Supercritical Steam Cycle Research Articles

A real-time phase transition modeling of supercritical steam cycle and load variation rate enhancement of thermal power plants under deep peak shaving

The ambitious green revolution to renewable energy sources in global power grids necessitates massive integration of solar and wind energy, which involves intermittent and unpredictable challenges. Thermal power plants are crucial in stabilizing the grid and addressing these challenges through flexibility reformation including deep peak shaving and frequent load variations since the unsteady state energy transfer and thermal dynamics during combustion and heat transformation in thermodynamic processes vary significantly. These conditions lead to issues such as furnace instability and latent heat of phase transition. This study introduces a novel approach to modeling phase transitions of supercritical steam cycle, and investigatesthe length, position, temperature, and energy transfer of the working medium and components under normal and low operational states. Conducting and analyzing the thermal feasible region associating the security of components and working medium this study establishes a control strategy for dynamic heat transfer to reduce component degradation effects andenhance load variation rate under flexible operations. Simulation model of a supercritical power unit based on the proposed method demonstrates an accuracy of 97.94%. Results from the optimal approach in maximizing load variation rate show the effectiveness and achieve 1.2%p.e./min most under transition process.

Subcritical and supercritical Rankine steam cycles, under elevated temperatures up to 900°C and absolute pressures up to 400 bara

The Rankine cycle is a conceptual arrangement of four processes as a closed vapor power thermodynamic cycle, where a working fluid (especially water as a liquid, as a vapor, and as a liquid-vapor mixture) can be used to convert heat into mechanical energy (shaft rotation). This cycle and its variants are widely used in electric power generation through utility-scale thermal power plants, such as coal-fired power plants and nuclear power plants. In the steam-based Rankine cycle, water should be pressurized and heated to be in the form of very hot high-pressure water vapor called “superheated steam,” before the useful process of expansion inside a steam turbine section occurs. If the absolute pressure and temperature of the superheated steam are both above the critical values for water (220.6 bara and 374.0°C), the cycle is classified as “supercritical.” Otherwise, the cycle is classified as “subcritical.” This study considers the impact of the temperature and pressure, independently, on the performance of a steam Rankine cycle. Starting from a representative condition for a subcritical cycle (600°C peak temperature and 50 bara peak absolute pressure), either the peak temperature or the peak absolute pressure of the cycle is increased with regular steps (up to 900°C, with a temperature step of 50°C, and up to 400 bara, with a pressure step of 50 bar). The variation of five scale-independent performance metrics is investigated in response to the elevated temperature and the elevated pressure. Thus, a total of 10 response curves are presented. When the temperature increased, all the five response variables were improved in a nearly linear profile. On the other hand, increasing the pressure did not give a monotonic linear improvement for each response variable. In particular, the cycle efficiency seemed to approach a limiting maximum value of 45% approximately, where further increases in the pressure cause diminishing improvements in the efficiency. When varying the peak pressure, an optimum minimum ratio of (water-mass-to-output-power) is found at 203 bara, although the cycle efficiency still increases beyond this value. In the present research work, the web-based tool for calculating steam properties by the British company Spirax Sarco Limited, and the software program mini-REFPROP by NIST (United States National Institute of Standards and Technology) were used for finding the necessary specific enthalpies (energy content) of water at different stages within the steam cycle. Both tools were found consistent with each other, as well as with the Python-based software package Cantera for simulating thermo-chemical-transport processes. The results showed that if the peak temperature reaches 900°C, a gain of about 5 percentage points (pp) in the thermal cycle efficiency becomes possible (compared to the case of having a base peak temperature of 600°C), as the predicted efficiency was found to increase from 38.60% (base case) to 43.67%. For the influence of the steam peak pressure, operating in the subcritical regime but close to the critical point appears to be a good choice given the gradual decline in efficiency gains at higher pressures. About 4.7 percentage point increase was found at the high subcritical peak pressure of 200 bara (compared to a base subcritical peak pressure of 50 bara). The results of this study also showed that the liquid water droplet mass fraction at the steam turbine exit diminishes from 11.00% at 600°C to only 1.48% at 900°C, which is favorable. This mass fraction grows from 11.00% at 50 bara to 27.89% at 400 bara, which is not acceptable. Every 100°C increase in the superheating temperature between 600°C and 900°C was found to cause aa increase in the cycle thermal efficiency by about 1.69 percentage points, and simultaneous a beneficial increase in the steam quality at the turbine exit by about 3.17 percentage points.

Supercritical CO2 power cycle

The article is focused on summarizing the issue of energy circuits working with supercritical carbon dioxide sCO2. Carbon dioxide is currently coming to the forefront of many research institutions with regard to its possible use in its supercritical conditions, thanks to which higher efficiency and compactness of equipment can be achieved compared to conventional steam-water cycles. The article describes the basic properties of this medium, including a description of sCO2 cycles (Brayton, Rankine, etc.). Furthermore, the possible use of energy cycles with sCO2 is discussed, especially in solar and nuclear power plants and in power plants burning fossil fuels. In the case of solar power plants, the sCO2 Brayton cycle can offer higher cycle efficiencies than using super-critical steam cycles. The use of sCO2 in nuclear or coal power plants in turn increases efficiency and reduces water consumption. In addition, the use of the sCO2 circuit in new nuclear reactors of the IV generation is currently being considered, in which the operating temperatures are in the range of 500 - 900 °C, i.e. they are generally higher than operating water-cooled reactors. Even though the use of CO2 refrigerant in power systems has been known for a long time (e.g. use in the first Czechoslovak power plant in Jaslovské Bohunice), they are still not used commercially in the energy industry. One of the reasons is the ongoing research into the behavior of materials at high temperatures in sCO2, corrosion protection, or the effect of carbon dioxide purity on behavior in the supercritical region.

Real-time modeling and optimization of molten salt storage with supercritical steam cycle for sustainable power generation and grid support

This research article presents an innovative approach to enhance sustainable power generation and grid support by integrating real-time modeling and optimization with Molten Salt Energy Storage (MSES) and a Supercritical Steam Cycle (s-SC). As renewable energy usage grows, intermittent resource availability challenges grid stability and reliable power supply. To address this, we develop a system that merges real-time modeling and optimization for precise control of MSES and s-SC components. This integration ensures uninterrupted energy generation, storage, and distribution, optimizing renewable energy use during high-demand periods. Mathematical models and simulations assess the system's dynamic behavior, performance, and economic viability. Rigorous techno-economic analysis highlights cost-effectiveness and environmental benefits. Findings reveal exceptional energy efficiency and grid support, making it a promising solution for sustainable power generation and grid stability amid renewable energy growth. Real-time modeling and optimization emerge as crucial components in modern energy systems. The Combined Heat and Power (CHP) system achieves 56% energy efficiency with off-design impacts considered and 63.61% without. Also, the overall system exergy efficiency decreased from 73.36% at design to approximately 63.55% under off-design scenarios. Regarding the economic aspect, the levelized cost of storage (LCOS) for the CHP system is estimated at 114.4 €/MWh with off-design conditions and 106.8 €/MWh without.

Cascading the Transcritical CO2 and Organic Rankine Cycles with Supercritical CO2 Cycles for Waste Heat Recovery

Concentrating solar power (CSP) applications can benefit from the superior thermophysical and chemical properties of supercritical CO2 (sCO2), which offers greater cycle efficiency in contrast to supercritical or superheated steam cycles. The transcritical CO2 (TCO2 cycle) excels in low-grade waste heat recovery (WHR), while the organic Rankine cycle (ORC) is also a potential option for WHR from sCO2 cycles. This study focuses on the thermodynamic assessment and optimization of combined power cycles, incorporating multiple bottoming cycles, to enhance overall thermal efficiency. The configurations employed include recompression, partial cooling, and main compression intercooling within the sCO2 cycle. Waste heat recovery is achieved using both TCO2 and ORC. The parametric analysis explores key variables such as turbine inlet temperature, main compressor inlet temperature, recuperator effectiveness, pressure ratios in the bottoming cycles, and condensation temperatures of the bottoming cycles. Furthermore, this research conducts performance analysis of the proposed combined cycle configurations. The results underscore the substantial enhancement of combined cycle performance with regard to thermal and exergy efficiency. A rise in the highest temperature that can occur in the sCO2 cycle leads to improved thermal efficiency. The Main Compressor Inlet Temperature (MCIT) exhibits an efficiency increase of up to 40°C–45°C, attributed to pseudocritical effects, followed by a decline. Among the various configurations, the combined partial cooling cycle generates the highest net output power. The study finds that the combined main compression model consistently outperforms other layouts, yielding a 2-2.5% increase in efficiency. Optimization of the intermediate pressure value for the partial cooling (PC) and main compression (MC) cycles at 10 MPa further contributes to enhanced performance. This study not only presents the optimized operating conditions for each combined cycle but also offers a comparative analysis of these models under different boundary conditions. The findings from this research significantly advance the utilization of waste heat and the development of clean power generation.

Techno-Economic Comparison of Supercritical CO2, Steam, and Organic Rankine Cycles for Waste Heat Recovery Applications

Abstract Supercritical CO2 (sCO2) is taking a growing interest in both industry and academic communities as a promising technology capable of high efficiency, flexibility, and competitive capital costs. Many possible applications are studied in the energy field, from nuclear power plants to concentrating solar power and waste heat recovery (WHR). To evaluate the competitiveness of sCO2 cycles relative to other competing technologies, mainly steam and organic fluid Rankine cycles (ORC), a specific techno-economic analysis is needed to fairly compare the different technologies for each application, in order to find the most appropriate market position of the innovative sCO2 plants, compared to the existing steam and ORC solutions. In the present study, techno-economic analysis and optimization have been conducted focusing on WHR applications, for different sizes and cycle parameters operating conditions using an in-house simulation tool. The analyzed cycles were first optimized by aiming at maximizing the net electrical power and then aiming at minimizing the specific capital cost. As a result, compared to traditional plants, we obtained that in the first case, the more complex sCO2 cycle configuration shows competitive performance, while in the second case, the simpler sCO2 cycle configuration has a lower specific cost for the same electrical power produced (with a difference of approximately −130 €/kW compared to the steam cycle). In general, while traditional technologies confirmed a good tradeoff between performance and cost, supercritical CO2 cycles show attractive characteristics for applications requiring simplicity and compactness, guaranteeing in the meantime other technical advantages such as water-free operation.

Coupling chemical looping combustion of solid fuels with advanced steam cycles for CO2 capture: A process modelling study

Chemical looping combustion is a cost-competitive solution for producing low carbon electricity. In this paper, we investigate by means of a process modelling study, the coupling of chemical looping combustion of solid fuels with advanced steam-based power cycles, viz. supercritical, ultra-supercritical and advanced ultra-supercritical Rankine cycles. The energy and exergy efficiencies of the various chemical looping combustion power plant configurations are compared against the reference plants without carbon capture. Our models incorporate practical considerations for reactor design. With an upper operating temperature limit of 950 °C, the maximum efficiencies achievable by integrated gasification combined cycle chemical looping combustion (IGCC–CLC) and in situ gasification chemical looping combustion power plants (iG-CLC) are 41.3% and 41.5%, respectively. Overall, iG-CLC emerges as the most efficient CLC configuration. Comparing to an integrated gasification combined cycle without carbon capture, the energy efficiency penalties for capturing CO2 from iG-CLC coupled with subcritical, supercritical, ultra-supercritical or advanced ultra-supercritical steam cycles are 5.1%, 5.0%, 5.2% or 13.0%, respectively. The biomass-fired chemical looping combustion power plants also show low energy efficiency penalties (<2.5%) compared to the reference biomass power plants without CO2 capture. Our modelling results suggest that chemical looping combustion will remain an attractive carbon capture technology for solid fuel power plants, in a future when supercritical steam turbines become the norm.

FACTOR ANALYSIS OF THE THERMAL SCHEME OF CHP WITH SUPER CRITICAL STEAM CYCLE ON THE BASIS OF EXERGY METHOD

The most promising direction of CHP modernization is the introduction of power units on supercritical steam parameters. Increasing steam parameters is one of the most effective ways to increase the efficiency of a CHP plant. Thus, the development of the concept of thermal schemes turbines for supercritical steam parameters, taking into account the characteristics of their operation at the existing CHP Ukraine is an actual scientific problem. The solution to this problem will make it possible to replace or modernize the power generating equipment that has exhausted its resource with modern power units that meet world economic and environmental standards. The method of exergy analysis is adapted to the study of thermal schemes of CHP plants with supercritical steam cycle. As an example of application of a method the exergy analysis of the power plant working on the one-stage thermal scheme is carried out. Within the framework of the proposed method, a thermodynamic and topology-exergetic model of the power plant is created. Based on the topology-exergetic model the indicators of thermodynamic efficiency of the power plant operating on supercritical parameters of steam are determined. It is proposed to apply the theory of experiment planning in exergy analysis of the thermal circuit of a CHP. With the involvement of this theory, a multifactor numerical experiment was conducted to determine the impact on the exergetic efficiency of the thermal scheme of CHP of the main determining variable factors, such as adiabatic and thermal efficiency of the plant, as well as the operating parameters. The generalized equation of functional interrelation of exergetic efficiency of system and exergetic efficiency of elements of thermal scheme of CHP is received. The proposed equation can be used as a tool for further training of neural networks and their application both in the design and in the diagnosis of energy efficiency of CHP. According to the results of the factor analysis, a rather high conservatism of the considered one-stage scheme of CHP to the change of the varied parameters was revealed. This indicates the presence of more rigid structural links between the elements, which is generally a positive aspect of the reconstruction.

Preliminary Analysis and Design of the Energy Conversion System for the Molten Salt Fast Reactor

The unique design features of the molten salt fast reactor (MSFR) should enable higher coolant temperatures than in conventional water reactors, with a significant improvement in the achievable thermodynamic performance. The use of a molten salt as both fuel and coolant, however, poses several advanced heat transfer challenges, such as the design of innovative heat exchangers and energy conversion systems. In this work, we address a preliminary but quantitative analysis of the energy conversion system for the MSFR, based on reference design data from the SAMOFAR H2020-EURATOM project. We consider three main technologies, i.e., the supercritical steam cycle, the closed helium cycle and the helium/steam combined cycle. Preliminary design results are presented for each technology, based on a simplified modelling approach. The considered cycles show promising efficiency improvements, with the best performance being proven by the supercritical steam cycle. The analysis also highlights the critical issue related to the risk of freezing of the molten salts within the secondary heat exchangers, due to the low inlet temperatures of the working fluids. Results show potential incompatibility between the freezing point of molten salts and the temperatures typical of steam cycles, while helium cycles offer the best chances of freezing avoidance. The combined cycle promises intermediate performance in terms of thermodynamic efficiency and thermal compatibility with molten salts comparable with closed helium cycles.

Integration of the 660 MW supercritical steam cycle with the NH3-based CO2 capture process: System integration mechanism and general correlation of energy penalty

Aqueous ammonia based post-combustion CO2 capture (PCC) is an attractive alternative to amine based technologies for reduction of CO2 emission from coal fired power stations. However its integration with power stations is not well studied. This research examined the system integration mechanism of the 660 MW supercritical steam cycle with a NH3-based PCC process. Three integration methods were proposed:Method 1 (steam extraction from the IP/LP crossover), Method: 2 (steam extraction from the IP/LP crossover and the addition of a new letdown turbine while the condensate is returned to the deaerator), and Method: 3 (steam extraction from the IP/LP crossover and addition of a new turbine while the condensate is returned to the condenser). Three cases were presented using the above three methods, and were designated as Case 1, Case 2, and Case 3, respectively. The original power plant was taken as the base case. Among three cases studied, the thermal efficiency of case 2 is the highest and at 36.08% with a decrease of thermal efficiency by 11.61 percentage points compared to the base case. A sensitivity analysis was performed to investigate the effect of important parameters including the concentration of NH3, CO2 loading, and stripper pressure on the regeneration duty of the capture process and the energy output of the integrated process. The minimum energy requirements of the capture process does not lead to the minimum energy penalty introduced on the power plant. The findings indicate that the energy penalty in PCC integrated power plant depends on the temperature of the extracted steam, the heat duty of the reboiler, and the stripper pressure. A general correlation of the energy penalty of ammonia based PCC onto a supercritical power plant was obtained from the simulation results, which can enable a reliable evaluation of the PCC energy penalty imposed on the power plant.

Development of a supercritical and an ultra-supercritical circulating fluidized bed boiler

The supercritical circulating fluidized bed (CFB) boiler, which combines the advantages of CFB combustion with low cost emission control and supercritical steam cycle with high efficiency of coal energy, is believed to be the future of CFB combustion technology. It is also of greatest importance for low rank coal utilization in China. Different from the supercritical pulverized coal boiler that has been developed more than 50 years, the supercritical CFB boiler is still a new one which requires further investigation.Without any precedentor engineering reference, Chinese researchers have conducted fundamental research, development, design of the supercritical CFB boilers independently. The design theory and key technology for supercritical CFB boiler were proposed. Key components and novel structures were invented. The first 600 MWe supercritical CFB boiler and its auxiliaries were successfully developed and demonstrated in Baima Power Plant, Shenhua Group as well as the simulator, control technology, installation technology, commissioning technology, system integration and operation technology. Compared with the 460 MWe supercritical CFB in Poland, developed in the same period and the only other supercritical one of commercial running in the word beside Baima, the 600 MWe one in Baima has a better performance. Besides, supercritical CFB boilers of 350 MWe have been developed and widely commercialized in China. In this paper, the updated progress of 660 MWe ultra-supercritical CFB boilers under development is introduced.

On low-grade waste heat utilization from a supercritical steam power plant using an ORC-bottoming cycle coupled with two sources of heat

This paper analyzes a waste heat recovery system based on a binary vapor cycle composed of an organic Rankine cycle (ORC) bottoming a supercritical steam cycle. The organic Rankine cycle is supplied by two heat sources. The first one is waste heat from a steam boiler, which condenses flue gases to 200MWt at 90°C and preheats the fluid with a low boiling point. The second one is a steam condenser, which also acts as a low-boiling-point fluid vapor generator. Steam condensation temperatures was tested in the range 55–115°C. Usage of a low-boiling-point fluid instead of steam in range of the low temperature (below 100°C) has several advantages. One advantage is the possibility for the effective utilization of a large amount of low-grade waste heat from a supercritical steam cycle. For the most efficient configuration, 22.92MW of additional electrical energy is generated. The thermal efficiency of the waste heat recovery system is 11.46%, which is 71.75% of the Carnot efficiency. Usage of an organic Rankine cycle for bottoming the supercritical steam cycle also provides cubature reduction of the power plant. For the most efficient case, a steam volume flow at the new steam turbine outlet is reduced by 88% compared to a reference stream turbine. The volume flow at the ORC turbine outflow is reduced by 54%. Numerical analyses of the thermodynamic cycles, before and after modifications, are carried out using computational flow mechanics, mainly, with in-house code.

Cogeneration Systems in Brazilian Sugarcane Industry: Current and Future Perspectives

Background: Cogeneration systems using biomass materials as woodships, agricultural and municipal solid waste, are well known and used in different places of the world. Today Brazilian sugarcane bagasse is an important energy source to these industries, most of them are self-sufficient in energy consumption and some generate energy surplus that is sold to the grid. There is a tendency forenlarging the electricity production at these industries and it is expected that in short to mid-term electricity produced from bagasse could become a product as important as ethanol or sugar. Methods: This study provides an overview of scientific papers and patents regarding the current situation of biomass cogeneration in Brazil and future prospects, focusing on the use of advanced cogeneration systems with integrated gasification combined andsupercritical steam cycles. Results: The results showed that much can still be done to improve the energetic efficiency at this sector. The current situation shows that although many companies are self-sufficient in terms of electricity just a few are able to sell electricity to the grid. There are many opportunities to better use the sugarcane bagasse and other biomass residues for energy production, from minor changes as improvements at the burning system to advanced power generation solutions. The minor changes can be accomplished with lower investment costs but with significant results for energy generation. Conclusion: The use of advanced power generation solutions as biomass gasification and supercritical steam cycles, proved to be highly efficient in energy production, generating a great electricity surplus.

Energy Environment Implication in Thermal Power Plant by using Supercritical Technology – Indian Scenario

In India, emissions of Green House Gases (GHGs) are increasing due to rise in energy demands to sustain economic growth. Coal is used as a dominant fuel in Indian thermal power plants but the efficiency of these is low in comparison with prevailing international standards. As such emissions of GHGs are much higher and feasible to achieve. The adoption of Clean Coal Technologies (CCTs) – like the Supercritical (SC) steam cycle – for new capacity addition in Indian thermal power plants will increase the efficiency of the Indian grid. These technologies are more environmentally and would help to meet increased energy demands. India has taken initiatives for the adoption of the technology as explained in the 11th plan of the Planning Commission. Finally, it is concluded from the study that SC and USC technology penetration would be helpful for reducing GHGs emission. The hypothetical scenarios analysis shows that up to 50% technology penetration for new capacity addition until 2027 would be helpful for reducing GHGs emission.

CO2 capture in advanced power plants fed by coal and equipped with OTM

Greenhouse gas emissions from human activities contribute greatly towards climate change. In the power generation sector, where fossil fuels are extensively used, these emissions could be reduced by capturing and storing the CO2 emitted. Between the different fossil fuels, coal is very interesting from an economic point of view (coal reservoirs are abundant and distributed homogenously on the earth) even if it produces a lot of carbon dioxide emissions.In this paper we have studied energy and economic performance of an integrated gasification combined cycle power plant (IGCC power plant equipped with an oxygen-blown gasifier) with CO2 capture based on the pre-combustion process and an advanced supercritical steam cycle (SSC) power plant with CO2 capture based on oxy-fuel combustion process. In these power plants great oxygen flow rates are necessary and so we have chosen an innovative technology for oxygen production based on oxygen transport membranes. The goal of this paper is the discussion of the main characteristics and performance of these membranes and the analysis of their integration in advanced coal-fired power plants. For each power plant, a full plant heat and mass balance is calculated in order to compare energy and environmental performance (net efficiency and CO2 specific emissions) and to evaluate the economic impacts of such CO2 emission abatement technologies.

Viability of fuel switching of a gas-fired power plant operating in chemical looping combustion mode

CLC (chemical looping combustion) promises to be a more efficient way of CO2 capture than conventional oxy-fuel combustion or post-combustion absorption. While much work has been done on CLC in the past two decades, the issue of multi-fuel compatibility has not been addressed sufficiently, especially with regard to plant layout and reactor design. In the present work, it is shown that this is non-trivial in the case of a CLC-based power plant. The underlying factors have been examined in depth and design criteria for fuel compatibility have been formulated. Based on these, a layout has been developed for a power plant which can run with either natural gas or syngas without requiring equipment changes either on the steam side or on the furnace side. The layout accounts for the higher CO2 compression costs associated with the use of syngas in place of natural gas. The ideal thermodynamic cycle efficiency, after accounting for the energy penalty of CO2 compression, is 43.11% and 41.08%, when a supercritical steam cycle is used with natural gas and syngas, respectively. It is shown that fuel switching can be enabled by incorporating the compatibility conditions at the design stage itself.

Efficiency improvement strategies for the feedwater heaters network designing in supercritical coal-fired power plants

Coal will continue playing a major role in worldwide electricity generation during next years. This trend will augment CO2 emission to the atmosphere. Improving power plant efficiency could alleviate the negative effect of coal consumption on CO2 emissions. Main efforts have been focused on supercritical boiler technology (once-through units) and materials development (austenitic steels) with the aim of accomplishing high steam parameters that allow this efficiency enhancement. However, improvement in supercritical steam parameters should be followed by an exhaustive review of the steam cycle design. This paper shows a strategy for the optimization of the feedwater heaters network and the flue gas heat recovery system design. Starting with the lay-out of a supercritical steam cycle using the best available technology, this paper analyses not only the steam cycle itself, but also its integration with the boiler cold-end. By means of thermodynamic optimization it is possible to propose new feedwater heat exchanger network configurations and reducing steam consumption from turbine bleeds, achieving optimum power plant efficiency. Simulations have been carried out using Aspen Plus software and optimization procedure is based on a sequential quadratic programming method that maximized overall plant efficiency taking turbine bleeds pressure as independent variables. Results show a feasible improvement of the overall plant efficiency of 0.7 points in comparison with state-of-the-art reference plant. This increase implies a direct reduction of CO2 emissions of about 1.3% compared with the best plant currently available. Moreover, an economic analysis confirms the feasibility of the proposals analysed and shows important additional yearly incomes.

Techno-economic analysis of biomass/coal Co-gasification IGCC systems with supercritical steam bottom cycle and carbon capture

In recent years, integrated gasification combined cycle technology has been gaining steady popularity for use in clean coal power operations with carbon capture and sequestration (CCS). This study focuses on investigating two approaches to improve efficiency and further reduce the greenhouse gas (GHG) emissions. First, replace the traditional subcritical Rankine steam cycle portion of the overall plant with a supercritical steam cycle. Second, add different amounts of biomass as feedstock to reduce emissions. Employing biomass as a feedstock has the advantage of being carbon neutral or even carbon negative if CCS is implemented. However, due to limited feedstock supply, such plants are usually small (2–50 MW), which results in lower efficiency and higher capital and production costs. Considering these challenges, it is more economically attractive and less technically challenging to co-combust or co-gasify biomass wastes with low-rank coals. Using the commercial software, Thermoflow®, this study analyzes the baseline plants around 235 MW and 267 MW for the subcritical and supercritical designs, respectively. Both post-combustion and pre-combustion CCS conditions are considered. The results clearly show that utilizing a certain type of biomass with low-rank coals up to 50% (wt.) can, in most cases, not only improve the efficiency and reduce overall emissions but may be economically advantageous, as well. Beyond a 10% Biomass Ratio, however, the efficiency begins to drop due to the rising pretreatment costs, but the system itself still remains more efficient than from using coal alone (between 0.2 and 0.3 points on average). The CO2 emissions decrease by about 7000 tons/MW-year compared to the baseline (no biomass), making the plant carbon negative with only 10% biomass in the feedstock. In addition, implementing a supercritical steam cycle raises the efficiency (1.6 percentage points) and lowers the capital costs ($300/kW), regardless of plant layout. Implementing post-combustion CCS consistently causes a drop in efficiency (at least 7–8 points) from the baseline and increases the costs by $3000–$4000/kW and $0.06–$0.07/kW-h. The SOx emissions also decrease by about 190 tons/year (7.6 × 10−6 tons/MW-year). Finally, the CCS cost is around $65–$72 per ton of CO2. For pre-combustion CCS, sour shift appears to be superior both economically and thermally to sweet shift in the current study. Sour shift is always cheaper, (by a difference of about $600/kW and $0.02-$0.03/kW-h), easier to implement, and also 2–3 percentage points more efficient. The economic difference is fairly marginal, but the trend is inversely proportional to the efficiency, with cost of electricity decreasing by 0.5 cents/kW-h from 0% to 10% biomass ratio (BMR) and rising 2.5 cents/kW-h from 10% to 50% BMR. Pre-combustion CCS plants are smaller than post-combustion ones and usually require 25% less energy for CCS due to their compact size for processing fuel flow only under higher pressure (450 psi), versus processing the combusted gases at near-atmospheric pressure. Finally, the CO2 removal cost for sour shift is around $20/ton, whereas sweet shift's cost is around $30/ton, which is much cheaper than that of post-combustion CCS: about $60–$70/ton. Copyright © 2014 John Wiley & Sons, Ltd.

A systematic approach for high temperature looping cycles integration

High temperature solid cycles are promising technologies for implementing large-scale CO2 capture facilities in the mid-term. Energy integration plays a major role in the development of these cycles. Waste energy from the capture process may be used to retrofit an existing power plant or to power a new steam cycle, thus diminishing the energy penalty that the process entails. A procedure based on pinch analysis for the integration of these systems, is proposed and tested using limestone as CO2 sorbent. Although Li4SiO4 has been already dismissed for this purpose, it is used to validate the systematic procedure under a very different problem in terms of available heat and initial temperatures of hot streams. In both scenarios the integration was designed to take advantage of all available heat of the process and to power a supercritical steam cycle, quantifying their minimum energy penalty. A sensitivity analysis for each process was also developed, and the heat exchanger network achieved by the proposed algorithm obtained the best results in costs terms.

Economic Potential of Innovative Receiver Concepts With Different Solar Field Configurations for Supercritical Steam Cycles

The cost reduction potential of solar power towers (SPT) is an important issue concerning its market introduction. Raising the steam process temperature and pressure can lead to a cost reduction due to increased overall plant efficiency. Thus, for new receiver configurations, a supercritical steam cycle operated at 300 bar/600 °C/610 °C live steam conditions was assumed. The considered systems include innovative direct absorption receivers, either with conventional or beam down heliostat field layouts. For the beam down option, the receiver is assumed to be a cylindrical vessel with a flow-through porous absorber structure at the internal lateral area of the cylinder. The direct absorption receiver option consists of a cylindrical barrel with downwards oriented aperture, whose absorber structure at the internal lateral area is cooled by a molten salt film. For the assessment, CFD based methods are developed and able to examine the receiver efficiency characteristics. Based on the receiver thermal efficiency characteristics and the solar field characteristics, the annual performance is evaluated using hourly time series. The assessment methodology is based on the European Concentrated Solar Thermal Roadmap (ECOSTAR) study and enables the prediction of the annual performance and the levelized cost of electricity (LCOE). Applying appropriate cost assumptions from literature, the LCOE are estimated for each considered SPT concept and compared to tubular receiver concepts with molten salt and liquid metal cooling. The power level of the compared concepts and the reference case is 200 MWel. The sensitivity of the specific cost assumptions is analyzed. No detailed evaluation is done for the thermal storage, but comparable storage utilization and costs are assumed for all cases. At optimized plant parameters, the results indicate a LCOE reduction potential of up to 0.5% for beam down and of up to 7.2% for the direct absorption receiver compared to today's state of the art molten salt solar tower technology.