Supercritical Pressure Boilers Research Articles

General numerical method for hydraulic and thermal modelling of the steam superheaters

Two methods for modelling high-temperature tubular cross-current heat exchangers are presented. Superheated steam flows inside the tubes, and flue gas flows outside perpendicular to the axis of the tubes. The methods proposed are based on the conservation equations of momentum and energy. In both methods, the heat exchanger is divided into finite volumes. The fluid temperatures at the outlet of the finite volume are calculated using closed-form explicit formulas. This makes the computer calculation time for the entire superheater very short. The pressure distribution in the superheater is determined from the numerical solution of the momentum conservation equation. A power correlation was determined to calculate the limiting Reynolds number above which the friction factordepends only on the relative roughness of the tube surface. Convective and radiative heat transfer were taken into account in the calculation of the heat flow rate on the gas side. The results of the calculation of a two-pass co-current heat exchanger were compared to assess the accuracy of the two methods, finding that the two methods give very similar results. The strength of method I is that the steam and flue gas temperatures inside a given finite volume can be determined. A model of a two-pass live steam superheater in a supercritical pressure boiler is presented. The calculated average steam and flue gas temperatures downstream of the superheater show good agreement with the corresponding temperatures determined using the heat exchanger's effectiveness and the measured results.

Diffusion-hardening effect on the technological properties of high-temperature steel

The results of research pipes diffusion hardening as an effective method for increasing the durability and reliability of power equipment are presented. The experience of commercial operation of pipes manufactured from diffusion chromized and heat-hardened steel 14 MoV6-3; on the heating surfaces of the supercritical pressure boilers are generalized. The possibility and effectiveness of this method on the example of capacities of Trypil'ska CHP are shown.

Numerical study of effects of vortex generators on heat transfer deterioration of supercritical water upward flow

The occurrence of heat transfer deterioration (HTD) in supercritical pressure boilers, where the wall temperature rises abruptly is an undesirable phenomenon that is limiting the design of new promising engineering applications. This may cause operational problems such as tube burnouts which could result in a catastrophic system failure. Understanding ways of eliminating HTD is of great importance for the design of safe and reliable supercritical pressure boilers. In this paper, vortex generators (VGs) are installed in circular and annular channels to investigate HTD phenomenon of supercritical water flowing upward at high heat flux and low mass flux using shear stress transport (SST) k-ω turbulence model in ANSYS-FLUENT. Results on wall temperature distribution for the smooth and enhanced channels are compared with available experimental data, and good agreements are obtained. The effects of VG’s size, position, and number on HTD are investigated. The results indicate that VG’s size slightly suppresses and delays HTD downstream of the VG, and there exists an optimum size beyond which HTD starts to aggravate. A strong effect of VGs on heat transfer coefficient (HTC) profiles is observed at locations where VGs are installed and at the downstream locations, with the normalized HTC showing that the wall temperature oscillates a couple of times before becoming stable once the flow returns to fully developed state. The VG’s position has the most significant effect on HTD for any single VG. Increasing the number of VGs installed in-line at the start of the major peak baselines significantly suppresses and delays the peak. Mechanism analysis based on radial distributions of velocity and turbulent kinetic energy (TKE) at different axial positions of both channels shows that HTD suppression is caused by the weakening of the buoyancy effect due to increased TKE near the wall downstream of the VG, whereas the delay is caused by the boundary layer recovery effect due to flow redevelopment after being disrupted by the VG.

Experimental investigation on two-phase flow instabilities of ultra supercritical pressure boiler with spirally water wall tubes

For a better design of 1000MW ultra supercritical pressure boiler with spirally water wall tubes, an experimental study has been performed in the State Key Laboratory of Multiphase Flow in Power Engineering, Xi’an Jiaotong University to investigate the instability of the steam-water two-phase flow inside a smooth tube with an inclined angle of 20degree from the horizon. The static hydrodynamic characteristic curves are obtained and the dynamic instabilities are also analyzed. The boundary conditions of the pressure drop oscillation and the density wave oscillation are proposed. The effects of pressure, mass flux, inlet and outlet throttle, inlet subcooling and the compressible volumes are analyzed primarily. The results demonstrate that the above parameters significantly influence the critical heat flux for the mentioned two types of oscillations and the density wave oscillations are the major type of oscillations in boilers and steam generators. The density wave oscillations occur at a higher heat flux than the pressure drop oscillations with the other operating parameters remaining constant. The inducing mechanisms of the above two types of oscillations are clarified. The variation ranges of critical heat flux and critical vapor quality are illustrated. Two empirical correlations predicting the onset of pressure drop oscillation and density wave oscillation are derived from the experimental data.

Study on the Burning Characteristics of Poor-Quality Anthracite in Supercritical W-Shaped Flame Boiler

With the good characteristics of high efficiency, energy saving and environmental protection, supercritical W-flame boiler can effectively solve the problems of clean and high efficiency combustion of poor-quality anthracite using for supercritical pressure boilers. In light of a 600MW supercritical W-shaped flame boiler, combustion models in fluent 6.3 were used to study the combustion law of poor-quality anthracite in the furnace, the effect of air distribution on the combustion process was analyzed. The results indicate that symmetrical air distribution can not form symmetrical flow field because of the structure effect of the nose of the furnace. The effect of the nose of the furnace can be effectively balanced by increasing the velocity on the front wall and there exists an optimal ratio of air distribution. In the central zone of the lower furnace, the temperature is high and the O2 concentration is low, which is beneficial to the ignition and combustion of pulverized coal. Because the pressure in the center of the furnace is higher than that near the side walls, the pulverized coal are forced to move towards the side walls, which can cause the sidewalls to be eroded by the flame and slagging. The study results have great significance for the optimization design and improving the efficiency of pulverized coal combustion of supercritical W-shaped flame boiler.

The effect of water chemistry on a change in the composition of gas phase in the steam-water path of a supercritical-pressure boiler

We present the results from an experimental research work on studying the behavior of the gas phase in the path of a supercritical-pressure boiler during its operation with different water chemistries, including all-volatile (hydrazine-ammonia), complexone, neutral oxygenated, and combined oxygenated-ammonia chemistries. It is shown that the minimal content of hydrogen in steam is achieved if feedwater is treated with oxygen.

Header-platen high-pressure heaters

We present a new schematic design of high-pressure heaters for the regeneration systems of turbine units used at nuclear and thermal power stations, which features better reliability, smaller weight and overall dimensions, and higher thermal efficiency as compared with those characteristic for the design of the well-known types of heaters. We also show that it is possible to construct heaters for high pressures typical for supercritical-pressure boilers with the use of existing domestically made materials.

A hydraulic drive of booster pumps

A proposal is made to use a hydraulic turbine as a drive for booster pumps in the feedwater systems of supercritical-pressure boilers.

Complex retrofit TGMP-314Ts boilers TETs-23 of OAO Mosenergo reducing emissions harmful substances atmosphere

A complex approach to the solution of a problem of the environmental safety of the supercritical pressure boilers in combination with the measures enhancing their economic efficiency, reliability in operation, and saving of resources is described.

Measurement of the thermal resistance of scale on the inner surfaces of boiler tubes

This paper proposes a method of measurement of the thermal resistance of scale on the inner surface of a boiler tube. The principle of the method is to measure the temperature rise due to the scale when the tube is radiantly heated from outside. An experiment was performed with a test piece composed of three tubes 300 mm in length, which had been cut out from a supercritical pressure boiler. A 120 mm × 140 mm area of the test piece was radiantly heated, boiling of water took place inside the tubes, and the temperature at the crest of the tube was measured with welded thermocouples 80 µm in diameter. Similar measurement was performed after cleaning the inside of the tubes with hydrochloric acid, and both measured data were compared. As an example of the results, the difference of the temperature rise was 8.24 K for a heat flux of 100 kW/m2, and the estimated thermal resistance of the scale was 0.082 m2K/kW. © 2002 Scripta Technica, Heat Trans Asian Res, 31(2): 117–127, 2002; DOI 10.1002/htj.10020

Measurement of the thermal resistance of scale on the inner surfaces of boiler tubes

AbstractThis paper proposes a method of measurement of the thermal resistance of scale on the inner surface of a boiler tube. The principle of the method is to measure the temperature rise due to the scale when the tube is radiantly heated from outside. An experiment was performed with a test piece composed of three tubes 300 mm in length, which had been cut out from a supercritical pressure boiler. A 120 mm × 140 mm area of the test piece was radiantly heated, boiling of water took place inside the tubes, and the temperature at the crest of the tube was measured with welded thermocouples 80 µm in diameter. Similar measurement was performed after cleaning the inside of the tubes with hydrochloric acid, and both measured data were compared. As an example of the results, the difference of the temperature rise was 8.24 K for a heat flux of 100 kW/m2, and the estimated thermal resistance of the scale was 0.082 m2K/kW. © 2002 Scripta Technica, Heat Trans Asian Res, 31(2): 117–127, 2002; DOI 10.1002/htj.10020

環境対応材料の現状と課題 （Ｉ） 環境対応材料の開発動向 超々臨界圧ボイラ用耐熱材料の開発動向

環境対応材料の現状と課題 （Ｉ） 環境対応材料の開発動向 超々臨界圧ボイラ用耐熱材料の開発動向

Measurement of the Thermal Resistance of Scale Adhered to Inner Surface of Boiler Tubes.

This paper proposes a method of measurement of the thermal resistance of scale adhered to the inner surface of a boiler tube. The principle of the method is to measure the temperature rise due to the scale when the tube is radiatively heated from outside. An experiment was performed with a test piece composed of three tubes of 30 cm in length, which had been cut away from a supercritical pressure boiler. 120 mm×140 mm area of the test pieces was radiatively heated, boiling of water took place inside the tubes, and the temperature at the top of the tube was measured with welded thermocouples of 80 μm, in diameter. Similar measurement was performed after cleaning the inside of the tubes with hydrochloric acid, and both measured data were compared. An example of the results is as follows;the difference of the temperature rise was 8.24 K for heat flux of 100 kW/m2, and the estimated thermal resistance of the scale was 0.082 m2 K/kW.

Experimental investigation of transient heat transfer in the once-through boiler water separator

The transient heat transfer between working fluid and inner wall of 600 MW supercritical pressure boiler’s water separator model during start-up was experimentally explored. The test conditions for water steam two-phase were as follows: pressure P=3–11 MPa, mass flow M=0.2–0.35 kg/s, and mass quality x=0.2–0.8; for subcooled water P=3–11 MPa, M=0.2–0.35 kg/s, and subcooled degree Δθ=10°C. By using an accurate and tractable inverse heat conduction solution, the correlations of single-phase and two-phase transient heat transfer coefficients were obtained. The experimental results demonstrated the heat transfer enhanced for subcooled water and water steam mixture compared with fully developed turbulent flow in tube. The increasing heat transfer effect may be attributed to the deformation or destruction of the boundary layer.

ボイラ混相流技術のあゆみ

The multiphase technology in power plant boiler during last ten years in Japan have been reviewed. The most important events on utility boiler are the appearance of coal fired supercritical sliding pressure operation boiler, the increase in steam pressure and temperature for higher plant efficiency, and the increase in number of gas turbine combined plants. Concerning these events, some key technology were developed in multiphase field. The detailed study on boiling heat transfer in rifled tube realized the vertical tube type boiler, which had more simple furnace wall structure than the spirally wound type ones. The ultra supercritical pressure boiler achieved 5% higher efficiency than the normal pressure ones. The natural circulation waste heat boiler with horizontal evaporating tubes, which enabled low cost construction, was designed under attentive thermal and hydraulic studies, and successfully started to operate. The condensing heat transfer of ammonia-water mixture was investigated and the high efficiency of the mixture cycle was demonstrated through test plant operation. Regarding fuel, coal oil mixture, coal water mixture, and orimulsion were introduced. For clean and efficient usage of coal, PFBC and IGCC are expected as the important future power generation system.

超超臨界圧用高強度オーステナイト鋼のクリープ破断強度に及ぼすNb,Ti及びC量の影響

超超臨界圧用高強度オーステナイト鋼のクリープ破断強度に及ぼすNb,Ti及びC量の影響

Study on Thermal Conductivity of Scale Deposits in Supercritical Pressure Boilers

本報告は超臨界圧ボイラ水壁管における内面スケールの熱伝導率を半円周加熱面を用いた超臨界圧水の管内強制対流条件下で測定したものである.スケール熱伝導率の算出は管外面熱流束およびスケールの円周方向厚さ分布を考慮した管壁温度分布解析に基づいた.その結果,従来明確にされていなかった超臨界圧ボイラ水壁管のスケール熱伝導率を流体圧力280ata,流体温度200～400℃の範囲で明らかにした.

Pressure Drops in Supercritical Boilers : 1st Report, Static Characteristics of Friction Pressure Drop

Static and dynamic characteristics of pressure drop in supercritical pressure boilers were studied. In this paper, experimental results of static pressure drop of CO2 at supercritical and relatively high subcritical pressures in a heated test tube were presented, and effects of various factors such as flow rate, heat flux, inlet temperature, and pressure were discussed. The calculated results by numerical integration using the friction coefficient of single phase flow agreed with the experimental results. The experimental results were well correlated by the dimensionless expression of pressure drop previously reported. This means that the results obtained by this CO2 experiment will be also applicable to the case of working fluid of H2O. Mean friction coefficients of supercritical fluid in the whole tube length were shown and an empirical equation of the coefficient for the heat flux was proposed.

Pressure Losses in Supercritical Pressure Boilers : 1st Report, Static Characteristics of Frictional Pressure Drop

Pressure Losses in Supercritical Pressure Boilers : 1st Report, Static Characteristics of Frictional Pressure Drop

Fluid Pressure Drop Testing on Once-Through Boilers

Boiler pressure drop testing has become a useful tool in evaluating the internal waterwall tube deposition on two once-through supercritical pressure boilers. This paper presents the results of five years of testing and describes test procedures, instrumentation requirements, and analysis techniques. The result of this test program has been the minimizing of unit forced outages due to waterwall tube failures.