(317c) Energy Integration through Retrofitting of Heat Exchanger Network at Equinor Kalundborg Oil Refinery

Heat integration studies are commonly performed in the wider chemical industry to map current energy utilization and identify potential improvements with respect to energy efficiency. In this regard there are several established methodologies such as: Pinch analysis, mathematical programming and hybrid methods [1][3][4][5]. One of the chief challenges in the practical application of retrofitting in HEN, remains the difficulty associated with the data collection and their validation. In this contribution, we report a heat integration studies to a full-scale refinery plant. We present a methodology that involves iterative application of a process simulator with plant data as well as Monte Carlo simulation to analyze the potential sources of uncertainty in the data collection part.

In 2019 Equinor oil refinery in Kalundborg Denmark used 2908103 MWh, in which 88% was fuel-gas and oil, 6.2% electricity, 2.7% steam and 3% natural-gas [2]. Combined with a Solomon index of 80.3, the potential for energy optimization and therefore also economical and environmentally prospects are substantial. An energy optimization was conducted at Equinor oil refinery in Kalundborg, based on the methodology of pinch analysis and HEN retrofitting. The optimization was constrained to the Naphtha hydrotreating section, Catalytic reforming section, VBGO/LVGO/LGO hydrotreating section and finally the hydrotreating section of KERO/LKERO and LGO.

Design duties of heat exchangers could not be used, as process parameters and composition changes from day to day. All unit operations in the 4 sections were simulated in PRO/II, whereas out the 36 heat exchangers, 17 are shell and tube, 15 are air coolers and 4 are red heaters. Average temperature, pressure, volume flow rate and assay of feed and residue was taken over a month. The date of month was chosen, when the refinery had been cleaned and fluctuations was relatively low, in order to easier balance mass and energy.

Based on the SRK EOS, enthalpies were segmented and exported into UniSim ExchangerNet, to evaluate the energy targets and network performance. Considering a base case of ΔT_min = 20°C retrofit solutions were proposed by locating pinch violations and inefficiencies.

The retrofit solutions were economically evaluated by considering the investment cost of new heat exchangers and the energy savings from each retrofit option. A sensitivity analysis was conducted by changing ΔT_min and investment cost.

Finally, a Monte Carlo simulation was conducted to evaluate the uncertainty of the pinch temperature, external minimum utility heat and external minimum cooling utility, by considering the fluctuation of temperature and massflow.

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