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.     

Biomass from agriculture in small-scale combined heat and power plants - A comparative life cycle assessment

Biomass produced on farm land is a renewable fuel that can prove suitable for small-scale combined heat and power (CHP) plants in rural areas. However, it can still be questioned if biomass-based energy generation is a good environmental choice with regards to the impact on greenhouse gas emissions, and if there are negative consequences of using of agricultural land for other purposes than food production.In this study, a simplified life cycle assessment (LCA) was conducted over four scenarios for supply of the entire demand of power and heat of a rural village. Three of the scenarios are based on utilization of biomass in 100 kW (e) combined heat and power (CHP) systems and the fourth is based on fossil fuel in a large-scale plant. The biomass systems analyzed were based on 1) biogas production with ley as substrate and the biogas combusted in a microturbine, 2) gasification of willow chips and the product gas combusted in an IC-engine and 3) combustion of willow chips for a Stirling engine. The two first scenarios also require a straw boiler.The results show that the biomass-based scenarios reduce greenhouse gas emissions considerably compared to the scenario based on fossil fuel, but have higher acidifying emissions. Scenario 1 has by far the best performance with respect to global warming potential and the advantage of utilizing a byproduct and thus not occupying extra land. Scenario 2 and 3 require less primary energy and less fossil energy input than 1, but set-aside land for willow production must be available. The low electric efficiency of scenario 3 makes it an unsuitable option.     

Life cycle assessment of greenhouse gas emissions of feedlot manure management practices: Land application versus gasification

Animal waste is an important source of anthropogenic GHG emissions, and in most cases, manure is managed by land application. Nevertheless, due to the huge amounts of manure produced annually, alternative manure management practices have been proposed, one of which is gasification, aimed to convert manure into clean energy-syngas. Syngas can be utilized to provide energy or power. At the same time, the byproduct of gasification, biochar, can be transported back to fields as a soil amendment. Environmental impacts are crucial in selecting the appropriate manure strategy. Therefore, GHG emissions during manure management systems (land application and gasification) were evaluated and compared by life cycle assessment (LCA) in our study. LCA is a universally accepted tool to determine GHG emissions associated with every stage of a system. Results showed that the net GHG emissions in land application scenario and gasification scenario were 119 and -643 kg CO₂-eq for one tonne of dry feedlot manure, respectively. Moreover, sensitive factors in the gasification scenario were efficiency of the biomass integrated gasification combined cycle (BIGCC) system and energy source of avoided electricity generation. Overall, due to the environmental effects of syngas and biochar, gasification of feedlot manure is a much more promising technique as a way to reduce GHG emissions than is land application.     

Adiabatic fixed-bed gasification of coal, dairy biomass, and feedlot biomass using an air–steam mixture as an oxidizing agent

Concentrated animal feeding operations, such as cattle feedlots and dairies, produce a large amount of manure, cattle biomass (CB), which can be included as renewable feedstock for locally based gasification for syngas (CO and H₂) production and subsequent use in power generation. Experimental results on effects of bed temperature and gas composition on the higher heating value (HHV) and energy recovery are presented for dairy biomass (DB) gasification using air and air–steam as oxidizers. Some experimental data are compared with adiabatic gasification modeling which includes atom balance conservation for assumed product species and chemical equilibrium analysis. Wyoming sub-bituminous coal (WYC) and Texas Lignite coal (TXL) are used as standard fuels for comparison purposes in modeling studies. Two main parameters are investigated in this study. One is the modified equivalence ratio (ER_M) defined as the ratio of stochiometric oxygen to total oxygen supplied in the oxidizing mixture of air and steam. The second is a measure of how much steam is in the oxidizer and is called the air steam ratio (ASTR), which is defined as the ratio of oxygen supplied in the air to the total oxygen supplied in the oxidizer. The results suggested that gasification of CB and coals under higher ER_M yield elevated concentrations of CO and CH₄, and low percentages of H₂ and CO₂, while higher ASTRs (less steam) produced mixtures poor in H₂, CO₂, and CH₄ and rich in CO with lower HHV. It was also found that FB and DB produced higher amounts of H₂ than WYC and TXL under the same ER_M and ASTR.     

The changing nature of life cycle assessment

LCA has evolved from its origins in energy analysis in the 1960s and 70s into a wide ranging tool used to determine impacts of products or systems over several environmental and resource issues. The approach has become more prevalent in research, industry and policy. Its use continues to expand as it seeks to encompass impacts as diverse as resource accounting and social well being. Carbon policy for bioenergy has driven many of these changes.Enabling assessment of complex issues over a life cycle basis is beneficial, but the process is sometimes difficult. LCA's use in framing is increasingly complex and more uncertain, and in some cases, irreconcilable. The charged environment surrounding biofuels and bioenergy exacerbates all of these. Reaching its full potential to help guide difficult policy discussions and emerging research involves successfully managing LCA's transition from attributional to consequential and from retrospective to prospective.This paper examines LCA's on-going evolution and its use within bioenergy deployment. The management of methodological growth in the context of the unique challenges associated with bioenergy and biofuels is explored. Changes seen in bioenergy LCA will bleed into other LCA arenas, especially where it is important that a sustainable solution is chosen.     

Sequential supercritical water gasification and partial oxidation of hog manure

The catalytic hydrogen production from hog manure using supercritical water gasification and partial oxidation was investigated in a batch reactor at a temperature of 500 °C, and pressure of 28 MPa using several metallic catalysts. Hog manure was characterized by a total and soluble chemical oxygen demand (TCOD, SCOD) of 57,000 and 28,000 mg/L, total and volatile suspended solids (TSS, VSS) of 25,000, 19,000, and ammonia of 2400 mg/L, respectively. The order of H₂ production was the following: Pd/AC > Ru/Al₂O₃ > Ru/AC > AC > NaOH, and the order of COD reduction efficiency was as follows: NaOH > Ru/AC > AC > Ru/Al₂O₃ > Pd/AC. The behavior of the volatile fatty acids (VFAs), ethanol, methanol, ammonia, H₂S, and sulfate was investigated experimentally and discussed. A 35% reduction in the H₂ and CH₄ yields was observed in the sequential gasification partial oxidation (oxidant at an 80% of theoretical requirement) experiments compared to the gasification experiments (catalyst only). Moreover, this reduction in gas yields was coincided with a 45% reduction in the liquid effluent chemical oxygen demand (COD), 60% reduction of the ammonia concentration in the liquid effluent, and 20% reduction in the H₂S concentration in the effluent gas.     

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.     

Combined heat and power system based on a proton conducting SOFC and a supercritical CO2 Brayton cycle triggered by biomass gasification

An integrated combined heat and power system was developed by combination of a proton conducting solid oxide fuel cell and a supercritical carbon dioxide Brayton cycle triggered by air-gasification of peach stone. Equivalence ratio, fuel cell temperature, fuel utilization factor and pressure ratio were considered as parameters with respect to power and heat productions as response variables. Analysis of variance showed that fuel utilization factor and fuel cell temperature with shares of 76.6% and 11.5% contribute the most on the power production while the most important factors on heat production are fuel utilization factor and equivalence ratio with shares of 54.1% and 44.8%, respectively. Power production is improved by increasing fuel cell temperature, decreasing equivalence ratio and decreasing fuel utilization factor. Regression models for predicting power (with R² of 98.47%) and heat (with R² of 91.77%) were proffered using analysis of variance with errors smaller than 1%. Multi-objective optimization results revealed that equivalence ratio of 4, fuel cell temperature of 680 °C, fuel utilization factor of 0.82 and pressure ratio of 5.11 were optimum conditions to achieve the maximum power (138 kW) and heat (195 kW).     

Calcium species evolution mechanism during coal pyrolysis and char gasification in H2O/CO2

The release mechanism of Ca during coal pyrolysis and char gasification in H₂O, CO₂ and their mixtures was studied. Sequential chemical extraction was used to determine the modes of occurrence of Ca in coal and char. The released Ca from coal pyrolysis and char gasification were captured and analyzed by activated carbon adsorption and X-ray photoelectron spectroscopy (XPS). Model compounds CaS and CaSO₄ were adopted to further reveal the released form of Ca under different atmospheres. The results indicate that Ca in coal is mainly released as CaCl₂ during the pyrolysis process, and the possible migration mechanism of Ca during pyrolysis was proposed. Ca in coal is mainly released in the form of CaCl₂, CaCO₃, and CaSO₄ during the gasification, and Ca is released as CaCl₂ under all conditions. In addition, Ca will be released as CaCO₃ under CO₂ atmosphere, as CaSO₄ under H₂O and H₂O/CO₂ atmospheres at 800 °C and 900 °C, released as CaSO₄ under all conditions at 1000 °C. This is closely related to the formation of CaO₂ intermediates during the gasification process.     

Syngas production by gasification of aquatic biomass with CO2/O2 and simultaneous removal of H2S and COS using char obtained in the gasification

Applicability of gulfweed as feedstock for a biomass-to-liquid (BTL) process was studied for both production of gas with high syngas (CO + H₂) content via gasification of gulfweed and removal of gaseous impurities using char obtained in the gasification. Gulfweed as aqueous biomass was gasified with He/CO₂/O₂ using a downdraft fixed-bed gasifier at ambient pressure and 900 °C at equivalence ratios (ER) of 0.1–0.3. The syngas content increased while the conversion to gas on a carbon basis decreased with decreasing ER. At an ER of 0.1 and He/CO₂/O₂ = 0/85/15%, the syngas content was maximized at 67.6% and conversion to gas on a carbon basis was 94.2%. The behavior of the desulfurization using char obtained during the gasification process at ER = 0.1 and He/CO₂/O₂ = 0/85/15% was investigated using a downdraft fixed-bed reactor at 250–550 °C under 3 atmospheres (H₂S/N₂, COS/N₂, and a mixture of gases composed of CO, CO₂, H₂, N₂, CH₄, H₂S, COS, and steam). The char had a higher COS removal capacity at 350 °C than commercial activated carbon because (Ca,Mg)S crystals were formed during desulfurization. The char simultaneously removed H₂S and COS from the mixture of gases at 450 °C more efficiently than did activated carbon. These results support this novel BTL process consisting of gasification of gulfweed with CO₂/O₂ and dry gas cleaning using self-supplied bed material.     

Life cycle assessment of olive pomace gasification for an up-draft fixed bed gasifier system

Biomass gasification has been considered as an important renewable energy alternative to deal with the environmental problems originating from fossil fuels and climate change effects. Olive pomace as a by-product of the olive oil production process is a significant biomass source. Although gasification technology is accepted as an environmentally friendly power system, the studies to determine its environmental impact via Life Cycle Assessment (LCA) are very limited. LCA is a key tool to evaluate all environmental impacts from the beginning to the end of the process. The aim of this study is to assess the overall environmental impacts of the olive pomace gasification for electricity generation and evaluation of its solid by-products namely biochar and tar. Four scenarios were compared to estimate the environmental impacts of gasification by-products with a LCA approach, following to the cradle-to-grave approach. The production of olive, olive pomace generation during its processing for olive oil production, gasification of olive pomace, construction of the gasifier, gas cleaning system and syngas composition have been included in the evaluations. It is clear from the analysis results that the scenarios have very low impact values in the case of beneficial usage of biochar in different industries. In terms of ozone layer depletion potential (2.74 × 10 ⁻⁶ kg CFC11 eq) and global warming potential (36.99 GWP100a), the paramount scenario from an environmental viewpoint is the scenario having the biochar and tar usage as a resource in another industry.     

Isothermal and non-isothermal kinetic study on CO2 gasification of torrefied forest residues

CO₂ gasification of torrefied forest residues (birch and spruce branches) was investigated by means of a thermogravimetric analyser operated non-isothermally (400–1273 K) and isothermally (1123 K) under the kinetic regime, followed by kinetic analyses assuming different models. For the non-isothermal gasification, the distributed activation energy model (DAEM) with four or five pseudo-components was assumed. It is found that the severity level of torrefaction had great influences on gasification behaviour as well as devolatilization step. The activation energy of non-isothermal gasification step of three samples varied in the range of 260–290 kJ/mol. The char reactivity decreased with increased torrefaction temperature. For the isothermal gasification, the random pore model (RPM), shrinking core model (SCM), and homogeneous model (HM) were tested. The result has confirmed the trend of decrease in char reactivity with increased torrefaction temperature observed from the non-isothermal gasification. However, different trends in char reactivity due to different wood types were observed by the two methods of gasification.     

A LCA (life cycle assessment) of the methanol production from sugarcane bagasse

Nowadays one of the most important environmental issues is the exponential increase of the greenhouse effect by the polluting action of the industrial and transport sectors. The production of biofuels is considered a viable alternative for the pollution mitigation but also to promote rural development. The work presents an analysis of the environmental impacts of the methanol production from sugarcane bagasse, taking into consideration the balance of the energy life cycle and its net environmental impacts, both are included in a LCA (Life Cycle Assessment) approach. The evaluation is done as a case study of a 100,000 t/y methanol plant, using sugarcane bagasse as raw material. The methanol is produced through the BTL (Biomass to Liquid) route. The results of the environmental impacts were compared to others LCA studies of biofuel and it was showed that there are significant differences of environmental performance among the existing biofuel production system, even for the same feedstock. The differences are dependent on many factors such as farming practices, technology of the biomass conversion. With relation to the result of output/input ratio, the methanol production from sugarcane bagasse showed to be a feasible alternative for the substitution of an amount of fossil methanol obtained from natural gas.     

Comparative analysis of Fischer-Tropsch and integrated gasification combined cycle biomass utilization

Use of agricultural biomass (switchgrass, prairie grasses) through Fischer-Tropsch (FT) conversion to liquid fuels is compared with biomass utilization via (IGCC) integrated gasification combined cycle electrical production. In the IGCC scenario, biomass is co-fired with coal, with biomass comprising 10% of the fuel input by energy content. In this case, the displaced coal is processed via FT methods so that liquid fuels are produced in both scenarios. Overall performance of the two options is compared on the basis of total energy yield (electricity, liquid fuels), carbon dioxide emissions, and total cost. Total energy yield is almost identical whether biomass is used for electrical power generation or liquid fuels synthesis. Carbon dioxide emissions are also approximately equal for the two pathways. Capital costs are more difficult to compare since scaling factors cause considerable uncertainty. With IGCC costs roughly equivalent for either scenario, cost differences between the pathways appear based on FT plant construction cost. Coal FT facility capital cost estimates for the plant scale in this study (721 MW_t LHV input) are estimated to be 410 (MUSD) million US Dollars while the similar scale biomass-only FT plant costs range from 430 MUSD to 590 MUSD.     

A life cycle approach to Green Public Procurement of building materials and elements: A case study on windows

Green Public Procurement (GPP) is a significant policy tool for reducing the environmental impacts of services and products throughout their whole life cycle. Scientific and easily verifiable environmental criteria, based on a life cycle approach, should be developed and used within procurement procedures. In this paper, Life Cycle Assessment (LCA) is applied to wood windows showing how it can support the criteria definition. After a foreword on GPP development in Italy, the evaluation features of the environmental performances of building materials and components are outlined. The LCA case study is then presented, describing the use of the analysis results to define the environmental criteria. LCA allowed to identify the main impacts and the critical processes of the window life cycle, giving a scientific framework to discuss GPP criteria with manufacturers associations and stakeholders. Nevertheless, it couldn’t help neither in identifying detailed criteria for GPP nor to define numerical thresholds to be used as reference in procurement procedures. The appropriate strategies should be selected taking into account the technical status of the market, the standard development and the voluntary industry commitments, involving manufacturers associations. Finally, some elements to develop a structured approach for GPP of construction materials are presented.     

A two-step approach to the hydrothermal gasification of carbohydrate-rich wastes: Process design and economic evaluation

A two-step approach to hydrothermal gasification of carbohydrate-rich wastes and wastewaters is a promising route for H₂ production and simultaneously as a water clean-up technology. Experimental data and kinetic models are used to further develop the process for industrial scale. In this work, a preliminary process design is conducted in order to assess the market potential of the two-step process. For stabilisation, two cases are considered: the use of excess vs. stoichiometric H₂, and for gasification, the utilisation of sequential reactors for gasification housing Pt and Ru catalysts is compared to a single reactor with Pt alone. A total of four options are conceptually designed and economically evaluated. Using state-of-the-art insights and process techniques and the current market scenario, a minimum H₂ selling price of 3.4 $ kg⁻¹ was obtained.A sensitivity study showed that the feedstock price, concentration and quantity, played a crucial role in the selling price of H₂. These variables are all correlated and are dependent on the industry from where the feedstock is obtained. Industrial wastewater streams rich in carbohydrate residues and associated with gate fees were found to be promising feedstock for the process.Further advancement in the areas of catalyst development (hydrothermal stability, affordability) as well as increased H₂ yields are necessary in order to improve the economics of this process on industrial scale.     

Life cycle assessment in buildings: The ENSLIC simplified method and guidelines

Life Cycle Assessment (LCA) is currently used to a very limited extent in the building sector, for several reasons. Firstly, making an LCA evaluation of a building demands a specific tool to handle the large dataset needed and this tool has to be adaptable to the different decisions taken throughout the life cycle of the building. Such tools have been developed in a few countries, but they are exceptions. However, useful experience has been gained in these countries, providing a valuable source of data for developing guidelines for application in other countries. Since the results of a building LCA may contain complex information, the great challenge is to devise efficient ways for communication of the results to users and clients.The simplified methodology presented in this paper adopt a systematic approach guiding the user through the Life Cycle process and clarifying key issues that usually cause difficulty, e.g. choice of assessment tool, definition of system boundaries, options for simplifying the process, etc. The guidelines were developed within the framework of the ENSLIC Building Project, which was co-funded by the European Commission Intelligent Energy for Europe Programme and by nine European organisations that included more than 15 LCA experts and architects.     

Effect of pore structure on CO2 gasification reactivity of biomass chars under high-temperature pyrolysis

The CO₂ gasification reactivity of pine sawdust chars (PS char) obtained from the different high-temperature pyrolysis is studied based on non-isothermal thermogravimetric method. Results show that the order of gasification reactivity is PS char-1073 > PS char-1273 > PS char-1473. Under the effect of high-temperature pyrolysis, the surface structure of biomass char is gradually destroyed and the pore structure parameters of specific surface area, total pore volume and average pore diameter increase. By means of the N₂ adsorption-desorption isotherms, it is seen that biomass char has more micro- and mesoporous at higher pyrolysis temperature. Besides, the PS char-1073 mostly has rich closed cylinder pores and parallel plate pores, and the PS char-1273 and PS char-1473 have plentiful open cylinder pores and parallel plate pores. An increase of pyrolysis temperature contributes to the development of porosity and improves diffusion path, which promotes the gasification reactivity. But, its effect on the decline of active site hinders the gasification reactivity. What's more, the kinetic model of distributed activation energy model (DAEM) is applied to calculate activation energy and pre-exponential factor with the integral and differential methods. The calculation results of integral method is more accurate and precise because the differential method is more sensitive than integral method for experimental noise. There is a compensation effect in the CO₂ gasification process.     

In-storage psychrophilic anaerobic digestion of swine manure: Acclimation of the microbial community

Covering a concrete manure storage tank with an air-tight floating membrane should induce anaerobic digestion of the stored manure. If the microbial community in the manure can acclimate to the ambient conditions, then In-Storage Psychrophilic Anaerobic Digestion (ISPAD) could be used by Canadian livestock producers to produce methane and stabilize manure. The objective of this study was to determine whether the microbial community in swine manure can successfully acclimate to the psychrophilic operating conditions in ISPAD and develop robust anaerobic digestion. This was done in the laboratory by analyzing manure from a three-year old full-scale pilot ISPAD facility located in St. Francois Xavier, Quebec, Canada, along with fresh manure and manure from an uncovered storage tank. Biochemical methane production assays performed at the three temperatures were used to quantify the performance of the microbial community and its temperature dependence. The ISPAD microbial community produced methane, in terms of VS added, at rates of 44.6, 9.8 and 8.5 dm³ kg⁻¹ d⁻¹, at 35, 18 and 8 °C, respectively. The ISPAD process reduced the organic matter content of the manure by 24% while releasing 63% of the potential methane in the manure, as opposed to the open storage tank where no measurable reduction in solids occurred, and only 15% of the potential methane was released. These results indicate that a robust, acclimated microbial community actively digests manure in the pilot ISPAD installation.