Table 7Operation Data at Different Loads of No。3 Boiler

94 % BMCR 85 % BMCR 72 % BMCR 50 % BMCR

Bed temperature 910～930℃ 840～850℃ 840～850℃ 840～850℃

Fluidized velocity 5。2 m/s 4。7 m/s 4。1 m/s 3。1 m/s

Primary air ratio 45 % 47 % 51 % 53%

Secondary air ratio 50 % 47 % 41 % 38%

Flue gas velocity in cyclone 6。8m/s 5。8m/s 4。3m/s 2。6m/s

The waterwall is arranged at the boundary layer of the furnace, the heat transfer is different from the heating surface located at the other area。 The heat transfer coeffi- cient of heating surface depends on the location of heat- ing surface, because the solids suspension concentration at waterwall are significantly higher than that at other heating surface with a corresponding added heat flux。 However, for example, the flue gas temperature of platen heating surface’s area is relatively high, which give rise

to the radiation ability。 The comprehensive effects ofthe

while superheated steam flow can be measured and cal- culated by a feed water flow meter and a desuperheating water flow meter of the boiler。 Reheat steam flow can be obtained by the turbine thermal balance calculation。 The absorbed heat of each heating surface can be calculated according to the measured enthalpy increment and flow, and then the heat transfer coefficient of each heating sur- face can be calculated through formula (3) and formula (4)。This test is conducted on No。2 boiler。

(T i T o ) (T o T i)

two factors result in the higher heat transfer coefficient of

Δt  f s f s

(4)

waterwall。 The heat transfer coefficient of No。2 boileris

(T i

ln f



T o )

higher than that of No。3 boiler, that is because the mois-

(T o T i )

f s

ture of lignite is very high, which enhance theradiation

heat transfer。 The heat transfer coefficient of No。3 boiler is also higher than that of No。1 boiler。 It is known that anthracite is very difficult to burn, in order to guarantee steam output and burning-out, particle size entering into furnace is small, which leads to high solid suspension concentration at the upper part of furnace, so it improves the heat transfer。 So the heat transfer coefficients of No。2 boiler and No。3 boiler are higher than that of No。3 boiler。

The heat transfer coefficient of the platen heating surface

According to thermocouple and pressure gauge read- ings, the steam enthalpy, at inlet and outlet of each platen heating surface in the furnace, can be obtained。 Mean-

Fig。 8 The heat transfer coefficient of the waterwall of No。1 Boiler

Fig。 9 The heat transfer coefficient of the waterwall of No。2 Boiler