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Among the carbon capture technologies, oxy-fuel combustion is more competitive in terms of efficiency and cost. However, pure oxygen is required for oxy-combustion, and the oxygen separation from the air by conventional methods is costly and energy-intensive. Ion transport membranes (ITMs) have shown considerable improvement in energy efficiency. The current ITMs suffer from low O2 permeation flux required for practical fuel conversion rates. The experimental and numerical methodologies are not much developed in studying the ITM integrated reactors. Therefore, using a porous medium can give much insight into the technology. Understanding the flow dynamics and combustion properties inside an oxygen transport membranes reactor (OTMR) is of utmost importance to developing efficient systems. Most studies have focused on analyzing face-to-face horizontal porous plate reactor designs. A horizontal reactor’s flame structure and buoyancy effect are substantially different from that of a vertical reactor. Hence, the current study aims to investigate oxy-methane combustion in a vertical face-to-face porous plate reactor to mimic the performance of an OTMR using computational fluid dynamics (CFD). Axial and transverse temperature profiles and species concentration profiles are analyzed concerning the feed inlet flow rates, inlet temperature, and oxidizer ratio in this work. The outlet and maximum temperatures vary from 1,587 K to 1,621 K and 1,751 K to 2,341 K upon increasing the oxidizer ratio from 0.20 to 0.35; correspondingly, it shows that the maximum temperature within the reactor is significantly affected by the oxidizer ratio. In the vertical OTMR, the maximum and outlet temperatures are lowered by 82 K and 53 K, respectively, compared to the horizontal one because of the uniform temperature distribution in the former case. This research will help to improve reactor design for OTMR applications. Further investigations on the flame structure and static flame stability are required for a better understanding and insight into the reactor design.

Using modified IEA-CFBC(International Energy Association-Circulating fluidized bed combustion) model, a 2 MWe oxy-fuel CFBC boiler is simulated and analyzed as a promising solution to reduce greenhouse gas emission from coal power plants. This study evaluated and compared the oxy-combustion characteristics of various coals. Also, the effects of CO2 concentration (71–79 vol%), bed temperature (850°C) and coal properties on combustion efficiencies, CO2 concentration, acid gas emissions were analyzed. Because of their higher N2 and S content, sub-bituminous and bituminous coals were found to have SOx and NOx concentrations higher than those of anthracite. These simulation results from Oxy-fuel CFBC simulation of various coals can be used as operating parameters for design and development of commercial Oxy-fuel CFBC boilers. [ABSTRACT FROM AUTHOR]

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To evaluate the energy efficiency of the energy conversion and transfer, and the dig energy-saving potential during coal-fired power generation, the energy-loss mechanism was determined through a comparative analysis of thermal and exergy equilibria. Energy loss is first identified as exergy destruction, which is then gradually collected and finally discharged in the form of waste heat through terminals such as a condenser. Furthermore, the exergy-destruction distribution represents the theoretical energy-saving potential, which occurs mainly in the boiler. Accordingly, an in-depth study was conducted on the technical approaches to reduce the combustion- and heat transfer-induced exergy-destruction and other exergy-destruction in the boiler. These technical approaches include elevating hot-air temperature, oxy combustion, reducing excess air coefficient, and increasing the main steam/reheated steam parameters. Results show that technical solutions of elevating the hot-air temperature, increasing the air oxygen content, elevating the main steam/reheated steam temperature, and increasing the main steam pressure can reduce the net coal-consumption rate of a coal-fired power unit by 6–9, 6–10, 11, and 5– 12 g/kW·h, respectively. These conclusions indicate the direction of the development of energy-saving technologies for coal-fired power generation.

Engineering efforts to handle contemporary energy supply challenges and mitigate pollutant emission lead towards more complicated systems. Power plants are supplementing with additional processing units, alternative production modes and higher level of automation. Wind and solar sources, biomass combustion, gasification, carbon capture and storage (CCS), and cogeneration have appeared as important players in the energy systems. The increasing complexity comprises a risk that the systems become less manageable and less stable than currently. Traditional steady-state engineering methods cannot fully address these challenges that are inherently dynamic in their nature. Dynamic process simulation appears as important tool to the systems design and optimisation tasks. A large variety of dynamic process modelling and simulation approaches has been presented recent years. This paper presents a brief review of methods and simulation packages that are generally applied for studying energy systems' transient behaviour. A CCS capable power plant is presented as an example of utilizing dynamic process simulation for virtual evaluation of a novel electricity production concept. The modelling was performed using two simulators Apros and Aspen Plus Dynamics, which were linked together for dynamic simulating the full chain of cryogenic oxygen distillation, oxy combustion, turbine islands and carbon dioxide purification and liquefaction operations. • Dynamic simulations for design and optimisation of contemporary energy systems have been reviewed. • A case study for evaluating oxy combustion CFB boiler cycle with carbon capturing is presented. • Co-simulation with two dynamic process simulation software: Apros and Aspen Plus Dynamics were shown. • Flexibility aspects of oxy combustion power plant are discussed. [ABSTRACT FROM AUTHOR]

Abstract The purpose of this study is to analyze the possibility of combining two innovative combustion technologies in large-scale pulverized coal fired plants: Moderate or Intense Low Oxygen Dilution (MILD) and oxy-combustion. The combination of both technologies, namely Oxy-MILD combustion, is expected to bring synergetic effects: NO x reduction, CO 2 capture possibility, fuel flexibility and uniformity of heat fluxes and species concentrations. In this work, the predictable advantages of adopting this technology, with respect to conventional boilers, are evaluated by means of CFD modeling, in terms of pollutant emissions and uniformity of heat fluxes. In a previous work, the developed CFD model was validated against available experimental data of MILD combustion in a pilot-scale furnace and it was demonstrated that the proposed model captures the combustion features with good accuracy. In order to identify the effective potential of Oxy-MILD combustion and its possible uses on an industrial scale, an application in the boiler is analyzed in the current work. Results show that the temperature and species concentration distributions reach an acceptable level of uniformity in the boiler; similarly, the wall heat flux profile is uniform along the boiler height, as in the fluidized bed technology. The CO 2 concentration at the boiler exit, for an excess oxygen ratio of 1.1, is about 95.8%; this value is slightly increased for lower excess oxygen ratio, even though in this case, incomplete combustion occurs. Finally, lower NO x (70 mg/MJ) than other technological solutions are obtained owing to the prevention of thermal and prompt NO x , owing to the absence of N 2 in the oxidizer, and to the re-burning mechanism, which is predominant especially when recycled NO x is considered. Highlights • The effective potential of Oxy-MILD combustion and its possible applications on industrial scale are presented. • The temperature and species concentration distributions reached an acceptable level of uniformity. • The wall heat flux profile was uniform along the boiler height comparable with the one of a fluidized bed boiler. • The predicted carbon dioxide concentration at the boiler outlet is about 95.8%. • The NO x are reduced under Oxy-MILD combustion with respect to traditional combustion in air. [ABSTRACT FROM AUTHOR]

Using modified IEA-CFBC(International Energy Association-Circulating fluidized bed combustion) model, a 2 MWe oxy-fuel CFBC boiler is simulated and analyzed as a promising solution to reduce greenhouse gas emission from coal power plants. This study evaluated and compared the oxy-combustion characteristics of various coals. Also, the effects of CO2 concentration (71–79 vol%), bed temperature (850°C) and coal properties on combustion efficiencies, CO2 concentration, acid gas emissions were analyzed. Because of their higher N2 and S content, sub-bituminous and bituminous coals were found to have SOx and NOx concentrations higher than those of anthracite. These simulation results from Oxy-fuel CFBC simulation of various coals can be used as operating parameters for design and development of commercial Oxy-fuel CFBC boilers. [ABSTRACT FROM AUTHOR]

This paper reports the results of thermal, energy, exergy and economic analysis involving a hard coal fired power plant with a two-column cryogenic oxygen unit and operating in an oxy combustion process. As a novelty it was assumed that the auxiliary steam turbine drives the oxygen unit compressor and the bleeding steam for this purpose is extracted between intermediate- and low-pressure stage (ILS) of the main turbine. Calculations were performed to consider a number of alternative designs, in which the principal issue was to consider capacity and efficiency loss of the power plant resulting from the drive of the compressor from a cryogenic oxygen unit. The results showed that steam from ILS of the main turbine could be used for driving air separation unit (ASU) compressor. However, smaller loss of power and efficiency may be achieved with electrical supply of ASU. An application of oxy-fuel process to power plant will cause a decrease of gross efficiency in power unit by 12% points by using steam from ILS and 11% points by using electric motor for driving ASU. Profitability of oxy combustion technology will be achieved when the CO 2 emissions price reaches a minimum of 52 Euro/EUAs. [ABSTRACT FROM AUTHOR]

This paper presents a way of predicting NOx emissions from circulating fluidized bed combustors (CFBC) in air-fired and oxyfuel conditions, using the Artificial Neural Network (ANN) Approach. The Original Neural Networks Model was successfully applied to calculate the NOx (i.e. NO + NO2) emissions from coal combustion under air-fired and oxygen-enriched conditions in several CFB boilers. The ANN model was shown to give quick and accurate results in response to the input pattern. The NOx emissions, evaluated using the developed ANN model are in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

This research examined the reduction of combustion-generated sulfur dioxide and nitrogen oxide emissions from a pulverized high-sulfur bituminous coal by co-firing it with a lignite coal and by substituting air with O 2 /CO 2 gases, of compositions pertinent to dry once through oxy-fuel combustion conditions. Oxygen mole fractions were in the range of 21–30%. The neat bituminous and lignite coals as well as a 50–50 wt% blend thereof were burned in a laboratory-scale electrically-heated drop-tube furnace under fuel-lean conditions. Coal particles were in the size range of 75–90 μm and the furnace was operated at 1400 K. Results showed that the SO 2 emissions from the lignite coal were drastically lower than those from the bituminous coal, whereas the NO x emissions were only mildly lower. Co-firing the high-sulfur bituminous coal and the low-sulfur lignite coal reduced the SO 2 emissions, under both air and oxy-combustion conditions, to values well-below those predicted by linear interpolation of the respective emissions of the two neat coals. This observation, in conjunction with ash analysis shows that the alkali-rich ashes of the lignite coal acted as sulfur sorbents for the copious SO 2 emissions of the bituminous coal. This behavior was contrasted to SO 2 sorption when the bituminous coal was co-injected with calcium- and sodium-based sorbents at analogous alkali to sulfur ratios. Co-firing of the coals reduced the NO x emissions only mildly, whereas the substitution of the background N 2 gas with CO 2 resulted in much more extensive NO x reductions. [ABSTRACT FROM AUTHOR]

The use of oxy-combustion for producing furnace stack gases with low nitrogen and high carbon dioxide concentrations is a potential method for economical sequestration of green house gases. A conventional air separation unit to provide oxygen compresses all the air feed and operates with one of the two cryogenic distillation columns at elevated pressure so heat integration can be employed. The use of recuperative vapor recompression has been recently proposed in which only a portion of a nitrogen stream is compressed to provide liquid reflux to two columns, which both operate at low pressure where the separation is easier. Steady-state designs have been developed and economically optimized. The purpose of this paper is to explore the dynamic controllability of this type of vapor recompression system for air separation. [ABSTRACT FROM AUTHOR]

The design of hydrogen production, purification, compression and carbon dioxide capture is developed as two types of heat-integrated processes. The SWP (SMR + WGS + PCC) is mainly composed of the steam methane reforming (SMR) reactor, the low temperature water–gas-shift (WGS) reactor and the process of hydrogen purification, compression and carbon dioxide capture (PCC), and the SCWP (SMR + CO2R + WGS + PCC) primarily consists of the SMR reactor, the carbon dioxide reforming of methane (CO2R) reactor, the WGS reactor and the PCC. From economic aspects, it is expectable that the SWP process is superior to the SCWP process due to lower energy demand and less equipment. From aspects of energy utilization and CO 2 capture, it is verified that the SCWP process is superior to the SWP process. [ABSTRACT FROM AUTHOR]

Dynamic process simulation provides a tool to evaluate operational issues of a new process concept before the plant construction. This paper studies a carbon capture and storage (CCS) capable power plant concept with a model including a supercritical once-through CFB boiler with gas and water steam sides, a turbine island, an interface from the air separation unit (ASU) and the control system to manage typical operational transients. Switching between the air and oxy firing modes is one of the key operations in oxy combustion processes. The selected mode switching strategy uses simultaneous linear ramps for the mass flows of the primary and secondary air, oxygen, and recirculated flue gas. The results show that the firing mode can be successfully switched within 25-37 min. The flue gas path difference between the air-firing and oxy-firing modes due to the flue gas recirculation causes significant differences in dynamic behaviour. The simulations emphasize importance of good control and coordination of the gas flows. Feedback control of the flue gas and/or oxidants O2 content during the mode switching is suggested to improve robustness against disturbances, for example, in oxygen delivery, flow measurements, fuel feeding and combustion. [ABSTRACT FROM AUTHOR]

The Oxy-combustion method of CO2 capture is considered to have several advantages over other methods for CO2 capture from coal based power plants. The capture process is energy intensive and hence expensive. Heat integration is often recommended to recover part of the energy expended in the capture process. In this study, pinch analysis is used as a tool to integrate heat from the CO2 capture process into the steam cycle of the power plant. This way of heat integration provides an opportunity to make better use of the available low grade heat at the power plant premises by approaching the minimum allowable temperature difference between the hot and the cold streams. This ultimately results in a better overall efficiency by generating additional power for the same fuel input and also by reducing the consumption of cooling required in the capture process. The resulting steam cycle will be a custom design for oxy-combustion coal based power plants and will be tightly integrated with the capture process. As this method brings a lot of changes to the steam cycle configuration, this is best suited for new power plants rather than retrofit of existing plants. Results show that the Pinch method of heat integration achieves better overall thermal efficiency compared to the conventional method of steam cycle design and heat integration. A techno-economic is however required to justify the efficiency gains achieved. Further work will be done later to optimize some of the simulation assumptions and to arrive at the network design. [ABSTRACT FROM AUTHOR]

Highlights: [•] The oxy combustion CCS CO2 capture technology was investigated in CFB power plants. [•] Oxy- and air-firing were compared, focusing on process dynamics and furnace control. [•] Oxy and air dynamics differ due to oxidant properties and the oxy flue gas recycle. [•] The separate pure O2 and RFG inputs give an extra degree of freedom for oxy control. [•] “Direct” and “sequenced” air to oxy switches were compared through 1-D simulations. [ABSTRACT FROM AUTHOR]

In this paper, thermodynamic analysis of a proposed innovative double Brayton cycle with the use of oxy combustion and capture of CO2, is presented. For that purpose, the computation flow mechanics (CFM) approach has been developed. The double Brayton cycle (DBC) consists of primary Brayton and secondary inverse Brayton cycle. Inversion means that the role of the compressor and the gas turbine is changed and firstly we have expansion before compression. Additionally, the working fluid in the DBC with the use of oxy combustion and CO2 capture contains a great amount of H2O and CO2 , and the condensation process of steam (H2O) overlaps in negative pressure conditions. The analysis has been done for variants values of the compression ratio, which determines the lowest pressure in the double Brayton cycle [ABSTRACT FROM AUTHOR]

Abstract: Simultaneous multi-variable gradient-based optimization is performed on a 300 MWe wet-recycling pressurized oxy-coal combustion process with carbon capture and sequestration. A direct contact separation column is utilized for practical and reliable low-temperature thermal recovery. The models for the components include realistic behavior like heat losses, steam leaks, pressure drops, and cycle irreversibilities. Moreover, constraints are used for technoeconomical considerations. Optimization involves 17 optimization variables and 10 constraints, with the objective of maximizing the thermal efficiency. The optimization procedure utilizes recent design rules and optimization procedures for optimal Rankine cycle performance speeding up the plant optimization process by eliminating variables and avoiding constraint violations. Moreover, the procedure partially alleviates convergence to suboptimal local optima. The basecase of the study is a comprehensively optimized cycle that utilizes a surface heat exchanger, a more thermodynamically-effective form of thermal recovery which however bears significant materials challenges. Upon optimization, the cycle utilizing the direct column is seen to be very attractive regarding efficiency and performance. Moreover, the optimization results unveil potential for reducing capital costs by eliminating the first carbon sequestration intercooled compressor and by showing possibilities of process intensification between the separation column and the carbon sequestration purification columns. [Copyright &y& Elsevier]

Coal combustion was simulated in a lab-scale furnace and a full scale utility boiler at air-burn, oxy-combustion with dry- and wet-flue gas recycles. Good agreement was obtained between the numerical predictions and experimental measurements. The study confirmed that certain dry and wet recycle ratios imitate the temperature and heat transfer characteristics found in air combustion. The performances of five grey models to predict the radiative properties of gases in the simulations were examined. Emissivity correlations developed for purely CO2 media were not found to be suitable to predict the property at low H2O/CO2 ratios encountered during dry-recycle. Therefore, a new total emissivity correlation and a weighted-sum-of-grey-gases (WSGG) model were formulated to address the shortcomings and inaccuracies in existing grey gas models under oxy-firing. The new WSGG model with 4 band intervals was found to perform well in test cases that were representative of air- and oxy-firing conditions in boilers. [ABSTRACT FROM AUTHOR]