Oxy-fuel Combustion Technology Research Articles

Fuel processing in a swirl flow: numerical modelling of combustion and gasification

This study presents the concept of a cyclone furnace for coal dust combustion and gasification under conditions of oxy-fuel combustion. A two-chamber design of the cyclone furnace allows for the separation of the process of heating, drying and devolatilization of fuel from processes of its combustion and gasification of carbon residue. The choice of process parameters helps control fuel gasification. Supplying the driving gas with a specific composition (O2, CO2) to the chamber PC1 ensures the control of temperature and composition of combustible gases obtained through gasification. These gases can be used as a fuel for power boilers and, consequently, allow for utilization of the oxy-fuel combustion technology in new or existing power boilers.

Experimental Study on NOx Reduction in Oxy-fuel Combustion Using Synthetic Coals with Pyridinic or Pyrrolic Nitrogen

Oxy-fuel combustion technology can capture carbon dioxide (CO2) in the large-scale and greatly lower nitrogen oxides (NOx) emission in coal-fired power plants. However, the influence of inherent minerals on NOx reduction still remains unclear and the impact of oxy-fuel combustion on the transformation of different nitrogen functional groups has yet to be fully understood. The present work aims to obtain a further understanding of the NOx reduction during oxy-fuel combustion using synthetic coals with pyrrolic or pyridinic nitrogen. Compared to pyridinic nitrogen, more of the pyrrolic nitrogen in synthetic coal was converted to NOx. The conversion ratio of nitric oxide (NO) first increased significantly with the rising oxygen content and then trended to an asymptotically constant as the oxygen (O2) content varied between 10–50%. The nitrogen dioxide (NO2) formation was roughly proportional to the oxygen content. The NO2 conversion was increased with particle size but the case of NO showed a non-monotonic variation. The catalytic effects of sodium carbonate (Na2CO3), calcium carbonate (CaCO3), and ferric oxide (Fe2O3) on the transformation of pyridinic nitrogen to NO were independent of the combustion atmosphere, while the alteration from air to the oxy-fuel combustion led to a change of mineral catalytic effect on the oxidation of pyrrolic nitrogen within the coal matrix.

Oxy-fuel combustion in a two-pass oxygen transport reactor for fire tube boiler application

Application of oxy-fuel combustion carbon capture technology to power plants is currently getting special attention as one of the means of curtailing CO2 emission responsible for the current climate change. The key concept of oxy-fuel combustion technology is the use of pure oxygen, obtained via air separation technologies, for combustion instead of air. Currently, the membrane separation technology is gaining high momentum due to its flexibility for different applications. Integrating oxygen transport membrane reactors to fire tube boilers has the prospects of concurrent permeation of oxygen, in-situ combustion as well as steam generation within a confined space, thus, potential for more compact boilers. Despite the in-situ prospects of the Oxygen Transport Membrane (OTM) integration, it comes with the heat transfer design challenges due to fragile nature of the membrane as well as maintaining the required operating temperatures for optimum performance. Hence the geometry as well as the heat transfer characteristics need to be well designed and the system needs to be thoroughly investigated for optimum performance. In this study, numerical modeling of a two-pass oxygen transport membrane reactor for oxygen permeation and oxy-fuel combustion characteristics analyses for fire tube boilers application was conducted. It was found that, for the non-reactive conditions, the effects of gases inlet temperature and mass flow rates on oxygen permeation along the length of the membrane was meager within the scope of this study. The gases inlet conditions dictate the rate of oxygen permeation under reactive conditions. Also, the gases inlet temperature and mass flow rates control the amount of heat transfer to the load. The sweep gas inlet condition was more critical to the stability of the combustion reaction. The current design of the proposed OTM reactor can deliver power output in the range from 1 to 5 MWe when applied to a typical fire-tube boiler.

Effects of acidic gases and operation parameters on denitrification in oxy-fuel CO2 compression process

Oxy-fuel combustion technology has great potential as a technically feasible method to significantly reduce CO2 emissions from coal-fired power plants. In an oxy-fuel combustion system, gas impurities such as SO2 and NOx must be removed before CO2 recovery because they can cause potential corrosion risk to CO2 compression and purification units (CPU). An attractive strategy is to simultaneously remove SO2 and NOx in the existing CO2 CPU system in place of traditional flue gas treatment device. Since NOx contains more than 90% of insoluble NO, the removal of NO has attracted much attention. In this study, NO removal efficiency in CO2 compression process were experimentally investigated on a pressurized reaction system. Effects of acidic gases (SO2, CO2) and operation parameters (pressure, temperature, initial O2 concentration and residence time) were taken into consideration. NO removal was achieved in pressurized reaction system as a result of oxidation to NO2 in the presence of O2 and the absorption of NO2 in water. NO conversion to NO2 was the key step for NO removal, which was strongly and positively dependent on the pressure and negatively dependent on the temperature. With the addition of 1000 ppm SO2 in simulated gases, NO removal efficiency was reduced by 8.1% at 2.0 MPa. The gas phase and liquid phase reactions between SO2 and NO2 suggested that partial NO2 was converted to insoluble NO when reacting with SO2. It was also found that NO removal efficiency in O2/CO2 atmosphere was slightly higher than that in O2/N2 atmosphere. The dissolution of CO2 in water increased the residence time as well as the acidity of the aqueous solution, which could facilitate the oxidation of NO.

Combustion characteristics and synergy behaviors of biomass and coal blending in oxy-fuel conditions: A single particle co-combustion method

Co-combustion biomass and coal can effectively reduce the emission of CO2. O2/H2O combustion is regarded as the next generation of oxy-fuel combustion technology. By co-combustion biomass and coal under oxy-fuel condition, the emission of CO2 can be minimized. This work investigates the co-combustion characteristics of single particles from pine sawdust (PS) and bituminous coal (BC) in O2/N2, O2/CO2 and O2/H2O atmospheres at different O2 mole fractions (21%, 30% and 40%). The experiments were carried out in a drop tube furnace (DTF), and a high speed camera was used to record the combustion process of fuel particles. The combustion temperature was measured by a two-color method. The experiments in O2/N2 atmosphere indicate that the particles from pine sawdust and bituminous coal all ignite homogeneously. After replacing H2O for N2, the combustion temperature of volatiles of blended fuel particles decreases, while the combustion temperature of char increases. The ignition delay time in O2/H2O atmosphere is shorter than that in O2/N2 or O2/CO2 atmosphere. The combustion temperature of volatiles of blended fuel particles increases as the mass fraction of bituminous coal increases, while the combustion temperature of char of blended fuel particles is higher than that of biomass or bituminous coal. The ignition delay time of blended fuel particles increases with the increasing mass fraction of bituminous coal, and the experimental ignition delay time of blend fuel particles is shorter than the theoretical one. These reveal a synergy during co-combustion process of pine sawdust and bituminous coal.

Ash and Flue Gas from Oil Shale Oxy-Fuel Circulating Fluidized Bed Combustion

Carbon dioxide emissions are considered a major environmental threat. To enable power production from carbon-containing fuels, carbon capture is required. Oxy-fuel combustion technology facilitates carbon capture by increasing the carbon dioxide concentration in flue gas. This study reports the results of calcium rich oil shale combustion in a 60 kWth circulating fluidized bed (CFB) combustor. The focus was on the composition of the formed flue gas and ash during air and oxy-fuel combustion. The fuel was typical Estonian oil shale characterized by high volatile and ash contents. No additional bed material was used in the CFB; the formed ash was enough for the purpose. Two modes of oxy-fuel combustion were investigated and compared with combustion in air. When N2 in the oxidizer was replaced with CO2, the CFB temperatures decreased by up to 100 °C. When oil shale was fired in the CFB with increased O2 content in CO2, the temperatures in the furnace were similar to combustion in air. In air mode, the emissions of SO2 and NOx were low (<14 and 141 mg/Nm3 @ 6% O2, respectively). Pollutant concentrations in the flue gas during oxy-fuel operations remained low (for OXY30 SO2 < 14 and NOx 130 mg/Nm3 @ 6% O2 and for OXY21 SO2 23 and NOx 156 mg/Nm3 @ 6% O2). Analyses of the collected ash samples showed a decreased extent of carbonate minerals decomposition during both oxy-fuel experiments. This results in decreased carbon dioxide emissions. The outcomes show that oxy-fuel CFB combustion of the oil shale ensures sulfur binding and decreases CO2 production.

Retrofitting carbon capture and storage to natural gas-fired power plants: A real-options approach

Abstract This paper presents a real-options approach to assess the value of retrofitting carbon capture and storage technology to an existing natural gas-fired base-load power plant. Operating in a deregulated electricity market, a power plant owner seeks to decide whether to retrofit and at what techno-economic conditions to retrofit carbon capture and storage. The value of the plant is determined based on clean spark spread options. Two alternative carbon capture and storage technologies, post-combustion and oxy-fuel combustion, are evaluated. Price uncertainties of electricity and natural gas are modeled as mean-reverting processes. The plant is abided by the emission reduction policy of carbon tax or price. Results show that a plant owner would opt for retrofitting post-combustion technology to an existing power plant if the carbon price hits to at least 140 dollars per ton of carbon dioxide, and would select oxy-fuel combustion technology if the carbon price moves further to 185 dollars per ton of carbon dioxide or above. Since parameters of carbon capture and storage vary widely across the literature, sensitivity tests of the expected values to different costs, prices, and volatility parameters are also presented for an insightful comparative view of which carbon capture and storage technology to adopt at what techno-economic conditions.

Quantifying carbon capture potential and cost of carbon capture technology application in the U.S. refining industry

Carbon capture (CC) technology is receiving increasing attention as a critical technology for climate change mitigation. Most previous studies focus on the application of CC technology in the power generation sector, while fewer studies have analyzed applications in the refining industry, which is one of the largest greenhouse gas (GHG) emissions sources in the U.S. industrial sector. Unlike the power generation sector, the refining industry has highly distributed CO2 emission sources. In this paper, bottom-up modeling and techno-economic analysis approaches are integrated to quantify the national CO2 emission reduction potential and costs of three types of CC technologies applied to U.S. refineries: (1) pre-combustion, (2) post-combustion, and (3) oxyfuel-combustion. Two scenarios are developed to compare different design strategies for CC systems; one is a distributed design scenario for post-combustion technology, the other is a centralized design scenario for pre-combustion and oxyfuel-combustion technology. The results of the two scenarios are compared, and the trade-offs between different design strategies are highlighted. The results shown in this study provide an intuitive and quantitative understanding of the potential of CC technology to reduce CO2 emissions from the U.S. refining industry. Such information is helpful to policymakers, oil companies, and energy/environmental analysts for strategic planning and systems design to manage future CO2 emissions of refineries.

Investigation on the thermodynamic calculation of a 35 MWth oxy-fuel combustion coal-fired boiler

Oxy-fuel combustion technology is one of the most promising technologies for CO2 capture from coal-fired power plants and is remarkably characterized by the recycled flue gas (RFG). RFGs and pure oxygen are substitute for air, which alter the thermodynamics and heat transfer features for an oxy-fuel combustion coal-fired boiler. Hence, conventional thermodynamic calculation method for air combustion need to be improved for oxy-fuel combustion. This study primarily proposed a modified thermodynamic calculation method, which is subsequently verified by the experimental data for a 35 MWth coal-fired boiler under oxy-fuel combustion with dry and wet recycle modes. Validation results indicate that the modified method could predict the temperatures well in the main heating surfaces of the boiler for oxy-fuel combustion. Given the fine distinction between calculated and experimental temperatures for the main heating surfaces, several key parameters in the main heating surfaces are corrected to improve the precision of the corrected method. Compared with air combustion, the fouling factors for oxy-fuel wet recycle and dry recycle increase, while the effective coefficients and ash deposition coefficients for oxy-fuel combustion reduce. Notably, the utilization coefficients for oxy-fuel are relative to those for air combustion. The heat transfer features in the main heating surfaces are also discussed. Consequently, heat transfer is mainly controlled by the radiative heat transfer of flue gas in the furnace and is determined by the heat capacity of flue gas in the horizontal and vertical heating surfaces under oxy-fuel combustion.

Thermodynamic assessment of zero-emission power, hydrogen and methanol production using captured CO2 from S-Graz oxy-fuel cycle and renewable hydrogen

Thermodynamic analysis of a novel combined system, including geothermal driven dual fluid organic Rankine cycle (ORC), S-Graz cycle, proton exchange membrane electrolyzer (PEME) and methanol synthesis unit (MSU) are carried out using energy and exergy principles. The presented system produces zero emission power and hydrogen using oxy-fuel combustion technology and splitting water into hydrogen and oxygen in the PEME, which consumes the dual fluid ORC produced power. Then, methanol production from captured CO2 and produced H2 is suggested to eliminate the captured CO2 from S-Graz cycle. The energy and exergy efficiencies and sustainability index of 14.7%, 42.43% and 1.737 are obtained for the presented cogeneration system, respectively. Also, results associated with the exergy destruction reveal that most of the destroyed exergy in the system is due to the dual fluid ORC in compare with the other units. Furthermore, it is observed that, within the dual fluid ORC, low pressure evaporator (LPE) is responsible for 33% of exergy destruction. Moreover, the results indicate that increasing higher pressure of the dual fluid ORC improves the system energetic and exergetic performance while an increment in geothermal hot water temperature leads to a reduction in system energy and exergy efficiencies.

Effects of O2 Feeding Strategy and Over-Fire Air Configuration on Oxy-Fuel Combustion Characteristics in an Opposed Wall-Fired Utility Boiler

Much attention has been focused on the flue gas recycle mode and O2 concentration in previous numerical studies on oxy-fuel utility boilers, while the effects of O2 feeding strategy and OFA configuration on oxy-fuel combustion characteristics in a 600 MW wall-fired utility boiler were mainly investigated in the present study. The results showed that the optimal O2 volume fraction for the oxy-fuel combustion of the wall-fired boiler was approximately 30%. The O2 feeding strategy of decreasing the O2 concentration in inner second air (denoted by [O2]ISA) could effectively reduce NOx formation without affecting the flame stability. In addition, staged oxy-fuel combustion could be achieved with the burner configuration of closing inner second air (ISA) nozzles meanwhile opening over fire air (OFA) nozzles. The NOx emission decreased significantly from 149.05 to 97.83 mg/MJ when the staged oxy-fuel combustion was employed. Furthermore, the burnout of char and CO under staged oxy-fuel condition was greatly affected by the velocity of OFA. Hence, a modified OFA configuration was proposed to promote the turbulent mixing condition in the upper furnace after the staged oxy-fuel combustion was adopted. With the application of the modified OFA configuration, the unburned carbon in fly ash decreased to the same level as that in air combustion (oxy-fuel combustion of 4.83% and air combustion of 4.67%), while the NOx emission remained at 96.48 mg/MJ. The present work will be helpful for the retrofitting of the existing utility boiler with oxy-fuel combustion technology.

Impact of Oxy-fuel Combustion on Ash Properties and Sintering Strength Development

For a successful implementation of the oxy-fuel combustion technology, a good understanding of ash-related issues has to be achieved. Knowledge is still lacking on how oxy-fuel combustion can affec...

Molecular Dynamics Study of Combustion Reactions in a Supercritical Environment. Part 2: Boxed MD Study of CO + OH → CO2 + H Reaction Kinetics.

Oxy-fuel combustion technology holds a great promise in both increasing the efficiency of the energy conversion and reducing environmental impact. However, effects of the higher pressures and replacement of the nitrogen with carbon dioxide diluent are not well understood at present. The title reaction is one of the most important processes in combustion. Despite numerous studies, the effects of supercritical carbon dioxide environment did not receive much attention in the past. Here we report the results of boxed molecular dynamics simulations of these effects at QM/MM theory level with periodical boundary conditions. The free energy barriers for HOCO intermediate formation and decomposition were tabulated in a wide range of pressures (1-1000 atm) and temperatures (400-1600 K). Pressure dependence of calculated rate constants for these reaction steps and overall reaction were analyzed. We found that the CO2 environment may increase these rate constants up to a factor of 25, at near critical conditions. At higher temperatures, this effect weakens significantly. Numerical values for parameters of extended Arrhenius equation, suitable for combustion kinetic modeling are reported.

Three-dimensional CFD simulation of oxy-fuel combustion in a circulating fluidized bed with warm flue gas recycle

Among various CO2 capture methods, the oxy-fuel combustion technology exhibits great potential for CO2 capture in an economical way. Based on a pilot-scale circulating fluidized bed (CFB) combustor, computational fluid dynamics (CFD) is applied to simulate the oxy-fuel CFB combustion with warm flue gas recycle (WFGR). In this work, the WFGR in the oxy-fuel CFB combustion is realized by the Eulerian-Eulerian CFD simulation. Detailed profile of the hydrodynamics, temperature, gas characteristics and pollutant emission is analyzed with good agreement between the simulated result and the experimental data achieved. Special attention is paid to the comparison of gas distribution under the combustion conditions with and without WFGR, illustrating the unique advantages of the oxy-fuel CFB combustion with WFGR in the CO2 capture and pollutant reduction. Besides, influence of the oxy atmosphere with different O2 concentrations (from 21% to 40%) on the overall performance is conducted, successfully predicting the oxy-fuel combustion with WFGR under a high O2 concentration and enriching the investigation method of the CFB combustion study.

Energy and exergy analyses of oxy-fuel combustion power plants with chemical looping air separation

This paper integrated chemical looping air separation (CLAS) with oxy-fuel combustion power plants. The results reveal that this type of oxy-fuel combustion technology displays higher energy efficiency than other systems such as post-combustion and oxy-fuel combustion with cryogenic air separation. Energy analysis reveals that the arrangement of a steam generation system based on a conventional pulverized coal power plant is more efficient for oxy-fuel combustion power plants with integrated CLAS technology. Thus, a power generation efficiency of 41.6% can be achieved. However, CO2 compression imposes an additional energy penalty of ~4%, resulting in a net power efficiency of 37.6%. On the other hand, exergy analysis reveals that the most significant exergy destruction portion of the system occurs in the combustion process. CO2 compression also imposes large exergy destruction. Finally, we concluded that the exergy destruction could be alleviated by reasonable arrangement of the heat exchangers.

Energy and exergy analyses of oxy-fuel combustion power plants with chemical looping air separation

This paper integrated chemical looping air separation (CLAS) with oxy-fuel combustion power plants. The results reveal that this type of oxy-fuel combustion technology displays higher energy efficiency than other systems such as post-combustion and oxy-fuel combustion with cryogenic air separation. Energy analysis reveals that the arrangement of a steam generation system based on a conventional pulverized coal power plant is more efficient for oxy-fuel combustion power plants with integrated CLAS technology. Thus, a power generation efficiency of 41.6% can be achieved. However, CO2 compression imposes an additional energy penalty of ~4%, resulting in a net power efficiency of 37.6%. On the other hand, exergy analysis reveals that the most significant exergy destruction portion of the system occurs in the combustion process. CO2 compression also imposes large exergy destruction. Finally, we concluded that the exergy destruction could be alleviated by reasonable arrangement of the heat exchangers.

Current activities for commercialization of oxyfuel power plant

While the efforts to control global warming are being strengthened all over the world, expectations for CO2 Capture, Utilization and Storage (CCUS) technology for coal fired power plants are increasing. IHI has been working on development of oxyfuel-combustion technology since 1989 with the aim of easily capturing and storage CO2 emitted from coal fired power plants. For the demonstration of oxyfuel-combustion technology, IHI participated in the Callide Oxyfuel Project with collaboration between Australian and Japanese under the financial support of Australian, Queensland state and Japanese governments. In the project, the oxyfuel-combustion process was applied to the existing coal power plant in Queensland, Australia, and demonstration was carried out and successfully completed without any significant technical barrier to commercialization in March, 2015. In Oxyfuel-combustion, the coal-fired boiler is operated with an inlet O2 content of 27 vol% in order to achieve the same furnace heat transfer as in conventional air-firing. The first outcome of oxyfuel-combustion is a significant reduction in NOx production, typically 60% reduction, measured in mgNOx/MJcoal. The second outcome of oxyfuel-combustion is a reduction in the actual volumetric flow of flue gas, typically a 60% to 70% reduction in gas flow measured as m3/h, and a proportionate increase in the CO2 content of the flue gas from ~ 15 vol% (dry) in airfiring mode to 70 to 80 vol% (dry) in Oxyfuel mode. In addition, CO2 product from the Callide Oxyfuel Project was injected into the Paaratte formation in the Otway Basin (Victoria) to investigate the geochemical effects of CO2 (normal product) and CO2 with added impurities. The recent research and development about characteristics of roller mill and electrical precipitator using combustion test facilities for the flexibility of plant design and the current commercialization activities of oxyfuel power plant are introduced in this paper.

Process simulation and optimization of municipal solid waste fired power plant with oxygen/carbon dioxide combustion for near zero carbon dioxide emission

As a new type of high-intensity combustion technology, oxy-fuel combustion technology can effectively reduce the generation and emission of pollutants, particularly near zero emission of carbon dioxide when applied to the waste incineration process. Compared to the conventional air waste-to-energy incineration power generation, the municipal solid waste oxy-fuel combustion power generation system is more complex, resulting in a relatively large space for optimization. In this work, a waste-to-energy incineration power plant in Shenzhen, China, is taken as the original object, and used to establish the process simulation of the conventional plant using Aspen plus. The results are compared and verified with the operation data. Based on the results, models or subsystems are set up for the air separation unit, the municipal solid waste oxy-fuel combustion power system and the flue gas processing compression system, respectively. Then, the subsystems are coupled and connected to establish the whole process simulation of the waste oxy-fuel combustion power plant, and the optimization analyses of the overall plant operating parameters are presented. The results show that the best supplying oxygen concentration is 96%, the carbon dioxide recovery rate of the entire system is 96.24%, and near-zero carbon dioxide emission is basically achieved. The energy consumptions sharing by the flue gas processing compression subsystem, the air separation subsystem, and the others account for 19.82%, 54.29%, and 25.89% of the total energy consumption, respectively. After coupling optimization analysis, the net power generation efficiency of the municipal solid waste oxy-fuel combustion plant increases 2.69%, from 6.88% to 9.57%.

Influence of Oxy-fuel Atmosphere on Microscopic Physical-Chemical Properties of High-alkali Ash at Softening Temperature

The utilization of high-alkali coals in Zhundong coalfield with oxy-fuel combustion technology has a great potential, however, the ash fusion properties of high-alkali coals are still unclear. Here, we studied the influence of oxy-fuel atmosphere on the microscopic properties of high-sodium ash. The change from air to oxy-fuel condition has a negligible influence on ash fusion temperatures, but exhibits certain impact on physical-chemical properties of high-alkali ash. Oxygen content presents a primary effect on the microscopic morphology of ash at softening temperature.

Combustion Characteristics of Single Particles from Bituminous Coal and Pine Sawdust in O2/N2, O2/CO2, and O2/H2O Atmospheres

Burning fuels in an O2/H2O atmosphere is regarded as the next generation of oxy-fuel combustion for CO2 capture and storage (CCS). By combining oxy-fuel combustion and biomass utilization technology, CO2 emissions could be further reduced. Therefore, this work focuses on investigating the combustion characteristics of single particles from bituminous coal (BC) and pine sawdust (PS) in O2/N2, O2/CO2 and O2/H2O atmospheres at different O2 mole fractions (21%, 30%, and 40%). The experiments were carried out in a drop tube furnace (DTF), and a high-speed camera was used to record the combustion processes of fuel particles. The combustion temperatures were measured by a two-color method. The results reveal that the particles from BC and PS all ignite homogeneously. Replacing N2 by CO2 results in a longer ignition delay time and lower combustion temperatures. After substituting H2O for N2, the ignition delay time is shortened, which is mainly caused by the steam gasification reaction (C + H2O → CO + H2) and steam shift reaction (CO + H2O → CO2 + H2). In addition, the combustion temperatures are first decreased at low O2 mole fractions, and then increased at high O2 mole fractions because the oxidation effect of H2O performs a more important role than its volumetric heat capacity and thermal radiation capacity. At the same condition, particles from PS ignite earlier because of their higher reactivity, but the combustion temperatures are lower than those of BC, which is owing to their lower calorific values.