Sequential optimization of cooler and pump networks with different types of cooling

Significance 

Energy crisis and environmental protection are among the major global concern today. Through sustainable development, the growing concern of energy conservation and reduction of carbon footprint can be effectively addressed through better resources utilization strategies. In particular, the stringent mitigation measures on the environment have motivated systematical optimization methods for water and energy integration based on heat exchanger network synthesis.

Heat exchanger network generally comprises of heat recovery networks with heater and cooler networks. As such, studies on the cooling water systems aimed at optimizing water consumption and heat transfer have been intensified. Despite considerable research on optimization of circulating cooling water systems, cooler networks with different cooling types such as dry and wet type air coolers have not been fully explored despite their potential economic benefits in terms of effective water and energy utilization.

Recently, Haitian Zhang, Professor Xiao Feng from Xi’an Jiaotong University in collaboration with Dr. Yufei Wang from China University of Petroleum and Zhen Zhang from Hualu Engineering and Technology Company assessed cooler networks with different cooling systems and pump networks with main-auxiliary pumps. Specifically, their main objective was to establish a superstructure-based model to minimize the annual operation cost and enhance the economic benefits of coupled networks in a sequential method. The superstructure-based mathematical model was set up by assuming one cooler type to be utilized for a hot stream to lower the temperature to the expected level. Their work is currently published in the research journal, Energy.

The authors took into consideration different cooling types: dry type air coolers, spray type air coolers and water coolers with circulating cooling water. Additionally, the auxiliary pumps added in the parallel branches with high pressure heads greatly optimized the pump network. The feasibility and effectiveness of the proposed model were verified using a case study.

The case study was performed under an ambient air temperature of 20°C. The annual operation costs comprised of the combined costs of the electricity expense of the fans and pumps as well as the water expense of both the spray and circulating water. Based on the optimization results of the networks, the proposed model achieved an expense reduction of 13% and 32% of the total annual costs for the cooler network and pump network respectively.

It was worth noting that the economic performance depended on the type of cooling method used attributed to their distinctive characteristics which also described their suitable application areas. For example, air coolers were suitable for cooling down hot air streams at high temperatures due to their low operating costs. Therefore, for good economic performance, dry type air cooler was suitable for hot streams with high inlet temperature while spray type air cooler was more appropriate for cooling down streams with moderate temperatures. Altogether, the study will advance sustainable development through efficient use of water and energy resources.

About the author

Haitian Zhang received a B.S. in Chemical Engineering and Technology (2016) and a M.S. degree in Chemical Engineering and Technology (2019) at Xi’an Jiaoting University (Xi’an, China). Her research interests and experience focus on cooler network optimization in terms of chemical process simulation and synthesis.

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About the author

Prof. Feng received a B.S. (1982), M.S. (1985) and PhD (1990) degrees in Engineering Thermal Physics at Xi’an Jiaoting University (Xi’an, China). Her research interests and experience focus on process integration, including energy, water, and hydrogen systems synthesis and optimization.

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About the author

Prof. Wang received a bachelor degree in Xi’an Jiaotong University in 2008 and a Doctor degree in The University of Manchester. He is now an associate professor in School of Chemical Engineering and Environment, China University of Petroleum. His Research interests focus on Energy system synthesis, energy-water nexus, and chemical industry layout design. He has published over 60 papers and 5 books/chapters.

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About the author

Zhen Zhang received a bachelor degree in Chemical Engineering and Process at Haerbin Institute Technology in 2005 and a master degree in Chemical Engineering at Xi’an Jiaotong University at 2008. He joined the Hualu Engineering and Technology Co., ltd at 2008. He is currently focused on engineering design as a Senior Engineer.

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Reference

Zhang, H., Feng, X., Wang, Y., & Zhang, Z. (2019). Sequential optimization of cooler and pump networks with different types of cooling. Energy, 179, 815-822.

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