稀酸预处理玉米秸秆条件优化的试验研究

采用稀硫酸对玉米秸秆进行预处理,采用DNS法测定玉米秸秆水解液中还原糖的含量,对水解温度、水解时间、稀硫酸质量分数、固液质量比4个因素进行单因素试验分析,再通过正交试验对预处理条件进行优化.试验结果表明,最佳预处理条件:水解温度为121℃,水解时间为1 h,稀硫酸质量分数为0.6%,固液质量比为10%.     

稻草秸秆多酶水解条件研究

研究了稻草秸秆经过稀酸预处理后的酶水解条件,得到用于生产燃料乙醇的还原糖。试验结果表明:稻草秸秆经1%(w/w)的稀硫酸浸润,液固比(v/w)为5∶1,在121℃条件下处理60min后,每克稻草秸秆的初始水解还原糖得率达到0.187g。预处理后,在45℃,pH4.8,120r/min,48h条件下,采用酶的添加量最优配比(每克秸秆添加木聚糖酶217IU,纤维素酶5.13FPU,果胶酶25μ,β-葡聚糖酶500μ,淀粉酶150μ)时,水解产生的还原糖浓度达到最大值84.22g/L,原料水解率为41.19%。在酶水解糖化过程中,当MgSO4,Tween80的添加量分别为0.0001,0.005g时对纤维素酶有激活作用。     

酸碱预处理后玉米秸秆的酶解工艺优化

对玉米秸秆进行酸碱预处理,在单因素实验基础上,以还原糖转化率为影响值设计正交实验,研究温度、pH值、液固比、酶浓度及酶解时间5因素对纤维素酶解过程的影响。得出玉米秸秆酶解最佳工艺条件为:温度48℃、pH值4.6、液固比20、酶浓度55 U/g;酶解时间44 h。在此工艺条件下还原糖转化率达到80.97%。结合红外光谱对秸秆中各组分特征基团分析表明,膨化后的玉米秸秆酶解的纤维素基团特征峰变化更为明显。     

稀硫酸预处理玉米秸秆条件的优化研究

对稀硫酸预处理玉米秸秆优化工艺条件进行了试验研究,在考察温度、时间、稀硫酸质量分数、固液质量比和玉米秸秆粒度5个单因素对预处理效果影响的基础上,采用响应面分析法对预处理条件进行优化,建立了以戊糖得率为响应值的二次回归方程模型,得到最佳预处理条件为水解温度120℃,水解时间75 min,稀硫酸质量分数1.0%,固液质量比1∶15,玉米秸秆颗粒为40目。此条件下,理论预测戊糖得率为65.018%,试验验证戊糖得率为64.37%,与预测值接近,说明预测模型可靠性较高,可应用于稀酸预处理条件的优化。     

碱和双氧水预处理玉米秸秆的试验研究

研究了在5%NaOH中加入不同质量分数的双氧水时,对玉米秸秆的预处理效果;在预处理后的玉米秸秆中加入纤维素酶,考察此时酶解还原糖得率随预处理程度的变化;对浸泡时间、双氧水浓度、固液比3个因素进行单因素试验。试验结果表明,质量分数为2.5%的浓度下,糖得率最大;在2.5%H2O2浸泡24 h,固液比对酶解糖化几乎没有影响;当浸泡时间为24,72,96 h时,糖得率相差甚微。设计正交试验对预处理的条件进行优化,分析预处理玉米秸秆的各因素,以木质素去除率为基准参数,得到水解木质纤维素的适宜预处理条件:5%NaOH下加入质量分数为2.5%的双氧水,浸泡时间为72 h,固液比为1∶20。预处理后木质素的去除率为61.52%;加入纤维素酶酶解,还原糖得率为39.30%。     

稀酸处理对秸秆厌氧发酵产氢的影响

以稻草秸秆为纤维素原料,先利用稀硫酸对其进行预处理,再利用活性污泥进行厌氧发酵产氢。试验研究了压力、温度、硫酸浓度、加压时间、固液比以及原料粒度对预处理结果的影响,并根据产氢量优化了预处理条件。试验结果表明:在硫酸浓度为0.7%、处理压力为0.1MPa、加压时间为60min、固液比为1∶12,秸秆原料过60目筛的情况下预处理效果最好,此时每克秸秆产氢量为113ml,秸秆中半纤维素、纤维素的利用率为87.47%,秸秆的有效利用率为52.38%。     

小麦秸秆转化为可发酵糖的研究

对小麦秸秆水解转化为可发酵糖进行了研究，考察了小麦秸秆预处理方法以及温度、pH值、酶用量、底物浓度和反应时间等因素对小麦秸秆酶水解的影响。试验结果表明，汽蒸加蒽醌方法是较好的预处理方法。酶解最佳工艺为：温度48℃，pH值5．2，酶解时间24h，酶用量与底物的最佳配比0．160：1；底物浓度≥1％，以1．5％～2．5％为宜，此时还原糖得率达32．4％。     

膨化玉米秸秆酶解糖化条件优化的研究

采用二次回归正交组合试验设计,以温度、pH值、底物浓度、加酶量和酶解糖化时间5个因素为变量,研究各因素在不同试验水平下对膨化玉米秸秆酶解糖化效率的影响,并对试验条件进行优化组合。结果表明,温度为50℃,pH值为4.8,底物浓度为95g/L,加酶量为40U/g底物,酶解糖化时间为60h,膨化玉米秸秆酶解效果最佳,该条件下还原糖含量达到28.61%。     

预处理过的稻草在两种不同溶液中酶解性能的比较

为降低生物质能源生产成本,采用去离子水作为酶解溶液。将分别经过0.75%稀硫酸、2%氢氧化钠和800 kGyγ辐照预处理过的稻草在去离子水中进行酶解糖化,然后分别与在缓冲液中对应预处理过的稻草的酶解性能进行比较。结果表明,在缓冲液中,氢氧化钠预处理过的稻草能正常酶解,酶解120 h后纤维素转化率能达到约95%,木聚糖转化率超过70%;在去离子水中,经该方法预处理过的稻草酶解受到强烈抑制;辐照预处理过的稻草和稀硫酸预处理过的稻草在去离子水中和缓冲液中的酶解性能基本一致,酶解120 h后,辐照预处理过的稻草的纤维素转化率约为79%,木聚糖转化率约为50%;硫酸预处理过的稻草的纤维素转化率约为85%,木聚糖转化率约为75%。     

酶酸联合水解玉米秸秆的实验研究

开发了一种通过酸酶联合水解处理玉米秸秆以得到可发酵单糖的工艺方法,进行了稀硫酸预处理玉米秸秆的研究。得到最佳的工艺条件,木糖收率达到84.90%。用纤维素酶水解酸处理过的玉米秸秆,考察了pH值、温度、时间对酶水解率的影响,结果表明:酶解温度为50℃,pH值为4.8,水解时间为60h时,酶水解率达到91.71%。该工艺达到了节能高效地转化玉米秸秆为可发酵单糖的目的。     

Ash-forming elements in four Scandinavian wood species. Part 1: Summer harvest

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.     

NEXT GENERATION ENGINEERED MATERIALS FOR ULTRA SUPERCRITICAL STEAM TURBINES

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%.     

Performance assessment of some ice TES systems

In this paper, a performance assessment of four main types of ice storage techniques for space cooling purposes, namely ice slurry systems, ice-on-coil systems (both internal and external melt), and encapsulated ice systems is conducted. A detailed analysis, coupled with a case study based on the literature data, follows. The ice making techniques are compared on the basis of energy and exergy performance criteria including charging, discharging and storage efficiencies, which make up the ice storage and retrieval process. Losses due to heat leakage and irreversibilities from entropy generation are included. A vapor-compression refrigeration cycle with R134a as the working fluid provides the cooling load, while the analysis is performed in both a full storage and partial storage process, with comparisons between these two. In the case of full storage, the energy efficiencies associated with the charging and discharging processes are well over 98% in all cases, while the exergy efficiencies ranged from 46% to 76% for the charging cycle and 18% to 24% for the discharging cycle. For the partial storage systems, all energy and exergy efficiencies were slightly less than that for full storage, due to the increasing effect wall heat leakage has on the decreased storage volume and load. The results show that energy analyses alone do not provide much useful insight into system behavior, since the vast majority of losses in all processes are a result of entropy generation which results from system irreversibilities.     

Aerodynamic performance effects of leading-edge geometry in gas-turbine blades

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.     

Effect of co-cultivation of Chlamydomonas reinhardtii with Azotobacter chroococcum on hydrogen production

Chlamydomonas reinhardtii cc124 and Azotobacter chroococcum bacteria were co-cultured with a series of volume ratios and under a variety of light densities to determine the optimal culture conditions and to investigate the mechanism by which co-cultivation improves H₂ yield. The results demonstrated that the optimal culture conditions for the highest H₂ production of the combined system were a 1:40 vol ratio of bacterial cultures to algal cultures under 200 μE m^?2 s^?1. Under these conditions, the maximal H₂ yield was 255 μmol mg^?1 Chl, which was approximately 15.9-fold of the control. The reasons for the improvement in H₂ yield included decreased O₂ content, enhanced algal growth, and increased H₂ase activity and starch content of the combined system.     

Natural-gas fueled spark-ignition (SI) and compression-ignition (CI) engine performance and emissions

Natural gas is a fossil fuel that has been used and investigated extensively for use in spark-ignition (SI) and compression-ignition (CI) engines. Compared with conventional gasoline engines, SI engines using natural gas can run at higher compression ratios, thus producing higher thermal efficiencies but also increased nitrogen oxide (NO_x) emissions, while producing lower emissions of carbon dioxide (CO₂), unburned hydrocarbons (HC) and carbon monoxide (CO). These engines also produce relatively less power than gasoline-fueled engines because of the convergence of one or more of three factors: a reduction in volumetric efficiency due to natural-gas injection in the intake manifold; the lower stoichiometric fuel/air ratio of natural gas compared to gasoline; and the lower equivalence ratio at which these engines may be run in order to reduce NO_x emissions. High NO_x emissions, especially at high loads, reduce with exhaust gas recirculation (EGR). However, EGR rates above a maximum value result in misfire and erratic engine operation. Hydrogen gas addition increases this EGR threshold significantly. In addition, hydrogen increases the flame speed of the natural gas-hydrogen mixture. Power levels can be increased with supercharging or turbocharging and intercooling. Natural gas is used to power CI engines via the dual-fuel mode, where a high-cetane fuel is injected along with the natural gas in order to provide a source of ignition for the charge. Thermal efficiency levels compared with normal diesel-fueled CI-engine operation are generally maintained with dual-fuel operation, and smoke levels are reduced significantly. At the same time, lower NO_x and CO₂ emissions, as well as higher HC and CO emissions compared with normal CI-engine operation at low and intermediate loads are recorded. These trends are caused by the low charge temperature and increased ignition delay, resulting in low combustion temperatures. Another factor is insufficient penetration and distribution of the pilot fuel in the charge, resulting in a lack of ignition centers. EGR admission at low and intermediate loads increases combustion temperatures, lowering unburned HC and CO emissions. Larger pilot fuel quantities at these load levels and hydrogen gas addition can also help increase combustion efficiency. Power output is lower at certain conditions than diesel-fueled engines, for reasons similar to those affecting power output of SI engines. In both cases the power output can be maintained with direct injection. Overall, natural gas can be used in both engine types; however further refinement and optimization of engines and fuel-injection systems is needed.     

Hydrogen production by steam-gasification of carbonaceous materials using concentrated solar energy – V. Reactor modeling,optimization, and scale-up

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.     

Assessment methods of material ageing using Sdobyrev''s creep rupture model

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. σ_red = σ₁ β + (1 − β)σ_i, where: σ₁-maximal principal stress, σ_i-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.     

Production of hydrogen from sewage biosolids in a continuously fed bioreactor: Effect of hydraulic retention time and sparging

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.     

汽轮机数字电液调节系统挂闸异常的技术完善

分析了200MW汽轮机数字电液调节系统在运行中存在的挂闸异常问题,采取了相应的技术处理措施,且运行实践效果良好。