• Energy Research

Carbon dioxide (CO2) emission forms the biggest portion of greenhouse gas emissions known to cause global warming, which can lead to climate change. One of the most widely recommended means of tack...

The entropy generation due to laminar mixed convection in the entrance of vertical channel between two isothermal/adiabatic parallel plates has been numerically investigated. The effects of the modified buoyancy parameter (Gr/Re) and other operating parameters such as the entrance temperature ratio (τ), Reynolds (Re), and Eckert (Ec) numbers on the entropy generation have been presented and discussed in this article. The optimum values of the modified buoyancy parameter (Gr/Re)optimum at which the entropy generation assumes its minimum has been obtained and found to be sensitive to the variation of the entrance temperature ratio (τ) while it is less sensitive to the variation of Re and Ec numbers. (Gr/Re)optimum was found to vary between 66.5 and 24 when τ varies between 1 and 2, respectively. On the other hand, (Gr/Re)optimum varies between 32 and 31 when Re number varies from 300 to 1500, respectively. The results revealed that the entropy generation increases with Ec that has almost no effect on the optimum value of the modified buoyancy parameter. The results also revealed that there exists an optimum value Re number at which the entropy generation assumes a minimum value. These values of Re number were found to be of minor independence on the buoyancy parameter since it varies between 480 for buoyancy-opposed flows and 490 for buoyancy-aided flows of Gr/Re = 90, respectively. The developments of other important parameters such as Bejan number have been also analyzed and presented.

The implementation of reduced syngas combustion mechanisms in numerical combustion studies has become inevitable in order to reduce the computational cost without compromising the predictions' accuracy. In this regard, the present study evaluates the predictive capabilities of selected detailed, reduced, and global syngas chemical mechanisms by comparing the numerical results with experimental laminar flame speed (LFS) values of lean premixed (LPM) syngas flames. The comparisons are carried out at varying equivalence ratios, syngas compositions, operating pressures, and preheat temperatures to represent a range of operating conditions of modern fuel flexible combustion systems. NOx emissions predicted by the detailed mechanism, GRI-Mech. 3.0, are also used to study the accuracy of the selected mechanisms under these operating conditions. Moreover, the selected mechanisms' accuracy in predicting the laminar flame thickness (LFT), species concentrations of the reactants, and OH profiles at different equivalence ratios and syngas compositions are investigated as well. The LFS is generally observed to increase with increasing equivalence ratio, hydrogen content in the syngas, and preheat temperature, while it is decreased with increasing operating pressure. This trend is followed by all mechanisms understudy. The global mechanisms of Watanabe–Otaka and Jones–Lindstedt for syngas are consistently observed to over-predict and under-predict the LFS up to an average of 60% and 80%, respectively. The reduced mechanism of Slavinskaya has an average error of less than 20%, which is comparable to the average error of the GRI-Mech. 3.0. It however over-predicts the flame thickness by up to 30% when compared to GRI-Mech. 3.0. The NO prediction by Li mechanism and the reduced mechanisms are observed to be within 10% prediction range of the GRI-Mech. 3.0 at intermediate equivalence ratio (φ=0.74) up to stoichiometry. Moving toward more lean conditions, there is significant difference between the GRI-Mech. 3.0 NO prediction and those of the reduced mechanisms due to relative importance of the prompt NOx at lower temperature compared to thermal NOx that is only accounted for by the GRI-Mech. 3.0.

Abstract Cooling the air before entering the compressor of a gas turbine of a combined cycle power plant is an effective method to boost the output power of both the gas and the steam turbines in hot regions. Usually, in hot area, the time at which the demand of power is highest coincides with the time of the largest drop of power generation due to the weather conditions, which shows the importance of air inlet cooling. However, fortunately, the daily peak period of electrical power demand coincides with the peak of solar radiation that is abundant in Saudi Arabia. This paper presents a novel system of cooling the gas turbine inlet air using a solar assisted absorption chiller. The study includes also a comparative analysis of a gas turbine combined cycle power plant performance when it is integrated with conventional and solar-assisted absorption chillers for inlet air cooling with the performance of the plant operating without inlet air cooling. The effect of ambient air temperature on the output power is investigated and reported. The advantage of air inlet cooling in boosting the power of the combined cycle in Dhahran is evident especially in summer. The study revealed that at the design hour under the weather conditions of Dhahran, KSA (July 17 th at 1 p.m.), the net power output of the plant drops from 267878 kW to 226361 kW at 48 °C (15.5% drop). While the gross power output of the gas turbine drops from 189472 kW to 151469 KW (20.1% drop) and the steam turbine from 84798 KW to 80495 KW (5.1% drop). Integrating conventional and solar-assisted absorption chillers increased the net power output of the combined cycle by 34964 KW and 37999 KW, respectively. Average and hourly performance during typical days have been conducted and presented. The plants without air inlet cooling system show higher carbon emissions (0.73 kg CO 2 /KWh) compared to the plant integrated with conventional and solar-assisted absorption chillers (0.509 kg CO 2 /KWh) and (0.508 kg CO 2 /KWh), respectively. Also, integrating a conventional absorption chiller shows the lowest levelized electricity cost.

AbstractShale reservoirs are characterized with very low productivity due to the high capillary pressure and the ultra-low rock permeability. This article presents an effective treatment to improve the hydrocarbon productivity for shale reservoirs by injecting thermochemical fluids. In this study, several measurements were carried out to determine the effectiveness of the presented treatment. Coreflood, rate transient analysis (RTA), and nuclear magnetic resonance (NMR) measurements were performed. The gas productivity was estimated, before and after the treatment, utilizing the gas flowrates and the pressure drop across the treated rocks. The improvement in gas productivity due to thermochemical fluids was estimated by calculating the productivity index (PI) and the absolute open flow (AOF) before and after the chemical injection. Also, the changes in the pore size distribution, due to chemical injection, were studied using NMR measurements. Results showed that thermochemical treatment can improve the gas productivity by 44%, increase the AOF by 450%, and reduce the capillary pressure by 47%. Also, NMR measurements showed that fractures were induced in the shale rocks after the treatment, which will improve the shale productivity. Ultimately, this study introduces, for the first time, the use of thermochemical fluids to improve the hydrocarbon productivity for shale reservoirs.

Abstract There has been much interest in the use of renewable resources for power generation as the world's energy demand and the concern over the rise in emissions increases. In the near term, however, renewable sources such as solar energy are expected to provide a small fraction of the world's energy demand due to intermittancy and storage problems. A potential solution is the use of hybrid solar-fossil fuel power generation. Previous work has shown the potential of steam redox reforming for hybridization. However, this type of reforming requires some water consumption (which may be infeasible in certain locations) as not all the water can be recovered through recycling. An alternative is to utilize dry (or CO 2 ) redox reforming. In this paper, a system analysis for a CO 2 redox reforming hybrid cycle and comparison of cycle and reformer performance between a CO 2 redox reformer and steam redox reformer hybrid cycle are presented. The effect of important operating parameters such as pressure, amount of reforming CO 2 , and the oxidation temperature on the reformer and cycle performance are discussed. Simulation results show that increasing the oxidation temperature or the amount of reforming CO 2 leads to higher reformer and cycle efficiencies. In addition, the comparison between the CO 2 and steam redox reformer hybrid cycles shows that the CO 2 cycle has the potential to have better overall performance.

Abstract Solar energy is an abundant resource in many countries in the Sunbelt, especially in the middle east, countries, where recent expansion in the utilization of natural gas for electricity generation has created a significant base for introducing integrated solar‐natural gas power plants (ISGPP) as an optimal solution for electricity generation in these countries. ISGPP reduces the need for thermal energy storage in traditional concentrated solar thermal plants and results in dispatchable power on demand at lower cost than stand-alone concentrated thermal power and much cheaper than photovoltaic plants. Moreover, integrating concentrated solar power (CSP) with conventional fossil fuel based thermal power plants is quite suitable for large-scale central electric power generation plants and it can be implemented in the design of new installed plants or during retrofitting of existing plants. The main objective of the present work is to investigate the possible modifications of an existing gas turbine cogeneration plant, which has a gas turbine of 150 MWe electricity generation capacity and produces steam at a rate of 81.4 at 394 °C and 45.88 bars for an industrial process, via integrating it with concentrated solar power system. In this regard, many simulations have been carried out using Thermoflow software to explore the thermo-economic performance of the gas turbine cogeneration plant integrated with LFR concentrated solar power field. Different electricity generating capacities of the gas turbine and different areas of solar collectors have been examined. Thermoflow software simulation results have been used to identify the optimal configuration and sizing of the gas turbine and the solar field of the integrated solar gas turbine cogeneration plant (ISGCPP) required to achieve the required steam generation with the minimum cost and environmental impact. The study revealed that ISGCPP can reduce the levelized electricity cost by 76–85% relative to the fully-solar-powered LFR power plant. Moreover, the study identified the configuration of ISGCPP with a gas turbine size of 50 MWe capacity and 93 ha of LFR solar field as the optimally integrated plant. It reduces the annual CO 2 emission by 100 k Tonne (18%) in comparison with that emitted by the corresponding conventional plant with 50 MWe and 400 k tonne (43.75%) compared with that emitted by the original conventional plant with a gas turbine if 150 MWe power generation capacity. The study revealed also that integrating the LFR technology with a gas turbine cogeneration power plant in locations with high solar insolation was proved to have more economic feasibility than CO 2 capturing technology. Under Dhahran weather conditions, the LEC of about 5 USȻ/kW h is obtained using the proposed optimally configured ISGCPP compared with about 7.5 USȻ/kW h obtained by the corresponding conventional cycle integrated with carbon capture technology. In other words, the ISGCPP reduces the LEC by 50% while achieving the same reduction of CO 2 emission by an equivalent conventional plant integrated with carbon capture technology.

AbstractIn situ combustion (ISC) in a one-dimensional combustion porous tube has been modeled numerically and presented in this article. The numerical model has been developed using the cmg stars (2017.10) software and it was used to model especial cases for validation against published experimental data. A comprehensive chemical reaction scheme has been developed and used to simulate the ISC process in the lab scale. Moreover, co-injection of oxygen with carbon dioxide (O2/CO2); and co-injection of enriched air (O2/N2) have been further investigated. In the case of using (O2/N2) as an oxidizer, increasing the oxygen ratio from 21% to 50% leads to increasing the oil recovery factor from 31.66% to 66.8%, respectively. In the case of using (O2/CO2) as an oxidizer, increasing the oxygen ratio from 21% to 50% leads to increasing the oil recovery factor from 35.77% to 70.3%, respectively. It was found that the co-injection of (O2/CO2) gives higher values of the oil recovery factor compared with that given when oxygen-enriched air (O2/N2) is injected for ISC. The change in the produced cumulative hydrogen and hydrogen sulfide is considered small whether using (O2/CO2) or (O2/N2) as an oxidizer.

The main purpose of this article is to present the results of an investigation on the economic and environmental impacts of applying Minimum Energy Performance Standards (MEPS) to the residential refrigerators in Saudi Arabia. The results are based on literature and market surveys conducted for this purpose. The energy consumption of different types of refrigerators in common use in Saudi Arabia were calculated and compared with those pertinent to the most energy efficient refrigerators that comply with the MEPS proposed by the Saudi Standards Organization (SASO) as well as that comply with Energy Star Standards. The possible energy savings over the next 20 years are estimated to range between 36.6 and 70.74 TWh depending on the scenario adopted to implement and enforce a MEPS program in Saudi Arabia. The associated possible reduction in carbon dioxide emission ranged between 22.24 and 42.97 million tonnes and results from avoiding burning an equivalent amount of crude oil that would have been burned to produce the saved energy. The amount of saved oil ranged between 61 and 117.92 million barrels of oil which worth an amount ranges between $ 6.77 and $ 13.09 billion.