Abstract Gas processing plants need to cope with varying and often uncertain conditions. Operators of gas processing plants in North Dakota (USA) typically face challenges with the mode of operation (ethane rejection or ethane recovery) and feed gas uncertainty (rich gas or lean gas). In terms of equipment reliability, flexibility and efficiency, these circumstances also place significant requirements on the compressor technology used. This case study will discuss the deployment of a mechanical refrigeration cycle using commercial-grade propane (95 to 98.5% propane, with the rest being heavy hydrocarbons, or HD5, or higher-grade propane). In the context of different compressor technologies available for such applications (this includes oil flooded screw, integrally geared centrifugal or inline centrifugal, the authors examine the performance characteristics of integrally geared compressor technology applied in gas processing plants. Inherently, oil-flooded screw compressor systems require regular maintenance to ensure the availability of oil-free process gas. In turn, when seals or coalescing filters are not maintained or do not perform as expected, oil may carry over with the process gas and flows to downstream. These events require extensive cleaning and can lead to plant downtime. By comparison, integrally geared compressors and inline centrifugal compressors are 100% oil-free (no oil in compression chamber / process), providing increased reliability while requiring less maintenance. Also, integrally geared technology can be supplied with tilting pad thrust bearings which allow these propane refrigeration compressors to start at a higher suction pressure (i.e., settle out conditions on hot summer days), thus providing superior rotor stability while saving the propane because there is no need to flare the gas to reduce the system settle out pressure (Patel and Struck 2017). With regards to the parameter of flexibility, the authors will discuss how the variable diffuser guide vanes (vDGVs) are helping to provide the process flexibility, thereby extending compressor turndown up to 50% without recycle. vDGVs can maintain a required and subsequently designed discharge pressure that gives operators flexibility with varying mole weight and head requirements. vDGVs also help with start-up during high settle-out conditions like those in refrigeration processes. It was found that integrally geared compressors are about 10% more efficient than oil-flooded screw compressors. As each impeller has its own casing and seals, it will allow for easy accommodation of side streams. Also, integral gearing can match the impeller geometry to the required speed which results in higher compression efficiency, while dry gas seals reduce process gas leakage to improve plant reliability. Lastly, it was found that an integrally geared refrigerant compressor delivers more than USD 200 000 per year in OPEX savings, in addition to lower CAPEX of up to approximately 20% (based on the study done for a 200 MMSCFD plant).

Abstract Waste heat is the by-product of industrial energy usage. Approximately one-third of the energy consumed by the oil and gas industry is discharged as thermal losses into the environment or via cooling systems. And the main reasons for waste heat discharge are process inefficiencies and technology limitations in the conversion of thermal to mechanical energy. Nevertheless, because the oil and gas industry demands large amounts of thermal, electrical and mechanical energy, a huge amount of waste heat is subsequently available. Organic Rankine Cycle (ORC) technology has made economical utilization of lower temperature heat sources possible. ORC's efficiency percentage for waste heat recovery varies between single digit to the mid-20s, depending on the waste heat source temperature and the cooling medium. Even the recovery of a few MW of thermal energy with a single-digit cycle efficiency for a plant consuming an average of 100 MW (134 102 hp) thermal energy is a considerable efficiency improvement. Studies by the Oakridge National Laboratory (USA) show that 75% of waste heat comes with sufficiently high temperatures (> 150°C, or > 302°F). This report projects a 2-5-year return of investment for ORC-based waste heat to power plant systems, which represents an attractive financial payback. The recovery of waste heat from oil and gas operations remains mostly underutilized. Furthermore, economically feasible power generation from waste heat has been limited to medium- to high- temperature waste heat resources. This paper will explore technical solutions to these challenges facing the oil and gas industry In this paper, three cases of waste heat from a gas turbine's exhaust flue gas are presented. The turbines have nominal output of 7.5, 15, and 25 MW (10 057, 20 115 and 33 525 hp) electrical power at an ambient air temperature of 15°C (59°F). A heat recovery unit (HRU) can recover thermal energy from exhaust flue gas. The heat recovery loop (HRL) could exchange thermal power with an ORC system, which in turn has the potential to produce electrical power. It will be demonstrated that this configuration has a HRL/ORC cycle efficiency of approximately 10% when the ambient air temperature is about 30°C (86°F).

Abstract Investors in small-scale LNG (SSLNG) face the grave challenge of achieving cost efficiency, operational efficiency, and energy efficiency in the equipment they use, all with maximum availability. In this context, the mixed refrigerant compressor's initial design plays a particularly substantial role – and challenge – in both the efficiency and the ROI of an SSLNG plant. In addressing the overall efficiency requirement of the mixed refrigerant compressor, the design must consider several key requirements, such as power consumption, seal leakage rates, and performance degradation during the life of the compressor. Regarding ROI, plant CAPEX, which consists of equipment cost and installation cost (i.e., space, complexity installation time), and OPEX (i.e., power, maintenance interval, and cost) play a vital role. This case study – written jointly by representatives from the turbomachinery OEM and from the end user of an SSLNG plant in China, respectively – will examine how different compressor technologies can address these different dimensions of efficiency requirements. Evaluating different compressor technology solutions for such applications, the authors will examine in detail how a mixed refrigerant compressor can be tailored to meet the needs of a specific plant's processes. Furthermore, the authors describe how a 27 MW (36 200 hp) integrally geared mixed refrigerant compressor deployed in a Chinese SSLNG plant in a single mixed refrigerant cycle supports the achieving of different efficiency parameters. In the compressor design, for example, choosing open or closed impellers can translate into substantial efficiency gains. The case study will also examine how inlet guide vanes (IGVs) allow operators to make full use of agile plant deployment while increasing compressor efficiency by up to 9%. By guiding and regulating inlet flow, IGVs provide more accurate process control at a constant discharge pressure. Variable IGVs can also offer a good operating range and superior partial-load performance for the differing conditions encountered in small-scale LNGs. The integrally geared compressor solution deployed in the case study is designed to deliver 98% reliability and 84% compressor efficiency. In addition, by incorporating seal support, lube oil, and the main compressor on the same skid (single-lift design) is up to 25% smaller than that of inline compressors. The integrally geared approach also allows for intercooling between stages, which improves both energy and cost efficiency by about 2%.

Abstract Today, small-scale liquified natural gas (SSLNG) plants are planned and built in different areas around the globe. Due to the overall market situation and competition, these projects are challenged to decrease capital expenditure (CAPEX), while becoming increasingly efficient to meet mid-size investors' operating expenditure (OPEX) targets and return on investment (ROI) expectations. The main challenges are the overall efficiency of the plant, seal leakage rates, operational flexibility and the plant's space limitations. To a big extent, the aforementioned points are closely connected to liquefaction technology selection (either single mixed refrigeration or nitrogen Brayton cycle) as well as the rotating equipment used: Firstly, regarding energy use, the refrigeration compressor is the main power consumer in an SSLNG plant (in addition to pumps and smaller compressors). Secondly, a large amount of process leakage is linked to the seals of the rotating equipment. Regarding the third point, operational flexibility, this parameter is closely related to the deployed compressor and expander, and their respective process characteristics. Lastly, the footprint and equipment size have an impact on the installation costs and ultimately CAPEX. Often, especially in a nitrogen Brayton cycle, compressors as well as warm and cold turboexpanders are supplied as single skid each: that is, a nitrogen compressor skid as well as both warm and cold expander compressors installed on another skid. To reach their future objectives, some SSLNG plant operators are taking new approaches that combine these two technologies: compressor and expander applications are installed on one single gearbox and skid – this is called a Compander. This approach is already used in other industry segments and applications, including LNG carriers. Atlas Copco's first land-based LNG refrigeration Compander was installed back in 2002 at a plant in Norway. The Compander design allows for only one gearbox on which compressor and expander stages are mounted, one oil system, one control system and one seal gas panel – instead of having all of these components twice. By applying these bridging technologies, SSLNG plants are finding new ways to improve OPEX while at the same time reducing the financial burden on new projects. In this case study, we discuss how SSLNG plants in Norway and customers in other places have implemented Atlas Copco Gas and Process integrally geared technology that merges the functions of a centrifugal compressor and turboexpander into one compact Compander unit. In addition, different configurations of separate compressors and expanders are discussed and compared to a single-skid (Compander) solution. During the discussion, the benefits of a Compander compared to single and separate equipment designs are evaluated.

Over the last few years, fuel economy improvement has driven the use of efficient multi-material structures in the car industry. The combination of dissimilar materials, such as metal-metal and metal-polymer, is a complex issue that requires the use of different and emerging joining techniques. In this context, self-pierce riveting (SPR) is an extremely suitable technique for joining two or more metal sheets, particularly when other techniques are not applicable. SPR requires short manufacturing times and provides both high strength and high fatigue resistance. Yet, this technique still faces some hurdles, such as joining Ultra High Strength Steels (UHSS) with high strength low ductility aluminum alloys, which can result in rivet cracking or aluminum button tearing. Suitable process parameters, including the rivet size and the die profile, are usually obtained through a physical testing procedure to satisfy the required joint specification. This is both expensive and time consuming. Finite element simulations of SPR are being increasingly used to reduce the number of physical tests and to estimate the tensile strength of the joint. The capability to accurately simulate aluminum to aluminum riveting has been demonstrated in recent studies. However, very few simulation studies have been conducted on the riveting of UHSS to aluminum, mainly because this type of joint is a relatively new customer demand driven by the rapid adoption of mixed material car body structures. New rivet designs have recently been developed for joining UHSS to aluminum, these rivets have increased column strength and increased stiffness to enable piercing through UHSS materials. In this study the insertion behavior of these higher strength rivets has been simulated and numerical analysis has been conducted to investigate the influence of the key process parameters on the joining result. The simulation results were compared to physical experimental results and good correlation was achieved.

Two separate stages are discernible as essential requirements in mitigating the effects of corrosion. Firstly, the right conditions must be created for effective protection, and secondly surfaces must be treated with the best available anti‐corrosion methods.