A steam utility network model for the evaluation of heat integration retrofits A case study of an oil refinery
This paper presents a real industrial example in which the steam utility network of a refinery is modelled in order to evaluate potential heat integration retrofits proposed for the site. Total site heat integration techniques have previously been used for the refinery to identify a number of possibilities for heat saving retrofits. However, the profitability and actual primary energy saving will depend on the configuration and operation of the utility system. The supply of utilities such as fuel, steam and electric power represents a significant operating cost for many process industries. A reduced use of utilities can improve process economics and reduce the environmental footprint of the process. Heat integration, within and between the refinery process units, is one way to improve the energy efficiency and reduce the use of steam and fuels. Such heat integration measures will affect steam consumption and generation at different steam pressure levels within the network. A refinery, typically, has flexibility in their operation of the steam network from a number of switchable steam turbine driven or motor driven pumps and compressors. Furthermore, due to seasonal variations the amount of internally generated refinery fuel gas will vary, leading to periods of steam over production as well as periods with a demand for additional purchased fuel. Consequently, the optimum operating strategy concerning steam production and the switchable mechanical drives is a trade off between the cost of fuel and electricity. Corresponding author 0258 1 2 This paper presents a few examples of heat integration retrofit measures from a case study of a large oil refinery. In order to evaluate expected changes in fuel and electricity imports to the refinery after implementation of the proposed retrofits, a steam system model has been developed using commercial software. The model enables an analysis of how the operation of boilers and turbines could be changed in effect of a proposed change. The steam system model has been tested and validated with real steady state data from three different operating scenarios. It can be used for simulation or optimization to answer how changes to steam balances at different pressure levels will affect the overall steam balances, generation of shaft power in turbines and electricity demand for pumps and compressors, and the consumption of fuel gas.