Abubakr Ayub

Role of the Pakistan Cement Industry towards the Achievement of Net Zero Goal by Mid-Century: A Review from a Waste Heat Recovery Perspective

ICAME 2023

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Thermodynamic optimization and performance study of supercritical CO2 thermodynamic power cycles with dry cooling using response surface method

International Communications in Heat and Mass Transfer

Harnessing Ocean Thermal Energy from Offshore Locations in Pakistan Using an Organic Rankine Cycle

ICAME-22

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Adoption of the CO2 + SO2 mixture as working fluid for transcritical cycles: A thermodynamic assessment with optimized equation of state

Energy Conversion and Management, 2022

This paper focuses on the use of the CO 2 + SO 2 binary mixture as innovative working fluid for c... more This paper focuses on the use of the CO 2 + SO 2 binary mixture as innovative working fluid for closed transcritical power cycles with a minimum temperature above 50 • C. Starting from a literature review of the available experimental data on the mixture, the PC-SAFT EoS is identified as a suitable model to characterize the mixture behavior. Once the proper thermodynamic model is selected for this mixture, a comparison between the innovative transcritical cycle and the sCO 2 cycle is proposed for various plant layouts in order to find out the advantages of the innovative mixture. The analysis is presented fixing the cycle maximum temperature at 700 • C and the maximum pressure at 250 bar: the results depict an increment in cycle electric efficiency and cycle specific work, along with a lower temperature of heat introduction in the cycle for any considered configuration of transcritical CO 2 + SO 2 cycle, when compared to pure sCO 2. An economic analysis of the power block is then performed to support the selection of the innovative working fluid. Two of the most promising plant layouts are evidenced: the recompression layout is selected for highly efficient power blocks, while the dual recuperated layout works effectively in applications characterized by higher hot source exploitation. The recompression layout adopting the CO 2 + SO 2 mixture presents a power block electric efficiency of 48.67% (2.33% higher than the respective sCO 2 cycle) and a reduction of the power block CAPEX from 1160 $/kW el to 1000 $/kW el when compared to the sCO2 configuration for a 100MW el size, while the dual recuperated layout exploiting the CO 2 + SO 2 mixture shows a power block electric efficiency of 39.58% (0.69% above the same sCO 2 cycle

Adoption of the CO2 + SO2 mixture as working fluid for transcritical cycles: A thermodynamic assessment with optimized equation of state

Energy Conversion and Management, 2022

This paper focuses on the use of the CO 2 + SO 2 binary mixture as innovative working fluid for c... more This paper focuses on the use of the CO 2 + SO 2 binary mixture as innovative working fluid for closed transcritical power cycles with a minimum temperature above 50 • C. Starting from a literature review of the available experimental data on the mixture, the PC-SAFT EoS is identified as a suitable model to characterize the mixture behavior. Once the proper thermodynamic model is selected for this mixture, a comparison between the innovative transcritical cycle and the sCO 2 cycle is proposed for various plant layouts in order to find out the advantages of the innovative mixture. The analysis is presented fixing the cycle maximum temperature at 700 • C and the maximum pressure at 250 bar: the results depict an increment in cycle electric efficiency and cycle specific work, along with a lower temperature of heat introduction in the cycle for any considered configuration of transcritical CO 2 + SO 2 cycle, when compared to pure sCO 2. An economic analysis of the power block is then performed to support the selection of the innovative working fluid. Two of the most promising plant layouts are evidenced: the recompression layout is selected for highly efficient power blocks, while the dual recuperated layout works effectively in applications characterized by higher hot source exploitation. The recompression layout adopting the CO 2 + SO 2 mixture presents a power block electric efficiency of 48.67% (2.33% higher than the respective sCO 2 cycle) and a reduction of the power block CAPEX from 1160 $/kW el to 1000 $/kW el when compared to the sCO2 configuration for a 100MW el size, while the dual recuperated layout exploiting the CO 2 + SO 2 mixture shows a power block electric efficiency of 39.58% (0.69% above the same sCO 2 cycle

Thermal efficiency gains enabled by using CO2 mixtures in supercritical power cycles

Energy, 2022

Abstract The present paper explores the utilisation of dopants to increase the critical temperatu... more Abstract The present paper explores the utilisation of dopants to increase the critical temperature of Carbon Dioxide (sCO2) as a solution towards maintaining the high thermal efficiencies of sCO2 cycles even when ambient temperatures compromise their feasibility. To this end, the impact of adopting CO2-based mixtures on the performance of power blocks representative of Concentrated Solar Power plants is explored, considering two possible dopants: hexafluorobenzene (C6F6) and titanium tetrachloride (TiCl4). The analysis is applied to a well-known cycle -Recuperated Rankine- and a less common layout -Precompression-. The latter is found capable of fully exploiting the interesting features of these non-conventional working fluids, enabling thermal efficiencies up to 2.3% higher than the simple recuperative configuration. Different scenarios for maximum cycle pressure (250–300 bar), turbine inlet temperature (550–700 ° C) and working fluid composition (10–25% molar fraction of dopant) are considered. The results in this work show that CO2-blends with 15–25%(v) of the cited dopants enable efficiencies well in excess of 50% for minimum cycle temperatures as high as 50 ° C. To verify this potential gain, the most representative pure sCO2 cycles have been optimised at two minimum cycle temperatures (32 ° C and 50 ° C), proving the superiority of the proposed blended technology in high ambient temperature applications.

Thermal efficiency gains enabled by using supercritical CO2 mixtures in Concentrated Solar Power applications

Supercritical Carbon Dioxide (sCO2) power cycles have been proposed for Concentrated Solar Power ... more Supercritical Carbon Dioxide (sCO2) power cycles have been proposed for Concentrated Solar Power (CSP) applications as a means to increase the performance and reduce the cost of state-of-the-art CSP systems. Nevertheless, the sensitivity of sCO2 systems to the usually hot ambient temperatures found in solar sites compromises the actual thermodynamic and economic gains that were originally anticipated by researchers of this innovative power cycle. In order to exploit the actual potential of sCO2 cycles, the utilization of dopants to shift the (pseudo)critical temperature of the working fluid to higher values is proposed here as a solution towards enabling exactly the same features of supercritical CO2 cycles even when ambient temperatures compromise the feasibility of the latter technology. To this end, this work explores the impact of adopting a CO2-based working mixture on the performance of a CSP power block, considering hexafluorobenzene (C6F6) and titanium tetrachloride (TiCl4) as possible dopants. Different cycle options and operating conditions are studied (250-300 bar and 550-700ºC) as well as molar fractions ranging between 10 and 25%. The results in this work confirm that CO2 blends with 15-25%(v) of the cited dopants enable efficiencies that are well in excess of 50% for minimum cycle temperatures as high as 50 or even 55ºC. It is also confirmed that, for these cycles, turbine inlet temperature and pressure hardly have any effect on the characteristics of the cycle that yields the best performance possible. In this regard, the last part of this work also shows that cycle layout should be an additional degree of freedom in the optimisation process inasmuch as the best performing layout changes depending on boundary conditions.

Experimental and analytical procedure for the characterization of innovative working fluids for power plants applications

Applied Thermal Engineering, 2020

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Advanced thermodynamic power cycles utilizing carbon dioxide based mixtures as working fluids for high temperature waste heat recovery

This paper proposed CO2 mixtures as working fluids in closed Brayton power cycles using flue gase... more This paper proposed CO2 mixtures as working fluids in closed Brayton power cycles using flue gases at relatively high temperature (400-450 °C) as waste heat source. Firstly, a comprehensive selection criterion is defined for choice of working fluids to be employed as additives in CO2 mixtures. Secondly, the thermodynamic properties of the mixtures are calculated at different molar compositions using an appropriate equation of state. The binary interaction parameters involved in the equation of state are obtained with the help of available experimental VLE data or by estimation method in case of nonavailability of the VLE data. As a benchmark, the study also investigates the thermodynamic performance of advanced sCO2 cycle layouts to compare with the performance of cycles operating with CO2 mixtures. Sensitivity analysis reveals that the power cycles operating with CO2-Novec5110 mixture (with 0.2 mole fraction of Novec fluids) show 3 percentage points rise in cycle thermodynamic effi...

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Adoption of the CO 2 + SO 2 mixture as working fluid for transcritical cycles: A thermodynamic assessment with optimized equation of state

Energy conversion and management, 2022

This paper focuses on the use of the CO 2 + SO 2 binary mixture as innovative working fluid for c... more This paper focuses on the use of the CO 2 + SO 2 binary mixture as innovative working fluid for closed transcritical power cycles with a minimum temperature above 50 • C. Starting from a literature review of the available experimental data on the mixture, the PC-SAFT EoS is identified as a suitable model to characterize the mixture behavior. Once the proper thermodynamic model is selected for this mixture, a comparison between the innovative transcritical cycle and the sCO 2 cycle is proposed for various plant layouts in order to find out the advantages of the innovative mixture. The analysis is presented fixing the cycle maximum temperature at 700 • C and the maximum pressure at 250 bar: the results depict an increment in cycle electric efficiency and cycle specific work, along with a lower temperature of heat introduction in the cycle for any considered configuration of transcritical CO 2 + SO 2 cycle, when compared to pure sCO 2. An economic analysis of the power block is then performed to support the selection of the innovative working fluid. Two of the most promising plant layouts are evidenced: the recompression layout is selected for highly efficient power blocks, while the dual recuperated layout works effectively in applications characterized by higher hot source exploitation. The recompression layout adopting the CO 2 + SO 2 mixture presents a power block electric efficiency of 48.67% (2.33% higher than the respective sCO 2 cycle) and a reduction of the power block CAPEX from 1160 $/kW el to 1000 $/kW el when compared to the sCO2 configuration for a 100MW el size, while the dual recuperated layout exploiting the CO 2 + SO 2 mixture shows a power block electric efficiency of 39.58% (0.69% above the same sCO 2 cycle

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Mathematical Modeling of In-cylinder process in a four stroke spark ignition engine using MATLAB (Final Year Project Report)

Thermal efficiency gains enabled by using CO 2 mixtures in supercritical power cycles

The present paper explores the utilisation of dopants to increase the critical temperature of Car... more The present paper explores the utilisation of dopants to increase the critical temperature of Carbon Dioxide (sCO 2) as a solution towards maintaining the high thermal efficiencies of sCO 2 cycles even when ambient temperatures compromise their feasibility. To this end, the impact of adopting CO 2-based mixtures on the performance of power blocks representative of Concentrated Solar Power plants is explored, considering two possible dopants: hexafluorobenzene (C 6 F 6) and titanium tetrachloride (TiCl 4). The analysis is applied to a well-known cycle-Recuperated Rankine-and a less common layout-Precompression-. The latter is found capable of fully exploiting the interesting features of these nonconventional working fluids, enabling thermal efficiencies up to 2.3% higher than the simple recuperative configuration. Different scenarios for maximum cycle pressure (250e300 bar), turbine inlet temperature (550e700 C) and working fluid composition (10e25% molar fraction of dopant) are considered. The results in this work show that CO 2-blends with 15e25%(v) of the cited dopants enable efficiencies well in excess of 50% for minimum cycle temperatures as high as 50 C. To verify this potential gain, the most representative pure sCO 2 cycles have been optimised at two minimum cycle temperatures (32 C and 50 C), proving the superiority of the proposed blended technology in high ambient temperature applications.

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THERMAL EFFICIENCY GAINS ENABLED BY USING SUPERCRITICAL CO2 MIXTURES IN CONCENTRATED SOLAR POWER APPLICATIONS

Supercritical Carbon Dioxide (sCO2) power cycles have been proposed for Concentrated Solar Power ... more Supercritical Carbon Dioxide (sCO2) power cycles have been proposed for Concentrated Solar Power (CSP) applications as a means to increase the performance and reduce the cost of state-of-the-art CSP systems. Nevertheless, the sensitivity of sCO2 systems to the usually hot ambient temperatures found in solar sites compromises the actual thermodynamic and economic gains that were originally anticipated by researchers of this innovative power cycle. In order to exploit the actual potential of sCO2 cycles, the utilization of dopants to shift the (pseudo)critical temperature of the working fluid to higher values is proposed here as a solution towards enabling exactly the same features of supercritical CO2 cycles even when ambient temperatures compromise the feasibility of the latter technology. To this end, this work explores the impact of adopting a CO2-based working mixture on the performance of a CSP power block, considering hexafluorobenzene (C6F6) and titanium tetrachloride (TiCl4) as possible dopants. Different cycle options and operating conditions are studied (250-300 bar and 550-700ºC) as well as molar fractions ranging between 10 and 25%. The results in this work confirm that CO2 blends with 15-25%(v) of the cited dopants enable efficiencies that are well in excess of 50% for minimum cycle temperatures as high as 50 or even 55ºC. It is also confirmed that, for these cycles, turbine inlet temperature and pressure hardly have any effect on the characteristics of the cycle that yields the best performance possible. In this regard, the last part of this work also shows that cycle layout should be an additional degree of freedom in the optimisation process inasmuch as the best performing layout changes depending on boundary conditions.

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ADVANCED THERMODYNAMIC POWER CYCLES UTILIZING CARBON DIOXIDE BASED MIXTURES AS WORKING FLUIDS FOR HIGH TEMPERATURE WASTE HEAT RECOVERY

This paper proposed CO2 mixtures as working fluids in closed Brayton power cycles using flue gase... more This paper proposed CO2 mixtures as working fluids in closed Brayton power cycles using flue gases at relatively high temperature (400-450 °C) as waste heat source. Firstly, a comprehensive selection criterion is defined for choice of working fluids to be employed as additives in CO2 mixtures. Secondly, the thermodynamic properties of the mixtures are calculated at different molar compositions using an appropriate equation of state. The binary interaction parameters involved in the equation of state are obtained with the help of available experimental VLE data or by estimation method in case of nonavailability of the VLE data. As a benchmark, the study also investigates the thermodynamic performance of advanced sCO2 cycle layouts to compare with the performance of cycles operating with CO2 mixtures. Sensitivity analysis reveals that the power cycles operating with CO2-Novec5110 mixture (with 0.2 mole fraction of Novec fluids) show 3 percentage points rise in cycle thermodynamic efficiency (0.219 versus 0.252) with lower cycle operating pressures as compared to recuperative with mass split sCO2 cycle. In case of CO2-R134a mixture working fluid (with 0.3 mole fraction of R134a), total efficiency of about 0.15 is obtained at cycle maximum pressure of 200 bars compared to simple recuperative sCO2 cycle with total efficiency of 0.13 at rather higher maximum pressure of 400 bars.

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Experimental and analytical procedure for the characterization of innovative working fluids for power plants applications

Applied Thermal Engineering, 2020

In the last years, several fluids have been proposed to replace steam as working fluid in power c... more In the last years, several fluids have been proposed to replace steam as working fluid in power cycle for con-verting thermal power into electricity. This paper describes the procedure to be adopted for the selection of any
innovative fluid which can be even mixtures of fluids. The first step consists of the working fluid characterization
in terms of thermodynamic properties through equations of state. The equations of state have to be calibrated on
experimental Vapour-Liquid Equilibrium measurements while, in the second step, the maximum operating
temperature is identified through thermal stability tests. Finally, the impact of the fluid thermodynamic prop-erties on the performance of the power cycle in which it is implemented must be assessed through modelling
tools. In this work, the procedure is discussed for the mixture of CO2and C6F14as a potential working fluid for
gas thermodynamic cycles with liquid phase compression. Results of the application of this mixture in a closed
cycle show the benefit of using a CO2/C6F14mixture which provides 3% points efficiency increase at 400 °C with
respect to the pure CO2together with a preliminary design of the expander.

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Carbon Dioxide Mixtures as Working Fluid for High-Temperature Heat Recovery: A Thermodynamic Comparison with Transcritical Organic Rankine Cycles

Energies

This study aims to provide a thermodynamic comparison between supercritical CO2 cycles and ORC cy... more This study aims to provide a thermodynamic comparison between supercritical CO2 cycles and ORC cycles utilizing flue gases as waste heat source. Moreover, the possibility of using CO2 mixtures as working fluids in transcritical cycles to enhance the performance of the thermodynamic cycle is explored. ORCs operating with pure working fluids show higher cyclic thermal and total efficiencies compared to supercritical CO2 cycles; thus, they represent a better option for high-temperature waste heat recovery provided that the thermal stability at a higher temperature has been assessed. Based on the improved global thermodynamic performance and good thermal stability of R134a, CO2-R134a is investigated as an illustrative, promising working fluid mixture for transcritical power cycles. The results show that a total efficiency of 0.1476 is obtained for the CO2-R134a mixture (0.3 mole fraction of R134a) at a maximum cycle pressure of 200 bars, which is 15.86% higher than the supercritical car...

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Exergetic, Economic and Exergo-Environmental Analysis of Bottoming Power Cycles Operating with CO2-Based Binary Mixture

Energies

This study focused on investigating the bottoming power cycles operating with CO2-based binary mi... more This study focused on investigating the bottoming power cycles operating with CO2-based binary mixture, taking into account exergetic, economic and exergo-environmental impact indices. The main intent is to assess the benefits of employing a CO2-based mixture working fluid in closed Brayton bottoming power cycles in comparison with pure CO2 working fluid. Firstly, selection criteria for the choice of suitable additive compound for CO2-based binary mixture is delineated and the composition of the binary mixture is decided based on required cycle minimum temperature. The decided CO2-C7H8 binary mixture with a 0.9 mole fraction of CO2 is analyzed in two cycle configurations: Simple regenerative cycle (SRC) and Partial heating cycle (PHC). Comparative analysis among two configurations with selected working fluid are carried out. Thermodynamic analyses at varying cycle pressure ratio shows that cycle with CO2-C7H8 mixture shows maximum power output and exergy efficiency at rather higher ...

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Exergetic performance and comparative assessment of bottoming power cycles operating with carbon dioxide–based binary mixture as working fluid

International Journal of Energy Research

Pure and Hydrocarbon Binary Mixtures as Possible Alternatives Working Fluids to the Usual Organic Rankine Cycles Biomass Conversion Systems

Energies

This study investigates the use of pure and hydrocarbons binary mixtures as potential alternative... more This study investigates the use of pure and hydrocarbons binary mixtures as potential alternatives working fluids in a usual biomass powered organic Rankine cycle (ORC). A typical biomass combined heat and power plant installed in Cremona (Italy) is considered as the benchmark. Eight pure hydrocarbons (linear and cyclic) and four binary mixtures of linear hydrocarbons were selected. The critical points of the binary mixtures at different composition were calculated using an in-house code developed in MATLAB© (R2018b) environment. Based on the critical point of a working fluid, supercritical and subcritical cycle configurations of ORC were analysed. A detailed thermodynamic comparison with benchmark cycle was carried out in view of cycle efficiency, maximum operating pressure, size of the turbine and heat exchangers. The supercritical cycles showed 0.02 to 0.03 points lower efficiency, whereas, subcritical cycles showed comparable efficiencies than that of the benchmark cycle. The cy...

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Exergetic optimization and comparison of combined gas turbine supercritical CO2 power cycles

Journal of Renewable and Sustainable Energy

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