Fuzzy disturbance rejection predictive control of ultra-supercritical once-through boiler-turbine unit

In order to overcome the wide-range load tracking and unknown disturbance issues of an ultra-supercritical boiler- turbine unit, a fuzzy disturbance rejection predictive control approach is proposed using the techniques of fuzzy scheduling, model predictive control and extended state observer. Local state-space models are established on the basis of nonlinearity analysis and subspace identification. To eiJiance thedisturbance rejection capability of the controller, a extended state observer is employed to estimate unnown disturbances and model mismatches. The disturbance estimation ennaced local predictive controllers ae subsequently devised based on the local models, the performance of which is further strengthened by incorporating the fuzzy scheduling technique. The simulation results verify the merits of the proposed strategy in achieving satisfactory wide-range load tracking ad disturbance rejection performance.

Ultra-Supercritical——A Preferential Choice for China to Develop Clean Coal Technology

The ultra-supercritical pressure coal-fired power-generation technology (USCT) isa mature, advanced and efficient power generation technology in the world. Comparisonsamong several principal clean coal power-generation technologies show that USCT withpollutant-emission control equipment is superior to others in efficiency, capacity, reliability,investment and environment protection etc. Analyzing the main problems existing in thermalpower industry, it is concluded that the USCT is the preferential choice for China to developclean coal power-generation technology at present. Considering the foundation of thepower industry, the manufacturing industry for power generating equipment and otherrelated industries, it is concluded that China has satisfied the qualifications to develop USCT.

Multi-model Predictive Control of Ultra-supercritical Coal-fired Power Unit

The control of ultra-supercritical(USC) power unit is a difficult issue for its characteristic of the nonlinearity, large dead time and coupling of the unit. In this paper, model predictive control(MPC) based on multi-model and double layered optimization is introduced for coordinated control of USC unit. The linear programming(LP) combined with quadratic programming(QP) is used in steady optimization for computation of the ideal value of dynamic optimization. Three inputs(i.e. valve opening, coal flow and feedwater flow) are employed to control three outputs(i.e. load, main steam temperature and main steam pressure). The step response models for the dynamic matrix control(DMC) are constructed using the three inputs and the three outputs. Piecewise models are built at selected operation points. Double-layered multi-model predictive controller is implemented in simulation with satisfactory performance.

Exergy Analysis and Thermal Optimization of a Double-Turbine Regeneration System in a Ultra-Supercritical Double-Reheat Unit

Improving the primary steam parameters is one of the most direct ways to improve the cycle efficiency of a powergeneration system. In the present study, the typical problem connected to the excessively high superheat degree ofextraction steam in an ultra-supercritical (USC) double-reheat unit is considered. Using a 1000 MW power plantas an example, two systems (case 1 and case 2) are proposed, both working in combination with a regenerativesteam turbine. The thermal performances of these two systems are compared with that of the original systemthrough a heat balance method and an exergy balance strategy. The results reveal that the two coupled systemscan significantly reduce the superheat degree of extraction steam, turbine heat rate, and coal consumption of theunit and improve the energy utilization efficiency. These results will provide useful theoretical guidance to futureinvestigators wishing to address the general problem relating to energy conservation and modelling of the coupledextraction steam regenerative system of USC double-reheat units.

Min-max fuzzy model predictive tracking control of boiler-turbine system for ultra-supercritical units

To improve the control performance of nonlinear ultra-supercritical(USC)thermal power units,an improved min-max fuzzy model predictive tracking control(FMPTC)strategy is proposed.First,a T-S fuzzy model is established to approximate the dynamics of the nonlinear boiler-turbine system.Then,based on an extended fuzzy model containing state variables and output variables,a min-max FMPTC is derived for output regulation while ensuring the closed-loop system stability and the inputs in their given constraints.For greater controller design freedom,the developed controller adopts a new state-and output-based objective function.In addition,the observer estimation error is regarded as a bounded disturbance,ensuring the stability of the entire closed-loop control system.Simulation results on a 1000 MW USC boiler-turbine model illustrate the effectiveness of the proposed approach.

Development Features of Supercritical (Ultra-Supercritical) Technology in the World and Experiences We Can Learn

The development and technical characteristics in different stages of supercritical (ultra-Supercritical) technology abroad are introduced in this paper. At the same time, according to the development trend of supercritical (ultra-supercritical) technology, the corresponding revelations are given in this paper. That is: It is an inevitable choice to develop supercritical (ultra-supercritical) technology if we want to improve the thermal efficiency and heat efficiency.

Study on Calculation Method for Partition of Heat Transfer in an Ultra-supercritical Boiler

Use a 1000MW ultra-supercritical tower boiler as the research object. On the basis of one dimensional model, simplify the tube heat transfer model and the radiation heat transfer model;establish the two-dimensional area calculation model with the regional method;?summarize the heat load distribution of flue gas temperature and water wall surface;and compare with the measured data. The error range of the result is acceptable on the project. The distribution of water wall surface heat load along the furnace width and the area where heat transfer deterioration?cause easily along the furnace height direction are studied with the model and algorithm on different boiler load conditions. All these provide the reference for the design and operation of the ultra supercritical boiler.

Vibration of 1000-MW Ultra-Supercritical Turbine-Generator Unit with Simens Technology

The layout features of unit shafting and their effects on vibration, as well as evaluation criteria, were introduced for a 1000-MW ultra-supercritical turbine-generator unit with Simens technology. Based on vibration diagnosis and treatment for more than 10 units, some typical vibration faults were summarized, such as the vibration fluctuation of the high pressure (HP) rotor, abnormal vibration increases of the No.3 bearing pedestal and large vibration of the exciter rotor during its critical speed range. The vibration characteristics and the causes of faults and countermeasures were analyzed. Three applications for further illustration were given. The vibration fault identification method, control measures, and applications can provide a reference for vibration diagnoses and treatment of same type units.

Energy-Saving Optimization Study on 700℃ Double Reheat Advanced Ultra-Supercritical Coal-Fired Power Generation System

700°C double reheat advanced ultra-supercritical power generation technology is one of the most important development directions for the efficient and clean utilization of coal.To solve the great exergy loss problem caused by the high superheat degrees of regenerative steam extractions in 700°C double reheat advanced ultra-supercritical power generation system,two optimization systems are proposed in this paper.System 1 is integrated with the back pressure extraction steam turbine,and system 2 is simultaneously integrated with both the outside steam cooler and back pressure extraction steam turbine.The system performance models are built by the Ebsilon Professional software.The performances of optimized systems are analyzed by the unit consumption method.The off-design performances of optimization systems are analyzed.The results show that:the standard power generation coal consumption rates of optimization systems 1 and 2 are decreased by 1.88 g·(kW·h)^(–1),2.97 g·(kW·h)^(–1)compared with that of the 700°C reference system;the average superheat degrees of regenerative steam extractions of optimized systems 1 and 2 are decreased by 122.2°C,140.7°C(100%turbine heat acceptance condition),respectively.The comparison results also show that the performance of the optimized system 2 is better than those of the optimized system 1 and the 700°C reference system.The power generation standard coal consumption rate and the power generation efficiency of the optimized system 2 are about 232.08 g·(kW·h)^(–1)and 52.96%(100%turbine heat acceptance condition),respectively.

Predictions of NOx/N2O emissions from an ultra-supercritical CFB boiler using a 2-D comprehensive CFD combustion model

NOx and N2O emissions from an ultra-supercritical circulating fluidized bed(CFB)boiler were predicted using a two dimensional(2-D)comprehensive computational fluid dynamics(CFD)combustion model.This model was developed from a three dimensional model for a supercritical CFB boiler previously constructed by our group.Based on an analysis of the NOx and N2O conversion processes in a CFB boiler,the primary formation and destruction reactions were introduced into the 2-D model and coupled.The resulting model was validated using data from the Baima 600 MW supercritical CFB boiler,and then applied to a 660 MW ultra-supercritical CFB boiler.The effects of excess air,the secondary air(SA)to(primary air(PA)plus SA)ratio and the SA injection height on NOx and N2O emissions were investigated.The results show that a higher excess air volume increases both NOx and N2O emissions,while increasing the SA/(PA+SA)ratio somewhat reduces both the NOx and N2O concentrations.On the basis of the results of this work,optimal locations for SA injection ports so as to lower NOx and N2O emissions are recommended.

Steam Pressure Control of 1000 MW Ultra-Supercritical Coal-Fired Power Unit Based on Multi-Model Predictive Control

Ultra-supercritical(USC) coal-fired unit is more and more popular in these years for its advantages.But the control of USC unit is a difficult issue for its characteristic of nonlinearity, large dead time and coupling among inputs and outputs. In this paper, model predictive control(MPC) method based on multi-model and double layered optimization is introduced for coordinated control of USC unit running in sliding pressure mode and fixed pressure mode. Three inputs(i.e. valve opening, coal flow and feedwater flow) are employed to control three outputs(i.e. output power, main steam temperature and main steam pressure). The step responses for the dynamic matrix control(DMC) are constructed using the three inputs by the three outputs under both pressure control mode. Piecewise models are built at selected operation points. In simulation, the output power follows load demand quickly and main steam temperature can be controlled around the setpoint closely in load tracking control. The simulation results show the effectiveness of the proposed methods.

Thermal-Hydraulic Calculation and Analysis on Evaporator System of a 1000 MW Ultra-Supercritical Pulverized Combustion Boiler with Double Reheat

A double reheat ultra-supercritical boiler is an important development direction for high-parameter and large-capacity coal-fired power plants due to its high thermal efficiency and environmental value.China has developed a 1000 MW double reheat ultra-supercritical boiler with steam parameters of 35 MPa at 605℃/613℃/613℃.Reasonable water wall design is one of the keys to safe and reliable operation of the boiler.In order to examine the thermal-hydraulic characteristics of the double reheat ultra-supercritical boiler,the water wall system was equivalent to a flow network comprising series-parallel circuits,linking circuits and pressure nodes,and a calculation model was built on account of the conservation equations of energy,momentum and mass.Through the iterative solving of nonlinear equations,the prediction parameters of the water wall at boiler maximum continue rate(BMCR),75%turbine heat-acceptance rate(THA)and 30%THA loads,including total pressure drops,flow distribution,outlet steam temperatures,fluid and metal temperatures were gotten.The results of calculation exhibit excellent thermal-hydraulic characteristics and substantiate the feasibility of the water wall design of the double reheat ultra-supercritical boiler.

Effect of SiO_(2) and B_(2)O_(3) on crystallization and structure of CaF2–CaO–Al_(2)O_(3)-based slag for electroslag remelting of ultra-supercritical rotor steel

Regarding development of the dedicated slag for electroslag remelting,crystallization characteristics of the slag exert a strong influence on the initial solidification of liquid metal in mold and surface quality of as-cast ingot.The crystallization behavior of CaF_(2)-CaO-Al_(2)O_(3)-based slag with varying SiO_(2)and B_(2)O_(3)contents and their correlation with the slag structure were investigated.Increasing SiO_(2)(0.24-8.95 mass%)and B_(2)O_(3)(0-3.20 mass%)contents lowers the crystallization temperature and suppresses the crystallization of the slag melts,as well as decreases the sizes of the crystalline phases.The crystalline phases precipitated during continuous cooling of the slag melts are faceted 11CaO·7Al_(2)O_(3)·CaF_(2),faceted or spherical CaF_(2),and non-faceted MgO·Al_(2)O_(3)(or MgO)in sequence irrespective of the SiO_(2)and B_(2)O_(3)contents of the slag.The polymerization degree of slag melts increases with increasing either SiO_(2)or B_(2)O_(3)contents.The crystallization of the slag melts is increasingly retarded with increasing the SiO_(2)and B_(2)O_(3)contents of the slag caused by increased component diffusion resistance originating from increased polymerization degree of the slag melts.

Coupled Heat Transfer Simulation of the Spiral Water Wall in a Double Reheat Ultra-supercritical Boiler

This paper presented a coupled heat transfer model combining the combustion in the furnace and the ultra-supercritical(USC) heat transfer in the water wall tubes. The thermal analysis of the spiral water wall in a 1000 MW double reheat USC boiler was conducted by the coupled heat transfer simulations. The simulation results show that there are two peak heat flux regions on each wall of spiral water wall, where the primary combustion zone and burnt-out zone locate respectively. In the full load condition, the maximal heat flux of the primary combustion zone is close to 500 kW/m^2, which is higher than that in the conventional single reheat USC boilers. The heat flux along the furnace width presents a parabolic shape that the values in the furnace center are much higher than that in the corner regions. The distribution of water wall temperature has a perfect accordance with the heat flux distribution of the parabolic shape curves, which can illustrate the distribution of water wall temperature is mainly determined by heat flux on the water wall. The maximal water wall temperature occurs at the middle width of furnace wall and approaches 530°C, which can be allowed by the metal material of water wall tube 12Cr1MoVG. In the primary combustion zone, the wall temperatures in half load are almost close to the values in 75% load condition, caused by the heat transfer deterioration of the subcritical pressure fluid under the high heat flux condition. The simulation results in this study are beneficial to the better design and operational optimization for the double reheat USC boilers.

Nickel-base superalloys for USC power plants

The advanced ultra-supercritical power plants of the future will utilize steam pressures and temperatures that are too high for traditional ferritic steels,thus requiring austenitic materials.Older nickel-base superalloys such as 263 and 617 were initially evaluated under the European THERMIE project beginning in the 1990s.An entirely new age-hardened alloy 740 which possesses exceptional fireside corrosion resistance and creep strength was also developed for boiler tubing capable of serving at 700C.Subsequently,interest in the USA considered other product forms such as steam header piping and steam turbine forgings for service as high as 760C.A more stable and weldable alloy version now called 740H was developed to meet these more demanding conditions.This paper summarizes the current status of work on alloys 740 and 740H.

Development of TP310HCbN(07Cr25Ni21CbN) austenitic stainless steel tubes

Improving the unit heat efficiency,reducing coal consumption and the emission of CO_2 and meeting the requirements of environmental protection and energy conservation is the goal of the boiler and the power industry.Developments of large capacity and high parameter ultra-supercritical(USC) units are the tendency of the power industry.There is no doubt that the development of USC units is based on the development of materials, especially the materials used for super-heater and reheater in high-temperature USC boiler.Due to the long time exposure to the harsh environment,such as bearing the 600℃steam oxidation,and withstanding the corrosive flue gas and fly ash erosion,the materials require not only good high-temperature strength,but also a good corrosion resistance.In consideration of the requirements cited above,foreign countries had developed TP310HCbN (07Cr25Ni21CbN) austenitic heat-resistant steel.However,the domestic demands for this material still depend on import and the cost is high,so the boiler and the power industry expects eagerly that these steels can be produced by domestic metallurgical industry,especially Baosteel,to replace the imported products.In order to satisfy the requirements of domestic manufacturing super-heater and reheater used in ultra-supercritical power boiler,after developed T23、T91、T92、S30432 high pressure boiler tube,Baosteel began to develop TP310HCbN (07Cr25Ni21CbN)austenitic stainless steel tube in January of 2007.This study describes the composition design, the manufacturing process of product,and the assessment of performance of Baosteel's TP310HCbN (07Cr25Ni21CbN).The data indicates that properties of Baosteel's TP310HCbN(07Cr25Ni21CbN) conform to the ASME SA-213 standard and GB5310 standard,so it can substitute the imported products and is suitable for manufacturing power station boiler of great capacity and high steam parameters.

Research on Comparisons of New Clean Power Generation Technologies

On the basis of introducing clean power generation technologies, the author calculated and analyzed the investment, economy and environmental protection of these technologies, posed his views of giving the priorities to the development of supercritical and ultra-supercritical pressure coal-fired power generation technologies and taking vigorous action to nuclear power generation technology within the following 5-10 years, exploiting wind power within the following 10-15 years, and suggested that the installed capacity of nuclear power reach 80-100 GW and that of wind power reach 50-80 GW by 2020.

Life Cycle Assessment Analysis and Comparison of 1000 MW S-CO_(2)Coal Fired Power Plant and 1000 MW USC Water-Steam Coal-Fired Power Plant

The objective of this paper is to understand the benefits that one can achieve for large-scale supercritical CO_(2)(S-CO_(2))coal-fired power plants.The aspects of energy environment and economy of 1000 MW S-CO_(2)coal-fired power generation system and 1000 MW ultra-supercritical(USC)water-steam Rankine cycle coal-fired power generation system are analyzed and compared at the similar main vapor parameters,by adopting the neural network genetic algorithm and life cycle assessment(LCA)methodology.Multi-objective optimization of the 1000 MW S-CO_(2)coal-fired power generation system is further carried out.The power generation efficiency,environmental impact load,and investment recovery period are adopted as the objective functions.The main vapor parameters of temperature and pressure are set as the decision variables.The results are concluded as follows.First,the total energy consumption of the S-CO_(2)coal-fired power generation system is 10.48 MJ/k Wh and the energy payback ratio is 34.37%.The performance is superior to the USC coal-fired power generation system.Second,the resource depletion index of the S-CO_(2)coal-fired power generation system is 4.38μPRchina,90,which is lower than that of the USC coal-fired power generation system,and the resource consumption is less.Third,the environmental impact load of the S-CO_(2)coal-fired power generation system is 0.742 m PEchina,90,which is less than that of the USC coal-fired power generation system,0.783 m PEchina,90.Among all environmental impact types,human toxicity potential HTP and global warming potential GWP account for the most environmental impact.Finally,the investment cost of the S-CO_(2)coal-fired power generation system is generally less than that of the USC coal-fired power generation system because the cost of the S-CO_(2)turbine is only half of the cost of the steam turbine.The optimal turbine inlet temperature T_(5)becomes smaller,and the optimal turbine inlet pressure is unchanged at 622.082°C/30 MPa.

Hot Deformation Behavior of GH738 for A-USC Turbine Blades

The hot deformation characteristics of GH738 superalloy over the temperature range of 1000 °C to 1 200 °C and strain range of 0.01 s^-1 to 10.0 s^-1 under a strain of 1.0 s^-1 were investigated through hot compression tests with a Gleeble-1500 simulation machine. The flow stress reached peak value before flow softening occurred. The average apparent activation energy（Q） of GH738 was calculated to be 430 k J/mol, and the stress index（n） is approximately 4.08. The processing map was developed based on flow stress data and dynamic materials model（DMM）. The map shows a dynamic recrystallization（DRX） domain in 1 050 °C to 1150 °C and 0.01 s^-1 to 1.0 s^-1 strain rate range with a peak efficiency of 45%, which is considered to be the optimum region for hot working. Moreover, the materials undergo flow instability in the temperature range of 1000 °C to 1050 °C and strain range of 1.0 s^-1 to 10.0 s^-1, and adiabatic shear bands can be observed in this domain.

Tensile Properties of Cast Alloy IN625 in Relation to δ Phase Precipitation

The relationship between the tensile properties and S(delta) phase precipitation in cast alloy IN625 was investigated in this paper. Although the influences of δ phase on the mechanical properties have been pointed out in our previous work, the relationship is still not directly determined due to the coexistence of γ"(gamma double prime) and δ precipitates. In order to exclude the effect from γ" phase, various fractions of δ precipitates with few γ" precipitates were obtained by a set of experimental alloys aging at 750 ℃, and tensile tests were conducted in parallel. The results showed that both yield strength and ultimate tensile strength increased nearly in linear with increasing δ phase fraction, while the elongation was relatively and limitedly affected by δ precipitation when the area fraction of δ phase was above 10%.