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某某学校毕业设计（论文）外文文献翻译（本科学生用）题 目：为了未来的发展，液化天然气工艺处理过程中应该注意的问题 学 生 姓 名： 学号： 学 部 （系）:城市建设工程学部专 业 年 级:级建筑环境与设备工程班指 导 教 师： 年月日 LNG PROCESS SELECTION CONSIDERATIONSFOR FUTURE DEVELOPMENTSJohn B. StoneSenior LNG ConsultantDawn L. RymerSenior Engineering SpecialistEric D. NelsonMachinery and Processing Technology SupervisorRobert D. DentonSenior Process ConsultantExxonMobil Upstream Research CompanyHouston, Texas, USAABSTRACTThe history of the LNG industry has been dominated by the constant search for economies of scale culminating in the current Qatar mega-trains undergoing final construction, commissioning,start-up and operations. While these large trains are appropriate for the large Qatar gas resources, future, smaller resource developments will necessitate different process selection strategies. The actual LNG process is only one of many factors affecting the optimal choice. The choice of equipment, especially cryogenic heat exchangers and refrigerant compressors, can overwhelm small differences in process efficiencies. ExxonMobil has been developing a dual mixed refrigerant (DMR) process that has the potential of offering the scalability and expandability required to meet the needs of new project developments, while also maximizing the number of equipment vendors to allow broader competition and keep costs under control. The process will also have the flexibility to accommodate a wide range of feed compositions, rates, and product sales requirements.BACKGROUNDThe startup of the 7.8 million tonnes per year (MTPA) trains in Qatar mark the most recent pinnacle in the search for economies of scale in the LNG industry. However, theapplication of these very large trains for general LNG applications is very limited. To produce this amount of LNG requires 42 MSCMD (1500 MSCFD) of feed gas. What is often overlooked in the discussion of large LNG trains is that a resource of about 370 GCM (13 TCF) is needed to support the operation of one such train over a 25-year life. This is nearly as large as the Arun field in Indonesia 425 GCM (15 TCF), which was the backbone of the LNG plant development in that region. For new LNG developments that are often built with a minimum of two identical trains, a truly world-class resource class of 750 GCM (26 TCF) would be required. Even for resources capable of supporting such large trains, very large gas treating and preparation trains with a minimum of parallel equipment are also needed to ensure that economies of scale are not lost in the non-LNG facilities. Given the limited supply of gas resources capable of supporting these large trains, future projects will need to find ways to maintain some cost advantages at smaller capacities. One way to do this is to improve the project execution by selecting a process that gives the maximum flexibility for utilizing compressors, heat exchangers, and drivers with multiple competing vendors. Another desirable feature is using refrigerant as a utility to allow for facilitated expansion if there is a possibility that several resources can be staged for expansion trains.PROCESS COMPARISONLNG process selection has often been highly influenced by the specific power consumption, i.e., refrigerant compression power divided by the train capacity. This is certainly an important parameter, since refrigerant compressors are the largest single cost and energy consumption components in an LNG train. Conventional wisdom would be that lower specific power consumption would result in lower refrigerant compression costs and additional LNG production from a fixed feed gas rate. In actuality it is a more complicated picture. Figure 1 plots the specific power consumptions for a variety of liquefaction processes against the number of cycles employed based on consistent conditions.SMR - Single Mixed RefrigerantC3MR - Propane pre-cooled Mixed RefrigerantC3MRN2 - Propane pre-cooled Mixed Refrigerant plus Nitrogen expander cycleCascade - Pure propane, ethylene, and methaneDMR-SWHE - Dual Mixed Refrigerant with single pressure levels and SWHEsDMR-BAHX - Dual Mixed Refrigerant with multiple pressure levels and BAHXsTMR - Triple Mixed RefrigerantFigure 1 - Process Specific Power ComparisonIn general, mixed refrigerant processes are more efficient than pure component processes and additional cycles improve efficiency. However, both of these efficiency improvements come at the expense of increased process complexity.Another factor that complicates the picture above is that it only considers a process comparison and not a refrigerant compressor or driver comparison. Differences in compressor efficiency, the need for a speed-increasing gear, or driver efficiency can overwhelm some of the differences shown. Considerations for the generation and distribution of electric power for motor driven LNG processes can further complicate the comparison.The LNG industry is changing in a number of areas that can also impact the selection of the best liquefaction process. While stick-built LNG plants are still the norm, modularization of LNG facilities are more attractive for offshore applications or where labor costs are very high and/or productivity is low. Modular construction is routinely applied for offshore oil processing. However, oil processing is much simpler than LNG production and process selection is generally not an important consideration. All these factors point to the need for more compact, lighter mechanical designs.Another important future consideration is the increasing need to reduce greenhouse gas emissions. Aeroderivative gas turbine drivers are an obvious choice for higher thermal efficiency or modular application but are not available in sizes as large as industrial gas turbines. Consequently, a process suitable for large 95 MW industrial gas turbines may not be well suited for a 35 MW aeroderivative gas turbine. Combined-cycle power generation is another option for achieving increased thermal efficiency and can be adapted to any of these processes, but is not well suited for modular construction or for offshore application due to the additional weight of motors, generators and distribution equipment as well as limited aeroderivative gas turbine choices for very large (100MW) power generators.The value of thermal efficiency can also become a more important process selection criterion when the feed gas to the LNG plant is relatively expensive or supply is limited. An efficient process can allow for a reduced cost development plan through a lower gas rate, or extend the gas production plateau from the reservoir to make a more profitable project.IMPACT OF EQUIPMENT COSTSOur process research comparing liquefaction processes has demonstrated that the primary difference in the costs for the different liquefaction processes is the choice of equipment utilized. Process licensors tailor their process to make it capital and thermally efficient given the owners preferences and constraints. However, they do not always have control over the cost (both equipment and installation) in the final analysis.Gas TurbinesGas turbine costs exhibit a reasonably high economy of scale. Large industrial gas turbines are the least expensive, but their cost advantage is lost in a modular or offshore environment due to their large weight and space requirements. Therefore, aeroderivative based designs will be more attractive. However, once the drivers are selected, then a process that is flexible in allowing a shift in refrigerant power loads to maximize the utilization of the available turbine power would be the best process. A multiple mixed refrigerant process, without the fixed atmospheric boiling temperatures characteristic of pure refrigerants, has the flexibility to allow such shifting. An alternative to mechanical-drive gas turbines would be electric motor drives with very large power generators for economy of scale. In this case, gas turbine costs would be lower because of standard designs, multiple manufacturers, and possibly greater economies of scale, but there would be additional costs for motors, spare turbine generators and power distribution which can reduce the overall efficiency in a simple cycle configuration. This efficiency loss can be overcome with combined cycle, but in simple or combined cycle the net result is usually a higher capital cost. The implementation of an all-electric drive configuration is even more difficult at reduced economies of scale where the use of larger lower cost turbines becomes problematic due to difficulties managing the dynamic response to electrical load changes spread across fewer units. In the end though, the choice of an all-electric drive configuration is condensed to a trade off between a higher capital cost and the increased plant availability that electric motors can achieve.CompressorsCompressors exhibit a very high economy of scale. Refrigerant compression costs areprimarily a function of the number of compressor cases needed. Consequently, it is important to minimize the number of compressor cases. Likewise it is important to limit the required rotor diameter of the centrifugal compressor wheels to stay within the capabilities of multiple vendors. This requires limiting the volumetric flow rate feeding these compressors through reduced refrigerant circulation or higher refrigerant suction pressure. Again the dual mixed refrigerant process allows the process designer the flexibility to optimize the compressor inlet suction volumetric rate to maximize throughput within the design capability of at least four suppliers.Heat ExchangersCryogenic heat exchanger costs are primarily related to the surface area supplied. There will always be a tradeoff between exchanger area and compressor power to reach a minimum overall cost. Spiral Wound Heat Exchangers (SWHEs) are the standard cryogenic heat transfer equipment for the base load LNG industry. SWHEs have an excellent service record in LNG service; however, they are expensive, have long delivery times, and are limited to two manufacturers.Another option is to use brazed aluminum heat exchangers (BAHXs), which have a lower cost per unit area than SWHEs, and can be aggregated easily into blocks of surface area to meet large heat transfer requirements effectively. BAHXs also easily accommodate side-streams which allow refrigerant systems with multiple pressure-levels to be readily incorporated. BAHXs have been demonstrated in LNG service in cascade processes and smaller mixed refrigerant processes. BAHXs are built in small units (cores) typically manifolded together and insulated in a cold box. A typical design would require about 30 cores to provide the exchanger area needed for a 3 MTPA LNG train. These exchangers are available from five manufacturers. Having multiple vendors ensures not only competitive prices, but also flexibility in acquiring the exchangers in time to meet the project schedule.PROCESS SELECTIONWhat would an ideal liquefaction process look like? It would be a DMR process such as shown in Figure 2 below for low specific power consumption and flexibility to optimize compressor design. Including multiple levels of cooling in the warm mixed refrigerant circuit allows more flexibility to meet compressors volumetric limitations. ExxonMobil has synthesized these traits with known liquefaction processes, adding our own proprietary optimizations resulting in this configuration.Figure 2 - ExxonMobil DMR-BAHX Process SchematicIt would utilize BAHX exchangers to provide: Multiple manufacturers for cost and schedule benefits, Economic scale up over a wide range of throughputs, Ease of modularizationThe BAHX exchangers would be protected from operational and design problems associated with multi-phase maldistribution by effecting refrigerant separation at each pressure level of the warm refrigerant and feeding only liquids to the BAHX cores while bypassing the vapor back to the compression system.It would utilize gas-turbine-driven centrifugal compressors large enough to capture the economy of scale available but small enough to ensure that multiple compressor vendors are capability of supplying the sizes needed.The results of our LNG process research applying these principles to a potential LNGdevelopment are shown in Figure 3. By using BAHXs and a dual mixed refrigerant process to match the best fit of compressors and drivers available from multiple vendors, the resulting process will have a lower specific power requirement, and could have a lower capital cost than traditional technologies. The DMR process with brazed aluminum heat exchangers shows a unit cost advantage across a broad range of plant capacities and optimizes the trade-offs of efficiency versus cost for a wide size range (3-6 MTPA) of plants. EFFICIENT EXPANSIONLNG plants have long benefited for profitable expansion trains, typically provided from the same large resource. While the number of discovered large fields available for multi-train development is shrinking, there is still the potential for economical expansion from nearby smaller resources. In many cases these other fields cannot be aggregated into one large project for a variety of reasons: difficulty aligning several commercial interests, waiting on reduced development costs for more difficult resources, or near-field discoveries identified after the LNG project is underway. For all of these reasons it is desirable to have an easily expandable LNGplant.Treating refrigerant as a utility is a way to maximize the expandability and reliability of a multtrain facility. In this configuration all of the refrigerants that serve the same process function are combined into a single header and delivered as required to the LNG liquefaction sections. The refrigerant as a utility concept can be done with any liquefaction process, but is most suited for dual mixed refrigerants where the refrigerant return pressures can be higher resulting in smaller piping for distribution of refrigerant across the LNG plant. Figure 4 shows one such configurationTreating refrigerant as a utility has several benefits: The trains do not necessarily need to be the same size, leading to customizableexpansion to match commercial needs. All the refrigerants can be re-tuned to match changes in feed gas composition tomachinery limits as new gas supplies are brought on-line. Any spare capacity identified by testing after start-up can be designed for and utilized during expansion. A mixture of gas turbine, steam turbine, and motor drivers can be used giving moreflexibility to the driver selection and energy utilization. In the event of driver failures, the liquefaction train may be able to turn-down instead of shut-down. During planned driver maintenance the other drivers can be run at their maximum rates and potentially take advantage of seasonal swings. A driver and hence refrigerant supply can be easily spared across the whole plant, increasing plant availability. Various cold streams, such as LNG-loading vapors, can be effectively integrated into the process scheme to allow the impact of flow fluctuations in these streams to be evenlyspread across all trains for operational stability.With these advantages, a refrigerant as a utility concept could be beneficial to provide options for any project with uncertainty in its expansion possibilities.CONCLUSIONIn conclusion, a dual mixed refrigerant process with brazed aluminum heat exchangers that treats refrigerant as a utility has the scalability, flexibility and expandability required for the next generation of LNG projects. The system incorporates the guiding principle that capital costs can be minimized by ensuring that there will be multiple vendors or contractors that can supply the equipment or services for the duties required. The design appropriately balances economies of scale against the expense of sole source purchase and results in a more readily scalable configuration. The refrigerant as a utility concept allows for effectively dealing with uncertain expansion plans while providing operational and design flexibility. ExxonMobil can incorporate these process characteristics with these key success factors to ensure a successful project: Demonstrated Mega-project management and execution expertise Close working relationships with equipment vendors Proven start-up and commissioning experience Rigorous technology qualification process Value-driven process and vendor selection procedure 为了未来的发展，液化天然气工艺处理过程中应该注意的问题John B.Stone高级液化天然气顾问Dawn L.Rymer高级工程专家Eric D.Nelson机械和加工技术主管Robert D.Denton高级工艺工程顾问埃克森美孚上游部门研究公司美国，德克萨斯州，休斯顿摘要液化天然气产业的历史已经被经济规模的扩张所控制着，并且在目前卡塔尔超级列车经历最后的建设、调试、启动和操作中达到发展的高峰。虽然这些大型的列车适合于卡塔尔大型的燃气资源，但是未来更节能的发展要求使不同的处理工艺方法成为必要性。现行的液化天然气处理工艺仅是影响最佳选择的诸多因素之一。设备的选择，尤其是低温热交换器和制冷压缩机的选择能够克服在效率方面的小差异。埃克森美孚国际公司已经在发展一种双极混合制冷工艺，这一工艺具有能够提供新的工程建设要求的潜力，同时也能使设备供应商的数量达到最大值，从而允许更广泛的竞争，并使成本处于可控的范围之内。这一工艺也能灵活地适应大范围的供给、价格和产品销售要求。背景在卡塔尔，每年780万吨载重的火车标志着目前在液化天然气工业方面经济规模探索的最高峰。然而，这些大型LNG火车的普偏应用是受限制的。生产此数量的液化天然气需要1500MSCFD的原料气。关于大型液化天然气火车的讨论中常常被人们忽略的是：维持这样的火车工作超过25年需要约 370 GCM的资源，这几乎和425 GCM的印度阿伦场一样大，这个产量是这个地区液化天然气厂的极限。对于新的液化天然气发展，拥有一个750 GCM的真正世界级的资源是必需的。即使资源能够支持如此庞大的火车，庞大的气体处理和备用火车也需要确保：在非液化天然气设施中，它也不会失去作用。考虑到将来有限的气体资源能够支持这些大型火车，将需要找到新的方法以更小的生产来维持成本的优势，做到这一点的一种方法就是选择一个过程，以提高工程的执行力，这个过程提高最大的灵活性去利用压缩机，热交换器，并且和许多竞争的供应商一起控制。如果有一种可能性，即一些能源可以应用到火车上，那么另一个可取的特点就是使用制冷剂作为一种实用工具，来允许其作用的扩展。工艺比较液化天然气的工艺过程往往受到具体功率（即火车做功除以压缩机做功）的高度影响，这显然是一个重要的参数，因为制冷压缩机在一辆液化天然气火车上是最大的成本和最大的能源消耗体。传统的观点认为：较低的功率消耗将会导致较低的制冷剂压缩成本和较低额外生产液化天然气的原料气。实际上它的描述很复杂，针对基于一定循环次数出现的各种各样的液化过程，图1绘制了具体的功率消耗过程。 在一般情况下，混合制冷剂工艺比单一制冷剂工艺更有效，并且额外的周期能提高工作效率，然而，工艺过程的复杂性都提高了工作效率。造成如上图表过程复杂的另一个因素是：它仅考虑了一个过程的比较，而不是一个制冷压缩机或驱动程序的比较。压缩机功率的不同、一个高速传动装置的需求、或者是驱动器的效率可以掩盖一些差异。考虑液化天然气摩托车中电能的产生和分配可以进一步使比较复杂化。液化天然气行业正在改变，在一些领域，也可以影响最好的液化过程。然而“棒内置”的液化天然气厂仍然传统，模块化的液化天然气设施对于近海地区的应用或者是劳动成本高且生产率低的地方更具吸引力。模块化结构通常适用于海上石油加工，然而石油加工过程比液化天然气的生产过程简单很多，工艺的选择一般不是重要的考虑因素。所有些因素都指向需要更紧凑、更轻的机械设计。未来另一个重要的考虑因素是对减少温室气体排放量不断增长的要求，对于更高的热效率或模块化的应用模式，航改燃气轮机驱动是显而易见的选择，因此，适合95兆瓦的大型工业燃气涡轮机的过程未必适合35兆瓦的航改燃气轮机。联合循环发电机是实现增加热效率的另一选择，可适应任何这些过程，但由于电动机、发电机和配电设施，以及选择发电机（100MW）受到限制的航改燃气轮机的额外重量，使它不适合模块化或境外申请。当液化天然气厂的原料气相对昂贵或者供应商有限的时候，热效率值也可以成为一个更重要的过程选择准则。一个有效率的进程可以通过较低的气量或者是从气田中扩大天然气生产平台来考虑降低成本，以此使工程更有利可图。设备成本的影响我们所做的比较液化工艺的研究已经证明：在不同的液化工艺的成本差异中最主要的不同处是对利用设备的选择。调整自己的过程，使其资本和热效率的过程中协议业主的编好和约束，然而，他们总不能在最后的分析中控制成本（包括设备及安装）。燃气涡轮机燃气涡轮机成本表现出相当高的经济性，大型的工业燃气涡轮机是最便宜的，但由于重量和体积大的原因，其成本优势在模块化或者是近海环境内未能体现，因此，航改的设计将是更具吸引力。然而，一旦驱动被选中，那么灵活地改变制冷负荷，从而最大限度地利用现有的涡轮动力，这将是最好的过程。没有单一制冷剂的固定沸点温度的特点，一个多元混合制冷的过程能够灵活地允许这样的转变。机械式驱动燃气轮机将是具有非常好的经济性的电动传动装置，在这种情况下，因为标准设计、多个厂家及有可能的更大经济性，燃气涡轮机的成本将会降低，但对于发动机、备用发电机和配电会有额外的费用，这些因素能在一个简单的周期配置中减少整体效率。联合循环可以克服效率损失，但是单一循环通常有较高的成本。全电动驱动器配置的实施，更是难以减少经济性，由于在较少的单位电力负荷变化的动态响应中管理困难，更低成本涡轮机的使用成了问题。最后，一个全电气化的驱动配置被认为是较高的成本和提高工厂的可用性之间的一个折中的选择。压缩机压缩机表现出非常高的经济性，制冷剂压缩成本主要是所需压缩机数量的函数，因此，最重要的是要减少压缩机的数量。同样重要的是要限制所需的转子离心压缩机车轮直径，这就要通过减少制冷剂循环量来限制体积流量或者是更高的制冷剂吸入压力供给这些压缩机。利用二次双混合制冷剂工艺使流程设计变得灵活，在至少四家供应商的能力范围内，以优化压缩机的进气口吸气容积来最大限度地提高生产量。这将会利用钎焊铝热交换器来提供：l 多个厂家的成本和进度的利益l 经济规模较大的吞吐量l 易于模块化钎焊铝热交换器在每个压力水平下影响制冷剂的分离，从操作和设计相关的问题中得到保护，只有液体输送到钎焊铝热交换器的核心部位，而绕过蒸汽回到压缩系统中。它会利用燃气轮机驱动离心压缩机达到足以获得经济性，但它必须确保多个压缩机供应商的供应。我们的液化天然气流程研究将这些原则应用到一个潜在的液化天然气发展中，其结果显示在图3中。通过使用钎焊铝热交换器和双混合制冷剂，使压缩机和驱动器达到最佳匹配，由此产生的过程将会有一个更低的功耗要求，并且有一个比传统技术更低的资本成本，钎焊铝热交换器的DMR过程表明一个单位耗资有优势。高效扩增LNG厂使扩张的火车长期受益，通常从同样大的资源中得到提供，虽然可用于多级列车发展的已发现的大油田的数量正在减少，但附近的小资源对经济的扩张仍是有潜力的。在许多情况下，这些其它领域不能聚合成一个大工程的各种原因有：一些商业利益的调整、为了更困难的资源而等待降低开发成本、或者是附近LNG工程资源正在进行中。对于所有这些原因，它需要一个有易于扩张的液化天然气工厂。作为一个实用的制冷剂，它是一种以最大限度来提高扩展性和可靠性的途径，在此配置中所有服务过程中的制冷剂合并成一个单一的头，并交付给LNG液化环节。作为通用的制冷剂可以用于任何液化过程，但最适合双混合制冷剂，制冷剂的回馈压力可以更高，从而导致较小的管道分布横跨制冷剂液化天然气厂，图4显示了一个这样的的配置。处理的制冷剂作为一种实用工具有几个好处：l 列车不一
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