Numerical modelling of fin side heat transfer and pressure loss for compact heat recovery steam generators

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Evaluation of SPUNG* and Other Equations of State for Use in Carbon Capture and Storage Modelling

AbstractIn this work, Equations of State (EoS) relevant for carbon capture and storage modelling have been evaluated for pure CO2 and CO2-mixtures with particular focus on the extended corresponding state approach, SPUNG/SRK. Our work continues the search of an EoS which is accurate, consistent and computationally fast for CO2-mixtures. These EoS have been evaluated: Soave-Redlich-Kwong (SRK), SRK with Peneloux shift, Peng-Robinson, Lee-Kesler, SPUNG/SRK and the multi-parameter approach GERG-2004. The EoS were compared to the accurate reference EoS by Span and Wagner for pure CO2. Only SPUNG/SRK and GERG-2004 predicted the density accurately near the critical point (< 1.5% Absolute Average Deviation (AAD)). For binary mixtures, Lee-Kesler and SPUNG/SRK had similar accuracy in density predictions. SRK had a sufficient accuracy for the gas phase below the critical point (<2.5%), and Peng Robinson had a decent accuracy for liquid mixtures (<3%). GERG-2004 was the most accurate EoS for all the single phase density predictions. It was also the best EoS for all the VLE predictions except for mixtures containing CO2 and O2, where it had deviations in the bubble point predictions (∼20% AAD). Even though multi-parameter EoS such as GERG-2004 are state-of-the-art for high accuracy predictions, this work shows that extended corresponding state EoS may be an excellent compromise between computational speed and accuracy. The SPUNG approach combines high accuracy with a versatile and transparent methodology. New experimental data may easily be taken into account to improve the predictive abilities in the two phase region. The approach may be improved and extended to enable applications for more difficult systems, such as polar mixtures with CO2 and H2O

Energy and Cost Evaluation of A Low-temperature CO2 Capture Unit for IGCC plants

AbstractThe application of CO2 capture by liquefaction has been investigated for an integrated gasification combined cycle (IGCC). Two configurations of the process are developed–one supplying CO2 at conditions suitable for pipeline transport and the second one producing liquid CO2 suitable for ship transport. The liquefaction process for CO2 capture is more efficient and compact compared to Selexol process for providing CO2 suitable for ship transport as the separation and liquefaction units are integrated in the process presented in this work. An economic analysis performed shows that CO2 capture by liquefaction is more cost efficient than corresponding Selexol-based separation processes by 9–11% in terms of the levelized cost of electricity and 35–37% in terms of CO2 avoidance costs

Achieving 50% weight reduction of offshore steam bottoming cycles

Adding a bottoming cycle to the gas turbines powering offshore oil and gas production plants allows additional power to be produced from recovered excess heat. Hence, the power demand of the platform can be met by burning less natural gas, and the CO2 emissions reduced by up to 25%. However, the weight of the current bottoming cycles must come down to enable widespread implementation. This work presents a thorough weight minimization of a steam bottoming cycle utilizing gas turbine exhaust heat. Unconventional, but feasible designs of heat exchangers, ductwork and structural components are considered along with materials switching. Overall weight reductions of 38% and 52% were achieved for a 16 MW and a 12 MW offshore bottoming cycle respectively when compared to a 16 MW reference system. Key factors in achieving the weight reduction were the use of small steam generator tubes with an inner diameter of only 10 mm, improved condenser design and the use of aluminium structural framework replacing steel. By more than halving the weight of the bottoming cycle, it's implementation potential on offshore platforms has been greatly improved and can move the oil and gas industry towards significantly reduced CO2 emissions.publishedVersio

Design optimization of compact gas turbine and steam combined cycles for combined heat and power production in a FPSO system–A case study

This case study aims to cover a wide range of relevant aspects related to combined cycle design, mechanical integrity and operational reliability for cogeneration of heat and power in FPSO systems. The methods consist of combined optimization of combined cycle thermodynamic design and geometry of steam generator; vibration analysis for flow induced vibrations; and thermal stress estimation of casings during cold start-stop scenarios. Challenges and opportunities for reliable water treatment systems are explored. The results show that small tubes, a compact tube bundle and a low condensation temperature reduces the once-trough steam generator (OTSG) weight. The vibrations numerical simulations in this work support the standard recommendations of using 35 times tube OD as upper limit for the unsupported tube length, which could be used as a reasonable design criterion. Thermal stresses analysis indicates that the design of beam arrangement, location, and stiffness of beams has a major impact on thermal stresses, and can be optimized to different plate thicknesses in order to avoid fatigue damage. Focus should be on reducing leaks of deaerator, steam turbine and condenser. It is recommended to add Na sensors after condenser and investigating the use of Electrodeionization (EDI) technology for make-up water production from seawater.publishedVersio

Identification of surface proteins in Enterococcus faecalis V583

<p>Abstract</p> <p>Background</p> <p>Surface proteins are a key to a deeper understanding of the behaviour of Gram-positive bacteria interacting with the human gastro-intestinal tract. Such proteins contribute to cell wall synthesis and maintenance and are important for interactions between the bacterial cell and the human host. Since they are exposed and may play roles in pathogenicity, surface proteins are interesting targets for drug design.</p> <p>Results</p> <p>Using methods based on proteolytic "shaving" of bacterial cells and subsequent mass spectrometry-based protein identification, we have identified surface-located proteins in <it>Enterococcus faecalis </it>V583. In total 69 unique proteins were identified, few of which have been identified and characterized previously. 33 of these proteins are predicted to be cytoplasmic, whereas the other 36 are predicted to have surface locations (31) or to be secreted (5). Lipid-anchored proteins were the most dominant among the identified surface proteins. The seemingly most abundant surface proteins included a membrane protein with a potentially shedded extracellular sulfatase domain that could act on the sulfate groups in mucin and a lipid-anchored fumarate reductase that could contribute to generation of reactive oxygen species.</p> <p>Conclusions</p> <p>The present proteome analysis gives an experimental impression of the protein landscape on the cell surface of the pathogenic bacterium <it>E. faecalis</it>. The 36 identified secreted (5) and surface (31) proteins included several proteins involved in cell wall synthesis, pheromone-regulated processes, and transport of solutes, as well as proteins with unknown function. These proteins stand out as interesting targets for further investigation of the interaction between <it>E. faecalis </it>and its environment.</p

Analysis of Thermodynamic Models for Simulation and Optimisation of Organic Rankine Cycles

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Techno-economic analyses of CO2 liquefaction: Impact of product pressure and impurities

As a first step towards identifying the optimal transport conditions for shipping CO2, this study investigates the impact of post-liquefaction delivery pressure on the design and cost of CO2 liquefaction for (a) pure CO2 (b) three impurity scenarios (c) two purity requirements. For pure CO2, the highest liquefaction cost is obtained at 7 bar amongst the range considered (7 to 70 bar), while a minimum lies around 40-50 bar. When different potential impurity scenarios are considered, impurities need to be purged for the low-pressure cases as these are not necessarily soluble in the liquefied CO2 stream. As a consequence, the liquefaction cost increases significantly for low-pressure cases (up to 34% compared to the pure CO2), and wider differences between the pressure levels are obtained. Purity requirements also have a significant impact on comparisons of delivery pressures, although this impact depends on both the impurities present and the purity requirement considered.Techno-economic analyses of CO2 liquefaction: Impact of product pressure and impuritiesacceptedVersio

Plate fin-and-tube heat exchanger computational fluid dynamics model

Insight into thermal–hydraulic correlations of plate fin-and-tube heat exchangers is of great interest in many industrial applications. Numerical simulations allow to efficiently and accurately obtain air-side heat transfer and pressure drop correlations for a broad variety of heat exchanger configurations, provided the numerical method is soundly validated against experimental measurements. In this contribution, we present a thoroughly validated computational fluid dynamics model applicable to solution of the conjugate heat-transfer problem in plate fin-and-tube heat exchangers. Favorable agreement with experimental work on four different geometries is demonstrated for high Reynolds numbers. Three out of four comparisons agree to within 20% with experiments. The computational model is applied to study the dependence of heat transfer and pressure drop in relation to the transverse tube array pitch. We show that minimizing the array angle results in enhanced fin efficiency. © 2021 The AuthorspublishedVersio

Dissecting the exergy balance of a hydrogen liquefier: Analysis of a scaled-up claude hydrogen liquefier with mixed refrigerant pre-cooling

For liquid hydrogen (LH2) to become an energy carrier in energy commodity markets at scales comparable to for instance LNG, liquefier capacities must be scaled up several orders of magnitude. While state-of-the-art liquefiers can provide specific power requirements down to 10 kWh/kg, a long-term target for scaled-up liquefier trains is 6 kWh/kg. High capacity will shift the cost weighting more towards operational expenditures, which motivates for measures to improve the efficiency. Detailed exergy analysis is the best means for gaining a clear understanding of all losses occurring in the liquefaction process. This work analyses in detail a hydrogen liquefier that is likely to be realisable without intermediate demonstration phases, and all irreversibilities are decomposed to the component level. The overall aim is to identify the most promising routes for improving the process. The overall power requirement is found to be 7.09 kWh/kg, with stand-alone exergy efficiencies of the mixed-refrigerant pre-cooling cycle and the cryogenic hydrogen Claude cycle of 42.5% and 38.4%, respectively. About 90% of the irreversibilities are attributed to the Claude cycle while the remainder is caused by pre-cooling to 114 K. For a component group subdivision, the main contributions to irreversibilities are hydrogen compression and intercooling (39%), cryogenic heat exchangers (21%), hydrogen turbine brakes (15%) and hydrogen turbines (13%). Efficiency improvement measures become increasingly attractive with scale in general, and several options exist. An effective modification is to recover shaft power from the cryogenic turbines. 80% shaft-to-shaft power recovery will reduce the power requirement to 6.57 kWh/kg. Another potent modification is to replace the single mixed refrigerant pre-cooling cycle with a more advanced mixed-refrigerant cascade cycle. For substantial scaling-up in the long term, promising solutions can be cryogenic refrigeration cycles with refrigerant mixtures of helium/neon/hydrogen, enabling the use of efficient and well scalable centrifugal compressors. © 2020 The Author(s)publishedVersio