Wastewater Reuse and Zero Discharge Cycles in Process PlantsEPA Grant Number: R828210
Title: Wastewater Reuse and Zero Discharge Cycles in Process Plants
Investigators: Bagajewicz, Miguel J. , Savelski, Mariano
Institution: University of Oklahoma
EPA Project Officer: Hahn, Intaek
Project Period: June 15, 2000 through June 14, 2001
Project Amount: $99,988
RFA: Technology for a Sustainable Environment (1999) RFA Text | Recipients Lists
Research Category: Sustainability , Pollution Prevention/Sustainable Development
Description:The purpose of this project is to continue the development of methodologies for the design and/or retrofit of environmentally benign water cycles in chemical and petrochemical processing units. This project is a continuation of EPA grant 825328010, which made several conceptual contributions. An industrial partner is participating in this new phase to prove these concepts and the new developments in practice.
End-of-pipe treatment solutions for wastewater cleanup are being replaced by water recycle/reuse and decentralized cleanup systems. Since the first formulations of the problem, which are graphical in nature, there have been several investigators that have addressed this problem using a variety of tools. Some of the limitations of these tools are numerical, but other are conceptual.
Approach:The group at the University of Oklahoma has been able to provide several innovative solution procedures for these problems. First, necessary and sufficient conditions of optimality of these problems have been developed. These conditions enable the formulation of linear problems for the single component case and tree searching for multicomponent cases. In addition, forbidden and compulsory cases can be analyzed. The group has been able to develop a methodology to solve this problem globally by hand. Other work has also been accomplished. The interaction between heat integration and water allocation has been rigorously solved overcoming the limitations of other approaches. Finally, methods to perform optimal retrofit have been proposed. Notwithstanding the value of these advances and some of the contributions of other researchers, the problem continues to offer theoretical and practical challenges. The water allocation problem and the wastewater cleanup problem have to be properly merged in a single problem so that decentralized cleanup can be appropriately addressed. Even though good methodologies exist for the solution of both problems separately, the simplifying assumptions of the original work have to be revisited. In particular the issue of fixed load in water polluting processes and fixed removal in wastewater cleanup need reformulation. The mathematical properties of the problem are thus changed and new procedures need to be developed. Procedures to reallocate water dynamically on the basis of existing process-t-o-process connections also need to be developed. The layout of a complex has important impact on the economics of reuse and has been ignored. The impact of mass exchange driving force on capital cost should be considered. Reactors have not been included and the interaction between heat and mass transfer has been ignored altogether. Mass exchanger network technology has not been fully exploited. Alternative locations of pollutant interception, via process modifications need to be developed. Finally, the ultimate goal of exploring solutions that enable zero discharge have not been properly discussed, much less solved. The concept of zero water discharge refers to closed circuits of water, such that water disposal is eliminated altogether. Closed circuits are appealing because end-of-pipe regeneration does not have to be conducted to the full extent required for disposal as water can be reused with higher level of contaminants. Additionally, the absence of a discharge eliminates internal administrative costs associated with the enforcement of EPA and local limits, as well as the interface with government agencies.
This project will be conducted primarily at the University of Oklahoma, as a continuation of the previous EPA grant. Phillips Petroleum is the Industrial partner. Dr. Savelski, who worked in this project for three years, will participate now as a co-PI at Rowan University. The methodology used to address the new posed challenges is the development of necessary conditions of optimum that can simplify the mathematical complexity of mathematical programming formulations, which are otherwise too cumbersome to solve. This project will have a significant impact on water usage and wastewater management for the chemical and petrochemical industry. It follows the guidelines of the DOE and NSF sponsored Workshops on these issues held in New Orleans (January 4-6, 1996) and the specific goals suggested by this program in the area of Engineering for Pollution Prevention. This technology is mature enough to be tested in sites. In addition, several conceptual contributions to the general engineering knowledge will be explored. Finally, the participation of undergraduates helps disseminating green process systems engineering concepts.
Specifically, this one-year project will address four of the many remaining challenges of this problem:
- Development of methodologies to address the design of systems that contain processes for which some contaminants have either a fixed outlet concentration or a load that is a function of the outlet concentration. Almost all the methods that have been developed consider fixed pollutant loads and maximum inlet/outlet concentrations.
- Extension of the existing tree search methods developed by the group at the University of Oklahoma to the consideration of Decentralized treatment. It is well known that these solutions reduce the fresh water consumption and discharge.
- Extension of the existing tree search methods developed by the group at the University of Oklahoma to the consideration of uncertainty in data. This has been the most important concern raised from practice.
- Evaluation of Zero Discharge solutions. Preliminary analysis will be performed using existing models to assess the potential economic impact if such cycles were to be adopted by industry.
The expected results of this project are therefore improved methods to handle the design and retrofit of water utilization systems in process plants. In addition the economical impact of zero discharge cycles will be assessed. These methods will be tested using data provided by the industrial partner (Phillips Petroleum). By providing these solutions industry will be able to continue reducing water usage and discharge, thus reducing pollution.