Untersuchung und Optimierung der Klärschlammverbrennung in stationären Wirbelschichtanlagen

The control of the combustion process of sewage sludge incineration plants has been very little investigated, because of the complexity of the sewage sludge material. Previous experiences and researches have shown that in the praxis most of the thermal waste treatment plants are still almost exclusively equipped with PI and PID controllers. Due to the inhomogeneity and the short-term fluctuations in the calorific value of the incinerated fuels, the required control performance cannot be achieved by using conventional control methods. Within the framework of this Work, the realization of an automatic stable operation of sewage sludge combustion in the stationary fluidized bed incinerator was investigated. Thus can make an important contribution to achieve better combustion control. A uniform and stable fluidization of the bed material are crucial for a homogeneous temperature distribution and an efficient combustion. In order to achieve this and thus to realize an optimal plant operating condition, two complex three-dimensional numerical models of the fluidized bed combustors were developed in the first part of this dissertation by using the commercial CFD software package Fluent 14.5. In addition to the numerical investigations, comparative experimental investigations were also carried out on the bubbling fluidized bed combustor. The results of the minimum fluidization velocity and the resulting pressure drop obtained from the numerical flow simulations were compared and validated with the experimental measurements.
The second part of this thesis deals with the mathematical modelling and controller design for the stationary fluidized bed incinerator Salierweg Bonn. The implementation was done in Matlab (version 2014b). At the beginning, an experimental multivariable system of the bubbling fluidized bed incinerator was developed from measured input and output variables of the unit. After developing the multivariable mathematical model, the accuracy of the control systems was checked and validated by using collected operational data. After the validation, the combustion control methods were designed and tested based on these developed multivariable control systems. To optimize the control quality, the decoupling controllers, which eliminate the interaction between the controlled variables, were also considered. In order to define all possible operating states of the bubbling fluidized bed incinerator and to meet all required conditions for various process variables, the control results of the decentralized PI and an adaptive fuzzy PI controller were evaluated and compared using Matlab simulations.
The main objective of the present work is the development of continuous and adaptive combustion control to the constantly changing properties of the sewage sludge fuel in order to optimize the combustion process, so that the system stability and optimum combustion for all changing operating conditions is assured.