Supercritical System Research Articles

Exergy Analysis of Supercritical CO2 System for Marine Diesel Engine Waste Heat Recovery Application

In this research is performed an exergy analysis of supercritical CO2 system which uses various waste heat flows from marine diesel engine to produce additional mechanical power. The performed exergy analysis contains whole system as well as each system component individually. The observed system produces useful mechanical power equal to 2299.47 kW which is transferred to the main propulsion propeller shaft. Additionally produced mechanical power by using waste heat only will reduce marine diesel engine fuel consumption and exhaust gas emissions. Main cooler has the highest exergy destruction of all system components and simultaneously the lowest exergy efficiency in the observed system, equal to 32.10% only. One of the possibilities how main cooler exergy efficiency can be increased is by decreasing water mass flow rate through the main cooler and simultaneously by increasing water temperature at the main cooler outlet. Observed system has five heat exchangers which are involved in the CO2 heating process, and it is interesting that the last CO2 heater (exhaust gas waste heat exchanger) increases the CO2 temperature more than all previous four heat exchangers. Whole analyzed waste heat recovery supercritical CO2 system has exergy destruction equal to 2161.68 kW and exergy efficiency of 51.54%. In comparison to a similar CO2 system which uses waste heat from marine gas turbine, system analyzed in this paper has approximately 12% lower exergy efficiency due to much lower waste heat temperature levels (from marine diesel engine) in comparison to temperature levels which occur at the marine gas turbine exhaust.

Investigation on a Supercritical Water Gasification System with CO2 as Transporting Medium

Investigation on a Supercritical Water Gasification System with CO2 as Transporting Medium

Mathematical optimization and prediction of Febuxostat xanthine oxidase inhibitor solubility through supercritical CO2 system using machine-learning approach

Scientific research towards the synthesis and discovery of novel therapeutic agents with optimal safety, great biological efficiency and acceptable toxicity profile is known as the driving force of pharmaceutical industry in the recent decades. This research study intends to mathematically predict the solubility of Febuxostat (FBX) as a prevalent type of xanthine oxidase inhibitor in the supercritical CO2 (SCCO2) system. For this purpose, Quantile Regression (QR), Multi Linear Regression (MLR), and Multilayer perceptron (MLP) were used to establish models for the prediction of solubility of FBX drug based on temperature and pressure features. The settings of the models were optimized based on their important hyper-parameters and then evaluated and compared. In the final evaluation, models MLP, MLR, and QR have R2 scores of 0.999, 0.941, and 0.854. Also, the RMSE error rate for model MLP is equal to 5.97E-02, for model MLR is equal to 4.77E-01, and for model QR is equal to 6.73E-01. Therefore, MLP can be recognized as the best model among these three methods. The MAPE error metric for this model is 8.26E-02.

Dyeing of Linen Fabrics in Supercritical CO2 Using a Reverse Micellar System with Ionic Liquid Domains

ABSTRACT In order to realize the anhydrous dyeing of linen fabric with reactive dyes in supercritical CO2, a supercritical CO2 ionic liquid reverse micelle system was constructed, and the dyeing process of linen fabric in this system was studied. In this system, linen fabric can be dyed with reactive dyes without special pretreatment. The results show that the dyeing depth of linen fabric can be significantly improved by increasing the amount of surfactant. With the increase in temperature, the dyeing depth first increases and then decreases. The dyeing pressure displays little effect on the dyeing depth. After dyeing, there are a lot of floating colors on the surface of the fabric. Increasing the temperature and prolonging the dyeing time are conducive to dye fixation on the fabric. Adding a certain amount of dimethyl sulfoxide (DMSO) to the system can improve the dyeing performance significantly. In this paper, the best dyeing conditions of linen fabric are as follows: w, 1.2; surfactant conc. 3.5 × 10−2 g/mL; T, 90°C; t, 180 min; p, 21MPa; DMSO concentration, 76.8 mmol/L.

Performance analysis and optimization study of a new supercritical CO2 solar tower power generation system integrated with steam Rankine cycle

Currently, the supercritical CO2 solar tower power generation (S-CO2 STPG) has become a research hotspot, but due to S-CO2 Brayton cycle characteristics, the solar energy utilization rate of the system is low. Therefore, a new S-CO2 STPG system integrated with steam Rankine (SR) cycle is first proposed. The SR cycle absorbs the waste heat of the S-CO2 Brayton cycle, and the introduction of the SR cycle can increase the solar energy utilization rate. The research is based on the simulation results, the system model is developed by Ebsilon, and system operation calculation is developed by MATLAB. The daily and monthly performances of the new S-CO2 STPG system integrated with SR cycle are compared with those of conventional S-CO2 STPG system in detail. The system location is Bakersfield. The comparative analysis results show that compared with the conventional system, the monthly power output for the new system rises significantly, especially in summer. The new system can effectively improve the solar energy utilization rate. The effect of SR cycle power output on new system performance is studied. Increasing SR cycle power output can improve the thermal energy storage subsystem and solar field subsystem performances. The optimal SR cycle power output is related to the solar radiation level. The Fargo, Bakersfield and Phoenix are selected as three places representing low-direct normal irradiance (DNI), medium-DNI and high-DNI districts, respectively. For the medium-DNI and high-DNI districts, the SR cycle power outputs corresponding to the optimal thermal performance and optimal economic performance are 20 MW and 15 MW, respectively; for the low-DNI district, those are 15 MW and 5 MW, respectively.

Early corrosion properties of titanium alloys, Ni-based alloys and stainless steel in supercritical water oxidation of sewage sludge

Supercritical water oxidation (SCWO) can efficiently and harmlessly dispose sewage sludge, while corrosion phenomena can lead to rapid shutdown and/or failure of expensive process equipments in a supercritical water system. The corrosion behavior of titanium alloys, Ni-based alloys and stainless steel exposed in supercritical water oxidation of sewage sludge at 450 °C, 26 MPa for 60 h was investigated by means of gravimetry, scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction. 316 SS (stainless steel) showed the highest corrosion rate, while TA10 had the lowest corrosion rate. The oxide scale on the surface of 316 SS contained magnetite and FeCr2O4, while Cr2O3 and NiCr2O4 were the main components of oxide layer on Inconel 600. Among them, magnetite and NiCr2O4 mainly existed in the inner oxide layers of SS 316 and Inconel 600, respectively. The lack of Cr2O3 on the 316 SS surface resulted in severe pitting corrosion and poor corrosion resistance.

Supercritical CO2 Extraction of Oil from Dried Avocado (Persea Americana Mill.) Fruit Pulp: Oil Yield, Solubility, and the Oil Characteristics

The purpose of this study was to investigate the applicability of supercritical fluid technology for extraction of avocado oil. The dried avocado fruit pulp (Persea americana Mill.) was extracted by using a semi-pilot supercritical extraction system. Effect of several process parameters, such as CO2 flow rate, particle size, pressure and temperature on total oil yield, free fatty acid, peroxide value, total phenolic and total flavonoid content in oil were assessed. Avocado oil was extracted within the range for flow rate of 10 and 15L/h, particle size of 2.0 and 3.0 mm, temperature of 34, 42 and 50 oC and pressure of 15, 20, 25 and 30 MPa. Kinetic curves clearly exhibited three periods of extraction (constant rate, falling rate and diffusion-controlled). Increasing flow rate, pressure, temperature or reducing particle size brought an increase in the oil yield and extraction rate. Overall, after 150 min of extraction, the oil in dried avocado was almost completely extracted. The oil yield by supercritical CO2 method (58.97%) obtained at 50 oC and 30 MPa was higher than that by Soxhlet method (55.83%). An increase in pressure (at constant temperature) brought an increase in free fatty acid values in oil but decrease in peroxide values and total phenolic content. On the other hand, the effect of temperature on those parameters was opposite. The oil by supercritical CO2 method was of better quality than that by Soxhlet method.

Removal of AAEMs from high alkali coal under supercritical CO2 fluid-citric acid extraction system

ABSTRACT In this paper, a method for dealkalization and upgrading of high alkali coal by supercritical CO2 fluid-citric acid extraction system is proposed. The leaching mechanism was explored by microstructural changes of elements and functional groups in coal samples, and single-factor optimization experiment was conducted. The result shows that supercritical CO2 fluid-citric acid extraction can effectively remove alkali and alkaline earth metals. The extraction mechanism is the reaction of H+ with inorganic minerals and the ion exchange of H+ with the form of phenolic hydroxyl and carboxyl groups. Under the optimum conditions, the removal rates of Ca and Mg are 44.95% and 65.75% respectively. The ash content of coal is 2.42%, and the content of Na2O (calculated by ash) is 1.13%, which meet the standards of power coal in China. Supercritical CO2 fluid-citric acid extraction is an effective and promising method for the cleaning of high alkali coal.

Thermodynamic and environmental analysis of auto-thermal supercritical water co-gasification polygeneration system of sewage sludge with coal

An auto-thermal supercritical water (SCW) co-gasification polygeneration system has been developed to treat sewage sludge (SS) with coal addition for H2 and heat production. Thermodynamic analysis based on Gibbs free energy minimization and life cycle environmental impact assessment of the system was performed under different conditions. The sensitivity analysis results show that H2 yield increased first and then decreased with the increase of preheated water when the proportion of dry coal to dry SS was less than 1.75 but decreased monotonically when the proportion was over 2. It is necessary to add 21% dry coal of raw SS amount when the system was energy self-sufficient to treat SS directly for avoiding pretreatment energy consumption. The largest exergy destruction was in the SCW gasification reactor which could be over 11500 kW for a 10 t/h processing requirement under 650 °C. The energy and exergy efficiency of the SS SCW co-gasification system can be improved effectively by adding coal, which can reach 79.5% and 47.9% under the preheated water ratio of 1 and the dry coal ratio of 3, respectively. Under this condition, 347.1 kg/h H2 and 20.5 t/h steam could be produced. The global warming potential (GWP) of the system was only 1.10–2.5 kg CO2-eq by the life cycle assessment considering carbon capture and storage (CCS) at a dry coal ratio of 3 based on the natural enrichment of CO2-rich gas by the SCW gasification technology.

An optimal split ratio in design and control of a recompression supercritical CO2 Brayton system

The sCO2 Brayton cycle is considered an alternative to the conventional Brayton and Rankine cycles. The recompression Brayton cycle is advantageous because of its simple cycle layout and high cycle efficiency. The split ratio (SR) is defined as the recompression fraction of the working fluid that significantly affects the corresponding parameters of the system, particularly the cycle efficiency. However, studies focusing on the influence of SR on the design and off-design performance remain limited. The factors influencing the optimal SR and regulation mechanism under the design and off-design conditions of recompression cycle are considered in this study. The results demonstrate that the optimal SR under the design conditions is primarily affected by the high pressure, low pressure and efficiency of the recuperators. The optimal SR decreases with a reduction in the load demand, and the recompression loop can be cut off under a low load to improve the cycle efficiency. A simplified control can be achieved by controlling the temperature difference at the flow merge point to achieve a higher system efficiency. Moreover, the SR regulation mechanism is unaffected by the load control method. These findings are of significance to recompression configuration with different design parameters.

Theoretical analysis of a novel PCHE with enhanced rib structures for high-power supercritical CO2 Brayton cycle system based on solar energy

A printed circuit heat exchanger (PCHE) is one of the most significant components in the supercritical CO2 (SCO2) Brayton cycle system based on concentrated solar power, whose performance significantly affects the efficiency and compactness of the system. To improve the performance of PCHE with semicircular-straight channels, rib structures placed on the top flat wall of the semicircular channel are proposed, which are achieved by the double sides etched heat transfer plates, and the effects of the distributions of rib structures on the performance of channels are also investigated. The thermal-hydraulic performance of the conventional semicircular channel and the semicircular channel with different rib structures are compared. The results indicate that rib structures lead to an apparent increase of turbulence kinetic energy in channels, and improve the synergy between velocity and temperature gradient fields, leading to the heat transfer enhancement. Among the channels with different rib structures, the comprehensive performance of the semicircular channel with the spacing distribution of short rib structures (channel DR3) is the best, which is relatively 19.3–19.8% higher than that of the conventional semicircular channel. When the channel DR3 is adopted in PCHE, the effectiveness of PCHE could reach 98.4–98.7%, the efficiency of the SCO2 Brayton cycle system based on solar power could be increased by 15.3%, and the compactness of the system could be improved by 3.8%. This present work is of great significance for deepening the understanding of PCHE heat transfer mechanism and performance optimisation, as well as improving the overall performance and compactness of large-scale SCO2-based power systems.

A self-condensation supercritical carbon dioxide Rankine cycle system realized by absorption refrigeration

A novel self-condensation supercritical carbon dioxide (sCO2) Rankine cycle system in which a lithium bromide-water absorption refrigeration cycle is used to utilize the waste heat of exhaust gas from the carbon dioxide power cycle and provides a cold source to condense the exhaust gas is proposed. The new system avoids the huge compression power consumption of the sCO2 Brayton cycle system by replacing the compressor with a more efficient pump and the requirement of an extra low-temperature cold source. The power consumption during pressurization, thermal efficiency and levelized cost of electricity (LCOE) of the new integrated system are 26.50% lower, 3.77% higher and 4.32% lower than those of the stand-alone regenerative sCO2 Brayton cycle system, respectively. Parametric analysis is carried out to study the effects of key parameters on the thermodynamic and economic performance of the integrated system. The results show that the generator temperature, maximum system pressure and maximum system temperature have a positive effect on the thermal efficiency and LCOE, while the evaporator temperature and minimum system pressure have a negative effect.

Theoretical and experimental study on the self-excited vibration of a flexible rotor system with floating spline

The internal friction of floating spline can cause self-excited vibration of a supercritical flexible rotor system. To address this issue, a high-efficiency dynamic modeling method is proposed to investigate the self-excited vibration behavior and instability evolution of the rotor. Experiments are conducted to validate the theoretical results. The coupled dynamic equations for the rotor system connected with the floating spline are derived through the combination of finite element method and lumped parameter model. A hybrid numerical approach of precise integration and Runge-Kutta method is adopted to examine the effects of the friction coefficient of spline’s tooth surface, torque, and eccentricity on the self-excited vibration of the rotor system. The results show that the spline friction leads to negative damping and inputs energy into the rotor system under supercritical conditions, triggering self-excited vibration when the input energy exceeds a specific level. With the same parameters, the experimentally obtained axial trajectory and primary frequency components are consistent with the theoretical results, verifying the accuracy of the proposed theoretical model. This study can serve as a useful theoretical guide for the dynamic stability design of flexible rotor systems with the floating spline.

Experimental research and energy analysis of a new type of dry ice powder pneumatic rock breaking technology

When the traditional drill and blast method is applied to rock crushing projects, it has strong vibration, loud noise and dust pollution, so it cannot be used in densely populated areas such as urban public works. We developed a supercritical CO2 true triaxial pneumatic rock-breaking experimental system, and conducted laboratory and field tests of dry ice powder pneumatic rock-breaking. The characteristics of the blast-induced vibration velocity waveform and the evolution of the vibration velocity and frequency with the focal distance were analyzed and discussed. The fracturing mechanism of dry ice powder pneumatic rock breaking is studied. The research results show that: (1) The vibration velocity induced by dry ice powder pneumatic rock breaking decays as a power function with the increase of the focal distance; (2) The vibration frequency caused by dry ice powder pneumatic rock breaking is mainly distributed in 1–120 Hz. Due to the dispersion effect, the dominant frequency of 10–30 Hz appears abnormally attenuated; (3) The traditional CO2 phase change fracturing energy calculation formula is also applicable to dry ice pneumatic rock breaking technology, and the trinitrotoluene (TNT) equivalent of fracturing energy is applicable to the Sadovsky formula; (4) Dry ice powder pneumatic rock breaking is shock wave and high-energy gas acting together to fracture rock, which can be divided into three stages, among which the gas wedge action of high-energy gas plays a dominant role in rock mass damage.

Techno-economic analysis of multi-tower solar particle power plants

Solar tower systems using solid particles as heat transfer and storage medium promise to achieve, in combination with advanced power cycles, lower levelized cost of electricity (LCOE) than state-of-the-art concepts. In this study the cost potential of a multi-tower solar power plant with centrifugal particle receiver is evaluated. Most of the underlying assumptions were chosen in accordance with those specified within the US-DoE Gen3 project “G3P3”. For the power block a high-efficiency supercritical CO2 system with 100MWe was assumed. The solar subsystem is built from 12 identical solar tower modules, each with heliostat field, tower, receiver and storage. The nominal thermal power of each module is 41MWth.Since the cost assumptions for the tower and the heat exchanger (HX) are still relatively uncertain, different correlations were used representing optimistic and conservative cases. For the particle receiver two outlet temperature levels were investigated, namely 800 °C and 1000 °C.The results of the techno-economic analysis indicate a strong impact of the cost assumptions for the primary heat exchanger and the tower. With 800 °C as particle outlet temperature, the estimated LCOE range from $56.18/MWh (optimistic values for tower and HX cost) to $67.30/MWh (conservative values for tower and HX cost).Increasing the particle outlet temperature to 1000 °C results in a significant reduction of LCOE (about 12% for the optimistic cases, down to $50.46/MWh). The reason for this is the significant reduction of heat exchanger area, particle inventory and particle mass flow, resulting from the larger temperature difference in the particle system. However, operating the system at such elevated particle temperatures will require some modifications to the components that are not fully reflected in the used cost correlations yet. Nevertheless, the results propose further investigation of this option. All in all the results indicate a clear potential to achieve the SunShot goal of less than $60/MWh.

Power supply circuit model and sliding mode control of supercritical unit boiler system commissioning

AbstractIn the process of power control and commissioning of supercritical unit boiler system, there are some problems such as large steady‐state error and slow response speed. In order to optimize the control performance of supercritical unit boiler system, the power supply loop model and sliding mode control method of supercritical unit boiler system debugging power supply are proposed. Firstly, the power supply circuit model is established according to the data of voltage doubling rectifier circuit, inverter circuit, high frequency transformer and LC resonant circuit. Secondly, the capacitance voltage value and the inductance current value are calculated in the power supply circuit model. Finally, based on the numerical results, a terminal sliding mode controller and a linear sliding mode controller are established to complete the double closed‐loop terminal sliding mode control and realize the power control of the debugging power supply. The experimental results show that when the input voltage is 50 V and the current is 14 V, the input voltage and current waveforms remain stable. When the input voltage is between 40 and 50 V, the change of switching frequency is small, only increasing from 22 to 26 kHz. The steady state of the power supply is high, and when the input voltage increases, the DC offset is 21.2. The convergence time in the calculation process is less than 200 ms. The instantaneous change of inductance is 0.7 A. The steady‐state error is less than 0.005 V. The output voltage distortion rate is less than 4%. It is proved that this method has strong control performance in the supercritical unit boiler system.

폐열회수 발전용 초임계 ORC 터빈 개발

In this study, a turbine applicable to a supercritical ORC power generation system with higher power generation efficiency than the typical ORC power generation system was developed. This paper describes the turbine design, fabrication and performance tests for developing a 100kW class power generation turbine. R-1234ze(E) was selected as the working fluid in consideration of Global Warming Potential. The overall turbine expansion ratio was 9, and the turbine consisted of a two-stage centrifugal turbine. The magnetic bearings were installed, and the turbine and generator were assembled into a single casing. The rotation speed was selected as 36,000rpm through the specific speed and the specific diameter analysis. Based on these analysis results, one-dimensional design, three-dimensional shape design, and three-dimensional performance analysis were conducted. Turbine components were fabricated based on CAD drawings and three-dimensional modeling. The assembled turbine was installed in a supercritical ORC power generation system. The cooling tubes were additionally installed to maintain a stable temperature inside the turbine. Through the performance test, it was confirmed that the developed turbine generated electric power of 100kW. In this paper, important matters to be considered when developing turbines for supercritical ORC power generation system were specifically mentioned.

Mass optimization of a recompression supercritical nitrous oxide and helium power system for space exploration

Due to high output power, long lifetime, high efficiency, and compact structure, the space nuclear power (SNP) system is considered an ideal choice for future large-scale and deep space missions. The system's mass, volume, and thermoelectric conversion efficiency directly affect and determine the system's performance compared with ground nuclear devices. The mass of the space nuclear power system is a vital parameter due to the limitation of cost, volume, and transportation. This study designed and optimized the recompression supercritical with nitrous oxide and helium (N2O–He) Brayton cycle with a small modular reactor for mass. Each Brayton cycle component model was developed to estimate the cycle performance systematically. The mass estimation model of the Brayton system includes a nuclear reactor, radiation shadow shield, Brayton cycle unit, recuperator, and radiator. A small modular reactor was designed to predict the minimum mass reactor suited to the given cycle conditions. The system mass optimization explored the trade-offs between the reactor, radiation shield, Brayton cycle unit, recuperator, and radiator to obtain the minimum mass of the space nuclear energy system to satisfy the operating requirements. Sensitivity parametric investigations are considered to evaluate the effects of crucial decision variables on the whole Brayton cycle mass. Furthermore, multi-objective optimization is performed to find optimum operating parameters to minimize the system mass. The results illustrate that the specific mass of the system is less than 20 kg/kW. The total mass of the whole system is 5605.93 kg using near-term materials, of which the Baryton Rotating Unit, radiator, and shadow shield mass dominate the total mass. The Brayton Rotating Unit, radiator, and radiation shield account for 44.64%, 32.53%, and 14.29%, respectively. It is concluded that after the dual-objective optimization analysis, the mass of the cycle decreased by 18.44%, which used the existing technical materials.

Thermal hydraulic characteristics of liquid sodium and supercritical CO2 in a diffusion bonded heat exchanger

Compact heat exchangers are being examined for use in advanced, high-temperature nuclear or concentrated solar power plants to improve thermal efficiencies and reduce capital costs. At the time of this work, no experimental investigation of liquid sodium in the popular diffusion-bonded heat exchanger design had been performed. This paper describes the thermal-hydraulic and overall operations performance observed during testing of a 316/L stainless steel “zig-zag” microchannel heat exchanger operating between a (0.5 kg/s) sodium loop and a (0.3 kg/s) recuperated supercritical CO2 system with outlet conditions up to 550 °C at 16 MPa. Observed pressure drop is presented in the form of an effective friction factor correlation which aligns closely with recent experimental data. The thermal performance of this heat exchanger, measured by its overall conductance under various flow conditions, was decomposed to examine the independent convection behaviors of both the CO2 and sodium streams. These results are presented in the form of Nusselt correlations fitted to the experimental data. The sodium heat transfer correlation aligns closely with the widely accepted Lubarsky-Kaufman correlation, while the CO2 heat transfer correlation lies between previous correlations developed by computational and experimental methods. This was the first long-duration use of sodium in a microchannels (∼ 1.8 mm hydraulic diameter) heat exchanger. The use of an oxide control system enabled trouble-free operation of the heat exchanger for over 150 h of high-temperature operation. This first-of-a-kind demonstration using liquid sodium and supercritical carbon dioxide shows great promise for further application of this technology in advanced nuclear or solar power plants.

Control strategies and dynamic experimental tests on the wide-range and rapid load regulation of a first pilot multi-megawatts fossil-fired supercritical CO2 power system

Supercritical CO2 (sCO2) power system is a research front in recent years due to its high efficiency and flexibility which is considered as a transformative power system in terms of consumption of the fluctuated and intermittent renewables. The merits of sCO2 power systems have been widely shown by small-scale test loops. However, it is still very lack of the investigations on the control strategies based on real-time dynamic operational data of large-scale multi-megawatts pilot power system, especially for wide-range and rapid load regulation to demonstrate the feasibility of large-scale utilization and commercialization. A worldwide first pilot multi-megawatts SMART (Supercritical CO2 Modular Advanced Research and Test) fossil-fired power system has been built and operated for more than 1000 h at TPRI (Thermal Power Research Institute), Xi’an, China with turbine inlet parameters of 20 MPa/600 °C/600 °C. The influence of key parameters on the dynamics of the system are experimental studied. In-depth tests of the wide-range load regulation and rapid load regulation of the SMART@TPRI power system are performed. The test results show that the key target parameters such as turbine inlet temperatures, compressor inlet temperature and pressure, sCO2 mass flow rate and exhaust flue gas temperature can be well regulated by a set of well-developed control modules to ensure an efficient and safe operation during load variations. The SMART@TPRI power system can run stably and flexibly within the whole range from 0 %Pe to 100 %Pe. The averaged load ramp and load reduction rate achieves 6.35 %Pe/min and −6.37 %Pe/min, respectively, which is almost 3 ∼ 4 times than that of steam power system, under the control strategy of sliding pressure with fixed turbine inlet temperature by a combination of several novel well-developed control modules.