Search Results (6)

Libya is facing a serious challenge in its sustainable development because of its complete dependence on traditional fuels in meeting its growing energy demand. On the other hand, more intensive energy utilization accommodating multiple energy resources, including renewables, has gained considerable attention. This article is motivated by the obvious need for research on this topic due to the shortage of applications concerning the prospects of the hybridization of energy systems for electric power generation in Libya. The 283 MW single-cycle gas turbine operating at the Sarir power plant located in the Libyan desert is considered a case study for a proposed Integrated Solar Combined Cycle (ISCC) system. By utilizing the common infrastructure of a gas-fired power plant and concentrating solar power (CSP) technology, a triple hybrid system is modeled using the EES programming tool. The triple hybrid system consists of (i) a closed Brayton cycle (BC), (ii) a Rankine cycle (RC), which uses heat derived from a parabolic collector field in addition to the waste heat of the BC, and (iii) an organic Rankine cycle (ORC), which is involved in recovering waste heat from the RC. A thermodynamic analysis of the developed triple combined power plant shows that the global power output ranges between 416 MW (in December) and a maximum of 452.9 MW, which was obtained in July. The highest overall system efficiency of 44.3% was achieved in December at a pressure ratio of 12 and 20% of steam fraction in the RC. The monthly capital investment cost for the ISCC facility varies between 52.59 USD/MWh and 58.19 USD/MWh. From an environmental perspective, the ISCC facility can achieve a carbon footprint of up to 319 kg/MWh on a monthly basis compared to 589 kg/MWh for the base BC plant, which represents a reduction of up to 46%. This study could stimulate decision makers to adopt ISCC power plants in Libya and in other developing oil-producing countries. Full article

This paper presents thermodynamic and improvement potential analyses of a helium closed-cycle gas turbine power plant (Oberhausen II) and dominant plant components at four loads. DESIGN LOAD represents optimal operating conditions that cannot be obtained in exploitation but can be used as a guideline for further improvements. In real plant exploitation, the highest plant efficiency is obtained at NOMINAL LOAD (31.27%). Considering all observed components, the regenerator (helium-helium heat exchanger) is the most sensitive to the ambient temperature change. An exact comparison shows that the efficiency decrease of an open-cycle gas turbine power plant during load decrease is approximately two and a half or more times higher in comparison to a closed-cycle gas turbine power plant. Plant improvement potential related to all turbomachines leads to the conclusion that further improvement of the most efficient turbomachine (High Pressure Turbine—HPT) will increase whole plant efficiency more than improvement of any other turbomachine. An increase in the HPT isentropic efficiency of 1% will result in an average increase in whole plant efficiency of more than 0.35% at all loads during plant exploitation. In the final part of this research, it is investigated whether the additional heater involvement in the plant operation results in a satisfactory increase in power plant efficiency. It is concluded that in real exploitation conditions (by assuming a reasonable helium pressure drop of 5% in the additional heater), an additional heating process cannot be an improvement possibility for the Oberhausen II power plant. Full article

To address the rising electricity demand and greenhouse gas concentration in the environment, considerable effort is being carried out across the globe on installing and operating renewable energy sources. However, the renewable energy production is affected by diurnal and seasonal variability. To ensure that the electric grid remains reliable and resilient even for the high penetration of renewables into the grid, various types of energy storage systems are being investigated. In this paper, a compressed-air energy storage (CAES) system integrated with a natural gas combined-cycle (NGCC) power plant is investigated where air is extracted from the gas turbine compressor or injected back into the gas turbine combustor when it is optimal to do so. First-principles dynamic models of the NGCC plant and CAES are developed along with the development of an economic model. The dynamic optimization of the integrated system is undertaken in the Python/Pyomo platform for maximizing the net present value (NPV). NPV optimization is undertaken for 14 regions/cases considering year-long locational marginal price (LMP) data with a 1 h interval. Design variables such as the storage capacity and storage pressure, as well as the operating variables such as the power plant load, air injection rate, and air extraction rate, are optimized. Results show that the integrated CAES system has a higher NPV than the NGCC-only system for all 14 regions, thus indicating the potential deployment of the integrated system under the assumption of the availability of caverns in close proximity to the NGCC plant. The levelized cost of storage is found to be in the range of 136–145 $/MWh. Roundtrip efficiency is found to be between 74.6–82.5%. A sensitivity study with respect to LMP shows that the LMP profile has a significant impact on the extent of air injection/extraction while capital expenditure reduction has a negligible effect. Full article

Today, with the increases in organic fuel prices and growing legislative restrictions aimed at increasing environmental safety and reducing our carbon footprint, the task of increasing thermal power plant efficiency is becoming more and more topical. Transforming combusting fuel thermal energy into electric power more efficiently will allow the reduction of the fuel cost fraction in the cost structure and decrease harmful emissions, especially greenhouse gases, as less fuel will be consumed. There are traditional ways of improving thermal power plant energy efficiency: increasing turbine inlet temperature and utilizing exhaust heat. An alternative way to improve energy efficiency is the use of supercritical CO₂ power cycles, which have a number of advantages over traditional ones due to carbon dioxide’s thermophysical properties. In particular, the use of carbon dioxide allows increasing efficiency by reducing compression and friction losses in the wheel spaces of the turbines; in addition, it is known that CO₂ turbomachinery has smaller dimensions compared to traditional steam and gas turbines of similar capacity. Furthermore, semi-closed oxy–fuel combustion power cycles can reduce greenhouse gases emissions by many times; at the same time, they have characteristics of efficiency and specific capital costs comparable with traditional cycles. Given the high volatility of fuel prices, as well as the rising prices of carbon dioxide emission allowances, changes in efficiency, capital costs and specific greenhouse gas emissions can lead to a change in the cost of electricity generation. In this paper, key closed and semi-closed supercritical CO₂ combustion power cycles and their promising modifications are considered from the point of view of energy, economic and environmental efficiency; the cycles that are optimal in terms of technical and economic characteristics are identified among those considered. Full article

This study aims to improve existing fossil gas turbine power plants by waste heat recovery. These power plants function with an air simple cycle (ASC) and are implemented where water resources are limited. Modeling and simulation of ASC and two advanced energy conversion systems are performed. They are the gas turbine–air bottoming cycle (GT-ABC) and gas turbine–supercritical carbon dioxide bottoming cycle (GT-sc-CO₂BC). The main intent is to assess the benefits of employing sc-CO₂ as a working fluid in a closed Brayton bottoming cycle compared to air, based on the energetic and exergetic performance and economic and environmental impact. Analyses of ASC, GT-ABC, and GT-sc-CO₂BC are performed for various topping gas turbine powers: large (plant 1); medium (plant 2); and low (plant 3). The results of the energetic and exergetic analyses indicate that there is a significant improvement in the output power (ranging from 22% to 25%); and energy and exergy efficiencies of GT-ABC and GT-sc-CO₂BC (up to 8% and 11%, respectively) compared to that of ASC. To provide better insight into the behavior of these technologies and achieve their better integration, we investigate the influence of varying the bottoming compressor pressure ratio, the ambient temperature, and the gas flow rate in the bottoming cycle. The results of the environmental and economic analyses show that the amount of CO₂ emissions in GT-sc-CO₂BC is reduced by 10% more than in GT ABC. The results also show that GT-ABC improves the NPV between 17.69% and 30% but GT-sc-CO₂BC improves it even more, between 25.79% and 33.30%. Full article

This paper presents a detailed exergetic analysis of a novel high-temperature Solar Assisted Combined Cycle (SACC) power plant. The system includes a solar field consisting of innovative high-temperature flat plate evacuated solar thermal collectors, a double stage LiBr-H₂O absorption chiller, pumps, heat exchangers, storage tanks, mixers, diverters, controllers and a simple single-pressure Combined Cycle (CC) power plant. Here, a high temperature solar cooling system is coupled with a conventional combined cycle, in order to pre-cool gas turbine inlet air in order to enhance system efficiency and electrical capacity. In this paper, the system is analyzed from an exergetic point of view, on the basis of an energy-economic model presented in a recent work, where the obtained main results show that SACC exhibits a higher electrical production and efficiency with respect to the conventional CC. The system performance is evaluated by a dynamic simulation, where detailed simulation models are implemented for all the components included in the system. In addition, for all the components and for the system as whole, energy and exergy balances are implemented in order to calculate the magnitude of the irreversibilities within the system. In fact, exergy analysis is used in order to assess: exergy destructions and exergetic efficiencies. Such parameters are used in order to evaluate the magnitude of the irreversibilities in the system and to identify the sources of such irreversibilities. Exergetic efficiencies and exergy destructions are dynamically calculated for the 1-year operation of the system. Similarly, exergetic results are also integrated on weekly and yearly bases in order to evaluate the corresponding irreversibilities. The results showed that the components of the Joule cycle (combustor, turbine and compressor) are the major sources of irreversibilities. System overall exergetic efficiency was around 48%. Average weekly solar collector exergetic efficiency ranged from 6.5% to 14.5%, significantly increasing during the summer season. Conversely, absorption chiller exergy efficiency varies from 7.7% to 20.2%, being higher during the winter season. Combustor exergy efficiency is stably close to 68%, whereas the exergy efficiencies of the remaining components are higher than 80%. Full article