Life cycle assessment of photovoltaic electricity generation

The paper presents the results of a life cycle assessment (LCA) of the electric generation by means of photovoltaic panels. It considers mass and energy flows over the whole production process starting from silica extraction to the final panel assembling, considering the most advanced and consolidate technologies for polycrystalline silicon panel production. Some considerations about the production cycle are reported; the most critical phases are the transformation of metallic silicon into solar silicon and the panel assembling. The former process is characterised by a great electricity consumption, even if the most efficient conversion technology is considered, the latter by the use of aluminium frame and glass roofing, which are very energy-intensive materials. Moreover, the energy pay back time (EPBT) and the potential for CO₂ mitigation have been evaluated, considering different geographic collocations of the photovoltaic plant with different values of solar radiation, latitude, altitude and national energetic mix for electricity production.     

Life cycle assessment of electricity generation in Mexico

This paper presents for the first time a Life Cycle Assessment (LCA) study of electricity generation in Mexico. The electricity mix in Mexico is dominated by fossil fuels, which contribute around 79% to the total primary energy; renewable energies contribute 16.5% (hydropower 13.5%, geothermal 3% and wind 0.02%) and the remaining 4.8% is from nuclear power. The LCA results show that 225 TWh of electricity generate about 129 million tonnes of CO₂ eq. per year, of which the majority (87%) is due to the combustion of fossil fuels. The renewables and nuclear contribute only 1.1% to the total CO₂ eq. Most of the other LCA impacts are also attributed to the fossil fuel options. The results have been compared with values reported for other countries with similar electricity mix, including Italy, Portugal and the UK, showing good agreement.     

生物质热解提质燃油全生命周期评估分析

运用GREET分析软件对新兴车用替代燃料——生物质热解提质燃油进行全生命周期分析,得到工艺路线不可再生能耗为0.295 MJ/MJ,温室气体排放为25.05 g二氧化碳当量,两项指数均远低于传统汽柴油,略优于其他生物质基燃料。热解提质制油工艺中生物原油改性提质过程为最大的能耗源与GHG排放源,各占整个工艺流程的40.28%和42.49%。     

Power generation using fast pyrolysis liquids from biomass

Power production from biomass derived pyrolysis liquids has been under development for the past few years. If technically successful, it would make decentralized bio-energy production possible. Several technologies and system components have been developed by academia, R&D organizations, and industrial companies in many countries. Much experience has been gained and many useful results published. The present work aims at reviewing the most significant experience in power generation from biomass liquids produced by fast pyrolysis processes. Power plant technologies addressed are diesel engines, gas turbines, and natural gas/steam power plants. Main results are reviewed and R&D needs identified for each technology. The analysis shows that even for the most promising solutions long-term demonstration has not yet been achieved. Pyrolysis liquid use in gas turbine plants and in co-firing mode in large power stations are technically most advanced. Recent work with diesel engines also appears quite promising.     

Distributed production of hydrogen by auto-thermal reforming of fast pyrolysis bio-oil

We demonstrated an auto-thermal reforming process for producing hydrogen from biomass pyrolysis liquids. Using a noble metal catalyst (0.5% Pt/Al₂O₃ from BASF) at a methane-equivalent space velocity of around 2000 h⁻¹, a reformer temperature of 800 °C–850 °C, a steam-to-carbon ratio of 2.8–4.0, and an oxygen-to-carbon ratio of 0.9–1.1, we produced 9–11 g of hydrogen per 100 g of fast pyrolysis bio-oil, which corresponds to 70%–83% of the stoichiometric potential. The elemental composition of bio-oil and the bio-oil carbon-to-gas conversion, which ranged from 70% to 89%, had the most significant impact on the yield of hydrogen. Because of incomplete volatility the remaining 11%–30% of bio-oil carbon formed deposits in the evaporator. Assuming the same process efficiency as that in the laboratory unit, the cost of hydrogen production in a 1500 kg/day plant was estimated at $4.26/kg with the feedstock, fast pyrolysis bio-oil, contributing 56.3% of the production cost.     

生物质快速热解制生物油的工艺分析

文章利用Aspen Plus软件建立了一个完整的生物质快速热解制生物油的流程模型,并详细描述模型的建立过程,模型包括原料的预处理、快速热解、焦炭和不冷凝气体的燃烧3个部分。通过对日处理2 000 t玉米秸秆的快速热解制生物油工厂各工段进行模拟,结果表明,整个生产过程各种形式的能耗为468.73×109J/h,能量产出为531.6×109J/h,能量产出大于能量消耗;将能量折算成标准煤用量后可知,生产1 kg生物油的能耗相当于0.758 8 kg标准煤,同时产出的能量相当于0.860 6 kg标准煤;焦炭的燃烧量为总量的86%时,可以满足快速热解过程的能量需求。     

Improving the quality of fast pyrolysis bio-oil by reduced pressure distillation

In the present study, reduced pressure distillation was performed to obtain distilled bio-oil from fast pyrolysis bio-oil. The experiments were completed at temperature 80 °C with a residual pressure of 15 mmHg. The distilled bio-oil yields of 61 wt% from reduced pressure distillation of fast pyrolysis bio-oil were obtained. The oxygen contents of the distilled bio-oil is 9.2 wt% and the distilled bio-oil has lower content of oxygen than the fast pyrolysis bio-oil. For this reason, compared with the fast pyrolysis bio-oil, the distilled bio-oil has higher heating value, lower corrosivity and better stability. The heating value of distilled bio-oil is 34.2 MJ/kg, which is about 2 times of that of fast pyrolysis bio-oil. It is found that the distilled bio-oil stored at 60 °C results in a weight loss of about 0.3% for mild steel and the distilled bio-oil’s viscosity hardly increases during storage. These properties of distilled bio-oil make it more suitable for fuel oil use or as a source of chemicals than fast pyrolysis bio-oil.     

太阳能热力发电的生命周期分析

应用生命周期分析法(LCA),对塔式太阳能热力电站所用设备材料的生产、运输、电站基本建设等3个过程进行了分析,分别计算出3个过程中的能耗及其对环境的影响,并与燃煤发电进行了比较。结果表明．太阳能热力电站每发电10MWh,即可节省能源3．78t标准煤,少向大气排放粉尘、CO2、NOx、SO2分别为498．7,9 933,49．94,78．75kg。太阳能热力发电具有显著的节能和环保效益。     

LCI (Life cycle inventory) analysis of fuels and electricity generation in Singapore

This article offers a unique three-stage approach in LCI analysis for generating the environmental profile of electricity generation in Singapore. The first stage focuses on fuels delivered to Singapore, next on electricity generated from various types of power production plants. The third stage integrates the entire life cycle study. The final gate-to-gate results show that the total CO₂ emissions from the national grid are 455.6 kg CO₂ per MWh without any loss in transmission and 467.0 kg CO₂ per MWh with 2.5% losses. The results for the entire cradle-to-gate energy production are: 586.3 kg CO₂ per MWh without considering any losses and 601.0 kg CO₂ per MWh with 2.5% transmission loss. For the rest of the LCI, the cradle-to-gate results (per MWh) are kg 0.19 CO (carbon monoxide), 0.06 kg N₂O (nitrous oxide), 1.94–1.99 kg NO_x (nitrogen oxides), 2.94–3.01 kg SO_x (sulphur oxides), 0.064–0.066 kg VOC (volatile organic compounds) and 0.078–0.080 kg PM (particulate matters). From gate-to-gate, the results are 0.12 kg CO, 0.0016 kg N₂O, 1.42–1.46 kg NO_x, 2.56–2.62 kg SO_x, 0.033–0.034 kg VOC and 0.067–0.069 kg PM. Emissions of CO₂ from energy generation, climate change mitigation and policies for energy security are also discussed.     

秸秆直燃发电系统的生命周期评价

以装机容量25 MW的生物质秸秆直燃发电系统为评价对象,进行生命周期评价.结果表明,秸秆直燃发电1万kWh,可吸收CO2 2502.87 kg,向环境排放SO237.39 kg,NOx90.37 kg,与燃煤发电相比,虽然氮氧化物的排放量有所增加,但减少了温室气体及硫氧化物的排放,污染物的排放主要发生在秸秆燃烧阶段.每发电1万kWh消耗能量15 340.2 MJ,秸秆预处理阶段是能量消耗的主要阶段,须要输入能量13 830.5MJ.秸秆直燃发电过程对环境影响的总负荷为35.18人当量.在此过程中,烟尘居环境影响总负荷的首位.     

Life cycle assessment of SNG from wood for heating, electricity, and transportation

The conversion of wood to synthetic natural gas (SNG) via gasification and catalytic methanation is a renewable close to commercialization technology that could substitute fossil fuels and alleviate global warming. In order to assure that it is beneficial from the environmental perspective, a cradle to grave life cycle assessment (LCA) of SNG from a first-of-its-kind polygeneration unit for heating, electricity generation, and transportation was conducted. These SNG systems were compared to fossil and conventional wood reference systems and environmental benefits from their substitution evaluated. Finally, we conduct sensitivity analysis for expected technological improvements and factors that could decrease environmental performance.It is shown that substituting fossil technologies with SNG systems is environmentally beneficial with regard to global warming and for selected technologies also with regard to aggregated environmental impacts. On the condition that process heat is used efficiently, technological improvements such as increased efficiency and denitrification could further increase this advantage. On the other hand, lower GHG emissions and aggregated impacts are partly compensated by other environmental effects, e.g. eutrophication, ecotoxicity, and respiratory disease caused by inorganics. Since more efficient alternatives exist for the generation of heat and electricity from wood, it is argued that SNG is best used for transportation. In the light of a growing demand for renewable transportation fuels and commercial scale technological development being only in its initial stage, the production of SNG from wood seems to be a promising technology for the near future.     

Investigation on hydrogen production by catalytic steam reforming of maize stalk fast pyrolysis bio-oil

Hydrogen production via catalytic steam reforming of maize stalk fast pyrolysis bio-oil over the nickel/alumina supported catalysts promoted with cerium was studied using a laboratory scale fixed bed coupled with Fourier transform infrared spectroscopy/thermal conductivity detection analysis (FTIR/TCD). The effects of nickel loading, reaction temperature, water to carbon molar ratio (WCMR) and bio-oil weight hourly space velocity (W_bHSV) on hydrogen production were investigated. The highest hydrogen yield of 71.4% was obtained over the 14.9%Ni-2.0%Ce/A1₂O₃ catalyst under the reforming conditions of temperature = 900 °C, WCMR = 6 and W_bHSV = 12 h⁻¹. Increasing reaction temperature from 600 to 900 °C resulted in the significant increase of hydrogen yield. The hydrogen yield was significantly enhanced by increasing the WCMR from 1 to 3, whereas it increased slightly by further increasing WCMR. The hydrogen yield decreased with the increase of W_bHSV. Meanwhile, the coke deposition percentage changed little with increasing W_bHSV up to 12 h⁻¹ and then it increased by 4.5% with the further increase of W_bHSV from 12 to 24 h⁻¹.     

Life cycle assessment of power generation alternatives for a stand-alone mobile house

This paper presents comparative life cycle assessment of nine different hybrid power generation solutions that meet the energy demand of a prototypical mobile home. In these nine solutions, photovoltaic panels and a wind turbine are used as the main energy source. Fuel cell and diesel generator are utilized as backup systems. Batteries, compressed H₂, and H₂ in metal hydrides are employed as backup energy storage. The findings of the study shows that renewable energy sources, although they are carbon-free, are not as environmentally friendly as may generally be thought. The comparative findings of this study indicate that a hybrid system with a wind turbine as a main power source and a diesel engine as backup power system is the most environmentally sound solution among the alternatives.     

A review on bio-oil production from biomass by using pyrolysis method

The paper provides an updated review on thermal conversion of biomass for the production of liquid products referred as bio-oil. This technology is described focusing on the characterization of feedstock, reactor design, products formation and upgrading. For feedstock characterization is covered in terms of several pretreatment methods. The reactor designs are illustrated number of design ranging from fixed bed to circulating fluidized bed. The properties of bio-oil composition have caused increasingly extensive research to be undertaken to address properties that need modification and this area is reviewed in terms of physical, catalytic and chemical upgrading. The mechanism of the products formation is also illustrated by several chemical routes. Reactor parameters such as heating rate, temperature of pyrolysis, catalysts etc are reviewed.     

Enhanced electricity generation using biomass materials

Renewable energy is a promising alternative solution for the energy requirements because it is clean and environmentally safe. Projections are important tools for long-term planning and policy settings. According to estimates, by 2040 approximately half of the global energy supply would be from renewable sources. Biomass can be converted into electric power through several methods. Heat is used to thermochemically convert biomass into a fuel oil which is then burned like petroleum to generate electricity. Biomass can also be burned directly to produce steam for electricity production or manufacturing processes. One alternative for producing electricity from biomass in a gas turbine is direct combustion of biomass as a primary energy source. Biomass is burned directly to produce steam, the steam turns a turbine which derives a generator thus electricity is generated.     

Life cycle assessment of H2 generation with high temperature electrolysis

Water electrolysis is a well-established process for hydrogen production but requires efficiency improvements to reduce costs. High temperature electrolysis (HTE) as a means to higher efficiency was advanced in the EU project RelHY. Through Life Cycle Assessment (LCA), also the environmental performance of five HTE-based hydrogen production systems was evaluated: operation with power and steam from a nuclear plant, continuous and intermittent operation with wind power and water, intermittent operation with natural gas or biogas reforming as back-up. Large scale natural gas reforming (NGR) was used as a reference. The LCA aims to identifying environmental hotspots of HTE plants and comparing their operation. The results show that stack manufacturing has the strongest impact during construction of the HTE plant while the impacts during H₂ production are largely due to power supply. All HTE variants studied lead to less life cycle CO₂-equivalent emissions than NGR. However, only the wind powered HTE variants without back-up use less energy than NGR. The other impacts and flows show different patterns. The results and limitations of the study are discussed.     

Life cycle assessment of flax shives derived second generation ethanol fueled automobiles in Spain

Biofuel use seems to have certain environmental, energy and socioeconomic advantages versus fossil fuel consumption. The substitution of fossil fuels with biofuels can be a useful tool to fulfil the Spanish and European policy in relation to mitigation of greenhouse gas (GHG) emissions and increase the security in energy supply. The continuous increase in energy consumption, dependence on energy and high petroleum prices has motivated increasing support for renewable energy promotion. In Spain (the third ethanol producer in Europe in 2007), ethanol from lignocellulosic feedstocks could be one of the most valuable and interesting possibilities for renewable transportation fuels due to the limited competition with food production and high net reduction of GHG emissions. This study is focused on flax shives, obtained as an agricultural co-product from flax crops dedicated to fibre production for specialty paper pulp manufacture as lignocellulosic biomass to produce second generation ethanol involving the use of cellulosic technology. The life cycle assessment (LCA) methodology was used to evaluate the environmental impacts of the production and use in a flexi fuel vehicle (FFV) of ethanol blends (10 and 85% in volume of ethanol with gasoline) versus conventional gasoline, throughout their whole life cycle in order to highlight the main sources of these impacts. The system boundaries include cultivation, extraction, processing and final use of fuels. Mass and economic allocation were considered to determine the effect on the results of different allocation approaches.The results of the study show that the allocation methods are essential for outcomes and decision-making. Using ethanol as transportation fuel could present better environmental performance than conventional gasoline in terms of global warming and fossil fuel consumption according to mass allocation. However, environmental credits could be achieved in terms of acidification, fossil fuel consumption and human toxicity according to economic allocation. Contributions to other impact categories such as eutrophication and photochemical oxidants formation were lower for conventional gasoline regardless of the allocation procedure selected. Agricultural activities related to feedstock production are notable contributors to the environmental performance. Thus, high yielding varieties, reduction of tillage activities and reduction in fertilization should help to reduce these impacts.     

Selective catalytic fast pyrolysis of Jatropha curcas residue with metal oxide impregnated activated carbon for upgrading bio-oil

Jatropha curcas waste was subjected to catalytic pyrolysis at 873 K using an analytical pyrolysis–gas chromatography/mass spectrometry in order to investigate the relative effect of various metal oxide/activated carbon (M/AC) catalysts on upgrading bio-oil from fast pyrolysis vapors of Jatropha waste residue. A commercial AC support was impregnated with Ce, Pd, Ru or Ni salts and calcined at 523 K to yield the 5 wt.% M/AC catalysts, which were then evaluated for their catalytic deoxygenation ability and selectivity towards desirable compounds. Without a catalyst, the main vapor products were fatty acids of 60.74% (area of GC/MS chromatogram), while aromatic and aliphatic hydrocarbon compounds were presented at only 11.32%. Catalytic pyrolysis with the AC and the M/AC catalysts reduced the oxygen-containing (including carboxylic acids) products in the pyrolytic vapors from 73.68% (no catalyst) to 1.60–36.25%, with Ce/AC being the most effective catalyst. Increasing the Jatropha waste residue to catalyst (J/C) ratio to 1:10 increased the aromatic and aliphatic hydrocarbon yields in the order of Ce/AC > AC > Pd/AC > Ni/AC, with the highest total hydrocarbon proportion obtained being 86.57%. Thus, these catalysts were effective for deoxygenation of the pyrolysis vapors to form hydrocarbons, with Ce/AC, which promotes aromatics, Pd/AC and Ni/AC as promising catalysts. In addition, only a low yield (0.62–7.80%) of toxic polycyclic aromatic hydrocarbons was obtained in the catalytic fast pyrolysis (highest with AC), which is one advantage of applying these catalysts to the pyrolysis process. The overall performance of these catalysts was acceptable and they can be considered for upgrading bio-oil.     

Characterization of bio-oil obtained from fruit pulp pyrolysis

Apricot pulps was pyrolyzed in a fixed-bed reactor under different pyrolysis conditions to determine the role of final temperature, sweeping gas flow rate and steam velocity on the product yields and liquid product composition with a heating rate of 5 °C/min. Final temperature range studied was between 300 and 700 °C and the highest liquid product yield was obtained at 550 °C. Liquid product yield increased significantly under nitrogen and steam atmospheres. For the optimum conditions, pyrolysis of peach pulp was furthermore studied. Liquid products obtained under the most suitable conditions were characterized by FTIR and ¹H-NMR. In addition, gas chromatography/mass spectrophotometer was achieved on all pyrolysis oils. Characterization showed that bio-oil could be a potential source for synthetic fuels and chemical feedstock.     

Upgrading of fast pyrolysis bio-oil over Fe modified ZSM-5 catalyst to enhance the formation of phenolic compounds

The present study is aimed to investigate the upgrading of beech sawdust pyrolysis bio-oil through catalytic cracking of its vapors over Fe-modified ZSM-5 zeolite in a fixed bed tubular reactor. The zeolite supported iron catalyst was successfully prepared with varying metal loading ratios (1, 5, 10 wt%) via dry impregnation method and further characterized by BET, XRD, and SEM-EDX techniques. TG/FT-IR/MS analysis was used for the detection of biomass thermal degradation. Product yields of non-catalytic and catalytic pyrolysis experiments were determined and the obtained results show that bio-oil yields decreased in the presence of catalysts. Besides, the bio-oil composition is characterized by GC/MS. It was indicated that the entity of the ZSM-5 and Fe/ZSM-5 catalyst reveal a significant enhancement quality of the pyrolysis products in comparison with non-catalytic experiment. The catalyst increased oxygen removal from the organic phase of bio-oil and further developed the production of desirable products such as phenolics and aromatic compounds.