Cryogenic CO2 condensation and membrane separation of syngas for large-scale LH2 production.

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Evaluation of different heat pump systems for sanitary hot water production using natural refrigerants

[EN] Heat pumps that work with a high degree of subcooling in subcritical systems have shown a significant margin of improvement when working with sanitary hot water applications. Recently, two different approaches to overcome the high degree of subcooling have been presented in the literature: with a subcooler (separate from the condenser) and by making all the subcooling in the condenser. In this paper, a comparative evaluation between both alternatives is presented, and the obtained results are compared with a representative solution already available on the market using natural refrigerants for this application. The results of this analysis have shown that in a system with subcooling in the condenser, it is possible to obtain a COP comparable to that of transcritical CO2 heat pump water heaters. Furthermore, the system with subcooling has been demonstrated experimentally as being capable of producing water up to 90ºC and has shown a COP up to 20% higher than some CO2 commercial products (catalogue data reference).This work has been developed in the Seventh Framework Program of the European Union by the project, Next Generation of Heat Pump Technologies (NEXTGHP), grant agreement 307169. The authors thank the support given. Part of the work presented was carried by Miquel Pitarch-Mocholí with the financial support of a PhD scholarship from the Universitat Politècnica de València. The authors would like also to acknowledge the Spanish ‘MINISTERIO DE ECONOMIA Y COMPETITIVIDAD’, through the project ref-ENE2014-53311-C2-1-P-AR ‘‘Aprovechamiento del calor residual a baja temperatura mediante bombas de calor para la produccion de agua caliente” for the given supportPitarch, M.; Navarro-Peris, E.; Gonzálvez-Maciá, J.; Corberán, JM. (2017). Evaluation of different heat pump systems for sanitary hot water production using natural refrigerants. Applied Energy. 190:911-919. https://doi.org/10.1016/j.apenergy.2016.12.166S91191919

Multiejector CO2 cooling system with evaporative gascooler for a supermarket application in tropical regions

In the present study, the performance of a 33 kW multiejector trans-critical CO2 cooling system is experimentally evaluated for a supermarket application with/without internal heat exchanger and evaporative cooling. In order to enhance the overall performance of the system for tropical regions, the testing is carried out at high ambient temperature (up to 46 °C) with 5 cm, 10 cm and 15 cm cooling pad thickness arrangements. The experimental results clearly projects that the evaporative cooler capacity reaches a maximum of 10 cm pad thickness. However, a minor improvement is observed in terms of Coefficient of Performance and Power Input Ratio beyond 10 cm pad thickness. Maximum improvement in COP with internal heat exchanger and evaporative cooler is 11% and 40% respectively. On the other hand, a maximum reduction in the system Power Input Ratio with internal heat exchanger and evaporative cooler is 8.5% and 26% respectively. However, a minor enhancement in Coefficient of Performance and Power Input Ratio of 4% and 6% are observed respectively with 15 cm cooling pad thickness. Furthermore, a comparative analysis is carried out with the existing and present experimental study to project the compatibility of an evaporative condenser in the ejector based CO2 cooling system. From the study, it is evident that the evaporative cooling arrangement for the gascooler of the CO2 system is suggested as a potential solution to the supermarket application at a high ambient temperature context. © 2021 Elsevier LtdacceptedVersio

Energy efficient multiejector CO2 cooling system for high ambient temperature

Experimental evaluation of a multiejector CO2 cooling system of 33 kW cooling capacity is conducted for an Indian supermarket at high ambient temperature context. The test-rig is designed to depict the actual supermarket cooling requirements in India with three different cooling temperature levels simultaneously; freezing, medium refrigeration and air-conditioning. The rig is equipped with a novel design consisting of two multiejectors; low ejection ratio ejector (LERE) and high ejection ratio ejector (HERE), in a series configuration. It is observed that the maximum pressure lift of 5.5 bar is obtained with this new design. Moreover, improvement in the overall system performance with the support of the internal heat exchanger (IHX) is evaluated. Enhancements observed in the maximum COP and PIR are 7.2% and 6.2% respectively. Furthermore, the test-rig performance with the flooding and non-flooding of the medium temperature evaporator (refrigeration) is evaluated. It is observed that the evaporator flooding reduces its superheat at the exit by 83.84%, leading to the overall reduction of PIR by 6.51%. The performance of the proposed system is also compared with the reported field data obtained at a low ambient temperature context. The results projected that the proposed cooling system with series multiejector configuration is a reliable choice for higher ambient temperatures and it is expected to outperform the existing systems at lower ambient temperatures.acceptedVersio

Performance evaluation of CO2 ejector system with parallel compressor for supermarket application

Evolution in modifications for CO2 system configuration came across from the last two decades has proven to hold the potential in order to improve the overall performance of the CO2 cooling system for various applications. However, performance of the CO2 system at high ambient context is not promising and comparable with popular conventional refrigerants. Due to its unique properties, the CO2 system possesses substantial losses at high ambient temperature due to the throttling process. System configuration with parallel compressor is proven as the most popular and efficient configuration for high ambient temperature (up to 46 °C). In this study performance evaluation of a CO2 multi-ejector based supermarket cooling system of 33 kW cooling capacity with compressor configuration is experimentally evaluated at high ambient temperature (up to 46 °C). Test facility is equipped with two-phase multi-ejector resulting in pressure lift due to the expansion work recovery. Removed flashes in flash gas tank or separator after passing through two-phase ejector, are further compressed with the help of auxiliary compressor configured in parallel but with an additional possession of low compression ratio. High stability with high gascooler pressure and CO2 system consistency at high gascooler outlet temperature is observed. Maximum reduction in the AUX compressor energy consumption observed is 8% for 46 bar & 10.7% for 48 bar receiver pressure at 36 ºC gascooler outlet temperature. Also, the Exergy efficiency of the system observed is 0.315 corresponding to 3.2 PIR at 46 ºC gascooler outlet temperature

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

Hydrogen re-liquefaction Process for Boil-off Gas Handling on a Large-scale Liquid Hydrogen Carrier

With the recent focus on hydrogen, seaborne shipping is considered an option for the large-scale transport of liquid hydrogen (LH2). For efficient shipping, boil-off gas (BOG) from the cargo tanks needs to be optimally utilized. This work suggests a BOG handling system (BHS) producing fuel for an LH2 carrier and liquefying excess BOG in a hydrogen Claude cycle. The process offers a simple configuration that does not require a refrigerant makeup facility. The simulation results of the BHS also show relatively low specific power consumption (5.7 to 2.6 kWh/kgLH2) with a good utilisation of cold energy in BOG. The sensitivity analysis with the BOG to fuel (BtF) ratio shows that a higher BtF gives a simpler configuration and a smaller size liquefier, saving capital costs. However, the optimal capacity of the BHS needs to be determined based on the techno-economic performance of the entire system of the LH2 carrier. Keywords: Hydrogen, Liquefaction, Liquid hydrogen carrier, Transport, Boil-off gas, Claude cycleacceptedVersio

Experimental evaluation of the energy efficiency of a CO2 refrigerating plant working in transcritical conditions

[EN] This work presents the experimental evaluation of the energy efficiency and optimal gas-cooler pressures of a single-stage refrigerating plant working with carbon dioxide as refrigerant in transcritical conditions. The performance of the plant was tested at three different evaporating temperatures (-0.9, -10.1 and -18.1 degrees C), for three gas-cooler refrigerant outlet temperatures (31.2, 33.6 and 40.0 degrees C) at each evaporating temperature and in a wide range of gas-cooler pressures (74.4-104.7 bar). The experimental tests enabled us to calculate accurately the optimal gas-cooler pressures and compare them with the most commonly used relations to define this value in single-stage refrigerating cycles operating with carbon dioxide in transcritical conditions. Furthermore, an analysis of the reduction in energy efficiency produced in the plant if the optimum pressure is not well defined is also presented.The authors are indebted to Frost-Trol S.A. (www.frosttrol.com) and the Spanish Ministry of Education and Science (ENE2006-09972/CON) for the economical support given to the present work and for the Grant BES-2007-16820 linked to the Ministry projectCabello, R.; Sanchez, D.; Llopis, R.; Torrella Alcaraz, E. (2008). Experimental evaluation of the energy efficiency of a CO2 refrigerating plant working in transcritical conditions. Applied Thermal Engineering. 28(13):1596-1604. https://doi.org/10.1016/j.applthermaleng.2007.10.026S15961604281

Large-scale production and transport of hydrogen from Norway to Europe and Japan: Value chain analysis and comparison of liquid hydrogen and ammonia as energy carriers

Low-carbon hydrogen is considered as one of the key measures to decarbonise continental Europe and Japan. Northern Norway has abundant renewable energy and natural gas resources which can be converted to low-carbon hydrogen. However, Norway is located relatively far away from these markets and finding efficient ways to transport this hydrogen to the end-user is critical. In this study, liquefied hydrogen (LH2) and ammonia (NH3), as H2-based energy carriers, are analysed and compared with respect to energy efficiency, CO2 footprint and cost. It is shown that the LH2 chain is more energy efficient and has a smaller CO2 footprint (20 and 23 kg-CO2/MWhth for Europe and Japan, respectively) than the NH3 chain (76 and 122 kg-CO2/MWhth). Furthermore, the study finds the levelized cost of hydrogen delivered to Rotterdam to be lower for LH2 (5.0 EUR/kg-H2) compared to NH3 (5.9 EUR/kg-H2), while the hydrogen costs of the two chains for transport to Japan are in a similar range (about 7 EUR/kg-H2). It is also shown that under optimistic assumptions, the costs associated with the LH2 chain (3.2 EUR/kg-H2) are close to meeting the 2030 hydrogen cost target of Japan (2.5 EUR/kg-H2). Keywords Techno-economic analysisLiquid hydrogenAmmoniaLong distance transportacceptedVersio