Introduction of sludge drying process

1 Overview of sludge drying

sludge is a solid sedimentary material produced during sewage treatment. According to its source, it can be divided into: Municipal sludge, pipe network sludge, river and lake sludge, and industrial sludge. The pollutants contained in the sludge generally have a high calorific value, but due to the presence of a large amount of water, this part of the calorific value cannot be used. If the sludge with high moisture content is incinerated, not only will the calorific value not be obtained, but also a large amount of fuel needs to be added to complete the combustion; the sludge after mechanical dehydration has a moisture content of about 80%, and its disposal difficulty and cost are also high. The sludge must be dried. The moisture content of the sludge is reduced to about 40%, and then it is incinerated. The heat generated by the incineration can meet the needs of drying part or even all the sludge. Regardless of whether it is used to manufacture building materials or other uses after incineration, reducing the moisture content is the key. Therefore, it can be said that sludge drying or semi-drying is the first step in sludge resource utilization.

2 Introduction of sludge drying process

At present, the commonly used sludge drying processes are as follows:

2.1 Rotary drum drying process

The rotary drum dryer is one of the traditional drying equipment. It adopts the direct heat exchange method in the sludge drying system. The main equipment of this drying system are: hot blast furnace, feeder, rotary drum dryer, cyclone dust collector, and water film dust removal. device, system induced draft fan, circulating pool, etc.

Features of this process:

(1) The structure is novel. A new type of dispersing device is adopted to fully disperse the wet sludge at the end of the dryer and dry it quickly, which overcomes the wall sticking phenomenon at the feeding end of the ordinary rotary drum dryer.

(2) The operation flexibility is large. The length of the dryer is not limited by the dispersing device, and the length of the dryer can be freely designed according to the initial characteristics of the material.

(3) High drying strength. Compared with other drying processes of the same scale, the drying strength is larger, which can reach 70kg(H2O)/h.m³.

(4) The process is short and easy to operate.

2.2 Dispersing drum drying process

The dispersing rotary drum dryer can directly dry the wet sludge without mixing, pulverizing and other processes, and the process is relatively simple. The dryer is short and the investment in the entire system is small. However, for the drying of wet sludge, the final moisture content can only reach 30%-40%. The dried sludge can be directly incinerated, and the heat generated by the incineration can be used for pre-drying the wet sludge.

The dispersing drum drying process is basically the same as the drum drying process.

Features of this process:

(1) Low thermal energy consumption. Due to the direct drying of wet sludge, the dryer is very short, so a higher inlet air temperature can be used. For sludge drying, the inlet air temperature can reach above 850°C. Therefore, the heat energy consumption is lower than that of the above-mentioned rotary drum dryer, and it takes 7659KJ of heat to remove each kilogram of water.

(2) Small footprint. Because the dispersing shaft has been running at high speed and the centrifugal force is large, the length of the dispersing drum is limited by the length of the dispersing shaft, and the general length is about 6 meters. Compared with the drum drying process, the area is smaller.

(3) Suitable for drying high-humidity and high-viscosity materials.

2.3 Blade drying process

The hollow blade dryer is mainly conducted to the material by the inner wall of the jacketed W-shaped groove and the wall of the hollow blade. During the drying process of the material, the hollow shaft with the hollow blade heats the material and stirs the material at the same time, thereby Update the heating surface.

Features of this process:

(1) Small footprint. The structure of the equipment is compact, and compared with the rotary drum drying process, the floor area is relatively small, which saves capital investment.

(2) High thermal efficiency. The wet sludge is pre-dried with the tail gas of the secondary dryer to make full use of the heat.

(3) Zero pollution discharge. After the heat in the dry exhaust gas is fully utilized, it is sent to the incineration boiler for combustion, and the pollutants in it are burned to ensure zero pollution discharge.

(4) Good dry environment. The entire drying system is in a closed-circuit cycle, and the exhaust gas produced in the drying process is directly sent to the sludge incineration boiler for combustion to burn off the odorous components to improve the drying environment.

2.4 Internal heating fluidized bed drying process

The sludge pump directly feeds the sludge into the inner heating fluidized bed. There is a high-speed rotating dispersing device just below the discharge opening in the fluidized bed, which can quickly disperse the wet sludge, increase the heat exchange area, and promote Moisture evaporates quickly. The heat source is steam, and the heat is indirectly transferred to the sludge through the heat exchanger, thereby evaporating water and drying the sludge.

Features of this process:

(1) Energy saving and high efficiency. Most of the heat is provided by the built-in heat exchange device with high heat exchange efficiency. The hot air is mainly used as the power medium to ensure normal fluidization, which is much lower than that of the conventional fluidized bed. reduce, and the drying efficiency is high.

(2) Small footprint and low investment.

(3) Reduce the pressure on environmental protection. Because the system operating gas velocity of the internally heated fluidized bed is lower than that of the conventional fluidized bed, it can effectively reduce the loss of material entrainment and entrainment in the fluidized bed, correspondingly reduce the load of the dust removal system, and has high safety.

3 Summary of sludge drying process

Comprehensively comparing the above sludge drying processes, we should choose the paddle drying process. This process has remarkable characteristics: energy saving, high efficiency, less land occupation, low investment, and high environmental benefits, which is very similar to the development direction of sludge treatment technology in my country. match. Among several commonly used drying processes, it has high feasibility and is the preferred route for sludge drying process.

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