Intermediate Point Temperature Research Articles

Short-Term Prediction of the Intermediate Point Temperature of a Supercritical Unit Based on the EEMD–LSTM Method

The quality of the intermediate point temperature control of a supercritical unit is directly related to the quality of the coal–water ratio and main steam temperature control of the supercritical unit, which is also related to the economy and safety of the unit. In order to improve the accuracy of short-term predictions of the intermediate point temperature, a short-term prediction model of the intermediate point temperature based on the EEMD (Ensemble Empirical Mode Decomposition)-LSTM (Long Short-Term Memory) model is proposed. This model uses the data of a 600 MW thermal power station in 2022 as a sample. The EEMD method is used to decompose the historical data into IMF components and residual components, and the correlation between each component and the original data is calculated. The relevant components are sent to the LSTM neural network, and all the sub-components are superimposed to obtain the final intermediate point temperature prediction results. At the same time, the BP and LSTM models are built to compare the errors with the proposed model. The results show that the single model will produce large errors when predicting the factors of large data fluctuations. The EEMD–LSTM coupling model can fully extract the detailed features and the prediction effect is obvious. The prediction accuracy of the EEMD–LSTM prediction model built in this paper is significantly better than that of the other two models. It has certain application value in the research field of intermediate point temperature prediction and can meet the requirements of short-term predictions of the intermediate point temperature.

A composite weighted human learning network and its application for modeling of the intermediate point temperature in USC

Ultra supercritical power plant (USC) is a complex system associated with nonlinearity, uncertainties and multivariable couplings. Generally, it is difficult to build an accurate model to approximate the dynamic behavior of USC. This paper presents a novel composite weighted human learning optimization network (CWHLO) to tackle the above-mentioned problem. Firstly, by fully using of the statistic characteristic of the history operating data, K-means clustering algorithm is applied to partition the raw date, which extremely reduces the operating nonlinearity. Then, an improved real-coded human learning optimization (HLO) is adopted to built linear models in local regions. Different from conventional methods, the advantage of the proposed CWHLO is that the nonlinear model of the object is effectively replaced by a real-time dynamic linear model, which is more suitable for other control methods. Finally, the CWHLO model is compared with the traditional recursive least square method (RLS), and four other meta-heuristic algorithms, to show the advantages in approximating the dynamic behavior of USC.

An optimized nonlinear generalized predictive control for steam temperature in an ultra supercritical unit

The optimize control of the ultra supercritical (USC) unit has been a major concern in power industry. The intermediate point temperature process is a multi-variable system with strong nonlinearity, large scale and great delay, which greatly affects the safety and economy of the USC unit. Generally, it is difficult to realize effective control by using conventional methods. This paper presents a nonlinear generalized predictive control based on a composite weighted human learning optimization network (CWHLO-GPC) to improve the control performance of intermediate point temperature. Based on the characteristics of the onsite measurement data, the heuristic information is incorporated into the CWHLO network, and expressed by different local linear models. Then, global controller is elaborately constituted based on a scheduling program inferred from the network. Compared with classical generalized predictive control (GPC), the non-convex problem is effectively solved by introducing CWHLO models into the convex quadratic program (QP) routine of local linear GPC. Finally, detailed analysis on set point tracking and interference resisting via simulation is addressed to illustrate the efficiency of the proposed strategy.

Performance upgrading of supercritical unit on preferable operation mode with promoting feed water temperature

Promoting feed water temperature (FWT) at low loads for supercritical unit has proved to be an effective technology to ensure denitrification capacity of Selective Catalytic Reduction (SCR). However, operational economy of unit is significantly reduced on conventional intermediate point temperature (IPT) setting mode. Hence, a superior operation strategy defined as IPT regulating mode for supercritical unit is proposed. Mathematical method was further developed. Then, operation characteristics on economy and pollutant emission of a 660 MW supercritical unit are investigated on IPT regulating mode. A series of influencing mechanisms were revealed. Simultaneously, individual significant parameters were compared with that of traditional operation strategy. Results shows, supercritical unit with increasing FWT achieve a better performance on IPT regulating mode. Compared with traditional operation strategy, NOx emission are fully up to requirement. Concurrently about 2.89 g/kWh in standard coal consumption rate is decreased and 37.3 MW increasing in power generation is achieved averagely. Moreover, such operation strategy also makes superheated steam temperature maintain rated value. Reheated steam temperature promotes by 27.3 ℃ averagely, and become more smooth and steady. This study also reveals that advantages of proposed strategy will be more prominent with higher FWT and lower operating load.

Compensation Design of Coordinated Control System for Supercritical Once-Through CHP Plants Based on Energy Analysis

To increase the flexibility of power generation, the supercritical once-through boiler combined heat and power (CHP) plant should improve its coordinated control system (CCS). The difficulty of CCS for supercritical once-through boiler unit is to determine the water-fuel ratio in the dynamic process. First, a CHP unit model is established and simplified into a three-input three-output object under pure condensing working conditions. Second, dynamic relative matrix gain method and simulation is used to analysis several once-through boiler coordinated control schemes commonly used in engineering in which the compensation link is designed on the basis of water-fuel ratio. Simulation results show that, the water following CCS scheme has better intermediate point temperature performance and worse throttle pressure performance than the fuel following CCS scheme. To improve pressure performance, the closed-loop characteristics of pressure response to fuel and feed water flow are analyzed and compared through wavelet analysis. Finally, a method for determining the inertia time constant in the dynamic compensation link by comparing the wavelet coefficients is proposed. Wavelet analysis show that the imbalance in the speed of energy changes to fuel and feed water flow is the essential cause of large fluctuations in intermediate point temperature and throttle pressure before turbine of the supercritical once-through boiler unit. Simulation results show that using the proposed dynamic compensation in water following CCS can effectively reduce fluctuations of the intermediate point temperature and fluctuations of throttle pressure before turbine when power load command changes.

Analysis of Gas Recirculation Influencing Factors of a Double Reheat 1000 MW Unit with the Reheat Steam Temperature under Control

In this paper, the simulation software EBSILON is used to simulate the reheat units, and the reheat temperature control mode is deeply explored. In the benchmark system, the influence of different load intermediate point temperature on the flue gas recirculation (FGR) is analyzed. Then, the effects of load, coal quality, excess air factor, and feed water temperature on FGR are studied under the premise of intermediate point temperature as design value, and the cause for FGR change is analyzed by comparing the cutoff bypass flue (CBF) system. The results show that under any load, the FGR decreases with the increase of the intermediate point temperature, while under low load, the change of the intermediate point temperature has a greater impact on the FGR rate. When the intermediate point temperature remains constant, the FGR plunge has an increase of load at low load and is almost unchanged at high load; the FGR rate of coal with low calorific value and high moisture content is low and the coal with low volatile and high ash content has great influence on reheat steam temperature; and the excess air factor and feed water temperature are inversely proportional to the flue gas recirculation rate. In the CBF system, the change trend is similar to the reference system, but under the same working condition, the FGR rate is higher than the latter.

Model establishment and performance evaluation of a modified regenerative system for a 660 MW supercritical unit running at the IPT-setting mode

Abstract: Improving denitrification efficiency of supercritical unit for peak load regulation by changing feed water temperature has become a focus of thermal power engineering under wide load. However, the effect mechanism of feed water temperature on the performance of supercritical unit is indistinct absolutely at the intermediate point temperature (IPT)-setting mode, which obstructs the performance optimization and the excavation of energy saving of supercritical unit with a change of feed water temperature aims at improving denitrification efficiency of supercritical unit. For the purpose, a closed cycle theory in which thermal power unit operating parameters interact and form a closed influence mechanism was defined and proposed, with such a core ideology, the performance analysis and assessment models under IPT-setting mode is constructed on the differential theory, energy balance and thermodynamics method, and the accuracy of established model is verified. These developed models are applied to assess the operational performance and to identify energy saving potential of supercritical unit for peak load regulation. Subsequently, a typical 660 MW ultra-supercritical coal fired power plant is selected as a reference case. Not only a quantitative analysis of effect of increasing feed water temperature adding HP heaters on supercritical unit performance is performed, but the effect of reducing feed water temperature stopping HP heaters on supercritical unit performance is implemented as well at the IPT-setting mode. Finally, the influence mechanism of feed water temperature on boiler thermal efficiency, steam turbine thermal consumption rate, standard coal consumption rate, power generation, denitrification efficiency, NOx production, steam temperature and other operating parameters of supercritical unit is absolutely revealed on IPT-setting mode. The investigation results show that the sensitivity of feed water temperature to supercritical unit performance varies greatly in different range of feed water temperature, especially when the feed water temperature is heated to the near the pseudo critical temperature, a dramatic change would take place in operation parameters of supercritical unit. Such a viewpoint is presented rigorously that increasing feed water temperature does not always achieve energy saving for supercritical units, also contrary to the existing viewpoint.

Investigation on Intermediate Point Temperature Adjustment in Once-Through Boiler Based on Enthalpy Distribution

The developed power plants take advantage of variable pressure operation in wide range of working condition, during which liquid physical property is influenced by pressure change to a great extent. It can result in complex heat transfer condition, even over-temperature in heated tubes. Based on enthalpy distribution, present paper studies the different degrees (1°C-15°C) of superheat in steam-water separator in four working conditions (30%, 50%, 75%, 100%). Meanwhile, the impact of pressure deviation (-10bar-10bar) on the enthalpy distribution is in scope in present paper.

A 12-Input-3-Output RBF Neural Network Model of Load and Main Steam Pressure Characteristics for Ultra-Supercritical Unit

In this paper, an 1000MW ultra-supercritical boiler unit was taken as the research case. The neural network, RBF, was used to build the model for the 1000MW ultra supercritical unit based on Matlab. The inputs of the model include fuel amount, feedwater flow,turbine valve opening demand. The outputs include unit load, main steam pressure and intermediate point temperature. The simulation results proved the validity of the model. The model can be used to improve the response rate of the unit load and optimize the coordinating control with certain practical engineering significance.

Research on Control Method for Intermediate Point Temperature of Supercritical Boiler Based on Active Disturbance Rejection Cascade Control

As the important signal of once-through boiler's water-fuel ratio control, intermediate point temperature of supercritical boiler plays a key role in the decision of steam and water’s boundary, the match of fuel and water, the control of main steam temperature. The condition of its control directly impacts the once-through boiler’s safety and economy running. For an uncertainty model, a good control quality can not be gained using the general PID controller when the unit load has great changes, so that the main steam temperature fluctuates greatly. According to this problem, a control system about intermediate point temperature of supercritical boiler based on active-disturbances-rejection multiple model was designed. Corresponding active disturbances rejection controller (ADRC) about different model in different operation points was designed. It can choose corresponding controller according to the operation condition so as to achieve an adaptive control of a wide range. The simulation results show that the system has a strong robustness and sufficient capability for control . DOI: http://dx.doi.org/10.11591/telkomnika.v11i7.2846 Full Text: PDF

Discussion of Ultra-supercritical Units Feed Water Control Strategy

This paper analyzes a certain power plant ultra-supercritical unit feed water control system, and has setting, optimized control system. Through analysis of operation, when Load on a large scale changes and intermediate point temperature control, this unit gets a good control effect. The control system offers ultra-supercritical units feed water control scheme for reference.