Oxy-combustion Technology Research Articles

Integration of alternative fuel production and combined cycle power plant using renewable energy sources

The article explores the integration of a methanol production system with a modern combined cycle power plant utilizing oxy-combustion technology, resulting in enhanced efficiency for both systems (synergy effect). The integration involves various components like a 90 MW wind farm, hydrogen generators, and methanol production units. Notably, CO2 preparation and compression for the methanol reactor within the power plant optimize methanol production and reduce energy consumption in the oxygen separation unit by supplementing oxygen through electrolysis. Utilizing oxygen from electrolysis also decreases energy consumption in the gas turbine's oxidant compressor. Additionally, compressing CO2 to lower pressures reduces energy consumption in the CCU installation. The article presents a methodology for quantifying energy efficiency for both the methanol production unit and the combined cycle power plant. Integration leads to significant efficiency increases, particularly for low-power generation setups and with greater contributions from renewable energy sources. For instance, in scenarios involving a gas turbine with 7.5 MW capacity, efficiency gains range from 0.8 to nearly 6 percentage points with multiple wind farms. This study is the first of its kind to demonstrate the synergistic advantages of directly integrating an oxy-combined cycle power plant with a methanol production facility. The integration results in heightened efficiency for both the power plant and the methanol production setup, contributing significantly to the advancement of hydrogen technology and the green deal initiative. The unique approach of utilizing hydrogen from electrolysis setups and CO2 derived from exhaust gases of power plants to generate liquid methanol, a superior energy carrier, is a significant contribution to the existing body of literature. The demonstrated synergistic outcomes of integrating a methanol production facility with combined cycle power plants stem from augmented unit efficiencies, overall installation improvements, and the amelioration of the ecological attributes of the power plant. The innovative character of this research endeavor is underscored by the fact that no existing installation worldwide currently pairs methanol production with a combined cycle power plant.

Assessment of carbon emissions’ effects on the investments in conventional and innovative waste-to-energy treatments

In the current scenario of transition to a Europe-wide circular economy (CE), the Waste-to-Energy (WtE) treatments represent a smart solution to generate renewable energy, reduce landfills and ensure sustainable waste management. The costs and environmental impacts of existing WtE treatments are very different for each available technology. In many cases, their identification is affected by a set of variable boundary conditions strongly dependent on local municipal requirements. In light of these considerations, the paper aims to compare the investment in three different WtE treatments (i.e., incineration, gasification, and flameless oxy-combustion) to identify the best solution to support the current transitional phase towards a CE condition. An overall yearly cost analysis was developed by varying local municipal requirements, including investment, operating, and carbon emissions costs. The overall yearly cost and the revenues, due to energy sales and tipping fees, allowed to evaluate the profitability of the investment in the plant lifetime to identify the best WtE treatment. The investment profitability was evaluated by adopting the Net Present Value (NPV) method by estimating the cash flow statement over the entire plant lifetime. The performance of the three WtE treatments, classified as “conventional” (i.e., gasification and incineration) and “innovative” (i.e., flameless oxy-combustion), were compared in a case study concerning Southern Italy's Metropolitan City of Bari. The applied methodology showed, in this case, that gasification, at the moment, has to be deemed as the most sustainable treatment for MSW management. Moreover, the study proved a high dependence between the carbon price and the profitability of the investment and, thus, in the next future the innovative oxy-combustion technology will gain an advantage over all the other technologies, when carbon price will be higher than 44 €/tonnesCO2.

Energy, economic and environmental analysis and comparison of the novel Oxy- combustion power systems

Oxy-combustion technologies are clean energy systems with zero emission; they have great potential when considering global warming and climate change. This study presents a detailed thermodynamic analysis in terms of energy, environment, and economy. Consequently, the results obtained for an oxy-combustion power system are presented in comparison with a conventional gas turbine power system. The results are presented as a function of the pressure ratio with regard to net power, input heat, system efficiency, sp ecific fue l consumption, equivalence ratio, fuel-air ratio, capital investment cost, fuel cost, oxygen cost, total cost, electricity revenue, and net profit. In addition, the study calculates the pollutant emissions from non-oxy-combustion systems and investigates the environmental costs. The pressure ratio for maximum net power has been obtained as 20.8 in the conventional gas turbine power system. Similarly, the pressure ratios for maximum net power in oxy-combustion power cycles with 26%, 28%, and 30% oxygen ratios are 23.3, 27.4 and 29.7, respectively. Results from 24% to 30% have been displayed to observe the effect of reactant oxygen in the oxy-combustion power cycles. The optimum c ycle c onditions have been determined by calculating the costs of system components, total revenues, and net profits at pressure ratios of 10, 20, 30 and 40. Finally, the results reveal the pressure ratio should be reduced to minimize the total costs per cycle. For maximum net profit, the pressure ratio in a conventional gas turbine power cycle has been calculated as 15.9; similarly, the pressure ratios in oxy-combustion power cycles with 26%, 28%, and 30% oxygen ratios have been respectively calculated as 12.8, 15.2 and 16.4.

Research of Carbon Emission Reduction Potentials in the Yellow River Basin, Based on Cluster Analysis and the Logarithmic Mean Divisia Index (LMDI) Method

China has implemented many green transition policies to reach its carbon peak target, some of which do not consider the actual carbon reduction pressures that localities can afford, thus lowering the living standards of residents and economic growth, which makes the green transition process unsustainable. The Yellow River Basin plays an important role in China’s energy, food, manufacturing, and ecological sectors. Thus, the design of green transition policies in the region needs to be modest and efficient. Based on the data of 100 prefecture-level cities in the Yellow River Basin from 2006 to 2017, this paper uses the K-means clustering to divide the carbon reduction potential of cities into four types. Most cities’ carbon reduction potentials are low or medium, unsuitable for adopting a rapid green transition. Based on the logarithmic mean Divisia index (LMDI) decomposition results and the carbon reduction potential, we designed different carbon-control pathways: Shandong and Henan should focus on increasing investment in green technology, especially oxy-combustion technology; Gansu, Ningxia, and Qinghai could partially offset carbon emissions through land use, land-use change and forestry (LULUCF) activities; Sichuan and Inner Mongolia should increase their energy-use efficiency; Shaanxi and Shanxi could use green finance to complete the upgrading of local industries. The above emission-reduction strategies can be actively pursued in cities with high emission reduction potential and should be implemented with caution in cities with low emission reduction potential. This paper provides a new and cost-effective perspective on carbon emission control in the Yellow River Basin.

Modeling and simulation of an integrated power-to-methanol approach via high temperature electrolysis and partial oxy-combustion technology

The Power to methanol (PtMeOH) approach based on water electrolysis and CO2 capture is studied. The novelties are the integration of solid oxide electrolysis, partial oxy-combustion capture technology and methanol synthesis process, and the development and validation with experimental data of a SOEC system model using Aspen Custom Modeler. Simultaneously, CO2 capture bench-scale unit and methanol synthesis process have been modeled and experimentally validated using Aspen Plus. These three systems have been thermally integrated in a final model to assess its high-performance operation. As a result, a clean, synthetic methanol is produced, which can be used as fuel or energy storage. In this lab-scale, a SOEC system of 1.2 kW and a synthetic flue gas of 7 l/min (40% CO2, 60% N2) are considered to obtain a methanol flow of 0.16 kg/h, with an overall efficiency of 29% for the integrated scenario. The SOEC system with an optimized BoP has the highest energy consumption, mainly due to water electrolysis, with 44% of total required energy. The novel power-to-methanol integrated in this work achieves around 20% reduction of the energy penalties estimated for the base case and makes use of oxygen from electrolysis for partial oxy-combustion and the water by-product of methanol synthesis in water electrolysis. The integrated model of the overall process is considered a useful tool for future works focused on further scale-up of the process.

Oxy-combustion Roadmap to Commercialization

Oxy-combustion is a form of low-carbon power generation, where the oxygen is separated from the air for combustion, yielding a flue gas consisting largely of CO2 and water, which in turn allows for relatively easy CO2 capture. Oxy-combustion comes in several forms, including atmospheric oxy-combustion, which can be done at conventional or higher flame temperatures, and a variety of pressurized oxy-combustion concepts. A special case of oxy-combustion is chemical looping combustion (CLC) where the air separation is done using an oxygen carrier, eliminating the need for an energy-intensive cryogenic air separation unit. Another special case, where the oxy-combustion is performed directly within the cycle, is the direct-fired supercritical CO2 (sCO2) power cycle (“Allam Cycle”). Oxy-combustion in its various forms has the potential to capture CO2 economically along with generating water and potentially other revenue streams. However, despite its potential, these technologies are not yet commercial, and their end states are hence unknown. Various oxy-combustion technologies are at different stages of maturity with multiple developers involved. Developing a roadmap that provides the status of the technology and its relative maturity level; reviews potential applications for oxy-combustion; assesses the performance, costs, and benefits; identifies the critical technical challenges that could limit successful commercial deployment; lays out a pathway to address those challenges; and includes a timeline required to reach commercial deployment, is necessary to get a better understanding of the potential of this novel technology. The Electric Power Research Institute, Inc. (EPRI) led a team that developed such an oxy-combustion roadmap, focusing on technologies that have established developers and are beyond lab-scale efforts. These technologies were: • Babcock & Wilcox Company’s (B&W) Coal Direct Chemical Looping: A CLC technology, which uses a form of oxy-combustion where the oxygen separation is done using an oxygen carrier, eliminating the need for an energy-intensive air separation. B&W utilizes iron-based oxygen carriers in its system. • Clean Energy Systems, Inc.’s (CES) Tri-Gen: One of several pressurized oxy-combustion processes that yield smaller components and allow the latent heat recovery of water at useful temperatures designed to improve efficiency. CES’ system uses platelet combustors and customized turbomachinery and heat exchangers with one of its initial targets focused on biomass. • General Electric’s (GE) Limestone Chemical Looping Combustion™: A CLC technology, GE uses a calcium-based oxygen carrier in its system. • Gas Technology Institute’s Oxy-Pressurized Fluidized-Bed Combustion: A pressurized oxy-combustion process that utilizes fluidized beds. • ITEA’s Flameless Pressurized Oxy-Combustion: A pressurized oxy-combustion process that utilizes flameless combustion. • Jupiter Oxygen Corporation’s High-Temperature Oxy-Combustion: A form of atmospheric oxy-combustion that employs high flame temperature through a modified burner designed to improve heat transfer. • Natural Resources Canada’s G2: A pressurized oxy-combustion process that is being designed to be coupled with an sCO2 power cycle. • NET Power, LLC / 8 Rivers, LLC Allam Cycles: Direct-fired, sCO2 power cycle that performs oxy-combustion in-situ, yielding a working fluid of CO2 and water that drives a turbine. NET Power, LLC is developing the natural gas version, while 8 Rivers, LLC is developing the coal-syngas version. • Washington University in St. Louis’ Staged, Pressurized Oxy-Combustion: A pressurized oxy-combustion process that stages the combustion using multiple boilers. The provides detailed information on each technology’s status and work done in the field, assess its maturity level, give data on its costs and performance (in some cases calculated independently by EPRI), review technology gaps that must be addressed, and present multiple timelines for when each is projected to be commercially ready―the first is a deliberate, conservative approach developed by EPRI, and the second was provided by the developer, which generally is an accelerated, more aggressive (and hence riskier) approach that seeks to shorten the timeline.

Thermodynamic Assessment of Membrane-Assisted Premixed and Non-Premixed Oxy-Fuel Combustion Power Cycles

Abstract This study focuses on the investigations of gas turbine power generation system that works on oxy-combustion technology utilizing membrane-assisted oxygen separation. The two investigated systems are (i) a premixed oxy-combustion power generation cycle utilizing an ion transport membrane (ITM)-based air separation unit (ASU) which selectively allows oxygen to permeate from the feeding air and (ii) a non-premixed oxy-fuel combustion power cycle, where oxygen separation takes place, with cogeneration of hydrogen in an integrated combustor. A gas turbine combined cycle that works on conventional air–methane combustion was considered as the base case for this work. Commercial software package Hysys V8 was utilized to conduct the process simulation for the proposed cycles. The two novel cycle designs were proposed and evaluated in comparison with that of the conventional cycle. The first law efficiency of the premixed combustion power cycle was calculated to be 45.9%, a loss of 2.4% as an energy penalty for the oxygen separation. The non-premixed cycle had the lowest first law efficiency of 39.6%, which was 8.7% lower than the efficiency of the base cycle. The lower effectiveness of the cycle could be attributed to the highly endothermic H2O splitting reaction for oxygen production. High irreversibility in the H2O-splitter and the reactor was identified as the main cause of exergy losses. The overall second law efficiency of the non-premixed power cycle was around 50% lesser than that of the other cycles. The energy penalty related to air separation is dominated as the parameter that reduces the efficiencies of the oxy-fuel combustion cycles; however, the premixed combustion cycle performance was found to be comparable to that of the conventional air-combustion cycle.

Soot formation characteristics in laminar coflow flames with application to oxy-combustion

Oxy-combustion is an effective carbon capture technology. Many oxy-combustion technologies utilize recycled flue gas (RFG) for dilution to control temperature and heat flux. As the concentration of dilution gas on the fuel and oxidant side changes, stoichiometric mixture fraction (Zst) and flame temperature will change and significantly impact the flame structure and soot formation characteristics. In this work, the effects of stoichiometric mixture fraction and flame temperature on soot formation characteristics in laminar diffusion flames are studied by diluting the fuel and changing the oxygen concentration. CO2 is used as a dilution gas to simulate the RFG in oxy-combustion. The numerical calculation combines gas reaction kinetics with a soot formation model. Soot nucleation, surface growth, oxidation processes are considered, as well as the distributions of temperature, soot concentration, and key substances. The experimental flame appearances and spectral radiation data are imaged by a hyperspectral imager, and the temperature and soot concentration are reconstructed. The results of experimental measurement and numerical calculation are compared to evaluate the applicability of the soot formation mechanism to oxy-combustion with elevated Zst and using CO2 as diluent. As the Zst increases, the flame changes into a blue flame, soot concentration and temperature in flames decrease, because nucleation and surface growth are both inhibited and oxidation is enhanced. As the flame temperature increases, the flame becomes brighter, numerical results indicate that soot formation and oxidation are both enhanced, while the promoting effect of temperature increase on surface growth is stronger than that of oxidation, resulting in an increase in soot concentration. This study provides a fundamental understanding of the effects of RFG utilization (fuel dilution and oxygen enhancement) on flame structure, temperature distribution, soot concentration and formation characteristics in non-premixed oxy-combustion systems.

Thermodynamic and economic performance of oxy-combustion power plants integrating chemical looping air separation

Abstract Oxygen supply from cryogenic air separation unit (ASU) causes high economic cost and energy penalty, which hinders the practicability of oxy-combustion technology. Chemical looping air separation (CLAS) as a thermodynamic-efficient and cost-effective approach can satisfy the oxygen demands for oxy-combustion power plants. To optimize process configuration and identify the effect of recycling position for oxy-combustion power plants integrating CLAS (i.e. OXY-CLAS), the paper focuses on process simulation, thermodynamic analysis and techno-economic evaluation of two typical OXY-CLAS systems. For sastifying the oxygen concentration demand in oxy-combustion, the mixture of recycled flue gas and steam is adopted as the reduction medium in CLAS. For OXY-CCLAS (using cold recycled flue gas as oxygen releasing medium in CLAS), its net efficiency and exergy efficiency are 4.80 and 4.54% points higher than those of oxy-combustion coupled with cryogenic ASU, respectively. Meanwhile, its cost of electricity is reduced about 12.18% whilst its CO2 avoidance cost and CO2 capture cost decrease about 48.14% and 39.34%, respectively. When compared between two OXY-CLAS systems, OXY-WCLAS (utilizing warm recycled flue gas in CLAS) exhibits better performance both on thermodynamic and economic aspects. The exergy efficiency of WCLAS system is 1.29% points higher than that of CCLAS system.

Thermodynamic analysis and optimization of an oxy-combustion combined cycle power plant based on a membrane reactor equipped with a high-temperature ion transport membrane ITM

This paper presents an advanced zero emission power plant (AZEP) which is a combined cycle power plant with a membrane reactor equipped with a high-temperature ion transport membrane (ITM). The membrane reactor, which is used as a replacement for a combustor in the gas turbine, combines three functions: combustion of fuel, oxygen separation from the air in the ITM, and heating of the oxygen-depleted air. Due to the membrane reactor, the AZEP does not need an energy-consuming external air separation unit, which is a significant advantage over other types of power plants which utilize oxy-combustion technology. The presented thermodynamic model for AZEP with an advanced numeric model of the ITM allows the user to perform thermodynamic analyses for a wide range of AZEP operating parameters and to select their optimal values, without the need to determine the geometric parameters of the ITM and heat exchangers. The obtained results allow one to indicate the basic features of this carbon capture technology. The selection of AZEP operating parameters is related to the balance between the power plant’s efficiency maximization and the limitation of the ITM and heat exchangers surface areas. This manuscript also presents an analysis of the possible AZEP plant development. The development model of the E-AZEP plant assumes a number of improvements in the parameters of the ITM and the entire membrane reactor, with respect to the AZEP plant basic model. The ITM assumes an improvement in the ionic conductivity (σion) by approx. 45%, by changing the value of the conductivity coefficient (C2) as well as increasing the maximum operating temperature of the membrane from 900 °C to 1000 °C. The work demonstrated the great influence of the membrane surface. In the model of the membrane reactor, a higher flue gas temperature was assumed at the combustion chamber outlet, equal to t1g = 1600 °C, which together with the assumption of temperature approximation ΔThe.HHX = 20 K gives an air temperature t3a = 1580 °C. With the current technological possibilities, AZEP plants are competitive compared to alternative solutions, but they do not have a significant advantage over them. However, overcoming the presented limitations may allow us to achieve an advantage in terms of achieved efficiency compared to alternative CO2 capture technologies. Achieving the air temperature at the inlet to the expander, at a level close to the temperatures used in J-class gas turbines (E-AZEP plant case), allows for a decrease in the efficiency when compared to modern combined cycle power plants, at a level of 3% points.

Application of computational chemistry for adsorption studies on metal–organic frameworks used for carbon capture

Abstract Computational chemistry is invaluable in calculating macroscopic and microscopic details of systems application in chemical industries which are involved in carbon capture through precombustion, post-combustion and oxy combustion technologies. This review discusses the role of computational chemistry for adsorption studies of metal–organic frameworks (MOFs) which can be utilized for carbon capture. Principles of quantum mechanics–molecular mechanics are used to devise the electrostatic charges and isotherm parameters on the MOFs. MOFs for carbon capture which can be compatible and which can withstand the severity in chemical industries can be effectively studied using grand canonical Monte Carlo simulation by selecting appropriate force fields. Since flue gases contain a host of other gases in addition to oxides of carbon, capture by MOFs has to be carefully modelled and the software useful for this study are mentioned in this review. The simulated adsorption isotherms should be compared with experimental adsorption isotherms to validate the study. The adsorption model for carbon dioxide adsorption on MOFs is generally reported to be type I reversible isotherm and the kinetics is in good agreement with pseudo-second-order kinetics. Graphical Abstract: Graphical Abstract

Demonstrating the applicability of chemical looping combustion for the regeneration of fluid catalytic cracking catalysts

Fluid Catalytic Cracking (FCC) units are responsible for roughly 25% of CO2 emissions from oil refineries, which themselves account for 4–6% of total global CO2 emissions. Although post- and oxy-combustion technologies have been proposed for CO2 capture in FCC, Chemical Looping Combustion (CLC) may also be a potential approach that has lower energy consumption. An equilibrium catalyst (ECat) was first modified with oxidised oxygen carriers (CuO, Co3O4, Mn2O3) using wet-impregnation, and their reduced states (Cu, CoO, Mn3O4, MnO) were generated by hydrogen reduction. To demonstrate that the impregnated reduced oxygen carriers had no significant negative effects on cracking, the prepared catalysts were used to crack n-hexadecane using the standard FCC microactivity test (ASTM D3907-13). The CLC behaviour of coke deposited on the reduced oxygen carrier impregnated ECats, was investigated with the stoichiometrically required amount of oxidised oxygen carrier impregnated ECat in lab scale fixed-bed and fluidised-bed reactors equipped with an online mass spectrometer to monitor CO2 release. Although the conversion and liquid to gas ratio were largely unaffected, coke selectivity did increase with the impregnation of reduced oxygen carriers. However, this increase is mostly attributed to solvent extractable coke. It is possible to reach about 90 vol% combustion efficiency of the coke deposited on ECat using mechanically mixed with CuO and Mn2O3, but the regeneration temperature required, 800 °C, is considerably higher than that under typical regenerator conditions of 650–750 °C for 30–60 min. However, relatively high combustion efficiencies of greater than 94 vol% of the coke deposited on reduced Cu and Mn3O4 impregnated ECat were achieved with the stoichiometrically required amount of CuO and Mn2O3 impregnated ECat at 750 °C for 45 min., close to conventional FCC regenerator conditions.

Oxy-CFB combustion technology for use in power-generation applications

Implementation of circulating fluidized bed (CFB) boilers in the energy sector has witnessed a steady increase owing to their afforded advantages of operational flexibility in terms of compliance with several low-grade fuels and in-situ DeSOx and DeNOx capabilities. In recent years, the rise in global warming and development of intermittent power-generation technologies have stressed the need for development of techniques to afford high-efficiency low-emission (HELE) power-generation, effective carbon capture and storage, and flexible operation of thermal power plants. To meet these demands, the Future Energy Plant Convergence Research Center (FEP CRC) has investigated oxy-combustion technologies for CFB boilers that use low-grade fuels with calorific values <5000 kcal/kg while maintaining high operational efficiency and low pollutant emission. Of key interest in this study is the operation of the proposed system under rapid load variations over a wide operating range, including an oxy-combustion test with high oxygen concentration more than 40% within oxidants. Efforts in this regard are underway through pilot experiments performed using demonstration-scale facilities and multidimensional numerical simulations. Additionally, studies have been performed to identify materials for use in the said high-efficiency boilers and develop techniques for exhaust-system water recovery. In this paper, the current conclusions from the research activities of FEP CRC will be presented.

The influence of the oxidizing atmosphere on the mass loss of biomass pellets combusted in the inert material stream

Biomass is a renewable energy source with high growth potential due to wide availability around the world. Wood pellets are commonly used biomass for modern energy production, however, due to the growing demand, the issue of sustainable development has encouraged many entrepreneurs to produce pellets from non-wood biomass. On the one hand, the versatile nature of biomass enables its use in all parts of the world, on the other hand, this diversity makes biomass a complex and difficult fuel. Especially because of the high percentage of alkali (potassium) and chlorine in some types of biomass that can generate problems during combustion. The production and use of pellets from various types of biomass, therefore, opens up opportunities and challenges for existing technologies. In recent years, fluidized combustion technology has been considered as one of the main directions of development of professional energy in the world. Fluidized bed boilers also allow the implementation of the dynamically developing oxy-combustion technology, which perfectly fits the prevailing trends due to the key advantages of increased energy conversion, as well as the possibility of direct sequestration of carbon dioxide. During experimental research, the mass loss of individual biomass pellets of various origin combusted in a laboratory reactor with a circulating fluid layer under various conditions of the furnace chamber (oxidizing atmosphere and intensity of inert material stream) was analyzed. The obtained results allow stating that the large variety of biomass offered by suppliers requires a thorough knowledge of its properties and determination of its impact on the process and installations when used in the power industry.

Partial oxy-combustion technology for energy efficient CO2 capture process

Partial oxy-combustion is considered a promising carbon capture and storage technology that can lead to further energy penalty reductions. The presence of large amounts of CO2 in the flue gas should enhance the driven force in the bulk gas and hence the absorption performance. A novel concept known as Shift to Low Temperature configuration has been developed in order to strengthen the potentialities of partial oxy-combustion. This novel configuration aims at relaxing the operating conditions in the stripper based on the benefits – kinetics and driven force – observed in the absorption unit by means of shifting the operational CO2 cyclic capacity of the solvents towards lower energy requirements for solvent regeneration. In this work, three partial oxy-combustion operating conditions were tested in an experimental bench-scale CO2 capture facility. Results from the test campaign were further compared with both post-combustion and partial oxy-combustion at conventional operating conditions. The energy requirements were further improved as this novel configuration was applied, particularly using 118 °C as stripping temperature in combination with 60%v/v CO2 in the flue gas. Under these operating conditions, the energy penalty was reduced by 11% with respect to conventional partial oxy-combustion operation using the same flue gas composition – from 4.55 to 4.05 GJ/t CO2 using MEA 30 wt% as solvent. The energy penalty was further decreased by up to 64% in comparison with the post-combustion test. The results endorse the use of large CO2 cyclic capacity solvents to enhance the potentialities of the Shift to Low Temperature configuration for carbon capture applications.

Sensitivity and Techno-Economic Analysis of Leading Oxy-Combustion Power Cycles with Full Carbon Capture: NetPower and Supercritical CES

The increasing concern on climate change has led to global efforts to reduce carbon dioxide (CO2) in the environment. It appears that by far the largest contribution to the greenhouse effect stems from emissions of carbon dioxide CO2. A large part of the CO2 emission are produced by the combustion of fossil fuels in conventional power plants and industrial processes. However, the Carbon Capture and Sequestration (CCS) technologies have been developed to minimise the CO2 emission to the atmosphere. Three main capture technologies (pre-combustion, post-combustion and oxy-fuel combustion) have been mainly developed for solid fuels (e.g., coal, biomass) combustion systems. However, there are many gas-fired power plants and industrial process burning natural gas as a cleaner fuel. Natural gas has the lowest CO2 emissions per unit of energy of all fossil fuels at about 14 kg C/GJ, compared to oil with about 20 kg C/GJ and coal with about 25 kg C/GJ. Although gas-fired plants emit less CO2 but still to achieve the environmental goals of the Paris Agreement it is essential to develop CCS technologies for the growing gas-fired systems. Among the available technologies, turbine-based oxy-combustion cycles (Oxyturbine cycles) are one of the most suitable carbon capture technologies for the gas-fired power plants. In this technology, natural gas is burned with pure oxygen, and temperature moderation is done by Flue Gas Recirculation (FGR) so that the exhaust gas includes mainly CO2 and water vapour ready for sequestration and storage. Recent developments in oxy-combustion technology have reduced the cost of capture and made it competitive with post- combustion technology. Several oxyturbine cycles have been introduced by means of thermodynamic analysis. However, only NetPower and Supercritical CES cycles have recently proceeded to the demonstration phase. The NetPower cycle recirculates only carbon dioxide as the working fluid, and the Supercritical CES cycle uses water as its working fluid. The Supercritical CES cycle that has best efficiency among other type of CES cycles includes high, medium and low-pressure turbines (HP, MP, and LP) and the exhaust gas from the high-pressure turbine is reheated and expanded in an MP and LP. Pure oxygen is produced in an Air Separation Unit (ASU) and directly inject into the combustion chamber. The NetPower cycle includes a single turbine with high inlet pressure and a main multi-stream heat exchanger. Pure oxygen is produced in the ASU and mixed with the recycled carbon dioxide, before being introducing to the combustion chamber. Both cycles include recycling loops and carbon dioxide purification sections. These novel cycles reduce the cost for power generation with complete CO2 capture and sequestration with nearly zero emission. In this paper, The NetPower and Supercritical CES Cycles are investigated by means of process simulation and the technologies and utilised facilities compared using sensitivity analysis. Both cycles are simulated with Aspen Plus software with the same initial conditions, and the simulation results are compared with IEA 2015 report for validation. The sensitivity of both cycles are analysed with respect to the Turbine Inlet Temperature (TIT), Combustion Outlet Pressure (COP) and Heat Exchanger Approach Temperature (HET). The efficiencies are extracted for both the NetPower and CES cycles, and partial load behaviour of the cycles are investigated. The initial results show that the NetPower cycle is more sensitive to the Turbine Inlet Temperature (TIT) variations in comparison with S-CES cycle. The results of this paper provide a platform for a comprehensive techno-economical and sensitivity analysis of the NetPower and Supercritical CES Cycles as the leading Oxy-combustion power cycles with full carbon capture.

Influence of various carbon capture technologies on the performance of natural gas-fired combined cycle power plants

Carbon capture and storage (CCS) technology has been studied actively in recent years to address global warming. This paper aimed to make a consistent comparison of different capture technologies applied to the natural gas-fired combined cycle (NGCC). Multiple power plant systems based on a standard NGCC using three different carbon capture technologies (post-combustion, pre-combustion, and oxycombustion) were proposed, and their net performance was compared. The optimal pressure ratio of the oxy-combustion technology system was obtained. The variations in the net cycle performance of the three systems were compared using the specific CO2 capture. The net power of the post-combustion capture scheme is lower than that of all other systems, but it has the highest efficiency. However, its biggest disadvantage is a much lower CO2 capture rate than the oxy-combustion capture which exhibits nearly 100 % capture rate. The conclusion is that the oxy-combustion capture would provide both the highest net efficiency and power output if a high capture rate of over 92 % was required.

Experimental study on partial oxy-combustion technology in a bench-scale CO2 capture unit

The reduction of CO2 emissions from anthropogenic sources in this century will require a higher reliance on carbon capture and storage (CCS) technologies. Post-combustion based on a regenerative chemical absorption is considered a mature and close-to-market option in near and mid-term. However, the high energy penalty related to solvent regeneration and solvent degradation are two of the main drawbacks hindering the deployment of this technology. Partial oxy-combustion is considered a promising CCS technology that can substantially decrease the reboiler duty due to the increase on the CO2 partial pressure in the flue gas and hence the driving force in the absorber compared to conventional post-combustion approaches. This work explores the potentialities of partial oxy-combustion in a bench-scale CO2 capture unit to evaluate the benefits on the CO2 separation stage. The experimental facility consists of a regenerative CO2 chemical absorption process with a CO2 removal capacity of 0.48 kg/h. The most relevant operating parameters such as temperature, CO2 loading and L/G ratios were evaluated under variations of the CO2 concentration of the flue gas, ranging between 15%v/v and 60%v/v CO2, in order to obtain the optimal reboiler duty associated to the solvent regeneration. Results showed that the use of four packing bed improved the CO2 absorption performance. Although the optimal L/G ratios were moved to higher values, they also achieved CO2 removal efficiencies over 95% and lower energy consumptions compared with the baseline case (post-combustion). Experiments carried out using a 60%v/v CO2 in the flue gas provided 95.7% of CO2 removal efficiency and the lowest reboiler duty (4.74 GJ/t CO2) which resulted in a 57% reduction of the specific energy consumption compared with the post-combustion run.

Investigation of Applicability of Polyimide Membranes for Air Separation in Oxy-MILD Zero-Emission Power Plants

Primary element of an oxy-combustion plants is ambient air separation unit. This paper presents the results of experimental research concerning the parameters of the separation of N2/O2 from ambient air, using capillary polymer membranes, potentially applicable in oxy-combustion technology, under variable operational conditions. Collected data were utilized to approximate continuous functions describing the variability of essential parameters of the air separation based on such membranes. The functions were introduced to develop a complete mathematical model of the separation unit, intended to be applied in oxy-Moderate or Intense Low Oxygen Dilution (oxy-MILD) zero-emission plants. Computational analyses were performed for three variants of the unit’s configuration: serial connection of membrane modules, unit with retentate recirculation and unit with permeate recirculation. The results of the research, in the form of sets of characteristic curves, depicting parameters of the separation process as a function of the variable operational conditions, show that crucial differences to the subsequent separation parameters (permeate purity, real selectivity coefficient, recovery coefficient) and with regard to the power consumed, were obtained. The highest parameters of the module were gained for serial connection, whereas the lowest – for permeate recirculation. The lowest energy consumption was acquired for the retentate recirculation variant.

Oxy-combustion of agro and wood biomass in a fluidized bed

Present trends in the global energy sector effectively drive the development of technologies using renewable energy sources and the improvement of combustion technology towards increasing its efficiency and removing environmentally harmful flue gases. One solution is to replace fossil energy sources with renewable sources, including biomass. The degree of biomass utilization depends on the size of resources and processing technology. There are more and more different types of biomass on the market. There are many technologies for its energetic use. In recent years, fluidized combustion technology has been considered as one of the main directions of development of professional energy in the world. Many units in the world in fluidized combustion technology use as primary or supplementary fuel: sludge, wood waste and biomass, as well as municipal waste, etc. Fluidized bed boilers also allow the implementation of the dynamically developing oxy-combustion technology, which perfectly fits the prevailing trends due to the key advantages of increased energy conversion, as well as the possibility of direct sequestration of carbon dioxide. During experimental research, the mass loss of biomass pellets of various origins was analyzed in an oxidizing and inert atmosphere in a two-phase flow with the use of inert material. The obtained results allow to state that the large variety of biomass offered by suppliers requires a thorough knowledge of its properties and determination of its impact on the process and installations when used in the power industry.