Drying treatment of solid waste electroplating sludge

Information source: website | release date: ; 2020-07-29 14:35:09 ; Views: 4710
Abstract: electroplating sludge mainly comes from solid waste produced by industrial electroplating plants. These wastes are mainly produced by liquid-phase chemical treatment of various electroplating waste liquid and electrolyte. Electroplating sludge has a large water content and complex composition, especially the heavy metals in it are more harmful. Therefore, the reduction, harmless and resource-based disposal of electroplating sludge is the focus of the current disposal of electroplating sludge.

1 summary

The reduction of electroplating sludge is mainly by drying, and the moisture content is 75% About the electroplating sludge is dried to a moisture content of 0 10% About (fully dried) or dried to moisture content 40% In order to meet the requirements of reduction, the next step of smelting and extraction of iron, copper, zinc and other metals. The drying of electroplating sludge has the following characteristics and requirements: the material is sticky and the fluidity is poor; the moisture content is high, the drying speed is slow, and the energy consumption is large; the tail gas has a peculiar smell, which needs to be treated; the material is required to be heated evenly and the operation environment is good, which can meet the target requirements at one time. Electroplating sludge is transported by shaftless screw conveyor After the material enters the blade, the material will be turned over and stirred by the rotation of the blade. The heating interface will be changed continuously. It will contact with the body and blade and be fully heated to evaporate the surface water contained in the material. At the same time, the material is transported to the outlet in a spiral path with the rotation of the impeller shaft, and continues to stir in the conveying process, so that the water seeping from the material continues to evaporate. *After that, the qualified products dried evenly are discharged from the outlet. A gas containing water vapor and a small amount of ultrafine solid particles is sent to Water film spray scrubber Filtered gas Meridians cold After settlement It is sent to the sewage treatment unit. The solid materials can be directly transported to landfill.

2.2 design principles

1) The sludge drying system is characterized by low energy consumption, low investment, small land occupation, convenient operation and management, and high sludge drying efficiency;

2) Equipment, equipment and electrical parts are products of well-known manufacturers with guaranteed quality;

3) In order to ensure the reliable and economic operation of sludge drying system, practical and feasible technical means should be adopted to improve the equipment level and make the production as automatic as possible;

2.3.2 selection of sludge thermal drying process scheme

     As early as In the 1940s, Japan and Europe and the United States have used direct heating drum dryer to dry sludge. After decades of development, the advantages of sludge thermal drying technology are gradually emerging

1) Reduction: with the decrease of sludge moisture content, the sludge volume decreases greatly;

2) Stabilization: with the decrease of sludge moisture content, the biological activity of sludge is inhibited, and the biological conversion process becomes extremely slow or broken. The product is odorless and pathogen free, which reduces the negative effects of sludge and makes the treated sludge more acceptable. The sludge will form granular or powdery stable products, and the sludge properties will be greatly improved. During the process of sludge thermal drying, acid soluble metals with strong migration ability and reducible and oxidizable heavy metals with potential migration ability can be transformed into inert residual heavy metals, thus playing a role in the stability of heavy metals in sludge.

3) Recycling: after heat drying, the calorific value of sludge is greatly increased to meet the requirements of self-sustaining combustion.

Therefore, no matter landfill, incineration, agricultural utilization or thermal energy utilization, sludge drying is an important Di step, which makes sludge drying play an increasingly important role in the whole sludge management system. twenty century ninety Since the s, the application of sludge drying technology in the treatment of municipal sludge has developed rapidly.

     Indirect heating wedge hollow paddle dryer

A. working principle

     It can indirectly heat or cool paste, granule, powder and paste materials, and complete the unit operations of drying, cooling, heating, sterilization, reaction, low-temperature calcination, etc. The special wedge-shaped stirring heat transfer blade in the equipment has high heat transfer efficiency and self-cleaning function of heat transfer surface.

     The wedge-shaped hollow blades are densely arranged on the hollow shaft, and the hot medium flows through the hollow shaft. The heat transfer area per unit effective volume is very large, and the temperature of the hot medium changes from -From 40 ℃ to 320 ℃, it can be steam or liquid type, such as hot water, heat transfer oil, etc. Indirect conduction heating, without carrying air to take away heat, heat is used to heat materials. The heat loss is only the heat dissipation to the environment through the insulation layer. The heat transfer surface of wedge blade has self-cleaning function. The relative movement of material particles and the wedge-shaped surface produces a washing effect, which can wash off the attached materials on the wedge-shaped surface, and keep a clean heat-transfer surface during operation. The shell of paddle dryer is W-shaped, and two to four hollow mixing shafts are arranged in the shell. The shell is provided with a sealed end cover and an upper cover to prevent dust leakage and collect solvent vapor. A baffle plate is set at the outlet to ensure the height of the material level, so that the heat transfer surface is covered by materials and fully play its role. The heat transfer medium flows through the shell jacket and the hollow stirring shaft through the rotary joint. The hollow stirring shaft has different internal structure according to the type of hot medium to ensure the best heat transfer effect.

B. process characteristics

(1) low energy consumption of pulp and leaf dryer: due to indirect heating, there is no large amount of air to take away heat, and the outer wall of the dryer is provided with insulation layer. For slurry materials, only 1.2kg water vapor is needed to evaporate 1kg water.

(2) pulp and leaf dryer system: the unit effective volume has a huge heat transfer surface, which shortens the processing time and reduces the equipment size. It greatly reduces the building area and building space

(3) a wide range of materials: different thermal media can be used to process both heat sensitive materials and materials requiring high temperature treatment. Common media are: steam, heat transfer oil, hot water, cooling water, etc. It can be operated continuously or intermittently, and can be used in many fields.

(4) less environmental pollution: there is little dust material entrained. The evaporation of solvent is very small, which is easy to handle. Closed circuit circulation can be used for contaminated materials or solvent recovery.

Low operating cost: low speed mixing and reasonable structure. The wear is small and the maintenance cost is very low.

(6) stable operation: due to the special compression expansion mixing effect of wedge-shaped blade, the material particles fully contact with the heat transfer surface, and the gradient of material temperature, humidity and mixing degree is very small in the axial range, so as to ensure the stability of the process.

C. disadvantages

     The heat transfer surface of the equipment is made of steel plate processing and welding. When steam is used as the hot medium, the weight of the equipment is large, and the one-time investment of the equipment is slightly higher.

D. scope of application

     The cost of operation is only one third of that of direct hot air dryer. It is especially suitable for solvent recovery, flammable and easy to oxidize heat sensitive materials. It is widely used in fine chemical industry, petrochemical industry and dyestuff industry.

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