Thermal runaway is a critical feature of microwave lignite drying, which leads to the combustion of lignite. An expert control system (ECS)-based multimode hybrid switching control strategy is developed to solve it. The control strategy has three control modes, which contain two proportional integral derivative modes and a zero mode. Two knowledge-based ECS interface machines of the hybrid switching control strategy are built for mode switching and auxiliary decision. Experimental results demonstrate that fixed microwave power levels lead to the thermal runaway phenomenon during lignite drying process. Using the proposed hybrid switching control strategy, the wet lignite can be safely and efficiently dried to achieve the objective (moisture content 7%). Finally, based on the drying curves, the microwave lignite drying behaviors are adequately represented by the Wang and Singh model, which provides the best description (R² = 0.9913) for the experimental results.

The aim of this paper is to present an explicit numerical algorithm based on improved spectral Galerkin method for solving the unsteady diffusion-convection-reaction equation. The principal characteristics of this approach give the explicit eigenvalues and eigenvectors based on the time-space separation method and boundary condition analysis. With the help of Fourier series and Galerkin truncation, we can obtain the finite-dimensional ordinary differential equations which facilitate the system analysis and controller design. By comparing with the finite element method, the numerical solutions are demonstrated via two examples. It is shown that the proposed method is effective.