Control oriented modeling and optimization of one dimensional packed bed model of underground coal gasification

To account for nonlinear nature and huge model uncertainties of underground coal gasification (UCG) process, a robust model based control strategy is to be employed. The available models in the literature do not lend themselves to control applications easily. In this work a control oriented one dimensional (1-D) packed bed model of UCG is developed, which can be used in a closed loop configuration with a robust controller to maintain a desired heating value of the exit gas mixture by manipulating the flow rate of injected gases. The model is also capable of predicting time and space profiles of some important parameters, which include solid temperature, composition of exit gas mixture, rates of different chemical reactions and expected life of the UCG reactor in response to different operating conditions and coal properties. Most of these parameters are either impossible or very expensive to measure. There is uncertainty in some coal properties which is addressed by optimizing few input parameters using sequential quadratic programming (SQP) algorithm, a nonlinear optimization technique. The model results are compared with actual field trials which show a good agreement for the calorific value of exit gas.