Commonly used sludge drying process

Commonly used sludge drying process

The current mainstream method is to dehydrate and dry the sludge (high moisture content) obtained after sewage treatment, and centrally dispose of the dried sludge, incineration or landfill.

The hard indicator of the disposal agency for the sludge is the moisture content. The sludge that does not meet the standard moisture content is prone to potential harm whether it is incinerated or landfilled. At the same time, reducing the moisture content is also important for enterprises to reduce the total amount of sludge and reduce disposal costs. Very important.

In the sludge drying process, it is mainly divided into mechanical pressing process and heating drying process.

Belt filter press dehydrator, screw press centrifuge

Advantages: The belt filter press dehydrator can run at low speed, without noise, and the processing capacity is large; the screw press centrifuge has a relatively large processing capacity and can operate continuously.

Disadvantages: The belt filter press has problems such as poor on-site environment, strong odor, and high humidity, which is easy to cause secondary pollution; while the screw press centrifuge consumes a lot of energy, usually, it can process 100t/d of sludge. , the motor power needs about 60kW. In addition, the moisture content of the sludge after the above two forms of treatment can only reach about 75~80%, which cannot meet the requirements of sludge incineration or landfill.

Diaphragm filter press drying process

The sludge produced in the process of sewage treatment is transported to the sludge treatment tank by the screw pump. After adding medicine and tempering (the medicine is PAM and flocculant), stirring treatment, the sludge fully reacts with the medicine, and the moisture content of the sludge is adjusted to 95%. ~97%, and then pumped to the sludge membrane filter press (plate and frame), and after filtration and pressing, it is decomposed into dry sludge and filtrate with low moisture content (the filtrate can be further recovered).

Advantages: The moisture content of the dewatered sludge is low, which basically meets the requirements of incineration, because the dewatering efficiency is very high in the low concentration stage, and the energy consumption is low after the grading treatment measures are adopted.

Disadvantages: The pressing time is long, and one cycle time is about 3 hours and 45 minutes; the material cannot be continuously discharged, the processing capacity of a single device is not large, and multiple devices are required to form a grading treatment group; a certain amount of flocculant (sawdust or quicklime) needs to be added. ).

Combined mechanical drying process

Two-stage mechanical dehydration: After the first-stage diaphragm filter press is dehydrated, a powerful belt filter press is added for two-stage dehydration. After the sludge solution with a moisture content of 97% is transported to the sludge tank for storage by the sludge pump, it is conditioned and tempered (the agent is PAM), fed through the screw pump to the diaphragm plate press to initially reduce the moisture content, and then passed through the belt conveyor. It is sent to a powerful belt press for filtration to further reduce the moisture content.

Advantages: The advantage of the diaphragm filter press is that the amount of flocculant is low, and the dehydration efficiency is high in the low concentration stage; the disadvantage is that the dehydration efficiency is low in the high concentration stage, resulting in long dehydration time and low output. The advantage of the powerful belt dehydrator is that the high-concentration section adopts continuous dehydration, and the efficiency is high; the disadvantage is that the dosage of the low-concentration section is high, resulting in high operating costs. The combined mechanical dewatering process uses a diaphragm filter press in the low-concentration section to initially dry the sludge moisture, and then uses a powerful belt machine for dewatering. land and investment.

Flue gas thermal drying process

Use the waste heat of boiler flue gas to dry the sludge, pass the first-level dewatering sludge in the sewage treatment plant, and thoroughly dry it until it meets the needs of terminal disposal (incineration or landfill). The drying equipment is a drum dryer. Originated in Japan and Germany.

Advantages: Use the waste heat of boiler flue gas to dry sludge, reduce the moisture content of sludge in sewage treatment plant without consuming new energy, make the operation cost lower in the sludge drying process, and open up a waste recycling , an effective way to treat waste with waste.

Disadvantages: For applications with a large amount of sludge treatment, the environmental protection of flue gas is difficult, and a large amount of flue gas must be treated twice; the safety and economy are poor, and the system equipment is huge; it is limited by the heat source boiler flue gas.

Steam thermal drying process

The medium pressure steam (1.2MPa) is used as the heat medium to heat and dry the sludge, so that the moisture content of the sludge can meet the needs of incineration or landfill disposal. The main drying equipment is disc type sludge dryer, etc.

Advantages: The steam does not contact with the sludge, and the steam can be reused after condensing; the equipment has a compact structure, and the device occupies a small area; the heat utilization rate is high, and the heat utilization rate can reach 90%; Part of auxiliary equipment is removed; it can adapt to changes in the moisture content of sludge, and the drying uniformity of the product is high.

Disadvantages: The cost of sludge drying is high; the equipment is easy to corrode during long-term operation.

Thermal oil drying process

The heat transfer oil is used as the heat medium to heat and dry the sludge, so that the moisture content of the sludge can meet the needs of incineration or landfill disposal.

Advantages: high thermal efficiency, up to 95%; suitable for unsupported thermal power plant projects; self-cleaning function to prevent material from scarring and sticking to walls; no dust pollution, clean operating environment, in line with environmental protection requirements.

Disadvantages: auxiliary fuel needs to be added, high energy consumption; sludge is not utilized as resources, and the drying equipment is sludge dryer.