| Description |
A digital control system for the thermal processing unit for tar sands has been constructed and tested. The thermal processing unit consists of three sections. In the first section, tar sands is fed into a fluidized pyrolysis reactor, where the bitumen is cracked into coke, oil and gaseous products at temperatures of 480°C to 500 C. In the second section, the coked sand is transferred by gravity from the pyrolysis reactor to the combustion reactor, a second fluidized bed, where the coked sand combusts with air to produce the energy required in the system. A potassium heat pipe is used to transfer the energy from the combustion reactor to the pyrolysis reactor. In the third section, the oil from the pyrolysis reactor is collected through a series of condensers. The digital control system consists of an HP-1000 host computer, an HP-2250 interface, and several actuators and sensors. The solids retention times in both reactors are controlled by two solids flow control valves. A digital PID algorithm plus valve linearization has been used to control the solids flow valves. The best control constants, K = 80, T. = 40, T, = 0 for the pyrolysis reactor, and K =50, T. =5, T, = 0 for the combustion reactor, were found experimentally. From the comparison of results, the digital PID algorithm plus valve linearization has much better controllability than the conventional pneumatic PI controller. The temperature in the pyrolysis reactor is controlled by the amount of energy transferred into the combustion reactor from the surroundings. An SCR power controller is used to regulate power into the heating wire wrapped around the reactor wall. The best PID algorithm controller constants, K = 1000, T. = 10, T, = 0 were found experimentally to control the thermal cracking of bitumen in the pyrolysis reactor. Pyrolysis of bitumen can be considered as only a disturbance to the system and its influence on the control system is insignificant. |
