Shankar Narasimhan S

Ensuring adequate supply of clean drinking water and electricity in several parts of the world continues to be a formidable challenge. In coastal areas facing this problem, desalination of sea water using Reverse Osmosis (RO) driven by solar power without batteries can be an appropriate technological solution. Variability in incident solar power is a significant operational issue. The focus of this work is optimal operation and control of the RO plant with guaranteed water purity. A steady state model is developed and validated using 'ROSA', a black-box software programme commonly used for simulating RO plants. Analysis of the optimal solution reveals that the feasible space (of available power) consists of two regions where different set of constraints are active. In one region salt concentration constraint is active and in another, the pressure constraint is active. Hence the optimal operation strategy can be implemented by active constraint control. © 2012 Elsevier B.V.

Current methods for the evolutionary synthesis of heat exchanger networks (HENs) using the concepts of paths and loops, do not guarantee optimality nor do they address the issue of the feasibility of an evolutionary modification step. In this work, an optimization problem formulation for the evolutionary synthesis of HEN is proposed. The principal advantage of using this approach is that it provides information on whether a specified evolutionary step (such as deletion of an existing exchanger) is feasible or not. Furthermore, it is useful in determining the optimal solution corresponding to each evolutionary step. A process graph representation of a HEN is proposed for formulating the optimization problem. This representation unifies the traditional concept of paths and loops and allows any evolutionary step to be accomplished by circulating appropriate enthalpy flows around a set of independent cycles of the HEN process graph. By exploiting this feature, a tight optimization problem is formulated for any evolutionary step. The efficacy of the proposed approach is demonstrated through examples both for energy as well as for total cost minimization. The proposed approach can be integrated with PDM methods, because it fits well with the PDM philosophy of allowing the design engineer to retain control while providing feedback on the best possible solution achievable corresponding to any evolutionary design modification chosen by the designer.

Optimal operation of municipal Water Distribution Networks (WDNs) is based on optimizing one or more performance metrics while meeting consumer demands and satisfying supply side and storage constraints. This can be achieved by implementing advanced control schemes such as Model Predictive Control (MPC). With the alarming decrease in fresh water supplies, the primary focus of online control strategies should be to conserve water. A novel control strategy that can handle both water sufficient and deficient cases is proposed for WDNs with storage facilities. Performance of the developed model based online control strategy is tested by numerical simulations of an illustrative WDN. © 2012 Elsevier B.V.

Seaborne trade in LPG or its constituents (liquid propane and butane) has been growing substantially and is projected to rise to 70 Mt by 2012. Loading LPG onto ship tankers, transporting and unloading LPG from tankers to inland terminals are time and energy intensive operations. The purpose of this study is to arrive at an optimal sequence of flow rates when unloading a given amount of LPG from the ship tanker to the inland storage tank. A distributed dynamic model accounting for heat transfer and fluid flow is developed. This model is used in a simulation based optimization framework to determine the optimal unloading sequence that minimizes material, demurrage and energy costs. © 2011 Elsevier B.V.