Utilization of compressed natural gas for the production of carbon nanotubes

The present work aims at utilizing compressed natural gas （CNG） as carbon source for the synthesis of carbon nanotubes （CNTs） over CoO-MoO/Al2O3 catalyst via catalytic chemical vapor deposition （CCVD） method. The as-produced carbonaceous product was characterized by thermal gravimetric analyzer （TGA）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM） and Raman spectroscopy. The experimental finding shows that CNTs were successfully produced from CNG while carbon nanofibers （CNFs） were formed as the side products. In addition, the catalytic activity and lifetime were found sustained and prolonged, as compared with using high purity methane as carbon source. The present study suggests an alternative route which can effectively produce CNTs and CNFs using low cost CNG.

A novel correlation approach for prediction of natural gas compressibility factor

Gas compressibility factor （z-Factor） is one of the most important parameters in upstream and downstream calculations of petroleum industries.The importance of z-Factor cannot be overemphasized in oil and gas engineering calculations.The experimental measurements,Equations of State （EoS） and empirical correlations are the most common sources of z-Factor calculations.There are more than twenty correlations available with two variables for calculating the z-Factor from fitting in an EoS or just through fitting techniques.However,these correlations are too complex,which require initial value and more complicated and longer computations or have magnitude error.The purpose of this study is to develop a new accurate correlation to rapidly estimate z-Factor.Result of this correlation is compared with large scale of database and experimental data also.Proposed correlation has 1.660 of Absolute Percent Relative Error （EABS） versus Standing and Katz chart and has also 3.221 of EABS versus experimental data.The output of this correlation can be directly assumed or be used as an initial value of other implicit correlations.This correlation is valid for gas coefficient of isothermal compressibility （cg） calculations also.

Rapidly Estimating Natural Gas Compressibility Factor

Natural gases containing sour components exhibit different gas compressibility factor （Z） behavior than do sweet gases. Therefore, a new accurate method should be developed to account for these differences. Several methods are available today for calculating the Z-factor from an equation of state. However, these equations are more complex than the foregoing correlations, involving a large number of parameters, which require more complicated and longer computations. The aim of this study is to develop a simplified calculation method for a rapid estimating Z-factor for sour natural gases containing as much as 90% total acid gas. In this article, two new correlations are first presented for calculating the pseudo- critical pressure and temperature of the gas mixture as a function of the gas specific gravity. Then, a simple correlation on the basis of the standard gas compressibility factor chart is introduced for a quick estimation of sweet gases＇ compressibility factor as a function of reduced pressure and temperature. Finally, a new corrective term related to the mole fractions of carbon dioxide and hydrogen sulfide is developed.

An efficient correlation for calculating compressibility factor of natural gases

Compressibility factor （z-factor） values of natural gases are necessary in most petroleum engineering calculations.Necessity arises when there are few available experimental data for the required composition,pressure and temperature conditions.One of the most common methods of calculating z-factor values is empirical correlation.Firstly,a new correlation based on the famous Standing-Katz （S-K） Chart is presented to predict z-factor values.The advantage of this correlation is that it is explicit in z and thus does not require an iterative solution as is required by other methods.Secondly,the comparison between new one and other correlations is carried out and the results indicate the superiority of the new correlation over the other correlations used to calculate z-factor.

Injection Strategy in Natural Gas–Diesel Dual-Fuel Premixed Charge Compression Ignition Combustion under Low Load Conditions

Dual-fuel premixed charge compression ignition (DF-PCCI) combustion has been proven to be a viable alternative to conventional diesel combustion in heavy-duty compression ignition engines due to its low nitrogen oxides (NOx) and particulate matter (PM) emissions. When natural gas (NG) is applied to a DF-PCCI engine, its low reactivity reduces the maximum pressure rise rate under high loads. However, the NG–diesel DF-PCCI engine suffers from low combustion efficiency under low loads. In this study, an injection strategy of fuel supply (NG and diesel) in a DF-PCCI engine was investigated in order to reduce both the fuel consumption and hydrocarbon (HC) and carbon monoxide (CO) emissions under low load conditions. A variation in the NG substitution and diesel start of energizing (SOE) was found to effectively control the formation of the fuel–air mixture. A double injection strategy of diesel was implemented to adjust the local reactivity of the mixture. Retardation of the diesel pilot SOE and a low fraction of the diesel pilot injection quantity were favorable for reducing the combustion loss. The introduction of exhaust gas recirculation (EGR) improved the fuel economy and reduced the NOx and PM emissions below Euro VI regulations by retarding the combustion phasing. The combination of an NG substitution of 40%, the double injection strategy of diesel, and a moderate EGR rate effectively improved the combustion efficiency and indicated efficiency, and reduced the HC and CO emissions under low load conditions.

Experimental determination and prediction of the compressibility factor of high CO_2 content natural gas with and without water vapor

In order to study the effect of different CO2 contents on gas compressibility factor（Z-factor）,the JEFRI-PVT apparatus has been used to measure the Z-factor of dry natural gas with CO2 content range from 10.74 to 70.42 mol%at the temperature range from 301.2 to 407.3 K and pressure range from 7 to 44 MPa.The results show that Z-factor decreases with increasing CO2 content in natural gas at constant temperature and increases with increasing temperature for natural gas with the same CO2 content.In addition,the Z-factor of water-saturated natural gas with high CO2 content has been measured.A comparison of the Z-factor between natural gas with and without saturated water vapor indicates that the former shows a higher Z-factor than the latter.Furthermore,Peng-Robinson,Hall-Yarborough,and Soave-Benedict-Webb- Rubin equations of state（EoS）are used for the calculation of Z-factor of high CO2 content natural gas with and without water vapor.The optimal binary interaction parameters（BIP）for PR EoS are presented.The measured Z-factor is compared with the calculated Z-factor based on three models,which shows that PR EoS combined with van der Waals mixing rule for gas without water and Huron-Vidal mixing rule for water-saturated gas,are in good agreement with the experimental data.

An accurate empirical correlation for predicting natural gas compressibility factors

The compressibility factor of natural gas is an important parameter in many gas and petroleum engineering calculations. This study presents a new empirical model for quick calculation of natural gas compressibility factors. The model was derived from 5844 experimental data of compressibility factors for a range of pseudo reduced pressures from 0.01 to 15 and pseudo reduced temperatures from 1 to 3. The accuracy of the new empirical correlation has been compared with commonly used existing methods. The comparison indicates the superiority of the new empirical model over the other methods used to calculate compressibility factor of natural gas with average absolute relative deviation percent （AARD%） of 0.6535.

LOLIMOT模型在CNG发动机NO_(x)排放预测试验中的应用

为解决在选择性催化还原技术(selective catalytic reduction,SCR)的控制策略开发中局部线性模型树(local linear model tree,LOLIMOT)排放模型预测精度不足的问题,提出一种通过优化空间边界,将原模型的超矩形输入空间约束在物理意义范围内的改进LOLIMOT模型。通过某天然气发动机的辨识试验,从分布特征和计算原理角度,分析了该方法对预测结果的影响。结果表明:与原算法相比,改进算法的线性相关度R2提升了1.9%,验证了改进策略的有效性。改进LOLIMOT算法具备较高的收敛速度和稳定性,在排放模型领域具备一定的应用优势。

Prediction of Volumetric Properties(p-v-T)of Natural Gas Mixtures Using Extended Tao-Mason Equation of State

A statistical-mechanical-based equation of state(EOS)for pure substances,the Tao-Mason equation of state,is successfully extended to prediction of the(p-v-T)properties of fourteen natural gas mixtures at temperatures from 225 K to 483 K and pressures up to 60.5 MPa.This work shows that the Tao-Mason equation of state for multicomponent natural gas is predictable with minimal input information,namely critical temperature,critical pressure,and the Pitzer acentric factor.The calculated results agree well with the experimental data.From a total of 963 data of density and 330 data of compressibility factor for natural gases examined in this work,the average absolute deviations(AAD)are 1.704%and 1.344%,respectively.The present EOS is further assessed through the comparisons with Peng-Robinson(PR)equation of state.For the all of mixtures Tao-Mason(TM)EOS outperforms the PR EOS.

Natural Gas Flaring—Alternative Solutions

Gas flaring is one of the major problems in the world. It consumes useful natural resources and produces harmful wastes, which have negative impacts on the society. It is one of the most tedious energy and environmental problems facing the world today. It is a multi-billion dollar waste, a local environmental catastrophe and environmental problem which has persisted for decades. From the year 1996-2010, in Nigeria, 12,602,480.25 million ft3 of natural gas was flared (NNPC). This is equivalent to losing about 12,967.952 × 1012 Btu of energy that would have been used to generate power or converted to other forms of energy. In 2015, the World Bank estimated that 140 billion cubic meters of natural gas produced with oil is flared annually, mostly in developing countries without gas processing infrastructures, or other means of utilizing the produced gas. It is widely known that flaring or even, venting of gas contributes significantly to greenhouse gas emissions, with negative impacts on the environment. Thus, alternative solutions to reduce or utilize the quantity of gas flared are crucial issues. Therefore, the need to study and provide detailed understanding of these alternative solutions to gas flaring is important. This paperoutlined the harmful effects of gas flaring and the different possible alternatives to gas flaring. The proposed alternative solutions are gas for secondary oil recovery, feedstock for petrochemical plants, domestic uses, LNG & CNG, as well as energy conservation by storing as gas hydrate for future use or other purposes. Gas hydrate is stable above the freezing point of water and sufficiently high pressure. It is relatively stable under its saturation temperature and pressure and also much denser than normal ice. This property of gas hydrate can be experimentally investigated and capitalized on, to effectively store natural gas as hydrate for energy conservation instead of flaring the gas wastefully. The alternative solutions will convincingly reduce and in the nearest future stop gas flaring globally.

提高压缩天然气(CNG)质量检测结果准确性的主要措施

从提升员工技能、加强设备管理、强化标准物质的监管、确认检测方法、满足环境要求、规范取样、规范操作、强化质量监督、严格质量保证9个方面提出了提高压缩天然气(CNG)质量检测结果准确性的措施,为保证压缩天然气(CNG)质量检测结果的准确性提供了保障。

CNG加气站设备安全风险评价指标体系

随着CNG汽车加气站网络的逐步形成,加气站设备役龄的增加,加气站安全形势日趋严峻。通过查阅标准文献、咨询专家和实地调查研究,重点对事故站进行统计和分析,采用条件广义方差极小法对定量指标进行遴选,建立CNG加气站设备安全风险评价指标体系通用层次模型。经过模型分解,确立加气站各大系统的安全性缺陷项目,从而建立了CNG加气站设备安全风险评价指标体系及评价标准。据此为政府职能部门进行CNG加气站设备安全性评价时提供决策依据,也可为加气站设备生产制造厂设备改型换代提供科技攻关方向。

城市CNG汽车加气站安全评价模型

城市CNG站的安全状况和国家财产、站场员工以及周边人民的生命安全紧密相关,因而对CNG站的安全现状做出科学评价具有重要意义。为此,提出了将改进的层次分析法和模糊综合评价相结合,建立一种评价CNG站安全现状的新模型:即用改进层次分析法分析影响CNG站安全的主要因素并确定其权重,用模糊综合评判对CNG站的安全状况进行综合评价;从人、物、管理和环境四个方面考虑了影响CNG站安全的16个主要因素,建立了CNG站安全评价层次结构模型;对安全现状建立了“优、良、中、及格、差”5个评价等级。从评价实例可以看出,此模型有实用价值,能为CNG站管理者提供新的评价方法,从而提高CNG站安全管理水平。

L-CNG加气站技术浅析

近年才兴起的液化-压缩天然气加气站(即L-CNG加气站)以LNG为气源,经高压液体泵加压后气化向CNG汽车加气,也可同时用低压液体泵向LNG汽车加气。为此,介绍了L-CNG加气站的特点和工艺流程,分析了其相对于传统压缩天然气加气站的优点:可同时为压缩天然气汽车和液化天然气汽车加注燃料,有巨大的应用前景和可观的经济、社会效益。给出了典型的L-CNG加气站的工艺流程及设备布置方案,着重对L-CNG加气站的LNG低温储存和装卸系统,以及低温低压充注系统和高压气化系统,包括LNG槽车、LNG低温泵、LNG气化器等进行了说明,并介绍了相关技术要求。最后提出L-CNG加气站是目前CNG加气站向LNG加气站过渡的看法。

CNG汽车加气站国产设备使用情况研究(Ⅱ)

CNG汽车加气站设备是加气站安全高效运行的物质基础。通过调查研究及理论分析、咨询专家、查阅标准文献,借鉴国外先进技术水平,客观分析了国产CNG汽车加气站设备的现状,并从设备的技术性、可靠性、安全性、可维修性和经济性等方面找出了与国外同类设备的差距,进而提出改进建议:①加强CNG汽车加气站设备关键技术攻关力度;②加强CNG汽车加气站设备专用检验设备的开发研究;③严把压力容器类设备制造资格关;④加快制订和完善CNG汽车加气站设备国家标准的步伐;⑤选择储气形式应因地制宜;⑥尽快建立区域性的CNG汽车加气站设备维修服务企业和设备操作维护人员培训基地;⑦CNG汽车加气站关键设备的国产化率亟待进一步提高;⑧加强行业管理,形成集团化生产。最后分析了CNG汽车加气站设备选型及安全风险评价基本原则,以及CNG汽车加气站设备技术水平改进的关键系统和关键部件。

CNG汽车加气站国产设备使用情况研究(I)

CNG汽车加气站设备是加气站安全高效运行的物质基础。通过调查研究及理论分析,咨询专家,查阅标准文献,借签国外先进技术水平,客观分析了国产CNG汽车加气站设备的现状,并从设备的技术性、可靠性、安全性、可维修性和经济性等方面找出了与国外同类设备的差距,进而得出改进建议:①加强CNG汽车加气站设备关键技术攻关力度;②加强CNG汽车加气站设备专用检验设备的开发研究迫在眉睫;③严把压力容器类设备制造资格关;④加快制订和完善CNG汽车加气站设备国家标准的步伐;⑤选择储气形式应因地制宜;⑥尽快建立区域性的CNG汽车加气站设备维修服务企业和设备操作维护人员培训基地;⑦CNG汽车加气站关键设备的国产化率亟待进一步提高;⑧加强行业管理,形成集团化生产。最后分析了CNG汽车加气站设备选型及安全风险评价基本原则,以及CNG汽车加气站设备技术水平改进的关键系统和关键部件。

基于灰色关联分析和IAHP的CNG加气站安全评价方法研究

建立了压缩天然气(CNG)加气站安全评价的指标体系和安全等级的评分标准,运用改进的层次分析法(IAHP)计算CNG加气站安全指标权重序列,运用灰色关联法计算参评序列与标准序列的关联度。最大关联度所对应的标准向量等级,即为CNG加气站所属的安全等级。IAHP采用"三标度"法确定判断矩阵,相对于层次分析法中的"九标度"法来说,更易于保持矩阵的一致性。应用笔者提出的理论与方法,对北京某CNG加气站的实际案例计算,验证该方法的有效性。计算结果表明:售气系统安全、气体储存和压缩系统安全、人员的违章操作情况、司机或加气站人员是否在站内抽烟、站内设施与站外建筑物防火距离等是CNG加气站安全的主要影响因素,应对其进行重点管理。

CNG汽车加气站净化设备技术水平评价体系研究

针对CNG汽车加气站净化设备,运用经济学、机械学、设备综合工程学等理论,通过数据采集和处理,提出我国CNG加气站净化系统设备技术水平评价指标体系,并对指标进行测度。建立加气站指标体系及其测度标准,可为加气站设备制造厂家设备改型换代提供借鉴,也可为加气站建设业主设备选型提供参考,对提高我国加气站设备国产化水平,加快我国天然气行业的发展有一定的指导意义。

CNG/CO_2气体发动机湍流火焰结构的大涡模拟

采用大涡模拟的方法对一台燃用压缩天然气(CNG)/CO2混合气体燃料的火花点火发动机缸内湍流涡团与火焰面的相互作用过程开展了模拟计算研究.基于OpenFOAM开源CFD程序包建立了AKTIMEuler点火模型和PaSR-LES燃烧模型,并采用耦合多面体顶点运动与梅斯基特算法的求解方法构建了发动机动网格.经过对计算结果的分析可知:随着可燃气体中惰性气体组分的增加,湍流火焰传播速率下降,涡对结构对火焰面皱褶的作用减弱,火焰面在达到相同皱褶度的时间向后推迟,其皱褶度的升高率也随之下降;随着发动机转速的增大,火焰面受到涡团卷吸与拉伸的作用增大,局部容易形成环形火焰面的现象.