Optimal Design of Thermal Membrane Distillation Systems for the Treatment of Shale Gas Flowback Water

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

Managing abnormal operation through process integration and cogeneration systems

Flaring is a common industrial practice that leads to substantial greenhouse gas emissions, health problems, and economic losses. When the causes, magnitudes, and frequency of flaring are properly understood and incorporated into the design and operation of the industrial plants, significant reduction in flaring can be achieved. In this paper, a process integration approach is presented to retrofit the process design to account for flaring and to consider the use of process cogeneration to mitigate flaring while gaining economic and environmental benefits. It is based on simultaneous design and operational optimization where key flaring sources, causes, and consequences of process upsets are identified then included in the energy profile of the process to design a combined heat and power system with special emphasis on discontinuous sources due to process upset. Environmental and economic benefits are weighed against the cost of process retrofitting. A base case study for an ethylene process is used to illustrate the applicability of the proposed approach and to evaluate the process performance under varying abnormal situation scenarios.NPRP grant #5-351-2-136 from the Qatar National Research Fund (a member of Qatar Foundation).Scopu

A systematic visual methodology to design ionic liquids and ionic liquid mixtures: Green solvent alternative for carbon capture

Ionic liquids (ILs) have gained great interest recently to substitute volatile organic compounds (VOCs), since their properties can be tuned to match certain targets and applications. Further to this, another possibility to optimise ILs for their specific application is through IL mixtures. In this work, an insightful and yet simple systematic approach to design pure ILs and their mixtures is presented. This newly presented approach allows the visualisation of IL mixture design problem, and hence provides insights and allows users to solve the problem visually. The visualisation of problem and solutions is achieved by applying property integration framework in this proposed methodology. In property integration framework, IL products design problem is mapped from property domain into cluster domain through property clustering technique. Therefore, the proposed methodology provides a property based platform to visualise the overall performance of the designed IL products with graphical tools. A feasible IL product is always designed to fit a purpose based on consideration of multiple target properties, but these properties can be contradicting one another. The presented approach allows multiple target properties consideration during the design process, by portraying these properties and target of each clearly on a single graphical tool. To date, the study of properties of pure ILs and IL mixtures is still in the infant phase, and these data are still scarce. Hence, some of the prediction models do not cover all available ILs. To overcome this problem, the proposed approach is developed to adapt property data of pure ILs directly, together with existing property prediction models to predict the properties of the designed IL mixtures. The presented approach is able to generate a list of potential solutions to users, and the final decision can be made by users accordingly, through further screening and experimental validations. An illustrative case study, which focuses on the design of carbon capture solvents, is solved to demonstrate the proposed approach.This work is supported by the Ministry of Science, Technology and Innovation (MOSTI) Malaysia under the Grant No. 06-02-12-SF0224.Scopu

A systematic approach to design task-specific ionic liquids and their optimal operating conditions

Carbon capture and storage (CCS) has gained great interest in recent years as a potential technology to mitigate industrial carbon dioxide (CO2) emissions. Ionic liquids (ILs) were identified as potential CO2 capturing solvents, due to their negligible vapour pressure, high thermal stability, and wide range of thermophysical properties. However, determining a task-specific IL merely through experimental studies is tedious and costly, as there are about a million possible combinations of cations and anions that may make up the ILs. This work presents a systematic approach to design an optimal IL for the purpose of carbon capture. The significant contribution of the presented approach in this work is the introduction of disjunctive programming to identify optimal operating conditions of the process involved while solving the IL synthesis problem. As studies show, the performance of ILs changes with the operating conditions, which in turn affects overall performance of the carbon capture process. Hence, the presented approach will determine the optimal IL by considering the effect of system operating conditions, and simultaneously determining optimal conditions of the carbon capture process. Operating conditions of the process are modelled as continuous variables; disjunctive programming can discretise these variables and reduce search space for results. Since most of the ILs to be designed are novel solvents, their thermophysical properties are estimated using the group contribution (GC) method. Appropriate structural constraints are defined to ensure the structure of the synthesised IL is feasible. An illustrative case study is solved to demonstrate the proposed approach.Scopu

Safety and techno-economic analysis of ethylene technologies

Recent growth in shale gas production has contributed to the interest in establishing numerous petrochemical plants for shale-gas monetization. The ethylene industry is one of the main beneficiaries of such growth because of the switch from the conventional naphtha feedstock to shale-gas constituents. Different technologies must be screened and compared. In addition to the typical approach of performing techno-economic analysis for comparing technologies, it is important to consider safety aspects early enough in the selection process. This paper presents a comparative approach for two ethylene-production technologies through techno-economic and safety analysis. The primary process route is a state of art process while other is a novel process that is still in development stage. The conventional process route is ethane steam cracking which is a well-established process. The competing candidate is ECLAIRS (Ethylene from Concentrated Liquid phase Acetylene- Integrated, Rapid and Safe) which is an emerging gas to ethylene process. A top level analysis is performed using key quantitative indicators of process, cost and inherent safety. The results show that the conventional technology of ethane cracking has an attractive process and economic potential while the emerging gas to ethylene technology is inherently safer. The areas of improvement are identified and a critical analysis of metrics is carried out.This paper was made possible by NPRP grant No 6-667-2-280 from the Qatar National Research Fund (a member of Qatar Foundation). The statements made herein are solely the responsibility of the authors.Scopu

Designing ionic liquid solvents for carbon capture using property-based visual approach

Recently, ionic liquids (ILs) have been introduced as potential carbon dioxide (CO2)-capturing solvents, as a substitute to conventional amine-based solvents. Conventional amine-based solvents that are used for CO2 capture show some drawbacks, such as high solvent loss, high regeneration energy requirement, and solvent degradation. These shortcomings can be potentially overcome if IL-based solvents are considered. ILs have negligible vapour pressure, high thermal stability, and wide range of thermophysical properties. Nonetheless, using experimentation to identify suitable ILs as CO2-capturing solvents is a tedious and costly task, as there are more than a million possible combinations of cations and anions that make up the ILs. Computer-aided tools have been previously developed for targeted IL design, which often involve non-linear programming. However, non-linear programming sometimes fails to converge, due to enlarged search space for optimal solution and its complex formulations. In this paper, the authors present a simple yet systematic visual approach to design IL solvents for carbon capture. Property integration framework is employed in this approach to systematically design IL, where the design problem can be mapped from the property domain into a cluster domain through clustering technique. The advantage of the visual approach is the ability to enumerate novel IL candidates. Group contribution (GC) method is included in the framework to estimate the properties of designed ILs. By combining property integration framework and GC method, the proposed approach is able to provide a property-based platform to visualise the performance of designed ILs on a ternary diagram. A case study is presented to illustrate the validity of the proposed approach.This work was supported by the Ministry of Science, Technology and Innovation (MOSTI) Malaysia under the Grant No. 06-02-12-SF0224. The financial support from the University of Nottingham Research Committee via Dean's PhD Scholarship is gratefully appreciated.Scopu

Design of Ionic Liquid as Carbon Capture Solvent for a Bioenergy System:Integration of Bioenergy and Carbon Capture Systems

Current atmospheric carbon dioxide (CO2) concentration has exceeded the safe limit of 350 ppm. One potential technology to remove CO2 from the atmosphere is the integrated bioenergy production and carbon capture system. A bioenergy production system produces multiple energy products from biomass, resulting in zero net increment of CO2 amount in the atmosphere. Meanwhile, CO2 produced from bioenergy production is separated for other purposes through carbon capture. To ensure the entire system is environmental friendly, an efficient and green carbon capture solvent should be utilized. Ionic liquids (ILs) are the potential solvents for this purpose, as they have negligible vapor pressure and high thermal stability. However, there are up to a million possible combinations of cations and anions that may make up ILs. This work presents a systematic approach to identify an optimal IL solvent to separate CO2 produced from a bioenergy system at the optimal conditions of carbon capture process. Following that, the bioenergy system is retrofitted to provide sufficient utilities to a carbon capture system to make sure that the entire process is self-sustainable. A case study involving an existing palm-based bioenergy system, integrated with carbon capture to produce CO2, is used to demonstrate the presented approach.Scopu