Exhaust Steam Research Articles

Study of new cascade heating system with multi-heat sources based on exhausted steam waste heat utilization in power plant

Utilizing waste heat of exhausted steam in power plant as a new type of heat source is a key direction to achieve both energy-saving and clean district heating. This paper firstly reviews current mature waste heat utilization technologies, including “absorption heat pump”, “increasing back pressure of turbine” and “decreasing return water temperature of heat network”. Using only one method is not applicable to recovery all the exhausted steam waste heat of multiple turbine units due to its respective limitations. In view of this technical difficulty, this paper proposes a new cascade heating system with multi-heat sources based on waste heat utilization. Extraction steam and exhausted steam are involved to achieve the cascade temperature-rise of heat network water. Corresponding evaluation methods are presented, including the last-stage safety of the large unit and the comprehensive energy efficiency of the new cogeneration heating system. Taking 2 × 300 MW water-cooled units as the example to actualize the new system, the effects of key parameters on energy efficiency and economy are analyzed, and then further researches about integration optimization of the new system are developed. In this study, first keep constant return water temperature of primary heat network, the optimal condition is gained. At this point, all the waste heat of exhausted steam is recovered, the energy consumption of power plant is reduced by 33% and the total cost per heat output ct is reduced by 22.3%, compared with conventional cogeneration system. Then reduce the return water temperature in different level, both the energy consumption and the total cost per heat output ct can be further lowered, the energy efficiency and the economy are better improved.

Analyze Experiment For Vigas and Pertamax to Performance and Exhaust Gas Emission for Gasoline Motor 2000cc

The purpose and target for this analyze experiment is we get the performance variabel from gasoline motor which used LGV for fuel and Pertamax, so can give knowledge to community if LGV can be using LGV for fuel to transportation industry and more economic. We used experiment method of engine gasoline motor with 2000 cc which is LGV and Pertamax for fuel. The experiment with static experiment tes above Dyno Test. The result is engine perform to subscribe Torque, power, fuel consumption. Beside the static test we did the Exhaust Steam Emission. The result is the used LGV with the commercial brand Vigas can increase the maximum Engine Power 20.86% and Average Power 14.1%, the maximum torque for Motor which is use LGV as fuel is smaller than Motor with Pertamax, the decrease is 0.94%.Using Vigas in Motor can increase the mileage until 6.9% compare with the Motor with pertamax.Air Fuel Ratio (AFR) for both of the fuels still below the standard, so still happen waste of fuel, specially in low compression.Using Vigas can reduce the Exhaust Steam Emission especially CO2

Numerical study of the thermo-flow performances of novel finned tubes for air-cooled condensers in power plant

Air-cooled condenser is the main equipment of the direct dry cooling system in a power plant, which rejects heat of the exhaust steam with the finned tube bundles. Therefore, the thermo-flow performances of the finned tubes have an important effect on the optimal operation of the direct dry cooling system. In this paper, the flow and heat transfer characteristics of the single row finned tubes with the conventional flat fins and novel jagged fins are investigated by numerical method. The flow and temperature fields of cooling air for the finned tubes are obtained. Moreover, the variations of the flow resistance and average convection heat transfer coefficient under different frontal velocity of air and jag number are presented. Finally, the correlating equations of the friction factor and Nusselt number versus the Reynolds number are fitted. The results show that with increasing the frontal velocity of air, the heat transfer performances of the finned tubes are enhanced but the pressure drop will increase accordingly, resulting in the average convection heat transfer coefficient and friction factor increasing. Meanwhile, with increasing the number of fin jag, the heat transfer performance is intensified. The present studies provide a reference in optimal designing for the air-cooled condenser of direct air cooling system.

Energy Analysis of Cascade Heating with High Back-Pressure Large-Scale Steam Turbine

To reduce the exergy loss that is caused by the high-grade extraction steam of traditional heating mode of combined heat and power (CHP) generating unit, a high back-pressure cascade heating technology for two jointly constructed large-scale steam turbine power generating units is proposed. The Unit 1 makes full use of the exhaust steam heat from high back-pressure turbine, and the Unit 2 uses the original heating mode of extracting steam condensation, which significantly reduces the flow rate of high-grade extraction steam. The typical 2 × 350 MW supercritical CHP units in northern China were selected as object. The boundary conditions for heating were determined based on the actual climatic conditions and heating demands. A model to analyze the performance of the high back-pressure cascade heating supply units for off-design operating conditions was developed. The load distributions between high back-pressure exhaust steam direct supply and extraction steam heating supply were described under various conditions, based on which, the heating efficiency of the CHP units with the high back-pressure cascade heating system was analyzed. The design heating load and maximum heating supply load were determined as well. The results indicate that the average coal consumption rate during the heating season is 205.46 g/kWh for the design heating load after the retrofit, which is about 51.99 g/kWh lower than that of the traditional heating mode. The coal consumption rate of 199.07 g/kWh can be achieved for the maximum heating load. Significant energy saving and CO2 emission reduction are obtained.

Modelling and Optimization of the Direct Air Cooling Power Generation Unit

Abstract Fossil fuel power plants dominate the energy structure in China. However, the water scarcity, in Southeast/Southwest China, results in the development of the dry cooling power plants. Direct air cooling condenser (DACC) is appealing for its water saving ability. In DACC, the exhaust steam is cooled and condensed to water by the air flow, which is provided by the fan array at the cost of electricity. There exists a varying optimal exhaust steam pressure under different air temperatures and loads. The static model of the turbine-DACC system is built to quantify the influences of the air temperatures and loads. An on-line optimization is used here to set the reference value of the exhaust steam pressure for the turbine-DACC system for economic operation. The objective is to maximize the net power production while satisfying the constraints on the safety pressure and the available air flowrate. The optimization is conducted in a model 660MW power plant selected on a random summer/winter day. The hourly optimal exhaust steam pressure and the operation instructions are calculated as the reference values for the control layer. The optimization results show that the optimal exhaust steam pressure may be too close to the safety limits in winter, suggesting the safety also to be considered in the optimization. In summer, the DACC system cannot satisfy the condensation load sometimes. Thus, a complementary cooling method, for example, the wet cooling, is needed to reduce the burden on the DACC system.

Анализ причин низкой экономичности цилиндра низкого давления паровой турбины К-200-130

Designing a low-pressure cylinder (LPC) with a one-and-a-half steam exhaust from it is the only way in which a larger steam flowrate can be passed to a condensing steam turbine’s condenser without increasing the length of the turbine last-stage blades. For implementing this idea, K. Baumann has developed a special next-to-last two-tier stage, which diverts part of the steam passing through the stage’s upper tier directly into the condenser in bypass of the last-stage bucket. In the former Soviet Union, this solution was implemented in a number of medium- and high-pressure turbines, as well as in the K-200-130 turbine produced by the Leningrad Metal Works (LMZ). However, field experience gained from operation of this turbine, as well as special investigations, showed that the LPC fitted with the Baumann stage had poor efficiency, and during the subsequent modernizations the Baumann stage was removed from the K-200-130 turbine’s LPC flow path. Factors that have caused dramatic degradation of the cylinder efficiency are analyzed. It is shown that the factors relating directly to the Bauman stage that were considered in the scientific literature could not play the key role in degrading the stage efficiency and, accordingly, in affecting the cylinder efficiency. It has been shown from the performed analysis that poor efficiency of the LPC equipped with the Baumann stage is not due to the stage itself, but due to the conditions of steam admission to it and to the K-200-130 LMZ turbine last stage. As a result, two out of four (in total) stages contained in this cylinder operate with dramatically degraded efficiency. These design drawbacks removed, the Baumann stage can well be used to increase the maximum possible steam passage through the LPC.

Dynamic modeling and operation optimization for the cold end system of thermal power plants during transient processes

This paper focuses on the dynamic modeling of the cold end system of a thermal power plant and its operation optimization during cycling load processes. A revised logarithm mean temperature difference is recommended to calculate the heat transfer quantity between exhaust steam and condenser tubes. With this method, a condenser model is developed with a maximum relative error limited within 3%. Coupled with a turbo-generator, a condenser, water pumps, and a cooling tower, a closed cooling system model is established. The total power supply (TPS) during cycling load is calculated and analyzed to optimize the operation during transient processes. A method for obtaining the maximum value of TPS is provided and used to calculate the optimal operating load rate points for switching pumps (OPSP). OPSP increases with the cycling load rate (Ve) during loading up processes decreases with Ve during loading down processes. When Ve is identical, OPSP declines with the ambient temperature for the loading up and down processes. TPS during transient processes is relevant with the switching pump load rate. The maximum value of difference in TPS with different switching pump periods is 691.4 (kW h) for switching pump numbers from 3 to 2 during loading down processes.

Performance Recovery of Natural Draft Dry Cooling Systems by Combined Air Leading Strategies

The cooling efficiency of natural draft dry cooling system (NDDCS) are vulnerable to ambient winds, so the implementation of measures against the wind effects is of great importance. This work presents the combined air leading strategies to recover the flow and heat transfer performances of NDDCS. Following the energy balance among the exhaust steam, circulating water, and cooling air, numerical models of natural draft dry cooling systems with the combined air leading strategies are developed. The cooling air streamlines, volume effectiveness, thermal efficiency and outlet water temperature for each cooling delta of the large-scale heat exchanger are obtained. The overall volume effectiveness, average outlet water temperature of NDDCS and steam turbine back pressure are calculated. The results show that with the air leading strategies inside or outside the dry-cooling tower, the thermo-flow performances of natural draft dry cooling system are improved under all wind conditions. The combined inner and outer air leading strategies are superior to other single strategy in the performance recovery, thus can be recommended for NDDCS in power generating units.

Anti-Freezing Mechanism Analysis of a Finned Flat Tube in an Air-Cooled Condenser

In cold winter weather, the air-cooled condensers (ACCs) face serious freezing risks, especially with part load of the power generating unit. Therefore, it is of benefit to investigate the heat transfer process between the turbine exhaust steam and cooling air, by which the freezing mechanism of the finned tube bundles can be revealed. In this work, the flow and heat transfer models of the cooling air coupling with the circulating water, are developed and numerically simulated for the anti-freezing analysis on basis of the finned tube bundles of the condenser cell. The local air-side heat transfer coefficient, condensate film development, and non-condensable gas development are obtained and analyzed in detail. The results show that, the most freezing risk happens at the fin base due to the highest air-side cooling capacity, besides the windward velocity, ambient temperature and turbine back pressure all determine the freezing risk with the constant inlet flow rate of the non-condensable gas. Furthermore, increasing fin thickness and decreasing fan rotating speed are the most effective anti-freezing measures. Additionally, increasing turbine back pressure can also be adopted to avoid ACC freezing, however the adjustment of outlet steam-air flow is not recommended.

Full operating conditions optimization study of new co-generation heating system based on waste heat utilization of exhausted steam

Utilizing the waste heat of exhausted steam in power plant as a new type of heat source is a key direction to achieve both energy-saving and clean urban heating. In order to recycle all the exhausted steam waste heat of multiple turbine units in designing condition, the authors’ research group proposed a new cascade heating system with multi-heat source and applied it in several air cooling power plants in China. This paper focused on the system integration improving and operation strategy formulating, the main studies included: (1) Established the calculation model of system heating characteristics, and analyzed the problems about energy efficiency of system and safety of air cooled condenser in full operating conditions. (2) Introduced the “equivalent electricity of heating” as the evaluation method of comprehensive energy efficiency of the new co-generation heating system. (3) Improved the integration of heating system to further realize energy cascade utilization between turbine units. (4) Aiming at the improved heating system, the comprehensive optimization ideas of operational parameters in full operating conditions were put forward. By above methods, on one hand the “equivalent electricity of heating” of the new co-generation heating system is decreased by 16%, the comprehensive energy efficiency of system is improved, on the other the freezing risk of air cooled condenser is relieved, the operation safety of system is improved.

Numerical Study on the Reduction of NOx Emissions From Pulse Detonation Combustion

A change in the combustion concept of gas turbines from conventional isobaric to constant volume combustion, such as in pulse detonation combustion (PDC), promises a significant increase in gas turbine efficiency. Current research focuses on the realization of reliable PDC operation and its challenging integration into a gas turbine. The topic of pollutant emissions from such systems has so far received very little attention. Few rare studies indicate that the extreme combustion conditions in PDC systems can lead to high emissions of nitrogen oxides (NOx). Therefore, it is essential already at this stage of development to begin working on primary measures for NOx emissions reduction if commercialization is to be feasible. The present study evaluates the potential of different primary methods for reducing NOx emissions produced during PDC of hydrogen. The considered primary methods involve utilization of lean combustion mixtures or its dilution by steam injection or exhaust gas recirculation. The influence of such measures on the detonability of the combustion mixture has been evaluated based on detonation cell sizes modeled with detailed chemistry. For the mixtures and operating conditions featuring promising detonability, NOx formation in the detonation wave has been simulated by solving the one-dimensional (1D) reacting Euler equations. The study enables an insight into the potential and limitations of considered measures for NOx emissions reduction and lays the groundwork for optimized operation of PDC systems.

A multi-featured model for estimation of thermodynamic properties, adiabatic flame temperature and equilibrium combustion products of fuels, fuel blends, surrogates and fuel additives

This study introduces a new multi-featured equilibrium combustion model for fuels, fuel blends and surrogates which estimates mole fractions, adiabatic flame temperature and thermodynamic properties of the equilibrium combustion products. The model enables simultaneous consideration of unlimited number of CαHβOγNδ type fuels of different ratios and also enables any CαHβOγNδ type fuel additive, Argon, H2O, CO, CO2, N2, and O2 to be considered among the reactants. Equilibrium mole fractions and adiabatic flame temperature are not only necessary for estimating thermodynamic properties of exhaust gases but also provide key data to obtain the non-equilibrium concentrations. As for thermodynamic properties, precise calculation is necessary for accurate performance estimations of internal combustion engines. Meeting these fundamental needs and providing combustion analysis of numerous fuel blends of various mixing ratios, this new model can be a recourse tool for researchers working on fuels, surrogates, emissions and internal combustion engine modelling. Simulations of any combustion process including existence of exhaust gas recirculation, supplementary firing, steam injection, argon dilution, water injection, fuel emulsification and reheat process in gas turbines can easily be conducted by integrating this validated model into thermodynamic cycle models.

Evaporation Plant for Recycling of Caustic Soda

The most important problem that humanity is expected to face in the coming century shall be environmental pollution. On one hand, the population of human beings are using natural resources rapidly, on the other hand, they are adding hundreds of pollutants in the form of metals, acids, bases and etc. Thus, they have created an abnormal situation which has resulted in an imbalance in the natural systems. As the industrialization improves, it creates pollution and also it creates jobs for the people. Especially in developed countries, for instance European countries and U.S.A. there are also many stringent restrictions for the environmental pollution, and there are many laws, political arrangements. Of course , a pollution free environment will require a high cost, often an expensive operation. However , it is much more costlier trying to undo the damage done. On the basis of concept tried to mention above human beings have studied on the subjects related with environmental pollution. They have established waste water treatment plants, many kinds of recycling and recovery plants, and etc. In this study , it has been tried to establish such an idea that a pollution free environment may be available if this technical process is used properly. So, the first goal of this study is to provide a concise statement of the requirements and opportunities for obtaining environmental benefits. The second objective will be to provide economical savings while providing the environmental benefits at the same time. To emphasize the great importance of above mentioned subjects the application of recycle technology for the sodium hydroxide (NaOH), which is named as caustic soda in industrial processes, realized by means of an evaporation plant is used. Caustic soda is used in textile industry for mercerizing process as it is used in many different processes. To give the cotton more strength and to obtain a smoother surface and an improved affinity the mercerizing is essential. After being finished the mercerizing operation, generally the process solution (containing caustic soda) is discharged to the environment,. e.g. , rivers, seas and sewage. In spite of the fact that this application is widely spread in use, it is forbidden in all developed countries to discharge the caustic soda solutions even at a 1% concentration since the caustic soda is highly basic (highly alkaline). For this reason it is very harmful for the environment. It is possible to extract the caustic soda from the caustic soda solutions before discharging it to the environment for preventing the harms of this material. The washing water containing NaOH will be concentrated by H 2 O evaporation and shall be recycled in the mercerizing system. The concentration may take place in a single or multiple – stage (double–stage) installation under vacuum or atmospheric pressure. The washing water to be concentrated is moved from the storage tank to the first evaporation stage and the thermal energy for evaporation operation is added by the steam. The vapor coming from the first evaporation stage is used for the next evaporation stage as the heating steam of this unit. The vapor from the last stage is condensed in a condenser. The condensed vapor can be safely discharged and the concentrated caustic soda can be reused for the subsequent mercerizing operation. So, both economical profits and environmental benefits can be provided by reusing the caustic soda for next processes , after it is recovered by the help of this way. Desalination unit in Jeddah which is the capital city of Saudi Arabia , is an example for this kind of operations.. This plant was established 1970’s and has been used as both a power station and a desalination unit. At this plant the exhaust steam coming from the steam turbines is used as the heating steam for evaporators of desalination unit. Unfortunately, in our country, even in İzmir, the waste water of textile industry is discharged to the environment. Because , the environmental laws are not adequate and the enterprisers think that a recycling plant is not an economical investment. However , it is stated in this study that such a concept is not right. It has been tried to show that such an investment, i.e., “An Evaporation Plant for Recycling of Caustic Soda” may be profitable if it is installed and operated properly, and also it has been tried to increase the attractivity of these kinds of plants . It is hoped that, the laws and stringent restrictions related with environment shall be arranged, so that we shall live in a healthy world.

Field operation of a 125kW ORC with ship engine jacket water

Improving ship system efficiency is a growing concern for the marine industry. New regulations imposed by the International Maritime Organization (IMO) have set efficiency targets for new and existing ships. These targets are outlined in the energy efficiency design index (EEDI) and will reach a maximum of 30% by 2025. In order to satisfy the regulations, ship owners are exploring new methods to improve the efficiency of existing systems. One such method is to capture and repurpose engine waste heat.Many ships employ exhaust steam boilers to recover heat from engine exhaust. This represents a source of high quality heat (≥ 200°C). At these temperatures, it is relatively easy to extract thermal energy. In contrast, low quality heat sources, such as engine jacket water (≤ 100°C), have been largely ignored. Steam production is impractical at such low temperatures. A new technology was needed to take advantage of low temperature heat sources on the ship.Calnetix Technologies, in conjunction with Mitsubishi Heavy Industries (MHI), developed an Organic Rankine Cycle (ORC) specifically designed to utilize engine jacket water as a heat source. The first prototype was successfully built, tested, and certified by Lloyd’s Registry (LR) and Nippon Kaiji Kyokai (NK) in March 2015. The system generates up to 125 kW from a heat source with temperature range 80°C to 95°C.This prototype was installed, commissioned, and placed into service on the Arnold Maersk container ship in April 2016. This paper will discuss difficulties which arose during the installation. It will also present and discuss data collected by the ORC’s sensors during its first several months of operation. Finally benefits of the ORC operation in conjunction with auxiliary ship systems will be explained.

A novel mechanism for exhaust steam waste heat recovery in combined heat and power unit

Combined heat and power (CHP) has been identified as an important approach for fossil fuel utilization with high efficiency and pollutant concentration control. In this study, an optimized process for in-depth exhaust steam utilization was proposed to further exploit the energy saving potential of CHP unit. In the novel system, the utilization of the exhaust steam was combined with the heating process for air and condensate water, largely recovering the waste heat and leading to an improvement in the performance of the CHP unit. EBSILON Professional was used to build the model; and compared with the reference system, thermodynamic analysis and techno-economic evaluation were conducted to reveal the characteristics of the novel system. The results showed that, in the design condition, the exhaust steam utilization ratio in the novel system had a significant increment of 22.74% than that in the reference system, leading to a sharp increase of 16.26% in heating capacity and 0.83MW in net electricity output, bringing about 5.06% improvement in net generating efficiency. Meanwhile, the net annual revenues of the novel system can reach 1.80 million USD.

Pseudo-online optimization of condenser pressure for the cold-end system with variable speed pumps

The operation conditions of the cold-end system have significant impact on the unit thermal economy. However, due to the difficulty of online determination of some key parameters, the condenser pressure optimization has been a challenging task for a long time. This paper proposes an online applicable approach to optimize the condenser pressure with variable speed pumps, taking the mass flow rate of the circulating water as the manipulating variable, to achieve better thermal economy. After the exhaust steam wetness fraction is online identified, the condenser thermodynamic characteristics under varying working conditions are investigated based on the effectiveness and steady-state energy balance of the condenser. By maximizing the net power benefit, defined as the difference between the unit power increment and the pump power consumption increment, the optimal mass flow rate of the circulating water is derived. To validate the approach, pseudo-online simulations are conducted with the history data from an ultra-supercritical unit. The retention time during which the set value of the mass flow rate of the circulating water remains constant is studied in context with the implementation of the manipulation strategy under on-site scenario. Simulation results reveal the energy-saving potential of condenser pressure optimization with the proposed approach.

Dynamic and Control of an Absorber - Desorber Plant at Heilbronn

The present work is based on an MEA absorption test campaign performed November 2013–January 2014 at EnBW's amine test pilot located in Heilbronn, Germany. The test campaign included transient step responses in steam, exhaust gas, solvent flow rate and in exhaust gas CO2 concentration. In addition, a test with simultaneous steps in all flow rates (exhaust gas, solvent and steam) was included.A dynamic model of the Heilbronn plant was then implemented in the dynamic simulator K-Spice® and tested against the step responses at the plant. In spite of some stead state deviations, the model was able to capture the process dynamics very well. For dynamic studies one can therefore assume that the model is representative for the plant. In the work presented here, two different control configurations were tested: 1) Ratio control in combination with a slow feed back control on the CO2 out of the absorber and 2) Control of CO2 out of the absorber by lean liquid flow rate and a temperature sensor up in the desorber packing. Both structures involve only simple PID control loops and are thus easy to implement. The proposed control configurations were tested by simulations with 30% changes in flue gas flow and composition. Both configurations showed good performance during the simulation testing, but the second one was superior as well as excellent with respect to tight CO2 recovery control. This may be an important property in supervisory control schemes.

Entransy dissipation based optimization of a large-scale dry cooling system

The natural draft dry cooling tower (NDDCT) with heat exchangers accounts for about 10 percent of the total investment of a power plant, so it is meaningful to optimize the geometric parameters to explore the potential that matching the cooling load of a power generating unit in the most cost effective way. The entransy dissipation equations of two typical irreversible heat transfer processes, including that the ambient air heated by heat exchangers and circulating water heated by the exhausted steam of turbine, are derived in this paper. Combined with the force balance equation of NDDCT, all parameters that may affect the performance and annual cost of a cooling system are took into consideration. Such constituted constraints are applied to the Lagrange multiplier optimization of such a system. Based on the mathematical relation and conditional extremum method, an optimization equation group aiming to obtain the minimum of total annual cost is constructed. Finally, a practical 600MW power generating unit is taken as an example to illustrate the applications of entransy dissipation based optimization principle. The result indicates that total annual cost of the dry cooling system can drop from $6 420 643 to $5 665 660.

Energy analysis of a lignite predrying power generation system with an efficient waste heat recovery system

ABSTRACTLignite has been extensively used for electricity generation in many regions worldwide. However, its high water content has obviously negative effect on plant thermal efficiency. Performance of lignite-fired power plant can be improved by predrying the lignite before combustion. In addition, recovery of waste heat from the dryer and the power generation system will enhance the plant thermal efficiency further. In the present study, a new lignite predrying power generation system integrated with an efficient waste heat recovery system was proposed. Both dryer exhaust waste heat and steam turbine exhaust latent heat were recovered to heat boiler feed water. Energy analysis indicates that system performance is improved significantly. The plant thermal efficiency increases linearly with drying degree and then increases at a lower rate. The generation of unused dryer exhaust changes the variation tendency of system performance with drying degree.

Exergy analysis and economic evaluation of the steam superheat utilization using regenerative turbine in ultra‐supercritical power plants under design/off‐design conditions

AbstractIn order to effectively utilize the steam superheat of ultra‐supercritical power plants, a regenerative turbine (RT) system was proposed. In the RT system, a portion of the high‐pressure turbine exhaust steam is sent to an extra turbine termed as RT, and the extracted steam of several regenerative heaters (RHs) would be extracted from the RT instead of the intermediate‐pressure turbine. The superheat degree of related extracted steam would decrease and the exergy destruction of the heat transfer process in RHs would be reduced. Thermodynamic and economic analyses of the RT system in a typical 1000 MW power plant were carried out. The results showed that the heat consumption rate would be reduced as compared to the conventional configuration. When the RT isentropic efficiency is set to 85%, the heat consumption rate of the RT system could decrease by 46.9 kJ/kWh as compared to that of the reference system without RT under design condition. The heat consumption rate decrement will be greater with higher RT isentropic efficiency. Meanwhile, thermodynamic analysis of the RT system under off‐design condition showed that the energy saving effect of the RT system would be decreased when the design conditions are no longer met. The exergy analysis showed that the total exergy destruction decrement of related RHs in the RT system decreases as the load drops down. Moreover, the economic analysis revealed that the net economic benefit of the RT system could reach 0.57 M$ per year, and would perform economically within a wide range fluctuations of power market conditions.