Once-through Boiler Research Articles

Solutions for the Implementation of Algorithms for Closed-Loop Control of the Frequency and Power of Large Power Plant Units Comprising Once-Through Boilers

Solutions for the Implementation of Algorithms for Closed-Loop Control of the Frequency and Power of Large Power Plant Units Comprising Once-Through Boilers

A flexible and deep peak shaving scheme for combined heat and power plant under full operating conditions

Improving the flexible and deep peak shaving capacity of combined heat and power (CHP) plant under full operating conditions to facilitate renewable energy consumption is the main choice of novel power system. Accordingly, a dry/wet state automatic conversion control scheme fuses the precise mechanism structure, reinforcement learning and multi-objective model predictive control (MPC) algorithms is designed to promote the deep peak shaving ability of CHP plant in this paper. Firstly, the detailed mechanism models of once-through boiler at dry and wet state are presented by analyzing the dynamic characteristics of steam-water flow. Secondly, the large-scale unknown parameters in mechanism models are identified via the Takagi-Sugeno fuzzy modeling, reinforcement learning algorithms and actual dry/wet state conversion data. Thanks to the proposed hybrid modeling strategy, the high-precision boiler-steam unit models at dry and wet state are rapid obtained. Then, to meet different peak shaving demands, the multi-objective MPC algorithm is respectively constructed under dry and wet state with the comprehensive consideration of operational constraints, load tracking error, algorithm stability, power generation cost, CO2 and NOx emission costs. Aiming at maximizing the peak shaving efficiency and flexible operation ability of plant, a dry/wet automatic control scheme combined the designed multi-objective MPC algorithms and identified dry/wet state models is proposed. Finally, the load variation rate of 5 % and 2 % RCM/min is respectively achieved in the dry/wet state conversion tests on a 350 MW CHP plant based on the proposed control scheme. Thus, the rapid and thorough dry/wet state conversion performance of once-through boiler has successfully improved the operational flexibility of CHP plant under full operating conditions.

Advances in zero liquid discharge multigeneration plants: A novel approach for integrated power generation, supercritical desalination, and salt production

In light of the escalating worldwide demand for energy and water resources, the imperative for developing sustainable multigeneration systems has gained prominence in recent research and development. This study aims to investigate the feasibility and performance of a novel multigeneration plant operating at supercritical conditions to simultaneously generate freshwater, power, and dry salt as a by-product while eliminating liquid discharge. This approach offers a promising solution to address the interconnected challenges of energy and water sustainability. The theory contends that combining supercritical desalination with power generation increases energy efficiency and water production rates, surpassing conventional systems. Therefore, a model is developed employing a supercritical once-through boiler capable of supplying the necessary heat duty required for steam generation from the integrated desalination plant, producing power. Additionally, multiple heat exchangers and flash separators are implemented, enhancing freshwater productivity and obtaining dry salt, eliminating the need for brine waste disposal. A thorough sensitivity analysis is conducted utilizing a robust model developed on Aspen HYSYS to ascertain the optimal operational parameters of the proposed plant. The findings of this study underscore the potential of concurrent production of 1.65 million m3/year of freshwater, 302.5 GWh of electricity, and 64,845 ton/year of dry salt for 0.38 $/m3, 0.07 $/kWh, and 0.02 $/kg, respectively. In conclusion, this research highlights the prospects of revolutionary progress in multigeneration systems for sustainable development.

Hybrid modeling of a circulating fluidized bed boiler for development of a prediction and prescription system for power plant operation

A novel hybrid modeling system of a circulating fluidized bed boiler was developed in this study. The proposed approach combines a computational fluid dynamics model, practice-oriented macro-scale models, and a data-driven reduced order model to capture both the physical and empirical behaviors of the boiler. The application of various modeling strategies allowed for capturing features of the simulated process at various scales and for developing a fast and accurate prediction system. The use of the computational fluid dynamics model improved the predictions of the practice-oriented macro-scale models providing more detailed flow information and the use of the reduced order model allowed for reducing the computation time by a factor of 1350. The hybrid model and its submodels were validated against real measurement data. The validation confirmed good accuracy in predicting key process variables. The developed model is used as a prediction and prescription system to enable operators to optimize the boiler operation and prevent abnormal events. The hybrid system is used for a supercritical, once-through boiler in Łagisza power plant in Poland, however, the presented modeling strategy can be applied in other power plants, which can improve efficiency, reduce emissions, enhance boiler availability, and ultimately contribute to more sustainable energy systems.

Design of Multi-Input Multi-Output Non-linear Model Predictive Control for Main Steam Temperature of Super Critical Boiler

Flexible operation of coal-fired power plants is becoming increasingly necessary for successful integration of large-scale renewable power generation into the power grid. The maximum ramp rate and the number of load cycles are generally limited by the thermal stress experienced by the boiler pressure parts, turbine metallurgy and creep and fatigue of critical thick-walled components Main steam temperature is a critical operating parameter that must be controlled within acceptable limits for safe operation. Main steam temperature deviation beyond acceptable limit has impact on boiler pressure parts and turbine material of construction due to creep and fatigue effect. Base load operating units do not require steep ramp rate and hence recommended ramping rates are kept low within the safe operating zone in comparison to the flexible operation of the units with wide range load change width. Thermal stresses are caused by the temperature changes inside the thick-walled components and turbine steam admission parameters. Hence, the quality of main steam temperature control plays a vital role in flexible operation of the coal fired units. Conventional cascaded PID temperature control loop architecture performs well at steady state condition within a limited variation of load change at low ramp rate but it acts slowly and performs poorly at transient operating conditions of flexible operation of the boiler turbine with wide range load variation and load cycle with high ramp rate and remains far from rated conditions. In this paper, a Multi-Input Multi-Output (MIMO) Non-linear Model Predictive Control (MPC) design for regulation of the main steam temperature of a Once-Through supercritical Boiler is proposed. The controller is based on a non-linear dynamic model which incorporates dynamics of the variables of interest. It has the capability to operate effectively across a wide load range while maintaining main steam temperature within acceptable limits. A notable advancement in this design of MPC is the incorporation of coal flow demand and feedwater flow demand as additional control inputs alongside primary and secondary spray flows. In simulation test cases, the MPC controller demonstrates satisfactory performance and computational efficiency.

Robust & nonlinear control of an ultra-supercritical coal fired once-through boiler-turbine unit in order to optimize the uncertain problem

The ultra-supercritical once-through boiler (OTB) unit is an advanced power generation technology with high plant efficiency and low emissions. However, it is difficult to realize a coordinate control for the ultra-supercritical OTB unit to achieve the fast and stable dynamic response during the load tracking and grid frequency disturbances and in the presence of unavoidable uncertainties. In this paper, an accurate grey box multivariable coupled nonlinear model of an ultra-supercritical boiler-turbine unit is considered. Steam pressure at throttle valve, specific enthalpy in separator and active power are adjusted at desired values by manipulation of the fuel rate command, feedwater rate command and throttle valve opening. In addition to the mentioned accurate model, limitations of operational parameters and uncertainty sources are considered in the controller design. This makes this research unique from previous works. According to affine nonlinear control theory, a nonlinear robust sliding mode controller is developed. Then using MATLAB μ - DK iteration syntax, a linear H-infinity (H∞) robust control is synthesized with selecting proper weight functions. This method is suitable for all types of power plants with a similar mathematical modeling approach. Simulations in MATLAB Simulink toolbox reveals that both designed controllers achieve appropriate performance in the presence of uncertainties and parameters’ limitations, but nonlinear controller has better performance. Finally, deficiencies of a linear controller with respect to the proposed designed robust controllers are denoted.

Virtual reference setting and its application in thermal power unit control

In thermal power units, superheater outlet temperature is a very important parameter, but because of its long delay time and large inertia, it is difficult to obtain good control effect by traditional control algorithm. In this paper, taking a supercritical once-through boiler as the research object, combined with the established superheated steam temperature object model, a two-degree-of-freedom superheater outlet temperature control system based on VRFT is designed, and compared with the conventional tuning method, it is proved that the virtual reference feedback tuning (VRFT) method has many advantages, such as simple design, less computation, no need to select initial parameters and good convergence, is an application-oriented direct control system design method.

Designing a Turning Guide Vane Using CFD for an Economizer of a Non-Furnace Boiler

Non-furnace boilers can improve the efficiency of industrial once-through boilers. However, temperature non-uniformity occurs in the economizer connected vertically to the boiler. Heat transfer performance is degraded by temperature non-uniformity. To solve this problem, a corbel was installed on the side wall of the economizer, and a baffle was installed on the transition duct. Consequently, although the thermal efficiency of the boiler was improved, significant temperature non-uniformity was still observed in the area upstream of the economizer. To address this issue, this study designed a turning guide vane (TGV) at the economizer inlet using computational fluid dynamics (CFD). First, CFD was performed for a case without a guide vane and a case with an existing baffle installed. By analyzing the streamlines obtained using CFD, two TGV designs were proposed. In the first design, guide vanes were installed along the desired streamline, and the concept of the existing TGV was followed. In the second design, an attempt was made to minimize the pressure drop by arranging guide vanes at the inlet. Both designs reduced the standard deviation of temperature by more than 30% and improved the volume goodness factor by 25%.

Increased hydraulic resistance in tubes of once-through boiler due to fouling: A case study of 650 MWe ligite fired unit

The analysis of pressure changes in water and steam flow along the entire once-through steam boiler tube system at the 650 MWe lignite fired Unit was carried out after the long operational period of almost 30 years without a chemical cleaning of the pipe system. A significant increase of the hydraulic resistance was recorded in comparison to the design values in the evaporator tubes, both in the water heating zone and in the evaporation zone with the two-phase mixture flow. The cause of this adverse effect is the formation of a wavy surface of the magnetite layer deposited on the inner wall of tubes. The significantly increased absolute roughness on the inner wall of tubes was determined on the basis of measured pressure drops at sections of the tube system and numerical calculation performed with a thermal-hydraulic model of single-phase and two-phase water and steam tube flows. The model is based on the steam-water two-fluid model with mass, momentum and energy balance equations and mechanistic correlations for the steam-water interface transfer processes. The model is suitable for the single and two-phase flow parameters prediction in the span from subcritical to supercritical and near critical pressure conditions. Conducted calculations provide detailed insight in the fluid pressure, velocity and temperature change in the boiler tube system. After the long operational period the pressure drop in evaporating tubes almost doubles in comparison to the design values. The presented results are a support to boiler's design, operational procedures and maintenance.

A review on dryout and Post-dryout heat transfer inside tubes and tube bundles

• Detailed review on dryout mechanism and dryout and post-dryout heat transfer. • Summarizing the dryout criterions and models of dryout and post-dryout heat transfer. • Elaborating the methods of dryout and post-dryout heat transfer enhancement. • Proposing further research suggestions of dryout and post-dryout heat transfer. The working medium changes from subcooled liquid through flow boiling to superheated vapor in actual once-through thermal equipment (such as once-through steam generators, once-through boilers). Dryout heat transfer deterioration inevitably occur in this vapor-liquid two-phase flow and heat transfer process. After dryout occurs completely, vapor almost completely covers the wall, resulting in a rapid deteriorating heat transfer performance and a sharp rising wall temperature, which puts forward higher requirements on the design, manufacture, and operation of the equipment. The mechanism of dryout is elaborated, and the dryout criterion is summarized in this paper. The three methods that are used to describe the mathematical model of dryout and post-dryout heat transfer are arranged, and the dryout and post-dryout heat transfer in the straight channel is introduced. Furthermore, the methods of enhancing dryout and post-dryout heat transfer are introduced such as changing the geometric structure (including changing the shape of the flow channel and processing the surface of the flow channel) and injecting liquid droplets, etc.

СТАНОВЛЕНИЕ СОВЕТСКИХ «ШАРАШЕК» В НАЧАЛЕ 1930-х гг.: ПРИЧИНЫ, ИНСТИТУТЫ, ПЕРСОНЫ

The problematic field of such a specific segment of forced labor as specialist design, technical departments and project bureaus which were created and operated under the OGPU auspices in the first half of the 1930s requires reinterpretation of its canonical research approaches. The paper considers the specific factors of the emergence of “sharashkas” network as an institutional manifestation and the result of stepped-up conservative subordination and forced exploitation by the Stalinist regime of the intellectual potential of the brainpower. The evolvement of the Special Bureaus was the embodiment of the basic characteristics of a mobilization-type campaign (the construct of “sabotage”, extraordinary measures of implementation, extensity, resource intensiveness, strife, unintended consequences). Throughout 1930–1934 imprisoned specialists became an object, a special accounting category and a target group for bureaucratic inter-agency negotiating between security and economic departments, and their deliverables were expropriated. The paradox of the full regime dependence of specialists on chekists and the inverse dependence of the latter on the results of the prisoners’ activities is observed. It is concluded that the established hybrid institution of regime labor comprised of all types of coexisting labor activity — service, compulsory, mobilization, forced — had no functional stability, prospects and capacity for selfdevelopment. An exception was the considered case of the creation of Design Bureau № 11 initiated by L. K. Ramzin, rearranged in 1934 into the Bureau of once-through boiler construction, which worked until the end of the Stalin era.

Failure analysis of the water-wall tube in once through Benson boiler

Failure analysis of a water wall tube of a once-through Benson boiler after 100,000 h of use of service is presented. A 15Mo3 material was used in the manufacture of the tube. In order to identify the root cause of the rupture, visual inspection, optical emission spectroscopy, microscopic examinations, mechanical strength measurements, and tube wall thickness measurements at various locations were performed on the failed tubes. Visual inspection revealed a fish mouth puncture opening with thin lips. As a result of optical spectroscopy, mechanical testing, and hardness measurements, the material was found to meet the requirements. Based on microstructure analysis, it appears that the pearlite spheroidized near the rupture site as a result of localized high temperatures. The failure mechanism of the tube was identified as a localized short-term overheating caused by high heat flux based on the results of all the tests and analyses conducted in this study.

Efficiency improvement technology of front and rear wall hedging boilers based on combustion optimization and balancing heating surface wall temperature

The ”efficiency improvement technology of front and rear wall hedging boilers based on combustion optimization and balancing heating surface wall temperature” is proposed and applied in a 1000MW unit of a power plant, which effectively reduces the large deviation of the heating surface wall temperature, increases the temperature of the main reheated steam, and improves the economy and safety.This paper introduces the principle of ”efficiency improvement technology of front and rear wall hedging boilers based on combustion optimization and balancing heating surface wall temperature”. It takes 1000MW unit as an example to introduce in detail how to use this technology to adjust combustion. The main steam increased by 6 °C, the reheat steam increased by 1.9 °C, the CO decreased from 2000–3000mg/Nm3 before adjustment to about 200 mg/Nm and the wall temperature deviation of the heating surface was significantly reduced. The technology can be widely used in ultra-supercritical once-through boilers with front and rear wall hedging swirl burners to improve the economy and safety of boilers, and has a broad space for promotion. The mutual restriction relationship between environmental performance and environmental protection, while taking into account the potential safety hazards caused by flue gas temperature deviation, establish a more comprehensive and complete combustion model.

Modeling of Steam Generation Process in the Supercritical Once-Though Boiler in the Thermal Power Plant with MATLAB Application

The paper establishes a simple and practical model for a water-wall system comprising supercritical once-through boilers. The mathematical model of the system is developed and built based on mass, energy and momentum balance equations. The system of equations gives the linear and differential algebraic equations expressed by pressure and temperature. The model is solved by a program written in the MATLAB application. The data in the literature are also provided for comparison, and good agreement with the model results. The MATLAB program could be applied for basic design of process in the supercritical once though boiler in the thermal power plants in Vietnam.

Simultaneous reduction of NOx emission and SOx emission aided by improved efficiency of a Once-Through Benson Type Coal Boiler

With significant contributions in global emissions of air pollutants, sustainable practices for coal-fired power generation are fundamental to mitigate global climate change, besides ensuring compliance to the local authorities, which is as critical as climate issues. Despite the importance of these issues, some gaps exist in the literature to develop practices capable of fostering emissions reduction of NOx and SOx. In this sense, the present study aimed to present a comprehensive approach to NOx emission and SOx emission reduction through improved efficiency of a once-through Benson type coal boiler in a coal-fired power plant. In improving efficiency, NOx and SOx emissions were strongly influenced by O2 concentration, coal mass flow, air/fuel ratio and coal calorific value. The optimum conditions that resulted in simultaneous reduction of NOx and SOx emissions were achieved when the O2 concentration was 3.28 vol% with the coal mass flow of 281 tonnes/hr. The results further suggested that NOx concentration was reduced by a large margin when the air/fuel ratio changed from the lean side to the rich side. The findings of this study help to establish benchmarks relating to a comprehensive assessment of SOx and NOx emissions reduction.

드럼보일러 증기발생기 수위 안정을 위한 급수펌프 유량제어특성 개선

In Korea, since the beginning of the 1990s, there has been a surge in the construction of high-efficiency coal-fired once-through boilers for 500 MW standard thermal power plants rather than drum (D/M) type steam generators. Furthermore, Old D/M type boilers have been retired without life extensions, and the capacity factor of remaining coal-fired power plants has been lowered owing to a government emission regulation policy on coal-fired power plants to reduce particulate matter since 2019. Recently, several issues with control systems of D/M type steam generators have been reported, including weekly start-up and shut-down and large-rapid load swings rather than constant operating patterns. The D/M level control system is one of the most important control systems in power plants, as it is directly influenced by the performance of the feedwater (FW) flow control system in terms of pump speed, flow control valve opening, and load runback controls, all of which affect FW flow and D/M level status. This study demonstrates how to reduce the parasitic power consumption during normal operating and regulate the steam generator level during runback operation by incorporating differential pressure control logic for flow compensation.

Increased Hydraulic Resistance in Tubes of Once-Through Boiler Due to Fouling: A Case Study of 650 Mwe Ligite Fired Unit

Increased Hydraulic Resistance in Tubes of Once-Through Boiler Due to Fouling: A Case Study of 650 Mwe Ligite Fired Unit

Numerical simulation of ash erosion in the selective catalytic reduction catalyst of power plant boiler

The selective catalytic reduction (SCR) catalyst of a 660 MW ultra-supercritical once-through boiler denitrification system suffered severe abrasion, causing the denitrification system to fail. Statistics showed the abrasion area focused on near side of the boiler. The formation mechanism of the catalyst abrasion is analyzed using general purpose computational fluid dynamics (CFD). The simulation results are consistent with the actual test data. It reveals that the catalyst abrasion is likely to be caused by the nonuniformity distribution of the fly ash particle field. The fly ash distribution and the gas velocity in different cases were obtained. Under the best case, the impact device can ensure fly ash particles in the upper part of catalyst move to the far boiler side of catalyst. It is shown that the flow field and fly ash particle distribution greatly improved after computation of the optimization.

Research and Design on the Coordinate Control System of Once-through Boiler Power Unit

Taking the 1000 MW ultra supercritical unit as an object of study, The nonlinear model is builded through mechanism analysis, which is linearized based on small error, the multi-variable decoupling controller is designed to achieve full decoupling of the input and output variables, and finally the three-input-three-output coordinated control system (CCS) is established. The control system is verified by coal quality and the specific enthalpy of feed water disturbance when load changing, the simulation result shows that the improved CCS has good control performance.

Application of Iterative Feedback Tuning Method in Superheated Steam Temperature Control System

Taking a 600 MW supercritical once-through boiler as the study object, this paper designed an IFT-based two-degree-of-freedom (DOF) PID superheated steam temperature control system. Besides, the IFT-PID controller was formed and compared with the conventional tuning method. The simulation results show that this method can be successfully applied to great-inertia and large-lag controlled objects, with evident superiority.