This work reports an extendible multiobjective optimization framework to find the optimal configuration of energy utilization and wastewater treatment facility of the process. It incorporates two sustainable energy integration alternative tools, i.e., a cogeneration (COGEN) unit and thermal membrane distillation (TMD), as available add-ons to the process during normal operation and for abnormal situation management. The objective of the framework is to reduce the environmental footprint of abnormal flares by enumerating and assessing possible process configurations in order to manage flares from uncertain sources and to utilize unused energy resources for wastewater treatment. The core of this optimization framework is developed using a genetic algorithm and its objective function is aimed at minimizing the total annualized cost which accounts for the fixed and operating costs of the system, the value of produced coproducts (i.e., power, wastewater treatment savings, income from permeate), and taxes/credits associated with greenhouse gases. An ethylene process plant is used to demonstrate the applicability of the developed framework. The results of different alternative configurations demonstrate the economic, energetic, and/or environmental tradeoffs of integrating TMD and the COGEN unit with the process plant both for flare mitigation and during normal operation. It was seen that the total annualized cost (TAC) dropped around 35% and the payback period reduced from 7.01 to 4.61 years when an integrated process plant (ethylene plant), utility unit (COGEN), and wastewater treatment facility (TMD) was considered instead of separate divisions. Moreover, utility savings were achieved up to 8% and annual incomes from coproducts were increased around 20% for the integrated ethylene plant, COGEN, and TMD unit. Besides, prolific recycling opportunities of unused flare streams and treated wastewater were identified to make some valuable products from waste streams.

The production of heavy oil and bitumen requires unconventional methods. One such approach is steam-assisted gravity drainage (SAGD). This technology has key advantages but is characterized with substantial levels of water consumption and discharge. Therefore, there is a need for effective water treatment and reuse methods in SAGD. This paper examines the use of an emerging technology: thermal membrane distillation (TMD) as an integral part of water treatment for SAGD. Synergistic effects are exploited from heat and mass integration of SAGD and TMD. Specifically, the hot produced water and blowdown water are evaluated for treatment using TMD because of their thermal content and because of the need for high levels of purity which can be achieved by TMD. Several design configurations and scenarios are proposed and evaluated to assess the technical and economic viability of including TMD as a process in water-management systems for SAGD. (C) 2015 Elsevier Ltd. All rights reserved.

Shale gas production is associated with the significant consumption of fresh water and discharge of wastewater. The flowback wastewater is tied to the hydraulic fracturing technology used for completing and stimulating the horizontal wells in the very tight formations characterizing the shale formation. Treatment and reuse of these large volumes of wastewater can lead to substantial savings in fresh water usage and reduction of the negative environmental impact thereby enhancing sustainability of the shale gas industry. Such treatment requires selective and cost-effective technology.Thermal membrane distillation (TMD) is an emerging technology that offers several advatanges such as high selectivity in separating water from inorganic solutes and modular nature that can accommodate a wide range of flows. It can also utilize low-level heats that are typically available from shale-gas production and processing.The objective of this work is to develop an optimization approach for the design of TMD systems to treat flowback water. A multi-period formulation is developed to account for the time-based variation in the flowrate and concentration of the flowback water. Modeling equations are used to relate design and operating variables to performance and cost. The optimization formulation also accounts for the period-based changes in the required design and operating variables and reconciles them over the selected periods. Other constraints include quality of the permeate and water-recovery ratio. The optimization formulation and design approach are applied to a case study for the treatment of flowback water for the Marcellus Shale Play. For 75% water recovery, the cost of the permeate is about $2.6/m3. As higher recoveries are sought, the cost per m3 of permeate increases due to capital productivity factors in dealing with the decreasing amount of flowback water over time. The results are reported using a Pareto chart that trades off recovery objectives with cost of treated water.

Thermal membrane distillation (TMD) is an emerging separation method which involves simultaneous heat and mass transfer through a hydrophobic semipermeable membrane. Traditionally, studies of this technology have focused on the performance of individual modules. Because of purity and recovery requirements, multiple TMD modules may be used in various configurations including series, parallel, and combinations. Furthermore, there may be a need to reroute streams from one module to another or to recycle a stream to the same unit. The objective is to develop a systematic approach to synthesize an optimal TMD network. A structural representation is developed to embed potential configurations of interest. A mathematical formulation is developed to transform the design problem into an optimization task that seeks to minimize the cost of the system. Two case studies are presented to illustrate the applicability of the developed approach and its merit over conventional design scenarios. © 2014 American Institute of Chemical Engineers AIChE J, 61: 448–463, 2015

With increasing attention to the environmental impact of discharging greenhouse gases (GHG) in general, and CO2 in particular, many are looking to carbon sequestration as an approach to reduce the carbon impact of stationary point sources of CO2. Although much of the focus has historically been on capturing and sequestering post-combustion CO2 from the burning of fossil fuels, there are many industrial processes that already require separation of CO2 that also contribute to GHG emissions. This CO2 can also be sequestered. One such process is the commercial production of liquefied natural gas, which necessitates the separation of CO2 from the hydrocarbon for liquefaction; resulting in a relatively pure CO2 stream which can be sequestered. The Gorgon project is one such commercial project. In the broader political environment of Australia's carbon tax system and government grants to offset the capital investment in carbon abatement technologies, the economics of the Gorgon project can be analyzed to determine the technical and economic parameters that make the carbon sequestration more or less feasible for this self-contained project. These findings can then be applied to any such project where a pure CO2 is a necessary by-product and a carbon tax is either in effect or being considered. This analysis is the primary objective of this article. In this context, a computer-based simulator was developed to analyze the impact of technical, market, and public policy factors on project economics. A base case was developed using the current project parameters and a number of alternative scenarios were then developed. Sensitivity analyses were conducted and a "best case" scenario was developed to look at what the appetite for investment could be to improve the sequestration of CO2. The article demonstrates that CCS project competitiveness can be simulated to analyze the impact of key technological, market, and policy changes on the project.

This paper presents an optimization approach for the design of thermal membrane distillation (TMD) systems that are thermally coupled with processing facilities. A superstructure representation and an optimization formulation are introduced to obtain simultaneously the optimization of the TMD unit and the heat-exchange network (HEN) that integrates heating and cooling in the process facility. The superstructure and associated optimization formulation seek to identify the system configuration along with design and operating variables such as heat-exchanger areas, membrane area, extent of thermal coupling between the process and TMD, and the TMD feed-preheating temperature. The objective function maximizes the net annual profit which accounts for the revenues from the sales of purified water, the avoided cost of the treated wastewater, and the total annualized costs accounting for the capital investment of the added heat transfer units and the TMD network, the operating costs for the heating and cooling utilities and the operating expenses for the TMD system. The proposed optimization formulation is applied to a case study where a TMD system is integrated with a methanol plant and the results show significant economic benefits for the implementation of the proposed methodology.

Thermal membrane distillation (TMD) is an emerging technology which is gaining an increasing level of interest in the area of high-purity separation especially in water treatment. It is driven primarily by heat which creates a vapor-pressure difference across a porous hydrophobic membrane. The integration of TMD with industrial processes offers several advantages. Excess low-level heat from the process can be used to drive TMD. This transfer of heat also reduces the cooling utility load for the process. Therefore, dual heat-reduction benefits accrue as a result of this heat integration. Additionally, process wastewater and utility water may be treated using TMD then recycle or reused in the process or sold to external users. This paper introduces a process integration framework from the thermal coupling of TMD networks and industrial processes. First, a three-parameter model is developed to quantify the water flux through the membranes as a function of heat and temperature. The model is validated using experimental data for direct-contact membrane distillation (DCMD). Next, the trans-shipment model for heat integration is extended to account for the coupling of the process and the TMD network and the need to optimize the extent of heating for the TMD feed. A discretization approach is used to linearize the thermal-coupling constraints. The mathematical-programming formulation is solved to identify the optimal heat integration strategies within the process and with the TMD network. The program also determines the optimal temperature to which the TMD feed should be heated and the system design and specification. A case study is solved to show the integration between a gas-to-methanol process and an adjacent desalination process. Three scenarios are considered: a standalone TMD network, TMD with thermal and water coupling with a process in an eco-industrial park setting, and TMD as part of the processing facility.