某電廠330mw機組八級熱力系統及管道通流部分的設計畢業論文-資料下載頁

　　

【正文】 represented as small rectangles. What will be called the east and west sides of the boiler are also indicated in the ?gure. Table 1 shows the tube bundle geometry for the primary and secondary reheaters and the tube material denomination for chromemoly alloy steels (T11 and T22) and austenitic stainless steel (TP304), the respective conductivities of which are 46 W/m K and 15 W/m K.3. Application of the modelThe model was applied to the power plant working under nominal load. We shall ?rst analyse the model solution for uniform steam ?ow for every tube in the serpentines and also uniform ?ow and temperature for the bustion gases: _ mg 188。 250:34 kg=sand Tg = 1191 K. Several estimated parameters that are included in the model will be varied for this situation in order to perform a theoretical study. The data from o?line measurements of velocities, temperatures and gases position will then be taken into account for the ?ow of gases. The solutions of the outlet temperatures in the walls of the tubes of the serpentine will be pared with the obtained measurements.. Inlet and outlet sections conditionsThe experimental o?line data will be obtained and subsequently introduced in the model as boundary conditions for the inlet and outlet sections. Furthermore,measurements will also be taken in an intermediate section,which will provide data to conduct the experimental validation of the model. It was decided to take the measurements approximately every metre at the west and east sides of the boiler. An in?uence zone, with surface A, was associated with each measurement point in the sections. Fig. 3 shows the in?uence areas de?ned for the inlet and outlet sections. Table 2 presents the values of the areas of the zones and the velocities, ux, as well as the temperatures and, cosa, the cosine of the angle between the velocity ponents (ux and uz).The mass ?ow rate of the gases is calculated from the ponent of the velocity, ux, the zone temperature, and the average pressure at the inlet section, being pg,inlet =101,075 Pa. Only the average measured pressure was introduced as a boundary condition in the outlet section, being pg,outlet = 101,068 Pa.. Side walls, ?oor and roof conditionsEmpirical correlations were used for the heat transfer coe?cients (radiative and convective), together with the ?uid temperature. The equations for dry saturated steam and for the twophase ?ow saturated liquid–vapour were obtained for a pressure inside the tubes of 170 kg/ following conditions were considered for the side walls with twophase ?ow: temperature inside the tubes Ti,v–l = K, vapour quality of xv = , tube mass ?ow rate _ mv–l 188。 1:64435 kg=s and external surroundings temperature T1 = 293 K. For the tubes of the roof, we considered: dry saturated steam at a temperature of Ti,v = K, the mass ?ow rate in each tube _ mv 188。 0:32887 kg=s and the temperature in the headers and connecting pipes chamber Tch = 573 K. Chen’s correlation was applied to calculate the heat transfer coe?cient for twophase ?ow, as suggested in [11]. To obtain the heat ?ux at the side walls and also at the roof, the following variables were considered: conductivity of the tubes, the use of extended surface connecting tubes, the simultaneous mechanisms of convection and radiation from the ?nned tubes and the surrounding bustion empirical method described by Lin, see also [9], was followed to calculate the radiative heat transfer coe?cient,which takes into account the distances between tubes, the emissivity of the wall, the outer diameter of the tube and other radiative properties of the gases.. Conditions inside the tubesSuperheated steam at a pressure of ps = 40 kg/cm2 was considered, the mass ?ow rate of steam in each tube being uniformly distributed: _ ms 188。 0:59188 kg=s. Two temperatures were considered for the steam entering the primary reheater: Ts,i,E = K for the 26 serpentines placed towards the east side and Ts,i,W = K for the 6 serpentines from those placed towards the west side.. Determination of the gas propertiesThermophysical properties were obtained as temperature functions, taking into account the gas volume position: % CO2, % H2O, % N2, % O2,0% CO, and % SO2. Density was calculated considering temperature and pressure variations and the mixture of ideal gases. Speci?c heat at constant pressure, dynamic viscosity and conductivity were calculated from the individual ponents, the data being taken from the National Institute of Standards and Technology (NIST) [12]. The properties of the mixture of gases were deduced from ideal behaviour and the application of Wilke’s expressions [13].. The auxiliary values consideredThe following values were introduced: emissivity of the walls ()。 domain volume (1271 m3)。 surface of the walls,including the ?ctitious surfaces of the inlet and the outlet (total = 745 m2)。 volume of ?ue gases expressed under normal conditions for the stoichiometric reaction per unit of mass of raw fuel (Vfumes = m3/kg)。 mass of ?ue gases produced under a stoichiometric reaction per unit of mass of fuel (Mfumes = kg/kg) and density of the gas expressed under normal conditions (qgNC = kg/m3).4. Model studyThe model includes parameters that were presented in a panion paper [1]. The values of these parameters are estimated in a ?rst stage。 these will be highlighted in bold and grouped together to constitute the reference denomination and description of the assayed cases are presented in Table 3.The parameters and values given in order to perform the parametric study are:? flt (coe?cient to be applied to the dynamics): 1, 20 and 400.? C (coe?cient to take into account the type of fuel): , and .? f (coe?cient of nonuniform sweeping of the tubes by gases, a constant): 1, and .? kp and ks (e?ective coe?cients of absorption of radiation from the primary and secondary reheaters).The e?ective absorption coe?cients present di?erent values for the primary and sec