Analysis on key points of sludge thermal drying process
Sludge thermal drying and incineration was the main method of sludge reduction, harmlessness, stabilization, and recycling. Aiming at the problems of jamming, difficulty in transportation, and low combustion
efficiency in the current sludge drying process, taking engineering practice as an example, the influence of moisture content on it was discussed. On the one hand, the moisture content affected the rheological properties of the sludge, and on the other hand, it induced the adhesion and adhesion characteristics of the sludge, which were all run through
the whole process of sludge drying. In actual exploration and operation, it was found that the above problems could be effectively solved when the moisture content was about 40%, and it had a significant effect on reducing steam consumption, sludge transfer and system modification incineration efficiency.
With the growth of the national economy and the continuous advancement of urbanization, the discharge of municipal sludge and industrial sludge has increased year by year. In order to ensure the reduction, harmlessness, stabilization and resource utilization of municipal sludge and industrial sludge, sludge thermal drying and incineration treatment, as a large-scale, thorough and efficient treatment form, has been used in the coordinated utilization of comprehensive energy in recent years. has been widely used. Sludge drying is to use steam equipment to reduce the moisture in the sludge to maintain it at a stable level. At present, typical sludge drying equipments are disc dryers and paddle dryers. The dried sludge is then coupled with coal or biomass before incineration. Among them, moisture content is an important parameter.
1. Moisture content
The moisture content of sludge has a great impact on the storage, transfer and disposal of sludge, and is also an important factor in the rational disposal of sludge. Under different moisture content, sludge will show different rheological properties. In addition, when the moisture is as high as 50% or more, the evaporation of moisture accompanies the whole process in the incineration process, making this process occupy a major position in the co-combustion, and as the moisture continues to evaporate, the latent heat of vaporization will take most of the heat in the furnace At the same time, it also increases the smoke exhaust loss of the boiler, which is not conducive to the economical operation of the sludge disposal process. Usually, the water content of sludge is very high. In order to facilitate transportation, dewatering should be carried out before drying, that is, entering the dryer for further deep dewatering to keep it at a stable level.
2 Adhesion and Bonding Properties
The adhesion and cohesion characteristics of the sludge are related to the temperature and moisture content of the sludge during drying. Adhesion mainly refers to the agglomeration characteristics of sludge, and adhesion refers to the adhesion characteristics of sludge, which is manifested as sticking to the drying equipment; it is generally believed that when the moisture content reaches about 50%, the adhesion and cohesion force reach the peak value. When the moisture is reduced to about 30%, the adhesion and cohesion are significantly reduced. Due to the adhesion and cohesion properties, there is a viscous zone in the sludge drying process. Kudra[3] analyzed the viscous zone in the sludge drying process, and believed that the sludge drying viscous zone was the result of the combined action of the macro parameters of temperature and water content during the sludge drying process. The viscosity should be strictly controlled during the drying process.
In the practice process of a power plant, it was found that the moisture content of sludge is particularly important for the sludge disposal process. If the moisture content is too high, it will affect the conditions of co-combustion of sludge. When the moisture content is too low (30% to 50%), the sludge The adhesion and adhesion characteristics of the dryer will reach the extreme value, which will make it difficult for the dryer to get out the mud, and even the situation of jamming. Practice has shown that controlling the moisture content at about 40% can effectively solve the above problems. In addition, the heat in the sludge drying heat transfer dynamic field is transferred to the material layer through the wall surface, and the material layer is then transferred to the material layer next door, part of which is lost through evaporation, and the other part is transferred to the air through convection and radiation. Among them, the thermal resistance is mainly concentrated in the evaporation of water on the sludge side, and measures to strengthen heat transfer should also be aimed at this.
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