Techno-Economic Study of CO2 Capture from an Existing Cement Plant Using MEA Scrubbing

Carbon dioxide is the major greenhouse gas responsible for global warming. Man-made CO₂ emissions contribute approximately 63% of greenhouse gases and the cement industry is responsible for approximately 5% of CO₂ emissions emitting nearly 900 kg of CO₂ per 1000 kg of cement. CO₂ from a cement plant was captured and purified to 98% using the monoethanolamine (MEA) based absorption process. The capture cost was $51 per tonne of CO₂ captured, representing approximately 90% of total cost. Steam was the main operating cost representing 39% of the total capture cost. Switching from coal to natural gas reduces CO₂ emissions by about 18%. At normal load, about 36 MW of waste heat is available for recovery to satisfy the parasitic heat requirements of MEA process; however, it is very difficult to recover.     

石化企业中间罐区VOCs治理工艺选择与流程优化

石化企业中间罐区VOCs排放量较大,多采用吸收、冷凝、膜分离及其组合工艺进行处理。本文采用AspenPlus软件分别对高、中、低浓度中间罐区VOCs废气应用上述3种工艺及其工艺组合的处理效果进行模拟计算。结果表明:中间罐区的VOCs经过不同组合的二级处理后,尾气VOCs质量浓度约为9～50 g/m~3,后续仍需采用深度处理工艺以满足新的国家及地方污染物排放标准要求;同时,对比3种工艺能耗情况,冷凝法最低,膜分离法次之,吸收法最高,约为冷凝法能耗的5～10倍。以上模拟计算结果与实际工况数据基本符合,证明采用Aspen Plus软件进行石化企业中间罐区VOCs治理工艺选择与流程优化是可行的,具有一定的参考价值。     

基于Aspen Plus的生物质燃烧NOx生成模拟

利用Aspen Plus软件平台建立了生物质燃烧模型,对燃烧中NOx的生成进行了模拟计算,计算结果与已有文献的试验结果较好地相符.在此基础上,研究了燃烧温度和过量空气系数对生物质燃烧NOx生成的影响规律.结果表明,生物质燃烧过程中NOx的生成量随温度和过量空气系数的增长而快速增长;应用Aspen Plus模拟生物质燃烧具有一定的可行性,而且其模型参数设置较为灵活,能够对多种生物质的燃烧进行热力学分析,可为生物质清洁燃烧技术提供有益参考.     

DNA damage in Populus tremuloides clones exposed to elevated O3

The effects of elevated concentrations of atmospheric tropospheric ozone (O₃) on DNA damage in five trembling aspen (Populus tremuloides Michx.) clones growing in a free-air enrichment experiment in the presence and absence of elevated concentrations of carbon dioxide (CO₂) were examined. Growing season mean hourly O₃ concentrations were 36.3 and 47.3 ppb for ambient and elevated O₃ plots, respectively. The 4th highest daily maximum 8-h ambient and elevated O₃ concentrations were 79 and 89 ppb, respectively. Elevated CO₂ averaged 524 ppm (+150 ppm) over the growing season. Exposure to O₃ and CO₂ in combination with O₃ increased DNA damage levels above background as measured by the comet assay. Ozone-tolerant clones 271 and 8L showed the highest levels of DNA damage under elevated O₃ compared with ambient air; whereas less tolerant clone 216 and sensitive clones 42E and 259 had comparably lower levels of DNA damage with no significant differences between elevated O₃ and ambient air. Clone 8L was demonstrated to have the highest level of excision DNA repair. In addition, clone 271 had the highest level of oxidative damage as measured by lipid peroxidation. The results suggest that variation in cellular responses to DNA damage between aspen clones may contribute to O₃ tolerance or sensitivity.     

Differential response of aspen and birch trees to heat stress under elevated carbon dioxide

The effect of high temperature on photosynthesis of isoprene-emitting (aspen) and non-isoprene-emitting (birch) trees were measured under elevated CO₂ and ambient conditions. Aspen trees tolerated heat better than birch trees and elevated CO₂ protected photosynthesis of both species against moderate heat stress. Elevated CO₂ increased carboxylation capacity, photosynthetic electron transport capacity, and triose phosphate use in both birch and aspen trees. High temperature (36-39 °C) decreased all of these parameters in birch regardless of CO₂ treatment, but only photosynthetic electron transport and triose phosphate use at ambient CO₂ were reduced in aspen. Among the two aspen clones tested, 271 showed higher thermotolerance than 42E possibly because of the higher isoprene-emission, especially under elevated CO₂. Our results indicate that isoprene-emitting trees may have a competitive advantage over non-isoprene emitting ones as temperatures rise, indicating that biological diversity may be affected in some ecosystems because of heat tolerance mechanisms.