Integrated Design of Effluent Treatment Systems

Abstract This paper presents some tools for integrated design and their application to an effluent treatment problem. The problem is to neutralise a set of acid waste streams to a specified tolerance. The task is made more difficult by the presence of substantial delays and by imperfect measurement response. Process configurations for which time delays prevent the performance requirements being met can be eliminated by a controllability test. The test is based on calculating the minimum time before a feedback control system can begin to counteract a disturbance and testing “whether the open-loop response for any combination of disturbances and process/measurement parameters violates a constraint before this time has elapsed. A variation of this test can be used to calculate the fraction of the disturbances which can be tolerated. This provides a measure of controllability which can be used to judge whether an implementable control scheme is likely to be successful. Application of this test to an example allowed many possible process and control systems to be eliminated. The use of pre-screening tests simplifies the final design problem of finding a minimum cost system which would actually satisfy the performance requirements for all combinations of disturbances and uncertain process or measurement parameters. In the example, the final design was tackled successfully using a general approach based on an outer approximation algorithm to find a solution satisfying the constraints over the set of disturbances and uncertain parameters. The paper shows that integrated design methods can be applied successfully to constrained, nonlinear, dynamic design problems with uncertainty