Abstract:

In the light of high energy consumption in sludge drying, a new process for sludge drying coupled with pyrolysis was proposed. The factors affecting the heat transfer of combustible gas(such as pyrolysis temperature and addition rate of poplar sawdust) and the influence of heating rate on pyrolysis products and system energy consumption were analyzed through the simulation with Aspen Plus software. The results indicated that when the co-pyrolysis of poplar sawdust and sludge was carried out, the addition rate of poplar sawdust must reach 43.5% to maintain a normal and stable operation of the system. When the pyrolysis temperature was 550 ℃, the yield of pyrolysis oil as the main component of combustible gas reached the maximum of 51.7%, and the system had the maximum heating capacity of 12.619 MJ/h. Additionally, it was found that when the heating rate increased, the yield of solid residue decreased, while the overall yield of pyrolysis oil and combustible gas increased. And when the heating rate decreased, the yield of pyrolytic oil and gas also decreased. Finally, the pilot plant scale-up test results showed that at a sludge feeding rate of 3 kg/h, the desired drying goal could be achieved at a minimum of residence time of 45 min and air flowrate of 40 L/min.

Key words: sludge treatment, Aspen Plus simulation, energy balance, process optimization, scale-up tests