Reading guidance：Deep dehydration methods for sludge mainly consist of natural air drying, heat drying dehydration, mechanical dehydration and electroosmotic dehydration. Natural air drying method can make the sludge m

     Deep dehydration methods for sludge mainly consist of natural air drying, heat drying dehydration, mechanical dehydration and electroosmotic dehydration. Natural air drying method can make the sludge moisture rate dropped to about 30%, but the processing cycle is too long facility covers an area of large area and affected by the climate. Thermal drying dehydration is the most effective sludge deep dehydration method, but large amounts of fossil fuel consumption and complex equipment make the investment and operation cost is high. Electro osmotic dehydration technology with solid particles is not easy to clog the advantages of filter media, and the dehydration process no phase change, so it can be in a relatively short time and low energy consumption will be sludge moisture rate fell to 60% but if further rely on Electro osmotic dehydration, power consumption increased rapidly will make the operation cost to rise sharply.
     By combining electro osmotic dehydration of low energy consumption and thermal drying efficiency, put forward the electro osmosis and thermal drying combined sludge deep dehydration method. Namely, the first electric penetration dewatering the sludge moisture content dropped to around 70%, and then thermal drying technology further deep dehydration to below 30%, fast, low cost to complete dehydration depth. The results from the following several aspects analysis:
  1. Change of characteristics of electro osmotic dehydration sludge drying process;
    The mechanical dehydration to the moisture content was 81% of the raw sludge with different degree of electro osmotic dewatering after dry heat treatment at 105 degrees Celsius, electro osmosis to water ratio of 76% anode mud cake surface with small cracks, with electroosmotic dehydration degree increased, the crack is more and more obvious. With the drying. The mud cake appeared edge cracking phenomenon, after the end of the dry cake basically split into pieces, and the electroosmotic dehydration after the lower water content of sludge drying after the rupture degree of mud cake bigger. This is due to the evaporation of water so that the drying shrinkage of sludge, crack phenomenon caused by shrinkage of the ultimate tensile stress is greater than the sludge when the cracks cause mud cake surface area increased and the sludge shrinkage rate and material surface area to volume ratio, the larger the ratio contraction rate more quickly.
2. Sludge drying characteristics under different temperature
    The raw sludge and different degree of electroosmotic dehydration sludge at 105 degrees Celsius to dry heat treatment, analysis of changes in the drying process of moisture content and drying rate. After electroosmotic dehydration of the sludge, the decline rate of moisture content of drying process were significantly faster in direct heat drying of sludge and sludge electrical penetration dehydration degree is high, the drying process of water rate decreased more quickly.
    Before drying to a certain degree of osmotic dehydration can effectively improve drying rate, drying time is shortened. Granular sludge with a slight negative charge and the surface adsorbed cations in solution to form electric double layer, under the action of electric field, solid adsorption of granular sludge surface cations carrying water to moving cathode, the formation of Electroosmosis. Water although not from the cathode prolapse of mud cake, but has from sludge moved inside to the particle clearance, reducing the subsequent desiccation resistance, so that the drying rate is improved.    In addition, electroosmotic dehydration is accompanied by the occurrence of electrochemical reaction, can make part of the adsorbed water and bound water to be released, making the subsequent drying dehydration easier. Electroosmotic dehydration needs different time to get different dehydration effect. The higher the electroosmotic level, the faster drying rate will be. Accordingly, the time used for reducing the same moisture content will be shorter.
  3. Analysis of energy consumption
    Some of these have been verified electro osmotic dehydration treatment on subsequent drying process has a favorable effect, that electro osmosis. Thermal drying process has technical advantages. In order to achieve high efficiency and energy saving technology in the practical application, also need to consider the energy consumption, reduce the cost of sludge treatment as soon as possible. Observed higher voltage during osmotic dehydration. The cake was formed a fever, heat loss, and calculating the same degree of electroosmotic dehydration under the average energy consumption ratio, the higher the voltage gradient, the dehydration process more energy than the average. Therefore, the actual dehydration with higher voltage gradient to reduce the dehydration time is not desirable, should be based on the effect of voltage on the thermal gradient the drying process and the total energy consumption, choose the best. By calculating the voltage gradient of different temperature, different voltage gradient of raw sludge direct drying with different levels of electroosmotic dehydration after heat drying to moisture content Total energy consumption for 20%.
    Electric heat drying before the osmotic dehydration can significantly reduce the total energy consumption of the sludge disposal and reduce the cost of sludge disposal. The increase of voltage gradient and high temperature leads to the increase in energy consumption, but the actual operation should take into account the specific situation to choose suitable electrical penetration and drying temperature, in order to achieve the best effect.
 

：Matters which should be paid attention to in the connection process of bearing in coal gasifier ：Optimization and improvement of hot rolling sludge dehydration system