(705b) A Novel Model Predictive Control Scheme for Sustainability: Application to Biomass/Coal Co-Gasification System

Industrial, business and government communities have begun to shift from economic stand-alone focus to inclusion of sustainability in the decision-making process. This shift is due to the adverse environmental impact and unsustainable development caused by human activities, including chemical industry releases. As a result, process systems engineering (PSE) approaches have been developed, predominantly for incorporating sustainability into chemical process design and optimization [1]. However, the development of sustainability-oriented control schemes is still scarce, especially when compared to the number of steady-state design and optimization studies available [2]. Process control plays a critical role in realizing the efficient, sustainable and safe operation of the chemical and energy systems defined by the process design and optimization studies. The main barriers that have been prevented the integration of sustainability into process control are: 1) complexity of integrated large-scale chemical and energy processes; and 2) existence of multiple objectives for optimization involving social, economic and environmental issues.

To fill this gap, a novel model predictive control (MPC) scheme is proposed to drive the system to a sustainable operating point that is defined using a multi-objective optimization algorithm. In particular, the sustainable MPC is formulated based on dimensionless sustainability performance indicators from the U.S. EPA’s GREENSCOPE (Gauging Reaction Effectiveness for the ENvironmental Sustainability of Chemistries with a Multi-Objective Process Evaluator) tool [3]. These established indicators are associated with the process state variables, releases, resource consumption, and products and can capture the sustainability information of the current process condition, including economic, environmental and social aspects. Such sustainability indicators are employed as hard/soft constraints in the implemented controller in order to maintain the process operation within a pre-defined sustainable zone, where the performance indicator values are higher than desired thresholds. To explicitly visualize the multidimensional sustainability indicators during transient, a multivariate plotting method is developed using dynamic radar diagrams.

The developed method is illustrated via a biomass/coal co-gasification process for syngas production with the end goal of methanol manufacturing. For this application, the whole process model is developed in Aspen Hysys based on existing literature information [4-5]. With the established models in Aspen and a link for data communication between Aspen and MATLAB, a multi-objective optimization problem is solved to maximize profit and optimize the process sustainability performance (e.g., environmental release and resource use minimization), by employing a genetic algorithm-based approach developed in MATLAB. In this presentation, the details on the application results of this novel framework for improving sustainability performance are discussed, focusing on the tradeoffs between using coal and biomass for the sustainable production of chemicals. The results show that the proposed sustainable MPC scheme can effectively drive the process to the optimal operating point, while maintaining the process within sustainable zones during transients.

References:

1. Daoutidis P, Zachar M, Jogwar SS. Sustainability and process control: A survey and perspective. J. Process Control. 2016;44:184–206.
2. Li S, Mirlekar G, Ruiz-Mercado GJ, Lima FV. Development of chemical process design and control for sustainability. Processes. 2016;4(3):23.
3. Ruiz-Mercado GJ, Gonzalez MA, Smith RL. Sustainability indicators for chemical processes: III. biodiesel case study. Ind. Eng. Chem. Res. 2013;52(20):6747–60.
4. Li S, Feliachi Y, Agbleze S, Ruiz-Mercado GJ, Smith RL, Meyer DE, Gonzalez MA, Lima FV. A process systems framework for rapid generation of life cycle inventories for pollution control and sustainability evaluation. Clean Technol. Environ. Policy. 2018. DOI: 10.1007/s10098-018-1530-6.
5. Robinson PJ, Luyben WL. Simple dynamic gasifier model that runs in Aspen Dynamics. Ind. Eng. Chem. Res. 2008;7784–92.