Near-zero Emissions Research Articles

Solar hydrogen production: Techno-economic analysis of a parabolic dish-supported high-temperature electrolysis system

The roadmap for the hydrogen uptake passes through the development of near-zero emission and/or renewable technologies for hydrogen production. This is the rationale for the investigation of renewable power-to-fuel, namely the coupling between high temperature electrolysis and concentrating solar power. The proposed plant is conceived to supply hydrogen for a small refuelling station. It is based on solid oxide electrolyser cell technology, which performs water electrochemical reduction, in order to produce a target of 150 kgd−1 of hydrogen. The plant is integrated with a parabolic dish solar field designed to provide both electricity and thermal energy, necessary for the electrolysis reaction to take place. Specifically, a modular multi-dish configuration is selected, in which electric power is produced by 30kWel solarized micro-gas turbines placed in the dishes’ focus. In addition to considering a pure renewable power input, a hybridization with natural gas is considered to face the variability of solar resource. Once a yearly H2 yield is estimated, a preliminary economic analysis is carried out and the levelised cost of hydrogen is subsequently obtained. It is found that the system can be operated at a nominal solar-to-hydrogen efficiency above 30%, with a solid oxide electrolysis cell efficiency around 80%. In hybrid conditions, 10 parabolic dishes (9 generating electricity through the micro-gas turbines, 1 supplying heat to the solid oxide electrolysis cell) are needed to produce the target 150 kgd−1 of hydrogen. In conclusion, the competitiveness of the plant is evaluated in comparison with other solar fuels technologies.

Advanced part-load control strategies for the Allam cycle

The Allam Cycle is a highly regenerative oxy-combustion cycle with very promising net electrical efficiency, low expected cost and near-zero emissions (being directly suitable for carbon capture and storage). In this cycle, the CO2 produced from the oxy-combustion is recycled as temperature moderator and the excess CO2 produced can be captured and stored. In this work, a detailed part-load model of the Allam Cycle is developed considering the off-design performance maps for the compressors, pumps and the turbine. To adjust the cycle load, different part-load control strategies are devised by combining turbine partial-admission, compressor variable guide vanes (at compressor inlet and diffuser) and minimum cycle pressure variation. These control strategies are compared at various part-load conditions ranging from 90% down to 20%. The study shows that the optimal control strategy varies depending on the cycle load. Furthermore, the increase of part-load cycle efficiency using advanced control strategies can reach up to 4.71 percentage points compared to a conventional strategy employing only variable compressor guide vanes. The research shows that close-to-maximum part-load efficiency can be achieved only with the optimized adjustment of compressors guide vanes and the minimum cycle pressure, while partial admission turbine turns out to be essential at very low loads (15–30% load).

Selective catalytic reduction (SCR) fault detection

Diesel vehicles have caused serious environmental problems in China. Hence, the Chinese government has launched serious actions against air pollution and imposed more stringent regulations on diesel vehicle emissions in the latest China VI standard. To fulfill this stringent legislation, two major technical routes, including the exhaust gas recirculation (EGR) and high-efficiency selective catalytic reduction (SCR) routes, have been developed for diesel engines. Moreover, complicated aftertreatment technologies have also been developed, including use of a diesel oxidation catalyst (DOC) for controlling carbon monoxide (CO) and hydrocarbon (HC) emissions, diesel particulate filter (DPF) for particle mass (PM) emission control, SCR for the control of NOx emission, and an ammonia slip catalyst (ASC) for the control of unreacted NH3. Due to the stringent requirements of the China VI standard, the aftertreatment system needs to be more deeply integrated with the engine system. In the future, aftertreatment technologies will need further upgrades to fulfill the requirements of the near-zero emission target for diesel vehicles.

Comprehensive kinetic study of combustion technologies for low environmental impact: MILD and OXY-fuel combustion of methane

The development of processes with near-zero emissions such as MILD, flameless, and OXY-fuel combustion are of great interest in various energy scenarios. The assessment and design of new burners to meet energy demands and pollution reduction strongly depends on an accurate description of the chemistry involved in the combustion process. The main outcome of this study is the collection and review of a vast amount of experimental data on MILD and OXY-fuel combustion of methane that have been reported in recent years, together with a thorough kinetic analysis to identify aspects of the mechanism that requires further revision. The CRECK core model presented here is developed upon the Aramco 2.0 mechanism [1], and further extends the validation objectives to MILD and OXY fuel combustion conditions. The aim of this work is not only the mechanism validation but also a better understanding of the combustion characteristics and critical reaction pathways in MILD, flameless, and OXY-fuel combustion.

Near-zero emission coal-fired power plant using advanced KM CDR process™

CCS is expected to be one of the major measures contributing to carbon reduction and meet net zero emission in near future. Fossil fuel power plants equipped with CCS can be considered to be zero-carbon power generation if nearly full CO2 recovery is feasible. The objective of this paper is to investigate the process performance and plant economics at 99.5% CO2 capture ratio that has not been studied before using MHIENG’s CO2 capture technology. It is expected that this work using experiences and empirical data that MHIENG has accumulated is more indicative of current commercial CCS technology and economics than previous work. The near-zero emission design proposed in this work using 50% additional absorption packing achieves 99.5% capture ratio with similar normalized OPEX ($/tonne CO2) and 6% higher normalized CAPEX compared to base case at 90% capture ratio. Near-zero emission coal-fired power plant is technically feasible using the Advanced KM CDR Process™ and KS-1™ solvent and will increase cost of CO2 captured by 3% compared to default design at 90% capture ratio.

Techno-economic analysis of the effects of heat integration and different carbon capture technologies on the performance of coal-based IGCC power plants

Coal-based Integrated Gasification Combined Cycle (IGCC) power plants show obvious gains over conventional pulverized coal power plants by achieving higher efficiency, lower carbon emissions and lower energy penalty for incorporating different carbon capture and storage (CCS) technologies. However, due to the lack of standardised designs, current IGCC-CCS projects are hindered by higher capital expenditures limiting their commercial implementation. Therefore, the key challenge is carrying out a techno-economic optimisation of IGCC-CCS power plants to ensure compatible power generation efficiency and accessibility. This study aims to optimise the performance of a coal-based IGCC plant with two different CCS technologies (double-stage Selexol absorption cycle and Ni-based chemical looping combustion (CLC) process) through intensive process simulation, heat integration and economic analysis. Heat integration has increased the net plant efficiency by more than 12% and decreased the levelised cost of electricity (LCOE) no less than 5 cents kWh−1. The CLC technology offered near-zero carbon emissions with higher plant efficiency and lower value of LCOE. Decreasing the CO2 capture rate by Selexol caused a decrease in LCOE and an increase in the corresponding CO2 specific emissions. Therefore, an appropriate decarbonisation scenario depends on a trade-off between the degree of carbon capture and the allowed CO2 specific emissions.

Can Governments Ban Materials with Large Carbon Footprint? Legal and Administrative Assessment of Product Carbon Requirements

This paper explores whether governments can ban carbon-intensive materials through product carbon requirements. By setting near-zero emission limits for the production of materials to be sold within a jurisdiction, governments would accelerate the phase out of carbon-intensive production processes. Their announcement could alert basic materials producers, financing institutions, and other relevant stakeholders, thus incentivising them to prepare for this shift by dedicating their innovation efforts and investments to climate friendly production processes and low-carbon materials. The paper analyses various product standards and technical regulations in the European context. The analysis of these standards and technical regulations offers an overview of the types of environmental requirements that the European Union has already adopted. Therefore, it provides a case study of the political, legal, and technical backgrounds for the development of product carbon requirements, both in the EU and beyond. Second, the paper presents an analysis of the provisions in WTO law that would apply to product carbon requirements, underlining the legal arguments in support of their adoption under international trade law.

Strategic Plan Method for Future Renewable Energy Technologies

In transmitting towards secure, clean, and efficient energy, the world requires to develop the future renewable energy technologies that contribute to reducing energy consumption and carbon footprint and enabling near-zero CO2 emissions. A number of complex factors such as performance limitations, innovation, industry rivalry, and competition can hasten technological change, and they must be watched closely to succeed in developing a vision for the new technology implementation. Numerous efforts have been focused on formulating a strategic plan for energy. However, there is limited consideration of the development of a strategic plan method for future renewable energy technologies. This study aimed to develop a strategic plan method to decide more appropriate and applicable renewable energy technologies. Development of the method for strategic planning requires an integrative approach taken from strategic management and planning concepts, technology innovation, as well as related knowledge in renewable energy technologies. Conceptual research methods are used to conduct the present study. The strategic plan method would assist the key decision-makers in developing a strategic plan to select more efficient, cost-competitive, and appropriate renewable energy technologies according to the real needs and desires of the community.

Sharing Cities: from vision to reality. A people, place and platform approach to implement Milan's Smart City strategy

Transforming Milan in a city is a strategic objective and political priority of the Municipality, which has taken up a variety of projects and experiments with the aim to transform the main suburbs of the city in areas. This paper presents Milan’s demonstration of a district allowed by the EU funded project “Sharing Cities”, aimed at creating a smart district with near-zero emissions in three different “lighthouse” cities, London, Lisbon, and Milan. The paper describes the first outcomes of such project in Milan, obtained through a variety of tools and actions based on a People, place and platform approach, aimed at involving the different stakeholders and applying solutions to foster innovation processes instrumental to the implementation of a city urban agenda.

Thermodynamic analysis of a Na-O-H thermochemical cycle coupled to a Gas Turbine Modular Helium Reactor (GT-MHR)

Hydrogen (H2) is considered a clean fuel because its combustion releases heat, water and near-zero carbon emissions. This substance can be produced through many routes, including thermochemical cycles in which water molecules are splited into oxygen and hydrogen through specific chemical reactions supported by an appropriate heat source at specific temperature conditions. There are a wide variety of thermochemical cycles under development, many of them require temperatures higher than 1000°C while others, like the cycles U-Eu-Br, Mg-Cl and Cu-Cl can operate below 550°C. The reduction in the temperature levels of a thermochemical process allows the use of various energy options, facilitating H2 production. So, the main aim of the paper is to analyze hydrogen production according to the Na-O-H thermochemical process whose required heat is supplied by a Gas Turbine Modular Helium Reactor (GT-MHR), a nuclear power plant (NPP) with low cost and low carbon emissions. The Na-O-H is a fresh chemical process that can operates at temperatures close to 400°C. The system will be studied in the software Engineering Equation Solver (EES) according to the first and second laws of thermodynamics. The results indicate that such system can produce around 3.654 kg/s of H2 considering a mass flow rate of 500 kg/s of helium coolant at 850°C coming from GT-MHR.

Inventory and fleet purchase decisions under a sustainable regulatory environment

ABSTRACTThis work studies the direct impacts of environmental policies on logistics practices. Specifically, the authors estimate the potential changes in inventory and fleet purchase decisions under a set of policies designed to improve the environmental efficiency of transport activities, through a reduction of overall transportation emissions; and requirements for a fleet mix to include zero and near-zero emission vehicle technologies, or, minimum vehicle type shares. The work introduces a constrained stochastic multi-objective joint replenishment problem (S-MJRP) to evaluate the policies while considering logistics costs and emissions as objectives. Moreover, the authors developed a solution algorithm and conducted empirical analyses. The results highlight the trade-off between capital investments in zero-emission vehicles and the logistics costs required to abide by the requirements of the mentioned regulatory policies. The results provide insights for both private and public stakeholders as they consider the logistics challenges and opportunities generated by these sustainability policies.

Ultrafine particle cleaning performance of an ion spray electrostatic air cleaner emitting zero ozone with diffusion charging by carbon fiber

A novel electrostatic precipitator (ESP)-type small air cleaner with an ion spray charger was developed and evaluated. Unlike conventional ESP air cleaners, the charger is located at the rear of the collection stage. Ions are emitted into ambient space by the fan of the air cleaner, and airborne particles are charged by nearby ions through a diffusion charging mechanism. A carbon fiber ionizer without a grounded metal plate was installed as the charger to minimize ozone emission. The novel air cleaner had a particle clean air delivery rate (CADR) for 0.3-μm particles of 0.863 m3/min at a fan flow rate of 2.0 m3/min and applied voltages of – 5 kV to the ionizer and collection plate. As the size of the particles increased from 0.25 to 1 μm, particle CADR increased from 0.6 to 1.6 m3/min. Near-zero ozone emission was generated in a closed chamber (30.4 m3), and the concentration decreased from an initial background level of 2.39 ppb–1.29 ppb after 12 h of continuous operation. Our study showed a close relationship between particle CADR and the number of charges per particle, and the number of charges per particle matched well with theoretical predictions based on diffusion charging theory. The particle CADR of ion spray ESPs was 3.63 times higher than that of a high-efficiency particulate air (HEPA) filter air cleaner of similar volume. In an actual environment (56.43 m3), the particle CADR was 0.798 m3/min, similar to the chamber test.

Results from an industrial size biogas-fed SOFC plant (the DEMOSOFC project)

The EU-funded DEMOSOFC project aims to demonstrate the technical and economic feasibility of operating a 174 kWe Solid Oxide Fuel Cell (SOFC) in a wastewater treatment plant. The fuel for the three SOFC modules (3 × 58 kWe) is biogas, which is available on-site from the anaerobic digestion of sludge collected from treated wastewater. The integrated biogas-SOFC plant includes three main units: 1) the biogas cleaning and compression section, 2) the three SOFC power modules, and 3) the heat recovery loop. Main advantages of the proposed layout are the net electric efficiency of the SOFC, which is in the range 50–55%, and the near-zero emissions. A specific focus of the demonstration project is the deep and reliable removal of harmful biogas contaminants. The presented work is related to the design of the SOFC system integrated into the wastewater treatment plant, followed by the analysis of the first results from the plant operation. We analyzed the biogas yearly profile to determine the optimal SOFC capacity to install that is 3 SOFC modules. The rational is to maintain high the capacity factor while minimizing the number of shutdown per year (due to biogas unavailability). First results from plant operation are also presented. The first SOFC module was activated in October 2017 and the second in October 2018. The measured SOFC efficiency from compressed biogas to AC power has always been higher than 50–52%, with peaks of 56%. Dedicated emissions measurements have been performed onsite during December 2017. Results on real biogas operation show NOx < 20 mg/m3, SO2 < 8 mg/m3 (detection limits for the instrument) and PM lower than ambient air values.

Solid oxide fuel cell operation in a solid oxide fuel cell–internal combustion engine hybrid system and the design point performance of the hybrid system

A solid oxide fuel cell (SOFC)–internal combustion engine (ICE) hybrid system is a recently-proposed distributed electric power generation system to achieave extremely high efficiency beyond that of current technologies. The objectives of this study are to find the operation characteristics of the SOFC in the hybrid system and determine the operational design point of the hybrid system. To accomplish these objectives, operation of a 5 kW-class SOFC–ICE hybrid system was analysed by integrating the experimental results of the internal combustion engine with the simulation models of other system components. Two unique characteristics of SOFC operation were found and analysed. First, the SOFC in the hybrid system should utilize anode inlet gas with low temperature (e.g., 750–800 K) and low external reforming rate (e.g., 30–40%), which decreases the SOFC temperature, especially at the entrance, where the current density becomes very low, decreasing SOFC performance. Second, the overall effects of pressure pulsation caused by the engine on SOFC operation are insignificant since the flow path between the SOFC and the engine acts as a damper, reducing the pressure pulsation amplitude. The estimated variations were 0.2 mV in SOFC cell voltage. To determine the operational design point of the hybrid system, parametric analyses of system operation were conducted while varying several control parameters, e.g., SOFC fuel utilization factor. The design point of system operation was determined by considering system performance and operational stability. Near-zero pollutant emissions and 59.0% system efficiency were achieved at the determined design point, a 7.9% absolute and 15.5% relative improvement compared to that of an SOFC stand-alone system.

Life cycle environmental impact assessment of fuel mix-based biomass co-firing plants with CO2 capture and storage

As a carbon-neutral renewable energy source, biomass co-firing with coal contributes to reducing the carbon intensity of pulverized coal power plants with CO2 capture and storage; thus, this process significantly reduces the greenhouse gas emissions of the power industry. However, various types of environmental impacts caused by co-firing have hindered the large-scale deployment of this technology. In this study, ten life cycle assessment models were developed based on the Integrated Environmental Control Model and GaBi software to quantify the performance parameters of different power plants and the influence of the co-firing ratio on various environmental impact categories. The system boundaries included raw material acquisition, raw material transport, energy conversion of power plants, CCS and brine treatment. The results indicated that a pulverized biomass/coal co-firing power plant with CCS can achieve near-zero emissions at a co-firing ratio of 25% and negative emissions of 877 kg CO2-e/MWh from a life-cycle perspective when coal is totally replaced. Co-firing biomass and coal in power plants has a passive impact on seven environmental categories, such as the eutrophication potential and toxicity potential, rather than on the global warming potential, abiotic resource depletion potential and acidification potential. The major causes of environmental burden shifting are energy penalties and indirect emissions from high-energy-consumption processes, especially emissions of N2O, NH3 and ethylene oxide released during biomass extraction and solvent preparation. The conclusions and recommendations presented in this paper may have implications for deep decarbonization in other industrial sectors.

A risk aversion optimal model for microenergy grid low carbon‐oriented operation considering power‐to‐gas and gas storage tank

Power-to-gas storage (P2GS) provides a new approach for clean energy accommodation, which could be used to support the development of the microenergy grid (MEG). This paper designs a novel structure of MEG including power sources, heating sources, and P2GS. The risk condition values (CVaR) is applied to analyze the uncertainties from wind power plant, photovoltaic power generation, and solar collectors, and a multiobjective optimal model is proposed for balancing the operation economic benefit and the risk level. Then different membership functions are selected for converting the multiobjective model into a mixed integer programming model. Finally, an industrial park in northern China was selected to verify the proposed model. The results show that (a) complementary effect exists in different clean energy sources and P2GS can convert excess energy into CH4 for power generation, which are better for achieving the power-to-gas-to-power cycle optimization effect. (b) The proposed optimal model could balance revenue and risk, rationally control its operation risk while pursuing the maximum operation benefits, which is better to achieve MEG's optimal equilibrium operation. (c) Maximum emission trade allowance could enhance MEG's enthusiasm for clean energy accommodation, and P2GS could be a feasible way for near-zero carbon emissions. Therefore, the proposed risk aversion optimal model could increase the economic benefits and control the risks and provide decision support for decision makers.

A thermodynamic analysis of a solar hybrid coal-based direct-fired supercritical carbon dioxide power cycle

Efficient utilization of coal for power generation with carbon capture as well as development of solar hybrid system are being aggressively researched currently. To advance the utilization of solar energy and achieve zero emission for coal-based power generation more efficiently, a novel direct-fired, oxy-combustion supercritical carbon dioxide power cycle integrated with the solar-driven coal gasification was proposed. In the proposed system, the concentrated solar energy is utilized for coal gasification, and then the produced syngas is combusted with high-purity oxygen to drive a semi-closed supercritical carbon dioxide power cycle with intensive heat recuperation and near-zero carbon emission. Detailed analytical models based on energy and material balance were developed and the overall system thermodynamic performance were determined by the process simulation. Results showed that, at the designate point, the proposed system can save 29.9% of coal consumption and the net system energy efficiency and exergy efficiency soar to 43.4% and 44.6%, respectively; and the annualized coal saving can reach 10.46 kilo tonnes with the annual solar-to-electricity efficiency at 16.9%. The proposed concept may provide a new approach to advancing solar-coal hybridization power generation with near-zero emission.

Methanol production from captured CO2 using hydrogenation and reforming technologies_ environmental and economic evaluation

Minimizing CO2 emission into the atmosphere to prevent climate change has required immense efforts from us. Flue gases from fossil fuel-based power plants and many heavy industries are considered main anthropogenic sources of releasing CO2. Although there is a popular solution to mitigate CO2 through CO2 capture and storage, its cost is still quite significant, and this prevents broad application. A newly proposed process to convert flue gases into methanol has grabbed a headline because it offers an opportunity to alleviate CO2 emissions and delivers a way to produce methanol (MeOH) from recycling feedstock. In this work, three approaches for mitigating CO2 including hydrogenation, bi- and tri-reforming are investigated for methanol production at three different capacities (300, 1500, and 3500 ton/day). The environmental and economic consequences are evaluated as a primary implementation for green process design. These evaluations pointed out that the processes based on reforming are the most appropriate direction for employment during the transition step of producing methanol from a carbon-based- to carbon-free program whereas the hydrogenation-based processes with hydrogen from renewable sources could be the proper implementation scenarios for a long-term plan to obtain near-zero emissions.

Research on ‘near-zero emission’ technological innovation diffusion based on co-evolutionary game approach

ABSTRACTAs air pollution becomes increasingly critical, ‘near-zero emission’ technological innovation in coal-fired plants are needed for the government and public consumers. The aim of this paper is to build the evolutionary game for analysing ‘near-zero emission’ technological innovation diffusion in coal-fired plants. According to bionics research of evolution, this paper introduces the co-evolutionary algorithm to simulate the diffusion. By modelling the evolutionary gaming behaviour of coal-fired plants, the simulation can capture the dynamics of coal-fired plants' strategy, which is adopting ‘near-zero emission’ technological innovation or not. It is key to model the diffusion under the electricity market and government regulation because it can provide some suggestions for promoting the diffusion. Simulations show that with no government regulations, the coal-fired plant fails to adopt the ‘near-zero emission’ technological innovation. However, the coal-fired plant for most profit should adopt independent R&D for ‘near-zero emission’ technology when the government provides subsidy incentives for the low-pollution coal-fired plant. With the promotion of subsidy incentives, all coal-fired plants will adopt ‘near-zero emission’ technology. Moreover, increasing the subsidy intensity has a significant role in promoting the diffusion.

Techno-economic analysis of oxy-fuel IGCC power plants using integrated intermittent chemical looping air separation

Three oxy-fuel IGCC power plants using different air separation technologies and carbon compression and compression (CCP) are developed to near-zero CO2 emission power systems. If capturing CO2 is treated as a byproduct, Design 2 by an integration of IGCC and natural gas-fueled integrated intermittent chemical looping air separation (NG-IICLAS) may have a promising economic potential. Through the techno-economic assessment of Design 2, its internal rate of return (IRR) by 17.99% is higher than a chemical looping combustion (CLC)-based IGCC power plant connecting carbon capture and storage (CCS) with IRR = 12.5%, its levelized cost of electricity (LCOE) by 69.92 €/MWh is close to the LCOE of supercritical coal-fired power plant in 2015, and its CO2 production cost by 12.35 €/ton is also close to the market price for CO2 in 2011. It is successfully verified that the investing in Design 2 is superior to other designs.