Amit Chakma

Inorganic membrane reactors

Abstract The availability of inorganic membranes which can withstand high temperatures has resulted in a wide ranging opportunity for the application of membranes in chemical reactors. Increased conversions, better selectivity, milder operating conditions and decreased separation load are some of the attractive features which are going to promote membranes as chemical reactors in many established and novel reaction systems. Established and emerging technologies in ceramics, semiconductors and metal plating such as slip casting, electroless plating, sputtering, and chemical and electrochemical vapor deposition techniques are being successfully adapted in the laboratory scale to produce membranes with high permeabilities and improved separation factors. It should soon be possible to categorize membrane technologies for different types of reactions. Further advancements in modifying the surface of the membranes to tailor them to specific catalytic and separation requirements will greatly enhance the versatility of the membranes as chemical reactors and separators in the future. This article reviews various applications of membrane reactors with particular emphasis on their application in high-temperature gas-phase reactions.

Production of hydrogen and sulfur from hydrogen sulfide

Abstract Hydrogen sulfide is a fairly abundant resource whose potential is not being fully utilized by the industry. It is in fact a mineral from which two valuable products, hydrogen and sulfur, can be extracted. No such extraction is done today. Sulfur, however, is recovered by partial oxidation by Claus process and low-quality steam is produced utilizing the heat of reaction. Efforts to produce both hydrogen and sulfur from hydrogen sulfide has been made in recent years through a diverse variety of technologies. These involve thermal, thermochemical, electrochemical, photochemical and plasmochemical methods. An attempt has been made in this paper to bring to focus the possibilities and limitations in each of these areas and find out the areas of prospective research and development. A method that has the potential to develop into a full-scale technology has been suggested.

AN INTERVAL-PARAMETER FUZZY NONLINEAR OPTIMIZATION MODEL FOR STREAM WATER QUALITY MANAGEMENT UNDER UNCERTAINTY

Planning for water quality management systems is complicated by a variety of uncertainties and nonlinearities, where difficulties in formulating and solving the resulting inexact nonlinear optimization problems exist. With the purpose of tackling such difficulties, this paper presents the development of an interval-fuzzy nonlinear programming (IFNP) model for water quality management under uncertainty. Methods of interval and fuzzy programming were integrated within a general framework to address uncertainties in the left- and right-hand sides of the nonlinear constraints. Uncertainties in water quality, pollutant loading, and the system objective were reflected through the developed IFNP model. The method of piecewise linearization was developed for dealing with the nonlinearity of the objective function. A case study for water quality management planning in the Changsha section of the Xiangjiang River was then conducted for demonstrating applicability of the developed IFNP model. The results demonstrated that the accuracy of solutions through linearized method normally rises positively with the increase of linearization levels. It was also indicated that the proposed linearization method was effective in dealing with IFNP problems; uncertainties can be communicated into optimization process and generate reliable solutions for decision variables and objectives; the decision alternatives can be obtained by adjusting different combinations of the decision variables within their solution intervals. It also suggested that the linearized method should be used under detailed error analysis in tackling IFNP problems.

Mathematical modelling of mass-transfer and hydrodynamics in CO2 absorbers packed with structured packings

Abstract This paper presents a mechanistic model that can predict mass-transfer performance and provide an insight into dynamic behavior within structured packings used for CO 2 absorption. The model was built upon the kinetics and thermodynamics of the absorption system, as well as the liquid irrigation features and the geometry of packing elements. A computer program (Fortran 90) was written to simulate CO 2 absorption into aqueous solutions of sodium hydroxide (NaOH) and monoethanolamine (MEA) in a column packed with Gempak 4A, Mellapak 500Y and Mellapak 500X. The simulation gave essential information, including the concentration of CO 2 in gas-phase, concentration of reactive species in the liquid-phase, system temperature, mass-transfer coefficients ( k G and k L ), and effective interfacial area ( a e ) for mass-transfer at different axial positions along the absorption column. The simulation also provided liquid distribution plots representing the quality of liquid distribution or maldistribution across the cross-section of the column. Verification of the model was achieved by comparing simulation results with experimental data. Very good agreement was found for wide ranges of operating and design parameters, including liquid load and initial liquid distribution pattern.

CO2 capture processes — Opportunities for improved energy efficiencies

CO2 capture from flue gas streams and disposal into geological formations has been considered as a technically feasible but a costly option for the reduction of CO2 emission into the atmosphere. CO2 capture is the major cost component. Therefore, there is considerable incentive in finding energy efficient and thus less costly processes for the capture of CO2 as compared to the conventional monoethanolamine (MEA) based processes. In this paper, some strategies for reduced energy consumption in a chemical solvent based separation process are identified and their impacts on the overall process are discussed.

A MCDM-based expert system for climate-change impact assessment and adaptation planning - A case study for the Georgia Basin, Canada

An MCDM-based expert system was developed to tackle the interrelationships between the climate change and the adaptation policies in terms of water resources management in the Georgia Basin, Canada. User interfaces of the developed expert system, named MAEAC (MCDM-based expert system for adaptation analysis under changing climate), was developed based on system configuration, knowledge acquisition, survey analysis, and MCDM-based policy analysis. A number of processes that were vulnerable to climate change were examined and pre-screened through extensive literature review, expert consultation and statistical analysis. Adaptation policies to impacts of temperature increase, precipitation-pattern variation and sea-level rise were comprehensively explicated and incorporated within the developed system. The MAEAC could be used for both acquiring knowledge of climate-change impacts on water resources in the Georgia Basin and supporting formulation of the relevant adaptation policies. It can also be applied to other watersheds to facilitate assessment of climate-change impacts on socio-economic and environmental sectors, as well as formulation of relevant adaptation policies.

Effects of operating and design parameters on CO2 absorption in columns with structured packings

This paper highlights the importance of operating and design parameters to mass-transfer in CO2 absorption in columns with structured packings. The study compares the performance of four stainless steel packings, Gempak 4A, Mellapak 500Y, Mellapak 500X, and Optiflow. Mass-transfer efficiency of these packings was determined by carrying out absorption experiments in a pilot-scale absorption unit with aqueous solutions of sodium hydroxide (NaOH) and monoethanolamine (MEA) as test liquid. The overall mass-transfer coefficients (KGae) were calculated from experimentally determined gas-phase CO2 concentration profiles within the test columns. The results of this study indicate that mass-transfer coefficient of these structured packings tested varies significantly not only with operating parameters such as liquid load, liquid CO2 loading and liquid temperature but also with design parameters, i.e. the pattern of packing arrangement and initial liquid distribution.

Heavy-Oil Recovery from Thin Pay Zones by Electromagnetic Heating

There are many heavy oil reservoirs with thin pay zones (less than 10 m). Conventional thermal recovery methods such as steam injection are not cost-effective for these thin reservoirs, due to excessive heat loss through the overburden. In order to minimize heat losses, it is necessary to be able to carry out controlled heating of the pay zone. One such way to introduce heat to the reservoir in a controlled manner is electromagnetic heating. This article describes laboratory studies on electromagnetic heating of a scaled model of a heavy oil reservoir with a thin pay zone. The combination of electromagnetic heating and gas injection with horizontal wells was studied. Higher electromagnetic frequencies provide faster heating rates and can over come problems associated with discontinuity of the media through which electro magnetic waves must propagate in the reservoir. Heat loss can also be minimized with the use of higher frequencies. For less viscous oils (less than 1000 mPs.s), it is not necessary to hea...

Separation of CO2 and SO2 from flue gas streams by liquid membranes

Laboratory studies on the separation of CO2 and SO2 from gas mixtures by liquid membranes are reported. The membrane set-up consisted of an immobilized Polyethyleneglycol (PEG 400) membrane in series with another immobilized Diethanolamine (DEA)/PEG 400 membrane. SO2 was preferentially separated in the PEG 400 membrane while the DEA/PEG400 membrane separated CO2. Highest separation factors obtained for CO2 and SO2 were, 220 and 140, respectively.

A dynamic optimization approach for nonrenewable energy resources management under uncertainty

Abstract This paper introduces an integrated dynamic optimization approach for nonrenewable energy (NRE) resources management under uncertainty. A hybrid inexact chance-constrained mixed-integer linear programming (ICCMILP) method is proposed, with an objective of maximizing economic return under constraints of resources availability and environmental regulations. In its solution process, the ICCMILP is transformed into two deterministic submodels, which correspond to the upper and lower bounds for the desired objective function value. Interval solutions, which are feasible and stable in the given decision space, can then be obtained by solving the two submodels sequentially. Thus, decision alternatives can be generated by adjusting decision variable values within their solution intervals. The obtained solutions are useful for decision makers to optimally allocate limited NRE resources over time for acquiring maximized benefit. Meanwhile, regional air quality could be maintained to keep the communities from health damage. Results of a hypothetical case study indicate that reasonable solutions for dynamic planning of NRE resources allocation in a regional system have been obtained. A number of decision alternatives were generated based on the ICCMILP solutions as well as the projected applicable conditions.