Eric Croiset

Performance comparison of Fick’s, dusty-gas and Stefan–Maxwell models to predict the concentration overpotential of a SOFC anode

Models for mass transport inside a porous SOFC anode were developed based on Fick’s model (FM), the dusty-gas model (DGM) and the Stefan–Maxwell model (SMM) to predict the concentration overpotential. All models were validated with experimental data for H2–H2O–Ar and CO–CO2 systems. The effect of pore size on all model predictions was discussed. It was concluded that the dusty-gas model is the most appropriate model to simulate gas transport phenomena inside a SOFC anode. However, this model requires numerical solution, whereas Fick’s and Stefan–Maxwell’s do not. It was found that the SMM, rather than the FM, is a good approximation of the dusty-gas model for H2–H2O system, except in the case of high current density, low H2 concentration and low porosity, where only the DGM is recommended. For the CO–CO2 system, there is no simple rule for selecting an alternate model to DGM. Depending on the CO concentration, porosity and current density, the FM or the SMM could be used. The only restriction is for small porosities where only the DGM should be used. This paper also demonstrated that only the DGM is recommended for a multicomponent system (H2–H2O–CO–CO2).

A multi-period optimization model for energy planning with CO2 emission consideration

A novel deterministic multi-period mixed-integer linear programming (MILP) model for the power generation planning of electric systems is described and evaluated in this paper. The model is developed with the objective of determining the optimal mix of energy supply sources and pollutant mitigation options that meet a specified electricity demand and CO(2) emission targets at minimum cost. Several time-dependent parameters are included in the model formulation; they include forecasted energy demand, fuel price variability, construction lead time, conservation initiatives, and increase in fixed operational and maintenance costs over time. The developed model is applied to two case studies. The objective of the case studies is to examine the economical, structural, and environmental effects that would result if the electricity sector was required to reduce its CO(2) emissions to a specified limit.

Techno-Economic Study of CO 2 Capture from Natural Gas Based Hydrogen Plants

Abstract Canadian oil sands are considered to be the second largest oil reserves in the world. However, the upgrading of bitumen from oil sands to synthetic crude oil (SCO) requires nearly ten times more hydrogen (H2) than conventional crude oils. The current H2 demand for oil sands operations is met mostly by steam reforming of natural gas (SMR). The future expansion of oil sands operations is likely to quadruple the demand of H2 for oil sand operations in the next decade. This paper presents modified process schemes that capture CO2 at minimum energy penalty in modern SMR plants. The approach is to simulate a base case H2 plant without CO2 capture and then look for the best operating conditions that minimize the energy penalty associated with CO2 capture while maximizing H2 production. The two CO2 capture schemes evaluated in this study include a membrane separation process and the monoethanolamine (MEA) absorption process. A low energy penalty is observed when there is lower CO2 production and higher steam production. The process simulation results show that the H2 plant with CO2 capture has to be operated at lower steam to carbon ratio (S/C), higher inlet temperature of the SMR and lower inlet temperatures for the water gas-shift (WGS) converters to attain lowest energy penalty. Also it is observed that both CO2 capture processes, the membrane process and the MEA absorption process, are comparable in terms of energy penalty and CO2 avoided when both are operated at conditions where lowest energy penalty exists.

Techno-Economic Study of CO2 Capture from an Existing Cement Plant Using MEA Scrubbing

Carbon dioxide is the major greenhouse gas responsible for global warming. Man-made CO2 emissions contribute approximately 63% of greenhouse gases and the cement industry is responsible for approximately 5% of CO2 emissions emitting nearly 900 kg of CO2 per 1000 kg of cement. CO2 from a cement plant was captured and purified to 98% using the monoethanolamine (MEA) based absorption process. The capture cost was

Simulation of Electrochemical Impedance Spectra of Solid Oxide Fuel Cells Using Transient Physical Models

51 per tonne of CO2 captured, representing approximately 90% of total cost. Steam was the main operating cost representing 39% of the total capture cost. Switching from coal to natural gas reduces CO2 emissions by about 18%. At normal load, about 36 MW of waste heat is available for recovery to satisfy the parasitic heat requirements of MEA process; however, it is very difficult to recover.

Design of a sorbent to enhance reactive adsorption of hydrogen sulfide.

A general electrochemical impedance spectroscopy (EIS) modeling approach by directly solving a one-dimensional transient model based on physical conservation laws was applied for simulating EIS spectra of an anode-supported solid oxide fuel cell (SOFC) button cell consisting of Ni-yttria-stabilized zirconia |Ni-scandia-stabilized zirconia (ScSZ)|ScSZ|lanthanum strontium manganate (LSM)-ScSZ multiple layers. The transient SOFC model has been solved for imposed sinusoidal voltage perturbations at different frequencies. The results have then been transformed into EIS spectra. Six parameters had to be tuned (three for the cathode and three for the anode) and have been estimated using data from a symmetric cathode cell and from a button cell. The experimental and simulated EIS spectra were in good agreement for a range of temperatures (750-850°C), of feed compositions (mixture of H 2 /H 2 O/N 2 ), and of oxidants (air and oxygen). This approach can help in interpreting EIS spectra, as illustrated by identifying the contribution of transport limitation.

A mixed-integer non-linear programming model for CO2 emission reduction in the power generation sector

A series of novel zinc oxide-silica composites with three-dimensionally ordered macropores (3DOM) structure were synthesized via colloidal crystal template method and used as sorbents for hydrogen sulfide (H2S) removal at room temperature for the first time. The performances of the prepared sorbents were evaluated by dynamic breakthrough testing. The materials were characterized before and after adsorption using scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). It was found that the composite with 3DOM structure exhibited remarkable desulfurization performance at room temperature and the enhancement of reactive adsorption of hydrogen sulfide was attributed to the unique structure features of 3DOM composites; high surface areas, nanocrystalline ZnO and the well-ordered interconnected macroporous with abundant mesopores. The introduction of silica could be conducive to support the 3DOM structure and the high dispersion of zinc oxide. Moisture in the H2S stream plays a crucial role in the removal process. The effects of Zn/Si ratio and the calcination temperature of 3DOM composites on H2S removal were studied. It demonstrated that the highest content of ZnO could reach up to 73 wt % and the optimum calcination temperature was 500 °C. The multiple adsorption/regeneration cycles showed that the 3DOM ZnO-SiO2 sorbent is stable and the sulfur capacity can still reach 67.4% of that of the fresh sorbent at the fifth cycle. These results indicate that 3DOM ZnO-SiO2 composites will be a promising sorbent for H2S removal at room temperature.

Simulation of a coal hydrogasification process with integrated CO2 capture

Electricity generation is considered to be one of the main contributing sources to the air pollution problem. It is, therefore, important to develop and implement effective control strategies to prevent the expected abrupt increase in emissions from this sector. Any control strategy must be suitable for local implementation and must also be economically viable. The main objective of this paper is to present optimisation models that can be used to determine the most cost effective strategy or combination of strategies to reduce CO2 emissions to a specific level. Optimisation results for an existing network of power plants show that it may be possible to reduce CO2 emissions by increasing power plant efficiency through a variety of adjustments in the plants. These include fuel balancing, fuel switching, and the implementation of improvement technologies to existing power plants to increase their thermal

Economics of CO2 Capture from a Coal-Fired Power Plant — a Sensitivity Analysis

Publisher Summary This chapter discusses a study in which the simulation of a novel hydrogasification process for power generation was performed. This process has been proposed by the Zero Emission Coal Alliance, known as the “ZECA” process. To investigate the process, simulations of the process were performed using the Aspen Plus software package. The steady state process model was developed based on equilibrium and stoichiometric reactors. The model includes heat integration as well as material recycle. A base set of conditions was tested based on the literature description and a sensitivity analysis of some operating parameters was performed. It was concluded that the base case process shows lower efficiencies than those reported in the literature. The main difference was found to be the power generation in the solid oxide fuel cell (SOFC). The current model is believed to be a more realistic representation of the SOFC and, therefore, the overall process.

A Decentralized Control Structure for a CO2 Compression, Capture and Purification process: An Uncertain Relative Gain Array Approach

Publisher Summary This chapter focuses on the economics of the capture of CO 2 from an existing pulverized coal-fired power plant. Coal-fired power plants are regarded as major emitters of pollutants, in particular of carbon dioxide. However, coal is still a very attractive fuel because of cheap, large, and widely distributed reserves. Increasing the efficiency of the coal plant will contribute to the reduction in the emissions of CO 2 . But it is unlikely that increased efficiency alone is sufficient to significantly reduce CO 2 emissions. A method to dramatically reduce the emissions of CO 2 in the short to medium term is the capture and sequestration of CO 2 . This chapter presents a sensitivity analysis on the cost of CO 2 captured. In particular, the chapter looks at the effect of improvement in solvent performance and oxygen separation cost (O 2 /CO 2 recycle case) on the overall cost of capturing CO 2 . The sensitivity analysis provides the economic benefits from possible cost reductions in the two CO 2 capture technologies. Preliminary results indicate that the O 2 /CO 2 recycle combustion process offers greater potential savings over the use of amine scrubbing.