Life cycle assessment of energy generation from biogas—Attributional vs. consequential approach

Many studies that apply life cycle assessment methodology avoid a strict differentiation between attributional (aLCA) and consequential (cLCA) life cycle assessment. The main distinction that can be made is that an aLCA approach describes a state of average production systems of an economic system while in contrast the consequential approach describes changes (induced by political decisions) in production systems within the economic system. The task of this study was to analyze a biogas system from an environmental point of view and thereby to work out the methodological differences of aLCA and cLCA approaches. The Life cycle inventory quantity primary energy demand (PED) as well as the impact categories global warming potential (GWP), eutrophication (EP), acidification (AP) and photochemical ozone creation potential (POCP) were analyzed. The aLCA approach was split into three scenarios, a physical, an economic and a core product focused one (with focus on the main product) to show the impact of by-product handling. The cLCA approach was split into a local scenario using on-site data and a general scenario using higher aggregated data to show the effects of substitution caused by the introduction of a new technology. The results of the two approaches were compared with the environmental impact of the current average and marginal German electricity mix. Global warming potential per functional unit varied between 3.8 g and 12.5 g of CO2 equivalent in the biogas scenarios. Compared to the average and marginal German electricity mix savings in PED, GWP and partly in AP and POCP can be achieved. However, high variations in the proportion to the reference electricity system, the total quantity results as well as the contribution of single processes to the total result were found. This makes it indispensable to distinguish accurately between the aLCA and the cLCA approach.     

Life cycle assessment of conventional and optimised Jatropha biodiesel fuels

The environmental benefits and energy savings of the production of Jatropha fuels and operation in a typical LPV in India were examined. A baseline scenario and alternative optimised routes were assessed, considering different pathways of energy recovery from Jatropha coproducts. The following impact categories were assessed: Non-Renewable Energy (NRE) consumption, Global Warming Potential (GWP), Terrestrial Acidification Potential (TAP) and Respiratory Inorganic Effects (RIE). At present, the life cycle impact of Jatropha production and use is competitive with conventional diesel in terms of NRE and GHG emissions; however it results in higher local environmental impacts (RIE and TAP categories). Under optimised farming and processing practices and recovery of Jatropha coproducts either via co-generation, gasification or FT-diesel synthesis routes, Jatropha fuels reduce the impact of NRE, GHG, and RIE. The energy recovery paths to generate surplus electricity through generation and gasification routes show a better performance than FT-diesel synthesis routes in terms of NRE and GWP impacts. Nevertheless, in terms of local air pollution indicators, the FT-diesel synthesis route reveals the lowest emissions.     

Characterisation of land types and agro-ecological conditions for production of Jatropha as a feedstock for biofuels in Zimbabwe

There is increasing interest in Zimbabwe in developing a biofuels industry based on the production of biodiesel using Jatropha as the main feedstock. This has led to the introduction of Jatropha as a commercial energy crop in the country. There are plans to grow 1220 km² of Jatropha which will supply about 365,000 t of seed. This will provide about 110 dam³ of biodiesel required to achieve a blending level of 10% with petro-diesel. The availability and suitability of land for the production of Jatropha cannot be taken for granted, particularly given the fact that the concept and practice of production of feedstocks for biofuels remain contested on the threat they pose to food security. Determining the land that is potentially available for biofuels is a non-trivial task. A multiplicity of factors needs to be considered. It is important to determine the spatial extent of areas with suitable growth conditions for Jatropha. The interaction of soil type and land use is an important interface in agriculture. Added to this is the need to balance food, fodder and fuel supply in land use planning. This paper attempts to assess the availability and suitability of various land types as well as agro-ecological conditions for the production of Jatropha in Zimbabwe.     

Life cycle GHG assessment of fossil fuel power plants with carbon capture and storage

The evaluation of life cycle greenhouse gas emissions from power generation with carbon capture and storage (CCS) is a critical factor in energy and policy analysis. The current paper examines life cycle emissions from three types of fossil-fuel-based power plants, namely supercritical pulverized coal (super-PC), natural gas combined cycle (NGCC) and integrated gasification combined cycle (IGCC), with and without CCS. Results show that, for a 90% CO₂ capture efficiency, life cycle GHG emissions are reduced by 75–84% depending on what technology is used. With GHG emissions less than 170 g/kWh, IGCC technology is found to be favorable to NGCC with CCS. Sensitivity analysis reveals that, for coal power plants, varying the CO₂ capture efficiency and the coal transport distance has a more pronounced effect on life cycle GHG emissions than changing the length of CO₂ transport pipeline. Finally, it is concluded from the current study that while the global warming potential is reduced when MEA-based CO₂ capture is employed, the increase in other air pollutants such as NO_x and NH₃ leads to higher eutrophication and acidification potentials.     

Environmental impacts of a standalone solar water splitting system for sustainable hydrogen production: A life cycle assessment

Hydrogen is broadly utilized in various industries. It can also be considered as a future clean energy carrier. Currently, hydrogen is mainly produced from typical fuels such as coal; however, there exist some other clean alternatives which use water decomposition techniques. Water splitting via the copper-chlorine (Cu–Cl) thermochemical cycle is a superb option for producing clean carbon-free fuel. Here, the life cycle assessment (LCA) technique is used to investigate the environmental consequences of an integrated solar Cu–Cl fuel production facility for large-scale hydrogen production. The impact of varying important input parameters including irradiation level, plant lifetime, and solar-to-hydrogen efficiency on various environmental impacts are investigated next. For instance, an improve in the solar-to-hydrogen efficiency from 15% to 30%, results in a reduction in the GWP from 1.25 to 6.27E-01 kg CO₂ eq. An uncertainty analysis using Monte Carlo simulation is conducted to deal with the study uncertainties. The results of the LCA show that the potential of acidification and global warming potential (GWP) of the current system are 8.27E-03 kg SO₂ eq. and 0.91 kg CO₂ eq./kg H₂, respectively. According to the sensitivity analysis, the plant lifetime has the highest effect on the total GWP of the plant with a range of 0.63–1.88 kg of CO₂ eq./kg H₂. Results comparison with past thermochemical-based studies shows that the GWP of the current integrated system is 7% smaller than that of a solar sulfur-iodine thermochemical cycle.     

Gas fired combined cycle plant in Singapore: energy use,GWP and cost—a life cycle approach

A life cycle assessment was performed to quantify the non-renewable (fossil) energy use and global warming potential (GWP) in electricity generation from a typical gas fired combined cycle power plant in Singapore. The cost of electricity generation was estimated using a life cycle cost analysis (LCCA) tool. The life cycle assessment (LCA) of a 367.5 MW gas fired combined cycle power plant operating in Singapore revealed that hidden processes consume about 8% additional energy in addition to the fuel embedded energy, and the hidden GWP is about 18%. The natural gas consumed during the operational phase accounted for 82% of the life cycle cost of electricity generation. An empirical relation between plant efficiency and life cycle energy use and GWP in addition to a scenario for electricity cost with varying gas prices and plant efficiency have been established.     

Technical options for optimization of production of Jatropha as a biofuel feedstock in arid and semi-arid areas of Zimbabwe

Biofuels are being promoted as sustainable alternatives to fossil fuels both from energy supply perspective as well as a technical option to respond to climate change. Various crops are grown throughout the world to supply feedstocks for the production of biofuels. In sub-Saharan Africa, Jatropha curcas is considered to be the most suitable feedstock for production of biodiesel. Zimbabwe is a tropical country with suitable growth conditions for Jatropha. Since 2005, the production of Jatropha has gathered momentum in the country. The plan for production of Jatropha has concentrated on boosting production areas. Not much attention has been given to technical issues that are important in optimizing the yield and quality norms of Jatropha seed. This paper discusses technical interventions at two levels of the value chain that are required to optimize production of Jatropha in the country as a commercially viable energy crop. Emphasis is placed on the need to supply elite planting materials to optimize seed yield and seed quality as well as consider suitable agro-techniques required to establish the Jatropha plantations. Given that the longevity of Jatropha trees is 50 years, the objective is to establish plantations based on improved germplasm rather than rely on wild type germplasm.     

Land use and second-generation biofuel feedstocks: The unconsidered impacts of Jatropha biodiesel in Rajasthan,India

Governments around the world see biofuels as a common solution to the multiple policy challenges posed by energy insecurity, climate change and falling farmer incomes. The Indian government has enthusiastically adopted a second-generation feedstock – the oilseed-bearing shrub, Jatropha curcas – for an ambitious national biodiesel program. Studies estimating the production capacity and potential land use implications of this program have typically assumed that the ‘waste land’ slated for Jatropha production has no economic value and that no activities of note will be displaced by plantation development. Here we examine the specific local impacts of rapid Jatropha plantation development on rural livelihoods and land use in Rajasthan, India. We find that in Jhadol Tehsil, Jatropha is planted on both government and private land, and has typically displaced grazing and forage collection. For those at the socioeconomic margins, these unconsidered impacts counteract the very benefits that the biofuel programs aim to create. The Rajasthan case demonstrates that local land-use impacts need to be integrated into decision-making for national targets and global biofuel promotion efforts.     

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.     

Growth and lipid accumulation properties of a freshwater microalga, Chlorella ellipsoidea YJ1, in domestic secondary effluents

The combination of microalga-based biodiesel production and wastewater treatment is a promising approach to solve problems related to the energy crisis as well as eutrophication in bodies of water. A freshwater microalga, Chlorella ellipsoidea YJ1, with a high capacity for biomass production and lipid accumulation in secondary effluent was isolated. C. ellipsoidea YJ1 could achieve a biomass of 425 mg L⁻¹ (dry weight) in domestic secondary effluent treated with activated sludge technology; and the lipid content per unit of algal biomass was as high as 43% (w/w) in this condition. The lipid growth rate of C. ellipsoidea YJ1 in domestic secondary effluents could attain 11.4 mg/L. Furthermore, after the cultivation of C. ellipsoidea YJ1, the removal efficiencies of nitrogen and phosphorus from the secondary effluent studied in this paper were more than 99% and 90%, respectively. Logistic and Monod models were used successfully to simulate the growth of C. ellipsoidea YJ1, and its maximum biomass and maximum population growth rate under different initial concentrations of nitrogen and phosphorus could be simulated and predicted using the models. .     

基于全生命周期的地热发电系统环境影响评价

为明确不同类型地热发电系统“获取、转化”环节的钻井、建设、运行、退役等不同过程对地热发电系统的环境影响贡献,本文建立了基于热力学优化模型的闪蒸/双工质地热发电系统全生命周期环境影响评价模型。进而,选取西藏羊八井、广东丰顺、华北油田及青海共和四种典型地热热储,整理和收集了我国地热发电系统的环境影响全生命周期环境影响清单,分析了地热发电站六个不同过程对三个主要环境影响潜值评价指标：酸化潜值、富营养化潜值和全球变暖潜值的影响规律。发现钻井完井过程分别平均占到地热电站酸化潜值、全球变暖潜值和富营养化潜值的46.28%、45.90%和27.52%,地下系统和地上系统的环境影响贡献相当;地热梯度与地热电站的全生命周期环境影响潜值有着负相关关系,梯度越大,环境影响潜值越低。。     

On-board reforming of biodiesel and bioethanol for high temperature PEM fuel cells: Comparison of autothermal reforming and steam reforming

In the 21st century biofuels will play an important role as alternative fuels in the transportation sector. In this paper different reforming options (steam reforming (SR) and autothermal reforming (ATR)) for the on-board conversion of bioethanol and biodiesel into a hydrogen-rich gas suitable for high temperature PEM (HTPEM) fuel cells are investigated using the simulation tool Aspen Plus. Special emphasis is placed on thermal heat integration. Methyl-oleate (C₁₉H₃₆O₂) is chosen as reference substance for biodiesel. Bioethanol is represented by ethanol (C₂H₅OH). For the steam reforming concept with heat integration a maximum fuel processing efficiency of 75.6% (76.3%) is obtained for biodiesel (bioethanol) at S/C = 3. For the autothermal reforming concept with heat integration a maximum fuel processing efficiency of 74.1% (75.1%) is obtained for biodiesel (bioethanol) at S/C = 2 and λ = 0.36 (0.35). Taking into account the better dynamic behaviour and lower system complexity of the reforming concept based on ATR, autothermal reforming in combination with a water gas shift reactor is considered as the preferred option for on-board reforming of biodiesel and bioethanol. Based on the simulation results optimum operating conditions for a novel 5 kW biofuel processor are derived.     

Production of microbial oil with high oleic acid content by Trichosporon capitatum

Microbial oils with high unsaturated fatty acids content, especially oleic acid content, are good feedstock for high quality biodiesel production. Trichosporon capitatum was found to accumulate lipid with around 80% oleic acid and 89% total unsaturated fatty acids content on nitrogen-limited medium. In order to improve its lipid yield, effects of medium components and culture conditions on cell growth and lipid accumulation were investigated. Optimization of media resulted in a 61% increase in the lipid yield of T. capitatum after cultivation at 28 °C and 160 rpm for 6 days. In addition, T. capitatum could grow well on cane molasses and afford a lipid yield comparable to that on synthetic nitrogen-limited medium. The biodiesel from the microbial oil produced by T. capitatum on cane molasses displayed a low cold filter plugging point (−15 °C), and so T. capitatum might be a promising strain to provide lipid suitable for high quality biodiesel production.     

Characteristics and composition of Jatropha gossypiifoliaand Jatropha curcas L. oils and application for biodiesel production

In this work two genus of the Jatropha family: the Jatropha gossypiifolia (JG) and Jatropha curcas L. (JC) were studied in order to delimitate their potential as raw material for biodiesel production. The oil content in wild seeds and some physical–chemical properties of the oils and the biodiesel obtained from them were evaluated. The studied physical–chemical properties of the JC and JG biodiesel are in acceptable range for use as biodiesel in diesel engines, showing a promising economic exploitation of these raw materials in semi-arid regions. However, further agronomic studies are needed in order to improve the seed production and the crude oil properties.     

Production of biodiesel from Jatropha oil catalyzed by nanosized solid basic catalyst

In this work, hydrotalcite-derived particles with Mg/Al molar ratio of 3/1 were synthesized by a coprecipitation method using urea as precipitating agent, subsequently with (MHT) microwave-hydrothermal treatment, and followed by calcination at 773 K for 6 h. These particles were micro-sized mixed Mg/Al oxides as characterized by SEM and AFM. But actually they were nanosized according to the calculations from XRD data. Because of their strong basicity, the nanoparticles were further used as catalyst for biodiesel production from Jatropha oil after pretreatment. Experiments were conducted with the solid basic catalyst in an ultrasonic reactor under different conditions. At the optimized condition, biodiesel yield of 95.2% was achieved, and the biodiesel properties were close to those of the German standard. The catalyst can be reused for 8 times.     

A facile and feasible method to evaluate and control the quality of Jatropha curcus L. seed oil for biodiesel feedstock: Gas chromatographic fingerprint

To establish a facile and feasible method to evaluate and control the quality of Jatropha curcus L. seed oil for biodiesel feedstock, Gas chromatographic (GC) fingerprint technology was introduced and employed. Initially, the chromatograms of the 13 oil samples from various plantation zones in Guizhou, China were obtained under optimized GC conditions. Ten common peaks were selected as the characteristic peaks for chemometrics, seven of which were identified and quantified by comparing with the standards. The mean chromatogram of S7 (n = 3) was selected as the reference spectrum for similarity analysis based on the influence of the fatty acid composition of the raw material on the fuel properties of resulting biodiesel. Furthermore, the result of SA was confirmed by hierarchical clustering analysis and principal component analysis. By this method, all samples can be classified into three groups. The similarity value of samples approaching 1.000 compared with sample 7 was indicative of the desired fuel properties of biodiesel, indicating the potential practical applications in the quality evaluation and control of biodiesel feedstock.     

Application of sweet sorghum for biodiesel production by heterotrophic microalga Chlorella protothecoides

Microalga Chlorella protothecoides can grow heterotrophically with glucose as the carbon source and accumulate high proportion of lipids. The microalgal lipids are suitable for biodiesel production. To further increase lipid yield and reduce biodiesel cost, sweet sorghum juice was investigated as an alternative carbon source to glucose in the present study. When the initial reducing sugar concentration was 10 g L⁻¹ in the culture medium, the dry cell yield and lipid content were 5.1 g L⁻¹ and 52.5% using enzymatic hydrolyzates of sweet sorghum juice as the carbon source after 120 h-culture in flasks. The lipid yield was 35.7% higher than that using glucose. When 3.0 g L⁻¹ yeast extract was added to the medium, the dry cell yield and lipid productivity was increased to 1.2 g L⁻¹ day⁻¹ and 586.8 mg L⁻¹ day⁻¹. Biodiesel produced from the lipid of C. protothecoides through acid catalyzed transesterification was analyzed by GC–MS, and the three most abundant components were oleic acid methyl ester, cetane acid methyl ester and linoleic acid methyl ester. The results indicate that sweet sorghum juice could effectively enhance algal lipid production, and its application may reduce the cost of algae-based biodiesel.     

Life cycle assessment of two palm oil production systems

In 2009 approx. 40 Mt of palm oil were produced globally. Growing demand for palm oil is driven by an increasing human population as well as subsidies for biodiesel and is likely to increase further in coming years. The production of 1 t crude palm oil requires 5 t of fresh fruit bunches (FFB). On average processing of 1 t FFB in palm oil mills generates 0.23 t empty fruit bunches (EFB) and 0.65 t palm oil mill effluents (POME) as residues. In this study it is assumed that land use change does not occur. In order to estimate the environmental impacts of palm oil production a worst and a best case scenario are assessed and compared in the present study using 1000 kg of FFB as functional unit.The production and treatment of one t FFB causes more than 460 kg CO_2eq in the worst case scenario and 110 kg CO_2eq in the best case scenario. The significant greenhouse gas (GHG) emission reduction is achieved by co-composting residues of the palm oil mill. Thus treating those residues appropriately is paramount for reducing environmental impacts particularly global warming potential (GWP) and eutrophication potential (EP).Another important contributor to the EP but also to the human toxicity potential (HTP) is the biomass powered combined heat and power (CHP) plant of palm oil mills. Frequently CHP plants of palm oil mills operate without flue gas cleaning. The CHP plant emits heavy metals and nitrogen oxides and these account for 93% of the HTP of the advanced palm oil production system, of which heavy metal emissions to air are responsible for 79%. The exact emission reduction potential from CHP plants could not be quantified due to existing data gaps, but it is apparent that cleaning the exhaust gas would reduce eutrophication, acidification and toxicity considerably.     

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.     

A pilot-scale high-rate biohydrogen production system with mixed microflora

A pilot-scale high-rate dark fermentative hydrogen production plant has been established in the campus of Feng Chia University to develop biohydrogen production pilot-plant technology. This pilot-plant system is composed of two feedstock storage tanks (0.75 m³ each), a nutrient storage tank (0.75 m³), a mixing tank (0.6 m³), an agitated granular sludge bed fermentor (working volume 0.4 m³), a gas-liquid-solid separator (0.4 m³) and a control panel. The seed mixed microflora was obtained from a lab-scale agitated granular sludge bed bioreactor. This pilot-scale fermentor was operated for 67 days at 35 °C, an organic loading rate (OLR) of 40-240 kg COD/m³/d, and the influent sucrose concentration of 20 and 40 kg COD/m³. Both biogas and hydrogen production rates increased with increasing OLR. However, the biomass concentration (volatile suspended solids, VSS) only increased with an increasing OLR at an OLR range of 40-120 kg COD/m³/d, whereas it decreased when OLR was too high (i.e., 240 kg COD/m³/d). The biogas consisted mainly of H₂ and CO₂ with a H₂ content range of 23.2-37.8%. At an OLR of 240 kg COD/m³/d, the hydrogen content in biogas reached its maximum value of 37% with a hydrogen production rate (HPR) of 15.59 m³/m³/d and a hydrogen yield of 1.04 mol H₂/mol sucrose. This HPR value is much higher than 5.26 m³/m³/d (fermented molasses substrate) and 1.56 m³/m³/d (glucose substrate) reported by other pilot-scale systems. Moreover, HPR was also greatly affected by pH. At an optimal pH of 5.5, the bacterial community became simple, while the efficient hydrogen producer Clostridium pasteurianum was dominant. The factors of energy output compared with the energy input (E_f) ranged from 13.65 to 28.68 on biohydrogen, which is higher than the E_f value on corn ethanol, biodiesel and sugarcane ethanol but in the similar range of cellulosic ethanol.