Efficiency Enhancement for Natural Gas Liquefaction with CO₂ Capture and Sequestration through Cycles Innovation and Process Optimization

Liquefied natural gas (LNG) plants are energy intensive. As a result, the power plants operating these LNG plants emit high amounts of CO2. To mitigate global warming that is caused by the increase in atmospheric CO2, CO2 capture and sequestration (CCS) using amine absorption is proposed. However, the major challenge of implementing this CCS system is the associated power requirement, increasing power consumption by about 15-25%. Therefore, the main scope of this work is to tackle this challenge by minimizing CCS power consumption as well as that of the entire LNG plant though system integration and rigorous optimization. The power consumption of the LNG plant was reduced through improving the process of liquefaction itself. In this work, a genetic algorithm (GA) was used to optimize a propane pre-cooled mixed-refrigerant (C3-MR) LNG plant modeled using HYSYS software. An optimization platform coupling Matlab with HYSYS was developed. New refrigerant mixtures were found, with savings in power consumption as high as 13%. LNG plants optimization with variable natural gas feed compositions was addressed and the solution was proposed through applying robust optimization techniques, resulting in a robust refrigerant which can liquefy a range of natural gas feeds. The second approach for reducing the power consumption is through process integration and waste heat utilization in the integrated CCS system. Four waste heat sources and six potential uses were uncovered and evaluated using HYSYS software. The developed models were verified against experimental data from the literature with good agreement. Net available power enhancement in one of the proposed CCS configuration is 16% more than the conventional CCS configuration. To reduce the CO2 pressurization power into a well for enhanced oil recovery (EOR) applications, five CO2 pressurization methods were explored. New CO2 liquefaction cycles were developed and modeled using HYSYS software. One of the developed liquefaction cycles using NH3 as a refrigerant resulted in 5% less power consumption than the conventional multi-stage compression cycle. Finally, a new concept of providing the CO2 regeneration heat is proposed. The proposed concept is using a heat pump to provide the regeneration heat as well as process heat and CO2 liquefaction heat. Seven configurations of heat pumps integrated with CCS were developed. One of the heat pumps consumes 24% less power than the conventional system or 59% less total equivalent power demand than the conventional system with steam extraction and CO2 compression

Evaluation and Soft-Optimization for R410A Low-GWP Replacement Candidates through Testing and Simulation

The Air-Conditioning, Heating, and Refrigeration Institute (AHRI) announced an industry-wide cooperative research program to evaluate alternative refrigerants that have low global warming potential (GWP). R410A is a common refrigerant for air conditioning and heat pumping application but has a GWP of 2088. Drop-in tests of three R410A low-GWP alternative refrigerants (R32, D2Y60 and L-41A) in a 3 ton split heat pump unit are performed according to ASHRAE Standard 116-1995 test matrix. The test matrix is expanded to include extended cooling and heating conditions which represent extreme weather conditions. The results show that R32 and L-41A are good replacement candidates for R410A. However, the capacity of D2Y60 is lower than that of R410A by an average of 18% for cooling and 14% for heating. An in-house component based vapor compression system simulation tool is validated against the experimental data. The heat exchanger model used in the system simulation uses an in-house finite volume model. The compressor model uses the 10-coefficient R410A compressor map. A total of 32 experiments are used in the validation. The results of the validation are in good agreement with the experiments. Most of the predicted COP and capacity results lie within 5% of the measured values. The largest error is in the case of low temperature and extended condition tests because the mass flow rates were estimated and not measured. Soft optimization options, by varying the size of the compressor, are carried out to match the capacity to that of R410A. As the compressor size increases, the mass flow rate, power consumption, and capacity increase, while the COP decreases

Modelica-based Heat Pump Model for Transient and Steady-State Simulation Using Low-GWP Refrigerants

Due to the relatively high global warming potential (GWP) value of R410A, much effort has been devoted to the exploration of potential refrigerants to replace R410A in the heat pump applications. Those studies involving natural refrigerants, which are of zero or single-digit GWP values, have not yet demonstrated the readiness for the substitution because of various reasons such as low cycle efficiency, toxicity and flammability. Henceforward, some synthetic refrigerants whose GWP values are significantly lower than R410A such as R32 and some R32-based blends such as D2Y60, are getting more attention. To evaluate the transient performance of those low-GWP refrigerants, a Modelica-based heat pump model is developed to simulate a heat pump cycle during both steady state operations and transient operations. The model includes an efficiency-based compressor model, two segmented heat exchanger models, a control volume-based valve model and segmented pipe models. The heat exchanger model is capable of simulating multi-bank multi-circuit tube-fin heat exchangers with an arbitrary number of segments. The pipe model is developed based on the segmented heat exchanger model, and its implementation provides for better charge prediction compared to single lump model. In order to speed up the simulations, accelerated refrigerant property routines were developed for R32 based on REFPROP. System-level steady-state and transient simulations for several alternative low-GWP working fluids, R32 and D2Y60, are conducted. The simulation results are compared with the published experimental data obtained from the Alternative Refrigerant Evaluation Program (AREP). The data includes steady-state operation data based on ASHRAE A, B and C tests, and transient data from ASHRAE D cyclic operation test. The validation of R32 and D2Y60 steady-state data shows a maximum deviation of 7.5% and an average deviation of 4%. The transient simulation well captures the dynamic performance of vapor compression cycle during start-up and shut-down

Steady State And Transient Validation Of Heat Pumps Using Alternative Lower-GWP Refrigerants

The need for making a shift from refrigerants with high Global Warming Potential (GWP) to those with lower GWP is becoming increasingly important. A broad spectrum of alternative refrigerants have been proposed and their performance needs to be investigated through simulation and testing. To evaluate the performance of these candidates, the Air Conditioning, Heating and Refrigeration Institute (AHRI) has announced an industry-wide research program for studying the performance of low GWP refrigerants for major product categories such as air conditioners, heat pumps, chillers and refrigerators. One such study investigated alternatives to R410A, namely R32, D2Y60 and L41a. The investigation was conducted using a 3-ton residential split heat pump unit. This paper presents Simulink®-based steady state and transient analysis of the heat pump unit using two of the alternative refrigerants, R32 and D2Y60. A simplified, finite control volume approach is used to model the heat exchangers, while the expansion valve and compressor are treated as quasi-steady state components. The steady state and transient results compare well with measured data and the transient trends of the model are reproduced as expected, although with faster system response due to the exclusion of a TXV and accumulator. The proposed model can reasonably predict both steady state and transient performance of the heat pump for all the refrigerants analyzed under the operating conditions simulated. The results show that comparable capacities to the R410A baseline can be obtained using R32, although with a lower COP due to degradations in compressor efficiencies. For D2Y60 cycles, the capacities and COP are generally lower than the baseline cycle

Tribological characteristics comparison of formulated palm trimethylolpropane ester and polyalphaolefin for cam/tappet interface of direct acting valve train system

Purpose There is a continuous drive in automotive sector to shift from conventional lubricants to environmental friendly ones without adversely affecting critical tribological performance parameters. Because of their favorable tribological properties, chemically modified vegetable oils such as palm trimethylolpropane ester (TMP) are one of the potential candidates for the said role. To prove the suitability of TMP for applications involving boundary-lubrication regime such as cam/tappet interface of direct acting valve train system, a logical step forward is to investigate their compatibility with conventional lubricant additives. Design/methodology/approach In this study, extreme pressure and tribological characteristics of TMP, formulated with glycerol mono-oleate (GMO), molybdenum dithiocarbamate (MoDTC) and zinc dialkyldithiophosphate (ZDDP), has been investigated using four-ball wear tester and valve train test rig. For comparison, additive-free and formulated versions of polyalphaolefin (PAO) were used as reference. Moreover, various surface characterization techniques were deployed to investigate mechanisms responsible for a particular tribological behavior. Findings In additive-free form, TMP demonstrated better extreme pressure characteristics compared to PAO and lubricant additives which are actually optimized for conventional base-oils such as PAO, are also proved to be compatible with TMP to some extent, especially ZDDP. During cylinder head tests, additive-free TMP proved to be more effective compared to PAO in reducing friction of cam/tappet interface, but opposite behavior was seen when formulated lubricants were used. Therefore, there is a need to synthesize specialized friction modifiers, anti-wear and extreme pressure additives for TMP before using it as engine lubricant base-oil. Originality/value In this study, additive-free and formulated versions of bio-lubricant are tested for cam/tappet interface of direct acting valve train system of commercial passenger car diesel engine for the very test time. Another important aspect of this research was comparison of important tribological performance parameters (friction torque, wear, rotational speed of tappet) of TMP-based lubricants with conventional lubricant base oil, that is, PAO and its formulated version

Tribological characteristics comparison of formulated palm trimethylolpropane ester and polyalphaolefin for cam/tappet interface of direct acting valve train system

Purpose: There is a continuous drive in automotive sector to shift from conventional lubricants to environmental friendly ones without adversely affecting critical tribological performance parameters. Because of their favorable tribological properties, chemically modified vegetable oils such as palm trimethylolpropane ester (TMP) are one of the potential candidates for the said role. To prove the suitability of TMP for applications involving boundary-lubrication regime such as cam/tappet interface of direct acting valve train system, a logical step forward is to investigate their compatibility with conventional lubricant additives. Design/methodology/approach: In this study, extreme pressure and tribological characteristics of TMP, formulated with glycerol mono-oleate (GMO), molybdenum dithiocarbamate (MoDTC) and zinc dialkyldithiophosphate (ZDDP), has been investigated using four-ball wear tester and valve train test rig. For comparison, additive-free and formulated versions of polyalphaolefin (PAO) were used as reference. Moreover, various surface characterization techniques were deployed to investigate mechanisms responsible for a particular tribological behavior. Findings: In additive-free form, TMP demonstrated better extreme pressure characteristics compared to PAO and lubricant additives which are actually optimized for conventional base-oils such as PAO, are also proved to be compatible with TMP to some extent, especially ZDDP. During cylinder head tests, additive-free TMP proved to be more effective compared to PAO in reducing friction of cam/tappet interface, but opposite behavior was seen when formulated lubricants were used. Therefore, there is a need to synthesize specialized friction modifiers, anti-wear and extreme pressure additives for TMP before using it as engine lubricant base-oil. Originality/value: In this study, additive-free and formulated versions of bio-lubricant are tested for cam/tappet interface of direct acting valve train system of commercial passenger car diesel engine for the very test time. Another important aspect of this research was comparison of important tribological performance parameters (friction torque, wear, rotational speed of tappet) of TMP-based lubricants with conventional lubricant base oil, that is, PAO and its formulated version

Laminar mixed convection boundary layer flow induced by a permeable surface stretched with prescribed skin friction boundary conditions

The mixed laminar boundary layer flow and heat transfer on a permeable stretched surface moving with prescribed skin friction are studied. Three major cases, which correspond to complete similarity solutions, are considered. The cases are combinations of power law indices n and m representing temperature and skin friction distributions, respectively. The first case ( n  = 0, m  = 0.5) corresponds to isothermal stretched surface with skin friction at the surface scales as x 1/4 . The second case ( n  = 1, m  = 1) is a linear temperature and skin friction distribution along the vertical stretched surface. The third case ( n  = −1, m  = 0) represents inverse temperature variation along the surface with prescribed skin friction of the order of x −1/2 . Similarity solutions are obtained for the surface stretched in a stagnant air with Prandtl number = 0.72. The effect of suction/injection velocity ( f w ) and the buoyancy parameter ( λ ) is studied in detail. The results show that the heat transfer coefficient along the surface is enhanced for assisting flow ( λ  > 0) at any value of f w for the first and second cases, while it is reduced for the third case. However, the opposite is true for the opposing flow ( λ  < 0). Furthermore, suction enhances the heat transfer coefficient, whereas injection degrades it at any fixed λ for the first and second prescribed skin friction boundary conditions, and the opposite is true for the third case

Comprehensive Investigation of Factors Influencing University Students’ Academic Performance in Saudi Arabia

Academic success in undergraduate programs is indicative of potential achievements for graduates in their professional careers. The reasons for an outstanding performance are complex and influenced by several principles and factors. An example of this complexity is that success factors might change depending on the culture of students. The relationship of 32 factors with the reported academic performance (RAP) was investigated by using a survey distributed over four key universities in Saudi Arabia. A total of 3565 Saudi undergraduate students completed the survey. The examined factors included those related to upbringing, K-12 education, and structured and unstructured activities. Statistical results validate that many factors had a significant relationship with the RAP. Among those factors, paternal’s education level and work field, type of intermediate and high schools, and the attendance of prayers in mosques were significantly associated with the reported performance. This study provides important insights into the potential root causes of success so that they can be targeted by educators and policy makers in the effort to enhance education outcomes

Free convection heat transfer inside square water-filled shallow enclosures.

Experimental study on free convection heat transfer was carried out inside shallow square enclosures filled with water. Two enclosures were used with size L × L × H (m3), where L and H are the side length and the inside thickness of the enclosure, respectively. Two different aspect ratios, κ = L/H, 7.143 and 12.0 were used. Constant heat flux boundary condition was applied at the bottom surface and stream of ambient air was applied at the top surface. Different values of constant heat fluxes were used as boundary conditions. For each aspect ratio of the enclosure, average Nusselt numbers were developed and correlated with the modified Rayleigh number. The results show that the heat transfer coefficient increases with the modified Rayleigh number with observed overlapping region between the two aspect ratios. A general overall correlation was developed using the aspect ratio as a parameter. The results also show that at the overlapping zone, the Nusselt number decreases as the aspect ratio increases for the fixed modified Rayleigh number

Thermal analysis, microstructure and acoustic characteristics of some hybrid natural insulating materials

Hybrid new insulating materials are proposed using different binders such as cornstarch, glue (wood adhesive) and white cement. Five hybrid samples were produced from date palm trees surface fibers (PTSF) and Apple of Sodom fibers (AOSF) for different ratio of mass and densities. One hybrid sample was produced from AOSF and agave fiber (AF) using glue (wood adhesive) as a binder. Thermal conductivity measurements were conducted for all samples at temperature ranging from 10 °C to 50 °C which resulted in average values of 0.04234–0.05291 W/m K. Microstructure analysis was conducted for AF using the scanning electron microscope (SEM) which resulted in an average diameter range of 170–259 μm. Infrared (FT- IR) Fourier transformation spectra of AF showed ranges of wavenumber functional groups. Thermogravimetric analysis (TGA and DTGA) was obtained for AF and showed that the fibers start to degrade and decompose at about 221 °C where the fiber loses 5% of its original mass. The Differential Scanning Calorimetry (DSC) analysis is also reported for AF and shows a broad endothermic transition range of 292–357 °C with a peak at 353 °C. Sound absorption coefficients were obtained for the hybrid samples and indicate the potential of using these samples for sound absorption. The current tests indicate the feasibility of using such hybrid samples as insulating materials for heat as well as sound absorption. The proposed tested hybrid samples are all natural, safe for human beings, utilize the wasted material and biodegradable therefore, it is good for saving our environment