Establishment method and application of comprehensive evaluation model for solid fuel used in sintering

Abstract

The present invention provides a method for establishing a comprehensive evaluation model for solid fuel for sintering and its application. It includes the following steps: S1, the comprehensive evaluation model for solid fuel for sintering considers the mixed combustion reaction behavior of different types of solid fuels in an adiabatic system based on the energy balance principle, and is mainly based on three main indicators: theoretical combustion temperature, harmful gas emission index and use cost index; S2, based on the above three main indicators, a fuel evaluation characteristic value K based on meeting production needs is established; S3, the fuel evaluation characteristic value K of the solid fuel batching scheme of a predetermined type and a predetermined ratio is calculated through the above comprehensive evaluation model, and the K value is compared and analyzed to quantitatively evaluate the advantages and disadvantages of different fuel batching schemes. The model is easy to calculate, and has important guiding significance for the selection and optimization of fuel types and ratios for on-site sintering production. At the same time, the modification of corresponding indicators can also be used for the evaluation of other types of sintering fuels.

Description

Technical Field

[0001] The invention relates to the technical field of metallurgy, and in particular to a method for establishing a comprehensive evaluation model for solid fuel for sintering and its application. Background Art

[0002] At present, with the development of the steel industry and the continuous improvement of the blast furnace clinker ratio, the supply of coke powder for sintering is in short supply. Many sintering sites use biomass charcoal, semi-coke, blast furnace dust ash or anthracite to replace or partially replace coke powder as solid fuel for sintering. However, due to the large differences in the combustion performance of these solid fuels and coke powder, the type and ratio of solid fuels used in the sintering mixture will have a significant impact on the sintering production cost, flue gas emissions and sintered ore quality.

[0003] Previously, most researchers used the sintering cup test method to directly compare the effects of various solid fuels on the sintering process and metallurgical properties, comprehensively evaluate the types and proportions of fuels used in the process and obtain the optimal solution. This method is not only costly, but also time-consuming and labor-intensive.

[0004] In recent years, some scholars have established various fuzzy mathematical models for the prediction of sintering material layer changes and end points, which are scientific. For example, the invention patent with application number CN201410205833.1 discloses a method for establishing a cost-effectiveness evaluation model for blast furnace coal injection. Based on the combustion reaction behavior of pulverized coal in the blast furnace, the concept of effective calorific value that pulverized coal can provide to the blast furnace is proposed. Eight indicators that affect the actual heat supply of pulverized coal and four indicators that affect the injection cost are determined, and a cost-effectiveness evaluation model for blast furnace pulverized coal or alternative fuel injection is established. For example, the invention patent with application number CN202011577155.3 discloses a sintering solid fuel control method based on thermal balance. According to the sintering mixture batching parameters and sintering process operation parameters collected at the current moment, an online thermal balance calculation model of the sintering machine is established to give a reference value for the sintering solid fuel ratio. When the iron-containing raw materials, flux, fuel or sintering process operation parameters in the sintering batching change, the optimization adjustment plan for the sintering solid fuel ratio is given in real time based on the online thermal balance calculation model.

[0005] However, the above models or establishment methods do not take into account the pollutant emissions and production costs of the sintering fuel combustion process, and are not suitable for use by corporate procurement departments under the current situation of increasing environmental pressure.

[0006] In view of this, in order to truly reflect the actual situation of solid fuel for sintering, a simple and easy evaluation model for solid fuel for sintering is explored. This paper proposes an evaluation model based on solid fuel industrial analysis, elemental analysis, combustion characteristics, crushing characteristics and use cost. The model is easy to calculate and has important guiding significance for the optimization of on-site fuel types and ratios. Summary of the invention

[0007] The purpose of the present invention is to provide a method for establishing a comprehensive evaluation model for solid fuel for sintering and its application.

[0008] To achieve the above-mentioned object of the invention, the present invention provides a method for establishing a comprehensive evaluation model of solid fuel for sintering, comprising the following steps:

[0009] S1, the comprehensive evaluation model of solid fuel for sintering is based on the energy balance principle and considers the mixed combustion reaction behavior of different types of solid fuels in an adiabatic system, mainly based on the theoretical combustion temperature T c , Harmful Gas Emission Index I e and the usage cost index W u On three main indicators;

[0010] S2, based on the above three main indicators, establish the fuel evaluation characteristic value K based on meeting production needs;

[0011] Fuel evaluation characteristic value = theoretical combustion temperature / (harmful gas emission index × use cost index), dimensionless; that is, ;

[0012] S3, calculating the fuel evaluation characteristic value K of the solid fuel batching scheme of a predetermined type and a predetermined ratio through the above comprehensive evaluation model, and comparing and analyzing the K value to quantitatively evaluate the advantages and disadvantages of different fuel batching schemes;

[0013] The larger the K value, the better the batching scheme, and the smaller the K value, the worse the batching scheme; based on this, the solid fuel selection scheme for sintering is optimized.

[0014] As a further improvement of the present invention, in step S1, the theoretical combustion temperature T c It includes the following sub-indicators: The calorific value of each fuel combustion Q i , initial temperature T0 and average specific heat capacity c p ;

[0015] The harmful gas emission index I e Includes the following sub-indicators: Fuel volatile content V i 、N element content N i and S content i ;

[0016] The usage cost index W u Includes the following sub-indicators: Factory price W i and grindability index H i ;

[0017] In addition, the above three main indicators in the comprehensive evaluation model of sintering solid fuel also include the following common sub-indicators: sintering mixture quality M s , fuel ratio Y f and the mass proportion of each fuel is X i .

[0018] The use of solid fuel in sintering production is mainly to provide heat for the mineralization reaction between iron ore and flux. Therefore, considering the theoretical combustion temperature of solid fuel under adiabatic system can more intuitively evaluate the suitability of fuel type and ratio.

[0019] When the fuel burns in the sintering material layer, it will not only undergo volatilization and analysis reactions, but also produce gases such as NO and SO2 that cause serious pollution to the atmospheric environment. This model innovatively proposes the harmful gas emission index as an important indicator for fuel use evaluation.

[0020] As a further improvement of the present invention, the theoretical combustion temperature T c The calculation formula is: theoretical combustion temperature = total calorific value of solid fuel combustion / [(mass of sintering mixture - mass of sintering mixture × fuel ratio) × average specific heat capacity] - initial temperature; the total calorific value of solid fuel combustion is the sum of the products of the calorific value of each fuel, the mass of sintering mixture, the fuel ratio and the mass proportion of each fuel;

[0021] Right now,

[0022] ;

[0023] in, is the correction factor, with an empirical value of 1.4, which is the ratio of the measured temperature of the sintering mixture to the theoretical calculated temperature; n is the total number of fuel types used; i is a corresponding fuel, i=1, 2, ..., n.

[0024] As a further improvement of the present invention, the harmful gas emission index I e The calculation formula is: Harmful gas emission index = sintering mixture mass × fuel ratio × mass proportion of each fuel × (volatile matter content + N element content + S element content);

[0025] Right now, .

[0026] As a further improvement of the present invention, the usage cost index W u The calculation formula is: cost index = sintering mixture mass × fuel ratio × mass proportion of each fuel × factory price / grindability index;

[0027] Right now, .

[0028] Before being used in production, solid fuel for sintering must be crushed and screened into particles less than 5mm before entering the silo, so both the factory price and grindability must be considered.

[0029] As a further improvement of the present invention, the grindability index H i The calculation method is as follows:

[0030] ;

[0031] Among them, Z i The mass of a fuel after crushing with a particle size less than 5 mm, kg; G i is the mass of a certain fuel before crushing, kg; t i The time taken for a certain type of fuel to break up, min.

[0032] Therefore, the cost index W can be u The calculation formula is used for transformation;

[0033] Right now, .

[0034] As a further improvement of the present invention, the specific calculation formula of the fuel evaluation characteristic value K is:

[0035]

[0036] .

[0037] As a further improvement of the present invention, in the comprehensive evaluation model of solid fuel for sintering, the calorific value Q of each fuel combustion is i is the low calorific value, which is measured and calculated according to national standards under dry basis conditions; initial temperature T0 and average specific heat capacity c p Sintering production parameters.

[0038] As a further improvement of the present invention, in the comprehensive evaluation model of solid fuel for sintering, the mass M of the sintering mixture s , fuel ratio Y f and the mass proportion of each fuel is X i All are sintering production parameters; fuel volatile content V i 、N element content N i and S content i All are measured and calculated under dry basis conditions in accordance with national standards.

[0039] As a further improvement of the present invention, the solid fuel includes but is not limited to one or a combination of biomass coke, semi-coke, blast furnace dust ash, anthracite, and coke powder.

[0040] As a further improvement of the present invention, in the comprehensive evaluation model of solid fuel for sintering, the theoretical combustion temperature can be corrected according to the lower calorific value of gas fuels such as natural gas, coke oven gas and blast furnace gas; the harmful gas emission index can be corrected according to the unit release of harmful gases such as NO and SO2 during the combustion of gas fuels such as natural gas, coke oven gas and blast furnace gas; the use cost index can be corrected according to the storage, processing and transportation technology of gas fuels such as natural gas, coke oven gas and blast furnace gas; after the index correction, the model can be directly used for the comprehensive evaluation of various sintering fuel usage schemes such as gas-gas mixing, gas-solid mixing, solid-solid mixing, etc.

[0041] As a further improvement of the present invention, when gas fuel is used for sintering, the mass proportion of the gas fuel in the model can be changed to volume proportion; the volatile matter content V corresponding to the gas fuel is i can be removed; and the corresponding N element content N i and S content i It can be changed to release NO per unit volume of gas fuel during combustion x and SO2 concentration, in mg / m 3 , both of which are measured by flue gas analysis experiments per unit volume of gas fuel combustion.

[0042] The beneficial effects of the present invention are:

[0043] 1. The method for establishing a comprehensive evaluation model for solid fuel for sintering provided by the present invention considers the mixed combustion reaction behavior of different types of fuels in an adiabatic system based on the energy balance principle, proposes the concept of theoretical combustion temperature of sintering raw materials, determines three indicators affecting pollutant emissions and two indicators affecting production costs, and establishes a comprehensive evaluation model for solid fuel for sintering. The model is easy to calculate and has important guiding significance for the selection and optimization of fuel types and proportions for on-site sintering production. At the same time, the modification of corresponding indicators can also be used for the evaluation of other types of sintering fuels.

[0044] 2. The comprehensive evaluation model of solid fuel for sintering provided by the present invention comprehensively considers the combustion reaction process and use cost of the fuel in sintering production, obtains the theoretical combustion temperature of the sintering mixture after the fuel combustion is completed through systematic theoretical analysis, and combines it with the environmental indicators of current production concern, and creatively proposes a calculation method for the harmful gas emission index of fuel combustion. On this basis, an evaluation model with the evaluation characteristic value K as an indicator is proposed. By comparing the size of the K value, it is easy to derive the advantages and disadvantages of different types of fuel ratios and obtain the best solid fuel use plan. The model is easy to calculate and easy to evaluate, and has important guiding significance for the optimization and selection of solid fuel for sintering.

[0045] 3. The comprehensive evaluation model for solid fuel for sintering provided by the present invention uses the harmful gas emission index as an important indicator for fuel use evaluation, which can effectively measure the degree of environmental pollution caused by different types of solid fuels used in sintering production. In the early stage of the combustion reaction, most of the volatile matter precipitated will adhere to the surface of the sintering flue and the main exhaust fan, affecting the service life of the equipment; a small part will be discharged into the atmosphere to form fine particles and cause haze. The NO x and SO2 generated during combustion, which are the main causes of acid rain. Therefore, the size of the harmful gas emission index obtained based on these three sub-indicators fully reflects the degree of harm caused by sintering fuel to the environment.

[0046] 4. The comprehensive evaluation model for solid fuel for sintering provided by the present invention can be directly applied to the comprehensive evaluation of various sintering fuel usage schemes such as gas-gas mixing, gas-solid mixing, solid-solid mixing, etc., by modifying the corresponding sub-indicators, and has a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 A schematic flow chart of a method for establishing a comprehensive evaluation model for solid fuel for sintering provided by the present invention. DETAILED DESCRIPTION

[0048] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0049] It should also be noted that, in order to avoid obscuring the present invention due to unnecessary details, only structures and / or processing steps closely related to the scheme of the present invention are shown in the drawings, while other details that are not closely related to the present invention are omitted.

[0050] In addition, it should be noted that the terms "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or apparatus.

[0051] See also Figure 1 As shown, the present invention provides a method for establishing a comprehensive evaluation model for sintering solid fuel, comprising the following steps:

[0052] S1, the comprehensive evaluation model of solid fuel for sintering is based on the energy balance principle and considers the mixed combustion reaction behavior of different types of solid fuels in an adiabatic system, mainly based on the theoretical combustion temperature T c , Harmful Gas Emission Index I e and the usage cost index W uOn three main indicators;

[0053] S2, based on the above three main indicators, establish the fuel evaluation characteristic value K based on meeting production needs;

[0054] Fuel evaluation characteristic value = theoretical combustion temperature / (harmful gas emission index × use cost index), dimensionless; that is, ;

[0055] S3, calculating the fuel evaluation characteristic value K of the solid fuel batching scheme of a predetermined type and a predetermined ratio through the above comprehensive evaluation model, and comparing and analyzing the K value to quantitatively evaluate the advantages and disadvantages of different fuel batching schemes;

[0056] The larger the K value, the better the batching scheme, and the smaller the K value, the worse the batching scheme; based on this, the solid fuel selection scheme for sintering is optimized.

[0057] Preferably, in step S1, the theoretical combustion temperature T c It includes the following sub-indicators: The calorific value of each fuel combustion Q i , initial temperature T0 and average specific heat capacity c p ;

[0058] The harmful gas emission index I e Includes the following sub-indicators: Fuel volatile content V i 、N element content N i and S content i ;

[0059] The usage cost index W u Includes the following sub-indicators: Factory price W i and grindability index H i ;

[0060] In addition, the above three main indicators in the comprehensive evaluation model of sintering solid fuel also include the following common sub-indicators: sintering mixture quality M s , fuel ratio Y f and the mass proportion of each fuel is X i .

[0061] Preferably, the theoretical combustion temperature T c The calculation formula is: theoretical combustion temperature = total calorific value of solid fuel combustion / [(mass of sintering mixture - mass of sintering mixture × fuel ratio) × average specific heat capacity] - initial temperature; the total calorific value of solid fuel combustion is the sum of the products of the calorific value of each fuel, the mass of sintering mixture, the fuel ratio and the mass proportion of each fuel;

[0062] Right now,

[0063] ;

[0064] in, is the correction factor, with an empirical value of 1.4, which is the ratio of the measured temperature of the sintering mixture to the theoretical calculated temperature; n is the total number of fuel types used; i is a corresponding fuel, i=1, 2, ..., n.

[0065] Preferably, the harmful gas emission index I e The calculation formula is: Harmful gas emission index = sintering mixture mass × fuel ratio × mass proportion of each fuel × (volatile matter content + N element content + S element content);

[0066] Right now, .

[0067] Preferably, the usage cost index W u The calculation formula is: cost index = sintering mixture mass × fuel ratio × mass proportion of each fuel × factory price / grindability index;

[0068] Right now, .

[0069] Preferably, the grindability index H i The calculation method is as follows:

[0070] ;

[0071] Among them, Z i The mass of a fuel after crushing with a particle size less than 5 mm, kg; G i is the mass of a certain fuel before crushing, kg; t i The time taken for a certain type of fuel to break up, min.

[0072] Preferably, the usage cost index W u The calculation formula can be further transformed;

[0073] Right now, .

[0074] Preferably, the specific calculation formula of the fuel evaluation characteristic value K is:

[0075]

[0076] .

[0077] Preferably, in the comprehensive evaluation model of solid fuel for sintering, the calorific value Q of each fuel combustion is i is the low calorific value, which is measured and calculated according to national standards under dry basis conditions; initial temperature T0 and average specific heat capacity c pSintering production parameters.

[0078] Preferably, in the comprehensive evaluation model of solid fuel for sintering, the mass M of the sintering mixture is s , fuel ratio Y f and the mass proportion of each fuel is X i All are sintering production parameters; fuel volatile content V i 、N element content N i and S content i All are measured and calculated under dry basis conditions in accordance with national standards.

[0079] Preferably, the solid fuel includes but is not limited to one or a combination of biomass coke, semi-coke, blast furnace dust ash, anthracite, and coke powder.

[0080] The present invention will be further described below with reference to specific embodiments.

[0081] Example 1

[0082] Embodiment 1 of the present invention provides a method for establishing a comprehensive evaluation model for sintering solid fuel, which is used for sintering solid fuel evaluation calculation, and is specifically performed in the following steps:

[0083] 1. Fuel industry analysis is carried out in accordance with the national standard CB212-91 to obtain the air-dried volatile matter of the coal.

[0084] 2. Fuel element analysis is carried out in accordance with the national standard GB 476-91 to obtain the N and S contents on an air-dried basis.

[0085] 3. The calorific value of the fuel is tested in accordance with the national standard GB213-87 and the low calorific value is calculated.

[0086] 4. Under the adiabatic system, the theoretical combustion temperature of the fuel combustion in the sintering mixture is calculated as follows:

[0087] ;

[0088] 5. The harmful gas emission index of fuel combustion is calculated as follows:

[0089] ;

[0090] 6. The grindability index of the fuel is calculated as follows:

[0091] ;

[0092] 7. The fuel cost index is calculated as follows: ;

[0093] 8. The evaluation characteristic value K in the comprehensive evaluation model of sintering solid fuel is calculated according to the following method:

[0094]

[0095] .

[0096] 9. The evaluation characteristic value K of different types of fuel is calculated as shown in the following table.

[0097] Table 1 shows the performance test data of different types of fuels

[0098]

[0099] Table 2 shows the evaluation index parameters of different types of fuel blending schemes

[0100]

[0101] Table 3 shows the evaluation index of different batching schemes calculated according to the calculation model

[0102]

[0103] From the calculation results in Table 3, it can be seen that the K value of Scheme 1 is the largest, and this batching scheme is the best; the K value of Scheme 3 is the smallest, and this batching scheme is the worst.

[0104] In summary, the present invention provides a method for establishing and applying a comprehensive evaluation model for solid fuel for sintering. It includes the following steps: S1, the comprehensive evaluation model for solid fuel for sintering considers the mixed combustion reaction behavior of different types of solid fuels under an adiabatic system based on the energy balance principle, and is mainly based on three main indicators: theoretical combustion temperature, harmful gas emission index and use cost index; S2, based on the above three main indicators, a fuel evaluation characteristic value K based on meeting production needs is established; S3, the fuel evaluation characteristic value K of the solid fuel batching scheme of a predetermined type and a predetermined ratio is calculated through the above comprehensive evaluation model, and the K value is compared and analyzed to quantitatively evaluate the advantages and disadvantages of different fuel batching schemes. The model is easy to calculate, and has important guiding significance for the selection and optimization of fuel types and ratios for on-site sintering production. At the same time, the modification of corresponding indicators can also be used for the evaluation of other types of sintering fuels.

[0105] The above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for establishing a comprehensive evaluation model for solid fuel for sintering, characterized in that: The steps include: S1, the comprehensive evaluation model of solid fuel for sintering is based on the energy balance principle and considers the mixed combustion reaction behavior of different types of solid fuels in an adiabatic system, mainly based on the theoretical combustion temperature T c , Harmful Gas Emission Index I e and the usage cost index W u On three main indicators; S2, based on the above three main indicators, establish the fuel evaluation characteristic value K based on meeting production needs; Fuel evaluation characteristic value = theoretical combustion temperature / (harmful gas emission index × use cost index), dimensionless; that is, ; S3, calculating the fuel evaluation characteristic value K of the solid fuel batching scheme of a predetermined type and a predetermined ratio through the above comprehensive evaluation model, and comparing and analyzing the K value to quantitatively evaluate the advantages and disadvantages of different fuel batching schemes; The larger the K value, the better the batching scheme, and the smaller the K value, the worse the batching scheme; based on this, the solid fuel selection scheme for sintering is optimized.

2. The method for establishing a comprehensive evaluation model for sintering solid fuel according to claim 1, characterized in that: In step S1, the theoretical combustion temperature T c It includes the following sub-indicators: The calorific value of each fuel combustion Q i , initial temperature T0 and average specific heat capacity c p ; The harmful gas emission index I e Includes the following sub-indicators: Fuel volatile content V i 、N element content N i and S content i ; The usage cost index W u Includes the following sub-indicators: Factory price W i and grindability index H i ; In addition, the above three main indicators in the comprehensive evaluation model of sintering solid fuel also include the following common sub-indicators: sintering mixture quality M s , fuel ratio Y f and the mass proportion of each fuel is X i .

3. The method for establishing a comprehensive evaluation model for sintering solid fuel according to claim 2, characterized in that: The theoretical combustion temperature T c The calculation formula is: theoretical combustion temperature = total calorific value of solid fuel combustion / [(mass of sintering mixture - mass of sintering mixture × fuel ratio) × average specific heat capacity] - initial temperature; the total calorific value of solid fuel combustion is the sum of the products of the calorific value of each fuel, the mass of sintering mixture, the fuel ratio and the mass proportion of each fuel; Right now, ； in, is the correction factor, with an empirical value of 1.4, which is the ratio of the measured temperature of the sintering mixture to the theoretical calculated temperature; n is the total number of fuel types used; i is a corresponding fuel, i=1, 2, ..., n.

4. The method for establishing a comprehensive evaluation model for sintering solid fuel according to claim 3, characterized in that: The harmful gas emission index I e The calculation formula is: Harmful gas emission index = sintering mixture mass × fuel ratio × mass proportion of each fuel × (volatile matter content + N element content + S element content); Right now, .

5. The method for establishing a comprehensive evaluation model for sintering solid fuel according to claim 3, characterized in that: The usage cost index W u The calculation formula is: cost index = sintering mixture mass × fuel ratio × mass proportion of each fuel × factory price / grindability index; Right now, .

6. The method for establishing a comprehensive evaluation model for sintering solid fuel according to claim 5, characterized in that: The grindability index H i The calculation method is as follows: ； Among them, Z i The mass of a fuel after crushing with a particle size less than 3 mm, kg; G i is the mass of a certain fuel before crushing, kg; t i The time taken for a certain fuel to break up, min; Therefore, the cost index W can be u The calculation formula is used for transformation; Right now, .

7. The method for establishing a comprehensive evaluation model for sintering solid fuel according to claim 6, characterized in that: The specific calculation formula of the fuel evaluation characteristic value K is: 。 8. The method for establishing a comprehensive evaluation model for sintering solid fuel according to claim 2, characterized in that: In the comprehensive evaluation model of solid fuel for sintering, the calorific value of each fuel combustion is Q i is the low calorific value, which is measured and calculated according to national standards under dry basis conditions; initial temperature T0 and average specific heat capacity c p is the sintering production parameter; in the comprehensive evaluation model of solid fuel for sintering, the sintering mixture quality M s , fuel ratio Y f and the mass proportion of each fuel is X i All are sintering production parameters; fuel volatile content V i 、N element content N i and S content i All are measured and calculated under dry basis conditions in accordance with national standards.

9. The method for establishing a comprehensive evaluation model for sintering solid fuel according to claim 1, characterized in that: The solid fuel includes, but is not limited to, one or a combination of biomass coke, semi-coke, blast furnace dust ash, anthracite, and coke powder.

10. An application of a comprehensive evaluation model for solid fuel for sintering obtained by the method for establishing a comprehensive evaluation model for solid fuel for sintering according to any one of claims 1 to 9, characterized in that: The comprehensive evaluation model for solid fuel for sintering is modified by the corresponding sub-indicators. When gas fuel is used for sintering, the mass proportion of gas fuel in the model can be changed to volume proportion; the volatile matter content V corresponding to the gas fuel is i can be removed; and the corresponding N element content N i and S content i It can be changed to release NO per unit volume of gas fuel during combustion x and SO2 concentration, in mg / m 3 , both of which are measured by unit volume of gas fuel combustion flue gas analysis experiments; after index correction, the model can be used for the comprehensive evaluation of three sintering fuel usage schemes: gas-gas mixing, gas-solid mixing, and solid-solid mixing.

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