The SLCS decomposition furnace is a type of decomposition furnace used by the Danish Smith Company in the cement industry since the 1980s. The basic process is shown in Figure 1. It is actually a combination of SLC decomposition furnaces that separate the three winds into the furnace for a single series of preheaters. SLCS decomposition furnaces are used in Shanghai No. 4 precalciner kiln system of Shanghai Cement Plant and Huaxin Cement Plant. According to Smith, the SLCS decomposing furnace is a kind of decomposing furnace that can adapt to medium or variable coal quality because it adopts the method of three winds directly into the furnace.

The temperature of the decomposition furnace can be adjusted by adjusting the proportion of the material in the four-stage cylinder into the decomposition furnace to meet the requirements of different coal quality. From the actual production of Huaxin Cement Co., Ltd. No. 4 kiln and Shanghai Cement Plant, the overall application effect of SLCS decomposition furnace is better, and the clinker production can exceed the design output. The Institute of Silicate Engineering of Nanjing University of Technology and Huaxin Cement Co., Ltd. jointly conducted a comprehensive operational diagnostic study of the Huaxin No. 4 kiln system. This paper takes the SLCS decomposition furnace as the object, and combines the original fuel situation, cold model test and thermal test and reverse calculation results to systematically comprehensively analyze and comment on it.

1 Main cold model test results and analysis 1. 1 Three-dimensional flow field of gas in SLCS decomposition furnace In the second self-modeling zone of gas flow (square of turbulent flow), the gas of the decomposition furnace is gasized by a gas three-dimensional flow field intelligent measurement system. The three-dimensional flow field is measured under the condition that the average wind speed of the decomposition furnace inlet is u = 36 m/s, and the three-dimensional flow field distribution of the gas of the decomposition furnace body is shown in Fig. 2. u is the axial velocity, u is the radial velocity, and p is the total static pressure.

Comparing the axial wind speed distribution with the axial wind speed distribution of the restricted jet flow, it can be seen that the gas flow in the SLCS decomposition furnace, especially in the middle and lower parts, is still basically a restricted jet flow, and is preheated with the Krupp vertical drum. The gas flow field inside the device is similar. The lower area can also be divided into several areas, as shown in Figure 3.

As can be seen from the figure, 1 is the injection zone, a conical area above the tertiary air inlet, and its axial wind speed basically maintains the inlet wind speed. Due to the high wind speed, this area is the main area where the pulverized coal and materials are dispersed and mixed. 2 The spray column area has the same flow direction as the inlet spray direction, but the axial speed decreases continuously along the flow direction. The relative velocity between the material and the gas flow in this area is relatively low, contributing less to material dispersion and material residence time. If the spray column area is too large, it will easily lead to a lower ratio of gas residence time, which affects the volumetric effective utilization efficiency of the decomposition furnace. 3 is a recirculation zone, an annular zone near the lower wall of the decomposition furnace. The gas flow direction in this area is opposite to that of the main body. Its function is to cause the reverse back mixing of the material in the decomposition furnace, thereby prolonging the residence time of the material in the decomposition furnace, and improving the volume utilization efficiency of the decomposition furnace. 4 is the vortex area, which is a spray. The area between the column area and the recirculation zone. The gas flow direction in this area is disordered and variable, and the speed is low. The main function is to make some materials migrate from the main flow area to the vicinity of the wall surface, and this part of material can fall down in the recirculation zone, thereby causing a certain degree of material backmixing.

Compared with the axial wind speed, the radial wind speed and the tangent wind speed are small, especially in the middle and above, which are basically the plug flow. Functionally speaking, the tangential and radial wind speeds are the basic reasons for the reverse backmixing and lateral disturbance of the materials in the decomposition furnace. Therefore, it can be considered that the gas flow field in the SLCS decomposition furnace belongs to the axial jet flow field, which is more conducive to materials. Vertical mixing. However, the radial wind speed caused by the injection is very low, the material is not easy to produce strong lateral mixing and the necessary reverse material back mixing, so the ratio of the average residence time of the powdery material to the gas in the decomposition furnace will be smaller, that is, decomposition The volume utilization of the furnace is not ideal. Under the condition of the gas flow field structure, if the ideal pulverized coal combustion and carbonate decomposition effect are to be achieved, the effective volume of the decomposition furnace or the furnace temperature of the decomposition furnace must be increased.

The gas flow in the gooseneck (referring to the elbow at the top of the decomposition furnace) is basically a flat flow in the axial direction, the velocity component in other directions is very small, and the velocity distribution is relatively uniform. Therefore, in addition to the speed difference between the material and the pulverized coal in the gooseneck, except for the acceleration of the inlet and the turning of the material due to the inertia, the material and the gas flow have a certain speed difference, the material will be basically close to the plunger flow, and the combustion and decomposition reaction can only be It has a very limited compensation effect, so it will affect the overall performance index of the decomposition furnace.

Study on the resistance characteristics of the decomposition furnace The resistance characteristics of the SLCS decomposition furnace to the gooseneck outlet measured under the cold model test conditions are shown in Fig. 4 (corrected by the inlet and outlet wind speed). Figure 5 shows the Euler number and the Reynolds number. The relationship curve. u is the decomposition furnace inlet and the average wind speed of the section, m/ sp is the pressure drop at the end of the decomposition furnace inlet to the end of the gooseneck, Pa Re is the Reynolds number corresponding to the diameter of the decomposition furnace and the average wind speed of the section, Re = Du gas density, Kg/m Eu is the Euler number based on the average wind speed of the SLCS decomposition furnace. Eu = p/ Qu corresponds to Eu. The resistance test results show that the resistance loss of the gooseneck portion is small, only tens of Pascals. The pre-decomposition system has little impact and can be ignored.

The resistance coefficient of SLCS decomposition furnace is compared with some furnace types. See Table 1. Compared with NSF and RSP decomposition furnace, the resistance coefficient of SLCS decomposition furnace is lower, but it is higher than that of low-resistance decomposition furnace such as DD furnace. .

The resistance coefficient of some domestic decomposition furnaces is compared with the furnace type. 1. The material residence time distribution of the SLCS decomposition furnace The material residence time distribution is the basic distribution parameter reflecting the basic law of the material movement inside the reactor like the decomposition furnace. Under the premise of good dispersion, the reactor can fully exert its function only if it meets the basic time required for various chemical reactions in the reactor. The measurement results of the residence time distribution of the SLCS decomposition furnace body are shown in Fig. 6. t is the average residence time of the material, st is the average residence time of the gas, and s R is the variance of the residence time distribution, which characterizes the degree of backmixing of the materials in the furnace.

fruit. 5之间之间。 The decomposition of the gas, the ratio of the residence time of the decomposition furnace body with the change of the wind speed is small, within a certain range is maintained between 2. 5 2. 6. Under the working conditions, the ratio of gas residence time of the SLCS decomposition furnace body is slightly lower than that of the SLC decomposition furnace and ILC decomposition furnace of Liuzhou Cement Plant. Therefore, the law of gas-solid two-phase motion in such a spurt type decomposition furnace can be considered. Basically consistent. Since the high diameter of the SLCS decomposition furnace is relatively high and the axial air outlet structure is adopted, the ratio of the gas residence time is slightly lowered.

Since the gas is purely pulsating, the material lacks mixing in the cross-sectional direction, and the variance of the degree of backmixing of the material is relatively low, and R is lower than 0. 3. This is because the proportion of the recirculation zone and the vortex zone is small, so that the material is made. The flow is generally close to the flat flow.

The ratio of the gas residence time of the decomposition furnace including the gooseneck is relatively large, and only decreases to 2.02.35, which means that the gooseneck is basically a plug flow, and there is almost no back mixing. The analysis results of the gas flow field are consistent. Therefore, this gooseneck as a part of the decomposition furnace is not economical in terms of space utilization. For materials and coal Li Changyong, etc.: The gas-solid two-phase motion law of SLCS decomposition furnace has little contribution to the study of powder residence time, and makes decomposition The overall performance index of the furnace is greatly reduced.

If the average temperature of the gas in the decomposition furnace is 900 e, the fuel consumption of the decomposition furnace is approximately 60, the heat consumption of the clinker is 3 345 kJ/kg, and the actual decomposition amount of the material in the furnace is 70, the amount of gas passing through the decomposition furnace is calculated. The residence time of each part of the gas and materials of the decomposition furnace calculated as 76. 2 m / s is shown in Table 2.

The material retention time of each part of the decomposition furnace part of the SLCS furnace body gooseneck bending tube decomposition furnace as a whole can be seen, the presence of goosenecks increased the volume of the decomposition furnace area by nearly 50, but the effective residence time only increased 22. This is improved The effect of pulverized coal combustion and the improvement of the decomposition rate of the raw meal of the furnace have a certain effect. At the same time, it is also desirable as a kind of compensation measure for the decomposing furnace type with poor performance, but the increase time is only 1/time of the total residence time of the decomposition furnace zone. Around 5, the effect is not ideal, and the effect on improving the combustion effect is relatively low, so it is not a good solution for the design of the new decomposition furnace. It is necessary to improve the performance index of the decomposition furnace by optimizing the overall structure of the decomposition furnace.

As can be seen from Table 3, the SL value of the SLCS furnace is the lowest compared to other furnace types. That is to say, the space utilization rate of the decomposition furnace is not high. The average residence time of the gas in the SLCS decomposition furnace of Huaxin Cement Plant is as long as 4.3 s, which is higher than the gas residence time of most decomposition furnaces. According to this calculation, the average residence time of the materials in the decomposition furnace is less than 10 s. . Considering that the absolute value of the recirculation zone in the actual decomposition furnace is large, the size of the mass in the furnace is large, and the interaction between the particles, etc., the particle residence time may be slightly higher than 10 s. From the fuel research results, The burning characteristics of the bituminous coal samples provided by the factory are relatively good, so the residence time of the coal powder in the decomposing furnace should be said to meet the basic requirements of combustion. The flammability test of suspended coal powder shows that when the average temperature in the furnace reaches 900 e, the burnt degree of pulverized coal in 10 s can reach close to 80. The actual decomposition furnace has high wind speed, large turbulence and good material dispersion. The actual burning degree of pulverized coal can reach 80 85, which can basically maintain the normal operation of the kiln system. Even if the output is appropriately increased, it has certain adaptability within a limited range. However, when the coal quality is poor, the burning rate of pulverized coal will be significantly reduced, the burning degree of the furnace will decrease, and the problem of insufficient combustion capacity of the decomposition furnace will be highlighted. The temperature of the exhaust gas from the pre-decomposition system will also be certain. Ascending, clinker heat consumption increases, which in turn will further affect the residence time and burnout of pulverized coal. At this time, only by increasing the temperature of the decomposition furnace can the burnout be improved and the production stability be maintained.

Comparison of gas residence time ratios of several decomposing furnaces When the volumetric volumetric production test of the furnace type furnace was conducted, the material dispersion and movement conditions in the decomposition furnace model were observed, and the material dispersion in the decomposition furnace was found to be good. The material in the lower part of the decomposition furnace is similar to the movement of the sterilizing bed. The concentration of the material in the area is relatively high, and the back mixing of the material is also significantly more severe. However, in the middle and upper part of the decomposition furnace, the concentration of the powder is significantly reduced. Only a fraction of the lower area, the material movement is basically a plunger flow, and no obvious material back mixing is observed, thus it is also proved from another aspect. The space utilization rate of the upper and upper areas of the decomposition furnace is low, which is the basic reason for the relatively low residence time ratio of the decomposition furnace gas, which is consistent with the flow field analysis result.

Observations show that the material in the gooseneck is basically a plunger flow, and the material is basically flashed in this part, and the contribution to the residence time of the coal powder and the material is small, and the oxygen content in the gas is relatively low. Therefore, the effect on improving combustion and decomposition reactions is also very limited.

In general, due to the lack of effective lateral mixing in the SLCS decomposition furnace, the ratio of gas residence time is small. In the current situation, it is only suitable to burn medium and high quality coal, and the adaptability to poor quality coal is poor. This kind of decomposition furnace is actually combined with the five-stage cyclone tube to form/decompose the belt 0, but the swirling force in the cyclone cylinder is large, the material is basically adhering to the movement, and the combustion environment is very poor, so it is difficult to burn the pulverized coal. Effective supplementation. At the same time, combustion science and technology are also likely to collect some of the mechanically incompletely burned pulverized coal from the decomposition furnace into the kiln, causing it to burn in the kiln, resulting in high kiln exhaust gas temperature and low oxygen content, which is bad for actual production. influences. When using low-volatility coal or low-quality coal as fuel, such problems will become more prominent, which will not only lead to an increase in the temperature of the exhaust gas from the preheater, but also an increase in heat consumption and a decrease in production, and may affect the kiln system. Stable operation. Therefore, it is necessary to improve the movement of materials and gases in the furnace, improve the dispersion and uniformity of materials through necessary structural improvements, prolong the effective residence time of coal powder and materials, and improve the utilization efficiency of the decomposition furnace, thereby improving Its overall performance indicators increase the adaptability to low-quality fuels. In the current situation, when the coal quality is poor, the combustion temperature of the decomposition furnace can only be increased by a part of the material entering the ascending flue to improve the pulverized coal burnt degree.

2 Conclusions 1) The furnace type is simple, the arrangement is convenient, the resistance loss is moderate, and the three winds are separately entered into the furnace and the third air in the furnace is not mixed with the kiln gas phase is the basic feature of the SLCS decomposition furnace.

2) The pulverized coal nozzle is installed at the joint between the furnace column and the lower cone. This part is a region where the gas flow field is relatively turbulent and the gas-solid two-phase mixing is sufficient, which is beneficial to the rapid combustion of pulverized coal in pure hot air. Since the concentration of pulverized coal in this area is the highest and the oxygen content is also close to the highest, it may be a relatively intense combustion reaction in the furnace, so the temperature will be much higher than the average temperature in the decomposition furnace and the outlet temperature of the decomposition furnace.

3) The average gas residence time ratio of the SLCS decomposition furnace (including gooseneck) used in the No. 4 kiln system of Huaxin Cement Plant is 2.22. When the clinker production is 2 000 t / h, the pulverized coal is in the actual decomposition furnace. The residence time is about 10 s, which basically satisfies the residence time necessary for the combustion of the pulverized coal used. Increasing the temperature of the decomposition furnace also has a certain adaptability to increase the output.

4) The three-dimensional flow field inside the SLCS decomposition furnace is more conducive to the good dispersion of the material. Therefore, the residence time of the solid particles in the decomposition furnace can be considered as a truly effective combustion and chemical reaction time. The good material dispersion effect is the basic premise to ensure the normal dispersion, heat transfer, combustion and decomposition reactions.

5) The solid-state residence time ratio of pulverized coal and material in the SLC body is 2.56, and the ratio in the gooseneck is only 1. 525. The volume of the gooseneck tube accounts for 1/3 of the volume of the entire decomposition furnace zone, and the material The residence time only accounts for 22. The total decomposition time is basically the furnace type that can meet the design output requirement and the volume utilization efficiency is relatively low. The adaptability to the actual production is obtained by greatly increasing the volume of the decomposition furnace. Not economical, so the decomposition furnace is not an ideal decomposition furnace.

Chen Quande, Cao Chen. New dry process cement production technology [M]. Beijing: Construction Engineering Press, Jane Yufu, Li Changyong. Development of a new gas three-dimensional flow field intelligent measurement system Hu Daohe, Gu Dagong, Li Changyong. Research on the working principle of the vertical cylinder preheater [J]. Silicic acid Hudaohe, Li Changyong, Cai Yuliang, et al. Application of Reverse Engineering Method in Cement Industry Li Changyong et al.: Study on gas-solid two-phase motion law of SLCS decomposition furnace

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