Where is the platen superheater located

The reason why the exfoliation frequency is greater for tubes of SS is probably that the tubes have been exposed to higher temperatures. SS 2. The principal cause of the exfoliation is said to be stresses which arise in the oxide during the cooling-down process associated with shutdowns.

The stresses give rise to longitudinal cracks in the oxide, and are formed as a result of differences in thermal expansion between the oxide and the tube material.

In addition, accounts are presented of oxidation constants and growth velocities, and thickness and running time. These data constitute a valuable basis for practical estimates of the operating temperature in routine checks and investigations into damage in superheater tubes. Lifetime evaluation of superheater tubes exposed to steam oxidation, high temperature corrosion and creep.

Advanced fossil fired plants operating at high steam temperatures require careful design of the superheaters. The German TRD design code normally used in Denmark is not precise enough for the design of superheaters with long lifetimes. The authors have developed a computer program to be used in the evaluation of superheater tube lifetime based on input related to tube dimensions, material, pressure, steam temperature, mass flux, heat flux and estimated corrosion rates.

The program is described in the paper. As far as practically feasible, the model seems to give a true picture of the reality. For superheaters exposed to high heat fluxes or low internal heat transfer coefficients as is the case for superheaters located in fluidized bed environments or radiant environments, the program has been extremely useful for evaluation of surface temperature, oxide formation and lifetime. The total uncertainty of the method is mainly influenced by the uncertainty of the determination of the corrosion rate.

More precise models describing the corrosion rate as a function of tube surface temperature, fuel parameters and boiler parameters need to be developed. The model describing the superheat regime single- phase, variable density fluid for subcritical pressure operation is also applicable to the study of once-through operation using supercritical pressure water.

DYNAM is written in complex variable notation. Thermomechanical CSM analysis of a superheater tube in transient state. The paper presents a thermomechanical computational solid mechanics analysis CSM of a pipe "double omega", used in the steam superheaters in circulating fluidized bed CFB boilers.

The complex cross-section shape of the "double omega" tubes requires more precise analysis in order to prevent from failure as a result of the excessive temperature and thermal stresses. The results have been obtained using the finite volume method for transient state of superheater. The calculation was carried out for the section of pipe made of low-alloy steel. Failure of boiler tubes is the main cause of unit outages of the plant, which further affects the reliability, availability and safety of the unit.

So failure analysis of boiler tubes is absolutely essential to predict the root cause of the failure and the steps are taken for future remedial action to prevent the failure in near future. Visual inspection, dimensional measurement, chemical analysis, metallographic examination and hardness measurement are conducted as the part of the investigative studies. Apart from these tests, mechanical testing and fractographic analysis are also conducted as supplements.

Finally, it is concluded that the superheater tube is failed due to graphitization for prolonged exposure of the tube at higher temperature. Directory of Open Access Journals Sweden. Full Text Available The paper investigates influence of change in quality of superheated steam temperature regulations on service life of super-heater metal.

Numerical values pertaining to increase of super-heater metal service life in case of transferring from manual regulation to standard system of automatic regulation SAR have been determined and in case of transferring from standard SAR to improved SAR.

The analysis of tabular data and plotted dependencies makes it possible to conclude that any change in conditions of convection super-heater metal work due to better quality of the regulation leads to essential increase of time period which is left till the completion of the service life of a super-heater heating surface. The explosive boiling processes of droplets of diethyl ether mm in diameter at the superheat limit were examined both experimentally and computationally.

Experimentally, droplet explosion was studied using a heated bubble column to bring the test droplet to the superheat limit. The droplet fluid was diethyl ether superheat limit C at 1 bar with immiscible glycerol employed as the heated host fluid. Tests were carried out at pressures between 0.

The pressure rise associated with the explosive boiling event was captured using a piezoelectric quartz pressure transducer with a 1 MHz DAQ system. High-speed imaging of the interfacial behavior during explosive boiling was performed using a Phantom v The imaging reveals features of the Rayleigh-Taylor instability at the vapor-liquid interface resulting from the unstable boiling process.

Computationally, Direct Numerical Simulations are performed at Southern Illinois University Carbondale to compliment the experimental tests. NSF Award Number Alkali chloride induced corrosion of superheaters under biomass firing conditions: Improved insights from laboratory scale studies. One of the major operational challenges experienced by power plants firing biomass is the high corrosion rate of superheaters. This limits the outlet steam temperature of the superheaters and consequently, the efficiency of the power plants.

The high corrosion rates have been attributed to the fo The high corrosion rates have been attributed However, complete understanding of the corrosion mechanism under biomass-firing conditions has not yet been achieved.

This is attributed partly to the complex nature of the corrosion process since there are many species produced from fuel combustion which can interact with one another Contamination prevention of superheaters and reheaters during initial startup and operation. The general precautions that should be taken to minimize the potential for harmful contamination or oxygen corrosion of power plant superheaters and reheaters during the period from field storage through operation are discussed and summarized.

Present boiler industry start-up and operating practices intended to minimize the introduction of solids to the superheater are, as proven by experience, adequate to avoid contamination-related problems. No basic changes to general industry practice are necessary.

What is needed, however, is a continuing awareness of the potential for contamination-related problems so that in the specific application of these practices all likely sources of contamination will be considered.

During long-term, high-temperature exposure of superheater tubes in thermal power plants, various oxides are formed on the inner side steamside of the tubes, and oxide spallation is a serious problem for the power plant industry.

Most often, oxidation in a steam atmosphere is investigated On real plant-exposed superheater tubes, the steamside oxides are solely investigated microscopically. The feasibility of X-ray diffraction for the characterization of steamside oxidation on real plant Essential differences between the steamside oxides formed on two different steels The shape, stability and breakage of pendant liquid bridges.

Pendant liquid bridges are defined as pendant drops supporting a solid axisymmetric endplate at their lower end. The stability and shape properties of such bridges are defined in terms of the capillary properties of the system and of the mass and radius of the lower free-floating endplate.

The forces acting in the pendant liquid bridge are defined exactly and expressed in dimensionless form. Numerical analysis has been used to derive the properties of a given bridge and it is shown that as the bridge grows by adding more liquid to the system a maximum volume is reached. At this maximum volume, the pendant bridge becomes unstable with the length of the bridge increasing spontaneously and irreversibly at constant volume. Finally the bridge breaks with the formation of a satellite drop or an extended thread.

The bifurcation and breakage processes have been recorded using a high-speed video camera with a digital recording rate of up to frames per second. The details of the shape of the bridge bifurcation and breakage for many pendant bridge systems have been recorded and it is shown that satellite drop formation after rupture is not always viscosity dependent.

Bifurcation and breakage in simulated low gravity demonstrated that breakage was very nearly symmetrical about a plane through the middle of the pendant bridge. Survey of the current state of knowledge of incipient boiling superheat in sodium. Superheat data obtained by various investigators indicate that many parameters affect this phenomenon.

Controlling parameters appear to be inert gas concentration, oxide concentration, system pressure, pressure-temperature history, rate of temperature rise, heat flux, flow rate, operating time on the system, surface conditions, and radiation. Of these, the two believed most influential in controlling incipient boiling superheat are the inert gas concentration and oxide concentration. Experimental results for the heat flux and rate of temperature rise appear to be the most inconsistent.

Phase 2. The Electro Magnetic Acoustic Transducer EMAT is a contactless thickness gauge for detection of corrosion on superheater tubes; it candidates as substitute for conventional manually operated contact UT transducers.

It is the aim of the project to demonstrate the usefulness of two simple EMAT systems, Panametrics and Sonatest, for fast and reliable tube thickness inspections in difficult-to-access superheater sections. The present Phase 2 of the project involves testing of the systems on real compact superheaters in remote operation with the help of a mechanical manipulator designed and built for the purpose.

The results are the following: - Both EMAT systems work well when tested in the field during handheld operation on tubes with a moderate thick layer of corrosion products and ash.

The practical obtainable speed of cross-panel inspection of easily accessible panels is approximately 6 tubes per minute 6 thickness readings per minute. The Panametrics system was not found suitable for this type of field work.

In its present design it needs few improvements. This speed is limited by the detection rate of the EMAT system and not by the travelling speed of the probe.

SEM scanning electron microscopy images and EDX energy dispersive X-ray analyses were performed on the deposit samples. Different strategies Overheating failure of superheater suspension tubes of a captive thermal power plant boiler.

Failure of boiler tubes is the foremost cause of forced boiler outages. One of the predominant failure mechanism of boiler tubes is the stress rupture failure in the form of either short term overheating or long term overheating which are normally encountered in superheater and reheater sections working in the creep range. The strength of the boiler tube depends on the stress level as well on the temperature of exposure in the creep range. An increase in either can reduce the time to rupture.

Time at the exposure temperature is an important factor based on which the failures are categorised as either short term or long term. Though there is no established time duration criteria demarcating the short or long term stress rupture failures, depending on the various manifestations on the failed samples, one can categorise the failure. This paper addresses one such stress rupture failure in the superheater section of a captive thermal power plant of a refinery.

Multiple failures on the suspension coil of a superheater section was investigated for the cause of failure. Laboratory investigation of the failed sample involved visual inspection, dimensional measurements, chemical analysis of internal deposits and microstructural study. On the basis of these, the failure was attributed to deposition of trisodium phosphate carried over by the feed water into the superheater section resulting in chokage and increase in local operating hoop stresses of the tube.

The ultimate failure was thus categorised as long term overheating failure. Nonlinear superheat and capacity control of a refrigeration plant. A new low order nonlinear model of the evaporator is developed and used in a backstepping design of a nonlinear controller. The stability of the proposed method is validated theoretically by Lyapunov Prevention of superheater corrosion caused by chlorine; Tulistimien kloorikorroosion estaeminen.

Also well managed and controlled combustion of waste fractions compared to their landfilling produces much less greenhouse gas emissions. In combustion of these fuels in high efficiency power plants notably increased superheater corrosion risk is prevailing, mainly caused by chlorine. Typical such fuels are forest, agricultural and household residues, biological sludge's of pulp and paper industry and RDF made from separated municipal and industrial solid waste.

The goal of the project is to develop clearly cheaper and more effective method to protect superheaters , which enables combustion of biomass and waste fuels with higher energy shares.

Tests in pilot and full scale power plants will reveal the potential and applicability of the developed method for commercial use. The first part of the paper provides a general introduction to the relations between Platen and Italy and summarizes the «complicated» genesis of this poetical cycle. Effective new chemicals to prevent corrosion due to chlorine in power plant superheaters.

Firing or co-firing of biomass in efficient power plants can lead to high-temperature corrosion of superheaters due to condensation of alkali chlorides into superheater deposits. Corrosion can be prevented if a significant portion of the alkali chlorides present in the flue gases is destroyed before reaching the superheaters. The alkali capturing power of aluminium and ferric sulphates was determined in a pilot-scale fluidised bed FB reactor.

The reagents were added in solution, through a spraying nozzle, to the upper part of the freeboard. Both the mass flow rate and type of sulphate affected the sulphation ability.

Thus, the cation, too, plays a role in the reaction. The design, fabrication, irradiation results, and post-irradiation examination for three superheater test fuel elements are described.

During the spring of these clusters, each consisting of six fuel rods, were successfully exposed in the superheater loop No. The diametrical gap between fuel and cladding was one of the main parameters and was chosen to be 0. Nature of fireside deposits in a bagasse and groundnut shell fired 20 MW thermal boiler. The nature of deposit formation on the fireside surfaces of the boiler tubes in the various parts water walls, platen superheater , final superheater , economizer, electrostatic precipitator etc.

The deposits in the various portions of the boiler were characterized by particle size analysis, chemical analysis, X-ray diffraction and scanning electron microscopy.

The deposits were found to be mainly quartz, alkali and alkaline earth silicates and sulfates. From the phase constitution and other microscopic characteristics of the deposit, it can be inferred that the silicates in the deposit formed through inertial impaction and the sulfates formed by vapor phase deposition. Srikanth, S. Materials Characterization Division; Nandakumar, K. Research and Development Section. Pen and platen , piezo-electric 21 Aug Engineering Materials. The set of five drawings defines a writing instrument system that will reliably verify signatures, thus providing a method useful in screening persons seeking entrance to restricted areas or access to computer programs.

Using a conventional ballpoint pen refill, the instrument's input derives from signals generated in its writing tip and from pressure exerted by a person writing his name or a code word on the platen tablet.

The basic principle is that accelerations of the writing tip and pressures exerted by the person writing are recorded in three axes. This combination of signals can be processed by a computer and compared with a record in the computer's memory, or a graphic transcription may be compared visually with an earlier record. Polyethene with pendant fullerene moieties. In addition, some suggestions on the material selection have been proposed. Integrated boiler, superheater , and decomposer for sulfuric acid decomposition.

A method and apparatus, constructed of ceramics and other corrosion resistant materials, for decomposing sulfuric acid into sulfur dioxide, oxygen and water using an integrated boiler, superheater , and decomposer unit comprising a bayonet-type, dual-tube, counter-flow heat exchanger with a catalytic insert and a central baffle to increase recuperation efficiency. Superheater corrosion in biomass-fired power plants: Investigation of Welds. Their corrosion rates were similar and increased This gives rise to specific corrosion problems not previously encountered in coal-fired power plants.

The type of corrosion attack can be directly ascribed to the composition of the deposit and the metal surface temperature. A test superheater was built into the straw The mechanism of attack was grain boundary attack as a precursor to selective chromium depletion of the alloy. In addition welds coupling various tubes sections were also investigated. It was seen that there was preferential attack around those welds that had a high nickel content.

The welds A fault tolerant superheat control strategy for supermarket refrigeration systems. The FTC strategy requires no a priori system knowledge or additional hardware and functions Tuning and performance evaluation of PID controller for superheater steam temperature control of MW boiler using gain phase assignment algorithm.

In superheater , steam temperature is controlled in a cascade control loop. To improve the superheater steam temperature control the controller's gains in a cascade control loop has to be tuned efficiently. The mathematical model of the superheater is derived by sets of nonlinear partial differential equations. The tuning methods taken for study here are designed for delay plus first order transfer function model.

Hence from the dynamical model of the superheater , a FOPTD model is derived using frequency response method. Then by using Chien-Hrones-Reswick Tuning Algorithm and Gain-Phase Assignment Algorithm optimum controller gains has been found out based on the least value of integral time weighted absolute error. This article is devoted to the memory of Vladimir P.

Skripov He has received worldwide recognition for his monograph on metastable liquids published in the English edition was published in We briefly discuss some studies deal with the phenomenon of attainable superheat of liquids and with measurements of thermophysical properties of liquids under conditions of a moderate degree of superheat. Main attention is paid to the studies performed by V. Skripov and his research group in the s and s.

Experimental methods which provided break-throughs in research on both spontaneous boiling-up kinetics and substance properties the specific volume, isobaric heat capacity, ultrasound speed, and viscosity in super-heated states are presented. A Stochastic mesoscopic model for predicting the globular grain structure and solute redistribution in cast alloys at low superheat. It is well known that casting at low superheat has a strong influence on the solidification morphology and macro- and microstructures of the cast alloy.

This paper describes a stochastic mesoscopic solidification model for predicting the grain structure and segregation in cast alloy at low superheat. The stochastic model was found to reasonably predict the observed grain structure and Al microsegregation. This makes the model a useful tool for controlling the structure of cast magnesium alloys. Preventing superheater corrosion by additives; Tulistimien kloorikorroosion estaeminen lisaeainein. Aho, M. The new superheater protection methods enable combustion of demanding biomass with higher portions than at present.

The results assist also to meet the goals of the use of logging residues in energy production in Finland. Superheater fouling in a BFB boiler firing wood-based fuel blends.

Wood pellets test 0 were not problematic for about ten years, contrary to a mixture of demolition wood, wood cuttings, compost overflow, paper sludge and roadside grass test 1 which caused excessive fouling at a superheater bundle.

Pen and platen , piezo-electric Engineering Materials. Pendant unit effect on electron tunneling in U-shaped molecules. The electron transfer reactions of three U-shaped donor-bridge-acceptor molecules with different pendant groups have been studied in different solvents as a function of temperature.

Analysis of the electron transfer kinetics in nonpolar and weakly polar solvents provides experimental reaction Gibbs energies that are used to parameterize a molecular solvation model.

This solvation model is then used to predict energetic parameters in the electron transfer rate constant expression and allow the electronic coupling between the electron donor and electron acceptor groups to be determined from the rate data.

The U-shaped molecules differ by alkylation of the aromatic pendant group, which lies in the 'line-of-sight' between the donor and acceptor groups. The findings show that the electronic coupling through the pendant group is similar for these molecules. Dynamic performances of wet turbine and steam-separator- superheater and their mathematical simulation as objects of temperature control.

A mathematical model of a turbine and steam-separator- superheater SSS as applied to solution of the tasks of steam temperature regulaton after SSS has been developed. SSS as objects of steam temperature control are considerably less inertial, than intermediate superheaters IS of power units in thermal power plants, since for typical SSS and IS considered the duration of transition process according to steam temperature after SSS is times loweA than for IS.

Phase 1. Corrosion of superheaters has become a severe problem in many biomass boilers and incineration plants. This new situation calls for frequent tube wall thickness testing of the superheaters during very short shut-downs. The EMAT can contactlessly generate an ultrasonic wave in the interphase between the external oxide and the metal. This means that measurements can be undertaken much quicker and with a much higher coverage simultaneously, without preceding blast operations.

The present Phase 1 of the project involves testing of the performance of the two systems in laboratory with the following results: 1. Both instruments work well on plate, tube, and pipe samples assuming the presence of an external oxide layer formed at a temperature above approximately deg C. Both instruments work well on all types of ferritic and martensitic steels but not on austenitic steels.

Both instruments work well independent of the thickness of the active oxide layer. Both instruments work well independent of tube diameter, wall thickness, and sample width. Both instruments work well over a very large range of wall thicknesses. Minimum tube wall thickness is less than 1.

The tolerable lift-off free distance between transducer and tube surface is 2. The tolerable lift-off is a measure of the thickness of ash deposits, which can be tolerated on the tube surface as well as the misplacement, which can be tolerated in case of remote tube testing.

The tolerable off-set between tube axis and probe axis is very large for both instruments Full Text Available A soft sensor for oxide scales on the steam side of superheater tubes of utility boiler under uneven circumferential loading is proposed for the first time. First finite volume method is employed to simulate oxide scales growth temperature on the steam side of superheater tube.

Then appropriate time and spatial intervals are selected to calculate oxide scales thickness along the circumferential direction. On the basis of the oxide scale thickness, the stress of oxide scales is calculated by the finite element method. At last, the oxide scale thickness and stress sensors are established on support vector machine SMV optimized by particle swarm optimization PSO with time and circumferential angles as inputs and oxide scale thickness and stress as outputs.

Temperature and stress calculation methods are validated by the operation data and experimental data, respectively. The soft sensor is applied to the superheater tubes of some power plant. Results show that the soft sensor can give enough accurate results for oxide scale thickness and stress in reasonable time. The forecasting model provides a convenient way for the research of the oxide scale failure. A steam superheater exchanger provided with two coaxial casings and an horizontal axis.

This invention concerns the general lay-out of an horizontal axis separator- superheater for supplying steam to a high power turbine, particularly for a nuclear power station.

The invention significantly reduces the length of the pipework connecting the superheated steam outlet and its inlet to the turbine. For this, the outer casing is provided with a coaxial internal annular sleeve in which are housed, one above the other, the separator and the bundle of superheater tubes through which circulates the water emulsion to be separated and steam to be superheated.

At the end of its treatment, the superheated steam spreads out in the space between the sleeve and the outer casing from whence it can be drawn off at any point of its periphery, thus making it possible to choose an extraction point as near as possible to the inlet of the turbine to be fed [fr.

Much progress in PT-based PSCs can be attributed to the design of novel PTs exhibiting intense and broad visible absorption with high charge carrier mobility to increase short-circuit current density Jsc, along with low-lying highest occupied molecular orbital HOMO levels to achieve large open circuit voltage Voc values. A promising strategy to tailor the photophysical properties and energy levels via covalently attaching electron donor and acceptor pendants on PTs backbone has attracted much attention recently.

The geometry, electron-donating capacity, and composition of conjugated pendants are supposed to be the crucial factors in adjusting the conformation, energy levels, and photovoltaic performance of PTs. This review will go over the most recent approaches that enable researchers to obtain in-depth information in the development of PTs comprising conjugated pendants for PSCs.

Vbpy was prepared from 4-methylpyridine. Absorption maximum, molar extinction coefficient, emission maximum and relative emission intensity of the polymeric complexes were studied. Probabilistic approach to determining the optimum replacement of a superheater stage in MW coal-fired boiler.

A creep-related tube failure occurred in the tertiary superheater that had been due to increased wall temperature caused by steam side formation of oxide layers. The theoretical lifetime of the components was calculated with the aid of the results of steam side oxide measurements and condition evaluation of the tertiary superheater with the aid of tube samples.

The objective is to establish an operation and maintenance schedule for the desired operating lifetime of , hours. Synthesis and photooxidation of styrene copolymer bearing camphorquinone pendant groups.

Review of Development Status of Nuclear Superheat ; Expose sur l'etat actuel des travaux concernant la surchauffe nucleaire; Obzor razrabotki voprosa o yadernykh peregrevatelyakh; Estudio de los progresos realizados en niateria de sobrecalentamiento nuclear. The development tasks, the initial core superheat fuel-element design, the range of experimental variables, and the expected results for the three-year fuel development programme are discussed.

A cette epoque, le '' Superheat Advance Demonstration Experiment'' SADE , finance par la societe, a permis d'obtenir, pour la premiere fois aux Etats-Unis, de la vapeur surchauffee par un dispositif nucleaire. Les auteurs du memoire font le point de la situation actuelle concernant la surchauffe nucleaire.

Ils decrivent, dans une premiere partie, les trois principales installations de surchauffe nucleaire utilisees par la General Electric et, dans la seconde, les deux principaux programmes de recherches sur la surchauffe ainsi que les resultats les plus importants obtenus jusqu'ici dans ce domaine.

Principales installations pour les experiences de surchauffe: a Breve description du SADE utilise dans le reacteur a eau bouillante de Vallecitos VBWR , avec tableaux des conditions dans lesquelles se deroulent les experiences, et des elements combustibles irradies pendant la periode comprise entre mai et juin ; puis examen critique des resultats les plus importants ainsi obtenus. Improved superheater tubing material - Ti and Nb bearing austenitic steel.

A newly developed 18 Cr-8 Ni stainless steel modified with small amounts of Ti and Nb has considerably high stress-rupture strength and is considered to be suitable for superheater material for power boilers. Data for stress-rupture and creep for long times, the strength of welded joints, the changes of characteristics due to exposure to high temperatures, etc.

Some investigations after trial services indicate that the experimental data are applicable to actual applications. Thermal load non-uniformity estimation for superheater tube bundle damage evaluation. Full Text Available Industrial boiler damage is a common phenomenon encountered in boiler operation which usually lasts several decades. Since boiler shutdown may be required because of localized failures, it is crucial to predict the most vulnerable parts.

If damage occurs, it is necessary to perform root cause analysis and devise corrective measures repairs, design modifications, etc.. Boiler tube bundles, such as those in superheaters , preheaters and reheaters, are the most exposed and often the most damaged boiler parts. Both short-term and long-term overheating are common causes of tube failures. In these cases, the design temperatures are exceeded, which often results in decrease of remaining creep life.

Advanced models for damage evaluation require temperature history, which is available only in rare cases when it has been measured and recorded for the whole service life. However, in most cases it is necessary to estimate the temperature history from available operation history data inlet and outlet pressures and temperatures etc.. The task may be very challenging because of the combination of complex flow behaviour in the flue gas domain and heat transfer phenomena.

This paper focuses on estimating thermal load non-uniformity on superheater tubes via Computational Fluid Dynamics CFD simulation of flue gas flow including heat transfer within the domain consisting of a furnace and a part of the first stage of the boiler. Electronic and steric influences of pendant amine groups on the protonation of molybdenum bis dinitrogen complexes.

Labios, Liezel A. For example, complexes containing mono-aryl substituted pendant amines are protonated at Mo and pendant amine to generate mono- and dicationic Mo—H species. This paper proposes a novel method for superheat control using only a single temperature sensor at the outlet of the evaporator, while eliminating the need for a pressure sensor.

Therefore temperature of these tubes and large difference with design temperature is a main reason for rupture on the superheater tubes. The studied boiler was divided into more than 1.

Therefore, the boiler geometry was prepared for the numerical analysis. In the majority of codes oriented on the CFD method, Reynolds and Navier-Stokes equations were used for remodeling the current [7] where defining the average time dependant properties for the current helps define the average time dependant Navier-Stokes equations as follow:. Here is the tensor of stress:. Eddy dissipation model was employed for the combustion calculations [9]. This model is predicated on the low-speed models and was first developed by [8].

It is presumed in this model that the fuel and oxidant come in separate vortexes in turbulent currents and they are mixed when the larger vortexes are turned into smaller ones and the smaller vortexes are disappeared as a result of viscosity in a way that the fuel and oxidant can be mixed. The value of R f would be resulted from the two equations above and the smallest value will be used in the calculations.

In order to solve the RTE, the P-1 radiation model was employed. For calculating the radiation properties of the mixture resulting from combustion, the weighted sum of gray gases model WSGGM was used. In order to create an accurate relationship between the pressure and speed in the continuity and momentum equations, the SIMPLE method was used.

Solution algorithm was also oriented on the segregated solver. Applying the relevant equations and proper models to solve them in the calculative slope of the studied boiler with real dimensions was the first step. Then, the identification of boundary conditions of the analysis slope was taken into consideration according to the data gathered from the power plant.

Then, with the observation of convergence in the answers, the primary results of simulation were produced. After carried out the computational iterations and convergence of the equations answer, temperature of the products resulting from combustion inside the boiler reaches about K. Figure 3 demonstrates fire vortex inner of boiler. Following the examination of combustion process inside the boiler, the thermal analysis of platen superheater tubes as the first set of superheater tubes which are exposed to a broad spectrum of flames resulting from combustion, was put into agenda.

All the three types of platen superheater tubes with long, medium and short lengths were analyzed from the view of their length. Platen superheaters comprise three set of twin tubes and each set constitute a single row of tubes and each row contains tubes. As said earlier, the main part of heat transfer in the platen superheaters is of the radiation sort, for the reason that they are located in the nearest distance to the burners in compare with the rest of superheater tubes, and also the convection heat transfer coefficient of the vapor in these tubes is low.

The superheat vapor flowing in these helical tubes undergoes a fall of pressure until reaching the pressure of outlet header box equal to However, the fall of pressure through each tube varies according to its length and its proportional knee. In the consequential results of simulation, all the three rows of studied tubes realized the pressure of outlet header box with a proper accurate.

Following this conclusion, the average speed of vapor in these three tubes would be different with together. Based on the results of the present research, the average speeds of vapor in these tubes, As the mass flow rate in the short tubes is more than of medium and long tubes which causes the speed of vapor in short tubes to be consequentially more than speed of vapor in medium and long tubes, the value of convection heat.

Figure 3. The fluid flow pattern colored by the fluid temperature. It means that the quantity of heat transfer from the crust of such tubes into the hot vapor inside them would be augmented. Comparing with the long length tubes, the same results can be concluded with slighter intensity in support of the tubes with medium length, as well.

Now, with regard to the results of numerical analysis and their comparison with the design temperature reported by the reference Isfahan Power plant Documents [5], the fact has become unambiguous that thermally, the temperature of medium and long tubes in zones such as the knees close to the outlet header would function in temperatures higher than the design temperature.

Figure 4 depicts the thermal variations of different types of platen superheater tubes and Figure 5 shows the pressure variations of superheat vapor inside these tubes. Then the following solutions have been applied:. We tried to direct the thermal pyramid resulting from combustion to the floor of the boiler by changing the angle of air channels and fuel nozzles to the surface of horizon.

Then, with regard to the two facing paradoxical goals i. For this purpose, twelve assumptive pages from the uppermost flat of the burners i. Then the average temperature was calculated for each of these 12 zones. Consequently, the effectuality of this solution on the quantity of temperature variations inside the boiler and the specified zones was examined by changing the angle of channels and nozzles in each flat of the burner. After identifying the critical zones which are prone to the maximization of temperature, local thermal shields were used for this parts of the platen superheater tubes.

Figure 4. Changes of temperature on superheater tubes without the thermal shields. Figure 5. Changes of vapor pressure inside the platen superheater tubes. In next step, some of parameters are calculated, such as partial pressure of combustion products, Adiabatic flame temperature [10,11] and average path length Le of radiance [11,12].

With these data, we could measure emissivity and absorptivity coefficients of combustion products by help from several practical data base table that belong to Hottel and Egbert [11,12]. These parameters have main role for calculation radiation heat transfer from flame or combustion products to superheater tubes, Please see to Figure 6.

Therefore, Radiation heat transfer to platen superheater tubes by combustion products is equal to:. It is place in low temperature zone of furnace so it is also called as low temperature super heater. The steam from latent super heater passes to the platen super heater for further heating. Platen Super heater: platen is a vertical single loop placed in the furnace with many parallel tubes carrying steam. Their characters can complement each other to get a fairly constant temperature at all loads thus minimum attemperation is required.

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