complex precipitate. and removed.

In step 1, the pretreated dilute black liquor is evaporated and concentrated, specifically: firstly adopting mixed-flow heating, during the heating process, the concentration of water vaporization escapes is concentrated to 45%, and then the residual heat of flue gas is used to heat and concentrate to the concentration value of 50% .

Step 2. The black liquor concentrated in step 1 is burned in a jet furnace. The high-temperature flue gas generated by the combustion of the organic matter in the black liquor rises in the furnace, and the inorganic matter melts from the chute below the combustion furnace into the dissolving tank, and dissolves. Form green liquor in dilute white liquor or water, and the components of green liquor include Na ₂ CO ₃ and Na ₂ S;

Step 2 is implemented according to the following steps:

Step 2.1, the first stage: when the black liquor entering the furnace is further dried to a concentration of 85% under the action of the hot furnace gas, black ash is formed, and the SO ₂ , SO ₃ and CO ₂ contained in the flue gas and the black liquor The active alkali and organically bound sodium react chemically; the free NaOH and most of Na ₂ S in the black liquor are transformed into Na ₂ CO ₃ , Na ₂ SO ₃ , Na ₂ SO ₄ and Na ₂ S ₂ O ₃ ;

Step 2.2, the second stage: the last remaining water of the black ash is gradually evaporated. When the temperature rises rapidly to 350℃～450℃, the organic matter is rapidly decomposed into CH ₃ OH, CH ₃ COOH, CH ₃ SH, H ₂ S , phenol, low molecular aldehyde acid and complex structure of alkyl sulfide organic gas, and mixed with the secondary air and tertiary air entering the furnace, gas-phase combustion occurs to generate SO ₂ , SO ₃ , CO, H ₂ O, H ₂ S gas; a part of the organic matter is carbonized and becomes elemental carbon for the reduction of mirabilite; in addition, the sodium compound formed by combining with the organic matter also undergoes a decomposition reaction to generate Na ₂ CO ₃ ;

In order to fully burn the black ash under reducing conditions, the air entering the furnace should be preheated to 140°C. Add above the black liquor spray gun, the air volume distribution ratio of the primary, secondary and tertiary air is roughly 50:20:30, the primary air pressure is 0.8KPa, and the secondary and tertiary air pressure is 1.5KPa.

Step 2.3, the third stage: the inorganic matter is melted at high temperature, and then mirabilite is added at the same time.

Step 3, causticizing the green liquor formed by the inorganic melt dissolved in dilute white liquor or water;

Step 3 is implemented according to the following steps:

Step 3.1, clarify the green liquor in the dissolving tank, remove the insoluble impurity green mud, then wash and precipitate the remaining crude green mud to recover the green liquor entrained in the green mud;

Step 3.2. Digest the clarified green liquor and the green liquor entrained in the green mud, the specific reaction is CaO+H ₂ O=Ca(OH) ₂ , and the feeding time is controlled at 60min. In order to further improve the causticizing efficiency, it is necessary to The CaO is ground, and the particle size is controlled to 3 μm;

Step 3.3. The initial causticized emulsion formed after lime digestion enters the separator, and after removing the undigested lime residue, it is sent to the continuous causticizer system for causticization. The specific reaction is Ca(OH) ₂ +Na ₂ CO ₃ = CaCO ₃ ↓+2NaOH;

Step 3.4, the concentrated white liquor from the continuous causticizer system is sent to the white liquor clarifier to remove the white mud in the white liquor;

Step 3.5. After further filtration treatment, the clarified white liquor is sent to the concentrated white liquor tank, and then sent to the cooking section. The white mud from the white liquor filtration equipment is sent to the white mud scrubber for dilution, washing and mixing with hot water. Afterwards, dilute white liquor and white mud emulsion are obtained;

In step 3.6, the dilute white liquor and white mud emulsion are sent to the centrifuge system for processing, part of the dilute white liquor is recovered again, and the white mud is sent to the white mud treatment system.

Step 4. Recycling the product produced by the green liquor causticization reaction is implemented according to the following steps:

Step 4.1, after the lime mud from the causticization section of the step 3 is sent into the calciner, evaporate and dry under the effect of high temperature furnace gas and form granular white mud;

Step 4.2. The dried white mud is further preheated to 600°C, and CaCO ₃ begins to decompose; then the white mud is heated to 825° C. At this time, CaCO ₃ begins to decompose rapidly, that is, it enters the calcination section to generate recyclable CaO. The reaction is: CaCO ₃ =CaO+CO ₂ ↑.

Example 2

A method for comprehensive recycling and utilization of pulping waste liquid of the present invention, the flowchart is shown in Figure 1, and is specifically implemented according to the following steps:

Step 1. Extract the dilute black liquor from the pulping and cooking liquor, then pretreat the dilute black liquor, and finally adopt the mixed-flow indirect evaporation method to evaporate and concentrate the pretreated dilute black liquor;

The dilute black liquor extracted in step 1 is composed of 70% combustible organic matter and 30% inorganic matter. The inorganic matter includes the residual chemicals in the cooking waste liquor, such as NaOH, Na ₂ S, and the raw materials for pulping. The metal salt base of organic compounds and the inorganic components brought by the pulping raw material itself.

In step 1, the pretreatment of the dilute black liquor includes slag removal, oxidation and silicon removal. The slag removal is to remove the fine fibers and various residues contained in the black liquor; the oxidation is to oxidize Na ₂ S in the black liquor to stable Na ₂ SO ₄ and Na ₂ S ₂ O ₃ , the specific reaction is: 2Na ₂ S+2O ₂ +H ₂ O=Na ₂ S ₂ O ₃ +2NaOH, Na ₂ S+2O ₂ =Na ₂ SO ₄ ; Using the bauxite desilicon method, an appropriate amount of bauxite is added to the black liquor before combustion, and the sodium aluminate formed during the combustion process reacts with sodium silicate in the green liquor to form a sodium aluminosilicate complex precipitate. and removed.

In step 1, the pretreated dilute black liquor is evaporated and concentrated, specifically: firstly adopting mixed-flow heating, during the heating process, the concentration of water vaporization escapes is concentrated to 45% to 48%, and then the waste heat of flue gas is used to heat and concentrate to the concentration value is 65%.

Step 2. The black liquor concentrated in step 1 is burned in a jet furnace. The high-temperature flue gas generated by the combustion of the organic matter in the black liquor rises in the furnace, and the inorganic matter melts from the chute below the combustion furnace into the dissolving tank, and dissolves. Form green liquor in dilute white liquor or water, and the components of green liquor include Na ₂ CO ₃ and Na ₂ S;

Step 2 is implemented according to the following steps:

Step 2.1, the first stage: when the black liquor entering the furnace is further dried to a concentration of 85% under the action of the hot furnace gas, black ash is formed, and the SO ₂ , SO ₃ and CO ₂ contained in the flue gas and the black liquor The active alkali and organically bound sodium react chemically; the free NaOH and most of Na ₂ S in the black liquor are transformed into Na ₂ CO ₃ , Na ₂ SO ₃ , Na ₂ SO ₄ and Na ₂ S ₂ O ₃ ;

Step 2.2, the second stage: the last remaining water of the black ash is gradually evaporated. When the temperature rises rapidly to 350℃～450℃, the organic matter is rapidly decomposed into CH ₃ OH, CH ₃ COOH, CH ₃ SH, H ₂ S , phenol, low molecular aldehyde acid and complex structure of alkyl sulfide organic gas, and mixed with the secondary air and tertiary air entering the furnace, gas-phase combustion occurs to generate SO ₂ , SO ₃ , CO, H ₂ O, H ₂ S gas; a part of the organic matter is carbonized and becomes elemental carbon for the reduction of mirabilite; in addition, the sodium compound formed by combining with the organic matter also undergoes a decomposition reaction to generate Na ₂ CO ₃ ;

In order to fully burn the black ash under reducing conditions, the air entering the furnace needs to be preheated to 140-150 °C, the primary air is added in the reduction area of the combustion furnace, and the secondary air is added above the reduction area and near the injection inlet of the black liquor, three times. The air is added above the black liquor spray gun. The air volume distribution ratio of the primary, secondary and tertiary air is roughly 50:20:30, the primary air pressure is 0.8-1.2KPa, and the secondary and tertiary air pressure is 3KPa.

Step 2.3, the third stage: the inorganic matter is melted at high temperature, and then mirabilite is added at the same time.

Step 3, causticizing the green liquor formed by the inorganic melt dissolved in dilute white liquor or water;

Step 3 is implemented according to the following steps:

Step 3.1, clarify the green liquor in the dissolving tank, remove the insoluble impurity green mud, then wash and precipitate the remaining crude green mud to recover the green liquor entrained in the green mud;

Step 3.2. Digest the clarified green liquor and the green liquor entrained in the green mud, the specific reaction is CaO+H ₂ O=Ca(OH) ₂ , and the feeding time is controlled at 130min. In order to further improve the causticizing efficiency, it is necessary to The CaO is ground, and the particle size is controlled to 4 μm;

Step 3.3. The initial causticized emulsion formed after lime digestion enters the separator, and after removing the undigested lime residue, it is sent to the continuous causticizer system for causticization. The specific reaction is Ca(OH) ₂ +Na ₂ CO ₃ = CaCO ₃ ↓+2NaOH;

Step 3.4, the concentrated white liquor from the continuous causticizer system is sent to the white liquor clarifier to remove the white mud in the white liquor;

Step 3.5. After further filtration treatment, the clarified white liquor is sent to the concentrated white liquor tank, and then sent to the cooking section. The white mud from the white liquor filtration equipment is sent to the white mud scrubber for dilution, washing and mixing with hot water. Afterwards, dilute white liquor and white mud emulsion are obtained;

In step 3.6, the dilute white liquor and white mud emulsion are sent to the centrifuge system for processing, part of the dilute white liquor is recovered again, and the white mud is sent to the white mud treatment system.

Step 4. Recycling the product produced by the green liquor causticization reaction is implemented according to the following steps:

Step 4.1, after the lime mud from the causticization section of the step 3 is sent into the calciner, evaporate and dry under the effect of high temperature furnace gas and form granular white mud;

Step 4.2. The dried white mud is further preheated to 600°C, and CaCO ₃ begins to decompose; then the white mud is heated to 825° C. At this time, CaCO ₃ begins to decompose rapidly, that is, it enters the calcination section to generate recyclable CaO. The reaction is: CaCO ₃ =CaO+CO ₂ ↑.

Example 3

A method for comprehensive recycling and utilization of pulping waste liquid of the present invention, the flowchart is shown in Figure 1, and is specifically implemented according to the following steps:

Step 1. Extract the dilute black liquor from the pulping and cooking liquor, then pretreat the dilute black liquor, and finally adopt the mixed-flow indirect evaporation method to evaporate and concentrate the pretreated dilute black liquor;

The dilute black liquor extracted in step 1 is composed of 70% combustible organic matter and 30% inorganic matter. The inorganic matter includes the residual chemicals in the cooking waste liquor, such as NaOH, Na ₂ S, and the raw materials for pulping. The metal salt base of organic compounds and the inorganic components brought by the pulping raw material itself.

In step 1, the pretreatment of the dilute black liquor includes slag removal, oxidation and silicon removal. The slag removal is to remove the fine fibers and various residues contained in the black liquor; the oxidation is to oxidize Na ₂ S in the black liquor to stable Na ₂ SO ₄ and Na ₂ S ₂ O ₃ , the specific reaction is: 2Na ₂ S+2O ₂ +H ₂ O=Na ₂ S ₂ O ₃ +2NaOH, Na ₂ S+2O ₂ =Na ₂ SO ₄ ; Using the bauxite desilicon method, an appropriate amount of bauxite is added to the black liquor before combustion, and the sodium aluminate formed during the combustion process reacts with sodium silicate in the green liquor to form a sodium aluminosilicate complex precipitate. and removed.

In step 1, the pretreated dilute black liquor is evaporated and concentrated, specifically: first, mixed-flow heating is adopted, and the concentration of water vaporized during the heating process is concentrated to 46%, and then the residual heat of flue gas is used to heat and concentrate to a concentration value of 60%. .

Step 2. The black liquor concentrated in step 1 is burned in a jet furnace. The high-temperature flue gas generated by the combustion of the organic matter in the black liquor rises in the furnace, and the inorganic matter melts from the chute below the combustion furnace into the dissolving tank, and dissolves. Form green liquor in dilute white liquor or water, and the components of green liquor include Na ₂ CO ₃ and Na ₂ S;

Step 2 is implemented according to the following steps:

Step 2.1, the first stage: when the black liquor entering the furnace is further dried to a concentration of 85% under the action of the hot furnace gas, black ash is formed, and the SO ₂ , SO ₃ and CO ₂ contained in the flue gas and the black liquor The active alkali and organically bound sodium react chemically; the free NaOH and most of Na ₂ S in the black liquor are transformed into Na ₂ CO ₃ , Na ₂ SO ₃ , Na ₂ SO ₄ and Na ₂ S ₂ O ₃ ;

Step 2.2, the second stage: the last remaining water of the black ash is gradually evaporated. When the temperature rises rapidly to 350℃～450℃, the organic matter is rapidly decomposed into CH ₃ OH, CH ₃ COOH, CH ₃ SH, H ₂ S , phenol, low molecular aldehyde acid and complex structure of alkyl sulfide organic gas, and mixed with the secondary air and tertiary air entering the furnace, gas-phase combustion occurs to generate SO ₂ , SO ₃ , CO, H ₂ O, H ₂ S gas; a part of the organic matter is carbonized and becomes elemental carbon for the reduction of mirabilite; in addition, the sodium compound formed by combining with the organic matter also undergoes a decomposition reaction to generate Na ₂ CO ₃ ;

In order to fully burn the black ash under reducing conditions, the air entering the furnace needs to be preheated to 140-150 °C, the primary air is added in the reduction area of the combustion furnace, and the secondary air is added above the reduction area and near the injection inlet of the black liquor, three times. The air is added above the black liquor spray gun. The air volume distribution ratio of the primary, secondary and tertiary air is roughly 50:20:30, the primary air pressure is 1.0KPa, and the secondary and tertiary air pressure is 2.2KPa.

Step 2.3, the third stage: the inorganic matter is melted at high temperature, and then mirabilite is added at the same time.

Step 3, causticizing the green liquor formed by the inorganic melt dissolved in dilute white liquor or water;

Step 3 is implemented according to the following steps:

Step 3.1, clarify the green liquor in the dissolving tank, remove the insoluble impurity green mud, then wash and precipitate the remaining crude green mud to recover the green liquor entrained in the green mud;

Step 3.2, the clarified green liquor and the green liquor entrained in the green mud are digested, the specific reaction is CaO+H ₂ O=Ca(OH) ₂ , and the feeding time is controlled at 60-130min, in order to further improve the causticizing efficiency , CaO needs to be ground, and the particle size is controlled to 3.5 μm;

Step 3.3. The initial causticized emulsion formed after lime digestion enters the separator, and after removing the undigested lime residue, it is sent to the continuous causticizer system for causticization. The specific reaction is Ca(OH) ₂ +Na ₂ CO ₃ = CaCO ₃ ↓+2NaOH;

Step 3.4, the concentrated white liquor from the continuous causticizer system is sent to the white liquor clarifier to remove the white mud in the white liquor;

Step 3.5. After further filtration treatment, the clarified white liquor is sent to the concentrated white liquor tank, and then sent to the cooking section. The white mud from the white liquor filtration equipment is sent to the white mud scrubber for dilution, washing and mixing with hot water. Afterwards, dilute white liquor and white mud emulsion are obtained;

In step 3.6, the dilute white liquor and white mud emulsion are sent to the centrifuge system for processing, part of the dilute white liquor is recovered again, and the white mud is sent to the white mud treatment system.

Step 4. Recycling the product produced by the green liquor causticization reaction is implemented according to the following steps:

Step 4.1, after the lime mud from the causticization section of the step 3 is sent into the calciner, evaporate and dry under the effect of high temperature furnace gas and form granular white mud;

Step 4.2. The dried white mud is further preheated to 600°C, and CaCO ₃ begins to decompose; then the white mud is heated to 825° C. At this time, CaCO ₃ begins to decompose rapidly, that is, it enters the calcination section to generate recyclable CaO. The reaction is: CaCO ₃ =CaO+CO ₂ ↑.

Claims (7)

1. a method for comprehensive recovery and utilization of pulping waste liquid, is characterized in that, specifically implements according to the following steps: Step 1. Extract the dilute black liquor from the pulping and cooking liquor, then pretreat the dilute black liquor, and finally adopt the mixed-flow indirect evaporation method to evaporate and concentrate the pretreated dilute black liquor; Step 2. The black liquor concentrated in step 1 is burned in a jet furnace. The high-temperature flue gas generated by the combustion of the organic matter in the black liquor rises in the furnace, and the inorganic matter melts from the chute below the combustion furnace into the dissolving tank, and dissolves. Form green liquor in dilute white liquor or water, and the components of green liquor include Na ₂ CO ₃ and Na ₂ S; Step 3, causticizing the green liquor formed by the inorganic melt dissolved in dilute white liquor or water; Step 4: Recycling the product produced by the causticization reaction of the green liquor. 2. The method for comprehensive recycling and utilization of pulping waste liquid according to claim 1, wherein the composition of the dilute black liquor extracted in the step 1 is 70% combustible organic matter, 30% inorganic matter , Inorganic substances include the residual chemicals in the cooking waste liquid, such as NaOH, Na ₂ S, and the metal salt bases combined with the organic substances in the pulping raw materials, and the inorganic components brought by the pulping raw materials themselves. 3. The method for comprehensive recycling and utilization of pulping waste liquor according to claim 1, characterized in that, in the step 1, the pretreatment of the dilute black liquor comprises slag removal, oxidation, and silicon removal, and slag removal is the removal of black liquor. The fine fibers and various residues contained in the black liquor are removed; oxidation is to oxidize Na ₂ S in the black liquor into stable Na ₂ SO ₄ and Na ₂ S ₂ O ₃ , and the specific reaction is: 2Na ₂ S+2O ₂ +H ₂ O=Na ₂ S ₂ O ₃ +2NaOH, Na ₂ S+2O ₂ =Na ₂ SO ₄ ; for silicon removal, the method of removing silicon from bauxite is adopted, and an appropriate amount of bauxite is added to the black liquor before burning. , The sodium aluminate formed during the combustion process reacts with sodium silicate in the green liquor to form a sodium aluminosilicate complex that is precipitated and removed. 4. the method for comprehensive recycling and utilization of a kind of pulping waste liquid according to claim 1, is characterized in that, in described step 1, the thin black liquor after pretreatment is evaporated and concentrated, is specially: first adopt mixed-flow heating , during the heating process, the water vaporization escape concentration is concentrated to 45% to 48%, and then the residual heat of the flue gas is used to heat and concentrate to the concentration value of 50% to 65%. 5. the method for comprehensive recycling of a kind of pulping waste liquid according to claim 1, is characterized in that, described step 2 is specifically implemented according to the following steps: Step 2.1, the first stage: when the black liquor entering the furnace is further dried to a concentration of 85% under the action of the hot furnace gas, black ash is formed, and the SO ₂ , SO ₃ and CO ₂ contained in the flue gas and the black liquor The active alkali and organically bound sodium react chemically; the free NaOH and most of Na ₂ S in the black liquor are transformed into Na ₂ CO ₃ , Na ₂ SO ₃ , Na ₂ SO ₄ and Na ₂ S ₂ O ₃ ; Step 2.2, the second stage: the last remaining water of the black ash is gradually evaporated. When the temperature rises rapidly to 350℃～450℃, the organic matter is rapidly decomposed into CH ₃ OH, CH ₃ COOH, CH ₃ SH, H ₂ S , phenol, low molecular aldehyde acid and complex structure of alkyl sulfide organic gas, and mixed with the secondary air and tertiary air entering the furnace, gas-phase combustion occurs to generate SO ₂ , SO ₃ , CO, H ₂ O, H ₂ S gas; a part of the organic matter is carbonized and becomes elemental carbon for the reduction of mirabilite; in addition, the sodium compound formed by combining with the organic matter also undergoes a decomposition reaction to generate Na ₂ CO ₃ ; In order to fully burn the black ash under reducing conditions, the air entering the furnace needs to be preheated to 140-150 °C, the primary air is added in the reduction area of the combustion furnace, and the secondary air is added above the reduction area and near the injection inlet of the black liquor, three times. The air is added above the black liquor spray gun. The air volume distribution ratio of the primary, secondary and tertiary air is roughly 50:20:30, the primary air pressure is 0.8~1.2KPa, and the secondary and tertiary air pressure is 1.5~3KPa. Step 2.3, the third stage: the inorganic matter is melted at high temperature, and then mirabilite is added at the same time. 6. the method for comprehensive recycling of a kind of pulping waste liquid according to claim 1, is characterized in that, described step 3 is specifically implemented according to the following steps: Step 3.1, clarify the green liquor in the dissolving tank, remove the insoluble impurity green mud, then wash and precipitate the remaining crude green mud to recover the green liquor entrained in the green mud; Step 3.2, the clarified green liquor and the green liquor entrained in the green mud are digested, the specific reaction is CaO+H ₂ O=Ca(OH) ₂ , and the feeding time is controlled at 60-130min, in order to further improve the causticizing efficiency , CaO needs to be ground, and the particle size is controlled to 3-4 μm; Step 3.3. The initial causticized emulsion formed after lime digestion enters the separator, and after removing the undigested lime residue, it is sent to the continuous causticizer system for causticization. The specific reaction is Ca(OH) ₂ +Na ₂ CO ₃ = CaCO ₃ ↓+2NaOH; Step 3.4, the concentrated white liquor from the continuous causticizer system is sent to the white liquor clarifier to remove the white mud in the white liquor; Step 3.5. After further filtration treatment, the clarified white liquor is sent to the concentrated white liquor tank, and then sent to the cooking section. The white mud from the white liquor filtration equipment is sent to the white mud scrubber for dilution, washing and mixing with hot water. Afterwards, dilute white liquor and white mud emulsion are obtained; In step 3.6, the dilute white liquor and white mud emulsion are sent to the centrifuge system for processing, part of the dilute white liquor is recovered again, and the white mud is sent to the white mud treatment system. 7. the method for comprehensive recycling of a kind of pulping waste liquid according to claim 6 is characterized in that, described step 4 is specifically implemented according to the following steps: Step 4.1, after the lime mud from the causticization section of the step 3 is sent into the calciner, evaporate and dry under the effect of high temperature furnace gas and form granular white mud; Step 4.2. The dried white mud is further preheated to 600°C, and CaCO ₃ begins to decompose; then the white mud is heated to 825° C. At this time, CaCO ₃ begins to decompose rapidly, that is, it enters the calcination section to generate recyclable CaO. The reaction is: CaCO ₃ =CaO+CO ₂ ↑.

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