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Article published in Industrial & Engineering Chemistry Research. Free download:https://pubs.acs.org/articlesonrequest/AOR-MC67TWM4RV9MVEIGBJCP

Hydrogen is an expensive utility in refineries. To reduce costs and save energy, a hydrogen system should be not only optimally designed but also optimally operated. In this paper, a mathematical model is proposed for determining optimal operation of a hydrogen network. Changes in the hydrogen demand of a hydrogen sink are assumed to vary with changes in the operational load. In the proposed model, if there is no connection between a source and a sink, the corresponding flow rate will be set as zero. In this way, the model is a linear programming model. A case study shows that the model is effective and very easy to solve.

Introducing purification devices into hydrogen systems can enhance the extent of hydrogen reuse. The economic performance of a purification device depends on its appropriate placement within a hydrogen system. This work presents an improved version of a previously published graphical method for integrating purification processes in hydrogen systems. A mathematical method is deduced for calculating the maximum hydrogen utility savings potential of a hydrogen system with purification reuse. The improved graphical method is able to handle the constraints of concentration and flow rate of a purification process when targeting the maximum hydrogen utility savings. The proposed method can be used for analyzing purification processes with any feed concentration. The graphical method is tested on two case studies.

Conventional cooling water networks usually operate in a parallel configuration. Converting a parallel design to a series arrangement can yield a significant reduction in fresh cooling water consumption because of water reuse. This paper presents a two-step methodology for retrofit design of cooling water networks. The proposed methodology can convert a parallel configuration to a series arrangement without investment in a new heat-transfer area. The series arrangement is assumed to contain two heat exchangers. The first heat exchanger in the series arrangement is designated as the supplier because it supplies reuse water to the second heat exchanger, which is called the receiver. To retrofit a cooling water network with a parallel arrangement of several heat exchangers, the first step of the methodology uses the concept of flow rate difference curve to classify the heat exchangers into the two categories of supplier and receiver. In the second step, receiver sensitivity graphs provide guidelines for syst...

Setting heat pumps correctly in a chemical process system can enhance the energy utilization ratio of the system, reduce the consumption of both the hot and cold utilities, and achieve utility savings and economic benefits. In this paper, for the case of introducing a single heat pump into a system, the dynamic changes of the grand composite curve and pinch temperature under different scenarios are analyzed using a graphical analysis method. The reasons and conditions for such changes are determined. It is shown that for cases that exhibit a change in pinch temperature more hot and cold utility savings may be obtained by using two heat pumps. Existing as well as new two-heat-pump arrangements that comply with the cross-pinch rule are presented.

Emergy analysis is useful for evaluating the resource utilization and environmental performance of industrial systems. However, emergy analysis in its current state can produce erroneous results when it is applied to systems with feedback structure. It is shown that traditional emergy algebra, if not applied properly, can cause violations of the tenet of total inheritance, which is one of the core notions in emergy theory. To overcome this deficiency, this paper proposes a new concept, called virtual emergy flow, for calculating the emergy of feedback structures. The utility of the virtual emergy flow concept is illustrated by the emergy analyses of two different types of feedback structures commonly found in chemical process systems as well as by a case study based on a power and methanol multiproduct system.