Design Considerations in Steam System Debottlenecking Using Process Integration

Steam boilers are used to generate steam in order to meet cold process requirements. The most common steam heat exchanger network layout found on chemical plants is that of a pure parallel design. This implies that the flowrate of steam needed for the system can be reduced, while maintaining the required duty, simply by changing the layout of the network. Phase change of saturated steam to saturated liquid plays a vital role in the targeting method as well as the design of the network layout. A graphical targeting method and a linear programming (LP) model have been developed to obtain the minimum steam flowrate, as well as the network layout. Furthermore, a mixed integer linear programming (MILP) model was developed which does the targeting and design simultaneously. In an illustrative example, the steam flowrate was reduced by 20.5% using the graphical targeting method and LP model, as well as with the MILP model. However, by using the graphical targeting method, the designer gains more insight to the overall design as opposed to the MILP model which is treated as black box approach. Furthermore, the effect of pressure drop (in the pipes and heat exchangers) on the return temperature to the steam boiler was found to be that as the overall pressure drop increased, the return temperature became less than the value obtained from the graphical targeting method and the MILP model.