On Modelling, Identification, and Control of a Reactor for Pyrolysis of Organic Materials

Abstract

The increased scarcity of fossil energy resources and the accelerated worsening of environmental pollution make the pyrolisis of organic materials of outstanding interest. For this reason, in the Institute of Automation Technology of University Bremen a laboratory-scale reactor has been installed for pyrolisis of coal originating from mechanically treated home waste.In the reactor, the organic mass to be pyrolised is heated both indirectly, via a set of heat exchanging tubes, and directly, by recycling the burner exhaust gas. The reactor is completely equipped by the conventional plant instrumentation and is directly attached to a process control computer.The major difficulty in control of the reactor is the simultaneous control of temperature and pressure at its head, e.g. of two strongly intercoupled process variables. For this purpose, a multivariable two-input, two-output controller has been designed, incorporating the mathematical model of the reactor, the parameters of which have to be repeatedly estimated by the use of actual measured values. The parameters of the heat balance equations are identified from temperature profiles in stationary heating state, and the kinetic parameters of the pyrolisis process via the analysis of pressure changes under defined temperature programs. Based on the results of parameter estimation, the control algorithms are used for gas flow and gas pressure control, taking the interconnection between the two process variables into account, considering the dynamic character of the heat and material balances of the process. The parameter estimation and control algorithms have been implemented in the process oriented, high-level programming language PEARL.It is to be pointed out that the control problem considered here is at the time being a crucial one, whose resolving should help to avoid the unsafe reactor state primarily caused by exothermic steps in the pyrolisis of cellulose containing biomass.The preliminary results obtained by simulation promise a technically acceptable solution of the problem and encourage further technical and algorithmic improvements that are carried out in the Institute.