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循环流化床(CFB)锅炉在燃用石油焦方面具有优势.在全烧石油焦时CFB锅炉效率可达93%,CO低于60 mg/Nm3,NOx排放在20 mg/Nm3以内,这得益于石油焦的高含碳量和低氮含量,但床温和过量空气系数要严格控制.提高煤的掺烧比例亦即燃料灰分增加能够提高炉膛物料浓度,在相同热输入条件下床温下降.理论计算发现,物料浓度增加了20%将导致换热系数上升约5%,对应地床温下降25℃左右,这与实际是一致的.根据理论分析,提出了减小循环量降低固体物料浓度可以提高床温的建议,该设想得到实践验证. 相似文献
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循环流化床传热系数的计算模型 总被引:1,自引:0,他引:1
本文在循环流化床流动模型的基础上建立了传热模型,流动模型根据实际运行情况考虑了颗粒的宽筛分,并把床层在轴向上分为密相床和稀相床两部分。在密相床内,传热按照鼓泡床传热微型进行计算;在稀相床内,传热模型建立在颗粒团更新的假设基础上,根据假设,床层由颗粒浓度很低的上升稀相和相对颗粒浓度较大的颗粒团两部分组成,两部分交替地与床壁面接触,床层和受热面间局部换热系数和颗粒浓度及两部分接触壁面的份额有关。模化结 相似文献
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通过对1 060t/h裤衩腿型循环流化床锅炉的大量变工况试验,获得了不同负荷率下的炉内压力分布,给出了该锅炉稀相区物料质量浓度的分布规律,并分析了流化风速和床压降对物料质量浓度分布的影响,得到物料质量浓度随流化风速和炉膛高度变化的关系式以及物料质量浓度随床压降和炉膛高度变化的关系式.结果表明:在床压降不变的条件下,流化风速与炉内平均物料质量浓度成正比;在流化风速不变的条件下,在一定的范围内,床压降与炉内平均物料质量浓度成正比,当床压降升高到某一临界值后,床压降与炉内平均物料质量浓度成反比. 相似文献
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回转式空气预热器非稳定换热的分析 总被引:1,自引:0,他引:1
根据回转式空气预热器的工作机理,分析了非稳定换热对其热力计算的影响,详细介绍了所建立的非稳定换热的计算模型,模型反映了空气预热器的转速、受热面的质量和比热、烟气和空气的流量和比热、各分仓的角度和受热面积、传热系数等诸多因素对非稳定换热的影响.以烟气和空气的流量、传热系数以及受热面动态热容的改变为例,给出了非稳定换热影响系数和受热面温度发生相应变化的计算结果.分析了各类因素的影响程度大小和模型的合理性.与目前仅根据空气预热器转速,插值计算非稳定换热影响系数的方法相比,该模型具有更好的合理性和广泛适用性.图6参5 相似文献
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介绍了300MW循环流化床锅炉磨损的机理,由于受炉内循环物料的长期磨损造成水冷壁以及外置床受热面的泄露,重点分析了其受热面泄露的处理原则,方法及注意事项,提出了300MW循环流化床锅炉受热面磨损的预防措施。 相似文献
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本文研究了直径15~100μm的碳水化合的颗粒在水平旋转筒反应器中的传热.用“渗透模型”机理讨论了粉体颗粒与旋转筒内壁面间的换热,推导出换热系数α与筒旋转速度、物料填充度之间的理论分析解。换热系数理论值和实验所得数据较为吻合。 相似文献
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某电厂690 t/h CFB锅炉运行中存在床温整体偏高现象,直接导致了锅炉炉内SO_2和NO_x排放浓度偏高问题,严重影响了机组正常发电生产的环保经济性。在与锅炉厂家讨论分析燃烧煤种、实际运行条件、分离器效率、蒸发受热面布置等多方面因素后,得出锅炉炉内蒸发受热面面积过小是造成床温偏高的主要原因。为此电厂实施了锅炉新增水冷蒸发屏受热面技术改造项目,在保证新增水冷蒸发屏安全可靠运行及锅炉热效率基础上,有效降低了锅炉运行床温、炉内脱硫Ca/S、炉内NO_x生成浓度,提高了锅炉炉内脱硫脱硝的效率,提升了生产的环保经济性。 相似文献
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Woody biomass in Finland and Sweden comprises mainly four wood species: spruce, pine, birch and aspen. To study the ash, which may cause problems for the combustion device, one tree of each species were cut down and prepared for comparisons with fuel samples. Well-defined samples of wood, bark and foliage were analyzed on 11 ash-forming elements: Si, Al, Fe, Ca, Mg, Mn, Na, K, P, S and Cl. The ash content in the wood tissues (0.2–0.7%) was low compared to the ash content in the bark tissues (1.9–6.4%) and the foliage (2.4–7.7%). The woods’ content of ash-forming elements was consequently low; the highest contents were of Ca (410–1340 ppm) and K (200–1310), followed by Mg (70–290), Mn (15–240) and P (0–350). Present in the wood was also Si (50–190), S (50–200) and Cl (30–110). The bark tissues showed much higher element contents; Ca (4800–19,100 ppm) and K (1600–6400) were the dominating elements, followed by Mg (210–2400), P (210–1200), Mn (110–1100) and S (310–750), but the Cl contents (40–330) were only moderately higher in the bark than in the wood. The young foliage (shoots and deciduous leaves) had the highest K (7100–25,000 ppm), P (1600–5300) and S (1100–2600) contents of all tissues, while the shoots of spruce had the highest Cl contents (820–1360) and its needles the highest Si content (5000–11,300). This paper presented a new approach in fuel characterization: the method excludes the presence of impurities, and focus on different categories of plant tissues. This made it possible to discuss the contents of ash element in a wide spectrum of fuel-types, which are of large importance for the energy production in Finland and Sweden. 相似文献
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《热能动力工程》2014,(5)
正1 ABSTRACT To reduce the effect of global warming on our climate,the levels of CO2emissions should be reduced.One way to do this is to increase the efficiency of electricity production from fossil fuels.This will in turn reduce the amount of CO2emissions for a given power output.Using US practice for efficiency calculations,then a move from a typical US plant running at 37%efficiency to a 760℃/38.5 MPa(1 400/5 580 psi)plant running at 48%efficiency would reduce CO2emissions by 170kg/MW.hr or 25%. 相似文献
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The purpose of this paper is to illustrate the advantages of the direct surface-curvature distribution blade-design method, originally proposed by Korakianitis, for the leading-edge design of turbine blades, and by extension for other types of airfoil shapes. The leading edge shape is critical in the blade design process, and it is quite difficult to completely control with inverse, semi-inverse or other direct-design methods. The blade-design method is briefly reviewed, and then the effort is concentrated on smoothly blending the leading edge shape (circle or ellipse, etc.) with the main part of the blade surface, in a manner that avoids leading-edge flow-disturbance and flow-separation regions. Specifically in the leading edge region we return to the second-order (parabolic) construction line coupled with a revised smoothing equation between the leading-edge shape and the main part of the blade. The Hodson–Dominy blade has been used as an example to show the ability of this blade-design method to remove leading-edge separation bubbles in gas turbine blades and other airfoil shapes that have very sharp changes in curvature near the leading edge. An additional gas turbine blade example has been used to illustrate the ability of this method to design leading edge shapes that avoid leading-edge separation bubbles at off-design conditions. This gas turbine blade example has inlet flow angle 0°, outlet flow angle −64.3°, and tangential lift coefficient 1.045, in a region of parameters where the leading edge shape is critical for the overall blade performance. Computed results at incidences of −10°, −5°, +5°, +10° are used to illustrate the complete removal of leading edge flow-disturbance regions, thus minimizing the possibility of leading-edge separation bubbles, while concurrently minimizing the stagnation pressure drop from inlet to outlet. These results using two difficult example cases of leading edge geometries illustrate the superiority and utility of this blade-design method when compared with other direct or inverse blade-design methods. 相似文献
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A chemical reactor for the steam-gasification of carbonaceous particles (e.g. coal, coke) is considered for using concentrated solar radiation as the energy source of high-temperature process heat. A two-phase reactor model that couples radiative, convective, and conductive heat transfer to the chemical kinetics is applied to optimize the reactor geometrical configuration and operational parameters (feedstock's initial particle size, feeding rates, and solar power input) for maximum reaction extent and solar-to-chemical energy conversion efficiency of a 5 kW prototype reactor and its scale-up to 300 kW. For the 300 kW reactor, complete reaction extent is predicted for an initial feedstock particle size up to 35 μm at residence times of less than 10 s and peak temperatures of 1818 K, yielding high-quality syngas with a calorific content that has been solar-upgraded by 19% over that of the petcoke gasified. 相似文献
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As part of a pilot study investigating the role of microorganisms in the immobilisation of As, Sb, B, Tl and Hg, the inorganic geochemistry of seven different active sinter deposits and their contact fluids were characterised. A comprehensive series of sequential extractions for a suite of trace elements was carried out on siliceous sinter and a mixed silica-carbonate sinter. The extractions showed whether metals were loosely exchangeable or bound to carbonate, oxide, organic or crystalline fractions. Hyperthermophilic microbial communities associated with sinters deposited from high temperature (92–94°C) fluids at a variety of geothermal sources were investigated using SEM. The rapidity and style of silicification of the hyperthermophiles can be correlated with the dissolved silica content of the fluid. Although high concentrations of Hg and Tl were found associated with the organic fraction of the sinters, there was no evidence to suggest that any of the heavy metals were associated preferentially with the hyperthermophiles at the high temperature (92–94°C) ends of the terrestrial thermal spring ecosystems studied. 相似文献
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The physical aspects of the activation energy, in higher and high temperatures, of the metal creep process were examined. The research results of creep-rupture in a uniaxial stress state and the criterion of creep-rupture in biaxial stress states, at two temperatures, are then presented. For these studies creep-rupture, taking case iron as an example the energy and pseudoenergy activation was determined. For complex stress states the criterion of creep-rupture was taken to be Sdobyrev's, i.e. σred = σ1 β + (1 − β)σi, where: σ1-maximal principal stress, σi-stress intensity, β-material constant (at variable temperature β = β(T)). The methods of assessment of the material ageing grade are given in percentages of ageing of new material in the following mechanical properties: 1) creep strength in uniaxial stress state, 2) activation energy in uniaxial stress state, 3) criterion creep strength in complex stress states, 4) activation pseudoenergy in complex stress states. The methods 1) and 3) are the relatively simplest because they result from experimental investigations only at nominal temperature of the structure work, however, for methods 2) and 4) it is necessary to perform the experimental investigations at least at two temperatures. 相似文献
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Jaime Massanet-Nicolau Alan Guwy Richard Dinsdale Giuliano Premier Sandra Esteves 《International Journal of Hydrogen Energy》2010
Hydrogen was produced from primary sewage biosolids via mesophilic anaerobic fermentation in a continuously fed bioreactor. Prior to fermentation the sewage biosolids were heated to 70 °C for 1 h to inactivate methanogens and during fermentation a cellulose degrading enzyme was added to improve substrate availability. Hydraulic retention times (HRT) of 18, 24, 36 and 48 h were evaluated for the duration of hydrogen production. Without sparging a hydraulic retention time of 24 h resulted in the longest period of hydrogen production (3 days), during which a hydrogen yield of 21.9 L H2 kg−1 VS added to the bioreactor was achieved. Methods of preventing the decline of hydrogen production during continuous fermentation were evaluated. Of the techniques evaluated using nitrogen gas to sparge the bioreactor contents proved to be more effective than flushing just the headspace of the bioreactor. Sparging at 0.06 L L min−1 successfully prevented a decline in hydrogen production and resulted in a yield of 27.0 L H2 kg−1 VS added, over a period of greater than 12 days or 12 HRT. The use of sparging also delayed the build up of acetic acid in the bioreactor, suggesting that it serves to inhibit homoacetogenesis and thus maintain hydrogen production. 相似文献