Near-zero Emissions Research Articles

An experimental investigation of particulate emission characteristics of catalytic diesel particulate filters during passive regeneration

The catalytic diesel particulate filter (CDPF) can effectively reduce diesel particulate emissions, but its outlet particulate emissions increase significantly during active and passive regeneration. Understanding the particle emission characteristics and oxidation mechanism during CDPF regeneration is a prerequisite for seeking improvement measures and achieving near-zero emissions from diesel engines. This study focused on the particle emission characteristics during passive regeneration not previously detailed in the engine literature dedicated to catalytic diesel particulate filters. The commercial carbon black (Printex-U, PU) was utilized to replace diesel soot and loaded onto the CDPF substrate here. Experimental tests were conducted to investigate the effect of regeneration temperature and soot load on the CDPF response to exhaust particles during passive regeneration. The results showed that the diesel oxidation catalyst (DOC) reduced the particle number (PN) upstream of the CDPF device. In addition, the regeneration temperature and soot load altered the ratio of penetrating particles (PP), secondary particles (SP), and blown-out particles (BP), resulting in a complex particle emission profile in terms of particle concentration and size at the CDPF outlet. Moreover, the higher regeneration temperature enhanced the oxidation of the particulate matter and raised the particle number, while increasing the particle load enhanced the capture effect of incoming particles but also led to enhanced catalytic oxidation and destruction of the microstructure of the particle layer, thus increasing the discharged particle emissions.

Techno-economic analysis and optimization of near-zero energy and emission neighborhoods using biomass waste

The present study aims to simulate and design a near-Zero Energy neighborhood in one of the most significant industrial cities for reducing greenhouse gas emissions. For this building, biomass wastes are used for energy production, and also energy storage is provided using a battery pack system. Additionally, the Fanger model is used to assess the passengers' thermal comfort, and information on hot water usage is given. The transient performance of the aforementioned building is tested for one year using TRNSYS software, which was employed for this simulation. Wind turbines are considered electricity generators for this building, and any extra energy generated is stored in a battery pack for usage when the wind speed is insufficient and electricity is needed. Hot water is created using a biomass waste system and is kept in a hot water tank after being burned using a burner. A humidifier is utilized to ventilate the building, and a heat pump provides both the building's heating and cooling needs. The produced hot water is used to supply the residents' hot water. In addition, The Fanger model is considered and used for the assessment of occupants' thermal comfort. Matlab software is a powerful software used for this task. According to the findings, a wind turbine with a 6 kW generation capacity may supply the building's power needs while also charging the batteries beyond their initial capacity, and the building will have zero energy. Additionally, biomass fuel is used to give the building the required water which should be hot. On average, 200 g of biomass and biofuel are used per hour to maintain this temperature.

Coal power decarbonization via biomass co-firing with carbon capture and storage: Tradeoff between exergy loss and GHG reduction

Co-firing of coal and biomass is a feasible pathway for low- or even negative-carbon transformation of power sector in countries that rely on coal. There are two main kinds of coal and biomass co-firing pathways: biomass gasification co-firing with pulverized coal (BGCPC) and biomass direct co-firing with pulverized coal (BDCPC). However, few attentions have been paid to the comparative study of techno-environmental assessments for the above two main technologies with or without carbon capture and storage (CCS). Here we present a comparative system evaluation framework based on chemical simulation and life cycle assessment (LCA) to compare the energy performances and environmental impacts of different biomass co-firing and CCS technology combinations. A new metric, global warming potential of per unit exergy efficiency loss (GWPUEL) is proposed to reveal the trade-off between greenhouse gas (GHG) emission abatement and exergy efficiency loss. Results show that BGCPC-CCS units of all capacities can achieve negative life-cycle GHG emissions under 25% co-firing ratio scenario, but only 1000 MW BDCPC-CCS units can achieve near-zero life-cycle GHG emissions. Though 300 MW units show the minimum carbon reduction potential among all the selected capacities, they can achieve the most promising GWPUEL benefits for their mild exergy efficiency loss after CCS retrofit. This indicator provides a comprehensive viewpoint to weigh the compromise between energy performance and environmental burdens of different bio-based and CCS technology combinations, further facilitating various decarbonization schemes of global power sector under the carbon neutrality target.

A near-zero carbon emission methanol production through CO2 hydrogenation integrated with renewable hydrogen: Process analysis, modification and evaluation

Carbon dioxide hydrogenation to produce methanol has the potential to liberate humanity from its reliance on fossil fuels, while simultaneously reducing carbon dioxide and developing the economy. This paper focuses on the effect of catalyst type and the process conditions such as temperature, pressure, H2/CO2 feed ratio, and space velocity on CO2 conversion and CH3OH selectivity. The net generated CO in the reaction system results in the loss of CO2 and H2 to the purge gas, which reduces the utilization efficiency of carbon and hydrogen. The specially designed catalysts and processes with recycling can improve CO2 conversion and CH3OH selectivity, and the CO flow rate difference can be close to zero in the total recycling condition. Starting from these ideas, the two kinds of near-zero carbon emission processes with total recycling (respectively named total recycling process after flash separation and named total recycling process after stripping separation) are proposed. The utilization efficiency of carbon and hydrogen are similar in the two processes, but hot and cold utilities in the latter are 17.96% and 15.11% lower than in the former, respectively. Through the process integration between reaction heat and double-effect distillation, the energy consumption is further reduced in the total recycling process after stripping separation. The utilization efficiency of CO2 is 99.88% in the total recycling process after stripping separation with double-effect distillation of the light split/reverse configuration, and the proposed process just requires cold utility.

Techno-economic analysis and life cycle analysis of e-fuel production using nuclear energy

Electrofuels, or e-fuels, are synthetic liquid hydrocarbon fuels which may be produced using carbon dioxide (CO2) and low carbon hydrogen (H2) as feedstock. They are of great interest because they have much lower carbon intensity compared to the conventional petroleum fuels and can utilize the existing fuel infrastructure owing to their ability to blend with or replace existing fuels. We modeled an e-fuel production process to produce low carbon jet, diesel, and naphtha using a reverse water gas shift process to produce synthesis gas, followed by a Fischer-Tropsch (FT) synthesis process. Nuclear energy is considered for e-fuel production due to its steady energy supply, near-zero carbon emissions, capability to produce hydrogen with high efficiency via high temperature electrolysis, and proximity to biogenic CO2 sources from nearby corn-ethanol plants in the United States. The modeled FT process achieved a high carbon conversion ratio of 99% by recycling CO2 and the use of oxy-combustion, and a process energy efficiency of approximately 70%. The life cycle greenhouse gases emissions are estimated to be 7 and −25 gCO2e/MJ, without and with steam coproduct credit, respectively, by using the Greenhouse gases, Regulated Emissions, and Energy use in Technologies (GREET®) model. Additionally, the process economics were evaluated for three scales corresponding to nuclear power plant capacities of 100, 400, and 1000 MWe, estimating a minimum fuel selling price (MFSP) of $3.61/gal ($0.95/L), $2.82/gal ($0.74/L), and $2.66/gal ($0.70/L) of FT fuel mix, respectively, by considering $3/kg of H2 tax credit prescribed in the recent Inflation Reduction Act.

Pathway and Cost-Benefit Analysis to Achieve China's Zero Hydrofluorocarbon Emissions.

Global hydrofluorocarbon (HFC) cumulative emissions will be more than 20 Gt CO2-equiv during 2020-2060 and have a non-negligible impact on global warming even in full compliance with the Kigali Amendment (KA). Fluorochemical manufacturers (including multinationals) in China have accounted for about 70% of global HFC production since 2015, of which about 60% is emitted outside China. This study built an integrated model (i.e., DECAF) to estimate both territorial and exported emissions of China under three scenarios and assess the corresponding climate effects as well as abatement costs. Achieving near-zero territorial emissions by 2060 could avoid 23 ± 4 Gt CO2-equiv of cumulative territorial emissions (compared to the 2019 Baseline scenario) during 2020-2060 at an average abatement cost of 9 ± 6 USD/t CO2-equiv. Under the near-zero emission (including territorial and abroad) pathway, radiative forcing from HFCs will peak in 2037 (60 ± 6 mW/m2) with a 33% peak reduction and 8 years in advance compared to the path regulated by the KA, and the radiative forcing by 2060 will be lower than that in 2019. Accelerated phase-out of HFC production in China could provide a possibility for rapid global HFC abatement and achieve greater climate benefits.

Kinetics of oxidative bio-ethanol reforming over bimetallic structured catalysts

The core of this work is a comprehensive investigation of ethanol oxidative reforming kinetics over a Pt–Ni/CeO2–Al2O3 catalyst in the presence of fuel grade bioethanol, which has been very rarely investigated in the past. The developed kinetic model also included the formation of solid carbon. The results show that the reaction scheme involving ethylene and acetaldehyde formation from ethanol, their subsequent decomposition, methane oxidation as well as steam reforming and water gas shift reaction is able to assure a satisfactory fitting of the experimental data. Moreover, the above formulation, deposited on a porous support (Ni–Fe foam), was employed for a very long stability test (almost 400 h) and subjected to several oxidation-reduction cycles: at 600 °C, after 170 h of time-on-stream, a stable ethanol conversion of 95% and hydrogen yield of 35% were recorded, with near-zero carbon emission during its thermochemical conversion for energy generation.

Effects of fuel injection and energy efficiency on the production and environmental parameters of electric arc furnace -heat recovery systems

A stoichiometric model of an electric arc furnace (EAF)-heat recovery system was constructed to display material, energy, and exergy behaviors, as well as production and environmental parameters, in order to study the effects of different fuel injection indexes. The injection of high-calorific value fuel (rather than hydrogen and biomass) reduces power consumption more effectively, but hydrogen utilization reduces the amount of off-gas and improves heat recovery slightly (0.06 MJ/Nm3) in the case of 30% energy efficiency. It is more efficient to directly use the energy released from fuel combustion in the furnace than to recover the heat in the off-gas, showing the importance to increase energy efficiency. In the scenario of improved equipment and technology using large amounts of hydrogen (20 m3/t) and biomass (40 kg/t), power consumption will reach 322 kWh/t. Near-zero carbon emissions (41.20 kg CO2/t) can be achieved in an EAF by using green power, green hydrogen, and advanced equipment and processes. However, realizing this process requires long-term transformation, including the use of coke oven gas rather than gray hydrogen, which has high upstream emissions. Moreover, there is a significant exergy loss in the off-gas heat recovery system (>70%), which requires the adoption of stoichiometric combustion and an increase in the efficiency of heat exchange.

Research on control strategy of photovoltaic hydrogen generation system based on Fuzzy PI control

Under the goal of carbon peak and neutrality, the search for efficient and clean green energy has attracted widespread attention. Photovoltaic (PV) hydrogen production has become a research hotspot because of its clean and near-zero carbon emissions. However, due to the influence of natural light, PV power generation is volatile and intermittent, reducing the system’s stability. In order to improve the stability of the system, a large number of power electronic devices and control strategies are applied to the PV hydrogen production system. Among them, the Buck circuit using proportional–integral (PI) control is the most widely used. However, the PI control has a long response time and large ripple, which affects the energy efficiency of PV hydrogen production. This paper proposes a PV hydrogen production system control strategy based on Fuzzy PI control. In the Matlab/Simulink environment, a simulation model of a PV hydrogen production system composed of PV cells, proton exchange membrane electrolyzers, and DC/DC units is built. The DC/DC unit uses a Buck circuit. Simulation analysis compares the output voltage and current ripple of the PV hydrogen production system model under different working conditions using the Fuzzy PI control and classical PI control strategies. Finally, the simulation results verify that the proposed control strategy reduces the system output voltage and current ripple.

Low-carbon technology diffusion and economic growth of China: an evolutionary general equilibrium framework

The thorough transition of energy system is required to achieve the Paris Agreement goal. Computable general equilibrium (CGE) models are a common tool for estimating the energy transition pathway and the impact of low-carbon policies on economic growth. However, CGE models encounter challenges on modeling diffusion of new technologies. This study proposed a novel evolutionary dynamic general equilibrium model to capture the nonlinear, path-dependent and S-shaped technology diffusion process, and examined the low-carbon transition pathway of power sector and its impact on economic growth of China. We found that imposing a moderate carbon tax and avoiding the over-reliance on coal-fired power could achieve the near-zero emissions of power sector, avoid the large economic loss and hasten the economic growth in the long term. The evolutionary framework may be useful for developing the next-generation model, particularly for simulating the diffusion of new technologies, and their structural effects on economic dynamics.

A Review of the Optimization Strategies and Methods Used to Locate Hydrogen Fuel Refueling Stations

Increasing sales of conventional fuel-based vehicles are leading to an increase in carbon emissions, which are dangerous to the environment. To reduce these, conventional fuel-based vehicles must be replaced with alternative fuel vehicles such as hydrogen-fueled. Hydrogen can fuel vehicles with near-zero greenhouse gas emissions. However, to increase the penetration of such alternative fuel vehicles, there needs to be adequate infrastructure, specifically, refueling infrastructure, in place. This paper presents a comprehensive review of the different optimization strategies and methods used in the location of hydrogen refueling stations. The findings of the review in this paper show that there are various methods which can be used to optimally locate refueling stations, the most popular being the p-median and flow-capture location models. It is also evident from the review that there are limited studies that consider location strategies of hydrogen refueling stations within a rural setting; most studies are focused on urban locations due to the high probability of penetration into these areas. Furthermore, it is apparent that there is still a need to incorporate factors such as the safety elements of hydrogen refueling station construction, and for risk assessments to provide more robust, realistic solutions for the optimal location of hydrogen refueling stations. Hence, the methods reviewed in this paper can be used and expanded upon to create useful and accurate models for a hydrogen refueling network. Furthermore, this paper will assist future studies to achieve an understanding of the extant studies on hydrogen refueling station and their optimal location strategies.

China’s Hydropower Resources and Development

Hydroenergy is developed due to its low-cost and near-zero pollution emission properties; therefore, the efficient management of hydroenergy is an important goal of sustainable development for any nation, especially for China, since it owns the most abundant water resources around the world. Developing hydroenergy is not only an effective response to the energy crisis but also a positive way to cope with climate change in China. Nevertheless, research on hydroenergy in China is still not comprehensive. This study reviews hydroenergy development in China by combining its geographical characteristics and hydroenergy reserves. The general condition of hydropower development including large- and medium-scale hydropower stations and small hydropower development is presented. This article illuminates the potential problems and existing challenges in China’s hydropower development and relevant exploitation suggestions are provided for hydropower development in the future.

Optimization and performance analysis of a near-zero emission SOFC hybrid system based on a supercritical CO2 cycle using solar energy

Renewable energy represented by solar energy has the characteristics of intermittency and fluctuation. To ensure that the grid can operate safely and stably after the large-scale grid connection of renewable energy power, a new hybrid system consisting of a solid oxide fuel cell (SOFC), a solar power tower plant, and a supercritical CO2 (S-CO2) Brayton cycle is proposed in this study from the perspective of energy, exergy, and economy. By utilizing the cold source loss of the S-CO2 cycle to provide part of the energy required for the alkaline electrolyzer, it can efficiently produce and store hydrogen, achieving zero greenhouse gas emissions while increasing efficiency. Meanwhile, the high-temperature exhaust gas from SOFC is recovered by the S-CO2 cycle. The system considers two operation modes, switching two types of S-CO2 cycle configurations to efficiently utilize solar energy according to the variation of solar radiation energy. The thermal efficiency of the proposed system is improved by 16.61% and 6.88% compared with the other two typical S-CO2 cycle power generation systems, and the net power output reaches 8.0 MW. A parameter study shows that increasing the split ratio is beneficial to improve the thermodynamic performance of the system. However, at a split ratio less than 0.76, it is beneficial to the total cost rate of the system. The results of multi-objective optimization show that the exergy efficiency of the combined system and the total system cost rate reach 56.86%, 513.10$/h and 56.45%, 481.59$/h for the system with an additional simple S-CO2 cycle and the system with an additional recompression S-CO2 cycle, respectively, and the optimum point is selected by the TOPSIS and LINMAP methods.

Computational Investigation of Combustion, Performance, and Emissions of a Diesel-Hydrogen Dual-Fuel Engine

This paper aims to expose the effect of hydrogen on the combustion, performance, and emissions of a high-speed diesel engine. For this purpose, a three-dimensional dynamic simulation model was developed using a reasonable turbulence model, and a simplified reaction kinetic mechanism was chosen based on experimental data. The results show that in the hydrogen enrichment conditions, hydrogen causes complete combustion of diesel fuel and results in a 17.7% increase in work capacity. However, the increase in combustion temperature resulted in higher NOx emissions. In the hydrogen substitution condition, the combustion phases are significantly earlier with the increased hydrogen substitution ratio (HSR), which is not conducive to power output. However, when the HSR is 30%, the CO, soot, and THC reach near-zero emissions. The effect of the injection timing is also studied at an HSR of 90%. When delayed by 10°, IMEP improves by 3.4% compared with diesel mode and 2.4% compared with dual-fuel mode. The NOx is reduced by 53% compared with the original dual-fuel mode. This study provides theoretical guidance for the application of hydrogen in rail transportation.

Carbon nanotubes@fly ash Janus composite membrane prepared from fly ash and waste plastics for efficient solar membrane distillation

Janus membranes have attracted many attentions due to their unique and excellent properties endowed by their asymmetric structure and chemical composition. In this study, a novel carbon nanotubes (CNTs)@fly ash Janus composite membrane with hierarchically oriented straight pores, prepared in two steps using industrial solid waste fly ash and white pollutant waste plastic as raw materials, is introduced into the field of solar membrane distillation. The fly ash membrane is fabricated by the combined phase tape inversion casting and sintering method, and CNTs are then in-situ grown on one side of the as-sintered fly ash membrane via the chemical vapor deposition technique to form CNTs@fly ash Janus membrane. The as-prepared Janus inorganic membrane exhibits good hydrophobicity with a contact angle of 133° as well as excellent gas permeability of 0.51 ± 0.01 × 107 L m−2 h−1 bar−1. When this membrane is used for solar membrane distillation, its interfacial evaporation rate can reach to 1.94 ± 0.01 kg m−2h−1 under one solar intensity, which is 2.19 times that of traditional natural evaporation. Coupled with its lower cost and environmental benefits, this novel Janus membrane is a potential hydrophobic separation membrane to achieve near-zero solid waste emission and efficient seawater desalination.

Research on Comprehensive Evaluation of Near-zero Carbon Emission Parks Based on Variable Weight Theory

Near-zero carbon emissions are the further deepening and implementation of low-carbon emissions and a dynamic process constantly moving towards zero carbon emissions. With the carbon formation life cycle as the core, the low-carbon park is divided into smart parks and ecological parks. They are starting from the four elements of planning, near-zero carbon technology, carbon emission management, and environmental health, and forming an index system architecture according to the park’s carbon emission traceability tracking system. When the park is in different stages of near-zero carbon development, the internal differences of evaluation indicators are also different. The constant weight evaluation method cannot reflect the impact of each indicator on the development of near-zero carbon, which will affect the accuracy of the evaluation results. By introducing variable weight theory, a penalty variable weight model is constructed, and the model is applied to the case park. Comparing the results of the constant-weight evaluation and variable-weight evaluation, it can be seen that the evaluation results of the variable-weight evaluation model are easier to distinguish the development level. The verification results show that the variable weight evaluation method is more suitable for the dynamic characteristics of near-zero carbon development.

Investigation of syngas combustion in a novel ultra-low emission 20-kW two-stage combustor

Two-stage rich-catalytic lean-swirl combustion is investigated in a 20-kW combustor using biomass-derived syngas as fuel. In the first stage, fuel-rich catalytic combustion of syngas (Фfirst = 4) is investigated using FeCr-alloy monolith and platinum (Pt) as a catalyst. The fuel undergoes partial conversion in the catalytic stage. The remaining unoxidized reactants from the first stage are burnt using additional air in the second stage. The flame is stabilized by two concentric swirling streams in the second stage, where the exhaust from the first stage flows through the inner stream, and the outer stream carries air. By changing the swirl direction of the inner stream, co or counter-swirl flame is established, whereas the overall equivalence ratio is changed by increasing the airflow rate. It is found that the flame topology is significantly different for the co-swirl and counter-swirl configurations. Transitions from a compact ‘M’ shaped flame to a shear-layer stabilized ‘V’-shaped flame is observed by changing the overall equivalence ratio. The combination of planar laser-induced fluorescence (PLIF) and particle image velocimetry (PIV) highlights the differences in the flow field and OH radical distribution, leading to the observed flame shape. The dynamic stability of the combustor is assessed using sound pressure level (decibel) obtained using a microphone and high-speed OH* chemiluminescence. Finally, the CO and NOx concentrations are measured at the combustor exit. The CO emission ranges from 10 ppm to 70 ppm, whereas the NOx emission is negligible in all conditions studied. Thus, the present study successfully demonstrates the feasibility of catalytic and twin-swirl combustion in achieving near-zero emissions while operating with biomass-derived syngas.

An Optimal Site Selection Framework for Near-Zero Carbon Emission Power Plants Based on Multiple Stakeholders

Near-zero carbon emission power (NZCEP) plants, consisting of gas-fired units; wind turbines; power-to-gas (P2G); and carbon capture, utilization and storage (CCUS) systems, have recently received a lot of attention due to their enormous benefits in reducing carbon emissions and increasing the consumption of renewable energy. However, a complex environment of interest and a combination of risks makes their development very slow. This paper establishes a risk analysis framework for NZCEP considering multi-stakeholder participation. Firstly, a synthetic risk factor system was constructed based on stakeholders’ interests. Subsequently, interval type II trapezoidal fuzzy numbers were used and final weights were calculated from both subjective and objective aspects. Finally, we applied an acronym in Portuguese of the interactive and multi-criteria decision-making (TODIM) method to site selection to achieve a balance of interests of all stakeholders. In addition, a case study was conducted. The case result demonstrates that Zhengzhou in Henan Province is the best choice for a NZCEP power plant. A further finding is that government plays an important role in the development of NZCEP plants, with site selection results being the most sensitive to changes in the government’s risk appetite. Moreover, human resources are an important factor in the siting of an NZCEP plant.

Low carbon hydrogen production in Canada via natural gas pyrolysis

Large scale, low cost, and low carbon intensity hydrogen production is needed to reduce emissions in the energy and transportation sectors. We present a techno-economic analysis and life cycle assessment of natural gas pyrolysis technologies for hydrogen production, with carbon black (CB) as a co-product. Four designs were considered based on the source of heat to the pyrolysis system, the combustion medium, and use of carbon capture (CC) technology. The oxygen-fired-CB design with CC is the most attractive from financial and environmental perspectives, superior to a conventional steam methane reformer (SMR) process with CC. The estimated pre-tax minimum hydrogen selling prices for the pyrolysis technologies range between $1.08/kg and $2.43/kg when natural gas (NG) costs $3.76/GJ. Key advantages include near-zero onsite GHG emissions of the oxygen-fired-CB design with CC and up to 41% lower GHG emissions compared to the SMR + CC process. The results indicate that natural gas pyrolysis may be a feasible pathway for hydrogen production.

Bibliometric Analysis for Carbon Neutrality with Hotspots, Frontiers, and Emerging Trends between 1991 and 2022.

The proposal of carbon neutrality is a manifestation of actively responding to global warming and sustainable development, which means all greenhouse gases achieve near-zero emissions. China is also fulfilling its national mission in this regard. This paper collected 4922 documents from the "Web of Science Core Database" and used Citespace (6.1.R2 Advanced) and Vosviewer (1.6.18) software and Bibliometrix functions to carry out descriptive statistics on the number of publications, cooperation mechanisms, and keyword hotspots, finding that the literature mainly focused on China's carbon neutrality, carbon emissions, energy efficiency, sustainable development, and other related topics in the past two years. Further, the 2060 carbon neutrality action plan for China is discussed, focusing on the implementation plan and technical route and proposing the corresponding plans. The purpose of this paper is to accelerate the pace of China's achievement of this goal and to provide feasible solutions and pathways to its achievement through insight into global carbon neutrality hotspots and new trends.