【導讀】主要由控制器、種肥箱、排種肥系統(tǒng)、鴨嘴式開溝器等零部件組成,適用于。種施肥、覆土一次完成。它采用了簡單可靠的機構和通用的零部件,具有攜帶方。便、使用可靠,耗材少、易加工、成本低等特點。我國是一個多山的國家,坡地占很大比例,大于15度的坡地占國土面積的60%,既可減少人工追肥時培土覆蓋的工序,減輕勞動強度,又可提高化肥的利用率。旱作農(nóng)業(yè)可持續(xù)發(fā)展的重要途徑。鍵設備，研制性能可靠、功能完善的機具是推廣工作的保障。成本與功能之間的矛盾。合理地利用化肥及研究施肥技術對我國農(nóng)業(yè)發(fā)展有著非常積極的意義。的不良影響,其經(jīng)濟、社會和生態(tài)效益顯著。主要有兩種,即實時控制施肥和處方信息控制施肥。這些機構控制難度大,價格高,進行,這樣能大大提高了水肥藕合效應和水肥利用效率。目前西歐谷物施肥播種機的工作幅寬

　　

【正文】 nd storage, the volume of inaccessible gas can be sign cost to In this study, the ect of this cushion gas is neglected when puting the store gaseous hydrogen because it is small when pared to other storage related costs. In addition, this study models hydrogen as an ideal gas. This approximation is sulciently accurate for the low temperatures and pressures considered in this study. 3. Hydrogen tower considerations Hydrogen storage creates a number of additional considerations in wind turbine tower design. Accelerated at mosphericcorrosion on the tower interior and hydrogen embrittlement may adversely aect the tower’ s ductility, yield strength, and fatigue life. Additionally, storing hydrogen at pressure signi4cantly increases the stresses on the tower. Therefore, wall reinforcement will likely be required. A structural analysis is required to evaluate how internal pressure may the tower’ s design life. . Corrosion Both atmosphericcorrosion and hydrogen embrittlement will ect the interior of a hydrogen tower. Conventional wind turbine towers are protected internally and externally from atmosphericcorrosion by paint. When a tower is used to store a pressurized gas, however, it bees subject to the guidelines set forth in the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code. The code states that paint is not an adequate form of protection for the interior of pressure vessels. Enough material must 寧夏大學機械工程學院 2021 屆畢業(yè)設計 therefore be added to anticipate atmospheric corrosion . Fortunately, the interior of a hydrogen tower is a controlled environment. Hydrogen from a PEM electrolyzer does not contain contaminants that cause atmospheric corrosion (of primary concern are sulfur dioxide and chlorine). The product hydrogen (which would be fully saturated with water vapor) could be dried to below the critical humidity level (less than 80% relative humidity) at minimal cost. Under these conditions, atmospheric corrosion would perate the steel’ s surface at the negligible rate of less than per year . Hydrogen attack One of the two primary modes of corrosion failure when steel is exposed to a hydrogen environment is hydrogen attack Although some sources do not distinguish hydrogen attack from hydrogen embrittlement (HE), other sources distinguish them by their diering responses to temperature. It is important not to confuse hydrogen attack, a phenomenon that occurs only at high temperatures, with HE, a phenomenon that primarily damages materials at ambient temperatures. Hydrogen attack, also known as hydrogeninduced cracking, is a process wherein hydrogen diuses through the steel’ s lattice structure, coalescing at voids and inclusions where the hydrogen reacts with the carbon present in the steel. This results in decarburization, as well as the formation of methane gas. The methane gas exerts an internal pressure, causing 4ssures or internal cracking. Hydrogen attack does not occur below 200℃ 。 for this reason it is monly called hightemperature hydrogen at tack. It is anticipated that hydrogen storage in turbine towers will be at or near ambient temperatures (25℃ – 30℃ ), which are far enough below the 200℃ threshold to make hydrogen attack an unlikely phenomenon. . Hydrogen embrittlement The term hydrogen embrittlement is monly used to describe hydrogen environment embrittlement (HEE) and internal hydrogen embrittlement. HEE is caused by subjecting metal to a hydrogenrich environment. During internal hydrogen embrittlement, hydrogen is produced inside a metal’ s structure, usually by a processing technique and is unlikely to be relevant to hydrogen towers. The term hydrogen embrittlement will refer to HEE for the remainder of this paper. HEE is a process in which atomic hydrogen (Has opposed to H2) 寧夏大學機械工程學院 2021 屆畢業(yè)設計 adsorbs to a metal’ s surface and causes brittle failure below the yield strength of an aected material. Many factors inAuence a po nent’ s susceptibility to hydrogen embrittlement. Those factors relevant to turbine towers consist of environ mental ects including temperature, pressure, and hydrogen purity, as well as material properties including grain size, hardness, and strength. This section explore how hydrogen embrittlement may ect a hydrogen tower. Evidence suggests that, unlike hydrogen attack, hydrogen environment embrittlement may be most severe at ambient temperatures Like hydrogen attack, however, HEE bees more severe with increasing pressure. Test data suggests that the degree of embrittlement is proportional to the square root of hydrogen gas pressure This suggests that designing turbine towers for relatively lowpressure storage may help prevent hydrogen embrittlement. It is fortunate, therefore, that the storage pressures under consideration are only about 10% of hydrogen pipeline operating pressures. Hydrogen gas purity is another major environmental factor controlling HEE. Experimental evidence has shown that crack propagation in a stressed specimen could be controlled by the introduction of oxygen into the hydrogen environment. Investigators demonstrated that a crack propagating in a pure hydrogen environment could be stopped with the introduction of as little as 200 ppm oxygen at atmospheric pressure Because the method of H2production under consideration is via an electrolyzer, gas will be readily available. Al though adding to H2can result in an explosive mixture, adding the necessary levels of is expected to have little ect on safety. This is because the required oxygen con centration (approximately 200 ppm) is far above the upper bustible limit of hydrogen in oxygen (94% by volume). Two hundred ppm oxygen in hydrogen represents % (by volume) of the oxygen required to create an explosive environment. Steel posed of larger grains with precipitates he