Near-zero Carbon Research Articles

Integrating biogas in regional energy systems to achieve near-zero carbon emissions

Recent years have witnessed an increasing proliferation of biomass technologies since biomass is recognized as a natural carbon-neutral fuel. Existing studies have paid extensive attention to the concept and modeling of zero-carbon energy systems or buildings. However, few studies have explored the multi-energy coupling method and techno-economic evaluation of biomass to achieve near-zero carbon systems. Therefore, we propose an optimal sizing framework for integrating waste-to-biogas in regional energy systems to achieve near-zero carbon emissions. To establish energy balance between supply and demand and regional self-sufficiency, biomass is added to the existing natural gas energy framework. Biomass produces biogas through anaerobic digestion reactions, and the biogas output can be constructed as an analytical function related to the anaerobic reaction environment temperature and reactant volume. Furthermore, this paper constructs a planning model with the goal of minimizing the investment and operating costs of biomass, solar and storage, respecting carbon emission constraints induced by local electricity and gas energy flows. The impact of carbon emission regulations on the investment of each component of the energy system is determined using a sensitivity analysis of carbon emissions. To solve the nonlinearity issues of the biogas production function, we propose a convexification method based on least squares fitting. Case studies based on realistic datasets demonstrate that, under the constraints of carbon emissions, the integration of biogas can significantly improve the supply adequacy of the energy system, reduce investment costs by up to 77.07%, and carbon emission reduction intensity is 5.11 kg CO2 kg-1 Biogas, all while lowering the Levelized Cost of Energy (LCOE). In comparison to prior research, the model provided in this paper more accurately portrays the biogas production process, lowers the system investment cost and LCOE, and emphasizes the benefits of biomass.

Polymeric membrane materials for green hydrogen production by water electrolysis: Progress and suggestions for future development

<p indent="0mm">Green hydrogen has gained much interest due to its low cost, sustainability, and environmental friendliness, especially when combined with water electrolysis technology powered by renewable energy resources. It has been recognized as one of the perfect solutions to achieve the goal of near-zero carbon emissions. According to the type of materials used to separate the anode and cathode and the ionic species it conduct, the electrolyzers can be divided into several categories, i.e., alkaline water electrolyzer (AWE) that involve the use of liquid electrolyte, proton exchange membrane water electrolyzer (PEMWE), solid oxide electrolyzer (SOE), and anion exchange membrane water electrolyzer (AEMWE). As the key component in different water electrolysis technologies, polymeric membrane materials, including proton exchange membrane (PEM), anion exchange membrane (AEM), and ion-solvating membranes (ISM), are of great importance, which serve as the ionic conductor and gas separator. Thus, the efficiency and durability of water electrolyzers are mainly determined by the properties of membranes, such as ionic conductivity, chemical stability, and mechanical properties. However, these unfavorable performance parameters of membranes still limited the worldwide commercialization of water electrolysis for the production of green hydrogen. In a typical AWE, a porous diaphragm made of asbestos or composite ceramic (or asbestos)/polymer materials (Zirfon, a state-of-the-art diaphragm) is used to separate the gas product and transport hydroxide ions. Although the mature AWE technology shows higher durability, low capital cost, and high compatibility with non-noble metal catalysts, they operate at low current densities lying between <sc>0.3−0.4 A cm⁻²,</sc> owning to the high ionic resistance and high gas permeation of the non-ionic separator membranes. The replacement of porous diaphragm with ionic polymeric membranes, such as PEM, AEM, and ISM based on polybenzimidazoles have attracted increasing attention in water electrolysers, due to their effectiveness of ion transport and gas tightness of the dense membrane. The acidic PEM allow the operation of water splitting with higher efficiency and current densities <sc>(500−2000 A cm⁻²).</sc> However, large-scale implementation of PEMWE technology is limited by the expensive PEM and precious platinum group metal (PGM) catalysts. When working under basic environment, the AWE using solid AEM and ISM combines the merits of traditional AWE and PEMWE, i.e., an alkaline working environment allows for the use of PGM-free catalysis and the solid hydroxide ion conducting membrane reduce the ionic resistance of the cells. Thus, the design of AEM and ISM materials plays a crucial role in the overall performance and durability of electrolytic cells. Currently, compared with PEMWE, the AEMs and ISMs with sufficient conductivity and satisfactory stability are still highly needed, due to the well-recognized vulnerable functional cations and polymer backbones in hot and alkali aqueous solutions. Thus, numerous chemical designs on AEMs are carried out. In this review, we summarized the research progress of polymeric membranes in water electrolysis for hydrogen production. We first compared the properties of membranes and electrolyzer device performance using different types of membranes, and analyzed the relationship between polymer structure and device performance; then, after analyzing the development and the technical advantages and disadvantages of PEM, AEM, and ISMs, the technical limitations and future developing trends of these technical routes were discussed. Finally, we also give a brief prospect on how to guide and encourage the future development of various technical pathways through the policy guidance, so as to realize the large-scale market penetration of water electrolysis technology for green hydrogen production.

Near-zero carbon stochastic dispatch optimization model for power-to-gas-based virtual power plant considering information gap status theory

PurposeThis study aims to form a new concept of power-to-gas-based virtual power plant (GVPP) and propose a low-carbon economic scheduling optimization model for GVPP considering carbon emission trading.Design/methodology/approachIn view of the strong uncertainty of wind power and photovoltaic power generation in GVPP, the information gap decision theory (IGDT) is used to measure the uncertainty tolerance threshold under different expected target deviations of the decision-makers. To verify the feasibility and effectiveness of the proposed model, nine-node energy hub was selected as the simulation system.FindingsGVPP can coordinate and optimize the output of electricity-to-gas and gas turbines according to the difference in gas and electricity prices in the electricity market and the natural gas market at different times. The IGDT method can be used to describe the impact of wind and solar uncertainty in GVPP. Carbon emission rights trading can increase the operating space of power to gas (P2G) and reduce the operating cost of GVPP.Research limitations/implicationsThis study considers the electrical conversion and spatio-temporal calming characteristics of P2G, integrates it with VPP into GVPP and uses the IGDT method to describe the impact of wind and solar uncertainty and then proposes a GVPP near-zero carbon random scheduling optimization model based on IGDT.Originality/valueThis study designed a novel structure of the GVPP integrating P2G, gas storage device into the VPP and proposed a basic near-zero carbon scheduling optimization model for GVPP under the optimization goal of minimizing operating costs. At last, this study constructed a stochastic scheduling optimization model for GVPP.

Direct solar-driven reduction of greenhouse gases into hydrocarbon fuels incorporating thermochemical energy storage via modified calcium looping

The Energy and Environment issue, so called E2E, has become an increasingly severe challenge to our society. The carbon neutrality target before the middle of this century requires an accelerated global transformation towards renewables and sustainable low carbon technologies. Since greenhouse gasses like CO2 and CH4 cause serious climate warming, here we report a modified calcium-looping (CaL) that directly harvest and utilize solar energy to capture and convert CO2 into syngas along with CH4, meanwhile it is accompanied with thermochemical energy storage to overcome the fluctuations of renewable energy. The full advantages of CaL in both carbon capture and utilization and thermal energy storage are taken for establishing such a renewable energy system with near-zero carbon emissions. We dope nanoscale Ni into CaCO3 to enhance the direct solar absorption of the composite material and simultaneously catalyze the in-situ CO2 conversion reaction. The experiment and demonstration of such a CaL are conducted in a fixed bed photo-reactor. The in-situ conversion ratio of CO2 reaches up to 85.6 %, which in reverse facilitates the decomposition of CaCO3. The carbon deposited from the methane decomposition in the calcination process can be eliminated in the subsequent carbonation process. The proposed system achieves negative emissions of greenhouse gas and systematically converts solar energy into hydrocarbon fuel, making it a competitive scheme for clean energy and carbon cycle economy.

Improving the economics of fossil-free steelmaking via co-production of methanol

Steelmaking is responsible for 7% of the global net emissions of carbon dioxide and heavily reducing emissions from currently dominating steelmaking processes is difficult and costly. Recently, new steelmaking processes based on the reduction of iron ore with hydrogen (H2) produced via water electrolysis have been suggested. If the electricity input to such processes is fossil-free, near-zero carbon dioxide emissions steelmaking is achievable. However, the high electricity demand of electrolysis is a significant implementation barrier. A H2 storage may alleviate this via allowing a larger share of H2 to be produced at low electricity prices. However, accurately forecasting electricity market dynamics is challenging. This increases the risk of investment in a H2 storage. Here we evaluate a novel methanol-based H2 storage concept for H2-based steelmaking that also allows for the co-production of methanol. During electricity price peaks, the methanol can be reformed to produce H2 for the steelmaking process. During prolonged periods of low electricity prices, excess methanol can be produced and sold off, thus improving the prospects of storage profitability. We use historical electricity prices and a process model to evaluate methanol and fossil-free steel co-production schemes. Methanol co-production is found to have the potential to improve the economics of H2 supply to a fossil-free steelmaking process by up to an average of 0.40 €/kg H2 across considered scenarios, equivalent to a 25.0% reduction in H2 production electricity costs.

Design and energy analysis of solid oxide fuel cell and gas turbine hybrid systems with membrane reactor

ABSTRACT The methanol-reforming solid oxide fuel cell (SOFC) emits high concentration of CO2 from the anode outlet. To achieve the goal of clean and low-carbon power generation, a CO2 capture unit is integrated with SOFC. In this work, the CO2 capture unit were set at different places in the conventional SOFC and gas turbine (GT) hybrid system. One was to place the water-gas-shift membrane reactor (WGSMR) at the anode inlet (SOFC-MRpre) and the other at the anode outlet (SOFC-MRpost). The key parameters, including the anode off-gas recycling ratio (RR), steam-to-carbon ratio (S/C), and operating pressure, have been investigated. Besides, the effects of the parameters on the power production, electrical efficiency, system efficiency, and CO2 capture capacity of the two processes were analyzed. It was found that the electrical and system efficiencies reached 53.3% and 41.8% for the SOFC-MRpre process, while 62.0% and 60.4% for the SOFC-MRpost process, respectively. The results show that placing the membrane reactor at the anode outlet can significantly reduce the energy consumption of the vacuum and blower, thus increasing the system efficiency. Besides, near-zero carbon emissions with only a 7.3% energy penalty can be achieved by the SOFC-MRpost process. These results reveal that the SOFC-MRpost process has more advantages than the SOFC-MRpre process.

Electrochemical proton insertion modulates the hydrogen evolution reaction on tungsten oxides.

The development of new electrocatalysts for the hydrogen evolution reaction (HER) could reduce the dependence on Pt and other rare metals and enable large-scale production of hydrogen with near-zero carbon emissions. Mechanistic insight into the electrocatalytic activity of a material helps to accelerate the development of new electrocatalysts. Alternative electrocatalyst materials such as transition metal oxides and sulfides can undergo insertion reactions that change their properties. Recent reports indicate that the presence of inserted ions can influence the electrocatalytic activity. Here, we utilized a materials chemistry approach to understand the role of proton insertion in the HER activity of the layered tungsten oxide hydrates (WO3·xH2O, x = 1, 2). We synthesized a series of tungsten oxide hydrates along with an octylamine-pillared tungsten oxide (OA-WO3). We used cyclic voltammetry to study the electrochemical reactivity of each material and performed ex situ x-ray diffraction and Raman spectroscopy to understand bulk and surface structural changes during electrochemical cycling. We show an inverse relationship between the degree of proton insertion and HER overpotential in tungsten oxides: the lack of proton insertion leads to a high overpotential for the HER. We discuss three hypotheses for how proton insertion leads to the HER activity in WO3·xH2O: (1) proton insertion changes the electronic band structure of WO3·xH2O, (2) the presence of bulk protons can influence ΔGH,ads at the surface sites, and (3) the inserted protons may participate in the HER mechanism on WO3·xH2O. Overall, this work shows the critical role of proton insertion in enabling the high HER activity in tungsten oxides.

Novel coal-to-methanol process with near-zero carbon emission: Pulverized coal gasification-integrated green hydrogen process

The coal-to-methanol (CTM) is an important technical route for methanol production. The process suffers from high CO2 emission and low energy efficiency due to the mismatch of H/C (hydrogen-to-carbon) ratio between raw coal and products. Hydrogen production from renewable energy can be introduced into the system to meet the H/C ratio. In this paper, a novel CTM process with near-zero carbon emission has been proposed, the direct CO2 emission is decreased from 1.9 to 0.035 t CO2·t−1 MeOH. The novel process avoids requirement of the water-gas shift unit to reduce the production of CO2 from the source, and a novel acid gas removal process is proposed to remove sour gas while ensuring the reduction of CO2 loss. Compared with traditional CTM, CO2 emission intensity, carbon utilization efficiency and energy efficiency of the novel process are 88.87% lower, 130.77% higher, and 39.64% higher, respectively. The novel process is economically feasible when the H2 price is less than 10.36 CNY·kg−1 H2 and the carbon tax is higher than 223.3 CNY·t−1 CO2. This study will enable both economic and environmental route for methanol production in the future and will facilitate future studies on the integration and management of CTM coupled renewable energy.

Integrated Energy Planning for Near-Zero Carbon Emission Demonstration District in Urban Areas: A Case Study of Meishan District in Ningbo, China

Reasonable regional integrated energy planning is an important prerequisite for the construction of a Near-Zero Carbon Emission Demonstration District (NCEDD). An integrated energy planning scheme that is based on a three-step planning method with the objective of achieving an NCEDD is proposed in this paper. First, the planning objectives should be determined. After that, the planning strategies should be established. Finally, the planning approaches should be proposed according to the previously determined objectives and strategies. A case study considering the integrated energy planning of the Meishan International Near-Zero Carbon Emission Demonstration District (MINCEDD) is investigated to explain the planning method. In addition, the planning results, which are indicated as indexes, are explained, analyzed, and compared to the ones of other districts. The indexes include a proportion of renewable energy to primary energy (73% by 2030 and 108% by 2050), a proportion of renewable power to total power consumption (98% by 2030 and 111% by 2050), and CO2 emission reduction rates (70% by 2030 and 100% by 2050) and are more advanced than other districts in China. This planning scheme and method can provide a reference for the integrated energy planning of NCEDDs in developed urban areas.

Reducing the emission of climate-altering substances in cementitious materials: A comparison between alkali-activated materials and Portland cement-based composites incorporating recycled tire rubber

Low carbon or near-zero carbon concrete technology is in line with the pillars of sustainable development, where industrial waste or low-carbon binders can reduce or eliminate consumption of Portland cement and natural resources, leading to less environmental pollution. This work presents an experimental study on the comparison between alkali-activated materials (also recognized as geopolymers) and a traditional cementitious matrix (Portland cement) incorporated with rubber particles, deriving from end-of-life tires, as replacement of raw mineral aggregates. To explore the potential of rubber-geopolymer compounds, an experimental comparative analysis with rubber-Portland mortars was performed. Initial investigations (microstructural/compositional analysis, porosity and water absorption measurements, and mechanical tests) were conducted on rubberized samples obtained by varying the binder, the sand-rubber replacement ratio (0 vol%, 50 vol%, and 100 vol%) and the rubber particle size (0–1 mm rubber fine aggregate and 1–3 mm rubber granules). The results revealed a greater compatibility of the alkali-activated matrix with tire rubber aggregates, resulting in better performance in terms of interfacial adhesion, reduced porosity rate, flexural strength, and toughness. However, compressive strength results showed a weaker mechanical performance of rubber-geopolymer mixes compared to Portland counterparts. As also verified by Si/Al elemental analysis, the structural quality and mechanical development of the geopolymer matrix was strongly influenced by the removal of sand as a Si-source. The potential embodied carbon emission performance and cost analysis were also estimated to evaluate the economic and environmental impact related to the use of recycled rubber as complete aggregate in Portland and geopolymer mixes. Sustainability analysis revealed the greater environmental friendliness of geopolymer formulations compared to those in ordinary cement, but higher production costs. The total addition of rubber aggregates induced an increase in emissions and costs (variable according to the type of matrix) which, however, does not directly correlate with the processing/price of the polymer fraction. Deepening the research on cleaner matrices and promoting the use of recycled materials in concrete applications could lead to a gap levelling between Portland and geopolymer rubber-based composites. Building on these findings, future study will focus on the optimization of the mix design as a function of rubber aggregates.

Carbon dioxide abatement by integration of methane bi-reforming process with ammonia and urea synthesis

The use of thermal power plants has been increasing lately, despite its use being associated with high greenhouse gases emissions, especially carbon dioxide. In the context of the Paris Agreement of 2015, carbon dioxide capture, storage and utilization techniques must be increasingly employed to reduce environmental impacts. The utilization of carbon dioxide from a power plant flue gas as feedstock to other chemicals synthesis (such as ammonia and urea) arises as a good alternative to achieve near-zero carbon dioxide emissions. The aim of this work is to propose an alternative route, based on the bi-reforming of methane, for the synthesis gas section of ammonia and urea production plants, in order to promote carbon dioxide abatement, comparing this innovative route with the conventional and century-long existing process. Technical and environmental metrics of the proposed and conventional routes were compared. Aspen Plus® process simulator was used to simulate the bi-reforming process and both routes for ammonia and urea synthesis and choose the operational parameters. Simulation results show that for a target production of 2000 tonne/day of urea, the proposed alternative route has the potential to abate 745 tonne/day of carbon dioxide, while the conventional route emits 1156 tonne/day of carbon dioxide. Comparison of technical metrics of both routes shows that the proposed route requires an electricity usage of 0.27 MWh/tonne of products while the conventional route requires 0.47 MWh/tonne of products. However, hydrogen yield in the conventional route is higher than in its counterpart, with 0.41 and 0.22 tonnes of hydrogen produced for each tonne of inlet natural gas in the conventional and proposed routes, respectively. Comparison of economic metrics of both configurations show that none of the routes are economically viable, however, the alternative route has better economic indicators besides successfully promotes carbon dioxide abatement.

Designing an Energy-Resilient Neighbourhood Using an Urban Building Energy Model

A climate resilient city, perforce, has an efficient and robust energy infrastructure that can harvest local energy resources and match energy sources and sinks that vary over space and time. This paper explores the use of an urban building energy model (UBEM) to examine the potential for creating a near-zero carbon neighbourhood in Dublin (Ireland) that is characterised by diverse land-uses and old and new building stock. UBEMs are a relatively new tool that allows the simulation of building energy demand across an urbanised landscape and can account for building layout, including the effects of overshadowing and the potential for facade retrofits and energy generation. In this research, a novel geographic database of buildings is created using archetypes, and the associated information on dimensions, fabric and energy systems is integrated into the Urban Modelling Interface (UMI). The model is used to simulate current and future energy demand based on climate change projections and to test scenarios that apply retrofits to the existing stock and that link proximate land-uses and land-covers. The latter allows a significant decoupling of the neighbourhood from an offsite electricity generation station with a high carbon output. The findings of this paper demonstrate that treating neighbourhoods as single energy entities rather than collections of individual sectors allows the development of bespoke carbon reducing scenarios that are geographically situated. The work shows the value of a neighbourhood-based approach to energy management using UBEMs.

Exergoeconomic analysis and optimization of the Allam cycle with liquefied natural gas cold exergy utilization

The Allam cycle is a promising oxy-fuel combustion power cycle with high electrical efficiency and near-zero carbon dioxide emissions. In this paper, the thermodynamic and exergoeconomic analyses are performed for a novel combined power and cooling oxy-fuel power cycle, which combines the Allam cycle with liquefied natural gas regasification process. Parametric study is conducted to investigate the effects of key cycle variables on the electrical and exergy efficiencies and total product unit cost of the proposed cycle. Multi-objective optimization is carried out to maximize the exergy efficiency and minimize the total product unit cost. The results show that Condenser 2 has the highest exergy destruction of 22.81 MW, followed by the combustor (22.72 MW). The combustor, Condenser 2 and gas turbine are the three most important components from exergoeconomic aspects. The introduction of adiabatic compression heat of the bypass stream has a positive impact on the system performance, especially when the outlet temperature of the combustor is low. The optimization results indicate that the exergy efficiency and the total product unit cost cannot reach the optimal values at the same time. The highest exergy efficiency of 50.31% and the lowest total product unit cost of 16.654 $/GJ are obtained respectively with different sets of cycle variables. In addition, the electrical efficiency of the optimized proposed cycle is up to around 65.7%, about 11 percentage points higher than that of the Allam cycle.

Policy incentives in carbon capture utilization and storage (CCUS) investment based on real options analysis

Carbon capture, carbon utilization and storage (CCUS) technology is an important potential technical support for coal power plants to maintain existing production structure while simultaneously achieving near-zero carbon emissions with the current energy structure in China being dominated by coal. However, CCUS technology is still at the early demonstration stage, and there are many uncertainties in the carbon trading market, technology and policy incentives that the traditional method is no longer able to handle. Based on the binomial tree real option model, this paper establishes a CCUS technology investment evaluation model that incorporates the uncertainties with carbon price, government subsidy, technological progress and carbon dioxide utilization ratios into the model, and investigates the influence of government incentive on CCUS technology investment in two scenarios in China. The numerical results in case study show that (1) If the subsidy is too low, no matter how high the lower limit of carbon price is set, enterprises will not invest. (2) When the proportion of government subsidy exceeds 0.33, a specific and accurate minimum carbon price is given to promote coal-fired plants immediate investment in CCUS technology based on the model. (3) Only the government subsidies cannot stimulate CCUS investment at this demonstration stage. These findings provide a reference for public policy decision-making and promotes the development and large-scale deployment of CCUS technology in China.

Power-to-gas-based VPP Stochastic Scheduling Optimization Model in View of Carbon Emission Constraints

Combining P2G and virtual power plant (Virtual power plant, VPP), this paper proposes a new concept of electrical interconnection virtual power plant (Power-to-gas-based VPP, GVPP). In addition, this paper proposes a GVPP low-carbon economic dispatch optimization model considering carbon emission rights trading. Furthermore, in view of the strong uncertainty of wind power and PV power generation in GVPP, the information gap decision theory is used to measure the uncertainty tolerance threshold of decision makers under different expected target deviations. In addition, a GVPP near-zero carbon random scheduling optimization model is established under the conventional and worst-case scenarios. In order to verify the feasibility and effectiveness of the proposed model, a 9-node energy hub was selected as the simulation system. The results show that: (1) GVPP can coordinate and optimize the output of electricity-to-gas and gas turbines according to the difference in gas and electricity prices in the electricity market and the natural gas market at different times. Moreover, it can use the two-way conversion of gas and electricity energy to form an electricity-gas-electricity cycle, thereby improving the system’s clean energy absorption capacity, reducing its own carbon emissions and the volatility of net output. (2) The IGDT method can be used to describe the impact of wind and wind uncertainty in GVPP. Decision makers can obtain the maximum tolerance for wind and wind uncertainty by setting a reasonable expected target deviation coefficient. For example, when the expected target deviation coefficient is 0.5, the corresponding degree of uncertainty is 0.142. In the worst scenario, the scheduling results obtained by this method are in line with the actual scheduling experience, which reflects the effectiveness of the method in this paper. In summary, the models and methods presented in this paper can be used to formulate optimal scheduling decision-making schemes for GVPP considering carbon trading and uncertainty.

Effect of oxygen supply method on the performance of a micro gas turbine-based triple combined cycle with oxy-combustion carbon capture

There is increasing interest in zero-carbon-emission power to prevent global warming. This study investigated an effective way to minimize the efficiency penalty and achieve near-zero carbon emission in a small-scale triple combined cycle. The power block of the cycle includes a solid oxide fuel cell, micro gas turbine, and organic Rankine cycle. The three oxy-combustion capture systems are a semi-closed cycle, a cycle using an ion transport membrane, and a cycle where the membrane is replaced with an air separation unit. A parametric analysis was performed to determine an optimal pressure ratio for each cycle. The performance characteristics of the three cycles and a cycle with conventional post-combustion capture were compared. It was found out that the cycle using an air separation unit is more efficient than the other two cycles and captures highly pure carbon dioxide. The efficiency penalty due to carbon capture is only 4.4%, resulting in 58% net efficiency. The most significant finding is that using the cryogenic air separation unit is more favorable than using the ion transport membrane to separate oxygen in a small triple combined cycle operating at low pressure, in contrast to one with high pressure.

Transportation strategies for a 1.5 °C world: A comparison of four countries

Decarbonizing transportation in emerging economies will be one of the key challenges in global climate change mitigation efforts. In this paper, pathways are developed towards achieving a 1.5° degree scenario for land-transport for four emerging economies (Brazil, India, Kenya and Vietnam). The aim is to highlight the key opportunities and challenges for low-carbon transport in countries with rapidly growing mobility demand. The main focus of this paper is to reconcile actual and required emission reduction targets and develop plausible pathways to achieve these targets. The paper also identifies potential strategies and measures for these countries to follow these pathways. The analysis considers the contributions of “avoid” (cutting travel growth), “shift” (to lower CO2 modes) and “improve” (vehicle and fuel CO2 characteristics) interventions to decarbonisation scenarios. These scenarios aim to inform renewed Nationally Determined Contributions and shed light on the feasibility of deep decarbonisation pathways that would be in line with the Paris Agreement. Results from this study show that achieving 1.5DS would require dramatic changes in travel patterns, technology and fuels, and major intensification of current policy approaches. Decarbonization solutions will need to include greater use and investment of efficient modes, major shifts toward near-zero carbon fuels such as clean electricity, systems integration, modal shift and urban planning solutions. Although the socio-economic situations and national transport systems differ between the selected countries, some fairly similar strategies appear likely to be core to the mitigation effort, such as rapid growth in light- and heavy-duty vehicle electrification and investments in public transit systems.

Indicative energy technology assessment of hydrogen processing from biogenic municipal waste

An indicative appraisal has been undertaken of a combined Anaerobic Digestion and Steam Methane Reforming process to produce sustainable hydrogen from organic waste. The anaerobic digestion plant was based on the plant in Tilburg (The Netherlands), and was modelled from the kerbside organic waste collections through to methane production. Data on biogenic waste was obtained from a collection trial in a municipal area in the UK. This was scaled-up to match that of a Tilburg-like anaerobic digestion plant. The waste collection trials enabled the catchment area for an anaerobic digestion plant on a commercial scale to be estimated. A thermodynamic evaluation of the combined process included energy and exergy analysis in order to determine the efficiency of each process, as well as to identify the areas that lead to inefficiencies. The overall energy efficiency was 75% and the overall exergy efficiency was 60%. The main energy losses were associated with compressor inefficiencies. In contrast, the main exergy consumption was found to be due to the fermentation in the digestion tanks. Other hydrogen process efficiencies vary from 21% to 86%, with the higher efficiencies belonging to non-renewable processes. However, the sustainable hydrogen produced comes from entirely renewable sources (biogenic waste) and has the benefit of near-zero carbon emissions in contrast to fossil fuels. Finally, the case study included an indicative financial assessment of the collection to processing chain. A discounted payback period of less than 20 years was estimated with a modest annual charge for householders.

Prospective carbon footprint comparison of hydrogen options

The Life Cycle Assessment methodology is often used to evaluate the environmental performance of hydrogen energy systems. However, even though hydrogen is usually seen as a strategic energy carrier for the future energy sector, there is a lack of case studies assessing its prospective life-cycle performance. In order to contribute to filling this gap, this work addresses a carbon footprint comparison of hydrogen options from a prospective standpoint. Four relevant hydrogen production pathways (steam methane reforming, grid-powered alkaline electrolysis, wind-powered alkaline electrolysis, and biomass gasification) under three time scenarios (reference, year 2030, and year 2050) are assessed, taking into account the expected evolution of key technical parameters such as efficiencies, lifespans, and the grid electricity mix. The results show a favourable carbon footprint of renewable hydrogen from biomass gasification and wind electrolysis, with a relatively steady near-zero carbon footprint. Despite the unfavourable carbon footprint results of conventional hydrogen from steam methane reforming and hydrogen from grid electrolysis, the latter is associated with a rapid trend towards a suitable long-term carbon footprint.

Thermal behaviour of ladle slag mortars containing ferrochrome slag aggregates

Concretes, depending on their application, may be exposed to elevated temperatures during their lifetime, especially when placed near or in a furnace or during an accidental fire. The thermal stability of alkali-activated mortars and hydrated mortars prepared using ladle slag and two different aggregates was studied. A commercial calcium aluminate cement was used as a comparison for the properties after exposure to temperatures up to 1000°C. All samples were characterised and analysed through a strength test, dilatometric analysis, thermogravimetric analysis, ultrasonic pulse velocity and scanning electron microscopy. The hydrated ladle slag mortars exhibited properties similar to or better than the commercial calcium aluminate cement, while the alkali-activated ladle slag's thermal properties were inferior to the hydrated ladle slag mortars. The tests also showed that the use of ferrochrome slag aggregates in hydrated ladle slag mortars exhibited similar properties to those using sand aggregate mortars. The damage behaviours of the mortars were dependent on the temperature-induced dehydration, dehydroxylation and thermal incompatibility between the paste and aggregates. The results from this study specify the possibilities of using 100% industrial by-product-based mortar and near-zero carbon dioxide emissions as a fire-resistant material in furnaces, buildings and fireplaces.