Life cycle assessment of hydrogen production from biomass gasification systems

In this study, a Life Cycle Assessment (LCA) of biomass-based hydrogen production is performed for a period from biomass production to the use of the produced hydrogen in Proton Exchange Membrane (PEM) fuel cell vehicles. The system considered is divided into three subsections as pre-treatment of biomass, hydrogen production plant and usage of hydrogen produced. Two different gasification systems, a Downdraft Gasifier (DG) and a Circulating Fluidized Bed Gasifier (CFBG), are considered and analyzed for hydrogen production using actual data taken from the literature. Fossil energy consumption rate and Green House Gas Emissions (GHG) are defined and indicated first. Next, the LCA results of DG and CFBG systems are compared for 1 MJ/s hydrogen production to compare with each other as well as with other hydrogen production systems. While the fossil energy consumption rate and emissions are calculated as 0.088 MJ/s and 6.27 CO₂ eqv. g/s in the DG system, they are 0.175 MJ/s and 17.13 CO₂ eqv. g/s in the CFBG system, respectively. The Coefficient of Hydrogen Production Performance (CHPP) (newly defined as a ratio of energy content of hydrogen produced from the system to the total energy content of fossil fuels used) of the CFBG and DG systems are then determined to be 5.71 and 11.36, respectively. Thus, the effects of some parameters, such as energy efficiency, ratio of cost of hydrogen, on natural gas and capital investments efficiency are investigated. Finally, the costs of GHG emissions reduction are calculated to be 0.0172 and 0.24 $/g for the DG and CFBG systems, respectively.     

Exergy analysis in the assessment of hydrogen production from UCG

The demand for H₂ increases rapidly with the gradual recognition of the potential of H₂ as an important secondary energy. At present, coal gasification is the main way to obtain hydrogen on a large scale and at a low cost in China. The underground coal gasification (UCG), as a kind of in-situ utilization technology that can exploit the unreachable deep coal resources, could become an alternative H₂ production pathway. This paper presents comparative study of energy utilization and resource consumption in H₂ production by UCG and typical surface coal gasification (SCG) technology, namely Lurgi fixed bed gasification, with 1.2 billion Nm³/a throughput of H₂ as example, to offer corresponding data support. The efficiency and the amount of resources consumed in constructing and operating each coal-to-hydrogen system under different conditions have been researched from exergetic point of view, which is not reported in existing literatures. In this paper, the exergy efficiency is calculated to be 40.48% and 40.98% for hydrogen production using UCG and SCG. The result indicates the competitiveness of UCG in the field of hydrogen production comparing with widely used coal gasification technology. The resource consumption is measured by cumulative exergy consumption (CExC), which is 8.17E+10 MJ and 6.57E+10 MJ for H₂ production from UCG and SCG. The result shows that although the H₂ production from UCG has higher CExC, it can significantly reduce the resource consumption of equipment comparing with H₂ production from SCG, indicating its advantage in total investment. It is found that the exergy efficiency increases with the rise in H₂O-to-O₂ and O₂-to-CO₂ ratio, while the value of CExC decreases with the appreciation of H₂O-to-O₂ ratio yet increases as the O₂-to-CO₂ ratio rises. In addition, the sensitivity analysis of production capacity reveals that the exergy efficiency gap and CExC gap between hydrogen production by UCG and SCG diminishes at smaller scale production capacities, showing that UCG is more suitable for small-scale hydrogen production.     

GHG emissions and energy performance of offshore wind power

This paper presents specific life cycle GHG emissions from wind power generation from six different 5 MW offshore wind turbine conceptual designs. In addition, the energy performance, expressed by the energy indicators Energy Payback Ratio (EPR) Energy Payback Time (EPT), is calculated for each of the concepts.There are currently few LCA studies in existence which analyse offshore wind turbines with rated power as great as 5 MW. The results, therefore, give valuable additional environmental information concerning large offshore wind power. The resulting GHG emissions vary between 18 and 31.4 g CO₂-equivalents per kWh while the energy performance, assessed as EPR and EPT, varies between 7.5 and 12.9, and 1.6 and 2.7 years, respectively. The relatively large ranges in GHG emissions and energy performance are chiefly the result of the differing steel masses required for the analysed platforms. One major conclusion from this study is that specific platform/foundation steel masses are important for the overall GHG emissions relating to offshore wind power. Other parameters of importance when comparing the environmental performance of offshore wind concepts are the lifetime of the turbines, wind conditions, distance to shore, and installation and decommissioning activities.Even though the GHG emissions from wind power vary to a relatively large degree, wind power can fully compete with other low GHG emission electricity technologies, such as nuclear, photovoltaic and hydro power.     

Potential for reducing GHG emissions and energy consumption from implementing the aluminum intensive vehicle fleet in China

The automobile industry in China has rapidly developed in recent years which resulted in an increase in gasoline usage and greenhouse gas (GHG) emissions. Focus on climate change has also accelerated to grow pressure on reducing vehicle weight and improving fuel efficiency. Aluminum (Al) as a light metal has demonstrated a great potential for weight savings in applications such as engine blocks, cylinder heads, wheels, hoods, tailgates etc. However, primary Al production requires intensive energy and the cost of Al is more than traditional steel, which may affect the total benefits realized from using Al in automobiles. Therefore, it is very essential to conduct a study to quantify the life cycle GHG emissions and energy consumption if the plan is to achieve fleet-wide Al intensive vehicles.     

Life cycle assessment of earth-abundant photocatalysts for enhanced photocatalytic hydrogen production

Hydrogen (H₂) can play a critical role in global greenhouse gas (GHG) mitigation. Photocatalytic water splitting using solar radiation is a promising H₂ technology. Titanium dioxide (TiO₂) and carbon nitride (g–C₃N₄)–based photocatalysts are the most widely used photocatalytic materials because of their activity and abundance. Several attempts have been made to improve the photocatalytic performance of these materials in terms of their activity level, life span, response to visible radiation, and stability. However, the environmental impacts of these modifications are often not included in existing studies. This research, therefore, develops a cradle-to-grave life cycle assessment (LCA) framework to evaluate and compare the GHG footprints of four alternative pathways: TiO₂ nanorods and fluorine-doped carbon nitride quantum dots embedded with TiO₂ (CNF: TNR/TiO₂), g-C₃N₄, and g-C₃N₄/BiOI composite. Unlike most studies that focus only on certain stages such as laboratory-scale photocatalytic fabrication, this study includes utility-scale cell production, assembly, operation, and end of life to give a more accurate and precise environmental performance estimation. The results show that g-C₃N₄/BiOI has the lowest GHG footprint (0.38 kg CO₂ eq per kg of H₂) and CNF: TNR/TiO₂ has the lowest energy payback time (0.4 years). In every pathway, energy use in material extraction processes makes up the largest GHG contribution, between 83% and 89%. Sensitivity and uncertainty analyses were conducted under the impact of various input parameters on the life cycle GHG emissions of hydrogen production. Photocatalytic water splitting is highly feasible for adaptation as a mainstream hydrogen production pathway in the future.     

Life cycle net energy and global warming impact assessment for hydrogen production via decomposition of ammonia recovered from source-separated human urine

Decomposition of ammonia derived from source-separated human urine is a renewable approach for hydrogen production. Life cycle net energy analysis and global warming impact of scaled-up hydrogen production via this technique are studied in this paper. Ammonia decomposition processes, including fixed-bed reactors with Ru/Al₂O₃ and Ni/Al₂O₃ as catalyst options are simulated using the Aspen Plus software, and the results are compared with published data for validation. The life cycle net energy indicators are assessed for three scenarios of ammonia generation: conventional air stripping, microbial fuel cell, and electrochemical cell methods at a unit basis of 1000 kg of H₂ production. Results show that the microbial fuel cell process is more energy-efficient and emits lower greenhouse gases. The net energy ratio of the microbial fuel cell method is 1.38, and 1.12, for Ru/Al₂O₃ and Ni/Al₂O₃, respectively. A comparative assessment of ammonia generation and decomposition options for environmentally-benign hydrogen production is discussed.     

Analysis of scenarios for the reduction of energy consumption and GHG emissions in transport in the Basque Country

Fossil energy depletion and fight against climate change force humanity to decarbonize the economy. By year 2050 CO₂ emissions will have to reduce globally at least 85%, and probably over 95% in developed countries.The modeling of the transportation of people and commodities in the Basque Autonomous Community (Spain) in year 2008 has allowed us to draw some conclusions about the challenges ahead. The exploration of several scenarios modeled in order to reduce energy consumption in transport shows that mobility in a decarbonized world will have to be more efficient, electrified when moving people and freight on land, based on renewable generation, and organized in such a way that guarantees very high occupancies of vehicles. All these elements will be indispensable, and even not sufficient if they are still not complemented with a reduction of mobility in absolute terms, so that economic transportation intensity—the ratio between transportation and whole economic activity—recovers to levels seen in the world four decades ago, prior to the development of present hypermobility.     

Life cycle assessment of hydrogen production from biomass gasification. Evaluation of different Spanish feedstocks

Gasification of biomass can be used for obtaining hydrogen reducing the total greenhouse gases emissions due the fixation of CO₂ during photosynthetic processes. The kind of raw materials is an important variable since has a great influence on the energy balance and environmental impacts. Wastes from forestry are considered as the most appropriate raw materials since they do not compete for land. The aim of this work is to determine the environmental feasibility of four Spanish lignocellulosic wastes (vine and almond pruning and forest waste coming from pine and eucalyptus plantation) for the production of hydrogen through gasification. LCA methodology was applied using global warming potential, acidification, eutrophication and the gross energy necessary for the production of 1 Nm³ of hydrogen as impact categories. As expected, the use of biomass instead of natural gas leads to the reduction of CO₂ emissions. Regarding to the different feedstocks, biomass coming from forestry is more environmental-friendly since does not need cropping procedures. Finally, the distribution of environmental charges between pruning wastes and fruits (grape and almond) and the use of obtained by-products have a great influence, reducing the environmental impacts.     

Cofiring versus biomass-fired power plants: GHG (Greenhouse Gases) emissions savings comparison by means of LCA (Life Cycle Assessment) methodology

One way of producing nearly CO₂ free electricity is by using biomass as a combustible. In many cases, removal of CO₂ in biomass grown is almost the same as the emissions for the bioelectricity production at the power plant. For this reason, bioelectricity is generally considered CO₂ neutral. For large-scale biomass electricity generation two alternatives can be considered: biomass-only fired power plants, or cofiring in an existing coal power plant. Among other factors, two important aspects should be analyzed in order to choose between the two options. Firstly, which is the most appealing alternative if their Greenhouse Gases (GHG) Emissions savings are taken into account. Secondly, which biomass resource is the best, if the highest impact reduction is sought. In order to quantify all the GHG emissions related to each system, a Life Cycle Assessment (LCA) methodology has been performed and all the processes involved in each alternative have been assessed in a cradle-to-grave manner. Sensitivity analyses of the most dominant parameters affecting GHG emissions, and comparisons between the obtained results, have also been carried out.     

Life-cycle greenhouse gas emissions and energy balances of sugarcane ethanol production in Mexico

The purpose of this work was to estimate GHG emissions and energy balances for the future expansion of sugarcane ethanol fuel production in Mexico with one current and four possible future modalities. We used the life cycle methodology that is recommended by the European Renewable Energy Directive (RED), which distinguished the following five system phases: direct Land Use Change (LUC); crop production; biomass transport to industry; industrial processing; and ethanol transport to admixture plants. Key variables affecting total GHG emissions and fossil energy used in ethanol production were LUC emissions, crop fertilization rates, the proportion of sugarcane areas that are burned to facilitate harvest, fossil fuels used in the industrial phase, and the method for allocation of emissions to co-products. The lower emissions and higher energy ratios that were observed in the present Brazilian case were mainly due to the lesser amount of fertilizers applied, also were due to the shorter distance of sugarcane transport, and to the smaller proportion of sugarcane areas that were burned to facilitate manual harvest. The resulting modality with the lowest emissions of equivalent carbon dioxide (CO_2e) was ethanol produced from direct juice and generating surplus electricity with 36.8 kgCO_2e/GJ_ethanol. This was achieved using bagasse as the only fuel source to satisfy industrial phase needs for electricity and steam. Mexican emissions were higher than those calculated for Brazil (27.5 kgCO_2e/GJ_ethanol) among all modalities. The Mexican modality with the highest ratio of renewable/fossil energy was also ethanol from sugarcane juice generating surplus electricity with 4.8 GJ_ethanol/GJ_fossil.     

Life cycle sustainability assessment of hydrogen from biomass gasification: A comparison with conventional hydrogen

Hydrogen is a key product for a cleaner energy sector. However, the suitability of the different hydrogen production options should be checked from a life-cycle perspective. The Life Cycle Sustainability Assessment (LCSA) methodology is helpful for this purpose, allowing a thorough interpretation of a product system's performance by integrating economic, environmental and social indicators. This work presents an LCSA of renewable hydrogen from biomass gasification, and its sustainability benchmarking against conventional hydrogen from steam methane reforming. Environmental (global warming and acidification), economic (levelised cost) and social (child labour, gender wage gap, and health expenditure) life-cycle indicators are characterised and jointly interpreted. The results show that hydrogen from biomass gasification cannot yet be thoroughly considered a sustainable alternative to conventional hydrogen mainly due to economic and social concerns. However, improvement actions leading to an increase in process efficiency would significantly enhance the system's performance in each of the three sustainability dimensions.     

Life cycle environmental and economic analyses of a hydrogen station with wind energy

This study aimed to identify the environmental and economic aspects of the wind-hydrogen system using life cycle assessment (LCA) and life cycle costing (LCC) methodologies. The target H₂ pathways are the H₂ pathway of water electrolysis (WE) with wind power (WE[Wind]) and the H₂ pathway of WE by Korean electricity mix (WE[KEM]). Conventional fuels (gasoline and diesel) are also included as target fuel pathways to identify the fuel pathways with economic and environmental advantages over conventional fuels. The key environmental issues in the transportation sector are analyzed in terms of fossil fuel consumption (FFC), regulated air pollutants (RAPs), abiotic resource depletion (ARD), and global warming (GW). The life cycle costs of the target fuel pathways consist of the well-to-tank (WTT) costs and the tank-to-wheel (TTW) costs. Moreover, two scenarios are analyzed to predict potential economic and environmental improvements offered by wind energy-powered hydrogen stations.     

Life cycle assessment of three types of hydrogen production methods using solar energy

A comprehensive life cycle assessment (LCA) is carried out for three methods of hydrogen production by solar energy: hydrogen production by PEM water electrolysis coupling photothermal power generation, hydrogen production by PEM water electrolysis coupling photovoltaic power generation, and hydrogen production by thermochemical water splitting method using S–I cycle coupling solar photothermal technology. The assessment also contains an evaluation of four environmental factors which are global warming potential, acidification potential, ozone depletion potential, and nutrient enrichment potential. After conducting a quantitative analysis of all three methods with environmental factors being considered, a conclusion has been drawn: The global warming potential and the acidification potential of the thermochemical water splitting by S–I cycle coupling solar photothermal technology are 1.02 kg CO₂-eq and 6.56E-3 kg SO₂-eq. And this method has significant advantages in the environmental impact of the whole ecosystem.     

Life cycle assessment of various hydrogen production methods

A comprehensive life cycle assessment (LCA) is reported for five methods of hydrogen production, namely steam reforming of natural gas, coal gasification, water electrolysis via wind and solar electrolysis, and thermochemical water splitting with a Cu–Cl cycle. Carbon dioxide equivalent emissions and energy equivalents of each method are quantified and compared. A case study is presented for a hydrogen fueling station in Toronto, Canada, and nearby hydrogen resources close to the fueling station. In terms of carbon dioxide equivalent emissions, thermochemical water splitting with the Cu–Cl cycle is found to be advantageous over the other methods, followed by wind and solar electrolysis. In terms of hydrogen production capacities, natural gas steam reforming, coal gasification and thermochemical water splitting with the Cu–Cl cycle methods are found to be advantageous over the renewable energy methods.     

A well to pump life cycle environmental impact assessment of some hydrogen production routes

In the present study, a comparative well to pump life cycle assessment is conducted on the hydrogen production routes of water electrolysis, biomass gasification, coal gasification, steam methane reforming, hydrogen production from ethanol and methanol. The CML 2001 impact assessment methodology is employed for assessment and comparison. Comparatively higher life cycle Carbon dioxide and Sulphur oxide emissions of 27.3 kg/kg H₂ and 50.0 g/kg H₂ respectively are determined for the water electrolysis hydrogen production route via U.S. electricity mix. In addition, the life cycle global warming potential of this route (28.6 kg CO_2eq/kg H₂) is found to be comparatively higher than other routes followed by coal gasification (23.7 kg CO_2eq/kg H₂)_. However, the ethanol based hydrogen production route is estimated to have comparatively higher life cycle emissions of nitrogen dioxide (19.6 g/kg H₂) and volatile organic compounds (10.3 g/kg H₂). Moreover, this route is determined to have a comparatively higher photochemical ozone creation potential of 0.0045 kg-ethene_eq/kg H₂ as well as eutrophication potential of 0.0043 kg PO_4eq/kg H_2. The results of this study are comparatively discussed to signify the importance of life cycle assessment in comparing the environmental sustainability of hydrogen production routes.     

Hydrogen production in underground coal gasification (UCG)

In this article, the rationales of the hydrogen production in underground coal gasification are explained. The experimental conditions and process of the underground gasification in the Liuzhuang Mine, Tangshan, Hebei Province are introduced, and the experimental results are analyzed. By adopting the new method of two-stage underground coal gasification with long channels and big sections, the daily water gas production reaches about 22,950 m³, with the maximum output of 53,550 m³, in which H₂ content is between 41 and 74%, with both CO and CH₄ contents over 7%. The daily average output of H₂ is 13,192 m³. Experimental results show that the two-stage underground gasification with multi-point air (steam) feed cannot only improve the average temperature of the gasifier effectively, but also shorten the cyclical time for the two stages by a wide margin, which makes the time longer by 0.96–1.18 times and 1.27–1.91 times, respectively, when water gas with a high content of H₂ is produced, as opposed to that of a traditional mode of pumping air (seam) with fixed points for field and model tests.     

Integration of underground coal gasification with a solid oxide fuel cell system for clean coal utilization

Underground coal gasification (UCG) is a promising clean coal technology. Typically, the syngas obtained from UCG is used for power generation via the steam turbine route. In the present paper, we consider UCG as a hydrogen generator and investigate the possibility of coupling it with a solid oxide fuel cell (SOFC) to generate electrical power directly. We show, through analysis, that integration with SOFC gives two specific advantages. Firstly, because of the high operating temperature of the SOFC, its anode exhaust can be used to produce steam required for the operation of UCG as well as for the reforming of the syngas for the SOFC. Secondly, the SOFC serves as a selective absorber of oxygen from air which paves the way for an efficient system of a carbon-neutral electrical power generation from underground coal. Thermodynamic analysis of the integrated system shows considerable improvement in the net thermal efficiency over that of a conventional combined cycle plant.     

Life cycle assessment of hydrogen production by methane decomposition using carbonaceous catalysts

Methane decomposition to yield hydrogen and carbon (CH₄ ? 2H₂ + C) is one of the cleanest alternatives, free of CO₂ emissions, for producing hydrogen from fossil fuels. This reaction can be catalyzed by metals, although they suffer a fast deactivation process, or by carbonaceous materials, which present the advantage of producing the catalyst from the carbon obtained in the reaction. In this work, the environmental performance of methane decomposition catalyzed by carbonaceous catalysts has been evaluated through Life Cycle Assessment tools, comparing it to other decomposition processes and steam methane reforming coupled to carbon capture systems. The results obtained showed that the decomposition using the autogenerated carbonaceous as catalyst is the best option when reaction conversions higher than 65% are attained. These were confirmed by 2015 and 2030 forecastings. Moreover, its environmental performance is highly increased when the produced carbon is used in other commercial applications. Thus, for a methane conversion of 70%, the application of 50% of the produced carbon would lead to a virtually zero-emissions process.     

Life cycle assessment of high temperature electrolysis for hydrogen production via nuclear energy

A life cycle assessment (LCA) of one proposed method of hydrogen production—the high temperature electrolysis of water vapor—is presented in this paper. High temperature electrolysis offers an advantage of higher energy efficiency over the conventional low-temperature alkaline electrolysis due to reduced cell potential and consequent electrical energy requirements. The primary energy source for the electrolysis will be advanced nuclear reactors operating at temperatures corresponding to those required for the high temperature electrolysis. The LCA examines the environmental impact of the combined advanced nuclear-high temperature electrolysis plant, focusing upon quantifying the emissions of carbon dioxide, sulfur dioxide, and nitrogen oxides per kilogram of hydrogen produced. The results are presented in terms of the global warming potential (GWP) and the acidification potential (AP) of the system. The GWP for the system is 2000 g carbon dioxide equivalent and the AP, 0.15 g equivalents of hydrogen ion equivalent per kilogram of hydrogen produced. The GWP and AP of this process are one-sixth and one-third, respectively, of those for the hydrogen production by steam reforming of natural gas, and are comparable to producing hydrogen from wind- or hydro-electricity powered conventional electrolysis.     

Life cycle CO2 emissions from power generation using hydrogen energy carriers

Hydrogen energy carriers such as liquid hydrogen (LH₂), methylcyclohexane (MCH), and ammonia (NH₃) are promising energy vectors in the clean energy systems currently being developed. However, their effectiveness in mitigating environmental emissions must be assessed by life cycle analyses throughout the supply chain. In this study, while focusing on hydrogen energy carriers, life cycle inventory analyses were conducted to estimate CO₂ emissions from the following types of power generation plants in Japan: a hydrogen (H₂) mono-firing power plant using LH₂ or MCH that originated from overseas renewable electricity; and NH₃ co-firing with fossil fuel and NH₃ mono-firing power plants using hydrogen energy carriers that originated from overseas natural gas or renewable electricity. Parameters related to the supply chains were collected by literature surveys, and the Japanese life cycle inventory database was primarily used to calculate the emissions. From the results, CO₂ hotspots of the target supply chains and potential measures are identified that become necessary to establish low-carbon supply chains.