Optimal reconfiguration of multi-plant water networks into an eco-industrial park (original) (raw)
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Profit-based grassroots design and retrofit of water networks in process plants
Computers & Chemical Engineering, 2009
In this paper, we present a methodology for the grassroots design and/or retrofit of water utilization systems using mathematical optimization to maximize net present value (NPV) and/or return of investment (ROI) instead of minimizing freshwater consumption. The examples show that the solutions where savings and/or profit are maximized can be different from those where freshwater is minimized. They also differ from each other when ROI or NPV are used. In addition, when the NPV objective is used, the optimum solutions also vary depending on the interest rate used to calculate the discount factor. (M.J. Bagajewicz). search for a cost-effective grassroots design for water network involving a single contaminant. Their method is applied both for municipal and industrial sites and is not based on mathematical optimization. Instead they suggest a hierarchical procedure where a sequence of priority water management steps is established: after a payback limit is set, several water network options are investigated. In this sequential procedure, the maximum water recovery of each option is determined and the plot of investment vs. annual savings is generated. If the total payback period does not agree with the one previously set, some processes can be replaced in order to achieve the desired payback period. Wan Alwi et al. extend their previously presented hierarchical method to account for other steps of the hierarchy, which includes process changes. consider an economic evaluation of a freshwater consumption-optimized water network. They analyze the profitability of the optimized network having the conventional water network as a baseline and applying incremental costs and benefits to rearrange the given network to a more operational friendly one. No regeneration processes are considered. Some insights of major contributors to the costs and benefits are presented. However, these findings cannot be necessarily generalized since they are based on a specific case example. In a second paper, , the optimized water network is found directly by optimizing the net present value (NPV) using an NLP model (using MINOS). The formulation of the NPV equation is based in the principal contributors of the incremental costs and benefits found in their previous work. The addition of regeneration processes is not considered either and a maximum allowed flowrate is imposed for each water-using unit. Their results confirm that a network obtained 0098-1354/$ -see front matter
Journal of Cleaner Production, 2012
Industrial water networks are designed in the first part by a multiobjective optimization strategy, where fresh water, regenerated water flow rates as well as the number of network connections (integer variables) are minimized. The problem is formulated as a Mixed-Integer Linear Programming problem (MILP) and solved by the ε-constraint method. The linearization of the problem is based on the necessary conditions of optimality defined by Savelski and Bagajewicz (2000). The approach is validated on a published example involving only one contaminant. In the second part the MILP strategy is implemented for designing an Eco-Industrial Park (EIP) involving three companies. Three scenarios are considered: EIP without regeneration unit, EIP where each company owns its regeneration unit and EIP where the three companies share regeneration unit(s). Three possible regeneration units can be chosen, and the MILP is solved under two kinds of conditions: limited or unlimited number of connections, same or different gains for each company. All these cases are compared according to the global equivalent cost expressed in fresh water and taking also into account the network complexity through the number of connections. The best EIP solution for the three companies can be determined.
Water Network Optimization with Wastewater Regeneration Models
Industrial & Engineering Chemistry Research, 2014
The conventional water network synthesis approach greatly simplifies wastewater treatment units by using fixed recoveries, creating a gap for their applicability to industrial processes. This work describes a unifying approach combining various technologies capable of removing all the major types of contaminants through the use of more realistic models. The following improvements are made over the typical superstructure-based water network models. First, unit-specific shortcut models are developed in place of the fixed contaminant removal model to describe contaminant mass transfer in wastewater treatment units. Shortcut wastewater treatment cost functions are also incorporated into the model. In addition, uncertainty in mass load of contaminant is considered to account for the range of operating conditions. Furthermore, the superstructure is modified to accommodate realistic potential structures. We present a modified Lagrangean-based decomposition algorithm in order to solve the resulting nonconvex Mixed-integer Nonlinear Programming (MINLP) problem efficiently. Several examples are presented to illustrate the effectiveness and limitations of the algorithm for obtaining the global optimal solutions. 1 Introduction With increasing costs, diminishing quality of supplies, and stricter environmental effluent standards set forth by the Environmental Protection Agency (EPA), water is playing an increasingly important role in the process industries. The primary water uses are process water, cooling water, and boiler feed water, with each use being emphasized by different industries. For example, the chemicals, petroleum refining, and metal sectors primarily use water for cooling, while paper and pulp and food processing mostly use water for process use. In a study by Carbon Disclosure Projects of 137 companies with total assets over $16 trillion, it has been reported that water has risen high on the corporate agenda[1]. Eighty nine percent of responding companies have developed specific water policies, strategies, and plans. Specifically, in the chemical sector, all ten companies surveyed recognize that there is a high growth potential for processes and products that support more efficient water use and water recycling. Consequently, it is essential to incorporate reuse schemes at the process design level for optimal water use. 1
Retrofit of Water Networks in Process Plants
2006
In this paper, we present a methodology for the retrofit of water utilization systems using mathematical optimization. The problem consists of determining the best re-piping and the capacity of a new treatment unit (if any) to be introduced to generate the best retrofit. Instead of reducing water consumption, or maximizing savings, we resort to analyze the problem using a more comprehensive view of savings and return of investment (ROI) within feasible freshwater usage ranges. The example shows that the solutions where savings and ROI are maxima are remarkably different.
Korean Journal of Chemical Engineering, 2007
This article considers new and existing technologies for water reuse networks for water and wastewater minimization. For the systematic design of water reuse networks, the theory of the water pinch methodology and the mathematical optimization are described, which are proved to be effective in identifying water reuse opportunities. As alternative solutions, evolutionary solutions and stochastic design approaches to water system design are also illustrated. And the project work flow and an example in a real plant are examined. Finally, as development is in the forefront in process industries, this paper will also explore some research challenges encountered in this field such as simultaneous water and energy minimization, energy-pinch design, and eco-industrial parks (EIP).
Planning Model for the Design and/or Retrofit of Industrial Water Systems
Industrial & Engineering Chemistry Research, 2011
Planning models for industrial water systems are needed to address future environmental regulations, increasing costs of freshwater, variability on the quality of the available freshwater source, and bottlenecks caused by expansion of the capacity plant, among other reasons. In this paper, we present a method to address an increase in plant capacity associated with new water-using units planned to be added through time and/or an increase in the mass load of existing water-using units. We compare this method with two ad-hoc alternatives, which exhibit good performance for the examples shown.
Journal of Environmental Management, 2009
Synthesis of distributed wastewater treatment plants (WTPs) has focused on cost reduction, but never on the reduction of environmental impacts. A mathematical optimization model was developed in this study to synthesize existing distributed and terminal WTPs into an environmentally friendly total wastewater treatment network system (TWTNS) from a life cycle perspective. Life cycle assessment (LCA) was performed to evaluate the environmental impacts of principal contributors in a TWTNS. The LCA results were integrated into the objective function of the model. The mass balances were formulated from the superstructure model, and the constraints were formulated to reflect real wastewater treatment situations in industrial plants. A case study validated the model and demonstrated the effect of the objective function on the configuration and environmental performance of a TWTNS. This model can be used to minimize environmental impacts of a TWTNS in retrofitting existing WTPs in line with cleaner production and sustainable development.
Dual-objective optimization of integrated water-wastewater networks
The dual-objective optimization of an integrated water/wastewater network (IWWN) is addressed by targeting for minimum fresh water consumption at the same time with operating costs reduction. An IWWN is a recycle system composed of two oriented graphs, the first encoding the water-using units (WUs) and the second, the treatment units (TUs). Although internal recycles are forbidden ab initio for the WUs graph, external recycles from the appropriate TU to the WU whose inlet restrictions are met by the partially treated water are encouraged. The corresponding mathematical model was written. A synthetic example is proposed and analyzed under several scenarios with respect to the fresh water consumption, the magnitude of internal and treated water reuse and the investment/operating costs related to the active pipes network. A comparison is made regarding the differences in network topology and fresh water consumption implied by different points from the Pareto front (PF).