秸秆能源化利用 相关英文文献

a li Mark P. McHenry * References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Agriculture, Ecosystems and Environment 129 (2009) 1–7 Key word word文档格式规范word作业纸小票打印word模板word简历模板免费word简历 s: Bio-char markets beyond traditional approach by directly applying carbon into soil. This paper provides an overview of the pyrolysis process and products and quantifies the amount of renewable energy Contents lists availab Agriculture, Ecosystem .e 1. Introduction Working Group III, in their contribution to the IPCC’s Fourth Assessment Report (AR4) stated the high agreement and much evidence that soil restoration and land use change mitigation measures can be implemented immediately by using existing technologies. Working Group III also stated the high agreement and much evidence that soil carbon sequestration is the mechanism responsible formost climate changemitigation potential (Paustian et al., 1997). The IPCC’s AR4 Synthesis Report confirmed that effective carbon-price signals can mobilise environmentally effective mitigation options in the agriculture and forestry sectors, including as improved land management practices that maintain soil carbon density and for soil carbon sequestration. However, to be able to successfully utilise soil carbon mitigation incentives, farmers will need to use iterative management processes that balance economic carbon sequestration benefitswith conventional production co-benefits, and attitudes to risk (Intergovernmental Panel on Climate Change, 2000). Decreasing the financial risks of farming in this period of relative climate policy uncertainty requires feasibility studies of synergies between conventional productivity and climate change mitigation and adaptation measures. Similarly, reducing farm investment risk in a changing climate will entail the greater use of * Tel.: +61 430 485 306. E-mail address: mpmchenry@gmail.com. Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2. Bio-char production and feedstock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 3. Bio-char and agricultural suitability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 4. Bio-char and alternative biomass products and services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 5. Bio-char production and greenhouse gas emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 6. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Charcoal Soil Carbon Renewable Biomass Western Australia generation and net carbon sequestration possible when using farm bio-waste to produce bio-char as a primary product. While this research provides approximate bio-char and energy production yields, costs, uses and risks, there is a need for additional research on the value of bio-char in conventional crop yields and adaptation and mitigation options. � 2008 Elsevier B.V. All rights reserved. A R T I C L E I N F O Article history: Received 22 June 2008 Received in revised form 31 July 2008 Accepted 5 August 2008 Available online 25 September 2008 A B S T R A C T Reducing the vulnerability of agriculture to climate change while increasing primary productivity requires mitigation and adaptation activities to generate profitable co-benefits to farms. The conversion of woody-wastes by pyrolysis to produce bio-char (biologically derived charcoal) is one potential option that can enhance natural rates of carbon sequestration in soils, reduce farm waste, and substitute renewable energy sources for fossil-derived fuel inputs. Bio-char has the potential to increase conventional agricultural productivity and enhance the ability of farmers to participate in carbon 0167-8 doi:10.1 School of Engineering and Energy, Murdoch University, 90 South Street, Murdoch, Western Australia 6150, Australia Review Agricultural bio-char production, renew carbon sequestration in Western Austra journal homepage: www 809/$ – see front matter � 2008 Elsevier B.V. All rights reserved. 016/j.agee.2008.08.006 ble energy generation and farm a: Certainty, uncertainty and risk le at ScienceDirect s and Environment l sev ier .com/ locate /agee ems monitoring to inform management practices that increase farm ecosystem stability and resilience to climate stress (Griffiths et al., 2000; Tobor-Kaplon et al., 2005; Harle et al., 2006; Brussaard et al., 2007). Therefore, sequestering carbon in agricultural soils is one such possible synergy that creates additional property rights for farmers, retains land values by soil conservation, andmay improve conventional yields by modulating soil ecosystem variability (Klein et al., 2007; Milne et al., 2007). There is considerable interest in finding reliable methods of sequestering carbon in agricultural soils to both reduce farm investment risk and cut atmospheric greenhouse gas concentra- tions, in a timeframe suitable to investors. Increasing the levels of soil organic carbon (SOC) by conventional agricultural manage- ment can take many years and involves significant uncertainty in regards to the resultant carbon fluxes (Denman et al., 2007). A report by the National Carbon Accounting System (NCAS) authored by Valzano et al. (2005), focussed on the impact of tillage on changes in SOC density in Australia. The report found that low tillage and stubble retention management practices only had an effect on SOC density up to depths of 30 cm in areas with mean annual temperatures between 12.8 and 17.4 8C and an average annual rainfall above 650 mm (Valzano et al., 2005). In Australian research plots that did show significant differences of SOC densities between using minimum disturbance methods and conventional tillage, the results have been modest. Farms using direct drill, retained stubble and moderate grazing production methods were found to have densities of around 57 t ha�1 up to 30 cm of depth, while nearby heavily grazed farms using multiple crop tillage (with either tyned or disc implements), had SOC densities of 43 t ha�1 up to 30 cm soil depths (Valzano et al., 2005). A study by Wright et al. (2007) on SOC and nitrogen levels over 20 years of various tillage regimes, found the no-tillage practices only increased SOC, dissolved organic carbon and total nitrogen by 28, 18 and 33% respectively, when compared to conventional tillage (Wright et al., 2007). While the benefit of using minimum tillage methods are clear for retaining natural SOC densities, sequestering sufficient volumes of SOC for carbon markets will likely require new approaches to purposefully add SOC to enhance existing carbon sinks. The conversion of biomass to long-lived soil carbon species results in a long-term carbon sink, as the biomass removes atmospheric carbon dioxide through photosynthesis. Bio-char carbon species range in complexity from graphite-like carbon to highmolecularweight aromatic rings,which are known to persist in soil for thousands tomillions of years (Graetz and Skjemstad, 2003). Unlike fossil fuels, biomass is a renewable sourceof carbonandusing it toproducebio-char can release energywithvirtuallynosulphuror mercury and very little nitrogen and ash waste (Antal and Gronli, 2003). Thus, producing bio-char from farm wood-waste appears to beonepromisingmethodof achieving greater levels of certainty and flexibility for integrating carbon sequestration accounting and renewable energy generation into conventional agricultural pro- duction (Lehmann, 2007). However, there remain large uncertain- ties of the effects of how bio-char applications to soil affect the surrounding ecology, and the productivity of particular crops in specific soil types and climates. This paper aims to reduce investment uncertainty for agriculturalists looking to diversify into converting biomass to bio-char and energy, with a special focus on experiences in Western Australia. 2. Bio-char production and feedstock Worldwide, 41 million tonnes (t) of bio-char (charcoal) is estimated to be produced annually for cooking and industrial M.P. McHenry / Agriculture, Ecosyst2 purposes (Food and Agriculture Organization of the United Nations, 2006) as cited in Lehmann et al. (2006). Conventional low efficiency production can result in losses of 80–90% of biomass weight (wet basis) and most of the energy content of the original biomass (Antal et al., 1996; Okello et al., 2001). If not produced according to sensible environmental parameters, the bio-char industry can lead to excessive deforestation, greenhouse gas emissions, particulate air pollution, and local health problems. However, many of these problems can be avoided by using the available clean and efficient bio-char production technologies (Lehmann et al., 2006). Using high efficiency technologies, it is possible to achievemass yields of around 30–40% (wet basis), energy yields of around 30% (contained in the charcoal), with fixed carbon contents of up to 90% of the original biomass. Obtaining these excellent conversion figures are dependent on the production technology used and the initial biomass feedstock properties (Mok et al., 1992; Antal et al., 1996). In addition to the production of solid carbon, around two- thirds of the energy ‘‘lost’’ in the conversion process can be captured as a useful gas, or used as a source of heat (Antal et al., 1996; Antal andGronli, 2003). Therefore themyriad of uses and the higher efficiency of modern available technology has the potential to provide a profitable incentive to sustain local biomass resources (Lehmann et al., 2006). At the instant of burning, the biomass carbon exposed to fire has three possible fates. The first, and least possible fate of biomass exposed to fire is that it remains unburnt. The other two possible fates are that it is either volatised to carbon dioxide and numerous other minor gas species, or it is pyrolised to bio-char or black carbon (Graetz and Skjemstad, 2003). Pyrolysis is the temperature- driven chemical decomposition of biomass fuel without combus- tion (Demirbas, 2004). In nature, pyrolised bio-char particles fall to the ground surface and the black carbon is incorporated in the particulate phase of the smoke (Graetz and Skjemstad, 2003; Demirbas, 2004). In commercial bio-char pyrolysis systems, the processes occurs in three steps: first, moisture and some volatiles are lost; second, unreacted residues are converted to volatiles, gasses and bio-char, and third, there is a slow chemical rearrangement of the bio-char (Demirbas, 2004). Generally, the lower the temperature at which pyrolysis occurs, the higher the carbon recovery of the original biomass (Lehmann et al., 2006). If the feedstock is dry and the bio-char yield is high, the heat produced canwarm the incoming feedstock sufficiently to initiate the pyrolising reactions to sustain the process (Antal and Gronli, 2003). The production of bio-char is favoured when there are low temperatures and low oxygen levels inside a pyrolysis chamber. At equal to, or greater than 400 8C, the biomass material is converted into fused aromatic ring bio-char structures with the loss of carbon dioxide (CO2), carbon monoxide (CO), water and hydrogen (H2). The hot combustion products (CO2 and H2) are further converted to a useful synthetic gas (a mixture of carbon monoxide and hydrogen) with significant amounts of heat (Graetz and Skjemstad, 2003; Demirbas, 2004). This process has the potential to be the lowest cost biomass to electrical energy conversion systems (Bridgewater and Peacocke, 2000) as cited in Lehmann et al. (2006). The energy content of oven dry wood varies from about 18 MJ kg�1 for some hardwoods and up to 21 MJ kg�1 for some softwood with high sap contents. As a rule of thumb, Western Australian hardwoods have 19 MJ kg�1 and softwoods 20 MJ kg�1 (Todd, 2001). This energy is more efficiently released when the feedstock is burnt directly, although direct burning diminishes the benefits of producing bio-char. The combustion of volatiles in the wood during pyrolysis releases around two-thirds of the energy in the wood as heat, which in turn may be used to raise and Environment 129 (2009) 1–7 steam or used for combustion in electricity generation technol- ems ogies (Baker et al., 1999). Pyrolysis at an elevated pressure improves bio-char yields as pyrolytic vapours are converted to secondary bio-char (Antal and Gronli, 2003). These slightly improved bio-char yields must be balanced against lower vapour yields used for energy generation. Also, higher bio-char production temperatures and pressures entail higher production costs than lower pyrolysis chamber temperatures and pressures. Therefore lower temperature pyrolysis at atmospheric pressuremay bemore suitable for small landholder production systems in rural areas, depending on the resources available (Kawamoto et al., 2005). Pyrolysis coupled with an organic matter return through bio- char applications addresses the dilemma soil degradation from widespread biomass extraction and bio-energy production. Bio- char production can also reduce transport costs of waste disposal as the bio-char mass is 70–80% less than the original wood-waste (Lehmann, 2007). Inmany cases, forestry and agricultural residues, such as mill off-cuts and nutshells have little value and their disposal incurs costs. Many of these wastes can be utilised in bio- char production. There is an extensive range of cropwastes that are suitable for pyrolysis in Australia include a variety of wasted species of broadacre grain trash,macadamia nut shells (Macadamia integrifolia/tetraphylla), olive pips (Olea europaea), wood blocks or woodchips, tree bark, and grass residues (Bridgewater and Peacocke, 2000). However, not all agricultural waste is suitable for bio-char production as it either a poor feedstock ormay provide ecological services, such as vegetable crops and field residues respectively (Lehmann et al., 2006). 3. Bio-char and agricultural suitability At the local scale, soil organic carbon levels shape agro- ecosystem function and influence soil fertility and physical properties, such as aggregate stability, water holding capacity and cation exchange capacity (CEC) (Milne et al., 2007). The ability of soils to retain nutrients in cation form that are available to plants can be increased using bio-char. The CEC of the bio-char itself can also be improved by producing the bio-char at higher temperatures (700–800 8C), although this is at the expense of lower carbon yields (�5% loss). The optimum bio-char production temperature in terms of carbon recovery, CEC and surface area is 500 8C (Lehmann, 2007). The CEC of freshly produced bio-char is relatively low, although it will increase over a few months when stored between 30 and 70 8C (Lehmann et al., 2003; Lehmann, 2007). Farmers should be aware that certain production conditions and feedstock types can cause the bio-char to be completely ineffective in retaining nutrients or be susceptible to microbial decay. Bio-char produced under 400 8C has a low surface area and may not be useful as an agricultural soil improver (Lehmann, 2007). The type of biomass feedstock and pyrolysis conditions will also affect the amount and type of substances produced. Some feedstocks and conditions will generate phytotoxic and potentially cancerogenous organic materials (Lima et al., 2005) as cited by Lehmann (2007). Sub-optimal pyrolysis conditions can also result in negligible net sequestration from low carbon recovery (Lehmann, 2007). Therefore, a farmer must be careful when choosing a particular pyrolysis system and when setting the operational conditions during pyrolysis. Further risk results from the lack of research about the safe level of bio-char application for many soil types. The levels of metal contaminants present in the original biomass feedstock often limit the safe level of bio-char addition. Exceeding the contaminant- limited biosolids application rate of copper (based on themaximum allowable solid contaminant concentrations) can be achieved by applying as little as 38 t of bio-char per hectare on a typical lateritic M.P. McHenry / Agriculture, Ecosyst soil (Department of Environmental Protection et al., 2002; Bridle, 2004). Other metal contaminants such as cadmium can exceed the contaminant rate by a bio-char application of 250 t ha�1. Metals such as zinc, mercury, arsenic, lead and nickel require much larger applications. Providing total phosphorus loadings equivalent to 100 kg ha�1 of superphosphate (9 kg of phosphorus), requires 160 kg of bio-char per hectare (Bridle, 2004). These application rates suggest that very high levels of bio-char additions comewith a risk of contaminating soils, but conservative use is comparably low risk in a similar manner to conventional fertiliser applications. Methods used to apply bio-char into agricultural soils depend on the bio-char physical properties and its intended function. Uniform mixing of bio-char into topsoils is used for improving soil biology, water holding capacity and nutrient availability, however this approach disturbs much of the existing soil structure and creates dust and erosion issues. Forming deep layers of bio-char under the surface is used to intercept nutrients in surface soils with low CEC, although has similar drawbacks to uniformmixing. Mechanical broadcasting of bio-char is useful for adsorbing leachable nutrients and herbicides and is a minimal disturbance method, although it doubtful whether this form of application is suitable for carbon sequestration purposes (Black- well et al., 2008). In addition to these common methods are deep-banding, seeding application, topdressing, aerial delivery, specific applica- tion to ailing vegetation at the root, and even ecological delivery via animal excreta (Blackwell et al., 2008). Understandably, the choice of application method for bio-char sequestration purposes should minimise impacts on the existing SOC species and primary crops. Disruption and compaction of soils should be kept to a minimum as disturbing organisms that contribute to aggregation can lead to lower microbial activity and lower productivity (Bronick and Lal, 2005). Tillage and mixing of soils also directly break up soil aggregates and exposes surfaces otherwise inacces- sible to decomposers which increases the carbon turnover rate (Post and Kwon, 2000). 4. Bio-char and alternative biomass products and services The integration of bio-char soil improver production and renewable energy generation in the form of biofuels, electricity and heat is a promising new industry (Lehmann et al., 2006). Producing bio-char and energy from wastes may both reduce waste disposal costs and provide cost-effective energy services that can be used by agricultural industries (Marris, 2006). In contrast to other renewable energy technologies, biomass can be used to produce a number of liquid, solid and gaseous fuels (Bridgewater and Peacocke, 2000). Currently hydrogen gas (as the energy carrier) and bio-oil are the two common fuels produced using pyrolysis technologies. Bio-oil production is themore advanced andmorewide-spread technology of the two (Lehmann et al., 2