Gaunt John L, Lehmann Johannes
College of Agriculture and Life Sciences, Cornell University, Ithaca, NY 14850, USA.
Environ Sci Technol. 2008 Jun 1;42(11):4152-8. doi: 10.1021/es071361i.
The implications for greenhouse gas emissions of optimizing a slow pyrolysis-based bioenergy system for biochar and energy production rather than solely for energy production were assessed. Scenarios for feedstock production were examined using a life-cycle approach. We considered both purpose grown bioenergy crops (BEC) and the use of crop wastes (CW) as feedstocks. The BEC scenarios involved a change from growing winter wheat to purpose grown miscanthus, switchgrass, and corn as bioenergy crops. The CW scenarios consider both corn stover and winter wheat straw as feedstocks. Our findings show that the avoided emissions are between 2 and 5 times greater when biochar is applied to agricultural land (2--19 Mg CO2 ha(-1) y(-1)) than used solely for fossil energy offsets. 41--64% of these emission reductions are related to the retention of C in biochar, the rest to offsetting fossil fuel use for energy, fertilizer savings, and avoided soil emissions other than CO2. Despite a reduction in energy output of approximately 30% where the slow pyrolysis technology is optimized to produce biochar for land application, the energy produced per unit energy input at 2--7 MJ/MJ is greater than that of comparable technologies such as ethanol from corn. The C emissions per MWh of electricity production range from 91-360 kg CO2 MWh(-1), before accounting for C offset due to the use of biochar are considerably below the lifecycle emissions associated with fossil fuel use for electricity generation (600-900 kg CO2 MWh(-1)). Low-temperature slow pyrolysis offers an energetically efficient strategy for bioenergy production, and the land application of biochar reduces greenhouse emissions to a greater extent than when the biochar is used to offset fossil fuel emissions.
评估了优化基于慢速热解的生物能源系统以生产生物炭和能源而非仅用于能源生产对温室气体排放的影响。使用生命周期方法研究了原料生产的情景。我们考虑了专门种植的生物能源作物（BEC）和将作物废弃物（CW）用作原料。BEC情景涉及从种植冬小麦转变为专门种植芒草、柳枝稷和玉米作为生物能源作物。CW情景将玉米秸秆和冬小麦秸秆都视为原料。我们的研究结果表明，当生物炭施用于农业土地时（2-19 Mg CO₂ ha⁻¹ y⁻¹），避免的排放量比仅用于抵消化石能源排放时大2至5倍。这些减排量的41%-64%与生物炭中碳的固定有关，其余部分与抵消能源使用中的化石燃料、节省肥料以及避免除二氧化碳之外的土壤排放有关。尽管在优化慢速热解技术以生产用于土地施用的生物炭时能源产出减少了约30%，但每单位能量输入产生的能量为2-7 MJ/MJ，高于诸如玉米乙醇等可比技术。在考虑生物炭使用带来的碳抵消之前，每兆瓦时电力生产的碳排放量范围为91-360 kg CO₂ MWh⁻¹，大大低于与使用化石燃料发电相关的生命周期排放量（600-900 kg CO₂ MWh⁻¹）。低温慢速热解为生物能源生产提供了一种能源高效的策略，并且生物炭在土地上的施用比将生物炭用于抵消化石燃料排放能更大程度地减少温室气体排放。
