Sludge drying technology has been widely used in the world and has become an important method for sludge disposal
(1) Reduction: due to the high water content, large volume and fluidity of sludge. After the above process, the sludge volume is reduced to one tenth of the original, and the sludge is transformed from liquid to solid, which is convenient for transportation and absorption.
(2) Stabilization: the content of organic matter in sludge is very high, which is easy to rot and produce odor. After the treatment in the digestion stage of the above process, part of the organic matter that is easy to corrupt is decomposed and transformed, which is not easy to corrupt, and the odor is greatly reduced, which is convenient for transportation and disposal.
(3) Harmless: sludge, especially the primary sludge, contains a large number of pathogenic bacteria, parasitic eggs and viruses, which is easy to cause large-scale spread of infectious diseases. After the digestion stage of the above process, most of the in-situ eggs, pathogens and viruses can be killed, and the sanitary index of the sludge can be greatly improved.
(4) Recycling: sludge is a kind of resource, which contains a lot of heat, and its calorific value is in the ten thousand ～ 15000kJ/kg( Dry mud ) It is higher than coal and coke. In addition, the sludge also contains rich nitrogen, phosphorus and potassium, which is an organic fertilizer with high fertilizer efficiency.
Sludge drying process mainly includes mechanical pressing drying process and heating drying drying process.
The mechanical press drying process includes ordinary mechanical drying process, diaphragm pressure filtration drying process, combined mechanical drying process and so on.
(1) Dewatering machine and dewatering belt press are commonly used. These two kinds of machinery are through the first press filtration, so that the initial concentration is about 97% The water content of sewage becomes 80% About the moisture content of the sludge.
(2) The membrane pressure filtration drying process refers to the sludge produced in the sewage treatment process is transported to the sludge treatment tank by pump, and then adjusted by adding chemicals ( medicament PAM And flocculant ) The water content of the sludge was adjusted to 0 95%~97% And then it is transported to the sludge membrane filter press by pump, and then decomposed into 45%~55% The dry sludge and filtrate of water can be incinerated in boiler.
(3) The combined mechanical dewatering is divided into two stages, that is, the first stage diaphragm filter press is dehydrated, and then the strong belt filter press is added to the second stage dehydration. The main process flow is: water content of sewage treatment plant 97% The sludge solution is transported to the sludge tank for storage by sludge pump, and then adjusted by adding chemicals ( medicament PAM) Through screw pump feeding to diaphragm plate press to 55% After the moisture content, it is sent to the strong belt press through the belt conveyor until the water content is 0 40% ~50% The dry sludge can be incinerated in the boiler.
The heating drying process includes flue gas drying process, steam drying process and heat transfer oil drying process.
(1) The flue gas thermal drying process mainly uses the waste heat of boiler flue gas to dry the sludge, and the sewage treatment plant is dehydrated by the first stage 80% Moisture content sludge 45% Water content sludge ( Controllable ) The main drying equipment is drum dryer ;
(2) Medium pressure steam drying process is used (1.2MPa) It is a heat medium to heat and dry the sludge and to dehydrate the sewage treatment plant 80% Moisture content sludge 45% Water content sludge ( Controllable ) The main drying equipment is disc Sludge dryer Etc.
(4) Thermal drying process of heat transfer oil is to use heat transfer oil as heat medium to heat and dry sludge and to dehydrate the sewage treatment plant 80% Moisture content sludge 45% Water content sludge ( Controllable ) The main drying equipment is Sludge Dryer Etc.
Sludge drying will continue to develop, improve and be welcomed. Sludge drying equipment is also developing to large-scale. Meanwhile, the safety performance of sludge drying equipment is constantly improved, including environmental friendliness. The economic feasibility of sludge drying has been significantly improved by the research on reducing energy consumption. Which sludge drying technology should be used should be judged according to the actual situation.