High separation efficiency of calcium carbide slag by spiral chute


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Spiral chute is used to purify carbide slag with high separation efficiency

The waste residue produced by acetylene gas preparation from calcium carbide is usually treated by landfill, which occupies land and pollutes the environment. The consumption of calcium carbide is huge in China, so the pollution of carbide slag is very serious. The main component of calcium carbide slag is Ca (OH) 2, which can be used to produce cement or other industrial raw materials after purification. The cost of purification of carbide slag by chemical method is huge, which can not be industrialized at present. Therefore, the physical purification of carbide slag is of great significance to the recycling of carbide slag resources.

 Spiral chute

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1. Feasibility of purifying carbide slag by spiral chute

After the carbide slag samples were dried by the dryer, they were divided into groups according to the particle size range. The standard hydrochloric acid solution was used for titration to determine the content of Ca (OH) 2 in the samples, and the iron content in the samples with different particle sizes was measured by magnetic separation. If the purity of calcium carbide slag is more than 95 μ m, it can be used in the preparation of calcium carbide particles.

2. Determination of structural parameters of spiral chute

The density, viscosity and operating pressure of 15% calcium carbide slag slurry are 1230kg / m3, 0.0018 PA · s and 0.1MPa, respectively. In order to ensure the purity of Ca (OH) 2 above 95%, the separation particle size was set to 40 μ M. In this paper, the standard spiral chute (cone angle = 10 °), the inlet diameter, overflow pipe diameter, cylindrical section length and overflow pipe insertion depth of spiral chute are selected, and the values given by Rietema are adopted.

Compared with single inlet spiral chute, symmetrical inlet spiral chute has better symmetry of flow field, reduces the loss of turbulent kinetic energy, thus improving the separation accuracy of spiral chute and reducing energy consumption. Therefore, we choose the spiral chute with symmetrical inlet for analysis. For the shape of inlet, previous studies have shown that rectangular inlet has higher separation efficiency than circular inlet. The main reasons are as follows: the rectangular inlet can have better contact with the wall of spiral chute, which can effectively avoid the dead zone caused by feed short circuit, and make the flow field in the inlet area more stable; secondly, in order to avoid the flow field disorder caused by the entrance jet impinging on the overflow pipe wall, it is appropriate to select the narrow rectangular inlet, and the long side should be close to the spiral chute wall. The size of the rectangular inlet is converted by the equivalent diameter formula, and the length width ratio is set as 2:1.

3. Causes of overflow coarsening of spiral chute and structure optimization

Previous studies have shown that when the spiral chute is working, the overflow will carry some coarse particles, which is called overflow coarsening. The main reason for the reduction of separation accuracy of hydrocyclone is overflow coarseness, which seriously affects the separation of hydrocyclone. There are two main reasons for the overflow coarsening: 1. There is short-circuit flow under the cover in the flow field of spiral chute, and the coarse particles involved in the short-circuit flow directly enter into the internal swirling flow without separation, resulting in the overflow coarsening; 2. A large number of coarse particles will be gathered in the underflow area of the spiral chute due to the separation effect, and some coarse particles will be brought into the overflow by the negative vortex generated by the rising air column, resulting in the overflow coarsening.

In view of the two causes of overflow run out, we optimize the spiral chute by using the annular teeth on the outer wall of the overflow pipe and the central column, so as to reduce the adverse effect of overflow thickening. In the optimized spiral chute structure, the annular teeth on the outer wall of the overflow pipe can effectively restrain or even eliminate the short-circuit flow, so as to eliminate the overflow coarsening caused by the short-circuit flow; the central column will replace the position of the air column, hinder the turbulence of the air column, make the shape and size of the air column more stable, and reduce the overflow run out caused by the turbulence of the air column.

After the optimization of spiral chute, the turbulence intensity of the fluid in the cylinder section decreases, while the turbulence intensity of the cone section increases, and the turbulence intensity of the cone section of the two hydrocyclones is greater than that of the column section. The results show that the higher turbulence intensity leads to the decrease of separation efficiency and the particle size increases with the increase of turbulence intensity. Therefore, after the optimization of spiral chute, the stability of the fluid in the column section is increased, and the stability of the fluid in the cone section is relatively weakened.

Through the study, we determined that the spiral chute for calcium carbide slag particles purification program is feasible, and can achieve good separation accuracy. Then we optimize the structure of spiral chute according to the reason of overflow and coarsening. The results show that after adding ring teeth and central column, the pressure drop of internal flow field decreases, the energy consumption decreases, the centrifugal force increases, and the separation efficiency increases. The spiral chute optimized by annular teeth and central column can achieve higher separation accuracy and higher separation efficiency. More details Welcome to consult the Red Star machine manufacturer

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