Abstract
Energy efficiency has become an important feature in the design of process plants with the rising cost of energy and the more stringent environmental regulations being implemented worldwide. In South Africa, as elsewhere, most process plants built during the era of cheap energy place little emphasis on the need for energy recovery due to the abundance of cheap utilities sources such as coal. In most of these plants, there exist significant potential for substantial process heat recovery by conceptual design of the heat recovery system. By maximizing heat recovery from the processes, there will be a reduction in the process utilities requirement and the associated environmental effects. Pinch analysis has been demonstrated to be a simple but very effective tool for heat integration and optimization of chemical plants. This study uses the pinch principle to retrofit the heat exchanger networks (HEN) of the crude distillation unit of an integrated petroleum refinery to evolve a HEN that features optimum energy recovery. The network was further relaxed by trading off energy cost with capital cost to obtain an optimal HEN topology not too different from the existing network. The simulation works were implemented in AspenPlus v8.0 environment. Analysis revealed that 34 per cent saving on energy usage per annum is realizable. This significant saving in energy also results in diminished gaseous pollutants associated with energy usage.
Highlights
The issues of energy sustainability and security [1] and the increasingly stringent environmental regulations have combined to elevate the challenge of energy efficiency to a high-priority issue [2] for energy intensive industries
It could be seen that the overlapping of the cold composite and the hot composite curve indicates a high possibility of process to process heat exchange
This study confirmed that Pinch Technology is a very practical, easy and intuitive method for attaining better process heat integration
Summary
The issues of energy sustainability and security [1] and the increasingly stringent environmental regulations have combined to elevate the challenge of energy efficiency to a high-priority issue [2] for energy intensive industries. Plants retrofitting towards cost-effective energy recovery and improved energy and utilities usage become attractive and are being implemented worldwide. Little emphasis was placed on optimal process heat recovery because of the cheap availability of utilities sources at the time of plant construction. Analyses of the energy recovery system of plants design with rule of thumbs have revealed potential significant savings in utilities usage [7, 8] by placing better matches between the process streams. A design that maximizes energy recovery using heat exchanger networks to match the process hot and cold streams, will result in minimal external heating and cooling requirements to meet the energy needs of the plant. Kemp [9] reported a potential saving of between 30 to 100 per cent in utilities usage in various units of a petroleum refinery
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