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Study of TBS Separation Effect Optimization
The lower separation limit of dense medium hydrocyclone and the upper limit of flotation machine are 0.5mm. However, in actual production, the separation efficiency of dense medium hydrocyclones for fine-grained is low, and the separation efficiency of coarse-grained grade is low, which leads to the ineffective separation of coarse coal slime between them, which will easily cause the problems of poor dielectric removal effect of dense medium products and low recovery rate of cleaned coal. Therefore, it is very important to optimize the separation effect of TBS. In this study, the production data of Gaohe coal washing plant are used for statistical analysis. The coarse coal slime of the plant (1.5-0.2mm) is sorted by TBS interference bed of MEP company in the UK.
TBS System Inspection
(1)Preparation system. The main task of the preparation system is to realize the classification of the materials in the water of the fine coal screen. Among them, the coarse particles are separated by TBS, and the finer particles are separated by flotation machine. In order to evaluate the classification effect of the classification cyclone, the samples of feed, overflow and underflow of the cyclone are collected respectively in the same period. The results show that the hydrocyclone has a good classification effect, overflow does not occur coarse, underflow - 0.125mm content accounts for 19.00% of the product yield, ash content is 29.68%, underflow entrainment is serious, especially - 0.074mm particle size still accounts for 10.92%, ash content is as high as 37.32%. This part of fine-grained materials will not be effectively separated in TBS, and most of them will enter the overflow of TBS.
(2)Sorting system. The main task of the separation system is to realize the separation of fine coal (1.5-0.25 mm) according to the density. In order to evaluate the separation effect of TBS in coal preparation plant, the samples of feed, overflow and underflow of TBS were collected in the same period. It can be seen from the distribution rate of each particle size fraction in TBS that the TBS interference bed separator, which is separated by density, has a relatively serious effect of grading according to the particle size, especially about 50% of the particles larger than 1 mm are distributed into the underflow, which is the fundamental reason for the low ash content of coarse-grained TBS underflow.
(3)Product post-processing system. The tailings are dehydrated by high-frequency screen and mixed with mixed coal for sale. The overflow concentrate is classified by concentration cyclone and combined with dense medium clean coal as clean coal product. The ash content of tailings affects the quality of total clean coal to a certain extent. The ash content of fine clean coal mainly depends on the effect of TBS, and to a certain extent, it is also related to the desliming effect of overflow of TBS. According to the above test results, there are 22.60% high ash fine particles (< 0.125mm) with ash content of 28.27% in TBS overflow products. If the removal efficiency is low, this part of material will seriously affect the quality of clean coal.
Optimization and Effect Evaluation of TBS System
(1)The influence of top water quantity on separation results. Under the condition of basically the same feed rate, the TBS separator was set at the density of 1.27g/cm3, the top water volume was changed, and the overflow and underflow samples were collected for screening. It is found that for the same size of materials, from the influence of different top water on the distribution curve of each particle size, it can be seen that with the increase of top water, the separation density of each particle size has a decreasing trend, and the performance of coarse particles is more obvious. When the top water volume increases from 90m3/h to 100m3/h, the separation density decreases less; when the top water volume increases from 100m3/h to 110m3/h, the separation density decreases more; under each top water quantity, the separation density decreases more The loss of coarse grain is more serious when the top water is 110m3/h.
(2)The influence of set density on separation results. The results show that: with the increase of density setting value, the actual separation density of each particle size increases; when the density setting value is 1.27g/cm3 and below, the low-density coarse particle loss is large; when the density setting value is 1.29g/cm3, the fine-grained separation density is higher, However, the ash content of > 0.125mm aggregate grade is still qualified; considering the site conditions, the set value of separation density should be about 1.28g/cm3.
(3)TBS separation effect tracking results. Through the above analysis, the separation parameters of TBS separator are optimized, and part of the pipe network transformation is completed. After optimization, the separation effect of TBS is obviously improved. Firstly, the ash content of coarse clean coal slurry is reduced. Before the optimization and transformation, the average ash content of + 0.125mm is 11.15%, which is higher than the product quality index required on site; the ash content of coarse clean coal slurry is reduced by about 2%, which meets the process requirements and the product quality is stable. At the same time, the content of TBS tail ash increased from 44.35% to more than 70%, the loss of clean coal was reduced, and the separation accuracy was significantly improved.
Numerical Simulation of Flow Field in TBS
(1)The initial and boundary conditions are calculated. This numerical simulation uses gambit 2.4.6, the preprocessing software provided by FLUENT software, according to the structural parameters of TBS used in Gaohe coal preparation plant, the physical model was constructed. The water phase was 20 ℃, the density was 998.2kg/m3, and the viscosity was 1.003 × 10-3pa · s. In the calculation of solid-liquid multiphase flow, the particle size and density of coal particles are assumed according to the actual situation, and mixed with continuous phase medium water in a certain proportion, and then fed to the interference bed separator. Inlet boundary conditions: slurry flow 175m3/h, top water flow 100m3/h.
Outlet boundary condition: the lower tailings discharge outlet is closed to study the distribution of fluid interference in the fluidized bed separator during the formation of fluidized bed.
Gravity field condition: considering the influence of gravity on the internal flow field of the separator, the gravity acceleration is set as - 9.81m/s2.
(2)Density distribution of solid-liquid multiphase flow. It can be seen from the density distribution inside the separator that the high-density area is mainly concentrated above the top water distribution plate and near the tailings discharge outlet, along the top water cloth plate up to the concentrate overflow port. With the increase of height, the density of suspended slurry gradually decreases, which indicates that the ascending water flow can realize the density stratification of non density particles. It can be seen from the density distribution of pulp along the cross-section of the separator with different heights that the density distribution of the three sectors of the separator is relatively uniform, so a stable bed can be formed in the actual material separation process according to the density.
(3)Solid particle concentration distribution in solid-liquid multiphase flow. It can be seen from the concentration distribution of different attribute particles in different height cross-sections of the interference bed separator that the high-density coarse particles are mainly concentrated above the top water distribution plate and near the tailings discharge outlet, and some of the low-density coarse particles gather above the top water distribution plate and near the tailing discharge outlet, and some of the low-density coarse particles move upward with the rising water flow As a result, these fine particles are mainly concentrated in the upper layer of the interference bed separator and enter the clean coal products with the overflow. This also shows that the interference bed separator has a suitable separation size range for the separation of materials according to the density.
Conclusion
In this study, through the current situation inspection of TBS coarse slime separation system in Gaohe coal preparation plant, the existing problems of the system were diagnosed. By reducing the diameter of underflow outlet, the grading particle size was increased to 0.23mm, and the entrainment of fine particles in underflow was reduced. Secondly, the operating conditions of the separator were optimized, and the influence law of operation parameters on the bottom overflow ash content and separation density of TBS was clarified, and the more reasonable operation system was determined. The clean coal + 0.125mm ash content was controlled below 9.5%, and the underflow tail coal + 0.125mm ash content was above 70%. The optimized TBS separation effect was good and the operation was stable.
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