A tightening global energy supply/demand balance and ever increasing environmental constraints necessitate constant re-evaluation of existing technologies and a sustained focus on developing innovative new designs – the need to conserve energy is more important than ever.

Within the context of production systems at most process plants, one means of achieving this is via the efficient integration and optimisation of the energy requirements associated with site utility systems. To that end we are pleased to report that PIL associate Kumar Prashant, collaborating with Simon Perry from Manchester University’s Centre for Process Integration, has recently published an insightful paper in ‘Chemical Engineering Transactions’ examining the optimal location and number of steam levels required to meet the external heating and cooling demands of a range of individual site processes.

Fig. 1 Total Site Profiles

The research undertaken in the course of preparing this report is set to assist end-users in minimising their operating costs and environmental footprint whilst maximising their capacity utilisation.

Designing an efficient site utility system is a large and complex affair, involving complex combinatorial elements and catering for a multitude of different objectives. Key design decisions that must be taken include selecting the appropriate (optimal) steam levels for the turbines involved, selecting a suitable number of turbines and configuring these judiciously.

Fig. 2 Cogeneration Targets

Optimising the number and location of steam levels involves considering steam demand at each level, the output power generated by the system’s turbines, as well as a range of boiler duty, fuel and cold utility requirements. The model developed and reported on in ‘Chemical Engineering Transactions’ makes use of Mixed Integer Linear Programming (MILP) techniques, implemented in a Visual Basic/Excel environment and linked to SITE-int – PIL’s proprietary simulation software – in order to extract the appropriate data for the total site.

This new approach to enabling an optimal pressure selection at site-wide steam mains can also be applied to improve the operational performance of existing sites.