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Climate effect of an integrated wheat production and bioenergy system with Low Temperature Circulating Fluidized Bed gasifier
Abstract
When removing biomass residues from the agriculture for bioenergy utilization, the nutrients and carbon stored within these "residual resources" are removed as-well. To mitigate these issues the energy industry must try to conserve and not destroy the nutrients. The paper analyses a novel integration between the agricultural system and the energy system through the Low Temperature Circulating Fluidized Bed (LT-CFB) gasifier from the perspective of wheat grain production and electricity generation using wheat straw, where the effects of removing the straw from the agricultural system are assessed along with the effects of recycling the nutrients and carbon back to the agricultural system. The methods used to assess the integration was Life Cycle Assessment (LCA) with IPCC's 2013 100 year global warming potential (GWP) as impact assessment method. The boundary was set from cradle to gate with two different functional units, kg grain and kW h electricity produced in Zealand, Denmark. Two cases were used in the analysis: 1. nutrient balances are regulated by mineral fertilization and 2. the nutrient balances are regulated by yield. The analysis compare three scenarios of gasifier operation based on carbon conversion to two references, no straw removal and straw combustion. The results show that the climate effect of removing the straws are mitigated by the carbon soil sequestration with biochar, and electricity and district heat substitution. Maximum biochar production outperforms maximum heat and power generation for most substituted electricity and district heating scenarios. Irrespective of the substituted technologies, the carbon conversion needs to be 80-86% to fully mitigate the effects of removing the straws from the agricultural system. This concludes that compromising on energy efficiency for biochar production can be beneficial in terms of climate change effect of an integrated wheat production and bioenergy system.
... Several works applied comprehensive Life Cycle Assessments to estimate the environmental consequences associated with the use of residual biomass [14,27,25,18,28], while others focused on the impact on the use of land [29,30] and soil [31]. Some studies examined the issue from a techno-economic perspective [32][33][34] and other works included considerations on the socio-economic effects, e.g. job creation [30,34]. ...
... job creation [30,34]. Moreover, other studies have analysed the recycling of nutrients and carbon into the soil from the products of biomass gasification [32] and anaerobic digestion [31], which can bring about positive effects for the energy system and the environment. Also, the generation of non-energy co-products, such as feed, contributes to a circular use of resources [14]. ...
... With respect to fertilising effects, some technologies considered for the utilisation of straw produce soil fertilisers: nitrogen (N), phosphorus (P 2 O 5 ) and potassium (K 2 O), with different NPK ratios. Ashes resulting from the gasification of biomass contain soil fertilisers [32]. Similarly, the anaerobic digestion process transforms the biomass into biogas and digestate, the latter having soil fertilising properties [31]. ...
... Wang et al. (2014) showed that increased biochar output at the expense of decreased energy production in the pyrolysis process resulted in lower net GHG emissions. Sigurjonsson et al. (2015) analyzed the consequences of utilization of wheat straw for energy in a wheat grain production system including scenarios where straw biochar was returned to the soil. They applied the concept of avoided atmospheric CO 2 load for quantifying the effect of biochar C sequestration (Sigurjonsson et al., 2015), using a methodology originally proposed by Petersen et al. (2013) for calculation of C sequestration factors in relation to lost C sequestration due to wheat straw removal. ...
... Sigurjonsson et al. (2015) analyzed the consequences of utilization of wheat straw for energy in a wheat grain production system including scenarios where straw biochar was returned to the soil. They applied the concept of avoided atmospheric CO 2 load for quantifying the effect of biochar C sequestration (Sigurjonsson et al., 2015), using a methodology originally proposed by Petersen et al. (2013) for calculation of C sequestration factors in relation to lost C sequestration due to wheat straw removal. Yet, whereas the methodology may be used in the context of biochar, there is so far a lack of documented C sequestration factors derived for biochar in relation to specific biochar properties. ...
... The present study identified biochar C sequestration, linked to biochar MRT, as the most important factor for the overall GHG emission in the WOSR cultivation scenarios. This finding is in line with other studies analyzing the consequences of pyrolysis processing of feedstocks and soil application of the biochar residue, when effects of indirect LUC are excluded (Hammond et al., 2011;Ibarrola et al., 2012;Roberts et al., 2010;Sigurjonsson et al., 2015). Yet, the results call for a discussion of the reliability of assumed biochar degradation properties. ...
Winter oilseed rape (WOSR) is the main crop for biodiesel in the EU, where legislation demands at least 50% savings in greenhouse gas (GHG) emissions as compared to fossil diesel. Thus industrial sectors search for optimized management systems to lower GHG emissions from oilseed rape cultivation. Recently, pyrolysis of biomass with subsequent soil amendment of biochar has shown potentials for GHG mitigation in terms of carbon (C) sequestration, avoidance of fossil based electricity, and mitigation of soil nitrous oxide (N 2 O) emissions. Here we analyzed three WOSR scenarios in terms of their global warming impact using a life cycle assessment approach. The first was a reference scenario with average Danish WOSR cultivation where straw residues were incorporated to the soil. The others were biochar scenarios in which the oilseed rape straw was pyrolysed to biochar at two process temperatures (400 and 800 °C) and returned to the field. The concept of avoided atmospheric CO 2 load was applied for calculation of C sequestration factors for biochar, which resulted in larger mitigation effects than derived from calculations of just the remaining C in soil. In total, GHG emissions were reduced by 73 to 83% in the two biochar scenarios as compared to the reference scenario, mainly due to increased C sequestration. The climate benefits were higher for pyrolysis of oilseed rape straw at 800 than at 400 °C. The results demonstrated that biochar has a potential to improve the life cycle GHG emissions of oilseed rape biodiesel, and highlighted the importance of consolidated key assumptions, such as biochar stability in soil and the CO 2 load of marginal grid electricity.
... Finally, other studies have explored GWP reduction in wheat production and CHP generation via wheat straw thermal gasification. One such analysis was conducted considering the application of a DH system with CHP, and the results for the energy system were related to electricity production [56]. ...
District heating and cooling networks represent a compelling energy system solution due to their capacity to integrate renewable energies and leverage local surpluses of thermal resources. The meticulous design and optimization of network infrastructure are imperative to fully exploiting the potential of these energy systems. The Life Cycle Assessment of district heating and cooling networks for the purpose of environmental sustainability is a crucial and increasingly demanded aspect, particularly in light of the progressively stringent European regulations. The Life Cycle Assessment methodology could offer an evaluation throughout the entire life cycle of such networks. The proposed review scrutinizes the application of the Life Cycle Assessment methodology to evaluating the environmental profile of district heating and cooling systems. The methods, findings, and challenges are examined through a literature review and case study analysis. The results highlight variations in the climate profile influenced by the network generation type and multifunctionality approaches. The analysis revealed a range of emission factors, spanning from 11 gCO2eq/kWhth to 470 gCO2eq/kWhth for district heating and 6 gCO2eq/kWhth to 64 gCO2eq/kWhth for district cooling. The discussion emphasizes integrating district heating and cooling network management considerations and addressing methodological challenges. This study concludes by proposing future research directions for developing a universal LCA-based tool for district heating and cooling network analysis.
... can also be used to produce different value-added products such as storable high energy density 33 fuels, chemicals and valuable ashes. Biomass feedstocks often have a high content of essential 34 nutrients that can be efficiently recycled in the form of ash or char for use as fertilizer and soil 35 enhancer [1]. 36 ...
Gasification of wheat straw, an agricultural residue with high ash content, was investigated in a low temperature circulating fluidized bed (LT-CFB) gasifier in combination with catalytic tar upgrading as a flexible process to co-produce high quality bio-oil, nutrient rich char, and utilize the producer gas for heat and power production. The change in product distribution and bio-oil quality was studied when conducting the catalytic treatment with HZSM-5/γ-Al2O3 and lower-cost γ Al2O3. The fuel properties of the raw and upgraded bio-oils were analyzed by elemental composition, moisture, total acid number, size exclusion chromatography, basic nitrogen content, gas chromatography−mass spectrometry with flame ionization detection (GC–MS/FID), 1H nuclear magnetic resonance (NMR), 13C NMR, and two-dimensional heteronuclear single-quantum correlation (2D HSQC) NMR. The operating temperature of the LT-CFB pyrolysis chamber determined the tar yield and quality in the producer gas. With decrease in pyrolysis temperature from 690 to 570 °C, the tar concentration in the producer gas increased while the higher heating value of the condensed oil phase decreased from ~35 to 30 MJ/kg and the oxygen content, moisture content and acidity of the bio-oil increased. Both HZSM-5/γ-Al2O3 and γ-Al2O3 were effective catalysts as the tar treatment improved the bio-oil quality in terms of increased heating value and revaporization efficiency, and a reduction in oxygen content, moisture content, total acid number, and basic nitrogen content. Catalytic vapor treatment, e.g. using HZSM-5/γ-Al2O3 at 500 °C, decreased the energy content in the condensed bio-oil slightly from ~22% to ~20%. The oil quality improved significantly, as the oxygen content (water-free) and TAN of the bio-oil decreased from 13 wt% O and 34 mg KOH/g to 11 wt% O and 3 mg KOH/g, respectively. The catalytically treated bio-oils are thus better suited for further processing in existing oil refineries.
... Therefore, the optimal deployment of regional crop straw should not be considered only in an individual energy system, but a portfolio based on the integrated conditions of energy and agricultural systems [31]. At the regional level, the focus on one system independently, for example the energy system, may incur the competition of feedstock use in the other existing system, and this may undermine the interactions and efficiency of regional straw utilization when considering the two systems as a whole. ...
Straw return-to-field is regarded as a very effective option to avoid straw burning during harvest seasons and has been widely implemented in China. However, whether straw return-to-field is good for croplands as well as existing straw utilization facilities is not a simple yes or no question. Taking Jiangsu Province as an example, this study constructs a cost-benefit analysis framework, within which six scenarios with different return-to-field ratios are carefully designed, and the net benefits of the croplands as well as the existing straw power plants are calculated and compared, considering both environmental and economic aspects. The results show that as the straw return-to-field ratio increases, the profit of straw power plants continues to decline, while the net benefit of the straw return-to-field in the croplands increases initially and then decreases, resulting in an initial increase followed by a decrease in the net benefit of the whole region. Based on the results, the optimal straw return-to-field ratio is recommended as approximately 60%, which is much lower than the current ratio (98%) in the case of Jiangsu Province. Therefore, integrated impacts on both croplands and related industries should be carefully considered when designing and implementing straw return-to-field and other agricultural policies.
... Data from a second charcoal-producing stove, the more extensively studied top-lit updraft (TLUD) stove [13,22,25,26], is presented for comparison. Both stoves use a low-oxygen environment to convert biomass to volatiles that are burned elsewhere, and to charcoal, which can be used as a soil amendment [27][28][29][30][31][32]. ...
In this study, a pyrolysis biomass cookstove with separate combustion and pyrolysis chambers (two-chamber stove) is investigated and compared to a widely-used char producing cookstove design (top-lit updraft, TLUD). The influence of pyrolysis fuel type (pellets of hardwood, corn stover, or switchgrass) on CO, NO, CO2 and particulate emissions, and the time dependence of particulate size distribution are quantified. Water boiling tests are conducted in a hood with pine wood as the combustion fuel for the two-chamber stove. Thermal and modified combustion efficiencies, and char yields and elemental compositions are reported. The sensitivity to fuel choice is far lower in the two-chamber stove than in the TLUD, thus making the two-chamber stove design well suited to challenging waste biomass fuels. The NO emission factors are positively related to the nitrogen content of biomass pellets, whereas the particulate emission factor (measured only for the two-chamber stove) follows an order of hardwood < switchgrass ≤ corn stover (i.e. woody biomass < herbaceous biomass). By mass, 70−80% of the particulates are smaller than 0.25 μm. This size range is the dominant fraction at all times during the water boiling test.
... Production of bioenergy through pyrolysis of waste biomass is becoming more important due to the limitations of first generation biofuels [47,48]. Integrated systems can use biogas and bio-oil for energy purposes while the biochar can be applied to soil [49][50][51]. The global annual unused crop waste could potentially produce biochar of about 1. 65 GtC/year along with biofuels [52]. ...
Biochar application to soil is a potentially scalable carbon management strategy with the capability of achieving negative greenhouse gas emissions. In addition, biochar is also linked to the water-energy-food nexus (WEFN) through its potential to modify soil properties to improve agricultural productivity. Potential benefits include increased yield and reduced demand for water, fertilizers and other inputs. However, the current literature on biochar is highly fragmented, with a significant research gap in system-level analysis to synchronize
production, logistics and application into a sustainable carbon management strategy. Process systems engineering (PSE) can provide a framework to allow the potential benefits of biochar systems to be optimized. This article gives an overview of biochar as a strategy to address carbon management and WEFN issues, reviews relevant scientific literature, analyzes bibliometric trends, and maps potential areas for the application of PSE to the planning of large-scale biochar systems.
... Compared with the carbon-neutral system of carbon sequestration by photosynthesis, the biochar produced by pyrolysis of biomass gives an opportunity to convert bioenergy into carbonnegative industry [8]. In other words, the application of biochar into a soil has been suggested as a means of abating climate change by sequestering carbon while simultaneously providing energy and increasing crop yield [8]. Thus, it is highly desirable to develop a feasible means for harnessing biomass as an initial feedstock for energy and biochar through various thermo-chemical routes [16][17][18][19][20][21][22][23][24][25]. Unlike typical solid carbonaceous fuels such as coal, biomass is highly O-functionalized and has a complex heterogeneous structure and low energy density. ...
This study focused on the mechanistic understanding of CO2 in pyrolysis process of agricultural waste to achieve waste management, energy recovery, and biochar fabrication. In order to scrutinize the genuine role of CO2 in the biomass pyrolysis, all pyrogenic products such as syngas, pyrolytic oil (i.e., tar), and biochar generated from pyrolysis of red pepper stalk in N2 and CO2 were characterized. Thermo-gravimetric analysis confirmed that during the thermolysis of red pepper stalk, the magnitude of exothermic reaction in CO2 from 220 to 400 °C was substantially different from that in N2, resulting in the different extents of carbonization. The physico-chemical properties of biochar produced in CO2 were varied compared to biochar produced in N2. For example, the surface area of biochar produced in CO2 was increased from 32.46 to 109.15 m2 g−1. This study validates the role of CO2 not only as expediting agent for the thermal cracking of volatile organic carbons (VOCs) but also as reacting agent with VOCs. This genuine influence of CO2 in pyrolysis of red pepper stalk led to enhanced generation of syngas, which consequently reduced tar production because VOCs evolving from devolatilization of biomass served as substrates for syngas via reaction between CO2 and VOCs. The enhanced generation of CO reached up to 3000 and 6000% at 600 and 690 °C, respectively, whereas 33.8% tar reduction in CO2 was identified at 600 °C.
Carbon capture and storage (CCS) is an essential greenhouse gas removal (GGR) technology used to achieve negative emissions in bioenergy plants using biomass feedstock (Bio-CCS). In this study, the climate mitigation potential of a novel GGR technology consisting in the production of renewable-derived plastics from municipal solid waste (MSW) refuse has been evaluated. This novel GGR technology allows for carbon storage, for variable periods, in stable materials (plastics), and thus overcomes the technical limitations of CCS. A time-dependent carbon cycle assessment has been conducted based on the Absolute Global surface Temperature change Potential (AGTP) metric. This new method to assess carbon emissions is presented against a traditional life cycle assessment (LCA). The production of renewable-derived plastics proves to be an effective GGR technology for both landfill- and incineration-dominant countries in Europe. The results obtained encourage the implementation of renewable-derived plastics in Integrated Assessment Models (IAMs) to assess their global potential in forecasting scenarios to achieve the ambitious climate change targets set in the European Union. Thanks to this study, a novel approach toward a green and sustainable economy has been established. This study will help to fill the gaps between bioenergy and renewable materials production.
Direct catalytic upgrading of biomass-derived fast pyrolysis vapors can occur in different process configurations, under either inert or hydrogen-containing atmospheres. This review summarizes the myriad of different catalysts studied, and benchmarks their deoxygenation performance by also taking into account the resulting decrease in bio-oil yield compared to a thermal pyrolysis oil. Generally, catalyst modifications aim at either improving the initial selectivity of the catalyst to more desirable oxygen-free hydrocarbons, and/or to improve the catalysts’ stability against deactivation by coking. Optimizing pore structure and acid site density/distribution of solid acid catalysts can slow down deactivation and prolong activity. Basic catalysts such as MgO and Na2O/gamma-Al2O3 are excellent ketonization catalysts favoring oxygen removal via decarboxylation, whereas solid acid catalysts such as zeolites primarily favor decarbonylation and dehydration. Basic catalysts can therefore produce bio-oils with higher H/C ratios. However, since their coke formation per surface area is higher, compared to microporous HZSM-5 zeolite, pre-coking (or imperfect regeneration) of these basic catalysts and operating for longer time-on-stream can be approaches to improve the oil yield. In-line vapor-phase upgrading with a dual bed comprising a solid acid catalyst followed by a basic catalyst active in ketonization and aldol condensation further improves deoxygenation, while maintaining high bio-oil carbon recovery. Also low-cost catalysts such as iron-rich red mud have deoxygenation activity. An improved bio-oil carbon recovery— compared at similar level of oxygen removal—can be obtained when changing from an inert atmosphere to a hydrogen-containing atmosphere and using an effective hydrodeoxygenation (HDO) catalyst. To keep costs low, this can be conducted at near-atmospheric pressure conditions. Pt/TiO2 and MoO3/TiO2 showed high activity and reduced coke formation. Stable performance has been demonstrated using Pt/TiO2 for 100+ reaction/regeneration cycles with woody biomass feedstock. If future works can demonstrate the same durability for lower cost biomass containing higher contents of ash, N, and S, this would considerably boost the commercial viability of near atmospheric pressure HDO. Further research should be directed into testing the durability of lower cost HDO catalysts such as MoO3/TiO2 and further improving the activity and stability of lower cost catalysts.
To achieve a 100 % renewable energy system, plants integrating the electricity, heating and transport sectors in a Smart Energy System are required. In this work, three different polygeneration plants producing biofuels and heat, while interacting with the electricity grid are presented. All plants were based on wheat straw gasification in a low temperature circulating fluidized bed gasifier. High quality bio-oil was produced by catalytically upgrading and condensing the tars in the produced gas. Additionally, bio-ash containing carbon was produced, which acts as fertilizer and carbon sequestration when returned to the fields. The three plants used the tar-free gas to produce electricity, synthetic natural gas (SNG) and dimethyl ether (DME), respectively. The electricity producing plant delivered electricity to the grid, while the SNG and DME production plants used electricity for producing electrolytic hydrogen to boost the fuel production. The plants were evaluated using energy and carbon efficiencies. The analysis showed that all plants achieved total energy efficiencies > 83 %, including process heat and district heating as by-products. The SNG production plant yielded the highest carbon efficiency (91 %) of carbon bound in bio-fuels and bio-ash, followed by the DME (50 %) and the electricity production plant (23 %).
Future mobility trends will be determined by how cities
in emerging economies address the huge challenges
associated with increasing urbanization and growing per
capita incomes. This chapter analyses mobility trends
and challenges in four megacities in four emerging
economy countries in three continents: São Paulo (Brazil),
Beijing (China), Delhi (India) and Cape Town (South
Africa). These four cities are quite diverse in terms of
their demographic and economic characteristics and
belong to C40 Cities. The four countries differ in terms
of their respective developments, trajectories, mobility
choices and impacts. All four cities have historically been
densely populated and with time have further densified,
except for Beijing.
In terms of mobility trends, Beijing has witnessed a
decline in walking and cycling, whereas in other cities
mode shares for non‐motorized transport (NMT) have
remained stable. São Paulo has most of its employment
heavily concentrated in its central areas, while its lowincome
residents have settled on the peripheries, where
a significant proportion of the poor population still
walks. The situation in Cape Town is similar, with a large
proportion of the population being poor and making
many walking trips. Delhi is similar to many Indian cities,
with mixed land use and a high share of walking and
cycling trips (around 40%). The shift in modal shares
from NMT is mainly to modes of public transport, where
available, and to private vehicles.
In fact, the mode shares of private motorized vehicles
have shown increasing trends except in São Paulo
and Beijing. Beijing has experienced a peak in car use whereas Cape Town has traditionally been a car‐based
economy, meaning that the share of car trips remains
high. Delhi has a better public transport system than
other Indian cities, despite which modes of private transport
account for 36% of all trips, and car ownership has
risen 3.5 times in ten years.
Freight transportation and the last-mile delivery of goods is an evident and strict necessity to city life to support its citizens, and the urban life in general. The transport of goods into the cities and the transport of waste and other returns is, however, associated with several unwanted effects such as traffic congestion, noise, accidents and local environmental impact. Freight transport is estimated to comprise about 15% of total traffic in cities. However, urban freight transport causes up to 50% of total traffic emissions (Dablanc, 2011). In this chapter, we start out by discussing the nature of urban freight transport and logistics. Then, we examine the implications of the current macro trends relevant to urban freight transport and logistics. Finally, we discuss various means to greening urban freight transport and logistics.
Urban mobility is in transformation. Examples of drivers underpinning this ongoing transformation are need for sustainable and clean solutions, urbanization, health concerns, growth of e-commerce, new types of vehicles, digitalization, sharing economy, exploitation of big data, artificial intelligence induced disruptions, etc. Overall, the current trends place high demands regarding introduction of new and changed mobility solutions that are embracing novel technologies and adequate (public) planning and management of those.
Adequate public planning includes the introduction - and regulatory implications – of new types of business models (generically often coined as “mobility as service” etc.). With new solutions, the efficiency and interplay of the transportation technologies may be improved but for a realized impact it is generally required that this be combined with behavioural change. Given the complexity of the area, a systemic approach is required including cross-disciplinary and cross-sectorial facilitation.
One key component to handle the ongoing transformation is to educate, upskill and empower stakeholders including present and future professionals and citizens. This, in turn, imposes challenges for the existing educational bodies, public authorities in terms of both meeting volume and content demands. This may include adjusting education policy frameworks, educational formats, methods and scope, qualification frameworks, stakeholder engagement processes by challenging the present structure in terms of disciplines and traditions. Anticipating future educational needs based on labor market needs is about responding to structural changes in demand for labor and of competence structures with agile training solutions. Given the complexity of urban spaces, the identification of skill gaps and corresponding actions require a close and continuous alignment of needs, objectives and efforts of all key actors in the field or urban mobility: educational institutions, municipalities, transport service providers, industry, legislators and the community.
The authors propose to a set of critical skills for future urban mobility taken into consideration the emergence of civic laboratories that reinventing the cities from bottom up through open data and open source platforms.
Rapid climate change mitigation requires carbon sequestration in addition to greenhouse gas emission reductions. Agriculture may have a high potential for carbon sequestration due to improved practices. However, it is not known how the global warming impacts of crop production could be mitigated especially within an agricultural system. The aim of this study is to evaluate possibilities to neutralize global warming impacts in crop production using biochar produced from side flows and buffer zone biomass. A life cycle assessment methodology is utilized in this research for oat production in the boreal climate zone. Global warming impact reductions are compared for three different side flow utilization options. Traditionally, side flows have been utilized in energy or fodder production, and these options are compared to biochar production at a system level. The potential to use buffer zone biomass for biochar production is also studied. Willow has been selected as a biomass source in buffer zones. Oat production leads to greenhouse gas emissions especially due to the use of fossil and mineral fertilizers in cultivation and heat energy, electricity and fuels in various process phases. The production of one metric ton of oat flakes from cradle to gate generates 700 kg of CO 2 eq emissions. Biochar and energy production from side flows enables a greater reduction in global warming impacts than the feed use of side flows. Buffer zones in willow biomass and biochar production may enable the full neutralization of the global warming potential of oat production within an agricultural system. Further research with actual measurements is required especially on biochar impacts on soil emissions such as N 2 O. This research shows that it could be possible to neutralize global warming impacts from crop production using available technologies and available biomass in agricultural systems. A framework is created for carbon neutral crop production using side flows and buffer zone biomass through biochar.
In a biorefinery context, pyrolysis and gasification are especially interesting as both platforms offer high feed and product flexibility, providing the possibility to convert many different biogenic feedstocks into a wide variety of products such as heat, electricity, chemicals, transport fuels, and high-value ash and char products. However, in order to increase the utilization of biomass pyrolysis and gasification and make it commercially interesting in future energy systems, new integrated biorefinery designs with optimized thermal concepts and combinations of different technologies are required to maximize product yield and value, increase the overall process efficiency, and improve the economic viability. The present chapter provides an insight on the versatility and potential of biomass pyrolysis and gasification processes and their products. It also describes some new concepts and solutions like process integration schemes, polygeneration strategies, biochar uses, and tar abatement strategies that can help to overcome the operational challenges that the technology is facing.
This paper aims to provide more accurate results in the life cycle assessment (LCA) of electricity generation from wheat straw grown in Spain through the inclusion of parameter uncertainty and variability in the inventories. We fitted statistical distributions for the all the parameter that were relevant for the assessment to take into account their inherent uncertainty and variability. When we found enough data, goodness of fit tests were performed to choose the best distribution for each parameter and, when this was not possible, we adjusted triangular or uniform distributions according to data available and expert judge. To obtain a more complete and realistic LCA, we considered the consequences of straw exportation for the agricultural system, specially the loss of soil organic carbon and the decrease of future fertility. We also took into account all the inputs, transformations and transports needed to generate electricity in a 25 MWe power plant by straw burning. The inventory data for the agricultural, the transport and the transformation phases were collected considering their most common values and ranges of variability for the Spanish case. We used Monte Carlo simulation and sensitivity analysis to obtain global warming potential (GWP) and fossil energy (FOSE) consumption of the system. These results were compared with those of the electricity generated from natural gas in Spanish power plants, as fossil reference energy system. Our results showed that for the majority of the simulations electricity from wheat straw biomass combustion produced less greenhouse gases (GHG) emissions and consumed less fossil energy than electricity from natural gas. However, only 58% of the simulations achieved the sustainability threshold of 60% GHG savings proposed by the European Union (EU). Our analysis showed that agricultural field works and the loss of soil organic carbon due to straw exportation were the most important phases for FOSE consumption and GWP respectively. According to parameters sensitivity analysis, the loss of soil organic carbon was completely dependent on the isohumic coefficient and the soil carbon content factor values. Due to this fact, local and specific estimates of these parameters are relevant tasks to be performed in order to reduce uncertainties and provide a definitive answer to the compliance of the EU sustainability criteria.
Bioenergy (i.e., bioheat and bioelectricity) could simultaneously address energy insecurity and climate change. However, bioenergy’s impact on climate change remains incomplete when land use changes
(LUC), soil organic carbon (SOC) changes, and the auxiliary energy consumption are not accounted for in the life cycle. Using data collected from Belgian farmers, combined heat and power (CHP) operators, and a life cycle approach, we compared 40 bioenergy pathways to a fossil-fuel CHP system. Bioenergy required between 0.024 and 0.204 MJ (0.86 MJth + 0.14 MJel)1, and the estimated energy ratio (energy output-to-input ratio) ranged from 5 to 42. SOC loss increased the greenhouse gas (GHG) emissions of residue based bioenergy. On average, the iLUC represented 67% of the total GHG emissions of bioenergy from perennial energy crops. However, the net LUC (i.e., dLUC + iLUC) effects substantially reduced the GHG emissions incurred during all phases of bioenergy production from perennial crops, turning most pathways based on energy crops to GHG sinks. Relative to fossil-fuel based CHP all bioenergy pathways
reduced GHG emissions by 8–114%. Fluidized bed technologies maximize the energy and the GHG benefits of all pathways. The size and the power-to-heat ratio for a given CHP influenced the energy and GHG
performance of these bioenergy pathways. Even with the inclusion of LUC, perennial crops had better GHG performance than agricultural and forest residues. Perennial crops have a high potential in the multidimensional approach to increase energy security and to mitigate climate change. The full impacts of bioenergy from these perennial energy crops must, however, be assessed before they can be deployed on a large scale.
A coupled physical-biogeochemical climate model that includes a dynamic global vegetation model and a representation of a coupled atmosphere-ocean general circulation model is driven by the nonintervention emission scenarios recently developed by the Intergovernmental Panel on Climate Change (IPCC). Atmospheric CO 2 , carbon sinks, radiative forcing by greenhouse gases (GHGs) and aerosols, changes in the fields of surface-air temperature, precipitation, cloud cover, ocean thermal expansion, and vegetation structure are projected. Up to 2100, atmospheric CO 2 increases to 540 ppm for the lowest and to 960 ppm for the highest emission scenario analyzed. Sensitivity analyses suggest an uncertainty in these projections of À10 to +30% for a given emission scenario. Radiative forcing is estimated to increase between 3 and 8 W m -2 between now and 2100. Simulated warmer conditions in North America and Eurasia affect ecosystem structure: boreal trees expand poleward in high latitudes and are partly replaced by temperate trees and grasses at lower latitudes. The consequences for terrestrial carbon storage depend on the assumed sensitivity of climate to radiative forcing, the sensitivity of soil respiration to temperature, and the rate of increase in radiative forcing by both CO 2 and other GHGs. In the most extreme cases, the terrestrial biosphere becomes a source of carbon during the second half of the century. High GHG emissions and high contributions of non-CO 2 agents to radiative forcing favor a transient terrestrial carbon source by enhancing warming and the associated release of soil carbon.
Bioenergy makes up a significant portion of the global primary energy pie, and its production from modernized technology is foreseen to substantially increase. The climate neutrality of biogenic CO2 emissions from bioenergy grown from sustainably managed biomass resource pools has recently been questioned. The temporary change caused in atmospheric CO2 concentration from biogenic carbon fluxes was found to be largely dependent on the length of biomass rotation period. In this work, we also show the importance of accounting for the unutilized biomass that is left to decompose in the resource pool and how the characterization factor for the climate impact of biogenic CO2 emissions changes whether residues are removed for bioenergy or not. With the case of Norwegian Spruce biomass grown in Norway, we found that significantly more biogenic CO2 emissions should be accounted towards contributing to global warming potential when residues are left in the forest. For a 100-year time horizon, the global warming potential bio factors suggest that between 44 and 62% of carbon-flux, neutral biogenic CO2 emissions at the energy conversion plant should be attributed to causing equivalent climate change potential as fossil-based CO2 emissions. For a given forest residue extraction scenario, the same factor should be applied to the combustion of any combination of stem and forest residues. Life cycle analysis practitioners should take these impacts into account and similar region/species specific factors should be developed.
In life cycle assessment (LCA), the same characterization factors are conventionally applied irrespective of when the emissions occur (the same importance is given to emissions in the past, present, and future). When the assessment is constrained by fixed timeframes, the appropriateness of this paradigm is questioned and the temporal distribution of emissions becomes of relevance. One typical example is the accounting for biogenic CO2 emissions and removals. This article proposes a methodology for assessing the climate impact of time‐distributed CO2 fluxes using probability distributions. Three selected wood applications, such as fuel, nonstructural panels, and housing construction materials are assessed. In all the cases, CO2 sequestration in growing trees is modeled with an appropriate forest growth function, whereas CO2 emissions from wood oxidation are modeled with different probability distributions, such as the delta function, the uniform distribution, the exponential distribution, and the chi‐square distribution. The combination of these CO2 fluxes with the global carbon cycle provides the respective changes caused in CO2 atmospheric concentration and hence in the radiative forcing. The latter is then used as basis for climate impact metrics. Results demonstrate the utility of using emission and removal functions rather than single pulses, which generally overestimate the climate impact of CO2 emissions, especially in presence of short time horizons. Characterization factors for biogenic CO2 are provided for selected combinations of biomass species, rotation periods, and probability distributions. The time discrepancy between biogenic CO2 emissions and capture through regrowth results in a certain climate impact, even for a system that is carbon neutral over time. For the oxidation rate of wooden products, the use of a chi‐square distribution appears the most reliable and appropriate option under a methodological perspective. The feasibility of its adoption in LCA and emission accounting from harvested wood products deserves further scientific considerations.
Recycling of residual products of bioenergy conversion processes is important for adding value to the technologies and as a potential beneficial soil fertility amendment. In this study, two different ash materials originating from low temperature circulating fluidized bed (LT-CFB) gasification of either wheat straw (SA) or residue fibers mainly from citrus peels (CP) were tested regarding their potential to be used as fertilizer on agricultural soils. A soil incubation study, a greenhouse experiment with barley and faba bean, and an accompanying outdoor experiment with maize were carried out to investigate the effects of the ashes on soil microbiological and chemical properties and on the response of the three crops. The ash treatments were compared with a control treatment that received only nitrogen, magnesium, and sulphur (CO) and a fully fertilized control (COPK). Soil microbial parameters were not significantly altered after ash application. SA was generally able to increase the levels of Olsen-P and of the ammonium acetate/acetic acid-extractable K in soil as well as to improve the yield of barley and maize, whereas faba bean did not react positively to ash amendment. CP did not show beneficial effects on soil nutrient levels or on crop biomass. We conclude from the results of this study, that—depending on the feedstock used—ashes from LT-CFB gasification of plant biomass can be used to replace mineral fertilizers if they are applied according to their nutrient content, the crop demand, and soil properties.
Biomass is a renewable resource from which a broad variety of commodities can be produced. However, the resource is scarce and must be used with care to avoid depleting future stock possibilities. Flexibility and efficiency in production are key characteristics for biomass conversion technologies in future energy systems. Thermal gasification of biomass is proved throughout this article to be both highly flexible and efficient if used optimally. Cogeneration processes with production of heat-and-power, heat-power-and-fuel or heat-power-and-fertilizer are described and compared. The following gasification platforms are included in the assessment: The Harboøre up draft gasifier with gas engine, the Güssing FICFB gasifier with gas engine or PDU, the LT-CFB gasifier with steam cycle and nutrient recycling and finally the TwoStage down draft gasifier with gas engine, micro gas turbine (MGT), SOFC, SOFC/MGT or catalytic fuel synthesis.
This paper assesses the environmental performance of biomass gasification for electricity production based on wheat straw and compares it with that of alternatives such as straw-fired electricity production and fossil fuel-fired electricity production. In the baseline simulation, we assume that the combustion of biomass and fossil fuel references for electricity production takes place in a combined heat and power plant, but as a sensitivity analysis, we also consider combustion in a condensing mode power plant where only electricity is produced. Our results show that the production of 1 kWh of electricity from straw through gasification would lead to a global warming potential of 0.08 kg CO2e, non-renewable energy use of 0.2 MJ primary, acidification of 1.3 g SO2e, respiratory inorganics of 0.08 g PM2.5e and eutrophication potential of −1.9 g NO3e. The production of electricity from straw based on gasification technology appears to be more environmentally friendly than straw direct combustion in all impact categories considered. The comparison with coal results in the same conclusion as that reached in the comparison with straw direct combustion. The comparison with natural gas shows that using straw gas as an alternative energy source reduces global warming, non-renewable energy use and eutrophication but increases acidification and respiratory inorganics. The relative performance of straw gasification versus direct combustion and fossil fuel references does not change with varying assumptions about whether or not heat recovery is considered.
This paper aims to address the question, “What is the environmental performance of crop residues as an alternative energy source to fossil fuels, and whether and how can it be improved?”. In order to address the issue, we compare electricity production from wheat straw to that from coal and natural gas. The results on the environmental performance of straw for energy utilization and the two fossil fuel references are displayed first for different midpoint categories and then aggregated into a single score. The midpoint impact assessment shows that substitution of straw either for coal or for natural gas reduces global warming, non-renewable energy use, human toxicity and ecotoxicity, but increases eutrophication, respiratory inorganics, acidification and photochemical ozone. The results at the aggregate level show that the use of straw biomass for conversion to energy scores better than that of coal but worse than natural gas. In order to investigate the question of whether and how a reduction in the single score per kW h of electricity produced from straw is feasible, we perform a scenario analysis where we consider two approaches. The first one is a potential significant reduction in emissions of nitrogen oxides (NOx) by implementing selective catalytic reduction technology and the second is a potential increase in power generation efficiency. The results of the scenario analysis show that both approaches are effective in enhancing the competitiveness of straw as an alternative energy source, though the second approach “increasing efficiency” is somewhat less attractive than the first “reducing NOx emissions”.
Purpose Biological sequestration can increase the carbon stocks of non-atmospheric reservoirs (e.g. land and land-based products). Since this contained carbon is sequestered from, and retained outside, the atmosphere for a period of time, the concentration of CO 2 in the atmosphere is temporar-ily reduced and some radiative forcing is avoided. Carbon removal from the atmosphere and storage in the biosphere or anthroposphere, therefore, has the potential to mitigate climate change, even if the carbon storage and associated benefits might be temporary. Life cycle assessment (LCA) and carbon footprinting (CF) are increasingly popular tools for the envi-ronmental assessment of products, that take into account their entire life cycle. There have been significant efforts to develop robust methods to account for the benefits, if any, of seques-tration and temporary storage and release of biogenic carbon. However, there is still no overall consensus on the most appropriate ways of considering and quantifying it. Method This paper reviews and discusses six available methods for accounting for the potential climate impacts of carbon sequestration and temporary storage or release of biogenic carbon in LCA and CF. Several viewpoints and approaches are presented in a structured manner to help decision-makers in their selection of an option from com-peting approaches for dealing with timing issues, including delayed emissions of fossil carbon. Results Key issues identified are that the benefits of tempo-rary carbon removals depend on the time horizon adopted when assessing climate change impacts and are therefore not purely science-based but include value judgments. We therefore did not recommend a preferred option out of the six alternatives presented here. Conclusions Further work is needed to combine aspects of scientific and socio-economic understanding with value judgements and ethical considerations.
Phosphorus (P) is an essential nutrient and a limited resource, yet excess P is applied to agricultural land and can cause environmental problems in areas with intensive animal farming. In this study, the fertilizing effects of P in several animal manure-based products (including thermal treatment) were tested after application to two agricultural soil types (Jyndevad soil: clay 5.1%, silt 4.1%, sand 88.9%, organic matter 2.1%, total C 1.2% soil dry matter (DM), total P 266mgkg−1 soil DM, pH 6.3; Rønhave soil: clay 15.4%, silt 32.6%, sand 49.6%, organic matter 2.3%, Total C 1.3% soil DM, total P 488mgkg−1 soil DM, pH 6.6). The first-year effect of P application was tested in a spring barley crop (Hordeum vulgare L.) and residual P effects were tested in a perennial ryegrass (Lolium perenne L.) crop the following year. Untreated ash from thermally gasified animal manure biogas residue (GA) and a corresponding neutralized acid extract of the ash (ExL) in liquid form were the products in focus. Other products in use were: pelletized pig manure biogas residue (PEL), incinerated PEL (IA), anaerobically digested pig slurry (DS), dried ExL, dried fraction of separated pig slurry (SS), thermally gasified SS (GAs), thermally gasified poultry manure (GAp), crushed triple super phosphate (TSP) and disodium phosphate (DSP) was used as reference P fertilizer. For application of 20kgPha−1 mineral P fertilizer replacement value (RV) in the second year in the sandy soil was 76% and 99% for GA, 79% and 123% for IA, 95% and 155% for PEL, 94% and 73% for ExL, 55% and 15% for ExD, 64% and 82% for SS, 104% and 109% for DS, 60% and 95% for GAp, 73% and 111% for GAs, where the first value is based on barley DM yield and the second on barley total P uptake. Tripling the GA application rate to 60kgPha−1 in both soils had no significant effect on barley DM yield and P uptake. The overall efficiency for liquid fertilizers was much higher than for solid ones and relative effectiveness (RE) of ExL was comparable to RE of DSP. Despite the low P level in soils, the ryegrass crop grew very well on both soils in the second year, and there was no detectable residual effect of the treatments on grass yield and P uptake. In conclusion, untreated ash and solid manures used in this study were not suitable as starter P fertilizer, but could be used to maintain the level of available P in soil, as there were indications that ash/manure P contributed significantly to plant P uptake during the growing season of barley.
In Life Cycle Assessment (LCA), carbon dioxide (CO2) emissions from biomass combustion are traditionally assumed climate neutral if the bioenergy system is CO2 flux neutral, i.e. the quantity of CO2 released approximately equals the amount of CO2 sequestered in biomass. This convention is a plausible assumption for fast growing biomass species, but is inappropriate for slower growing biomass, like forests. In this case, the climate impact from biomass combustion can be potentially underestimated if CO2 emissions are ignored, or overestimated, if biogenic CO2 is considered equal to anthropogenic CO2. The estimation of the effective climate impact should take into account how the CO2 fluxes are distributed over time: the emission of CO2 from bioenergy approximately occurs at a single point in time, while the absorption by the new trees is spread over several decades. Our research target is to include this dynamic time dimension in unit-based impact analysis, using a boreal forest stand as case study. The boreal forest growth is modelled with an appropriate function, and is investigated under different forestry regimes (affecting the growth rate and the year of harvest). Specific atmospheric decay functions for biomass-derived CO2 are then elaborated for selected combinations of forest management options. The contribution to global warming is finally quantified using the GWPbio index as climate metric. Results estimates the effects of these practices on the characterization factor used for the global warming potential of CO2 from bioenergy, and point out the key role played by the selected time horizon.
Establishing the link between atmospheric CO2 concentration and anthropogenic carbon emissions requires the development of complex carbon cycle models of the primary sinks, the ocean and terrestrial biosphere. Once such models have been developed, the potential exists to use pulse response functions to characterize their behaviour. However, the application of response functions based on a pulse increase in atmospheric CO2 to characterize oceanic uptake, the conventional technique, does not yield a very accurate result due to nonlinearities in the aquatic carbon chemistry. Here, we propose the use of an ocean mixed-layer pulse response function that characterizes the surface to deep ocean mixing in combination with a separate equation describing air-sea exchange. The use of a mixed-layer pulse response function avoids the problem arising from the nonlinearities of the carbon chemistry and gives therefore more accurate results. The response function is also valid for tracers other than carbon. We found that tracer uptake of the HILDA and Box-Diffusion model can be represented exactly by the new method. For the Princeton 3-D model, we find that the agreement between the complete model and its pulse substitute is better than 4% for the cumulative uptake of anthropogenic carbon for the period 1765–2300 applying the IPCC stabilization scenarios S450 and S750 and better than 2% for the simulated inventory and surface concentration of bomb-produced radiocarbon. By contrast, the use of atmospheric response functions gives deviations up to 73% for the cumulative CO2 uptake as calculated with the Princeton 3-D model. We introduce the use of a decay response function for calculating the potential carbon storage on land as a substitute for terrestrial biosphere models that describe the overturning of assimilated carbon. This, in combination with an equation describing the net primary productivity permits us to exactly characterize simple biosphere models. As the time scales of biospheric overturning are one key aspect to determine the amount of anthropogenic carbon which might be sequestered by the biosphere, we suggest that decay response functions should be used as a simple and standardized measure to compare different models and to improve understanding of their behaviour. We provide analytical formulations for mixed-layer and terrestrial biosphere decay pulse response functions which permit us to easily build a substitute for the ‘Bern’ carbon cycle model (HILDA). Furthermore, mixed-layer response functions for the Box-Diffusion, a 2-D model, and the Princeton 3-D model are given.
A novel computer model is presented which describes the flow of C and N in the soil. It employs a structure with conceptual compartments. Organic matter is represented by seven different compartments, two for added matter, two for soil microbial biomass, one for microbial residues, one for native (‘humified’) organic matter, and one for inert organic matter. The latter pool represents both truly inert matter, and matter with negligible turnover in a time-span of decades to a century. This paper describes the parameterisation and performance of this model on selected long-term field carbon and radiocarbon data from United Kingdom, Sweden and Denmark. Previously unpublished radiocarbon data series from Denmark are included. Statistical methods were employed to estimate parameters, and obtain proximate confidence intervals for these parameters. Simulations in good agreement with measured values could be achieved, using the same set of parameters on all sites. It was demonstrated that the inert pool might constitute any amount between approx. 10 and 50% of total soil C, so that modelling cannot be used as a tool to obtain narrow estimates for this pool.
An extended overview of the chemical composition of biomass was conducted. The general considerations and some problems related to biomass and particularly the composition of this fuel are discussed. Reference peer-reviewed data for chemical composition of 86 varieties of biomass, including traditional and complete proximate, ultimate and ash analyses (21 characteristics), were used to describe the biomass system. It was shown that the chemical composition of biomass and especially ash components are highly variable due to the extremely high variations of moisture, ash yield, and different genetic types of inorganic matter in biomass. However, when the proximate and ultimate data are recalculated respectively on dry and dry ash-free basis, the characteristics show quite narrow ranges. In decreasing order of abundance, the elements in biomass are commonly C, O, H, N, Ca, K, Si, Mg, Al, S, Fe, P, Cl, Na, Mn, and Ti. It was identified that the chemical distinctions among the specified natural and anthropogenic biomass groups and sub-groups are significant and they are related to different biomass sources and origin, namely from plant and animal products or from mixtures of plant, animal, and manufacture materials. Respective chemical data for 38 solid fossil fuels were also applied as subsidiary information for clarifying the biomass composition and for comparisons. It was found that the chemical composition of natural biomass system is simpler than that of solid fossil fuels. However, the semi-biomass system is quite complicated as a result of incorporation of various non-biomass materials during biomass processing. It was identified that the biomass composition is significantly different from that of coal and the variations among biomass composition were also found to be greater than for coal. Natural biomass is: (1) highly enriched in Mn > K > P > Cl > Ca > (Mg, Na) > O > moisture > volatile matter; (2) slightly enriched in H; and (3) depleted in ash, Al, C, Fe, N, S, Si, and Ti in comparison with coal. The correlations and associations among 20 chemical characteristics are also studied to find some basic trends and important relationships occurring in the natural biomass system. As a result of that five strong and important associations, namely: (1) C–H; (2) N–S–Cl; (3) Si–Al–Fe–Na–Ti; (4) Ca–Mg–Mn; and (5) K–P–S–Cl; were identified and discussed. The potential applications of these associations for initial and preliminary classification, prediction and indicator purposes related to biomass were also introduced or suggested. However, future detailed data on the phase–mineral composition of biomass are required to explain actually such chemical trends and associations.
Existing models of soil organic matter (SOM) turnover are implemented within rigid and often complex modelling environments, which makes the testing of influence of SOM model structure a rather difficult task. A new soil carbon turnover simulation tool is presented (c-tool v. 1.0). It facilitates the construction of a wide range of user-definable SOM models based on linked SOM pools and a decay described for each pool by first order kinetics. Simulation of carbon isotopes 13C and 14C is facilitated. No programming is necessary for defining or redefining models, as the model structure is given in set-up files. The program is fast, and can utilise a range of time-steps, which enhances the computation of steady level SOM contents. The ability of c-tool to mimic and analyse an existing model was tested using the daisy SOM-model as an example. It was found that both the reduction of the vertically layered SOM-model in daisy to one layer, and the exclusion of C/N interactions only had small effects on the simulated development in soil carbon content during a 30-year period. This suggests that C/N interactions and vertical layering may initially be ignored when constructing and calibrating models for SOM turnover, which reduces model complexity and input demands considerably. The steady level carbon content was simulated for two soils and a range of management types. An analysis of the model's sensitivity in simulated steady level carbon content to variation in carbon-input and key parameters was performed, and simulated isotope tagging was demonstrated as a powerful method for analysing carbon flows.
The paper reviews the development of the energy sys- tem simulation tool DNA (Dynamic Network Analy- sis). DNA has been developed since 1989 to be able to handle models of any kind of energy system based on the control volume approach, usually systems of lumped parameter components. DNA has proven to be a useful tool in the analysis and optimization of sev- eral types of thermal systems: Steam turbines, gas tur- bines, fuels cells, gasification, refrigeration and heat pumps for both conventional fossil fuels and different types of biomass. DNA is applicable for models of both steady state and dynamic operation. The program decides at runtime to apply the DAE solver if the system contains differen- tial equations. This makes it easy to extend an existing steady state model to simulate dynamic operation of the plant. The use of the program is illustrated by ex- amples of gas turbine models. The paper also gives an overview of the recent imple- mentation of DNA as a Matlab extension (Mex).
Nutrient-balance assessments are valuable tools for delineating the consequences of farming on soil fertility. Various approaches and methods for different situations have been used. This bulletin presents a state-of-the-art overview of nutrient-balance studies. It brings out the evolution of the approaches and methods, provides for comparisons among them, features the improvements made, and highlights remaining issues. The analysis would be useful in further development of the assessment methodologies as reliable tools for devising time-scale soil fertility management interventions.
Methods of assessment of direct field emissions for lcis of agricultural production systems
- T Nemecek
- J Schnetzer
Centre of the Netherlands. Phyllis2, database for biomass and waste
- E Research
Ministeriet for Fødevarer, Landbrug og Fiskeri
- Naturerhvervstyrelsen
Anthropogenic and natural radiative forcing
- Myhre
Danmarks Meteorologiske Institut
- Danmarks Dmi
- Climate
Life cycle inventories of agricultural production systems
- T Nemecek
- T Kagi
Energy in synthetic fertilizers and pesticides: revisited, ORNL/Sub/90-99732/2. Oak Ridge National Laboratory
- M G Bhat
- B C English
- A F Turhollow
- H O Nyangito
Fourth assessment report: climate change 2007: working group iii report: mitigation of climate change
- Ipcc