Steam Flow Research Articles

A Numerical Simulation Approach for Superheated Steam Flow during Multipoint Steam Injection in Horizontal Well

Superheated steam flow during multipoint steam injection technology has a good effect on improving the steam absorption profile of heavy oil thermal recovery wells, enhancing the production degree of horizontal section of thermal recovery wells, and enhancing oil recovery. Based on the structure of multipoint steam injection horizontal string, considering the characteristics of variable mass flow, pressure drop of steam-liquid two-phase flow, and throttling pressure difference of steam injection valve in the process of steam injection, this paper establishes the calculation model of various parameters of multipoint steam injection horizontal wellbore and calculates the distribution of steam injection rate, temperature, pressure gradient, and dryness along the section of multipoint steam injection in horizontal wellbore. The results show that the temperature and pressure decrease gradually from heel to toe, and the steam dryness decreases gradually. Considering the influence of throttle pressure difference of steam injection valve and pressure drop of gas-liquid two-phase flow in the wellbore, the traditional calculation model of steam injection thermodynamic parameters is optimized, and the optimization of wellbore structure and steam injection parameters is an effective method to achieve uniform steam injection in horizontal wells. The steam injection uniformity of horizontal wells can be effectively improved by adjusting the steam injection valve spacing and steam injection parameters. When the steam injection volume is 200 m3/d and the steam injection valve spacing is 20 m, a more stable steam injection effect can be obtained. The findings of this study can help for better understanding of improving the uniformity of steam injection and enhancing the recovery factor.

Study of pretreatment methods for peach drying

The pretreatment for peach drying is essential to enhance the efficiency of the drying process. This paper investigates the impact of various pretreatments (ethanol, ultrasound in water and ethanol, and microwave) on hot-air drying, microwave drying, and hot-air combined with microwaves (microwave finishing). Hot air drying revealed that ethanol pretreatment significantly reduced drying time by up to 23.5%, attributed to its osmotic effect and ability to dissolve food matrix constituents. Ultrasound pretreatment showed mixed results, with high amplitude (90%) and extended duration (30 min) yielding a 17.6% reduction in drying time. Microwave pretreatment demonstrated remarkable efficiency, reducing drying time by 58.8%, attributed to volumetric heating and steam flow induced by microwaves. Diffusion coefficients were calculated, with ethanol pretreatment exhibiting positive effects, while ultrasound and microwave pretreatments showed varying influences. Microwave drying post-pretreatment drastically reduced drying time, and the efficiency was further evaluated through microwave-finishing. Ethanol and ultrasound pretreatments improved final moisture content and drying rates during both drying stages, while microwave pretreatment resulted in severe overheating and quality loss. The scanning electron microscope images showed variations in the microstructure of the pretreated peach cubes compared to untreated ones. Ethanol pretreatment led to a more compact structure, while ultrasound pretreatment in water resulted in a porous structure. The combination of ethanol and ultrasound pretreatments exhibited more pronounced effects, particularly for hot air and microwave-finishing drying, where the cubes showed significant deterioration.

Pyrolysis and catalytic steam gasification of olive oil waste in two stages

A study of the pyrolysis and catalytic gasification of a waste from the extraction of olive oil has been carried out. The work objective was to characterize the solid and gaseous phases generated in the process for their possible utilization in energy generation. The experimental system consists of two cylindrical stainless steel reactors connected in series. A conventional pyrolysis is produced in the first reactor. In the second reactor, the gases and liquids generated in the first one pass through a dolomite catalytic bed where the cracking of the heavier components is produced. Also, in this second reactor, a steam stream is continuously introduced. The influence of temperature (500-700 ºC), quantity of catalyst (25-100 g) and steam flow rate (0-1.40 mL/min) has been determined. Also, the dolomite effectiveness as catalyst was evaluated For this motive, experiments, without reactivating dolomite, were carried out (0-6 runs), and the yields of solids, liquids and gases were determined. An increase in reaction temperature leads to a decrease in solid and liquid yield and to an increase in the gas phase yield. The presence of catalyst and the quantity of the same, originate an important decrease in the liquid phase yield and a high increase in the gas phase yield, especially important in the case of hydrogen. On the other hand, the catalyst is very stable and does not lose activity during at least six cycles of reaction. The presence of steam, increase the yield of hydrogen, but the increase of the steam flow rate, do not generate significant changes in the products distribution.

Simulation study on transport characteristics of leakage gas from the condenser of power plant

Exploring the transport characteristics of leakage gas in the condenser can facilitate quicker identification of leak points when using Helium tracer gas method for detection. We construct a 3-D physical model of the condenser to simulate the Helium gas leakage process within the tube bundle. On the steam side, we adopt RNG k-?, porous media, steam condensation, and convective diffusion models to describe steam and leakage gas-flow. On the waterside, we use the tube bundle thermal resistance model to describe the steam-water heat transfer. The research concludes with three key points. When the centripetal pressure gradient is insufficient, there will be leakage gas enrichment, resulting in flowing out in the form of diffusion. When there is no centripetal pressure gradient in the tube bundle region, it will extract only a small amount of upstream leakage gas along with steam through the flow. When reaching a stable level for leakage gas, the leakage intensity is proportional to the outlets? flow rate but is independent of the transport form. The deviation of the mass-flow rate decreases with the mesh quantity increasing, which is less than 2% when the mesh quantity is over 638228. The deviation between simulated and actual values of the two parameters is less than 5%, which reveals the good agreement between numerical calculation and actual work conditions. These conclusions can assist employees and researchers in evaluating data on leak points and enhancing detection techniques.

CRITERION METHOD FOR MODELLING THERMODYNAMIC INSTABILITY IN MIXING HEATERS OF TURBO INSTALLATIONS

The relevance of the issue of modelling the conditions and consequences of thermodynamic instability in mixing heaters is confirmed by the analysis of the experience of operating turbo installations and the problem of hydrodynamic shocks and their impact on the functioning of the equipment. A thermodynamic mathematical model of heat and mass transfer processes in the volume of mixing heaters has been developed, which, unlike known approaches, takes into account the influence of fluctuating deviations of thermodynamic parameters from the equilibrium state on the conditions of thermodynamic instability. The analysis of the obtained criteria and conditions of thermodynamic instability and hydrodynamic shocks was carried out. Based on the developed model, an original method of determining the conditions and consequences of thermodynamic instability in the volume of mixing heaters is presented. The criterion of thermodynamic instability in the developed method defines the conditions of simultaneous change of pressure and mass in the two-phase volume of the mixing heater. The conditions for the occurrence of thermodynamic instability in mixing heaters are determined, which significantly depend on the ratio of steam and condensate flow rates. The results obtained in the work can be applied for: development of systems for diagnosing the state of mixing heaters based on the regularly controlled parameters of the turbo installation, substantiating technical solutions for preventing thermodynamic instability and hydrodynamic “shocks” on the design of heaters, substantiating technical solutions for modernization of turbo installation systems. These issues determine the need for further analysis of the feasibility of modernizing thermodynamic instability modelling methods in mixing heaters of NPP turbo-installations. Keywords: thermodynamic instability, mixing heaters of turbo installations

Analysis of Measurement Accuracy and Reliability of Intelligent Instrumentation in Process Control

Abstract Intelligent instrumentation plays a crucial role in industrial applications, with its measurement accuracy and reliability directly influencing operational efficiency. This article presents the integration of the HART communication protocol to enhance data transmission within smart instruments, focusing on internal structure and process control optimization. A HART smart instrument multiplexer system is established, utilizing an analog PID control algorithm for data regulation and optimal control techniques for automatic parameter adjustment. Additionally, the three-parameter Weibull distribution is employed to assess the reliability of smart meters, deriving distribution characteristics and estimating parameters through failure rate analysis. The performance of the designed HART smart meter multiplexer system is thoroughly evaluated, including control performance, reliability, channel function, and measurement accuracy. Notably, the system demonstrates a minimal overshoot in analog PID control at 0.911%, with a steady-state error range of -5°C to 4°C. Furthermore, the implementation of this system significantly reduces the risk of hazardous failures by 41.91%. In conditions of 350°C temperature and 1.2MPa pressure, the system accurately measures superheated steam flow with a relative error of only 0.05%. By optimizing the settings of smart instruments, this system not only enhances measurement accuracy in industrial production but also improves reliability, supporting diverse applications in the chemical industry.

Industrial test of post combustion CO2 capture by reactive absorption with two new solvents in natural gas power plant

The post-combustion chemical decarbonization process is one of the key technology selections for the low-carbon development of natural gas power plants. The high energy consumption of amine regeneration is hindering its commercial application. In this paper, two new mixed amines solvent 15%Diethylaminoethanol (DEEA) +9% Piperazine (PZ)+ 6% Monoethanolamine (MEA) named DT01-3 and 22% 1,4-butanediamine (BDA)+ 4% N-Methyldiethanolamine (MDEA) + 4% 2-Amino-2-methyl-1-propanol (AMP) named DT02-2 are verified by the 3000Nm3/h industrial demonstration system. The steady state condition was gradually established by adjusting the main parameters such as flue gas flow rate, absorber inlet flue gas temperature, solvent circulation flow rate, regeneration tower operation pressure, steam flow rate and so on with the goal of maintaining ≥90% of the capture efficiency. The results show that the CO2 capture efficiency of DT01-3 and DT02-2 is 91.23% and 90.81% respectively. The regeneration heat consumption is 3.65 GJ/tCO2 and 3.73 GJ/tCO2. The amines consumption is 0.95kg/tCO2,1.1kg/tCO2. The operating cost of DT01-3 and DT02-2 is 336.37 CNY/t,346.04 CNY/t, which is 20.94%,18.68% lower compared with MEA.

Numerical investigation of boiler waterwall corrosion by integrated tube temperature prediction and sulfur evolution model

High temperature corrosion has become one of the leading causes of boiler waterwall tube failures because of the wide application of air-staged combustion in coal-fired boilers. High temperature corrosion is strongly affected by the H2S concentration and wall tube temperature distributions in the furnace. Particularly, the corrosion rate increases exponentially with the increase of tube temperature. However, by far most of the numerical studies on high temperature corrosion only considered the effects of H2S concentration while the critical effects of tube temperature were overlooked. Thus, this paper presents a comprehensive corrosion model that incorporates the key effects of both tube temperature and H2S concentration. Specifically, the tube temperature is predicted by a coupled combustion and hydrodynamic model that integrates the critical effects of both the boiler gas flow and steam flow on waterwall tube temperature. The H2S concentration is predicted by a sulfur evolution model describing the devolatilization process of coal sulfur species and their subsequent gaseous reactions. The tube temperature prediction model and H2S evolution model provide all the key parameters for accurate prediction of boiler waterwall corrosion. The corrosion model is applied to a 350 MW supercritical wall-fired boiler. The results show that the tube temperature varies significantly over the boiler waterwall, and hence, has significant impacts on the distribution of wall tube corrosion. Particularly, local high tube temperature zones could form on the waterwall areas of relatively low H2S concentration leading to substantially higher tube corrosion rates than the adjacent wall areas. The results demonstrate the importance of incorporating both the wall tube temperature and H2S concentration in the prediction of boiler waterwall corrosion.

A study of co-firing palm kernel shell on the Nagan Raya coal-fired power plant

Co-firing biomass with coal in existing utility boilers is seen as one strategy for promoting renewable energy with low upfront costs and little to no impact on the boilers' high efficiency. The purpose of this research is to analyse the fuel characteristics and performance of palm kernel shell co-firing at Nagan Raya Coal-Fired Power Plant (CFPP) at various percentages of palm kernel shell combination. The analysis is conducted based on the operational data obtained from Nagan Raya Power Plant. In this study, the characteristics of fuel and the performance of a power plant are analysed based on percentages of fuel variations, namely 100% coal, 95% coal-5% palm kernel shell, and 90% coal-10% palm kernel shell. The results reveal that co-firing's biomass ratio boosted operation parameters, including main steam pressure, temperature, and flow rate. Subsequently, co-firing with 90% coal-10% palm kernel shell has enhanced the power plant output to 90,7 MW compared to those with 100% coal, 95% coal-5% palm kernel shell, namely 89,3 MW and 90,4 MW, respectively

CFD analysis of PHWR exposed core under postulated severe accident condition

A two-dimensional steady-state thermal-hydraulic analyses of the exposed core with varying levels of exposure is carried out for heat transfer assessment. Low-frequency postulated severe accident without mitigating actions leads to exposure of fuel channels in Pressurised Heavy Water Reactors (PHWRs). Such exposure of fuel channels leads to their heat-up which is governed by interdependent heat transfer mechanisms such as radiation, convection and conduction heat transfer. In order to understand such a complex behaviour as well as to plan the severe accident management guidelines, numerical analyses of the exposed core are required. In this paper, one-of-a-kind thermal-hydraulic analyses of the exposed reactor-scale core geometry are presented for row-wise exposures of fuel channels. These numerical analyses are terminated at the onset of fuel channel disassembly i.e., loss of geometrical intactness of the exposed core. The interesting interdependency of convection and radiation heat transfer on fuel channel heat-up is brought out in this study. The dominance of convection heat transfer is observed for initial exposures of the fuel channels. However, for the advanced stages of fuel channel exposures, the heat transfer is observed to be dominated by radiation heat transfer. Intriguingly, it is observed that the convective cooling of exposed fuel channels by steam flow is counter-acted by exothermic heat generation arising from Zircaloy and steam interaction. Moreover, it is interesting to note that the disassembly of fuel channels is restricted to central regions of the exposed core.

Impact of Stack Temperature on Solid Oxide Electrolysis System Operation for Lunar Production of Hydrogen and Oxygen Propellants

Solid oxide electrolysis (SOEC) systems have the potential to produce hydrogen and oxygen propellant from lunar ice found in the permanently shadowed cream on the moon. Because SOEC systems electrolyze steam instead of liquid water as in more conventional alkaline and proton-exchange membrane electrolysis systems, they require lower stack voltages for thermal-neutral operation (about 1.29 V/cell vs. 1.48 V/cell for liquid-fed cells) and thus can have lower stack specific energy as defined by stack power requirements per kg of hydrogen produced. However, at a system level, power requirements in a remote lunar setting for vaporizing the steam and flowing it through the stack increase system-level power demands such that the advantages of the SOEC system are reduced due to the balance of plant loads contributing as much as 20 to 25% of the system energy at 800 deg. C. Our team at Mines collaborated with our partners at OxEon Energy to demonstrate an SOEC system with a stack operating temperature of 800 deg. C that demonstrated an overall system-level specific energy just below 50 kWh electric per kg of hydrogen. That study and a supporting model validation study provided a basis for showing the viability for high-temperature SOEC to be scaled-up for lunar production of hydrogen and oxygen propellant for propulsion. The current study builds on that previous work by exploring the impact of SOEC stack temperature on both the stack and balance of plant power requirements. This study explores the trade-offs between reduced balance of plant parasitics and increased stack mass with lower SOEC operating temperatures and explores the advantages of higher conducting mixed-ionic-electronic conducting electrolytes with electron blocking layers to increase current densities at lower temperatures.This study was performed using stack and balance of plant models that have been calibrated in the lab-scale demonstration of an SOEC system with an electrically driven steam generator, a scroll-compressor for driving the steam flow, and cathode and anode exhaust recuperators for heat recovery to the stack inlet steam flow. The system also includes H2 drying from the SOEC cathode exhaust by heat exchange with the incoming water stream. The current study looks updates the previous model by replacing the compressor with a higher pressure steam generator and an expansion valve that allows the operation of the system without the parasitic loads of a compressor. In the current study, three different electrolytes traditional yttrium-stabilized zirconia (YSZ), higher conductivity scandium-stabilized zirconia (ScSZ), and mixed ionic-electronic conducting gadolinium-doped ceria (GDC) with a YSZ blocking layer. The GDC bilayer electrolyte cells have the highest conductivity and allow for reasonable hydrogen production at operating temperatures below 700 deg. C. The results show that the lower operating temperatures enabled by the GDC bilayer electrolyte and by the ScSZ electrolytes not only reduce the system mass with smaller heat exchangers and thermal insulation, but also lower requirements for steam generation by enabling more heat recovery in the steam generator. The impact of stack operating temperatures on the feasibility of scaling up a lunar-deployed SOEC system to produce more than 1 kg/h are presented to further emphasize the feasibility of SOEC systems as part of a lunar propellant production facility.

Increasing the production efficiency of metal nanoparticles using electron beam deposition in a vacuum

Approaches to increase the efficiency of the use of materials that evaporate with subsequent deposition in a vacuum have been analyzed. The high efficiency and advantage of deposition from an evaporator with a directed vapor flow in a vacuum compared to a classical crucible evaporation scheme are shown. The optimal technological modes of deposition from the evaporator to achieve homogeneity of the directional steam flow were determined. The dependence between the temperature of the target, the efficiency of the evaporation scheme and the distance of the evaporator from the target was determined experimentally.

Digital twin modeling and operation optimization of the steam turbine system of thermal power plants

The increasing deployment of renewable energy sources necessitates peak regulation services from thermal power plants, impacting their energy efficiency. Central to these plants, the steam turbine system significantly influences their operational efficiency. A digital twin model of this system was developed, integrating mechanism-driven and data-driven modeling methods. The neural network data-driven approach was specifically utilized for parameters such as feedwater pump speed and steam flow rate to the pump turbine. Other parameters were modeled with mechanism data hybrid driven modeling method. This model computes vital metrics such as low-pressure turbine exhaust steam enthalpy, work done and heat absorption per unit mass of steam, system efficiency, feedwater mass flow rate, and water-coal ratio—key for evaluating and enhancing the system's energy efficiency. An investigation into a reference case showed a decline in efficiency below design levels due to aging. By optimizing the live steam pressure and the cold-end system, relative improvements in energy efficiency of 0.35 % and 0.14 %, respectively, were achievable.

Study on the effect of cyclic catalytic pyrolysis on sludge pyrolysis products

Pyrolysis technology has become a hot issue in the industry of harmless treatment of sludge in recent years. The present ex-situ catalysis process suffers from the defects of unidirectional flow of pyrolysis steam, easy to form coke buildup on the catalyst surface, and poor heating value of the output heavy tar, which is difficult to be reutilized. This paper designed a cyclic catalytic cracking by pyrolytic steam process to optimize the above defects: under the optimal experimental conditions (pyrolysis starting temperature was 500 ℃, final temperature was 800 ℃, iron-based carbon catalyst dosage was 4 g, and motor speed was 1050 r/min), this process generated more pyrolysis gas and light tar. The increase in pyrolysis temperature had the most significant effect on pyrolysis gas yield, the dosage of iron-based carbon catalyst had the most significant effect on pyrolysis gas composition, and the increase in motor speed had the most significant effect on tar cracking. The cyclic catalytic cracking by the pyrolytic steam process can increase the residence time of pyrolysis steam in the reaction unit and promote the secondary cracking, catalytic, and reforming effects of tar.

Operation optimization of electricity-steam coupled industrial energy system considering steam accumulator

Steam system plays a crucial role in industrial energy usage. Steam generation in the industry domain is transferring from coal-fired or gas-fired plant/boiler to green-electricity steamer for net-zero purpose. The increasing coupling of the electricity-steam energy system in the industry domain, called electricity-steam coupled industrial energy system (ES-IES), brings enormous challenges to the system day-ahead operation optimization due to the uncertainties of renewable generation and the nonlinearities of the system mathematical model. Therefore, this paper introduces the steam accumulator (SA) into the steam system to mitigate the renewable fluctuations, proposes an isothermal linearization method of the steam flow model, and optimizes the operation based on an interactive iteration scheme between optimization and simulation for the global optimum and a balance between accuracy and speed. Results show that considering the storage characteristics of SA and the complementary coordination of electricity and steam through coupling equipment can significantly optimize the operation of ES-IES with an increase in the renewable energy consumption rate by 23.81 % and a decrease in the total operating cost by 11.39 %. The static payback period for the investment of EB and SA is 7 years, indicating a favorable application prospect.

Usable thermal energy stored in the district heating system for peak shaving: A dynamic simulation study

The operational efficiency of district heating system (DHS) relies on the effective use of stored thermal energy, which spans from heating sources to heat users. Enhancing the operational flexibility of the combined heat and power (CHP) unit necessitates a quantitative evaluation of DHS’s usable thermal energy storage to optimize its utilization over time. This evaluation is subject to variability due to the scale, topological structure, and dynamic behaviors of the DHS, presenting a complex challenge. Therefore, the maximum maintenance time and room temperature recovery time were defined as indicators to estimate the usable thermal energy of the DHS for peak shaving in this study, and the dynamic DHS models were constructed for this purpose. Simulations reveal that upon cessation of heating steam flow, standard indoor temperature requirements can be preserved for approximately 2 h. These models facilitate the determination of the optimal maximum maintenance time for various scenarios, thereby maximizing thermal energy utilization within the DHS. Additionally, an analytical derivation of a simplified model for maximum maintenance time calculation, suitable for integration with control systems, is presented. The deviation of this model from actual values is below 10%.

Deep learning-assisted multi-objective optimization of coke dry quenching system efficiency

Coke dry quenching is a promising technology for energy saving and environmental protection in the industrial sectors. Prediction of system efficiency index (SEI) and dynamic adjustment of operating parameters are essential to ensure high system efficiency. In this study, a deep learning-assisted multi-objective optimization framework was proposed to improve coke quenching efficiency and steam production simultaneously. Firstly, numerous on-site process parameters were collected as the data basis for subsequent model construction, and a system-level heat balance model was established and validated for real-time calculation of coke burning loss rate. Then, an attention-based one-dimensional convolutional neural network was developed as a data-driven surrogate model to establish the mapping relationship between the operating parameters and SEI. Finally, the Non-dominated Sorting Genetic Algorithm II was combined with the Technique for Order of Preference by Similarity to Ideal Solution to rapidly identify the optimal operating parameters under different loads. The optimization results also provided a new insight into the system dynamic characteristics. The results show that the surrogate model can swiftly and precisely predict SEI, with R2 exceeding 0.9. Compared with initial operating conditions, the optimal decision scheme has improved SEI by 82 %, with the optimal coke burning loss rate and main steam flow rate of 0.56 % and 83.6 t/h, respectively. This work will provide valuable decision aids for technicians to reach the desired system efficiency.

Optimization of operating conditions in the steam turbine blade cascade using the black-box method

Water droplets cause corrosion and erosion, condensation loss, and thermal efficiency reduction in low-pressure steam turbines. In this study, multi-objective optimization was carried out using the black-box method through the automatic linking of a genetic algorithm (GA) and a computational fluid dynamics (CFD) code to find the optimal values of two design variables (inlet stagnation temperature and cascade pressure ratio) to reduce wetness in the last stages of turbines. The wet steam flow numerical model was used to calculate the optimization parameters, including wetness fraction rate, mean droplet radius, erosion rate, condensation loss rate, kinetic energy rate, and mass flow rate. Examining the validation results showed a good agreement between the experimental data and the numerical outcomes. According to the optimization results, the inlet stagnation temperature and the cascade pressure ratio were proposed to be 388.67 (K) and 0.55 (−), respectively. In particular, the suggested optimal temperature and pressure ratio improved the liquid mass fraction and mean droplet radius by about 32% and 29%, respectively. Also, in the identified optimal operating state, the ratios of erosion, condensation loss, and kinetic energy fell by 76%, 32.7%, and 15.85%, respectively, while the mass flow rate ratio rose by 0.68%.

Influence of pore structure on steam disinfection heat and mass transfer in Yunnan red loam

The obstacles to the continuous cropping of Chinese herbs in Yunnan have become increasingly prominent. Many soil-borne diseases can infect the roots of crops, affect the growth of crops, and eventually lead to quality and yield reduction. Soil steam disinfection can still be used as one of the first methods to solve the problem of continuous cropping obstacles of Chinese herbs such as Panax notoginseng. However, the steam will condense into a large amount of liquid water when it is cold, which will cause soil pore blockage and seriously affect the steam diffusion efficiency. Therefore, it is necessary to study the influence mechanism of the pore structure of Yunnan red loam on heat and mass transfer of steam disinfection. The experimental research was conducted on steam disinfection's heat and mass transfer patterns under different soil pore structure conditions. Image processing technology was used to collect accurate soil profiles and to establish real soil pore structure analysis. Then, fluid simulation technology was used to simulate the heat and mass transfer process and trend of steam distribution within the soil profile under different soil pore structures. The results showed that the steam heat flow of <2 mm, 2–4 mm and 4–6 mm treatments were uniformly diffused in the form of matrix flow in a 1/4 ellipse, and the effective disinfection range was 18 cm horizontal distance and 20 cm vertical distance, in which the highest temperature could reach more than 90 °C. The steam heat flow of the 6–8 mm and >8 mm treatment groups diffused irregularly in large pore steam flow. Therefore, some devices for breaking soil and rotary tillage need to finely rotate the soil in the future. The end effector's disinfection pipe spacing can refer to the effective disinfection range.

Green synthesis of Kenaf-based activated carbons with excellent rate capability and cycle-life via hydrothermal-co-activation process for high-performance capacitive energy storage

The invention of high-performance electrode materials through a simple and green approach is always important for energy storage applications. Herein, we have prepared highly porous activated carbons (ACs) from biomass kenaf (KF) by hydrothermal and steam activation methods. A number of optimization experiments, such as hydrothermal pre-treatment (100, 150 and 200 °C), steam activation temperature (600, 700, 800, and 900 °C) and time of steam flow (15, 30, 60 and 90 min) were performed to control the specific surface area, micro- and/or meso-pores, total pore volume for an excellent electrochemical performance. The as-obtained porous ACs exhibited a high specific surface area (∼1733 m2/g) with high total pore volume (∼0.916 cm3/g) and high mesopore volume (∼28.4%), which are beneficial for the excellent double layer formation over the surface of activated electrode and also provide transport channel for an effective diffusion of electrolyte ions. The as-derived ACs were used as electrode materials for the fabrication of symmetric supercapacitor device in 6 M KOH. The fabricated device exhibited a high energy density of 4.86 Wh kg−1 at power density of 2500 W kg−1 with outstanding stability (∼96.3%) over 10,000 charge-discharge cycles.