Supercritical Steam Research Articles

Environmental Geological Problems in Southwest China: A Case Study from the Researches of Regional Landslide Hazards

Humans have paid a lot of attention to environmental geological challenges in recent years. Landslides, being one of the most prevalent geological disasters, are characterized by their suddenness and destructiveness. Southwest China is prone to landslides and debris flows due to its unique geological structure. This paper uses landslides in southwest China as an example, focusing on research on landslide initiation mechanisms and outlining modern landslide monitoring devices and prediction models. Landslides are caused by external variables such as persistent precipitation, groundwater movement, and significant seismic activity, as well as interior reasons such as fine particle rearrangement and the action of positive pore water. The reduction of the friction coefficient of the shear surface, which is induced by the increase of the shear rate, the supercritical carbon dioxide and superheated steam of the shear zone, and the mineral recrystallization process on the shear surface, all have an important impact on reducing the friction coefficient of the shear surface, is a key factor in the occurrence of high-speed remote landslides. Real-time landslide monitoring using space-air-ground and acoustic emission technology, as well as the creation of machine learning-based forecast models, have aided in the research of landslide development and early warning.

Numerical analysis of environment-friendly solar aided coal-fired supercritical thermal power plant cycle integrated with dual heat exchangers

The hybrid solar-coal supercritical steam thermal system has been developed in current research work. The proposed system uses a double-tank heat storage system to increase the stability of the solar tower system, and two heat exchangers to transfer heat from molten salt in the solar tower system to steam in a supercritical coal-fired thermal system. TRNSYS software has been used as a platform to build a model of the solar coal-fired hybrid supercritical steam thermal system. Local weather data is imported to simulate the characteristic year’s operation of a hybrid system under design and off-design working conditions. The variation of heat transferred from solar system to supercritical steam thermal system, power generated from supercritical steam thermal system, solar-electrical generation capacity, efficiency and proportion of solar power generation are compared and analyzed. The results show that after the system is integrated, the tower solar steam production mechanism will increase the output power of supercritical steam thermal system and reduce thermal efficiency of the integrated system. When boiler steam flow rate is kept at less than reference flow rate after joining with solar steam flow rate, total steam flow rate exceeds the reference flow rate, while solar steam flow rate increases.

Experimental and kinetic study of vacuum residue cracking over zirconium based catalysts

In this study, thermal cracking and catalytic cracking over zirconium-based catalysts of the vacuum residue were achieved in the presence of supercritical steam at 400–450 °C, 20 bar, and 2–4 h. Two different catalysts (ZrFeNi and ZrCoNi) were prepared using a sol–gel precipitation method and characterized using X-ray diffraction, EDX-spectrum, scanning electron microscopy, and BET surface area. The results showed the lowest VR conversion was achieved in the thermal cracking, catalytic cracking using ZrFeNi and catalytic cracking using ZrCoNi were 31.7, 35.3, and 38% while the highest VR conversion was achieved in the thermal cracking, catalytic cracking using ZrFeNi and catalytic cracking using ZrCoNi were 38.6, 71.1 and 76.3%. A new kinetic model of the eight lumps and 28 reaction steps were developed to describe the VR cracking while a genetic algorithm optimization method was used to predict the optimum set of kinetic parameters in which all computations were achieved using MATLAB version 2020a.

Simulation of an Advanced Geothermal Energy Conversion Plant in Perú

This investigation aims to simulate an efficient plant that generates energy through a solar-geothermal hybrid energy conversion system with supercritical steam, Therminol VP1, geothermal fluid and R134a refrigerant. The goal is to exemplify a hybrid solution that optimizes and takes advantage of the existing properties of the solar and geothermal power cycles. The geothermal part of the process, the primary cycle, is augmented by the solar thermal cycle to obtain a high-efficiency result. In addition, it allows the reader to understand the ideal process of this type of plant and a thermodynamic analysis represented by creating a detailed model block flow diagram, which is then turned into a dynamic one used to examine the selected parameters such as temperature, flow rate, and pressure variations. The dynamic model approximated the thermal values of the heat exchangers and the working fluids in the exchangers, solar collectors, piping and in the storage tanks.

A standalone solar thermochemical water splitting hydrogen plant with high-temperature molten salt: Thermodynamic and economic analyses and multi-objective optimization

Alternative methods for clean production of hydrogen have been proposed recently. Some of these methods utilize water instead of hydrocarbons as the hydrogen source. The copper-chlorine (Cu–Cl) thermochemical cycle is one of the most promising methods that attracted the attention of numerous researchers and organizations in recent years. In this paper, the design and integration of a standalone solar power tower (SPT) system with LiNaK high-temperature carbonate molten salt with a four-step Cu–Cl cycle is investigated. The integrated system does not rely on external or auxiliary energy sources such as grid electricity or natural gas. The proposed system is investigated in terms of thermodynamic and economic analyses, and the system performance and hydrogen production cost are determined. For the base case, the thermal efficiencies of the Cu–Cl cycle, supercritical steam Rankine cycle, and overall system are 40.4%, 45.74%, and 28.77%, respectively. The hydrogen capacity of the system is 1530.4 kg/h, and the total capital investment is 811.04 million dollars. The levelized cost of hydrogen is estimated as $9.47/kg H2. Based on the multi-objective optimization results, the optimal system design has an overall thermal efficiency and levelized cost of hydrogen of 29.18% and $7.58/kg H2, respectively.

Optimal structure design of supercritical CO2 power cycle for gas turbine waste heat recovery: A superstructure method

The supercritical CO2 power cycle is an effective way for gas turbine waste heat recovery due to its compact system structure and high efficiency. The stepwise optimization of operating parameters and system structure in the early research results in a great limitation of the search space on the optimal structure, consequently, there are still huge challenges in determining the optimal structure of the supercritical CO2 power cycle for waste heat recovery. Therefore, this study proposed a new superstructure of supercritical CO2 cycle for waste heat recovery based on the concept of splitting, which could optimization system structure and design parameters simultaneously. Taking the net power output as the objective function, the optimal structure of supercritical CO2 cycle under different boundary conditions and equipment parameters are investigated. The results show that the superstructure method produces new cycle structures which are not reported before, which is mainly embodied in the flow split and compression structure of the cold end. Compared with traditional supercritical CO2 and steam Rankine cycles at the heat source temperature of 400–600 °C, the maximum net power output obtained by the superstructure method are increased by 4.09–6.94% and 11.65–21.23%, respectively.

An evaluation of power conversion systems for land-based nuclear microreactors: Can aeroderivative engines facilitate near-term deployment?

Power conversion cycles (Subcritical Steam, Supercritical Steam, Open Air Brayton, Recuperated Air Brayton, Combined Cycle, Closed Brayton Supercritical CO2 (sCO2), and Stirling) are evaluated for land-based nuclear microreactors based on technical maturity, system efficiency, size, cost and maintainability, safety implications, and siting considerations. Based upon these criteria, Air Brayton systems were selected for further evaluation. A brief history of the development and applications of Brayton power systems is given, followed by a description of how these thermal-to-electrical energy conversion systems might be integrated with a nuclear microreactor. Modeling is performed for optimized cycles operating at 3 MW(e) with turbine inlet temperatures of 500 °C, 650 °C and 850 °C, corresponding to: a) sodium fast, b) molten salt or heat pipe, and c) helium or sodium thermal reactors, coupled with three types of Brayton power conversion units (PCUs): 1) simple open-cycle gas turbine, 2) recuperated open-cycle gas turbine, and 3) recuperated and intercooled open-cycle gas turbine. Aeroderivative turboshaft engines employing the simple Brayton cycle and two industrial gas turbine engines employing recuperated air Brayton cycles are also analyzed. These engines offer mature technology that can facilitate near-term deployment with a modest improvement in efficiency.

Broadband microwave absorption performance and theoretical dielectric properties model of hollow porous carbon spheres/expanded polypropylene composite foams

Hollow porous carbon spheres (HPCS)/Expanded polypropylene (EPP) composite foams were prepared by rapid expansion of supercritical solution and steam chest molding. Due to the uniform and continuous foam structure, HPCS/EPP foams can maintain better loss ability at lower permittivity. Excellent impedance matching enables them to achieve ultra-broad absorption bandwidth of over 17 GHz. Furthermore, the high frequency dielectric properties of HPCS/EPP foams with unique dual percolation microstructure were described by the Two Exponent Phenomenological Percolation Equation (TEPPE) in a two-step framework. It was revealed that the fitting values of the complex permittivity of the foams with different expansion ratios are in good agreement with the experimental values in the frequency band from 0.5 to 18 GHz. This work introduces a new approach for predicting and optimizing the electromagnetic properties of ternary foamed composites.

Contact Interaction of Steam Turbine Inner Casing Elements During Plastic Deformation

A structure’s material plasticity influence on the pattern of contact interaction of its elements during operation is studied. The stress-strain state problem for the inner casing of a steam turbine high-pressure cylinder operating at supercritical steam parameters (over 240 atm and 565 °C) is solved. The problem is solved by using a finite-element software package. A model of thermoplasticity with kinematic and isotropic hardening is considered. In carrying out the study, experimental strain curves were used for the materials of the connection. The main dependencies used in solving the problem are given. The method of solving the thermal contact problem of interaction of flange connector elements in the conditions of plasticity is based on the application of a contact layer model. To be able to take into account changes in the load from the fastening in the process of combined strain of both the fastening and the casing, first proposed is a method of the three-dimensional modeling of the thermal tightening of the fastening of the horizontal casing connector by applying the linear coefficient of linear expansion of the material. The proposed approach allows modeling the stress of the initial tightening of studs by specifying a fictitious change (decrease) of the coefficient of linear expansion of a stud given as a separate body in the calculation scheme. The magnitude of the specified change in the coefficient of linear expansion is determined from the relationship between the stress of the initial tightening in the stud and the required, for its creation, elongation, which is implemented in the calculation scheme in the presence of different values of linear expansion of both the stud and the casing. To conduct the numerical experiment, an ordered finite-element grid of the casing design was constructed. A 20-node finite element was used in the construction of the casing grid and the fastening. The effect of force loads and the temperature field, in which the structural element under consideration is operated, is taken into account. An analysis of the results of distribution of equivalent stresses and contact pressure during operation is carried out. The difference between the obtained results and the results of solving the problem in the elastic formulation is noted.

Theoretical analysis of power generation applying supercritical steam and high-pressure combustion chamber consuming biomass slurry

Theoretical analysis of power generation applying supercritical steam and high-pressure combustion chamber consuming biomass slurry

Artificial intelligence based operational strategy development and implementation for vibration reduction of a supercritical steam turbine shaft bearing

The vibrations of bearings holding the high-speed shaft of a steam turbine are critically controlled for the safe and reliable power generation at the power plants. In this paper, two artificial intelligence (AI) process models, i.e., artificial neural network (ANN) and support vector machine (SVM) based relative vibration modeling of a steam turbine shaft bearing of a 660 MW supercritical steam turbine system is presented. After extensive data processing and machine learning based visualization tests performed on the raw operational data, ANN and SVM models are trained, validated and compared by external validation tests. ANN has outperformed SVM in terms of better prediction capability and is, therefore, deployed for simulating the constructed operating scenarios. ANN process model is tested for the complete load range of power plant, i.e., from 353 MW to 662 MW and 4.07% reduction in the relative vibration of the bearing is predicted by the network. Further, various vibration reduction operating strategies are developed and tested on the validated and robust ANN process model. A selected operating strategy which has predicted a promising reduction in the relative vibration of bearing is selected. In order to confirm the effectiveness of the prediction of the ANN process model, the selected operating strategy is implemented on the actual operation of the power plant. The resulting reduction in the relative vibrations of the turbine’s bearing, which is less than the alarm limit, are confirmed. This cements the role of ANN process model to be used as an operational excellence tool resulting in vibration reduction of high-speed rotating equipment.

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.

Fatigue life prediction of a supercritical steam turbine rotor based on neural networks

The safety and stability of rotors are significantly important for smooth operations of steam turbines. To predict the fatigue life of a 350 MW supercritical steam turbine rotor online, a data-driven based neural network is proposed in this paper. Finite element analysis is employed to determine the danger zones of the whole rotor and then a large sample dataset consisted of temperatures and stresses is established for subsequent neural network training. Different from the traditional thermo-elasto-plastic or finite element methods, the proposed approach can effectively calculate temperatures and stresses at the danger zones by inputting measured parameters. The Neuber rule and Manson-Coffin equation are used to estimate the fatigue life of the rotor. It is shown that the proposed neural network-based method can assess the operating status of steam turbine during different cold startups and provide a feasible online health monitoring methodology for steam turbine rotor, without dealing with the quite challenging thermo-mechanical analysis.

DEVELOPMENT OF CONCEPTUAL TECHNICAL SOLUTIONS AND METHODS OF THEIR IMPLEMENTATION DURING THE DESIGN OF A DUST COAL STEAM GENERATOR OF SUPER-SUPER CRITICAL PARAMETERS OF STEAM 28 MPa / 600 °С / 600 °C FOR 300 MW ENERGY UNIT. PART 2

In the second part of the work, using the mathematical model described in first unit, a direct-flow pulverized coal boiler with supercritical steam parameters of 28 MPa /600 °C /600 °C was calculated for a 300 MW power unit at loads of 50–70 %. It is shown that: a) the temperature of contaminated screens 1234 °С in the active combustion zone, where 92 % of the initial fuel burns out, is lower than the temperature of slagging beginning (1268 °С) of ДГ-100 coal, which indicates the slag-free operation of the screens of the lower radiation part (LRP) b) over the entire range of the boiler load change of 50–100 %, the temperature at the exit from the active combustion zone will be higher than the minimum permissible temperature of 1250 °C, below which the flame is attenuated; c) upon transition to 50 % load, the temperature of gases at the outlet from the active combustion zone decreases from 1506 °C to 1342 °C, as a result of which the specific thermal stress of the LRP screens decreases by 1.469 times, while the feed water consumption at the inlet of the boiler falls by 2 times, which leads to an increase in the temperature of the LRP steam, the middle and upper radiation parts, screens of the ceiling and rotating chamber; d) to reduce the thermal stratification of the inlet stage of the secondary steam superheater (ППП1), and as a consequence, the pipe wall temperature, it is necessary to divide the ППП1 surface into two packets, installing an intermediate mixing manifold between them with full steam mixing. Bibl. 5, Fig. 13, Tab. 3.

Environmentally friendly acetic acid/steam explosion/supercritical carbon dioxide system for the pre-treatment of wheat straw.

It is well established that pretreatment of lignocellulosic biomass is required to achieve an effective enzymatic saccharification process. At the present time, most of the touted pre-treatment technologies would cause environmental pollution and unsustainable water use for the pretreated material prior to enzymatic saccharification. To address these shortcomings, the pretreatment technology which combines the supercritical CO2, SC-CO2 (a green solvent), acetic acid, and steam explosion was used to assess the pretreatment of wheat straw for enzymatic saccharification. The effects of solvent concentration, impregnation temperature and time, pre-treatment time, and temperature, as well as SC-CO2 pressure, contact time, and temperature, were evaluated. The results identified that at the optimum SC-CO2 pressure of 18 MPa, the highest amount of reducing sugars (RS) was produced from the cellulosic pulp using Acetic acid/Steam/SC-CO2 at 200 °C for 30 min, a value 20% more than the pulp produced with the Water/Steam/SC-CO2. The effectiveness of the pretreatment process was attributed not only to delignification and defibrillation but also to the exposure of the cellulose structure evidenced from the proportion of the β-glycosidic linkages as shown by FTIR. Passing SC-CO2 after the pretreatment reduces the amounts of fermentation inhibitors and eliminates the use of wash water.

Formation of amorphous silica nanoparticles and its impact on permeability of fractured granite in superhot geothermal environments

Superhot geothermal environments in granitic crusts of approximately 400–500 °C are a frontier of geothermal energy. In the development of such environments, there is a concern of a reduction of permeability of fractured granite due to the formation of fine particles of amorphous silica induced by the phase change from subcritical water to supercritical water or superheated steam. However, the formation of silica particles and a resultant reduction in permeability have not been demonstrated to date. Therefore, experiments were conducted on the formation of amorphous silica particles with various combinations of temperature (430–500 °C) and pressure (20–30 MPa), in which the phase change of Si-containing water from liquid to either supercritical fluid or vapor was induced. Amorphous silica nanoparticles occurred under all conditions with smaller particles for higher temperature. The permeability of fractured granite was also observed to decrease significantly within several hours during injection of the particles into rock at 450 °C and 30 MPa under a confining stress of 40 MPa, with slower permeability reduction at a smaller number of particles or in the presence of larger aperture fractures. The present study suggests that the nanoparticles are likely to form and destroy the permeability in superhot geothermal environments, against which countermeasures should be investigated.

Analysis of the dual-fuel combined cycle power plants with a parallel operating scheme efficiency

The article addresses the problems of local power plants operating on fossil fuels such as gas and coal. As a solution to the problem, it is proposed to consider dual-fuel combined cycle power plants with a parallel operating scheme. This type of combined cycle technology is good variant for integration into coal predominating districts. Therefore, the efficiency of dual-fuel combined cycle power plants operating at subcritical (p 0 = 13 MPa, t 0 = 540 °C) and supercritical (p 0 = 24 MPa, t 0 = 545 °C) initial steam parameters are discussed in the article. The thermal model and a calculation methodology for the installation under consideration are proposed. The results of the installation’s technical and economic indicators analysis are presented. Additionally article sets out the assessment of capital costs, Net Present Value and the possibility of using the technology under study within the framework of the considering region.

Performance evaluation of a supercritical circulating fluidized bed boiler for power generation under flexible operation

It is well known that the Łagisza power plant in Poland is the world’s first supercritical circulating fluidized bed (CFB) boiler, whose commercial operation started on June 2009. It has attracted a great deal of interest and operational data are publicly available, therefore it has been chosen as the object of the present study aimed at assessing load and fuel flexibility of supercritical CFB plants. First, the thermal cycle was modelled, by means of the commercial code Thermoflex®, at nominal and part load conditions for validation purposes. After having verified the validity of the applied modelling and simulation tool, the advantage of having supercritical steam combined with CFB boiler over subcritical steam and pulverized coal (PC) boiler, respectively, was quantified in terms of electric efficiency. As a next step, the designed fuel, i.e. locally mined hard coal, was replaced with biomass: 100% biomass firing was taken into account in the case of subcritical CFB boiler whereas the maximum share of biomass with coal was set at 50% with supercritical CFB boiler, consistently with the guidelines provided by the world leading manufacturers of CFB units. A broad range of biomass types was tested to conceive mixtures of fuel capable of preserving quite high performance, despite the energy consumption in pretreatment. However, the overall efficiency penalty, due to biomass co-firing, was found to potentially undermine the benefit of supercritical steam conditions compared to conventional subcritical power cycles. Indeed, the use of low-quality biomass in thermal power generation based on steam Rankine cycle may frustrate efforts to push the steam cycle boundaries.

Investigation of an integrated solar thermochemical plant for hydrogen production using high-temperature molten salt

One of the most promising methods for producing hydrogen is the use of a water splitting process utilising the copper-chlorine (Cu-Cl) thermochemical cycle. The Cu-Cl cycle uses heat and electricity to produce hydrogen and oxygen from the decomposition of water molecules. In this paper, a new solar-powered integrated system is proposed which utilises (LiNaK)2CO3 high-temperature carbonate molten salt as both a heat transfer fluid and a thermal energy storage medium to provide the required heat for the Cu-Cl cycle reactors and heat exchangers. The system is integrated with a supercritical regenerative steam Rankine cycle (SRC) which produces the required electricity for the electrolyser unit. Thermodynamic and economic analyses were conducted to evaluate the proposed system in terms of hydrogen production cost and system performance. For the base case, the integrated system was found to be capable of producing 823.71 kg/h of hydrogen. The system is optimised for two objective parameters, overall system thermal efficiency and the levelized cost of hydrogen. The results of optimisation analysis indicated that, for the optimal Pareto solution, the overall system thermal efficiency and levelized cost of hydrogen were 29.17%, and $7.58/kg of H2, respectively.