Near-zero Emissions Research Articles

Gas switching reforming for flexible power and hydrogen production to balance variable renewables

Variable renewable energy (VRE) is expected to play a major role in the decarbonization of the electricity sector. However, decarbonization via VRE requires a fleet of flexible dispatchable plants with low CO2 emissions to supply clean power during times with limited wind and sunlight. These plants will need to operate at reduced capacity factors with frequent ramps in electricity output, posing techno-economic challenges. This study therefore presents an economic assessment of a new near-zero emission power plant designed for this purpose. The gas switching reforming combined cycle (GSR-CC) plant can produce electricity during times of low VRE output and hydrogen during times of high VRE output. This product flexibility allows the plant to operate continuously, even when high VRE output makes electricity production uneconomical. Although the CO2 avoidance cost of the GSR-CC plant (€61/ton) was similar to the benchmark post-combustion CO2 capture plant under baseload operation, GSR-CC clearly outperformed the benchmark in a more realistic scenario where continued VRE expansion forces power plants into mid-load operation (45% capacity factor). In this scenario, GSR-CC promises a 5 %-point higher annualized investment return than the post-combustion benchmark. GSR-CC therefore appears to be a promising concept for a future scenario with high VRE market share and CO2 prices, provided that a large market for clean hydrogen is established.

Achieving Near-Zero Methane Emissions Coal Mining

Achieving Near-Zero Methane Emissions Coal Mining

Fuzzy Rule-Based and Particle Swarm Optimisation MPPT Techniques for a Fuel Cell Stack

The negative environmental impact and the rapidly declining reserve of fossil fuel-based energy sources for electricity generation is a big challenge to finding sustainable alternatives. This scenario is complicated by the ever-increasing world population growth demanding a higher standard of living. A fuel cell system is able to generate electricity and water with higher energy efficiency while producing near-zero emissions. A common fuel cell stack displays a nonlinear power characteristic as a result of internal limitations and operating parameters such as temperature, hydrogen and oxygen partial pressures and humidity levels, leading to a reduced overall system performance. It is therefore important to extract as much power as possible from the stack, thus hindering excessive fuel use. This study considers and compares two Maximum Power Point Tracking (MPPT) approaches; one based on the Mamdani Fuzzy Inference System and the other on the Particle Swarm Optimisation (PSO) algorithm to maintain the output power of a fuel cell stack extremely close to its maximum. To ensure that, the power converter interfaced to the fuel cell unit must be able to continuously self-modify its parameters, hence changing its voltage and current depending upon the Maximum Power Point position. While various methods exist for Maximum Power Point tracker design, this paper analyses the response characteristics of a Mamdani Fuzzy Inference Engine and the Particle Swarm Optimisation technique. The investigation was conducted on a 53 kW Proton Exchange Membrane Fuel Cell interfaced to a DC-to-DC boost converter supplying 1.2 kV from a 625 V input DC voltage. The modelling was accomplished using a Matlab/Simulink environment. The results showed that the MPPT controller based on the PSO algorithm presented better tracking efficiency as compared to the Mamdani controller. Furthermore, the rise time of the PSO controller was slightly shorter than the Mamdani controller and the overshoot of the PSO controller was 2% lower than that of the Mamdani controller.

Near-zero emissions with high thermal efficiency realized by optimizing jet plume location relative to combustion chamber wall, jet geometry and injection timing in a direct-injection hydrogen engine

Thermal efficiency was substantially improved and NOx emissions were reduced to a level at a single-digit ppm with PCC combustion by optimizing such characteristics as the direction, number and diameter of the injected jet and controlling the injection timing and also by combining with combustion of lean mixture. Output power declined by lean mixture was recovered by supercharging in keeping NOx emissions remained at the same level, while thermal efficiency was improved furthermore by slightly re-optimizing jet conditions. As a result, hydrogen engine which does not emit any CO2 and particulate matter in principle is worth to be called near-zero emission engines in both name and reality.

Study on the integrated system of LNG oxy-fuel power plant and the application of supercritical CO2

With the increasing acceleration of urbanization, the amount of urban sewage is raising dramatically. Supercritical CO2 extraction is a promising method for wastewater treatment, and how to obtain supercritical CO2 with low cost has become a hot issue. In this work, the liquefied natural gas (LNG) oxy-fuel combustion power system integrated with supercritical CO2 wastewater treatment process was proposed to realize near-zero CO2 emissions and sewage disposal. The captured CO2 was partly transformed to supercritical CO2 and further applied to wastewater treatment process, which significantly reduced the cost of sewage treatment. The parametric analyses of gas turbine discharge pressure and the amount of treated sewage on the system efficiency were carried out. The results showed that the optimal gas turbine discharge pressure was 0.1 MPa, and the corresponding gross power generation efficiency was 0.69. The amount of treated sewage directly affected the system efficiency. The upper limit amount of treated sewage was 32 t/h with the supercritical CO2 flow rate of 5000 kmol/h when the captured CO2 was not utilized in the wastewater treatment. When the sewage amount to be processed exceeded this value, the liquid CO2 stored in the tank was utilized. As the treated sewage flow rate increased, the corresponding power generation efficiency loss showed an increment. When the mass flow rate of treated sewage was 32 t/h, the net power generation efficiency was 0.47 under the optimized conditions, and the corresponding exergy efficiency was 0.38. The near-zero carbon emissions and low cost wastewater treatment were achieved in the proposed system.

Thermodynamic analysis of a novel oxy-combustion supercritical carbon dioxide power cycle integrating solar-driven coal gasification

To advance the utilization of both coal resources and solar energy, a novel oxy-combustion supercritical carbon dioxide (sCO2) power cycle with solar-driven coal gasification integration was proposed and analyzed. In the proposed system, the concentrated solar energy is utilized for coal gasification to produce syngas for oxy-combustion to drive sCO2 power cycle with near-zero emission and the heat from air separation and hot syngas is recovered for coal drying, steam generation and sCO2 heating in a cascade way. Through introducing solar heat for coal gasification, the raw coal consumption is reduced and the oxygen production process can be eliminated, leading to a higher net system efficiency. The oxy-combustion power cycle can also be simplified owing to the better matching between the process waste heat and the steam generation for gasification. Detailed thermodynamic analysis showed that, the proposed system can save 28.3% of coal consumption with the net efficiency improvement of 1.6 percentage points, compared with the reference system. The solar-to-electricity efficiency can also reach as high as 23.3%.

A methodological review on material growth and synthesis of solar-driven water splitting photoelectrochemical cells.

As a renewable and sustainable energy source and an alternative to fossil fuels, solar-driven water splitting with photoelectrochemical (PEC) cell is a promising approach to obtain hydrogen fuel with its near-zero carbon emission pathway by transforming incident sunlight, the most abundant energy source. Because of its importance and future prospects, a number of architectures with their own features have been formed by various synthesis and growth methods. Because the materials themselves are one of the most dominant components, they determine the solar-to-hydrogen efficiency of the PEC cells. Thus, several representative PEC cells were reviewed by categorizing them as per synthesis and/or growth methods such as physical vapor deposition, chemical vapor deposition, electrochemical deposition, etc. This review provides researchers with an overview and acts as a guide for research on solar-driven water splitting PEC cells.

Blue skies over China: The effect of pollution-control on solar power generation and revenues.

Air pollution is the single most important environmental health risk, causing about 7 million premature deaths annually worldwide. China is the world’s largest emitter of anthropogenic air pollutants, which causes major negative health consequences. The Chinese government has implemented several policies to reduce air pollution, with success in some but far from all sectors. In addition to the health benefits, reducing air pollution will have side-benefits, such as an increase in the electricity generated by the solar photovoltaic panels via an increase in surface solar irradiance through a reduction of haze and aerosol-impacted clouds. We use the global aerosol-climate model ECHAM6-HAM2 with the bottom-up emissions inventory from the Community Emission Data System and quantify the geographically specific increases in generation and economic revenue to the Chinese solar photovoltaic fleet as a result of reducing or eliminating air pollution from the energy, industrial, transport, and residential and commercial sectors. We find that by 2040, the gains will be substantial: the projected solar photovoltaic fleet would produce between 85–158 TWh/year of additional power in clean compared to polluted air, generating US$6.9–10.1 billion of additional annual revenues in the solar photovoltaic sector alone. Furthermore, we quantify the cost of adopting best-practice emission standards in all sectors and find that the revenue gains from the increased solar photovoltaic generation could offset up to about 13–17% of the costs of strong air pollution control measures designed to reach near-zero emissions in all sectors. Hence, reducing air pollution in China will not only have clear health benefits, but the side-effect of increased solar power generation would also offset a sizeable share of the costs of air pollution control measures.

Techno-economic analysis of solar-assisted post-combustion carbon capture to a pilot cogeneration system in Mexico

This research evaluates the integration of solar-assisted post-combustion carbon capture into an experimental cogeneration system. A cogeneration system modelled in Thermoflex 25® that includes a 200 kW Capstone microturbine coupled with a thermal oil recovery system was installed at the National Institute of Electricity and Clean Energies (INEEL). Three optimized systems were considered for the economic analysis, namely: a microturbine cogeneration system (COGEN), a microturbine cogeneration system with post-combustion carbon capture plant (COGEN-CCS) and a microturbine cogeneration system with solar-assisted post-combustion carbon capture (COGEN-CCS + SOLAR). The cogeneration system was modelled using Natural Gas (NG) as fuel, applying characteristics typical of Mexico, to obtain the composition of exhaust gas (EG), and thus simulate the CO2 capture system in Aspen Hysys V8.6® using monoethanolamine (MEA) as solvent. Results show that the implementation of CCS results in a sizeable increase in the Levelized Cost Of Electricity (LCOE) (approximately 86%) with near-zero emissions and without the possibility of supplying energy to the process. In addition COGEN-CCS + SOLAR improves overall system performance. CO2 emissions per kilowatt increased by 0.2% with regard to COGEN-CCS, while the LCOE increased by 230% compared to the COGEN case, with near-zero emissions. The use of solar energy would help increase the cogeneration efficiency when coupled with CO2 capture.

Transitioning to low-carbon suburbs in hot-arid regions: A case-study of Emirati villas in Abu Dhabi

The continued and global popularity of single-family homes indicates that a scalable, yet regionally appropriate strategy for achieving zero-carbon suburban development is needed in the coming decades. This need is especially critical in the hyper-arid region around the Arabian Gulf where per-person carbon emissions are among the highest in the world. Using geometrically sensitive simulation models for a household's building energy, water, and automobile use, this paper uses Emirati neighborhoods in Abu Dhabi, UAE as a case study to estimate emissions for a baseline and set of future possible scenarios towards transitioning single-family households in the region to low, and eventually near-zero operational carbon emissions. An analysis of the combined impact of energy efficiency gains through (1) technology adoption and better design, (2) carbon intensity reduction from renewable energy transitions, and (3) carbon sequestration from parcel scale tree planting is presented. From a baseline CO2 emissions of 64.3 tons per household per year for new construction, the study finds future emissions potential reductions of 33.7%–49.0% from improved house design, 98.1% from electrification and solar energy sourcing, and 99.4% from combined design and technology improvements. This study also finds that if the water-energy nexus in Abu Dhabi transitioned to solar-powered, reverse-osmosis desalination, trees would become net carbon sinks (0.6–1.9 kg CO2/m2/yr). As a result, in the future, low-density neighborhoods with dense areas of tree planting may become a sustainable housing typology when measured by net operational emissions. This fact would upend multiple current assumptions by Western planners about sustainable transitions for arid regions.

Introducing a hybrid oxy-fuel power generation and natural gas/ carbon dioxide liquefaction process with thermodynamic and economic analysis

Oxy-fuel power generation and carbon dioxide capture as a downstream process is a near-zero emission energy system. The captured carbon dioxide can be liquefied but carbon dioxide liquefaction process needs considerable amounts of energy. Liquefied natural gas plays an important role in natural gas transportation. However, its production is known as an energy-intensive process. In this study, a novel integrated process of liquefied natural gas production, oxy-fuel electrical power generation cycle and cryogenic carbon dioxide capture and liquefaction is proposed and investigated by chemical process simulators. Effective operating parameters of the process and its components are thermodynamically analyzed. In this regard, effect of the turbine inlet temperature and pressure ratio, oxidant, oxygen and propane flow rates on the power generation and electrical efficiency of the oxy-fuel cycle, carbon dioxide liquefaction temperature and pressure and liquefied natural gas production rate are examined. The obtained results indicate that, the proposed process can be used to design of the actual plants with optimal operating performance. Specific power consumption of the liquefied natural gas process is about of 0.281 kWh/kg LNG. Also, to verify the accuracy of the process performance, the exergy analysis was performed for the process and all of its components. Through this analysis the exergy efficiency of the oxyfuel power cycle and natural gas liquefaction process are gained 69% and 51% respectively. Economic analysis of the process shows that prime cost of the product and period of return are 0.299US$/kgLNG and 2.392 years respectively.

Influence of H2O phase state on system efficiency in O2/H2O combustion power plant

In this work, oxy-fuel combustion with H2O as diluent in natural gas power plant is proposed, and the effect of phases of H2O on the overall system efficiency is investigated. Three different phase states of H2O, liquid water, steam and liquid-steam mixture are investigated, and the corresponding systems GST-L, GT-S and GT-M system are simulated and compared. To overcome the problem that the steam Rankin cycle cannot fully utilize the latent heat of water, the transcritical CO2 (T-CO2) cycle is introduced. The thermal analysis results show that the GT-M system with steam-water mixture as diluent performs the best, and the energy and exergy efficiency is 60.86% and 49.29%, respectively. The GST-L system takes the second place, and the GT-S system shows the lowest efficiency. The results reveal that steam-water mixture is the best phase of H2O recycled to control the combustion temperature, and the integration of gas turbine and T-CO2 cycle can fully utilize the thermal energy of flue gas to generate electricity. Therefore, the high-efficiency power generation with near-zero carbon emissions is achieved.

Effects of silicoaluminate oxide and coal blending on combustion behaviors and kinetics of zhundong coal under oxy-fuel condition

Oxy-fuel combustion of high-alkali coal is beneficial for near-zero emission of pollutants in power plants and has the potential for extensive, efficient, and safe utilization of Zhundong coal in future. The present work was performed on oxy-fuel combustion of Zhundong coal, while the effects of silicoaluminate oxide and coal blending on oxy-fuel combustion characteristics and kinetics of high-alkali coal were further studied using thermogravimetric analysis. The thermogravimetric curves of Zhundong coals present two obvious stages but the contrastive coals are different. The increase in oxygen content weakens the impact of coal property on oxy-fuel combustion behavior of high-alkali coal. The addition of Al2O3 and kaolin results in a slight decline of the peak combustion rate, while the influences of SiO2 and diatomite additives are negligible. The additive fraction of silicoaluminate oxide gives rise to a non-monotonic impact on combustion characteristics of Zhundong coal. The interaction effect within blended coal could cause a reduction in reaction rate during the intense combustion stage, while its influence on kinetics is intensified during the later stage of oxy-fuel combustion. The impact extent of silicoaluminate oxide and coal blending on oxy-fuel combustion kinetics of high-alkali coal is highly associated with additive species and individual coals.

Advanced Cooling in Gas Turbines 2016 Max Jakob Memorial Award Paper

Gas turbines have been extensively used for aircraft engine propulsion, land-based power generation, and industrial applications. Power output and thermal efficiency of gas turbines increase with increasing turbine rotor inlet temperatures (RIT). Currently, advanced gas turbines operate at turbine RIT around 1700 °C far higher than the yielding point of the blade material temperature about 1200 °C. Therefore, turbine rotor blades need to be cooled by 3–5% of high-pressure compressor air around 700 °C. To design an efficient turbine blade cooling system, it is critical to have a thorough understanding of gas turbine heat transfer characteristics within complex three-dimensional (3D) unsteady high-turbulence flow conditions. Moreover, recent research trend focuses on aircraft gas turbines that operate at even higher RIT up to 2000 °C with a limited amount of cooling air, and land-based power generation gas turbines (including 300–400 MW combined cycles with 60% efficiency) burn alternative syngas fuels with higher heat load to turbine components. It is important to understand gas turbine heat transfer problems with efficient cooling strategies under new harsh working environments. Advanced cooling technology and durable thermal barrier coatings (TBCs) play most critical roles for development of new-generation high-efficiency gas turbines with near-zero emissions for safe and long-life operation. This paper reviews basic gas turbine heat transfer issues with advanced cooling technologies and documents important relevant papers for future research references.

Chasing shadows: technology and socioeconomic barriers versus climate targets for iron and steel industry

Purpose: To analyse the potential of various scenarios for reduction of carbon footprint of iron and steel sector and to reveal plausible pathways for modernisation. Design/methodology/approach: Several scenarios have been developed in order to assess the dynamics and extent of decarbonisation required to meet the global climate change mitigation target. This includes deployment of the best available technologies, increased share of secondary steel production route and deployment of innovative ironmaking technologies with various decarbonisation extent achieved in a variable timeframe. Findings: The window of opportunities to ensure compliance of steel sector development with climate goal still exists though shrinks. Modernisation shall include global deployment of best available technologies, increased share of secondary steel production and rapid deployment of innovative technologies including carbon capture and storage. Delayed modernisation will require much deeper decarbonisation, which will increase the total cost of mitigation. International policies shall be put in place to ensure availability of funding and to assist technology transfer. Short term transition strategies shall be employed as soon as possible for bridging long term climate change mitigation strategies and current state of the iron and steel industry worldwide. Research limitations/implications: Methodology applied takes into account the best available technologies and some novel ironmaking methods with the potential for commercialisation during the next decade; however, it is implied that the radically innovative iron- and steelmaking technologies with near-zero CO2 emissions will not be mature enough to deliver tangible impact on the sector’s carbon footprint before 2050. Practical implications: Obtained results can be helpful for definition of the modernisation strategies (both state-level and corporate) for the iron and steel industry. Originality/value: Dynamics and extent of decarbonisation required to meet global climate change mitigation targets have been revealed and the results can be valuable for assessment of the consistency of sectoral climate strategies with global targets.

Situation and measures of China’s CO2 emission mitigation after the Paris Agreement

Global response to climate change has entered the phase of full implementation of the Paris Agreement. To control the global temperature rise below 2°C, all countries must make more efforts to reduce emission. China has combined its goal of emission reduction for combating climate change with its domestic sustainable development strategy to promote energy revolution and the transition of economic development to low-carbon patterns. Through reinforcing the commitment and action before 2020, the CO2 intensity of GDP can decrease by more than 50% by 2020 compared with that of 2005, and the external commitment target of a 40%–45% decrease can be over fulfilled. Currently, under the new economic normal, China further strengthens the policy measure, vigorously saves energy, enhances energy use efficiency and the economic output benefit, and simultaneously develops new and renewable energy and accelerates energy structural decarbonization, so that the annual decrease rate of the CO2 intensity of GDP keeps a high level of more than 4% and remains increasing. Thus, the decrease rate of the CO2 intensity of GDP will exceed the GDP growth rate, and then CO2 emission will peak around 2030. This will promote the fundamental turning of economic development mode, and lay a foundation for the establishment of a sustainable energy system with near-zero emissions and with new and renewable energy as the main body in the second half of this century. China implements the concept of green low-carbon development and accelerates the low carbon transition of energy and economy to achieve win-win results in economic growth and CO2 emission mitigation, and these policies and actions will also provide experiences for many other developing countries. On the other hand, China will continue to play a positive and constructive leading role in the implementation of the Paris Agreement internationally, and promote the construction of new mechanisms of win-win cooperation, fairness and justice and common development for global climate governance. Moreover, China will make an effort to build a community of common destiny for mankind, promote pragmatic cooperation among countries, especially among developing countries, and take combating climate change as a new development opportunity for jointly moving toward climate-friendly low-carbon economic development path.

DOE funds two SOFC projects at Mohawk, West Virginia

The US Department of Energy's Office of Fossil Energy has selected two projects to receive $2.8 million in federal funding for cost-shared research & development of solid oxide fuel cell technology for cost-competitive, fossil-based power generation with near-zero emissions.

Thermodynamic analysis of a novel dual expansion coal-fueled direct-fired supercritical carbon dioxide power cycle

The direct-fired supercritical CO2 power cycle not only has the potential of reaching high efficiency but also has inherent ability to capture almost all of the combustion derived CO2. A novel direct-fired supercritical CO2 power cycle layout is proposed in this paper, using the syngas produced by coal gasification as the fuel. The proposed cycle layout is specially designed to facilitate heat integration between the power cycle, the fuel conversion process and other auxiliary subsystems. Heat from the air compressor intercooler and the low temperature syngas is introduced to the regenerator to correct its imbalanced heat exchange, a typical problem of the supercritical CO2 power cycle that is caused by the abrupt physical property variation. Design considerations of the proposed cycle layout are discussed in detail. The result shows that the net efficiency is 42.1%, with near-zero CO2 emissions. The proposed cycle layout is then further modified by integrating more heat from the oxygen compressors and the syngas compressor, which reduces the hot end temperature difference of the regenerator to less than 10 °C and increases the net efficiency to 43.7%. Heat integration through novel cycle layout has been proved essential to guarantee the high efficiency of the supercritical CO2 power cycle.

Chemical kinetics simulation of semi-dry dechlorination in coal-fired flue gas

HCl in coal-fired flue gas has adverse impact on the environment, equipment, and the flue gas desulfurization (FGD) system. The existence of HCl also increases the difficulty of the treatment of desulfurization waste water. Semi-dry dechlorination technology is put forward to attach chlorine to fly ash by spraying in alkaline solution. Simultaneously, desulphurization waste water is used as the solvent of alkali, and this could help realize the target of near-zero emission of desulfurization waste water. CHEMKIN is used to build a chemical kinetics model, which is based on the measured components of flue gas in a coal-fired power plant. NaOH is set as the alkali absorbent in the model. Both the competitive relationship of SO2 and HCl and the effects of different factors on HCl reaction efficiency are analyzed. SO2 with high concentration would compete for more NaOH, but when Na/Cl (ratio in mole) is 1, the reaction efficiency of HCl achieves 22.28%, and it is positively correlated with Na/Cl. When Na/Cl surpasses 5, the reaction efficiency of HCl increases to beyond 70%. As Na/Cl continues to increase, there is a slower growth of HCl reaction efficiency and it finally achieves 100% when Na/Cl reaches 12. With a fixed value of Na/Cl, a change of 1000 mg/m3 in SO2 concentration would change the reaction efficiency of HCl about 13%. The effect of flue temperature on HCl reaction efficiency is not significant. Acid gases in flue gas react with NaOH completely in 0.1 s and come to equilibrium after about 1 s.

Release and Transformation Behaviors of Sodium, Calcium, and Iron during Oxy-fuel Combustion of Zhundong Coals

Zhundong coal has attracted an increasing concern due to its super-huge reserve but high content of alkali metals. Oxy-fuel combustion of Zhundong coal benefits the near-zero emission of pollutants in coal-fired power plants and promotes the large-scale utilization of high-alkali coal. However, few efforts if any have been conducted on oxy-fuel combustion of Zhundong coal. The previous studies related to Zhundong coal were mainly focused on sodium behaviors but little work has been performed on calcium and iron, while calcium and iron are very likely to generate significant influences on fouling problems in combustion of Zhundong coal. The present study aimed to elucidate the release and transformation behaviors of sodium, calcium, and iron in oxy-fuel combustion of Zhundong coal using a fixed-bed reactor. Experimental results indicated that calcium in Zhundong coal was mainly present as ammonium acetate-soluble form, while the iron existed in forms of hydrochloric acid-soluble and insoluble. With the inc...