Premixed combustion of alternative fuels under varying conditions of temperature and pressure

Temperature, pressure and CO2 and H2 addition to CH4 effects on turbulent and laminar burning velocity have been found and discussed. Novel turbulent burning velocity determination methods are presented and uncertainties have been discussed. Turbulent burning velocity correlation with nondimensional numbers have been found and flames structures have been analysed.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Comparative Analysis of Isochoric and Isobaric Adiabatic Compressed Air Energy Storage

Adiabatic Compressed Air Energy Storage (ACAES) is regarded as a promising, grid scale, medium-to-long duration energy storage technology. In ACAES, the air storage may be isochoric (constant volume) or isobaric (constant pressure). Isochoric storage, wherein the internal pressure cycles between an upper and lower limit as the system charges and discharges is mechanically simpler, however, it leads to undesirable thermodynamic consequences which are detrimental to the ACAES overall performance. Isobaric storage can be a valuable alternative: the storage volume varies to offset the pressure and temperature changes that would otherwise occur as air mass enters or leaves the high-pressure storage. In this paper we develop a thermodynamic model based on expected ACAES and existing CAES system features to compare the effects of isochoric and isobaric storage. Importantly, off-design compressor performance due to the sliding storage pressure is included by using a second degree polynomial fit for the isentropic compressor efficiency. For our modelled systems, the isobaric system round-trip efficiency (RTE) reaches 61.5%. The isochoric system achieves 57.8% even when no compressor off-design performance decrease is taken into account. This fact is associated to inherent losses due to throttling and mixing of heat stored at different temperatures. In our base-case scenario where the isentropic compressor efficiency varies between (Formula presented.) and (Formula presented.), the isochoric system RTE is approximately 10% lower than the isobaric. These results indicate that isobaric storage for CAES is worth further development. We suggest that subsequent work investigate the exergy flows as well as the scalability challenges with isobaric storage mechanisms.</p

How pressure affects costs of power conversion machinery in compressed air energy storage; Part I:Compressors and expanders

This study addresses a critical economic aspect in compressed air energy storage that has not been discussed much in existing literature: the impact of operating pressure on machinery capital cots. It aims to answer whether the cost per unit of power for power conversion systems changes with the maximum storage pressure. Considering that higher storage pressures are associated with greater energy density, enhanced energy storage capabilities and improved system efficiency. This paper helps clarify uncertainties in initial cost estimations for power-generation plants. Effects of operating pressure on the components and overall sizes and consequently costs of power conversion machinery are individually investigated in two parts. Part I encompasses the compressor and expanders, and part II comprehensively discusses the effects of the operating pressure on the costs of heat exchangers. The analysis employs a conceptual engineering approach, revealing that higher intake pressure reduces overall compressor/expander size, leading to cost savings. Additionally, increasing the number of compression stages for higher storage pressures enhances exergy storage cost-effectiveness. To establish an advanced adiabatic CAES plant with a storage pressure of 200 bar instead of 50 bar, there is potential for a 6 % reduction in $/kW expenditure.</p

Improving the performance of a shell and tube latent heat thermal energy storage through modifications of heat transfer pipes:A comprehensive investigation on various configurations

The modification of the geometric configurations of heat transfer pipes in shell and tube Latent Heat Thermal Energy Storage (LHTES) systems not only enhances the melting process of the phase change material (PCM) but also improves the overall performance of these systems. This study aims to investigate ways to enhance the performance of LHTES systems by employing heat transfer pipes with various fin and twisted tape arrangements in a horizontal orientation. The Finite Volume Method and Enthalpy-Porosity method are employed to simulate the melting process. Stearic acid is used as the PCM material, while water serves as the heat transfer fluid. Eight different geometric configurations are modelled in the LHTES system: base case, horizontal fins, vertical fins, helical fins, horizontal tape, vertical tape, twisted tape and helical fins with twisted tape. The results show that within the time range of 0 and 29 min, the combined configuration of helical fins with twisted tape consistently demonstrates the fastest melting process. After 29 min, the configuration with vertical fins exhibits a marginally faster melting process than the combined configuration of helical fins with twisted tape. The configurations involving tapes also contribute to accelerated melting, although to a lesser extent than those with fins. Particularly, twisted tape proves highly effective in facilitating faster melting. The complete melting process times for configurations with vertical fins, helical fins, and combined helical fins with twisted tape are 38.7 %, 23.5 % and 32.7 % faster compared to the base case which is ∼69 min. Among the configurations, using tapes results in higher flow resistance and surface area compared to the base case. The attractive features of these configurations make them ideal for creating efficient and space-saving energy storage systems. This study provides crucial insights into essential heat and mass transfer processes, which can be leveraged to develop advanced LHTES systems for enhanced performance and sustainable energy solutions.</p

How pressure affects costs of power conversion machinery in compressed air energy storage; part II:Heat exchangers

In the field of compressed air energy storage, a critical economic aspect that has been overlooked in existing literature relates to the influence of storage pressure on the capital cost of power conversion system. In Part I, a comprehensive study was conducted to address this question focusing on compressors and expanders. This part is devoted to the heat exchangers and basically assesses the engineering rationale behind the relationship between the cost per kW for HXs and operating pressure. Based on the performed analysis, the operating pressure of a HX impacts two crucial cost-related factors: the heat transfer area and required tube thicknesses. Higher operating pressures are associated with the smaller heat transfer area tending to lower costs, but increasing pressure raises tube thickness requirements, tending to increase costs. Below approximately 200 bar, the former effect prevails over the latter, leading to cost reductions with rising pressure. Conversely, at higher pressures, the latter effect outweighs the former, resulting in cost increases with increasing pressure. On the other hand, as the number of compression stages is increased to attain higher storage pressures, there is a noteworthy variation in the cost contribution of HXs. Specifically, the contribution of HX costs within the PCS machinery escalates from 10 % at a storage pressure of 30 bar to approximately 35% at a storage pressure of 350bar. This cost increase is accompanied by a substantial reduction in costs associated with other PCS machinery components (compressors and expanders), ultimately justifying the advantages of operating at higher storage pressures.</p

How pressure affects costs of power conversion machinery in compressed air energy storage; Part I:Compressors and expanders

This study addresses a critical economic aspect in compressed air energy storage that has not been discussed much in existing literature: the impact of operating pressure on machinery capital cots. It aims to answer whether the cost per unit of power for power conversion systems changes with the maximum storage pressure. Considering that higher storage pressures are associated with greater energy density, enhanced energy storage capabilities and improved system efficiency. This paper helps clarify uncertainties in initial cost estimations for power-generation plants. Effects of operating pressure on the components and overall sizes and consequently costs of power conversion machinery are individually investigated in two parts. Part I encompasses the compressor and expanders, and part II comprehensively discusses the effects of the operating pressure on the costs of heat exchangers. The analysis employs a conceptual engineering approach, revealing that higher intake pressure reduces overall compressor/expander size, leading to cost savings. Additionally, increasing the number of compression stages for higher storage pressures enhances exergy storage cost-effectiveness. To establish an advanced adiabatic CAES plant with a storage pressure of 200 bar instead of 50 bar, there is potential for a 6 % reduction in $/kW expenditure.</p

Low temperature district heating network planning with the focus on distribution energy losses

An integrated conceptual planning framework has been developed to assist designing for high resource efficient, low carbon urban district heating systems. This paper focuses on distribution energy losses of a district heating system for an existing urban settlement. The planning framework consists of a methodological approach and a set of simulation tools to investigate two scenarios – low temperature and high temperature district heating networks. In this framework a dynamic building simulation program predicting energy demand of a case study area, an industrial software tool for piping systems design, and a mathematical optimization tool are integrated for assessing energy and exergy losses. Some preliminary results are shown at the end of the paper demonstrating the benefits of low temperature district heating networks and potential of the planning framework

How pressure affects costs of power conversion machinery in compressed air energy storage; Part I: Compressors and expanders

This study addresses a critical economic aspect in compressed air energy storage that has not been discussed much in existing literature: the impact of operating pressure on machinery capital cots. It aims to answer whether the cost per unit of power for power conversion systems changes with the maximum storage pressure. Considering that higher storage pressures are associated with greater energy density, enhanced energy storage capabilities and improved system efficiency. This paper helps clarify uncertainties in initial cost estimations for power-generation plants. Effects of operating pressure on the components and overall sizes and consequently costs of power conversion machinery are individually investigated in two parts. Part I encompasses the compressor and expanders, and part II comprehensively discusses the effects of the operating pressure on the costs of heat exchangers. The analysis employs a conceptual engineering approach, revealing that higher intake pressure reduces overall compressor/expander size, leading to cost savings. Additionally, increasing the number of compression stages for higher storage pressures enhances exergy storage cost-effectiveness. To establish an advanced adiabatic CAES plant with a storage pressure of 200 bar instead of 50 bar, there is potential for a 6 % reduction in $/kW expenditure