Regenerative Rankine Cycle Research Articles

A comparative study between parabolic trough and solar tower technologies in Solar Rankine Cycle and Integrated Solar Combined Cycle plants

Simulations were carried out to predict the performance of a Solar Rankine Cycle (SRC) and an Integrated Solar Combined Cycle (ISCC) when combined with two different solar field configurations based on parabolic trough and power tower systems. For the selected cases, yearly plant performance was computed under real operating conditions on a one hour basis. A computing procedure was developed by integrating two commercial softwares with in-house computer code. Thermodynamic performance was featured for every plant configuration both at nominal and part load conditions. A single reheat regenerative Rankine cycle was chosen for the SRC plant whereas a commercial gas turbine, i.e. Siemens SGT-800, with a dual pressure heat recovery steam generator (HRSG) was assumed for the ISCC plant. As far as the heat transfer fluid (HTF) is concerned, molten salt was chosen to transfer heat to the water loop in the SRC. Synthetic oil was considered in the ISCC plant. Plants were assumed to be located in a Southern Spain site.The comparative analysis was mainly focused on the influence of CSP technology on global solar energy conversion efficiency of both SRC and ISCC plants. Special attention was devoted to assess trough collectors (PTCs) against the solar tower (ST) system in terms of intercepted radiation and thermal power sent to the power block. The ISCC coupled with a ST was found to assure the highest annual solar-to-electric efficiency of 21.8%. This is the result of both higher collection efficiency of ST compared to PTCs and higher conversion efficiency of solar energy introduced into the combined cycle, as compared to SRC.

Improvement of regenerative Rankine cycle using absorption heat boosters

In the present work, a new technique is proposed for feedwater heating in Low Pressure (LP) turbine section of regenerative Rankine cycle. Main objective of this technique is to minimise exergy destruction in feedwater heating. The proposed technique comprised of using absorption heat boosters i.e. Absorption Heat Pump (AHP) and Absorption Heat Transformer (AHT) with LiBr–water as the working fluid. Heat booster consumes heat in the form of low quality steam from LP turbine, deliver it at better quality in absorber, and in some configuration, condenser. This heat is used for feedwater heating, which results in reduction in exergy destruction in the process. Various configurations of LP turbine section with absorption heat booster have been simulated. Results show that overall increased power output as high as 0.54% from LP turbine can be obtained. Exergy analysis of LP turbine section with heat booster shows that exergy saved through this technique get transformed into equal amount of additional power output.

Thermodynamic Performance Analysis of Ammonia-Water Rankine Cycles Using Heat Sources of High and Low Temperatures

In this study, thermodynamic performances of ammonia-water Rankine (AWR) cycle and regenerative Rankine (AWRR) cycle are comparatively investigated. Special attention is focused on the effects of ammonia concentration and turbine inlet pressure on the performance of system using heat sources of high temperature of 300 oC and low temperature of 150 oC. The behavior of important system variables including mass flow ratio of working fluid, net work production, and thermal efficiency are closely examined. Results show that performance characteristics for heat sources of high and low temperatures are quite different each other. For the high-temperature source, the thermal efficiency has a minimum in AWR system while it has a maximum in AWRR with respect to ammonia concentration in the range of 65% to 75%. For low-temperature source, however, the thermal efficiency decreases with ammonia concentration in the range of ammonia concentration higher than 95% for both AWR system and AWRR system and the effect of regenerator is negligible.

Heat integration of regenerative Rankine cycle and process surplus heat through graphical targeting and mathematical modeling technique

Heat Integration, an effective energy-saving technology, has been popularized in many fields. In the current paper, Pinch-based Heat Integration technology is applied in the Heat Integration of process surplus heat (PSH) and regenerative Rankine cycle (RRC)-based steam power plant. PSH is recovered by preheating boiler feed water (BFW) to reduce consumption of steam extracted from the turbine. A systematic hybrid methodology of graphical targeting and mathematical modeling is developed. The objective function is minimal fuel consumption of steam power plant, rather than maximal heat recovery. The terminal temperature and heat load of process-heated BFW are two decision variables. The graphical targeting method is proposed to ascertain the bounds and constraints of the two decision variables. A mathematical model incorporating rigorous simulation of turbine is formulated to achieve the optimal Heat Integration scheme. Two case studies, one pertaining to the Heat Integration of RRC and PSH at low temperature and the other involving the Heat Integration of RRC and PSH at medium temperature, are elaborated. The results show that significant fuel savings and cold utility reductions are achieved by using the proposed methodology. Compared with other methods of PSH utilization, the proposed Heat Integration scheme is more feasible and effective.

A double-pinch criterion for regenerative Rankine cycles

A double-pinch criterion for closed feedwater heaters (FWH) of regenerative Rankine cycles is presented. The FWHs are modeled as counter-current heat exchangers. Thus, two potential pinch positions in the FWH exist: (i) at the exit of the bleed (drain) and (ii) at the onset of condensation. For a given heat duty in the FWH, feed inlet temperature and flowrate, the extraction flowrate and pressure should be chosen to achieve the same minimal approach temperature at the two potential pinch points. An analytical proof is given for a fixed pinch value for the case that the drain enters the condenser, based on weak assumptions. Additionally, the criterion is numerically demonstrated for fixed pinch value and for fixed heat exchanger area using the most common configurations: drain to condenser, drain to deaerator, and drain cascaded to next FWH. A similar criterion is developed for the case that the drain is pumped (upwards or downwards) and mixed with the feedwater. The double pinch criterion simplifies the optimization procedure and results in significant efficiency increase for fixed heat exchanger area. For numerical reasons it is advisable to use the pressure as the optimization variable and calculate the heat duty and mass flowrate.

A non-conventional interpretation of thermal regeneration in steam cycles

The paper aims to contribute to a better understanding of the thermodynamic concept of heat regeneration in steam power plants with a finite number of bleedings. A regenerative Rankine cycle is compared to a complex system (CHC – complete hybrid cycle) composed by one non-regenerative Rankine cycle (HEC – hybrid engine cycle) and more reverse cycles (RCs – reverse cycles), as many as the number of the bleedings, able to pump heat from the condenser to a series of surface feedwater heaters, disposed upstream of the steam plant boiler. The COPs (coefficients of performance) of the heat pumps are evaluated, and new interesting formulations of the efficiency of the regenerative steam cycle are proposed.In particular a steam cycle with two bleedings is analyzed, neglecting heat losses and pressure drops in the boiler and considering irreversibility only along the expansion line of the steam turbine and into the feedwater heaters. The efficiency and the work of the regenerative cycle are compared to the analogous values of the CHC cycle composed by one simple steam cycle (HEC) and two heat pump cycles (RCs), with steam as the working fluid. The two reverse cycles are considered completely reversible and raising heat from the condenser temperature to the bled steam condensing temperature. The paper shows the most significant results of the study in order to analyze the regenerative cycle and the CHC cycle in comparison with the non-regenerative Rankine cycle; in particular, the analysis is focused on the evaluation of the useful work, the heat supplied and the heat rejected for the examined cycles.

Trigeneration scheme for energy efficiency enhancement in a natural gas processing plant through turbine exhaust gas waste heat utilization

The performance of Natural Gas Processing Plants (NGPPs) can be enhanced with the integration of Combined Cooling, Heating and Power (CCHP) generation schemes. This paper analyzes the integration of a trigeneration scheme within a NGPP, that utilizes waste heat from gas turbine exhaust gases to generate process steam in a Waste Heat Recovery Steam Generator (WHRSG). Part of the steam generated is used to power double-effect water–lithium bromide (H2O–LiBr) absorption chillers that provide gas turbine compressor inlet air-cooling. Another portion of the steam is utilized to meet part furnace heating load, and supplement plant electrical power in a combined regenerative Rankine cycle. A detailed techno-economic analysis of scheme performance is presented based on thermodynamic predictions obtained using Engineering Equation Solver (EES). The results indicate that the trigeneration system could recover 79.7MW of gas turbine waste heat, 37.1MW of which could be utilized by three steam-fired H2O–LiBr absorption chillers to provide 45MW of cooling at 5°C. This could save approximately 9MW of electric energy required by a typical compression chiller, while providing the same amount of cooling. In addition, the combined cycle generates 22.6MW of additional electrical energy for the plant, while process heating reduces furnace oil consumption by 0.23 MSCM per annum. Overall, the trigeneration scheme would result in annual natural gas fuel savings of approximately 1879 MSCM, and annual operating cost savings of approximately US$ 20.9 million, with a payback period of 1year. This study highlights the significant economical and environmental benefits that could be achieved through implementation of the proposed integrated cogeneration scheme in NGPPs, particularly in elevated ambient temperature and humidity conditions such as encountered in Middle East facilities.

암모니아-물 작동유체의 부분증발유동을 적용한 재생 랭킨사이클에 관한 연구

ABSTRACT:The power cycle using ammonia-water mixture as a working fluid is a possible way to improve efficiency of the system of low-temperature source. In this work thermodynamic performance of the ammonia-water regenerative Rankine cycle with partial-boiling flow is analyzed for purpose of extracting maximum power from the source. Effects of the system parameters such as mass fraction of ammonia, turbine inlet pressure or ratio of partial-boiling flow on the system are parametrically investigated. Results show that the power output increases with the mass fraction of ammonia but has a maximum value with respect to the turbine inlet pressure, and is able to reach 22 kW per unit mass flow rate of source air at 180℃.Keywords:Rankine cycle(랭킨사이클), Regeneration(재생), Partial-boiling(부분증발), Ammonia- water mixture(암모니아-물 혼합물), Maximum specific work(최대비동력) †Corresponding author Tel.: +82-54-478-7292; fax: +82-54-478-7319 E-mail address: khkim@kumoh.ac.kr 기 호 설 명   ：정압비열 [kJ/kgK] ：깁스자유에너지 [kJ/kg] ：비엔탈피 [kJ/kg]

저온 열원 활용을 위한 암모니아-물 재생 랭킨 사이클의 성능 해석

It is a great interest to convert more energy in the heat source into the power and to improve the efficiency of power generating processes. Since the efficiency of power generating processes becomes poorer as the temperature of the source decreases, to use an ammonia-water mixture instead of water as working fluid is a possible way to improve the efficiency of the system. In this work performance of ammonia-water regenerative Rankine cycle is investigated for the purpose of extracting maximum power from low-temperature waste heat in the form of sensible energy. Special attention is paid to the effect of system parameters such as mass fraction of ammonia and turbine inlet pressure on the characteristics of system. Results show that the power output increases with the mass fraction of ammonia in the mixture, however workable range of the mass fraction becomes narrower as turbine inlet pressure increases and is able to reach 16.5kW per unit mass flow rate of source air at .

An efficient way to use medium-or-low temperature solar heat for power generation – integration into conventional power plant

This paper demonstrates that the medium-or-low temperature solar heat can be used to generate power efficiently by integrating into conventional coal-fired power plants. In so-called solar aided power generation (SAPG) technology, medium-or-low temperature solar heat is used to replace parts of bled-off steams in regenerative Rankine cycle to pre-heat feedwater. Thermal oil can be used as solar heat carrier and no solar steam needs to be generated, therefore the pressure of solar system can be much lower than that of the solar collector using water/steam as the heat carrier. A 200 MW coal-fired thermal power plant is selected as the case study to demonstrate the advantages of the SAPG technology in terms of solar to power efficiency, specific fuel and steam consumption rates, under various integration scenarios. The results indicate that there is a great potential and effect for low or medium solar heat to be used for power generation purposes through SAPG approach.

Multi-point and Multi-level Solar Integration into a Conventional Coal-Fired Power Plant

Solar-aided power generation (SAPG) is capable of integrating solar thermal energy into a conventional thermal power plant, at multi-points and multi-levels, to replace parts of steam extractions in the regenerative Rankine cycle. The integration assists the power plant to reduce coal (gas) consumption and pollution emission or to increase power output. The overall efficiencies of the SAPG plants with different solar replacements of extraction steam have been studied in this paper. The results indicate that the solar thermal to electricity conversion efficiencies of the SAPG system are higher than those of a solar-alone power plant with the same temperature level of solar input. The efficiency with solar input at 330 °C can be as high as 45% theoretically in a SAPG plant. Even the low-temperature solar heat at about 85 °C can be used in the SAPG system to heat the lower temperature feedwater, and the solar to electricity efficiency is nearly 10%. However, the low-temperature heat resource is very hard to be used for power generation in other types of solar power plants. Therefore, the SAPG plant is one of the most efficient ways for solar thermal power generation.

Solar thermal aided power generation

Fossil fuel based power generation is and will still be the back bone of our world economy, albeit such form of power generation significantly contributes to global CO 2 emissions. Solar energy is a clean, environmental friendly energy source for power generation, however solar photovoltaic electricity generation is not practical for large commercial scales due to its cost and high-tech nature. Solar thermal is another way to use solar energy to generate power. Many attempts to establish solar (solo) thermal power stations have been practiced all over the world. Although there are some advantages in solo solar thermal power systems, the efficiencies and costs of these systems are not so attractive. Alternately by modifying, if possible, the existing coal-fired power stations to generate green sustainable power, a much more efficient means of power generation can be reached. This paper presents the concept of solar aided power generation in conventional coal-fired power stations, i.e., integrating solar (thermal) energy into conventional fossil fuelled power generation cycles (termed as solar aided thermal power). The solar aided power generation (SAPG) concept has technically been derived to use the strong points of the two technologies (traditional regenerative Rankine cycle with relatively higher efficiency and solar heating at relatively low temperature range). The SAPG does not only contribute to increase the efficiencies of the conventional power station and reduce its emission of the greenhouse gases, but also provides a better way to use solar heat to generate the power. This paper presents the advantages of the SAPG at conceptual level.

Analysis of a repowering proposal to the power generation system of a steel mill plant through the exergetic cost method

The rational use of energy became a priority for all industries in Brazil after the energetic rationing in 2001. The aim of this work is to assess a proposal of a power generation system for Companhia Siderúrgica Tubarão, a steel mill plant. The current system is based on a regenerative Rankine cycle using two gases from steel production—blast furnace gas (BFG) and coke oven gas (COG)—to generate electric power and occasionally steam for the process. The proposed system is a combined cycle comprising two gas turbines, two heat recovery steam generators (HRSGs), and a steam turbine. The fuel for the gas turbines is BFG, and the supplementary firing of HRSG uses COG. The proposed HRSGs work at three pressure levels. The system was assessed by means of two thermoeconomic methodologies, Theory of Exergetic Cost and Thermoeconomic Functional Analysis; exergetic and monetary costs of power production were calculated and compared to the respective values of the current system.

Thermoeconomic analysis of a power/water cogeneration plant

Cogeneration plants for simultaneous production of water and electricity are widely used in the Arabian Gulf region. They have proven to be more thermodynamically efficient and economically feasible than single purpose power generation and water production plants. Yet, there is no standard or universally applied methodology for determining unit cost of electric power generation and desalinated water production by dual purpose plants. A comprehensive literature survey to critically assess and evaluate different methods for cost application in power/water cogeneration plants is reported in this paper. Based on this analysis, an in-depth thermoeconomic study is carried out on a selected power/water cogeneration plant that employs a regenerative Rankine cycle. The system incorporates a boiler, back pressure turbine (supplying steam to two MSF distillers), a deaerator and two feed water heaters. The turbine generation is rated at 118 MW, while MSF distiller is rated at 7.7 MIGD at a top brine temperature of 105 °C. An appropriate costing procedure based on the available energy accounting method which divides benefits of the cogeneration configuration equitably between electricity generation and water production is used to determine the unit costs of electricity and water. Capital charges of common equipment such as the boiler, deaerator and feed water heaters as well as boiler fuel costs are distributed between power generated and desalinated water according to available energy consumption of the major subsystems. A detailed sensitivity analysis was performed to examine the impact of the variation of fuel cost, load and availability factors in addition to capital recovery factor on electricity and water production costs.

Effect of Feedwater Temperature Rise in Heaters on Regenerative Rankine Cycle Performance

In this article, the performance of regenerative power plants in terms of second law of thermodynamics is discussed. The performance of the cycle is improved with the addition of backward cascaded-type and open-type feedwater heaters. This improvement is obtained by the reduction in irreversible losses as the number of feedwater heaters increases. A conventional energy-balance approach is used to calculate the irreversible losses in the cycle. The irreversible losses of each component of the cycle is given in a dimensionless ratio and from that ratio one can easily see the fraction of the irreversible losses of each component with respect to the power output, which means the irreversible losses can be obtained directly from the power output. The boiler causes the maximum fraction of the total irreversible losses among the components of the cycle. These losses are reduced by introducing feedwater heaters into the cycle. The irreversibilities in the cycle are examined according to the effect of varying the total temperature rise across the feedwater heaters.

Industrial Cogeneration: Analysis of Energy Parks

A novel implementation of “manufacturing” thermal and electrical demand to match power plant design in the context of an industrial park is studied. The novelty of the “energy park” concept introduces several areas requiring detailed consideration. Three of these—manufacturing load profile through tenant identification, power plant design and energy costs, and pricing—are addressed. A computer model which calculated economic and thermomechanical performance is utilized. A specific site in southeastern Massachusetts is used as the study's focus. The consumers used are a paper mill, a food processor, and a local hospital. The regenerative Rankine cycle power plant is designed to meet a maximum steam demand of 13kg/s(105lbm/hr) at all times and electrical demand [3,000 kWe peak] most of the time. An economic analysis driven by derived aggregate energy demand is performed. Both daily and monthly demand fluctuations are considered. This analysis is accomplished using PC‐based spreadsheet software. The total average cost of energy (1982 dollars), assuming electrical and thermal energy are priced equally, is $0.0116/MJ ($12.19/BTU). Pricing strategies to reduce cost and shift demand profile are considered.

The Thermodynamic Performance of Two Combined Cycle Power Plants Integrated With Two Coal Gasification Systems

Thermodynamic models of both an adiabatic and an endothermic coal gasifier integrated with either a waste heat combined cycle or a supercharged boiler combined cycle are developed. The adiabatic gasification process requires air and steam, while the endothermic gasification process requires only steam. The combined cycle is composed of an open Brayton cycle and a superheated regenerative Rankine cycle without reheat. Certain components are added to each configuration in an effort to improve thermodynamic performance. From the results, it appears that with consideration of the pollution criteria, the station efficiencies for each configuration are within 1 percentage point of each other when flue gas recirculation is used as a means to control the nitric oxide. With a gas turbine inlet temperature of 2000°F, and with consideration of the pollution criteria, the configuration employing an adiabatic gasifier and a waste heat system is marginally the best with a station efficiency of only 37 percent.

Perspectives for the Liquid Phase Compression Gas Turbine

The possibility of performing a liquid phase compression in closed cycle gas turbine through the use of particular working fluids is discussed. From the results of calculations carried out for different fluids there is evidence that efficiency of the resulting cycle is considerably higher than that of regenerative Brayton cycles and comparable with that of regenerative Rankine cycles. The working fluid selection is recognized as the major problem in view of practical applications. Available data strongly support the conclusion that fluids meeting the needed requirements, at least for moderate temperature operation, can be found. Nuclear power stations appear to be one of the most promising fields of application of the liquid phase compression cycle.