1, high temperature carbonization. No pressure is applied during carbonization, and the temperature is 649-982℃. Firstly, the sludge was dried to a water content of about 30%, and then carbonized and granulated at high temperature in a carbonizer. Carbonized particles can be used as low-grade fuel, and its calorific value is about 8 360-65 438+02 540 kJ/kg (Japan or America). This technology can realize sludge reduction and recycling, but it has not been widely used at present because of its complex process, high operating cost and low calorific value content in products, and the largest scale is 30 wet sludge.
2. Medium temperature carbonization. No pressure is applied during carbonization, and the temperature is 426~537℃. First, the sludge is dried to a water content of about 90%, and then decomposed in a carbonator. In this process, oil, reaction water (steam condensate), biogas (uncondensed air) and solid carbide are produced. In addition, the technology carbonizes the sludge after drying, and the economic benefit is not obvious. There are no other potential users except a processing plant in Australia.
3. Low temperature carbonization. No need to dry before carbonization. During carbonization, the pressure rises to 6~8 MPa and the carbonization temperature is 365,438 0 5℃. Carbonized sludge is in liquid state, and the moisture content after dehydration is below 50%. After drying and granulating, it can be used as low-grade fuel, and its calorific value is about 15048 ~ 20482 kJ/kg (USA). This technology decomposes all the biomass in the sludge by heating and pressurizing, and 75% of the water in the sludge can be removed only by mechanical method, which greatly saves the energy consumption in operation. The complete decomposition of sludge ensures the complete stability of sludge. In the process of sludge carbonization, most of the calorific value of sludge is retained, which creates conditions for energy reuse after pyrolysis.
4. Sludge hydrothermal drying technology. Sludge hydrothermal drying technology can improve the dewatering performance and anaerobic digestion performance at the same time by heating sludge, hydrolyzing viscous organic matter in sludge at a certain temperature and pressure, and destroying the colloidal structure of sludge. With the increase of hydrothermal reaction temperature and pressure, particle collision increases, and the collision between particles leads to the destruction of colloid structure, which separates bound water from solid particles. Without adding flocculant, the moisture content of mechanical dehydration of sludge after hydrothermal treatment is greatly reduced. Macroscopically, sludge hydrolysis shows that the concentration of volatile suspended solids decreases and the concentrations of COD, BOD and ammonia nitrogen increase. Hydrothermal drying technology adopts slurry reactor, which improves the treatment efficiency of the system by flashing exhaust, back mixing, preheating slurry and cooperative stirring of steam and machinery. In the hydrothermal reactor, direct mixed heating with steam countercurrent is adopted to strengthen the mass transfer and heat transfer process, which can avoid local overheating, coking and carbonization. In the continuous flash reactor, the effective recovery of system energy is realized.