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SQL查询思路优化与语句优化
数据库查询优化是取得良好执行性能并简化管理的关键因素,SQL查询是一个有序的查询,不同语句的使用和使用顺序将直接影响其查询速度。查询速度的快慢直接影响着数据库的推广与应用,本文就优化思路及语句书写优化两方面进行讨论,提出优化方法及语句实现。...
2020-09-29 10:54:18浏览：42
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乙烯直接氯化制二氯乙烷的工艺分析
采用300 mL反应釜进行乙烯直接氯化的实验,对低温、中温和高温氯化3种乙烯直接氯化工艺的二氯乙烷选择性和系统热负荷进行比较,考察NaCl助催化剂用量和乙烯与氯气的分压比对二氯乙烷选择性的影响.实验结果表明,与低温氯化工艺相比,中温和高温氯化工艺二氯乙烷的选择性分别降低了约0.10％和0.25％,但系统热负荷与低温工艺相比从624.7 kJ/h分别降至304.1 kJ/h和265.2 kJ/h;NaCl助催化剂的加入可打破FeCl3的二聚体,当NaCl与FeCl3的摩尔比为1∶3时能明显提高二氯乙烷的选择性;乙烯与氯气的分压比为1.25时,低温、中温和高温3种氯化工艺的二氯乙烷选择性分别可达到99.90％,99.86％,99.81％....
2020-09-29 10:54:18浏览：53
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乙苯/苯乙烯生产过程的优化运行研究
针对乙苯/苯乙烯实际生产装置,分别建立了烷基化、烷基转移、乙苯精馏、乙苯脱氢、苯乙烯精馏生产过程的机理模型,该机理模型与实际生产过程误差范围在2％左右.以该模型为基础进行系统优化操作设计,生产装置实际运行结果表明:基于该优化操作系统,可有效降低装置的能耗,为其他乙苯/苯乙烯装置的优化运行奠定了基础....
2020-09-29 10:54:18浏览：52
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低温乙烯泵运行故障分析
简要介绍了VS6型立式筒袋泵在输送低温介质时发生的机械密封泄漏的情况,就产生问题的原因进行了简要分析,提出了避免以及解决此类问题的技术方法....
2020-09-28 16:47:12浏览：40
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乙烯厂污水回用实例介绍
在乙烯厂中，因污染因子多，污水含油高等因素限制了污水回用技术的推广。此外，在环保要求愈来愈严格的今天，浓排水的妥善处理是另一个影响因素。在某石化企业的应用实例中，采用曝气生物滤池+臭氧+超滤+反渗透双膜法处理污水，回用于循环冷却水，同时采用臭氧氧化将难处理的反渗透浓排水处理到满足地方污水指标。工程实践证明这些方法在乙烯厂的污水回用处理中行之有效。...
2020-09-28 16:47:12浏览：38
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医院污水特点与处理技术
生活污水、工业废水是我国水体的主要污染源.对此,目前的污水处理技术已基本成熟并趋于完善.而医院污水成分复杂,含有有毒、有害污染物,且部分污水还带有相关疾病的传染源.2003年“非典”以后,很多国家对医院的污水处理要求更高更严密.医院污水处理涉及疾病的防疫、控制和防止二次污染的产生,一旦疏漏,对社会环境、自然环境都会造成重大影响.因此,医院污水的处理,尤其是传染病污水的处理非常重要....
2020-09-25 09:10:57浏览：24
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高煤阶煤层气井煤粉产出对渗透率影响研究
高煤阶煤层气井在钻井、开采过程中由于机械碰撞、气液冲刷、压力波动等外力作用，不可避免的会产生煤粉，煤粉的产出一方面有利于形成气液产出通道，但另一方面如果过快、过多的产出使气水流动出现障碍，引起产气量下降，同时频繁的检泵作业导致气井的解吸一吸附过程交错进行，严重影响了气井的正常生产；本文通过煤粉产出与渗透率的关系、排采速度对煤粉产出的影响等室内模拟实验，论证了高煤阶煤层气井煤粉产出控制的重要性。...
2020-09-18 16:34:07浏览：67
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宋新庄煤矿选煤厂选煤工艺的选择
为提高宋新庄煤矿选煤厂选煤效率，分析了选煤厂入选原煤性质，根据产品用户对煤质的要求，确定选煤厂产品结构。以产品结构多样化、灵活性为目的，分析了选煤厂分选粒度及块煤、末煤的分选工艺。结果表明，宋新庄煤矿生产原煤为不黏煤，属低灰煤，矸石易泥化。块煤（200~25 mm）采用重介质浅槽分选机分选，末煤（〈25 mm）采用无压给料三产品重介质旋流器分选，并留有弛张筛进行6 mm 干法筛分，〈6 mm 粉煤不分选的旁路。宋新庄煤矿选煤厂可生产优质的大块煤（200~50 mm）、中块煤（50~25 mm）、精煤（〈25 mm）、混煤（〈50 mm 或〈25 mm）等产品，供应煤气化原料用煤、动力发电用煤、民用煤等。...
2020-09-18 16:34:07浏览：43
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不同煤种对混煤自固硫的影响
以平朔煤作为中硫煤,选用三个典型低硫煤与其进行不同比例掺配,并研究了煤种对混煤固硫效果的影响.结果表明：混煤固硫率的大小与（Ca＋Mg）/S摩尔比和灰中（CaO＋MgO）的含量有关;低、低（Ca＋Mg）/S摩尔比煤掺配后,混煤的（CaO＋MgO）利用率随（Ca＋Mg）/S摩尔比的增大呈整体下降趋势,降硫效果主要取决于配煤对硫分的稀释作用;低、高（Ca＋Mg）/S摩尔比煤掺配后,混煤的（CaO＋MgO）利用率在（Ca＋Mg）/S摩尔比为0.8～1时达到最大值,降硫效果取决于配煤对硫分的稀释作用和自身固硫作用....
2020-09-15 12:28:59浏览：36
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New evidence for the origin of natural gas in Ordos Basin from hydrocarbons of oil water
The chief aim of the present work is to investigate the controversy origin of natural gas in the Ordos Basin by using the hydrocarbons of oil water. New evidence has been found: There is relatively high content of light hydrocarbons and low content of heavy components in the hydrocarbons fraction of oil water in the middle gas field of the Majiagou Formation, Ordovician reservoir. The hydrocarbons of oil water in Well Shan 12 and Well Shan 78 have relatively high abundance of tricyclic terpane. Tricyclic terpane/hopane of the two samples are 1.48 and 0.36, respectively. They also show that pregnane and hompregnane are in relatively high abundance with lower hopane/sterane ratio. Pr/Ph is less than 2.0. These characteristics reflected the source input of marine carbonate sedimentary environment. In contrast, the hydrocarbon of Well Shan 81 is lack of tricyclic terpane series and pregnane. It has a high hopane/sterane ratio and Pr/Ph is 3.27. These parameters are typical character of terrestrial organic matter. Furthermore, the hydrocarbons of oil water in Well Shan 37 and Well Shan 34 is between the two typical situations. They have little content of tricyclic terpanes. They may be derived from a mixing source of marine carbonate and terrestrial organic matter input. Similarly, the maturity parameters approve this suggestion. The samples of Well Shan 12 and Well Shan 78 which derived from marine carbonate have relatively high maturity and samples derived from terrestrial organic matter have lower maturity. The maturity of the hydrocarbons of mixing source is between these two situations. The suggestion coincides with the geological background and source rocks distribution....
2020-09-15 12:28:59浏览：50
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The Genetic Mechanism and Model of Deep-Basin Gas Accumulation and Methods for Predicting the Favora
As a kind of abnormal natural gas formed with special mechanism, the deep-basin gas, accumulated in thelower parts of a basin or syncline and trapped by a tight reservoir, has such characteristics as gas-water inversion, abnormalpressure, continuous distribution and tremendous reserves. Being a geological product of the evolution of petroliferousbasins by the end of the middle-late stages, the formation of a deep-basin gas accumulation must meet four conditions, i.e.,continuous and sufficient gas supply, tight reservoirs in continuous distribution, good sealing caps and stable structures.The areas, where the expansion force of natural gas is smaller than the sum of the capillary force and the hydrostaticpressure within tight reservoirs, are favorable for forming deep-basin gas pools. The range delineated by the above twoforces corresponds to that of the deep-basin gas trap. Within the scope of the deep-basin gas trap, the balance relationshipbetween the amounts of ingoing and overflowing gases determines the gas-bearing area of the deep-basin gas pool. The gasvolume in regions with high porosity and high permeability is worth exploring under current technical conditions and it isequivalent to the practical resources (about 10%-20% of the deep-basin gas). Based on studies of deep-basin gasformation conditions, the theory of force balance and the equation of material balance, the favorable areas and gas-containing ranges, as well as possible gas-rich regions are preliminarily predicted in the deep-basin gas pools in the UpperPaleozoic He-8 segment of the Ordos basin....
2020-09-15 12:28:59浏览：53
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Probe into Environmental Kuznets Characteristics and Causes of Wastewater,Waste Gas, and Solid Waste
Environmental Kuznets characteristics and causes of waste water, waste gas, and solid wastes in Wuhan city was researched; By comparing the variation of "three wastes", i.e. waste water, waste gas, and solid wastes, the model between standardized per capita GDP and values of "three wastes" discharge was established and the causes were analyzed based on the theory of environmental economics. The results show that 1) the total amount is fluctuantly increasing, but the discharges of the three kinds are temporarily different, 2) the curve conforms to the three-power function, in which the curve descends from 1985 to 1994, and the curve preliminary shows the environmental Kuznets characteristics from 1995 to 2001, 3) the simulated calculation illustrates that the turning point of this environmental Kuznets curve would be over 25007.25 Yuan per caprta, and 4) the economic development, changing of industry structure, energy resource structure, and environmental policies are the main factors leading to the Environmental Kuznets Curve in Wuhan city....
2020-09-15 12:28:59浏览：70
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MECHANISM ON DISTRIBUTION OF PILOT FUEL SPRAY AND COMPRESSING IGNITION IN PREMIXED NATURAL GAS ENGIN
Numerical simulations of pilot fuel spray and compressing ignition for pre-mixed natural gas ignited by pilot diesel are described. By means of these modeling, the dual fuel and diesel fuel ignition mechanism of some phenomena investigated on an optional engine by technology of high-speed CCD is analyzed. It is demonstrated that the longer delay of ignition in dual fuel engine is not mainly caused by change of the mixture thermodynamics parameters. The analysis results illustrate that the ignition of pre-mixed natural gas ignited by pilot diesel taking place in dual fuel engine is a process of homogenous charge compression ignition....
2020-09-15 12:28:59浏览：70
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Origin of natural sulphur-bearing immiscible inclusions and H2S in oolite gas reservoir, Eastern Sic
Based on results of microscopic observation and laser Raman analysis about fluid inclusions, multiple special forms of immiscible inclusions that contain sulphur, liquid hydrocarbon, bitumen, etc. were discovered in samples collected from the H2S gas reservoir-containing carbonates in the Lower Triassic Feixianguan Formation in the Jinzhu-Luojia area, Kai County, Sichuan Province. Based on the lithology and burial history of the strata involved as well as measurement results of homogenization temperature of fluid inclusions, bitumen reflectivity, etc., it is concluded that the H2S in the gas reservoir resulted from the thermal reaction between hydrocarbons in reservoir and CaSO4 in the gypsum-bearing dolostone section at the high temperature (140℃―170℃) oil-cracked gas formation stage in Late Cretaceous. Thereafter, research on a great number of immiscible inclusions in the reservoir reveals that elemental sulphur resulted from oxidation of part of the earlier-formed H2S and further reaction between sulphates, hydrocarbons and H2S in geological fluids in H2S-bearing gas reservoir at a temperature of 86℃―89℃ and a pressure of 340×105Pa and during the regional uplift stage as characterized by temperature decrease and pressure decrease in Tertiary. Meanwhile, gypsum, anhydrite and calcite formed at this stage would trap particles like elemental sulphur and result in a variety of special forms of immiscible inclusions, and these inclusions would contain information concerning the complexity of the fluids in the reservoir and the origin of H2S and natural sulphur in the gas reservoir....
2020-09-15 12:28:59浏览：51
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