Net Power Plant Efficiency Research Articles

The concept of creating a maneuverable power plant based on a small modular reactor

Purpose. To develop a maneuverable power plant (MPP) based on the NuScale small modular reactor (SMR) by selecting a thermal scheme structure for a steam turbine installation using minimal additional equipment and ensuring its operation in both nominal and peak modes with maximum efficiency. This also includes ensuring its maneuverability through the use of hydrogen technologies for generating, storing, and returning energy to the steam turbine cycle. Methodology. The study employed the method of mathematical modeling of thermodynamic cycles of thermal schemes of steam turbine installations (STI) with concentrated parameters, which makes it possible to describe the dynamics of systems consisting of discrete elements that are thermodynamic systems. Findings. Various structural options for the thermal scheme of the MPP based on the NuScale SMR for nominal operation were developed and mathematically modeled, followed by a comparative analysis of their energy efficiency. As a result, a scheme and operational parameters were selected with the highest electrical efficiency (net), which allows increasing the net efficiency of the NuScale SMR-based power plant from the developers’ announced 28 to 32.8 %. A thermal scheme for the MPP based on the SMR with an energy storage system was proposed. Applying this scheme allows increasing the net efficiency of a power plant based on NuScale SMR in peak mode to 34.8 %. Originality. A concept for creation and schematic solution for a prospective MPP based on an SMR capable of accumulating electrical energy was proposed. The main innovative solution regarding the structure of the technological scheme of the MPP based on the SMR is the organization of its operation in nominal and peak modes, which fundamentally differ in the thermodynamic cycle. In the nominal mode, the steam turbine installation operates on a thermodynamic cycle with steam separation, and in the peak mode without it, by increasing the temperature of fresh steam as a result of burning hydrogen and oxygen. Hydrogen and oxygen are produced in an electrolyzer during the power plant’s operation in the nominal mode by using the generated electricity “excess”. Practical value. Small modular reactors are currently mainly in the development stage. Additionally, the non-nuclear part of the SMR-based power plant, namely the STI, has not received sufficient attention, as evidenced by the literature. However, it plays a crucial role in the overall efficiency of the installation. The study focuses on the highly relevant issue of improving the efficiency of an SMR-based power plant by developing the structure of the STI thermal scheme involving hydrogen technologies. This will help reduce dependence on fossil hydrocarbons in the total volume of primary fuel and enable sustainable functioning of the Ukrainian energy system, as well as contribute to the preservation and improvement of the environmental state.

Estimation of fuel operating ranges of fusion power plants

The fuel operating ranges of fusion tokamak-based power plants are estimated using the improved engineering breakeven equation. The Lawson criterion equations are derived in the form of a triple product with a focus on engineering breakeven and the subbreakeven operating range. The relationship of fuel parameters to the power plant net efficiency is outlined. Analysis shows that the operating ranges of the suitable fuel parameters form a closed area, the size of which affects the net efficiency of the power plant.The obtained fuel operating ranges confirm the well-known fact that DT fuel is currently the only fusion fuel useable in tokamak-based fusion power plants. It is also shown that the energy utilization of pB fuel is possible in the subbreakeven operating range but is conditioned by the very high efficiency of the power plant equipment. For the utilization of DD, DHe3, and pB fuels, the required magnetic fields are indicatively estimated.

Thermo-economic analyses of the waste heat and water recovery system from flue gas by heat pump integrated with different heat utilization ways in coal-fired power plant

To recover the waste heat and water simultaneously from flue gas after wet desulphurization, a novel method by adding a flash evaporation device and heat pump system was proposed. The thermal-economic theoretical models for systems integrated with three different heat utilization ways were established based on the method of equivalent enthalpy drop. A typical 300 MW coal-fired power plant was selected as a case to compare the thermo-economic performance. Results show that when the flue gas temperature decreased from 50°C to 30°C, the amounts of recovered waste heat and water could be up to 65.2MW and 81.4t/h, respectively. At the same heat output of 11.3 MW from heat pump, the heat utilization way of pre-heating air exhibited the best energy-saving performance with the net efficiency of power plant increasing to 42.46% from 42.3%.

Investigation of the use of steam coil preheater to increase the net efficiency of thermal power plant

Conventionally, regenerative feed water heating is used to increase the net efficiency of a thermal power plant. In this method, extracted steam from the steam turbine is used to increase feed water temperature before feed water is sent to the boiler. Increasing the number of feed water heaters or the mass flow rates of extracted steam causes the net power plant efficiency to increase. However, there is a practical limit of the number of feed water heaters. Furthermore, there is an upper limit of the mass flow rate of extracted steam for a feed water heater. Consequently, there is an upper limit of the net power plant efficiency in a conventional design of power plant that relies only on regenerative feed water heating. In this paper, it is argued that the net power plant efficiency can be increased beyond this limit by using extracted steam to increase air temperature in steam coil air preheater before air enters the boiler. Models of boiler, steam turbine, and steam coil air preheater are used to demonstrate that the net efficiency of 50-MW power plant is increased by 2.32% due to the integration of steam coil air preheater having the area of 500 m 2 .

The use of steam dryer with heat recovery to decrease the minimum exhaust flue gas temperature and increase the net efficiency of thermal power plant

Net power plant efficiency is the ratio of exportable electrical power output to the product of fuel consumption rate and fuel heating value. Conventionally, power plants are designed to attain the maximum net power plant efficiency by using regenerative feed water heating, in which extracted steam from steam turbine is used to increase feed water temperature. An important factor that determines the net power plant efficiency is the temperature of flue gas exhausted from the power plant. Decreasing this temperature increases the net power plant efficiency. However, exhaust flue gas temperature should not be lower than the lower limit in order to avoid the corrosion resulting from condensation of sulfuric acid vapor in flue gas on heat exchanger tubes. The lower limit can be raised by reducing fuel moisture content and raising air temperature at boiler inlet. In this paper, it is proposed that low-pressure extracted steam should be used for fuel drying in steam dryer, and vapor released from steam dryer should be used for air heating in heat recovery air preheater. By doing so, the lower limit of exhaust flue gas temperature is decreased, and the net efficiency of the power plant is increased. A case study of a 600-MW lignite-fired power plant is used to demonstrate that the integration of steam dryer and heat recovery air preheater is economically justified.

Innovative system configuration analysis and design principle study for different capacity supercritical carbon dioxide coal-fired power plant

The paper constructs the innovative supercritical carbon dioxide (S-CO2) cycle and boiler coupling thermodynamic model, based on comprehensive system analysis of the S-CO2 cycle, S-CO2 boiler and medium temperature heat recovery. The results reveal that moderate cycle maximum pressure and single reheat cycle configuration show the higher cycle efficiency for S-CO2 cycle with the high boiler pressure drop. High temperature flue gas recirculation mode with large proportion and double rectangular furnace boiler layout can increase the boiler heating surface area and lower the heat duty distribution within S-CO2 boiler, which can eliminate the impact of excessive mass flow and increased average endothermic temperature in the S-CO2 cycle. Besides, the system design method and economic evaluation of S-CO2 coal-fired power plants have been constructed. Single split flow cycle configuration is recommended for the 300 MW S-CO2 power plants. And double split flow cycle configuration is compulsory for 1000 MW power plants, showing 50.13% overall power plant net efficiency and 0.705 CNY/kW·h levelized cost of energy (LCOE) at 620 °C/32 MPa. As for the 600 MW capacity power plants, the former configuration considers the boiler heating exchanger layout simplicity, and the latter configuration increases 0.36% overall power plant net efficiency.

Experimental study of NOx emissions in a 30 kWth pressurized oxy-coal fluidized bed combustor

As one of the most promising carbon capture technologies for coal-fired power plants, oxy-coal combustion has attracted wide interests during the last two decades. In comparison to atmospheric oxy-fuel combustion, pressurized oxy-fuel combustion has the potential to further reduce the energy penalties caused by the carbon capture and storage and improve the net power plant efficiency. Although many researchers have investigated the NOx emissions of atmospheric oxy-coal combustion, the NOx emission behaviors under pressurized oxy-coal combustion conditions are much less understood and further comprehensive experimental investigations with continuous fuel-feeding pressurized oxy-coal combustion systems are needed in order to fill this knowledge gap. In the present study, a series of oxy-coal combustion experiments were conducted in a 30 kWth pressurized fluidized bed combustor. The effects of combustion pressure, bed temperature and excess oxygen on the NOx emissions were investigated systematically. The experimental results have shown that an increase in combustion pressure from 0.1 MPa to 0.4 MPa leads to a significant reduction in NOx emissions. An increase in bed temperature or excess oxygen results in higher NOx emissions under the higher combustion pressure conditions, which is consistent with what is observed under the atmospheric pressure combustion condition. Besides, it is found that the promoting effect of temperature increase on NOx emissions under the higher combustion pressures is weaker than that under the atmospheric pressure.

Process integration and design for maximizing energy efficiency of a coal-fired power plant integrated with amine-based CO2 capture process

System-wide integration of post-combustion CO2 capture process into a coal-fired power plant is an effective and practical strategy to improve cost-effectiveness for capturing CO2 emissions from the power sector. Considerable reduction of the net energy efficiency of a power plant by 20–40% is inevitable due to energy requirements for the CO2 capture and power requirement for the CO2 compression. Hence, this study focuses on minimizing the net efficiency penalty through integrated design of coal-fired power plant with CO2 capture process in a holistic and systematic manner. In order to analyze the techno-economic impact of integrated process on the net power plant efficiency, overall process models are developed in a commercial simulator Aspen Plus®, in which a 550 MWnet supercritical coal-fired power plant is simulated and validated. A pilot-scale post-combustion CO2 capture process based on MEA, together with CO2 compression, is modeled and scaled-up to meet the commercial-scale capacity. Simulation-assisted optimization is performed to enhance the overall performance of capture-integrated power generation through fully exploiting system interactions and examining relevant economic trade-offs. A case study is carried out to evaluate the effect of several heat integration options and demonstrate a considerable benefit for reducing the net efficiency penalty.

Influences of syngas pretreatment on the performance and energy distribution in an IGCC power plant

Raw syngas pretreatment mainly includes cooling and cleanup and has significant influences on the performance of integrated gasification combined cycle (IGCC) power plant. This investigation sets up IGCC system model based on coal water slurry gasification by using Thermoflex software, aiming to survey how syngas quenching, syngas cooling temperature variation and syngas hot desulfurization will affect the performance as well as energy distribution of an IGCC power plant. The validity of IGCC model was verified by simulating the well-known commercial Tampa Polk IGCC power plant via comparing calculation results with reference data. Then four cases of IGCC power plants adopting different raw syngas pretreatment conditions were simulated based on the verified Tampa Polk IGCC model. Calculation results indicated that, comparing with base case, syngas quenching and an increase of 50°C in syngas cooling temperature both caused larger energy loss by syngas condensate water, leading to 7% and 0.4% decrease in power plant net efficiency. On the contrary, syngas hot desulfurization promoted gas turbine power output and prevented energy loss by syngas condensate water, resulting in a rise of net efficiency by 1.3%. Based on detailed energy distribution analyses, it is concluded that a reasonable syngas pretreatment route should be essentially beneficial to reduce exergy loss caused by irreversible heat transfer processes during syngas cooling and cleanup.

An operational approach for the designing of an energy integrated oxy-fuel CFB power plant

In order to increase the overall net electric efficiency and consequently to decrease the energy penalty in oxy-fired systems, heat integration configurations must be proposed. Coupling among the Air Separation Unit (ASU), the Compression and Purification Unit (CPU) and flue gases leaving the boiler becomes critical to obtain good efficiency figures. Many solutions have tried to show outstanding efficiency results but practical proposals are necessary to develop the technology. The use of flue gases waste energy to recycle flue gases heating up, oxygen preheating and increasing temperature of feedwater to steam cycle has been proposed to surpass the efficiency reduction. Nevertheless, care should be taken as potential problems would appear if only theoretical analysis is carried out.This work deals with a suitable and flexible design to increase the overall efficiency of an oxy-fuel combustion power plant working with high O2 concentration. Waste energy has been integrated avoiding any potential risk/damage into a new designed steam cycle. Applied solutions try to use lower cost proven materials in heat exchangers and simple equipment designs avoiding gas-gas heaters. Novel arrangements are presented, such as indirect heat exchangers, plastic heaters or different configurations integrating high pressure feedwater and low pressure condensate mass flows. Finally, results are compared with a previously optimized power plant design without operational restrictions and just a slight reduction in power plant net efficiency (less than 1%) was observed between both concepts.

Minimization of CO2 capture energy penalty in second generation oxy-fuel power plants

Oxy-combustion is one of the most promising technologies to reduce CO2 emissions from coal-fired power plants. Nevertheless, as CO2 capture system there is an important energy penalty and efficiency of the overall power plant substantially decreases. It is well accepted that the application of first generation post-combustion and oxy-fuel combustion technologies reduce the power plant efficiency in 10–12 efficiency points.Air separation unit (ASU) and compression and purification unit (CPU) are the main energy consumers in the oxy-fuel process. Moreover, the oxidant flow, which is a mixture of O2 and recirculated flue gases (RFG), requires a high heating demand in order to preheat it before the boiler inlet.This paper presents a methodology for the minimization of the energy penalty in oxy-fuel power plants that also includes ASU and CPU optimized designs with lower energy consumption, a boiler working with a high oxygen concentration (up to 40%v) in oxidant and waste energy integrated with a new designed steam cycle. Results show an important increase in power plant net efficiency (36.42%, LHV basis) regarding oxy-fuel reference power plant (32.91%). As a consequence, energy penalty can be reduced from original 10.5 points to 7.3 points.

Detailed plant layout studies of oxy-enriched CO2 pulverized coal combustion-based power plant with CO2 enrichment

Coal plays a vital role in electricity generation worldwide and is expected to contribute significantly to thermal power generation for the foreseeable future, especially in countries such as India. Carbon capture and sequestration technologies therefore become imperative in order to minimize CO2 emissions. A systematic and comprehensive assessment of the most promising of these technologies—consisting of supercritical boiler parameters, oxy-coal combustion, and low temperature flashing for simultaneous CO2 and SO2 capture—for typical Indian environmental and fuel conditions has been carried out in the present study. The results show that up to 93.3 % of CO2 and 95 % of SO2 generated during combustion can be captured while producing a sequestration-ready CO2 stream of 95.5 mol% purity compressed to a supercritical pressure of 110 bar. The energy penalty for this suite of technologies amounts to about 8.5 % drop in the net power plant efficiency to 33 % despite adopting efficiency measures such as supercritical boiler technologies.

Model development and process simulation of postcombustion carbon capture technology with aqueous AMP/PZ solvent

This study presents the development, application, and uncertainty analysis of a process simulation model for postcombustion CO2 capture with an AMP/PZ solvent blend based on state of the art knowledge on AMP/PZ solvent technology. The development includes the improvement of the physical property models of a software package designed for simulation of acid gas treatment and CO2 capture technologies. The improvement particularly consisted of regression of AMP–PZ binary interaction parameters. The model was applied to a case study of postcombustion CO2 capture from an Advanced Super Critical Pulverized Coal power plant. Uncertainly analysis was undertaken by validating the physical property models against laboratory measurements reported in literature; by comparing model results with pilot study results, and by evaluating the strength of the model with a novel method called pedigree analysis. The results show that AMP/PZ postcombustion technology performs better than MEA technology on most performance indicators, e.g., the Specific Reboiler Duty is reduced from 3.6GJ/t CO2for MEA, to 2.9 GJ/t CO2 for AMP/PZ, and the specific cooling water requirement is reduced from 4.1 to 3.4GJ/t CO2. Only amine slip to the atmosphere increases with AMP/PZ technology: from 0.18g/t CO2 to 15.3g/t CO2, although this value is still within emission limits from existing regulatory frameworks. The coal power plant net efficiency with AMP/PZ capture amounts to a value of 37.2%LHV, compared to 46.1%LHV for the case without CCS and 36.2%LHV in case of CCS with MEA. The uncertainty analysis shows that the model is well capable of predicting experimental and pilot result. The remaining uncertainty is mostly in the reaction kinetics and in the flowsheet design. Validation could be further improved, by more elaborate comparison to independent measures of physical properties, and by comparison of the model outputs to results from large demonstration or commercial size capture plants.

Thermodynamic analysis and economic evaluation of a 1000 MW bituminous coal fired power plant incorporating low-temperature pre-drying (LTPD)

Low-temperature pre-drying (LTPD) of lignite has been identified as an effective approach to improve the efficiency of lignite fired power plants. In this study, an improved concept for the pre-drying of medium moisture bituminous coals using flue gas waste heat was proposed and its feasibility was assessed. In the proposed configuration, the boiler exhaust flue gas is drawn to dryers to heat and pre-dry the raw coal, removing a large proportion of the coal moisture and leading to an improvement in the energy efficiency of the power plant. Thermodynamic analysis and economic evaluation were performed based on a typical 1000 MW bituminous coal fired power plant incorporating the proposed LTPD concept. The results showed that the net power plant efficiency gain is as much as 0.4 percentage point with additional net power output of 9.3 MW as compared to the reference plant without coal pre-drying. This was attributed to the reduction in the moisture content from 10.3 to 2.7 wt%. The additional net economic benefit attained due to the coal pre-drying was estimated to reach $1.91 M per year. This work provides a broadly applicable and economically feasible approach to further improve the energy efficiency of power plants firing coals with medium moisture contents.

An improved configuration of low-temperature pre-drying using waste heat integrated in an air-cooled lignite fired power plant

An improved low-temperature lignite pre-drying configuration using waste heat integrated in an air-cooled lignite fired power plant was proposed and examined in this study. In the proposed configuration, a portion of the steam exhaust from the low-pressure turbines condenses and then releases the latent heat in tubes embedded in a fluidized bed lignite dryer to heat the raw lignite while the warmed air from the air-cooled condensers is utilized as the fluidizing and drying medium, passing through the fluidized dryer. Through employing the proposed drying system, a part of the rejected heat of the air-cooled condensers could be recovered efficiently and beneficially utilized to dry and upgrade the raw lignite, thus leading to an improvement in the overall energy efficiency of the power plant. The results of a detailed thermodynamic analysis showed that, for a typical 600 MW air-cooled lignite fired power plant using the proposed configuration, the net power plant efficiency could be improved by 1.3 percent points with additional net power output of 19.7 MWe as compared to the reference plant without lignite pre-drying. The levelised cost of electricity (LCOE) is reduced from $47.3/MWh in the reference power plant to $45.1/MWh in the proposed power plant.

A novel lignite-fired power plant integrated with a vacuum dryer: System design and thermodynamic analysis

Pre-drying of lignite before feeding to the boiler is a potential way to increase the net efficiency of lignite-fired power plants. Lignite pre-drying is, however, a high energy consumption process with a high risk of spontaneous ignition. If the lignite is dried at low temperature, the possibility of spontaneous ignition of lignite in the drying process could be lowed. Furthermore that low temperature energy could be used as the drying heating source may result in a high net efficiency of the power plant. Therefore, we designed a lignite-fired power plant integrated with a vacuum dryer. We also thermodynamically analyzed a reference case of a 1000 MW power plant by using theoretical models developed. The results show that the net efficiency of power plant can be increased by 2.39% or 1.88% absolutely, if a low-pressure steam or heat pump is used to provide the drying heat source, respectively. From analyzing main factors, we discovered that the net efficiency of the power plant increases with the drying degree and decreases with the operating pressure of the dryer, and the heat pump is a better choice to provide the heating source for drying purposes with its second-law efficiency higher than 0.76.

A Novel Lignite Pre-drying System Incorporating a Supplementary Steam Cycle Integrated with a Lignite Fired Supercritical Power Plant

A novel lignite pre-drying system incorporating a supplementary steam cycle integrated with a lignite fired supercritical power plant was proposed and thermodynamically evaluated using the EBSILON Professional software. Differing from the conventional pre-drying systems, the steam bleed for the dryer in the proposed system is drawn from the intermediate pressure turbine and put through a separated turbine called T-turbine. With the T-turbine installed, the superheating requirement of the bleed for the dryer and for some regenerative heaters is significantly reduced, thus leading to a further increase in the lignite fired power plant efficiency. The simulation results show that the net power plant efficiency improved by 2.6% and the cost of electricity reduced by up to 1.26 $/MWh can be achieved, compared with the reference case. The exergy destruction can also be significantly reduced in the proposed lignite pre-drying system. The concept of the novel integrated system may provide a promising method for lignite pre-drying in the future generation lignite power plants.

Conceptual study of a high efficiency coal-fired power plant with CO2 capture using a supercritical CO2 Brayton cycle

A concept of coal-fired power plant built around a supercritical CO2 Brayton power cycle and 90% post-combustion CO2 capture have been designed. The power cycle has been adapted to the coal-fired boiler thermal output, this boiler has been roughly designed in order to assess the power cycle pressure drop and its cost, an adapted CO2 capture process has been designed and finally the overall heat integration of the power plant has been proposed. Due to the high complexity of such as plant, this paper does not intend to provide definitive evaluation of the concept but to explore its potential.A coal power plant with CO2 power cycle without carbon capture could achieve a net efficiency of 50% (LHV) with a maximal temperature and pressure of 620 °C and 300 bar, these performances has to be validated but the first results on pilot plant are encouraging. The CO2 capture process use monoethanolamine as solvent and is equipped with vapor recompression systems in order to reduce the heat needed from the CO2 cycle. It achieves around 2.2 GJ/tCO2 of specific boiler duty with 145 kWh/tCO2 of electrical auxiliary consumption including compression to 110 bar. The energetic evaluation of the overall power plant carried out highlights the promising potential of CO2 supercritical cycle. A net power plant efficiency of 41.3% (LHV), with carbon capture and CO2 compression to 110 bar, seem to be achievable with available or close-to-available equipment.A technical-economic evaluation of the designed power plant has been performed. It shows a levelized cost of electricity reduction of 15%, and a cost of avoided CO2 reduction of 45%, without transport and storage, compared to a reference supercritical coal-fired power plant equipped with standard carbon capture process.

Natural Gas Combined Cycle Power Plant Integrated to Capture Plant

A natural gas combined cycle (NGCC) power plant with capacity of about 430 MW integrated to a chemical solvent absorber/stripping capture plant is investigated. The capture ratio is 90%, and the captured CO2 is compressed to 75 bar, liquefied, and finally pumped up to 110 bar. Both full load and partial load conditions are studied. The energy penalty for CO2 capture is 398.4 kWhel/ton of CO2, which causes a 7.5%-points reduction in the power plant net efficiency. From this energy penalty, 4.6%-points is related to the steam extraction and 2.9%-points is related to electricity consumption. The integration of the power plant with the compression section of the capture plant for preheating the water to the heat recovery steam generator (HRSG) will not improve the net plant efficiency. From the partial load investigation, the net efficiency of the variable IGVs gas turbine is shown to be about 6.2%-points higher than the efficiency of the constant IGVs gas turbine at 50% load. Also, the power plant with the throttled valve configuration for steam extraction has a better performance than the sliding configuration steam extraction.

Experimental research on the performance of CO2-loaded solutions of MEA and DEA at regeneration conditions

Amine-based post combustion CO2 capture is considered as one of the most advanced technologies to be implemented in new and existing coal-fired power plants for CCS. Although it has proven technically viable, it has not been installed on a large-scale application yet. The main drawback of the process is the high energy requirement for the regeneration of the amine solution. Values around 4MJ/kg of CO2 for the standard MEA-based process have been reported. The heat duty must be supplied by means of low-pressure steam from the power plant, which causes a decrease in the power plant net efficiency of up to 13%-points. Therefore, improvements in process technology and solvent development are important to reduce the penalty in the power plant efficiency.Results from lab-scale research on the absorption and desorption of MEA and DEA at different concentrations are presented and discussed. Absorption and desorption capacities, as well as the regeneration of the CO2-loaded solutions in a stripper column and the influence of different operating parameters have been experimentally investigated.