Design and pilot test for feeder of biomass shaftless screw continuous pyrolysis device

Abstract: Biomass continuous pyrolysis is a promising technology of biomass energy utilization. The technology has a lot of advantages, for example, the device applied in the technology is simple, can run continuously and stably, which is easy to be widely used, reaction conditions are easy to control, the efficiency is high. Continuous feeder is one of the core components of continuous pyrolysis reactor, which is generally a screw feeder, but shaft screw feeder of continuous pyrolysis reactor has problem of high energy consumption because of its high weight. What’s more, it is easy to interference between screw and cylinder wall so that the device often need to stop and repair. It is difficult to operate continuously, which leads to low efficiency. However, these problems can be solved by applying shaftless screw to continuous pyrolysis reactor. The design of shaftless screw feeder with feeding capacity of 150 kg/h was introduced in this paper. Rice husk was used to carry out transport tests at room temperature and pyrolysis tests at the temperature of (700±50) ℃ to study its feeding characteristic and pyrolysis characteristic. Shaft diameter, outside diameter, pitch of helix of the screw without shaft is 80, 400, 200 mm respectively. The distance between the outer diameter of the screw and the wall of the pipe is 20 mm. The diameter of pyrolysis tube is 456 mm and the thickness of pyrolysis tube’s wall is 8 mm. What’s more, a diesel combustion engine was used to produce heat for the feeder. The power of the diesel engine ranged from 58 to 116 kW. In addition, a motor was used to drive shaftless screw rotation, its main technology parameters: power rating: 5.5 kW, rated speed: 1 450 r/min, reduction ratio: 29. Test results showed that When the transport frequency was 50 Hz, the feeding amount of screw feeder without shaft was 224.3 kg/h>150 kg/h. Obviously, the actual feeding amount of screw feeder was higher than the theoretical value. Rice husk was filled in the shaftless screw feeder densely due to the extruding effect of shaftless screw in the process of conveying. Continuous pyrolysis experiments of rice husk under different pyrolysis time were conducted in the case that the maximum temperature of heating chamber was 700 ℃. With the pyrolysis time increased, the volatile content of rice husk char decreased from 22.45% to 13.6%, the ash content increased from 29.38% to 33.44%, and the fixed carbon content increased from 48.17% to 52.96%. According to the results of industrial analysis of rice husk carbon, most of the volatiles in rice husk have been released. In addition, the pyrolysis time has a slight influence on the calorific value of rice husk char. The high calorific value of rice husk char increased from19.307 MJ/kg to 20.821 MJ/kg with the increase of pyrolysis time. Thus, the shaftless screw feeder designed in this paper reached the requirements, providing design basis for industrial application of biomass continuous pyrolysis reactor.