Industrial production and people's daily lives always produce sewage, and the pressure of sewage treatment is not small. The current mainstream method is to dewater and dry the sludge obtained after sewage treatment (high water content), and to concentrate the sludge after drying, incinerate or landfill.
The disposal organization has requirements for sludge. A hard indicator is the water content. The sludge with insufficient moisture content is likely to cause potential damage whether it is incinerated or landfilled. At the same time, reducing the water content reduces the total sludge for enterprises. It is also important to reduce the cost of disposal.
In the sludge drying process, mainly divided as the mechanical pressing process and the heating drying process .
1、Belt press filter dewatering machine, screw press centrifuge
Advantages: The belt type filter press dehydrator can run at low speed, no noise, and has a large processing capacity; the screw press type centrifuge has relatively large processing capacity and can be continuously operated.
Disadvantages: belt filter press has poor on-site environment, large odor, large moisture, and easy to cause secondary pollution; while screw press centrifuges consume a lot of energy, usually, 100t/d sludge is treated. The motor power needs about 60kW. In addition, the water content of the above two forms can only reach about 75~80%, which cannot meet the requirements of sludge incineration or landfill.
2、Diaphragm filter drying process
The sludge generated in the sewage treatment process is transported to the sludge treatment tank through the pump, and is sterilized and sterilized (pharmaceutical PAM and flocculant), stirred, and the sludge and the agent are fully reacted, and the sludge moisture content is adjusted to 95%~97. %, then pumped to the sludge diaphragm filter press, after filtration and crushing, it is decomposed into dry sludge with low water content and filtrate (the filtrate can be further recovered).
Advantages: The dewatered sludge has a low moisture content, which basically meets the incineration requirements, because the dewatering efficiency is high in the low concentration stage, and the energy consumption is lower after the classification treatment is adopted.
Disadvantages: long pressing time, one cycle time is about 3 hours and 45 minutes; can not be continuously discharged, single equipment processing capacity is not large, need multiple equipment to form a classification treatment group; need to increase a certain amount of flocculant (wood chips or quicklime ).
3、Combined mechanical drying process
The secondary mechanical dewatering: after the first-stage diaphragm filter press is dehydrated, the second-stage dewatering of the powerful belt filter press is increased. The 97% moisture content sludge solution is transported to the sludge tank after being stored by the sludge pump, and is then sterilized by the medicinal solution (pharmaceutical PAM). After the screw pump is fed to the diaphragm plate press to initially reduce the water content, the belt conveyor is sent. Pressurizing the belt press to further reduce the moisture content.
Advantages: The advantage of the membrane 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 yield. The advantage of the strong belt type dewatering machine is that the high concentration section adopts continuous dewatering, and the efficiency is high;
Disadvantage：the low concentration of the medicament is high, resulting in high operating costs. The combined mechanical dewatering process uses a diaphragm filter press in the low-concentration section to pre-dry the sludge moisture and then dewater it with a strong belt machine, thus giving full play to the advantages of the two equipments, which is beneficial to reducing operating costs and saving Land and investment.
4、Flue gas heat drying process
The boiler waste gas is used to dry the sludge, and the sewage treatment plant is thoroughly dried by the first-stage dewatered sludge until it meets the end disposal demand (incineration or landfill). The drying equipment is a drum drying machine, mainly Originated in Japan and Germany.
Advantages: Using boiler flue gas waste heat to dry sludge, the water content of sludge in sewage treatment plant can be reduced without using new energy, and the operating cost in sludge drying process is low, opening up a waste cycle. Use, to effectively eliminate waste.
Disadvantages: For applications with large sludge treatment, the environmental treatment of flue gas is difficult, and a large amount of flue gas must be treated twice; safety and economy are poor, system equipment is huge; and it is limited by the heat of the boiler.
5、Steam hot drying process
The medium-pressure steam (1.2 MPa) is used as a heat medium to heat the dried sludge, so that the moisture content of the sludge can meet the needs of incineration or landfill disposal. The main drying equipment is a disc sludge dryer.
Advantages: steam and sludge are not in contact, steam can be reused after condensing; compact structure, small equipment footprint; high heat utilization rate, heat utilization rate up to 90%; small amount of exhaust gas treatment, corresponding reduction or province Part of the auxiliary equipment; can adapt to the change of sludge moisture content, and the product has uniform drying uniformity.
Disadvantages: The sludge drying cost is high; the equipment is easy to corrode in long-term operation.
6、Thermal oil heat drying process
The heat transfer oil is used as a heat medium to heat the dried sludge, so that the moisture content of the sludge meets the needs of incineration or landfill disposal.
Advantages: high thermal efficiency, up to 95%; suitable for non-supporting thermal power plant projects; self-cleaning action to prevent material crusting and sticking; no dust pollution, clean operating environment, in line with environmental requirements.
Disadvantages: need to add auxiliary fuel, high energy consumption; sludge is not used to utilize the drying equipment as a sludge dryer.