Automatic Control Laboratory, University of Mons, Mons, Belgium.
Bioprocess Biosyst Eng. 2012 May;35(4):565-78. doi: 10.1007/s00449-011-0629-5. Epub 2011 Dec 14.
This paper presents an optimizing start-up strategy for a bio-methanator. The goal of the control strategy is to maximize the outflow rate of methane in anaerobic digestion processes, which can be described by a two-population model. The methodology relies on a thorough analysis of the system dynamics and involves the solution of two optimization problems: steady-state optimization for determining the optimal operating point and transient optimization. The latter is a classical optimal control problem, which can be solved using the maximum principle of Pontryagin. The proposed control law is of the bang-bang type. The process is driven from an initial state to a small neighborhood of the optimal steady state by switching the manipulated variable (dilution rate) from the minimum to the maximum value at a certain time instant. Then the dilution rate is set to the optimal value and the system settles down in the optimal steady state. This control law ensures the convergence of the system to the optimal steady state and substantially increases its stability region. The region of attraction of the steady state corresponding to maximum production of methane is considerably enlarged. In some cases, which are related to the possibility of selecting the minimum dilution rate below a certain level, the stability region of the optimal steady state equals the interior of the state space. Aside its efficiency, which is evaluated not only in terms of biogas production but also from the perspective of treatment of the organic load, the strategy is also characterized by simplicity, being thus appropriate for implementation in real-life systems. Another important advantage is its generality: this technique may be applied to any anaerobic digestion process, for which the acidogenesis and methanogenesis are, respectively, characterized by Monod and Haldane kinetics.
本文提出了一种生物甲烷化器的优化启动策略。该控制策略的目标是最大限度地提高厌氧消化过程中甲烷的流出率，这可以用一个两种群模型来描述。该方法依赖于对系统动力学的深入分析，并涉及两个优化问题的求解：稳态优化以确定最佳操作点，以及瞬态优化。后者是一个经典的最优控制问题，可以使用庞特里亚金的最大原理来解决。所提出的控制律是Bang-Bang 型的。该过程通过在某个时间点将操纵变量（稀释率）从最小值切换到最大值，从初始状态驱动到最优稳态的小邻域。然后将稀释率设置为最优值，系统在最优稳态下稳定下来。该控制律确保系统收敛到最优稳态，并显著增加其稳定区域。与最大甲烷产量对应的稳态的吸引区域大大扩大。在某些情况下，由于可能选择低于某个水平的最小稀释率，最优稳态的稳定区域等于状态空间的内部。除了效率，不仅从沼气生产的角度，而且从处理有机负荷的角度进行评估外，该策略还具有简单性的特点，因此适合在实际系统中实施。另一个重要的优势是其通用性：这种技术可应用于任何厌氧消化过程，其中酸化和产甲烷分别以 Monod 和 Haldane 动力学为特征。
