Combination of Sorption-Enhanced Steam Methane Reforming and Electricity Generation by MCFC: Concept and Numerical Simulation Analysis

Abstract

Reformed gas made by the steam methane reforming(SMR) process is used as fuel feed to MCFC, but it is not as good as pure hydrogen due to the presence of CO₂ and CO. The sorption-enhanced steam methane reforming(SE-SMR) process can reduce CO₂ and CO to a low level and produce high purity hydrogen. Considering the merits of similar operating temperatures (about 500°C) and carbon dioxide recycle, a novel concept of a six-step sorption-enhanced steam methane reforming (SE-SMR) combined with electricity generation by molten carbonate fuel cell (MCFC) is proposed. In the present paper, a cycle of the SE-SMR process, which include the steps of reaction/adsorption, depressurization, gas purges (nitrogen and reformed gas, respectively), and pressurization with reformed gas, is modeled and analyzed. The process stream in the SE-SMR process is used as anode feed in MCFC. According to the result of numerical simulation, a fuel cell grade hydrogen product (above 80% purity) at the SE-SMR temperature of 450°C can be obtained. A carbon dioxide recycle mechanism is developed for cathode feed of MCFC from flue gas by burning with excess air to achieve a proper CO₂/air ratio (about 30:70). The novel electricity generation system, which can operate at lower energy consumption and high purity hydrogen feed is helpful for the MCFC'S performance and life time.     

Dynamic modeling of CO2 absorption from coal-fired power plants into an aqueous monoethanolamine solution

Among carbon capture and storage (CCS), the post-combustion capture of carbon dioxide (CO₂) by means of chemical absorption is actually the most developed process. Steady state process simulation turned out as a powerful tool for the design of such CO₂ scrubbers. Besides steady state modeling, transient process simulations deliver valuable information on the dynamic behavior of the system. Dynamic interactions of the power plant with the CO₂ separation plant can be described by such models. Within this work a dynamic process simulation model of the absorption unit of a CO₂ separation plant was developed. For describing the chemical absorption of CO₂ into an aqueous monoethanolamine solution a rate based approach was used. All models were developed within the Aspen Custom Modeler^® simulation environment. Thermo physical properties as well as transport properties were taken from the electrolyte non-random-two-liquid model provided by the Aspen Properties^® database. Within this work two simulation cases are presented. In a first simulation the inlet temperature of the flue gas and the lean solvent into the absorber column was changed. The results were validated by using experimental data from the CO₂SEPPL test rig located at the Dürnrohr power station. In a second simulation the flue gas flow to the separation plant was increased. Due to the unavailability of experimental data a validation of the results from the second simulation could not be achieved.     

Concentration of carbon dioxide by a high-temperature electrochemical membrane cell

The electrochemical carbon dioxide concentrator has emerged over the last few years as the best technique for carbon dioxide control in a manned spacecraft. Preliminary investigations have shown that the Molten Carbonate Fuel Cell (MCFC) can be successfully converted into a molten carbonate CO₂ concentrator (MCCDC) for CO₂ removal from a space-cabin [1]. The present investigation involved studying the MCCDC cell performance without use of a fuel for anode depolarization. Cathode CO₂ removal efficiencies of 97% were achieved with 0.25% CO₂ inlet concentration. Anode CO₂ concentrations were as high as 3.4% for 0.25% CO₂ and 5.8% for 1% CO₂ inlet concentration. Anode polarizations were approximately four times higher than cathode polarizations, which are considerably higher than in the MCFC. Anode exchange current densities were much smaller than cathode exchange current densities, suggesting poor anode-electrolyte contact. The total mathematical model consists of simple cathode and anode representations, combining activation and gas-phase diffusion. This treatment is capable of accurately correlating cell performance as a function of the process variables, such as flowrate, temperature, and CO₂ inlet concentration.     

Gas Analysis by In Situ Combustion in Heavy‐Oil Recovery Process: Experimental and Modeling Studies

Enormous efforts have been made to facilitate produced‐gas analyses by in situ combustion implication in heavy‐oil recovery processes. Robust intelligence‐based approaches such as artificial neural network (ANN) and hybrid methods were accomplished to monitor CO₂/O₂/CO. Implemented optimization approaches like particle swarm optimization (PSO) and hybrid approach focused on pinpointing accurate interconnection weights through the proposed ANN model. Solutions acquired from the developed approaches were compared with the pertinent experimental in situ combustion data samples. Implication of hybrid genetic algorithm and PSO in gas analysis estimation can lead to more reliable in situ combustion quality predictions, simulation design, and further plans of heavy‐oil recovery methods.     

Hybrid FSC membrane for CO2 removal from natural gas: Experimental,process simulation,and economic feasibility analysis

The novel fixed‐site‐carrier (FSC) membranes were prepared by coating carbon nanotubes reinforced polyvinylamine/polyvinyl alcohol selective layer on top of ultrafiltration polysulfone support. Small pilot‐scale modules with membrane area of 110–330 cm² were tested with high pressure permeation rig. The prepared hybrid FSC membranes show high CO₂ permeance of 0.084–0.218 m³ (STP)/(m² h bar) with CO₂/CH₄ selectivity of 17.9–34.7 at different feed pressures up to 40 bar for a 10% CO₂ feed gas. Operating parameters of feed pressure, flow rate, and CO₂ concentration were found to significantly influence membrane performance. HYSYS simulation integrated with ChemBrane and cost estimation was conducted to evaluate techno‐economic feasibility of a membrane process for natural gas (NG) sweetening. Simulation results indicated that the developed FSC membranes could be a promising candidate for CO₂ removal from low CO₂ concentration (10%) NGs with a low NG sweetening cost of 5.73E?3 $/Nm³ sweet NG produced. © 2014 American Institute of Chemical Engineers AIChE J 60: 4174–4184, 2014     

A New Numerical Approach for a Detailed Multicomponent Gas Separation Membrane Model and AspenPlus Simulation

A new numerical solution approach for a widely accepted model developed earlier by Pan [1] for multicomponent gas separation by high‐flux asymmetric membranes is presented. The advantage of the new technique is that it can easily be incorporated into commercial process simulators such as AspenPlus^TM [2] as a user‐model for an overall membrane process study and for the design and simulation of hybrid processes (i.e., membrane plus chemical absorption or membrane plus physical absorption). The proposed technique does not require initial estimates of the pressure, flow and concentration profiles inside the fiber as does in Pan's original approach, thus allowing faster execution of the model equations. The numerical solution was formulated as an initial value problem (IVP). Either Adams‐Moulton's or Gear's backward differentiation formulas (BDF) method was used for solving the non‐linear differential equations, and a modified Powell hybrid algorithm with a finite‐difference approximation of the Jacobian was used to solve the non‐linear algebraic equations. The model predictions were validated with experimental data reported in the literature for different types of membrane gas separation systems with or without purge streams. The robustness of the new numerical technique was also tested by simulating the stiff type of problems such as air dehydration. This demonstrates the potential of the new solution technique to handle different membrane systems conveniently. As an illustration, a multi‐stage membrane plant with recycle and purge streams has been designed and simulated for CO₂ capture from a 500 MW power plant flue gas as a first step to build hybrid processes and also to make an economic comparison among different existing separation technologies available for CO₂ separation from flue gas.     

Using short‐term resource scheduling for assessing effectiveness of CCS within electricity generation subsector

A new methodology for assessing the effectiveness of carbon capture and storage (CCS) that does explicitly consider the detailed operation of the target electricity system is proposed. The electricity system simulation consists of three phases, each one using a modified version of an economic dispatch problem that seeks to maximize the producers’ and consumers’ surplus while satisfying the technical constraints of the system. The economic dispatch is formulated as a dynamic mixed‐integer nonlinear programming problem and implemented in general algebraic modelling system (GAMS). The generating unit with CCS is designed and simulated using Aspen Plus®. In the first case study, the operation of the IEEE RTS ’96 (Institute of Electrical and Electronics Engineers One‐Area Reliability Test System—1996) is simulated with greenhouse gas (GHG) regulation implemented in the form of CO₂ permits that generators need to acquire for every unit of CO₂ that it is emitted. In the second case study, CCS is added at one of the buses and the operation of the modified IEEE RTS ’96 is again simulated with and without GHG regulation. The results suggest that the detailed operation of the target electricity system should be considered in future assessments of CCS and a general procedure for undertaking this for any GHG mitigation option is proposed. Future work will use the novel methodology for assessing the effectiveness of generating units with flexible CO₂ capture. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4210–4234, 2015     

Komplementäre Dekarbonisierung der Erzeugung von Elektroenergie und Gewinnung synthetischer Kraftstoffe durch Erneuerbare Energien und fossile Energieträger

The concept of complementary decarbonisation of power generation from renewable energy sources and fossil fuels consists of their integration in one system. A technology network in the form of a CCU‐combined power plant is proposed for the energy generation from fossil fuels by a coal power plant with CO₂ recovery from the exhaust gases and a pyrolysis of natural gas to hydrogen and carbon as a basic technology. This technology network is completed by a reverse water‐gas shift reaction for the conversion of the CO₂ to CO, which will react with the hydrogen in a Fischer‐Tropsch synthesis for synthetic diesel. The recovered energy from the exothermic Fischer‐Tropsch synthesis meets the energy needs of CO₂ scrubbing. The carbon from the pyrolysis can replace other fossil carbon or can be sequestered.     

Modelling of an IGCC plant with carbon capture for 2020

Currently several industrial scale IGCC - carbon capture demonstration plants are being planned. Thermodynamic simulations are a useful tool to investigate the optimal plant configuration. In order to demonstrate the potential of the next generation of IGCC with CCS a thermodynamic model was developed using conventional but improved technology. The plant concept was verified and simulated for a generic hard coal and lignite. The simulation showed a net efficiency (LHV) of 38.5% and 41.9% for hard coal and lignite, respectively.The results are consistent with current studies but also indicate that major simulations were too optimistic. The auxiliary demand of an IGCC plant with carbon capture can be expected with 21 to 24% based on gross output. The drop in efficiency compared to the none-capture case is estimated with roughly 11 to 12%-points. During a sensitivity study the impact of process changes on plant efficiency and economics is evaluated. Releasing the captured CO₂ without compression is found to be economically favourable at CO₂ prices below 15 €/t and electricity prices above 100 €/MWh. Further the impact of carbon capture rate is quantified and an efficiency potential is indicated for lower CO₂ quality.     

Application of high‐pressure swing adsorption process for improvement of CO2 recovery system from flue gas

Although the super cold separator applied to the system for CO₂ recovery from flue gas can produce pure CO₂ liquid, the CO₂ recovery efficiency is low. Therefore, the addition of a PSA plant was considered for the secondary CO₂ recovery from the noncon‐densing gas to improve the efficiency. The PSA plant was operated for adsorption at the same pressure as that of the super cold separator and for desorption at the atmospheric pressure. From both the simulation and the experimental data, it was confirmed that CO₂ could be concentrated from 50% in the noncondensing gas to 70% in the recovery gas by the PSA plant and the CO₂ recovery efficiency of the plant was about 90%.     

Optimization of energy usage for fleet‐wide power generating system under carbon mitigation options

This article presents a fleet‐wide model for energy planning that can be used to determine the optimal structure necessary to meet a given CO₂ reduction target while maintaining or enhancing power to the grid. The model incorporates power generation as well as CO₂ emissions from a fleet of generating stations (hydroelectric, fossil fuel, nuclear, and wind). The model is formulated as a mixed integer program and is used to optimize an existing fleet as well as recommend new additional generating stations, carbon capture and storage, and retrofit actions to meet a CO₂ reduction target and electricity demand at a minimum overall cost. The model was applied to the energy supply system operated by Ontario power generation (OPG) for the province of Ontario, Canada. In 2002, OPG operated 79 electricity generating stations; 5 are fueled with coal (with a total of 23 boilers), 1 by natural gas (4 boilers), 3 nuclear, 69 hydroelectric and 1 wind turbine generating a total of 115.8 TWh. No CO₂ capture process existed at any OPG power plant; about 36.7 million tonnes of CO₂ was emitted in 2002, mainly from fossil fuel power plants. Four electricity demand scenarios were considered over a span of 10 years and for each case the size of new power generation capacity with and without capture was obtained. Six supplemental electricity generating technologies have been allowed for: subcritical pulverized coal‐fired (PC), PC with carbon capture (PC+CCS), integrated gasification combined cycle (IGCC), IGCC with carbon capture (IGCC+CCS), natural gas combined cycle (NGCC), and NGCC with carbon capture (NGCC+CCS). The optimization results showed that fuel balancing alone can contribute to the reduction of CO₂ emissions by only 3% and a slight, 1.6%, reduction in the cost of electricity compared to a calculated base case. It was found that a 20% CO₂ reduction at current electricity demand could be achieved by implementing fuel balancing and switching 8 out of 23 coal‐fired boilers to natural gas. However, as demand increases, more coal‐fired boilers needed to be switched to natural gas as well as the building of new NGCC and NGCC+CCS for replacing the aging coal‐fired power plants. To achieve a 40% CO₂ reduction at 1.0% demand growth rate, four new plants (2 NGCC, 2 NGCC+CCS) as well as carbon capture processes needed to be built. If greater than 60% CO₂ reductions are required, NGCC, NGCC+CCS, and IGCC+CCS power plants needed to be put online in addition to carbon capture processes on coal‐fired power plants. The volatility of natural gas prices was found to have a significant impact on the optimal CO₂ mitigation strategy and on the cost of electricity generation. Increasing the natural gas prices resulted in early aggressive CO₂ mitigation strategies especially at higher growth rate demands. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Synthesis and gas transport properties of novel hyperbranched polyimide–silica hybrid membranes

Physical and gas transport properties of hyperbranched polyimide (HBPI)—silica hybrid membranes prepared with a dianhydride monomer, 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride (6FDA), and triamine monomers, 1,3,5‐tris(4‐aminophenoxy)triazine (TAPOTZ), and 1,3,5‐tris(4‐aminophenyl)benzene (TAPB), were investigated and compared with those of 6FDA‐TAPOB HBPI system synthesized from 6FDA and 1,3,5‐tris(4‐aminophenoxy)benzene (TAPOB). Glass transition and 5% weight‐loss temperatures of the 6FDA‐based HBPI–silica hybrid membranes were increased with increasing silica content. 6FDA‐TAPOTZ HBPI system, however, showed relatively low 5% weight‐loss temperatures, suggesting thermal instability of triazine‐ring in the TAPOTZ moiety. CO₂/CH₄ permselectivity of the HBPI–silica hybrid membranes were increased with increasing silica content, tending to exceed the upper bound for CO₂/CH₄ separation. This result indicated that free volume elements effective for CO₂/CH₄ separation were created by the incorporation of silica for the HBPI–silica hybrid systems. Especially, 6FDA‐TAPB HBPI system had high gas permeabilities and CO₂/CH₄ separation ability, arising from high fractional free volume and characteristic size and distribution of free volume elements. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

(CO2 + 2‐propanol) mixture as a foaming agent for polystyrene: A simple thermodynamic model for the high pressure VLE‐phase diagrams taking into account the foam vitrification

The equation of state model developed by Lacombe and Sanchez (J Phys Chem 1976, 80, 2352) is used in the form proposed later by Sanchez and Stone (Polymer Blends, Vol. 1: Formulation, 2000; Chapter 2) to correlate experimental vapor‐liquid equilibrium (VLE) data for the three binaries and the ternary systems. Experimental data from the binary systems carbon dioxide‐isopropyl alcohol (CO₂‐IPrOH), isopropyl alcohol‐polystyrene (IPrOH‐PS), and carbon dioxide‐polystyrene (CO₂‐PS) are used to calculate VLE properties for the ternary system CO₂‐IPrOH‐PS. Two‐dimensional VLE‐phase diagrams were calculated and used to describe from a thermodynamic point of view the pressure, volume, and temperature values that characterize a thermoplastic foam evolution process, from the extruder to the foaming die. For different initial mixture CO₂ + IPrOH concentrations, pressure reduction produces liquid foaming until the vitrification curve arrests the final foam volume expansion. The dependence of the vitreous transition with the system CO₂ + IPrOH concentration while foaming is represented by the Chow (Macromolecules 1980, 13, 362) equation. The calculation procedure is proposed as a design tool to reduce the amount of experimental data usually needed as a requirement previous to the design stage. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2663–2671, 2007     

Experimental Validation of a Multidimensional Model for an Indirect Temperature Swing Adsorption Unit

Conventional temperature swing adsorption (TSA) is mainly applied for the removal of trace contaminants. Indirectly heated and cooled adsorbers were developed to make bulk separation economically feasible. A quasi-continuous TSA process to remove CO₂ from an N₂/CO₂ mixture with a pilot plant is established. The experimentally determined data are taken to validate and to adjust a 2D simulation model. For the validation, the CO₂ desorption, the N₂ recovery rate as well as the axial temperature profile are compared. The successful model validation can be seen in the good agreement between simulation and experimental results. Moreover, this process is able to separate high amounts of CO₂ and to produce a nearly CO₂-free product stream.     

Dynamic analysis of the absorption/desorption loop of a carbon capture plant using an object-oriented approach

Post-combustion capture of CO₂ is regarded as a possible technology in order to reduce CO₂ emission to the atmosphere. This paper provides a dynamic analysis of the absorption/desorption loop of a carbon capture plant with the help of a simulation model, built using the object-oriented Modelica Library Thermal Separation. The solvent used is an amino-acid salt.The dynamic behaviour is investigated for a reduction in regeneration heat flow rate but constant flue gas flow rate. Hereby four different control strategies are compared, one keeping the lean solvent loading constant, one keeping the solvent flow rate constant, one where flue gas bypasses the capture plant and a last one where an additional solvent tank is introduced. The simulation shows i.e. that for a constant lean solvent loading the response of the absorbed CO₂ flow rate is much faster than for a constant solvent flow rate.Also the effect on the dynamic behaviour is investigated, comparing the whole cycle model to a stand-alone desorber model and to a stand-alone absorber model respectively. It was found that the dynamic responses on a short time scale are very similiar, but different on a long time scale.     

Thermodynamic Simulation of CO2 Capture for an IGCC Power Plant using the Calcium Looping Cycle

A CO₂ capture process for an integrated gasification combined cycle (IGCC) power plant using the calcium looping cycle was proposed. The CO₂ capture process using natural and modified limestone was simulated and investigated with the software package Aspen Plus. It incorporated a fresh feed of sorbent to compensate for the decay in CO₂ capture activity during long‐term cycles. The sorbent flow ratios have significant effect on the CO₂ capture efficiency and net efficiency of the CO₂ capture system. The IGCC power plant, using the modified limestone, exhibits higher CO₂ capture efficiency than that using the natural limetone at the same sorbent flow ratios. The system net efficiency using the natural and modified limestones achieves 41.7 % and 43.1 %, respectively, at the CO₂ capture efficiency of 90 % without the effect of sulfation.     

High‐efficiency power production from coal with carbon capture

A zero‐emissions power plant with high efficiency is presented. Syngas, produced by the gasification of coal, is shifted to produce H₂ which in turn fuels stacks of solid oxide fuel cells. Because the fuel cells maintain separate anode and cathode streams, air can be used as the oxygen source without diluting the fuel exhaust with nitrogen. This enables recovery of CO₂ from the exhaust with a very small energy penalty. As a result, an absorption‐based CO₂ recovery process is avoided, as well as the production of large quantities of high‐purity O₂, allowing a high overall thermal efficiency and essentially eliminating the energy penalty for carbon capture. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

Activated Carbon from Renewable Material as an Efficient Support for Palladium Oxidation Catalysts

Activated carbon prepared from cocoa pod husk, which is an abundant agricultural waste, was employed as a green support for palladium oxidation catalysts. Systematic characterization of the support and palladium catalysts by atomic emission spectroscopy, N₂ and CO₂ physisorption measurements, X‐ray powder diffraction, infrared spectroscopy, electron microscopy, temperature‐programmed reduction by hydrogen, and temperature‐programmed desorption of NH₃ and CO₂ allowed detailed monitoring of their characteristics. Subsequently, the catalytic performance and selectivity in the oxidation of ethanol as a model volatile organic compound (VOC) was studied and linked to physicochemical properties of the catalysts.     

Life cycle assessment of ISPRA Mark 9 thermochemical cycle for nuclear hydrogen production

The nuclear energy driven thermochemical cycle is one of the potential water‐splitting processes for producing hydrogen, presumed to be the transportation fuel of the future. A life cycle assessment (LCA) of one such system, which utilizes nuclear energy to drive the ISPRA Mark 9 thermochemical cycle, is presented in this paper. The results of the LCA are presented in terms of the emissions of greenhouse gases (CO₂‐equivalent) and acid gases (SO₂‐equivalent). The contributions of the thermochemical plant to the emissions were determined through the estimation of material and energy requirements for chemical inventory, raw materials consumption and plant fabrication/installation. The greenhouse gas emissions from the system are 2515 g CO₂‐equivalent kg^?1 H₂ produced and acid gas emissions 11.252 g SO₂‐equivalent kg^?1 H₂ produced. A comparison of this hydrogen production route with other routes, including steam reforming of methane and high‐temperature electrolysis, is also presented in the paper. Copyright © 2006 Society of Chemical Industry     

Study of cerium species in molten Li2CO3–Na2CO3 in the conditions used in molten carbonate fuel cells. Part II: Potentiometric and voltammetric behaviour

The electrochemical behaviour of metallic cerium and cerium dioxide is analysed in molten Li₂CO₃–Na₂CO₃ under the anodic and cathodic conditions used for the molten carbonate fuel cells (MCFC). Chronopotentiometric measurements on metallic cerium rods or foils show the influence of CeO₂ growth and the deviation from its stoichiometric composition. A study of the voltammetric characteristics of dissolved cerium at a gold electrode, of metallic cerium and cerium oxide is carried out in both oxidising and reducing MCFC atmospheres. Experimental evidence is given for the existence of a solid–solid cerium system: Ce₂O₃(s)|CeO₂(s) and a system relative to dissolved cerium species Ce₂O₃(l)|CeO₂(l). These systems are in agreement with thermodynamic predictions. Other more complex phenomena involving interactions with alkali species are discussed.