Properties and Workability of New Creep Strength Enhanced Steels as Known Grades 23, 24, 911 and 92
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The improvement of thermal efficiency by increasing the operating temperature and pressure of boilers has recently led to the development of new creep-resistant steels. For 9–12% Cr steels, grade T/P91, developed at the end of the seventies by CE (Combustion Engineering) and ORNL (Oak Ridge National Laboratories) [1] in the USA, marked the starting point for these developments. With its excellent mechanical characteristics at elevated temperatures and good workability, it was rapidly adopted worldwide for erecting new power generators. The tube design temperature is limited to around 610°C (1130°F) inside the combustion chamber. This limit depends on such factors as heat flow and corrosion. Steam lines in P91 are generally operated at temperatures below or slightly above 600°C (1112°F). More recent developments to produce new grades such as T/P911 and T/P92, have improved mechanical properties at high temperatures, in particular an increase in creep strength of 10 to 30% in 100,000 hrs at 600°C (1112°F). This makes it possible to reduce the wall thickness of the pipes and consequently improve their behavior to thermal fatigue. The new grades T/P23 and T/P24 are well suited for boiler components working at lower temperatures. While these grades were initially developed for manufacturing the water wall panels of Ultra Super Critical Boilers (USCB), they are also used for the superheaters and reheaters of conventional boilers and Heat Recovery Steam Generators (HRSG) in combined cycles. In addition to their excellent workability, they have the advantage to be used without post-weld heat treatment in case of thin wall tubes. Furthermore, owing to the good creep properties, they can be used to replace P22 and for some applications even P91, with the advantage of lower costs. This paper sets out the characteristics of these new grades and gives the main recommendations for processing them.Keywords:
Superheater
Boiler thermal calculation is necessary to design and transform boiler.With the computers application,there are many boiler manufacturers to developed computer programs of boiler thermal calculation,but those programs can not be used,widely.By analyzing、 summarizing and simplifying current boilers thermal calculation and thermal programs,the superheater convection thermal calculation of the simulation software is design in MATLAB,and it is used in the procedures of Hohhot HG-670/13.7-YM13 boiler plant simulation analysis.The results show that the simulation software can check the superheater convection thermal calculation,and it has the function of the choice of coal in the operation.
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Abstract The author discusses the problem of designing a high-pressure boiler to deliver steam at high temperatures. The problem becomes more difficult as the capacity increases since proper selection and maintenance of boiler materials, design of the separate boiler and furnace units, and maintenance of the latter becomes increasingly more difficult if superheat control and steam purity are to be maintained. The author analyzes these design features and points out the compromises necessary to meet varying operating conditions. He discusses superheater design, maintenance of heat-absorbing surfaces, boiler circulation, relation of furnace-exit temperatures to slagging and boiler performance, and safe metal temperatures in water-walls and superheaters.
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This paper briefly introduced the structure of DHN type saturated steam boiler, and taking the DHN-type saturated steam boiler as an example, the modification scheme to meet the needs of the production process steam was presented by improving the boiler steam temperature, neither changing the structure of boiler pressure parts nor increasing the operating pressure, and the main parameters of the before and after modification were tested, it achieved good economic benefit through the practical operation and provided the theoretical basis for the transformation of small steam boiler.
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Flash boiler
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In coal burning boilers examination of power plants,high temperature corrosion orion can be found on high-temperaturesurfaces,such as water wall tubes,superheater tubes and reheater tubes.This article analyzes the main reasons caused high temperature corrosion of water wall tubes,platen superheater tubes and high temperature superbeater tubes of the BWB-1025/18.44-M boiler of one power plant.Some measures were presented to release high temperature corrosion.Also,the experimental results and experiences were concluded.
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Because of over-temperature of the main steam and the tube-wall of convection superheater, as well as the desuperheating water is not abundant, a boiler in one power plant can’t carry full load in operation for a long term. Through adjustment test, the operation mode has been adjusted, making the boiler can carry full load in operation under condition of burning two coal sorts.
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Abstract Tube burst occurred on Rear Platen Superheater in No.4 boiler of a power plant. Failed to timely discharge condensate water after an emergency shutdown boiler, and then start again, which leading to water blocking in superheater unit caused tube burst. Contrasting the water blocking accidents recent years in this boiler, corresponding preventive measures are formulated, which have certain reference value to theproblems of tubeburst caused by water blocking of the same type boiler.
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The operation of steam boilers with high efficiency requires control of thermo-hydraulic and strength parameters in the on-line mode. During operation under transient conditions, there are significant temperature differences over the circumference of the horizontal pressure vessels. This occurrence is caused by the different values of heat transfer coefficients on the inner surface of the boiler drum in the water and steam region. Large thermal stresses can occur in partially filled horizontal vessels. This takes place in large steam generator drums, superheater headers, and steam pipelines. The paper presents a method for determination of thermo-flow parameters for steam boilers. This method allows performing the calculations of the boiler furnace chamber and heating flow rates absorbed by superheater stages. These parameters are important for monitoring the performance of the power unit and determining the degree of the furnace chamber slagging. Knowledge of these parameters allows determining the degree of the furnace chamber slagging. The calculation can be performed in online mode and use to monitoring of steam boiler. The presented method allows to the operation of steam boiler with high efficiency.
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The characteristics on steam temperature deviation of superheater for supercritical opposed firing boiler are described,the causes and presents countermeasures are analyzed,by which steam temperature deviation have markedly improve,and the boiler sets’ operation safety and economy have thereby been noticeably raised.
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