牛粪在沼气发酵过程中的水解酶酶活变化研究

实验研究了牛粪在沼气发酵过程中蛋白酶、液化型淀粉酶、糖化型淀粉酶、脂肪酶和纤维素酶的酶活变化与沼气产量之间的关系。实验结果表明，这几种水解酶的酶活峰值正好处在沼气产气量的峰值期间。     

羊粪沼气发酵过程中的纤维素酶酶活力与沼气产气量的关系研究

试验研究了在羊粪沼气发酵过程中纤维素酶酶活力与沼气产气量的变化关系.结果表明:在羊粪沼气发酵过程中,纤维素酶酶活力的大小与沼气产气量随时间表征出一致的变化趋势,但产气量的变化在时间上要落后于纤维素酶酶活力的变化,即在纤维素酶达到一峰值的下一时刻,产气量达到一峰值.     

沼气发酵过程中几种水解酶活性的变化规律研究

研究了猪粪的沼气发酵过程中几种水解酶活性的变化。结果表明，酶活性大小与沼气产量的大小是相关的。各种酶酶活最大时，产气量正好处于高峰。其中酸性和中性蛋白酶酶活力发酵第５天呈现象最大，分别为１０．４和６．７μｇ酷氨酸／（ｍＬ．ｍｉｎ）；碱性蛋白酶酶活在发酵第１４天呈现最大，为９．３μｇ酷氨酶／（ｍＬ．ｍｉｎ）；脂肪酶酶活最大值亦在第１４天，为９１．１８μｇ脂肪酸／（ｍＬ．ｍｉｎ）；纤维素酶麦活出现滞后     

城市有机生活垃圾高温厌氧转化生物质能研究

在国内外已有的研究基础上,对城市有机生活垃圾的高温厌氧（批量）消化工艺实验进行了初步探索,研究了在55℃的高温条件下累积产气量与消化时间的关系,C／N比与产气量的关系,消化过程中pH值变化,并研究了垃圾高温发酵实验过程中沼气中的CH4和CO2的含量变化,其中甲烷含量最高可达75．3％。实验结果表明,城市生活垃圾高温消化的降解效果较好,产气量较高,启动时间短。     

餐厨垃圾和牛粪联合厌氧消化动力学探讨

将纯餐厨垃圾、纯牛粪、餐厨垃圾和牛粪以1∶1比例混合为原料,进行联合厌氧消化产气潜能实验,研究和比较3组原料的单位累计产气量、累计产气量、产气速率、pH,CH4含量等参数的变化,通过对产气量进行拟合和以及一级水解动力学分析,发现单组分的系统比较适合一级水解模型。在多组分的系统中,在消化的开始阶段,当易水解的组分如蛋白质、脂质浓度较高时,水解产气比较符合一级水解模型;在消化的中后半部分,当易水解的组分浓度变低,难水解的组分如纤维素等浓度升高时,水解产气与一级水解模型有些偏差,考虑水解组分差别采用Contois模型更合适。     

不同温度预处理的污泥消化与两相消化工艺的产气研究

将热水解技术与中温-微生物水解酸化-厌氧消化技术相结合处理污泥,研究了污泥的产气性能。小试试验中,原泥经过150℃和170℃热水解处理后厌氧消化,VS产气率较原泥分别增加9.01%和14.70%;原泥及其经过150℃,170℃热水解处理后采用两相消化,VS产气率较单相消化分别增加7.05%,7.63%和10.48%。中试试验中,150℃热水解污泥单相消化后VS产气率为346.88 L/kg,两相消化后VS产气率达到了481.62 L/kg,两相消化较单相消化VS产气率增加38.84%。     

碱剂预处理秸秆与活性污泥混合厌氧消化试验研究

秸秆经碱预处理后进行中温混合厌氧消化表现出典型的水解酸化和甲烷化过程,碱预处理秸秆的厌氧消化周期在27 d左右,未预处理的秸秆在试验的33 d内未有明显的厌氧消化反应发生,碱预处理秸秆缩短了其厌氧消化周期。从产气率、产气量分析,NaOH预处理试验组好于氨水预处理试验组。     

生物产酸对木薯酒精废水发酵联产氢气和甲烷的影响

在温度为36.0±0.5℃,初始pH值为4.5,5.5,6.5和7.5条件下进行生物产酸过程,当初始pH值为6.5,获得最大生物产酸率为53.13%,产酸过程进行168 h后再进行厌氧消化过程。用修改的Modified Gompertz模型处理两级厌氧消化与直接厌氧消化的实验数据,获得最大比产气量、最大比产气速率和滞留时间等厌氧消化动力学参数。拟合结果表明,初始pH值为7.5,6.5和5.5实验组的两级厌氧消化比直接厌氧消化的产气效果好,初始pH值为4.5的两级厌氧消化产气效果相对较差。初始pH值6.5的实验组产气效果最优,以单位质量MLVSS计的最大比产氢量和最大比产甲烷量分别为90.63 mL/g和199.33 mL/g。以单位质量MLVSS计的最大比产氢速率和产甲烷速率分别为13.00 mL/(g·h)和1.37 mL/(g·h)。两级厌氧消化比直接厌氧消化处理木薯酒精废水的能源转化率提高了19.01%。     

餐厨垃圾厌氧消化的工艺比选研究

研究了餐厨垃圾两段法厌氧消化工艺与整体一段法的性能差异。两种工艺的累积产气量几乎不存在差异,产气率分别达到135．66L／kgVS和134．56L／kgVS。两种工艺相比,一段法的产气周期短,但是产气的稳定性不佳,在整个消化过程中产气量波动明显,规律性不明显。研究认为：对于餐厨垃圾的厌氧消化．整体一段法的产气周期短,工艺运行简单,应用到工业化生产上,一段法具有明显优势。     

微波辅助MgO/SBA-15预处理对玉米秸秆厌氧消化的影响

为探索微波辅助MgO/SBA-15预处理玉米秸秆对其厌氧消化产气的影响,采用Mg O/SBA-15对玉米秸秆进行预处理,并在中温条件下进行厌氧消化产气试验。试验结果表明:微波辅助Mg O/SBA-15预处理玉米秸秆能有效破坏其原始构态,提高纤维素回收率和底物的可生物降解性,为厌氧发酵产沼气奠定良好的基础。在MgO/SBA-15与干基质的质量比分别为0%、10%、20%的条件下,预处理后的玉米秸秆厌氧消化产气能力较未预处理组有较大提高,厌氧消化启动时间有所提前。与对照组相比,经10%和20%MgO/SBA-15预处理的玉米秸秆单位挥发性固体(volatile solid,VS)产气量分别可提高55.28%和41.00%;90%最大产气量厌氧消化时间分别缩短1d和0 d;VS减少率分别提高7.3%和4.1%。综合考察预处理效果、日产气量、累积产气量和厌氧消化启动时间,相比于质量比20%的MgO/SBA-15组,质量比为10%的Mg O/SBA-15预处理效果更好。     

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.     

Contents in Volume 23,2014

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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.     

Controls on the Karaha–Telaga Bodas geothermal reservoir,Indonesia

Karaha–Telaga Bodas is a partially vapor-dominated, fracture-controlled geothermal system located adjacent to Galunggung Volcano in western Java, Indonesia. The geothermal system consists of: (1) a caprock, ranging from several hundred to 1600 m in thickness, and characterized by a steep, conductive temperature gradient and low permeability; (2) an underlying vapor-dominated zone that extends below sea level; and (3) a deep liquid-dominated zone with measured temperatures up to 353 °C. Heat is provided by a tabular granodiorite stock encountered at about 3 km depth. A structural analysis of the geothermal system shows that the effective base of the reservoir is controlled either by the boundary between brittle and ductile deformational regimes or by the closure and collapse of fractures within volcanic rocks located above the brittle/ductile transition. The base of the caprock is determined by the distribution of initially low-permeability lithologies above the reservoir; the extent of pervasive clay alteration that has significantly reduced primary rock permeabilities; the distribution of secondary minerals deposited by descending waters; and, locally, by a downward change from a strike-slip to an extensional stress regime. Fluid-producing zones are controlled by both matrix and fracture permeabilities. High matrix permeabilities are associated with lacustrine, pyroclastic, and epiclastic deposits. Productive fractures are those showing the greatest tendency to slip and dilate under the present-day stress conditions. Although the reservoir appears to be in pressure communication across its length, fluid, and gas chemistries vary laterally, suggesting the presence of isolated convection cells.     

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.