Studying the Role of System Aggregation in Energy Targeting: A Case Study of a Swedish Oil Refinery

Elin Svensson,Matteo Morandin,Simon Harvey,Stavros Papadokonstantakis

doi:10.3390/en13040958

Elin Svensson, Matteo Morandin + Show 2 more

Open Access

https://doi.org/10.3390/en13040958

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Abstract

The definition of appropriate energy targets for large industrial processes is a difficult task since operability, safety and plant layout aspects represent important limitations to direct process integration. The role of heat exchange limitations in the definition of appropriate energy targets for large process sites was studied in this work. A computational framework was used which allows to estimate the optimal distribution of process stream heat loads in different subsystems and to select and size a site wide utility system. A complex Swedish refinery site is used as a case study. Various system aggregations, representing different patterns of heat exchange limitations between process units and utility configurations were explored to identify trade-offs and bottlenecks for energy saving opportunities. The results show that in spite of the aforementioned limitations direct heat integration still plays a significant role for the refinery energy efficiency. For example, the targeted hot utility demand is reduced by 50–65% by allowing process-to-process heat exchange within process units even when a steam utility system is available for indirect heat recovery. Furthermore, it was found that direct process heat integration is motivated primarily at process unit level, since the heat savings that can be achieved by allowing direct heat recovery between adjacent process units (25–42%) are in the same range as those that can be obtained by combining unit process-to-process integration with site-wide indirect heat recovery via the steam system (27–42%).

Highlights

Energy targeting is typically performed in the early stages of chemical process design in which the minimum energy requirement (MER) of the process is estimated [1]
The results presented above for the case study refinery indicate that from a hot utility standpoint there is no actual benefit in implementing direct heat exchange between adjacent units since similar targets can be achieved by indirect heat exchange through the steam network
The scenarios analysed range from allowing direct process heat exchange across the entire site to requiring that any heat recovery must be achieved through the steam utility system

Summary

Introduction

Energy targeting is typically performed in the early stages of chemical process design in which the minimum energy requirement (MER) of the process is estimated [1]. To set targets in the early stages of design is essential to develop processes that use as little energy as is economically reasonable. In complex thermal systems, knowing the minimum theoretical heat demand that has to be provided by an external source (hot utility) can be of great help for the engineer for guiding process design [3]. Setting targets for heat recovery is an important step in retrofit situations [4] in order to estimate the potential energy savings that can be achieved by rearranging and modifying the existing heat exchange network. Chew et al [5]

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