A complete sludge pyrolysis system includes storage and transport systems, drying system, pyrolysis system, combustion system, energy recovery system and exhaust gas purification system. The storage and transportation of sludge is the beginning of the entire pyrolysis process, which plays a role in the storage of sludge and transporting sludge into the drying system. The water content of the sludge in WWTP is generally about 80% and can’t pyrolysis directly. The water content in the sludge is reduced to 20% -25% by the drying system. Pyrolysis refers to generating gaseous and solid products from the solid sludge in the anaerobic environment.
The gaseous product is pyrolysis gas, which is a kind of combustible gas. The pyrolysis gas generated in the pyrolysis equipment contains certain hazardous substances which can be burned so that the energy can be utilized and the harmful substances can be completely converted into oxidized flue gas. The harmful substances in the pyrolysis gas can be removed by the methods that deal with the smoke. The clean pyrolysis gas can supply heat for the engine or gas turbine. The anaerobic environment of the system reduces or prevents the formation of polycyclic aromatic hydrocarbons.
The solid product is residue after sludge pyrolysis. The structure is easy to wet, so the charging device should be equipped with anti-jamming devices. In addition, the chemical property of the pyrolysis residue is stable and can be resistant to strong acid corrosion. The heavy metals in sludge is hardened and is difficult to re-precipitation.
The pyrolysis gas goes into the combustion chamber along with the exhaust gas in the sludge storage chamber through the cyclone, so as to prevent odor leakage. The flue gas generated by the combustion chamber is preferentially used for heating the pyrolysis reactor. The temperature of the flue gas in the pyrolysis reactor outlet is 600℃, and this part of the flue gas reenter the heat boiler for waste heat utilization. When the system itself can’t maintain its own its own balance of energy, the combustion chamber needs additional fuel (natural gas or oil) as a supplement to achieve the purpose of maintaining the system energy.
The flue gas that after heating for the reactor enters the waste heat boiler and the generated steam is used to dry the sludge. For different process conditions, different energy recovery options can be selected.
The pyrolysis of solid waste is carried out under normal pressure. But in practice, in order to avoid odors, a certain negative pressure is generally maintained in the pyrolysis reactor.