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In order to reduce the waste heat emission and environmental impact of industrial processes, Organic Rankine Cycle (ORC) is gradually used for energy recovery. ORC is regarded as the most promising measure for converting low-grade heat into electricity, but commercial applications are still limited due to the high investments and poor economic returns. However, the simultaneous optimization of ORC and Heat Integration can improve system economy. This work proposes a techno-economic optimization model involving the area estimate of heat exchanger based on vertical heat transfer for optimization of ORC and Heat Integration. This model determines the selection of working fluids, the optimal operating parameters of ORC including temperatures, pressures, and flowrate of working fluids. Both of the supercritical and subcritical conditions can be considered in this model. To solve this optimization problem, a bi-level optimization approach is developed, where the outer level uses Genetic Algorithm to identify the promising working fluids and optimize the temperatures and pressures of ORC, and the inner level is an NLP model to find the optimal flowrate of ORC and the vertical matches of streams by minimizing total annual cost. The results represent the necessity of simultaneous optimization of Organic Rankine Cycle and Heat Integration.

Molecular reconstruction is an effective tool to predict the detailed composition of complex mixtures under obtainable bulk properties and chemical details. With the introduction of statistical distribution, although the number of variables in the model is reduced, the ranges of statistical distribution parameters have a great influence on the prediction accuracy. A novel parameter estimation method using the analysis of the probability density plot of gamma distribution based on the basic available information is proposed to obtain parameter ranges with wide universality and non-specificity. The obtained ranges are used in a molecular reconstruction model to predict the bulk properties and molecular composition of naphtha. The model assumes molecular composition within each homologous series follows a gamma distribution against carbon number. The results of a naphtha sample show that the calculated bulk properties and molecular composition are in good agreement with the experimental values.

Hydrogen resource can be saved by reuse and purification reuse between refineries. Thus, it’s necessary to optimize the inter-plant hydrogen network in a petrochemical complex. In a petrochemical complex, purifiers are employed to recover hydrogen components from off gas. However, purifier models such as PSA, membrane units have non-linear characteristics. Even if minimizing hydrogen utility, mathematical programming models adopted by most of the researchers belong to the non-convex and non-linear models, not guaranteeing global optimal solution. In this paper, a novel mathematic programming model for the optimization of inter-plant hydrogen network with purification unit is presented. If only the hydrogen utility consumption is minimized, the model is linear, guaranteeing global optimal solution. If the object comes to economic benefits such as pipeline cost, the objective function is nonlinear. The hydrogen utilities in refinery can be reduced by the inter-plant optimization and the number of inter-plant connections can be optimized to minimum. Case study indicates that the model is effective.

There is a growing interest in developing Total Site Heat Integration methods, since Total Site Heat Integration offers an energy-saving opportunity across multiple plants beyond the traditional intra-plant plant integration. Total Site heat integration can be achieved indirectly by non-isothermal utility loop, such as hot water and thermal oil. The parameters of non-isothermal utility loop, interconnectivity patterns directly determine the energy saving and the capital cost. In this work, a transshipment type Total Site heat exchanger network (HEN) model using non-isothermal utility loop is developed. A new representation method of non-isothermal utility loop is proposed based on transshipment type HEN model to avoid non-linear terms. The model is formulated as a MINLP problem with all linear constraints. The operating cost, capital cost of heat exchangers, pumping and piping cost are holistically considered and optimized. The case study demonstrates the effectiveness of the proposed model.