Dual-pressure System Research Articles

Energy, exergy, emergy, and economic evaluation of a novel two-stage solar Rankine power plant.

This paper studies a solar-powered organic Rankine cycle-integrated cooling and electricity co-generation system. This system consists of a steam cycle, an organic Rankine cycle, the parabolic trough solar collectors' field, and a gas turbine cycle as well as a cooling heat exchanger for the co-production of power and cooling. The steam generator in this cycle is a dual pressure system that works with the thermal energy received from the solar collectors. The proposed process is analyzed thermodynamically and economically using the novel emergoeconomic approach. Then, to find the optimum operating parameters of the power plant, multi-objective optimization is performed by implementing the novel water cycle algorithm. The objectives of this optimization process are to maximize the system's efficiency and to minimize the monetary emergy rate of the products. This study shows an increase of 8% in the exergy efficiency (from 40.2 to 48.2%) after the optimization. The production cost decreased by 6.1% from 18.8 to 17.6 USD/GJ, and the emergoeconomic rate decreased by 18.9% from 27.1 to 22 sej/s. Furthermore, the power production in the proposed cycle compared to the base cycle increased by 111.7MW in the gas cycle and 39.4MW in the steam cycle.

Thermo-economic evaluations of dual pressure organic Rankine cycle (DPORC) driven by geothermal heat source

The thermo-economic evaluation of the dual pressure organic Rankine cycle system was presented based on the geothermal heat sources ranging from 100 to 180 °C. Two kinds of heat exchangers were selected to form four specific configuration layouts. The comparison between single and dual pressure systems was carried out. Moreover, the influence of economic parameters on cycle performance was analyzed. The electricity production cost (EPC), payback period (ppd), and saving-to-investment ratio are among the crucial considerations when the two stage evaporating pressures and pinch point temperatures are selected as independent variables. The results indicate that the dual pressure system possesses optimal EPC with the variation of low-evaporating pressure and the configuration layouts of type-FF and type-FP perform better. The cost of heat exchangers accounts for the largest proportion in the total cost of the system, followed by the expander. It can also be found that, for R1233zd, the average increasing rate of 20.87% in Wnet brings no economic benefits to the dual pressure system because the EPC also increases 12.98% averagely compared to the single pressure system. In addition, the impact of the annual loan interest rate, on-grid electricity price, and carbon tax of the system economic performance was discussed.

An innovative Organic Rankine Cycle system for integrated cooling and heat recovery

Converting a portion of the waste heat into usable power by implementing Rankine and Organic Rankine Cycles (ORC) on long-haul trucks is seen as a potential way to improve the overall system efficiency. To identify techno-economical heat sources across the drive cycle of a Heavy Duty Diesel Engine (HDDE), an energy and exergy analysis was performed on all the available heat streams. As a result, to recover the combined exhaust gases and coolant heat, a reference cascade system was analysed. Owing to the nature of this application, a size vs. performance optimisation was performed for the cascade system utilising water and R245fa fluid combination. Despite a 1.8% Brake Thermal Efficiency (BTE) improvement, the key consideration in the research and development efforts for ORC systems was identified as the investigation of technical paths that may improve the practicality of such a heat-to-power conversion concept. For this, simple holistic solutions were considered vital to meet the impending CO2 regulations. To provide a potential solution, an innovative dual-pressure ORC system is therefore proposed to partially address the shortcomings of the cascade system. This innovative system is a function of new working fluids (i.e. water blends), its associated cycle operating mode and a novel architecture (i.e. direct engine block heat recovery). A screening and evaluation methodology applied to water–organic blends is presented. Simulations conducted in Aspen HYSYS V8 showed that, compared to the reference cascade system, the proposed dual-pressure system has the potential to deliver an average of 20% improvement in the system power, a 50% reduction in the total heat exchanger footprint, and a reduced system complexity. These advantages bode well for an integrated and relatively compact engine cooling and exhaust heat recovery solution for future automotive HDDEs. Implementation of the proposed system at mid-speed high-load engine operating condition increased the overall BTE from 41.4% to a maximum of 43.6%.

Evaluation of CO2 liquefaction processes for ship-based carbon capture and storage (CCS) in terms of life cycle cost (LCC) considering availability

This study compared four liquefaction systems based on the life cycle cost (LCC) analysis, in order to select the optimal CO2 liquefaction system for ship-based carbon capture and storage (CCS). Three open processes and one closed process were considered: the Linde Hampson system, the Linde dual-pressure system, the precooled Linde Hampson system, and the closed system. The design parameters including pressure, temperature and refrigerant type were determined through repeated simulations or process optimizations. LCC analyses were employed for the evaluation of the four systems, considering the capital expenditure (CAPEX), the operational expenditure (OPEX), and the unavailability cost. The results showed that the OPEX value was the most dominant cost, accounting for over 80% of the LCC. The CAPEX and unavailability cost took 11% and 9%, respectively. The Linde Hampson system and Linde dual-pressure system showed higher CAPEX and OPEX values than those of the other systems. The closed system showed the lowest LCC while the precooled Linde Hampson system had only slightly higher values than the closed system. A sensitivity analysis was conducted to reveal the influence of several factors. LCC was re-estimated depending on different liquefaction conditions, disposal amounts, cooling water temperatures, electricity prices, CO2 trade costs, and uncertainty of the employed methodology. The LCC results had approximately 7% uncertainty, caused by the unreliability of the method for CAPEX estimation.

Evolution of the vertebrate cardio-pulmonary system.

Vertebrate lungs have long been thought to have evolved in fishes largely as an adaptation for life in hypoxic water. This view overlooks the possibility that lungs may have functioned to supply the heart with oxygen and may continue to serve this function in extant fishes. The myocardium of most vertebrates is avascular and obtains oxygen from luminal blood. Because oxygen-rich pulmonary blood mixes with oxygen-poor systemic blood before entering the heart of air-breathing fishes, lung ventilation may supply the myocardium with oxygen and expand aerobic exercise capabilities. Although sustained exercise in tetrapods is facilitated by septation of the heart and the formation of a dual pressure system, a divided cardio-pulmonary system may conflict with myocardial oxygenation because the right side of the heart is isolated from pulmonary oxygen. This may have contributed to the evolution of the coronary circulation.

Advanced Combined Cycle Alternatives With the Latest Gas Turbines

The last decade has seen remarkable improvements in industrial gas turbine size and performances. There is no doubt that the coming years are holding the promise of even more progress in these fields. As a consequence, the fuel utilization achieved by combined cycle power plants has been steadily increased. This is, however, also because of the developments in the heat recovery technology. Advances on the gas turbine side justify the development of new combined cycle schemes, with more advanced heat recovery capabilities. Hence, the system performance is spiraling upward. In this paper, we look at some of the heat recovery possibilities with the newly available gas turbine engines, characterized by a high exhaust temperature, a high specific work, and the integration of some gas turbine cooling with the boiler. The schemes range from classical dual pressure systems, to triple pressure systems with reheat in supercritical steam conditions. For each system, an optimum set of variables (steam pressures, etc.) is proposed. The effect of some changes on the steam cycle parameters, like increasing the steam temperatures above 570°C are also considered. Emphasis is also put on the influence of some special features or arrangements of the heat recovery steam generators, not only from a thermodynamic point of view.