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In the design of chemical/energy production systems, a major challenge is how to quantify the sustainability of the systems. Concerns on economic return and environmental impacts have been well received by researchers and practitioners. However, the irreversibility of the process has not been taken into consideration yet. Based on the first and second laws of thermodynamics, exergy analysis allows accounting for irreversibility in the process and provides a detailed mechanism for tracking the transformation of energy and chemicals. Sustainability assessment in the societal dimension is mostly a “soft” activity, as the aspects to be considered and the method of evaluation are frequently subjective. How to assess the societal impact of a process in the early design stage remains as a challenging issue. This paper will present a sustainability assessment method incorporating economic, environmental, efficiency, and societal concerns. The efficiency assessment is conducted through exergy analysis, while the societal concerns are measured by an enhanced inherent safety index method. In conjunction with a multicriteria decision-analysis method, this methodology will provide critical guidance to the designers. The efficacy of this methodology will be demonstrated through a case study on biodiesel production processes. The results show that the new heterogeneous catalyst process performs better than the traditional homogeneous process in every dimension.

Flaring is crucial to chemical plant safety. However, excessive flaring, especially the intensive flaring during the chemical plant start-up operation, emits huge amounts of volatile organic compounds (VOCs) and highly reactive VOCs, which meanwhile results in tremendous industrial material and energy loss. Thus, the flare emission should be minimized if at all possible. This paper presents a general methodology on flare minimization for chemical plant start-up operations via plantwide dynamic simulation. The methodology starts with setup and validation of plantwide steady-state and dynamic simulation models. The validated dynamic model is then systematically transformed to the initial state of start-up and thereafter virtually run to check the plant start-up procedures. Any infeasible or risky scenarios will be fed back to plant engineers for operation improvement. The plantwide dynamic simulation provides an insight into process dynamic behaviors, which is crucial for the plant to minimize the flaring while maintaining operational feasibility and safety. The efficacy of the developed methodology has been demonstrated by a real start-up test.

Thermodynamic analysis of tri-reforming reactions to produce synthesis gas has been conducted by total Gibbs energy minimization to understand the effects of process variables, such as temperature (200−1000 °C), pressure (1−20 atm), and inlet O 2 /CH 4 (0−1.0), H 2 O/CH 4 (0−3.0), and CO 2 /CH 4 (0−3.0) mole ratios on the product distribution. The results reveal that high temperature and low pressure are favorable to achieve high H 2 production and CO 2 conversion. In addition, excessive additions of H 2 O, O 2 , and CO 2 bring about lower H 2 yield and CO 2 conversion, while low concentrations of H 2 O, O 2 , and CO 2 result in more intense carbon formation. To attain the maximum H 2 yield and high CO 2 conversion coupled with a desired synthesis gas (H 2 /CO) ratio for the downstream methanol production and effective elimination of carbon formation, the corresponding optimum feed ratio in tri-reforming process is identified to be CH 4 /CO 2 /H 2 O/O 2 = 1:0.291:0.576:0.088.