Prediction method for calorific value of broadleaf wood sulfate pulping black liquor

Abstract

The invention provides a method for predicting the calorific value of broadleaf wood sulfate pulping black liquor, which is characterized in that the black liquor condition of production operation caused by a raw material structure to be put into use is predicted according to a prediction equation, the prediction equation is y (QN) = 0.6725 x (QS)-121.41, and the fitting degree R2 = 0.9394. The error between the predicted value and the measured value of the calorific value of the broadleaf wood sulfate pulping black liquor obtained according to the prediction equation is less than 10%, which indicates that the prediction equation is high in accuracy. According to the prediction equation in the prediction method, the recovery heat value of the sulfate pulping black liquor taking different broadleaf wood species as raw materials is predicted, so that the raw material ratio is reasonably and effectively used in the industrial production process, an alkali recovery system is stabilized, and production operation is stabilized. The prediction method is small in error, high in accuracy and good in application prospect.

Description

Technical Field

[0001] The invention relates to the technical field of pulping and papermaking, and in particular to a method for predicting the calorific value of black liquor from hardwood kraft pulping. Background Art

[0002] Kraft black liquor is a black mixed liquid formed by the decomposition and dissolution of organic matter in fiber raw materials (such as wood) in the high temperature, high pressure and strong alkaline environment in the kraft pulping process. It not only contains organic components of wood such as lignin and hemicellulose, but also contains high concentrations of alkaline chemicals (such as sodium hydroxide, sodium sulfide, etc.). In the production process of industrial kraft pulping plants, the treatment of black liquor is a very important link, especially its alkali recovery system. The core functions of this system include removing water through evaporation and concentration processes, incinerating organic matter in black liquor, and recovering the calorific value of black liquor and chemicals (such as sodium hydroxide and sodium sulfide) in it. This recovered heat can not only be used for the heating system of the plant area, but also help restore alkaline chemicals, reduce the demand for purchased raw materials, and improve the recycling rate of resources.

[0003] In the kraft pulping process, a stable and efficient alkali recovery system is crucial. In order to achieve thermal energy balance in the production process and ensure the stable operation of the system, the calorific value recovery of black liquor needs to be precisely controlled. The calorific value of black liquor not only determines whether the alkali recovery system can meet the energy supply requirements, but also directly affects the economic benefits and environmental protection of the entire pulping process. Therefore, how to maintain the stability of the calorific value of black liquor, improve the calorific value recovery rate, and reduce energy consumption have become urgent problems to be solved in modern pulp mills.

[0004] Hardwood, as one of the commonly used raw materials in kraft pulping, has a significant impact on the properties and recovered calorific value of black liquor due to its chemical composition and structural characteristics during the cooking process. Different hardwood species have different lignin content, cellulose content, hemicellulose content and chemical composition of the species, which will lead to differences in the composition of black liquor, which will directly affect the calorific value and combustion efficiency of the black liquor. Generally, species with higher lignin content will result in higher calorific value in black liquor, because lignin is a richer source of organic matter and can release more heat during the incineration process. The calorific value and composition of black liquor of other species such as poplar and beech may be different due to lower fiber content or differences in lignin structure.

[0005] Therefore, scientific evaluation of the calorific value of black liquor from kraft pulping of different hardwood species can help pulp mills better understand the impact of different tree species on the properties of black liquor and optimize the raw material ratio accordingly. In the industrial production process, the rational selection and allocation of raw materials based on the differences in the calorific value of black liquor from different tree species can ensure that the calorific value and chemical composition of the black liquor are in an ideal state and help stabilize the operation of the alkali recovery system. This can not only effectively improve the calorific value recovery efficiency of black liquor and reduce energy consumption, but also ensure the recycling of chemicals in the production process, reduce dependence on external resources, and reduce production costs. Therefore, in-depth research on the calorific value of black liquor from kraft pulping of different hardwood species has very important industrial application value and can provide reliable technical support for energy utilization and chemical recovery in the kraft pulping process. Summary of the invention

[0006] In view of this, the present invention proposes a method for predicting the calorific value of hardwood kraft pulping black liquor.

[0007] The technical solution of the present invention is achieved in this way:

[0008] A method for predicting the calorific value of hardwood kraft pulping black liquor, comprising the following specific steps:

[0009] (1) Weigh the absolute dry mass of wood chips, denoted as M, and add them into a cooking tank. According to the cooking characteristics of different wood species, add cooking white liquor after alkali recovery treatment. The Kappa value of the pulp after the wood species is cooked is controlled by different alkali amounts, denoted as A. After the cooking is completed, weigh the black liquor and pulp mixture, denoted as M1, and then squeeze out part of the black liquor for analysis. After the pulp is washed with black liquor, its yield is calculated, denoted as Y, and the amount of black liquor produced per unit wood chip cooking M0 is calculated according to formula (1);

[0010] M0=(M1-M×Y) / M×10 3 (1)

[0011] In formula (1), the unit of M is g, the unit of M1 is g, and the unit of M0 is kg·kg -1 ;

[0012] (2) Dry the black liquor sample obtained in (1) to obtain a black liquor solid, grind it into powder, and analyze the combustion calorific value of the black liquor solid according to the coal calorific value determination method. The calorific value is the lower calorific value measured under constant volume conditions, recorded as Q n , according to formula (2), the calorific value Q that can be recovered from the black liquor produced by cooking a unit of wood chips is calculated;

[0013] Q=M0×Q n (2)

[0014] In formula (2), Q n The unit is kcal·kg-1 , the unit of Q is kcal·kg -1 ; The method for determining the calorific value of coal is based on GB / T 213-2008;

[0015] (3) When multiple types of wood species are mixed for pulping, the Q value of each wood species is multiplied by its wood chip ratio P during mixed cooking, and then added together. That is, the heat value Q that can be recovered from the black liquor produced by the mixed cooking per unit wood chip is calculated according to formula (3): S ;

[0016] Q S =Q1×P1+ Q2×P2+Q3×P3… (3)

[0017] (4) The linear regression analysis was used to obtain the Q S With Q N The linear relationship between Q S With Q N The functional relationship of is, formula (4) is the prediction equation, where Q N The low calorific value of the dilute black liquor in the actual industrial production process is measured, and the black liquor condition brought about by the raw material structure to be put into use is predicted according to the prediction equation;

[0018] y(Q N )=0.6725x(Q S )-121.41 (4)

[0019] Among them, the fitting degree R of formula (4) 2 =0.9394.

[0020] Furthermore, in step (1), the cooking conditions are: temperature of 148-152° C., heating time of 85-95 min, heat preservation time of 230-250 min, sulfidation degree of 30-40%, and liquid ratio of 3.5-4.5.

[0021] Furthermore, in step (1), the A value is 15-20.

[0022] Furthermore, the calculation formula of Y is: Y=(slurry after washing with black liquor-slurry before washing with black liquor) / slurry before washing with black liquor×100%.

[0023] Furthermore, in step (2), the drying temperature is 95-115° C. and the drying time is 2-4 hours.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The prediction equation in the prediction method of the present invention is used to predict the recovered calorific value of kraft pulping black liquor using different hardwood species as raw materials, so as to guide the industrial production process to reasonably and effectively use the raw material ratio, stabilize the alkali recovery system, and stabilize the production operation. The prediction method of the present invention has small error, high accuracy, and good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Calorific value Q of black liquor for pulping different wood species S With Q N Fitting relationship diagram. DETAILED DESCRIPTION

[0027] In order to better understand the technical content of the present invention, specific embodiments are provided below to further illustrate the present invention.

[0028] Unless otherwise specified, the experimental methods used in the embodiments of the present invention are all conventional methods.

[0029] Unless otherwise specified, the materials, reagents, etc. used in the embodiments of the present invention can be obtained from commercial sources.

[0030] Example 1

[0031] A method for predicting the calorific value of hardwood kraft pulping black liquor, comprising the following specific steps:

[0032] (1) Weigh the absolute dry mass of wood chips (M, g) and add them to a cooking tank. According to the cooking characteristics of different tree species, add cooking white liquor after alkali recovery treatment. The cooking conditions are: temperature 152°C, heating time 90 min, holding time 240 min, sulfidation degree 35%, and liquid ratio 4.0. The Kappa value of the pulp after cooking of the tree species is controlled by different alkali amounts, which is recorded as A (depending on the predicted Kappa value of the production pulp, ranging from 15 to 20). After the cooking is completed, the black liquor and pulp mixture are weighed and recorded as M1 (M, g). Then, part of the black liquor is squeezed out for analysis. The yield of the pulp after washing the black liquor is calculated and recorded as Y, Y = (slurry after washing the black liquor - pulp before washing the black liquor) / pulp before washing the black liquor × 100%, and the amount of black liquor produced by cooking unit wood chips M0 (kg kg) is calculated according to formula (1). -1 );

[0033] M0=(M1-M×Y) / M×10 3 (1)

[0034] (2) The black liquor sample of (1) was dried at 105°C for 3 h to obtain a black liquor solid, which was ground into powder. The combustion calorific value of the black liquor solid was analyzed according to the coal calorific value determination method GB / T 213-2008. The calorific value is the lower calorific value measured under constant volume conditions, denoted as Q n(kcal·kg -1 ), the calorific value Q (kcal·kg -1 );

[0035] Q=M0×Q n (2)

[0036] (3) When multiple types of wood species are mixed for pulping, the Q value of each wood species is multiplied by its wood chip ratio P during mixed cooking, and then added together. That is, the heat value Q that can be recovered from the black liquor produced by the mixed cooking per unit wood chip is calculated according to formula (3): S ;

[0037] Q S =Q1×P1+ Q2×P2+Q3×P3… (3)

[0038] (4) Measurement of Q N It is the low calorific value of the dilute black liquor measured in the actual industrial production process. S With Q N The linear relationship between Q S With Q N The functional relationship of .

[0039] Example 2

[0040] When different wood species are mixed and cooked for pulping, the heat value Q that can be recovered from the black liquor produced by the mixed cooking per unit wood chip is S The calorific value Q of the black liquor from hardwood kraft pulping was calculated by the prediction method of Example 1, and the low calorific value Q of the dilute black liquor measured in the actual industrial production process was recorded. N , the results are shown in Table 1.

[0041] Table 1

[0042]

[0043]

[0044] From the data in Table 1, we can see that Q S With Q N There is a significant linear relationship between them. By fitting these data, we can establish Q S With Q N The functional relationship is the prediction equation y(Q N )=0.6725x(Q S )-121.41, see Figure 1, using prediction equations to predict the black liquor conditions brought about by the raw material structure to be put into use can provide important decision-making support in the early stage of production operation, which has important practical significance for production scheduling and optimization.

[0045] Example 3

[0046] When multiple types of raw materials are mixed and cooked in different proportions for pulping, the characteristics of different species will have different effects on the chemical composition and calorific value of black liquor during the production process. The predicted value obtained according to the prediction equation of Example 2 and the low calorific value (measured value) of black liquor measured in the actual industrial production process are shown in Table 2.

[0047] Table 2

[0048]

[0049] As can be seen from Table 2, the errors between the predicted values ​​and the measured values ​​of the calorific value of the black liquor from the hardwood kraft pulping process calculated by the prediction equation proposed in the present invention are less than 10%. This result shows that the prediction equation has high accuracy and reliability in practical applications. Since the error is less than 10%, this equation can effectively reflect the changing trend of the calorific value of the black liquor, and can provide a more accurate calorific value prediction in actual production, providing strong support for the optimization of the production process and energy efficiency management. The prediction equation can be used as an important tool to control and adjust the calorific value of black liquor in the production process, help improve resource utilization efficiency and reduce energy consumption, and provide a scientific basis and technical support for the green development of the pulp and paper industry.

[0050] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for predicting the calorific value of black liquor from hardwood kraft pulping, characterized in that: The specific steps include: (1) Weigh the absolute dry mass of wood chips, denoted as M, and add them into a cooking tank. According to the cooking characteristics of different wood species, add cooking white liquor after alkali recovery treatment. The Kappa value of the pulp after the wood species is cooked is controlled by different alkali amounts, denoted as A. After the cooking is completed, weigh the black liquor and pulp mixture, denoted as M1, and then squeeze out part of the black liquor for analysis. After the pulp is washed with black liquor, its yield is calculated, denoted as Y, and the amount of black liquor produced per unit wood chip cooking M0 is calculated according to formula (1); M0=(M1-M×Y) / M×10 3 (1) (2) Dry the black liquor sample obtained in (1) to obtain a black liquor solid, grind it into powder, and analyze the combustion calorific value of the black liquor solid according to the coal calorific value determination method. The calorific value is the lower calorific value measured under constant volume conditions, recorded as Q n , according to formula (2), the calorific value Q that can be recovered from the black liquor produced by cooking a unit of wood chips is calculated; Q=M0×Q n (2) (3) When multiple types of wood species are mixed for pulping, the Q value of each wood species is multiplied by its wood chip ratio P during mixed cooking, and then added together. That is, the heat value Q that can be recovered from the black liquor produced by the mixed cooking per unit wood chip is calculated according to formula (3): S ; Q S =Q1×P1+Q2×P2+Q3×P3… (3) (4) The linear regression analysis was used to obtain the Q S With Q N The linear relationship between Q S With Q N The functional relationship of is, formula (4) is the prediction equation, where Q N The low calorific value of the dilute black liquor in the actual industrial production process is measured, and the black liquor condition brought about by the raw material structure to be put into use is predicted according to the prediction equation; y(Q N )=0.6725x(Q S )-121.41 (4) Among them, the fitting degree R of formula (4) 2 =0.9394.

2. The method for predicting the calorific value of hardwood kraft pulping black liquor according to claim 1, characterized in that: In step (1), the cooking conditions are: temperature of 148-152° C., heating time of 85-95 min, heat preservation time of 230-250 min, sulfidation degree of 30-40%, and liquid ratio of 3.5-4.

5.

3. The method for predicting the calorific value of hardwood kraft pulping black liquor according to claim 1, characterized in that: In step (1), the A value is 15-20.

4. The method for predicting the calorific value of hardwood kraft pulping black liquor according to claim 1, characterized in that: In step (1), the calculation formula of Y is: Y=(slurry after washing with black liquor-slurry before washing with black liquor) / slurry before washing with black liquor×100%.

5. The method for predicting the calorific value of hardwood kraft pulping black liquor according to claim 1, characterized in that: In step (2), the drying temperature is 95-115° C. and the drying time is 2-4 hours.

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