Influence of variations in cost factors in structural optimisation of heat recovery systems with moist air streams

Optimal solutions of heat recovery systems at paper machines (HRS), where both the specific heat flow rates and the overall heat transfer coefficients are strongly nonlinear, were analysed in respect of the influence of variations in the hot utility price (HU-price) and the annuity factor. A model for structural optimisation that takes into account the nonlinearities of the HRS was applied. In the study the variations in the areas and the topologies over a large range of HU-price and annuity factor were analysed. The sensitivity of the solutions on the nonlinear area costs was studied by solving the problem with varying total area costs, relative to the area cost of the optimal solution. The dependence of the total HRS-cost, the individual match areas and the hot utility consumption was analysed. The individual areas of the included matches showed particular variations at the boundaries of the topology changes.