Fig。 10 The heat transfer coefficient of the waterwall of No。3 Boiler

The calculated results of the platen heating surface are shown in Fig。 11, indicating that the heat transfer coeffi- cient of different heating surfaces increases gradually with the increase in boiler load。 The heat transfer coeffi- cients of SSⅠ, SSⅡ and HTR are 156 W/(m2·℃), 162 W/(m2·℃) and 172 W/(m2·℃), respectively, at 95。6 %

BMCR。 The heat transfer is affected by the structure and dimensionofheatingsurface，bed temperature，steam

temperature, emissivity of tube wall, solids suspension concentration and fluidization velocity etc。 and the main effecting factors are the solids suspension concentration and bed temperatures。 With increasing boiler load, the solid suspension concentration and the bed temperature are increasing monotonically。 The bed temperature mainly affects the radiation heat transfer of flue gas。 The increasing of bed temperature can greatly enhance the heat transfer capacity of flue gas。 Furthermore, bed tem- perature also affects the particle convection theoretic heat transfer coefficient, the higher the bed temperature, the greater the particle convection theoretic heat transfer coefficient, then the greater the convection heat transfer of flue gas。 The convection heat transfer coefficient of

flue gas is mainly affected by the solids suspension con- centration, so with the increasing solids suspension con- centration, the total heat transfer coefficient is higher。 These are the most important improvement factors for the heat transfer in the furnace。 With increasing these two factors, the heat transfer coefficient is higher obviously。

Fig。 11 The heat transfer coefficients of the platen heating surfaces of No。2 Boiler

The heat transfer coefficient of the EHE

The heat transfer coefficient calculation method of each heating surface of EHE is similar to that of platen heating surface。 According to thermocouple and pressure gauge readings, the steam enthalpy, at inlet and outlet of EHE, can be obtained。 Meanwhile the absorbed heat of each heating surface, superheated steam flow and reheat steam flow can be obtained by calculation。 And then the heat transfer coefficient of each heating surface can be calculated through formula (3) and formula (4)。

Fig。12 shows that heat transfer coefficient of each heating surface increases with boiler load increasing。 Because with the boiler load increasing, the ability to do work of the primary steam increases, correspondingly its parameters is improved, then the heat transfer in EHE is enhanced, so that heat transfer coefficient increases。

At around 100％BMCR load, the heat transfercoeffi-

Fig。12The heat transfer coefficients of heat surface in EHE

cients of MTSⅠ, MTSⅡ, HTR and LTS are 262 W/(m2·K), 302W/(m2·K), 240 W/(m2·K), 253W/(m2·K)

respectively，EHEeffectivelyimprovesthe utilization

rate of heating surface with such high heat transfer coef- ficient, and reduce the metal consumption of the heating surface, that is also one of the reasons why EHE is widely used。

The heat transfer coefficient of the steam-cooled cy- clone separator

The heat transfer coefficient calculation method of the heating surface of the water-cooled (steam-cooled) cy- clone separator is similar to that of platen heating surface and external heat exchanger。

Fig。8 shows the variation of heat transfer coefficient with different boiler loads。 At 98％BMCR load around, the heat transfer coefficient is 58。6 W/(m2·K), And heat transfer coefficient of the heating surface increases with the boiler load increasing。 That’s because with the boiler load increasing, the solid circulation quantity and gas superficial velocity increase。 The heat transfer coefficient

increases linearly with the increase of solid circulation quantity。 For higher solids loading, large numbers of sol- ids enter into the cyclone which in turn increases the concentration at the wall surface。 Hence, the heat transfer coefficient is higher for high solids circulation quantity。 Fluidization velocity also has great effect on the heat transfer coefficient。 The flow of gas solids suspension into the cyclone increase with the velocity increasing which causes the particles to make many more turns in the cyclone。 Moreover, it enhances turbulence at higher velocities so the heat transfer is enhanced because of rapid intermixing of gas solids suspension。 Owing to the above reasons, the heat transfer coefficient is high at high velocity。