Modellering och optimering av spillvärmesystem på Shell Raffinaderi AB för ökad fjärrvärmeleverans

Abstract

In this diploma work has been investigated how optimisation can increase low temperature waste heat recovery from Shell Refinery in Gothenburg. The waste heat recovery system at Shell delivers heat to the district heating network of Gothenburg. The waste heat comes from cooling and condensation of process streams. The optimisation is done by changing the distribution of water flow through the heat exchangers so an optimum of heat recovery can be achieved for a given delivery temperature: The optimisation is done with a new model in MA TLAB and with Shell's own optimisation tool, SMOC (Shell Multivariable Optimising Controller), which is used for online optimisation. A detailed heat exchanger model was constructed. The model takes the flow of water and the flow of the oil product in the heat exchanger into consideration. The heat exchangers are divided into "to be optimised" and "not to be optimised". The flow in "not to be optimised" heat exchangers is constant, in "to be optimised" heat exchanger the flow is variable so an ortimum can be found. The optimisation result gave a possible heat recovery of about 2 MW (2%) for both SMOC and MATLAB. However there were some differences between individual heat exchangers. This indicates that Shell's heat recovery system has a flat optimum. Due to the fact that not all of the heat exchangers were available for optimisation the real heat recovery can be expected to be somewhat greater. To further increase the heat recovery retrofit of the heat exchanger network may be the best alternative and an investigation of this has been done.