Energy and Power Engineering, 2013, 5, 311-314
doi:10.4236/epe.2013.54B061 Published Online July 2013 (http://www.scirp.org/journal/epe)
Study on Calculation Method for P artition of Heat
Transfer in an Ultra-supercritical Boiler
Ye Teng1, Zhongxiao Zhang1,2, X u da n Liu2, Wei Liu2, Tuo Zhou1, Ming Zhu1
1School of Energy and Power Engineering, University of Shanghai for Science and Technology, Shanghai, China
2School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai, China
Received March, 2013
ABSTRACT
Use a 1000MW ultra-supercritical tower boiler as the research object. On the basis of one dimensional model, simplify
the tube heat transfer model and the radiation heat transfer model; establish the two-dimensional area calculation model
with the regional method; summarize the heat load distribution of flue gas temperature and water wall surface; and
compare with the measured data. The error range of the result is acceptable on the project. The distribution of water
wall surface heat load along the furnace width and the area where heat transfer deterioration cause easily along the
furnace height direction are studied with the model and algorithm on different boiler load conditions. All these provide
the reference for the design and operation of the ultra supercritical boiler.
Keywords: Ultra-supercritical; Flue Gas Temperature; Heat Load; Heat Transfer Deterioration
1. Introduction
Ultra-supercritical unit with the features of large capacity,
high parameter and low energy consumption, has become
an important development direction in China [1]. Part of
heat, which is given off by burning pulverized coal, is
transferred to the water wall. However, the process is
quite complicated. Under the supercritical pressure, the
increase of surface heat flux on water wall will cause the
tube heat transfer deterioration [2], due to the large spe-
cific heat region [3]. In addition, uneven temperature
field in furnace, and flame center deviation, will lead to a
series of accidents such as high local temperature of the
tube surface, boiler slogging and so on.
In order to solve or improve the above problems, we
need to establish a mathematical model to study the heat
transfer process inside the furnace. Boiler thermody-
namic calculation standard of furnace heat transfer is
based on a variety of zero-dimension models, but it can
only provide a few parameter values, and this method
will generate large errors during the calculation of large
capacity boiler. We can study on heat transfer character-
istics along height, width, depth direction in furnace by
promoting the zero-dimension model to multi-dimension
model.
In this paper, we use zone method to establish th e two-
dimensional area calculation model on the basis of one-
dimensional partition model [4]. And we analyze the
distribution characteristic of the water wall temperature;
witch can provide a reference for the large capacity boi-
ler design and operation.
2. Two-dimensional Area Mathematical
Model
This paper studies a 2955 t/h ultra-supercritical boiler
(once-through boiler with spiral pipes by variable pres-
sure operation, single furnace tower layout, tangential
firing, controlling temperature by swing nozzle, balanced
ventilation, suspension structure of all steel). The char-
acteristics of design coal are shown in Table 1, and basic
design parameters of the boiler are shown in Table 2.
2.1. Simplifying Assumptions
On consideration of the extremely complex process in-
side furnace, we need to simplify the heat transfer proc-
ess in a reasonable manner to get the law of heat load on
water wall surface and water wall temperature [5, 6].
This paper made the following assumptions:
Table 1. The design data of coal.
Item Data
Car % 64.15
Har % 3.61
Oar % 0.78
Nar % 0.71
Sar % 0.43
Aar % 12
Mar % 14
Qar,net kJ·kg-1 23420

Y. TENG ET AL.
312
Table 2. Design parameters at BMCR.
Item Data
Superheated steam flow/t·h-1 2955
Superheater outlet steam pressure/MPa 27.9
Superheater outlet steam temperature/℃ 605
Reheat steam flow/t·h-1 2443
Reheater inlet steam pressure/MPa 6.2
Reheater outlet steam pressure/MPa 6.03
Reheater inlet steam temperature/℃ 367
Reheater outlet steam temperature/℃ 603
 Separate heat transfer and combustion process in-
side the furnace, and get flame temperature distribution
along the height direction by one-dimensional model [4,
7].
 View flame located in the center of furnace as a
blackbody, and cylindrical distribution in the main com-
bustion zone.
 Furnace flue gas and water wall are regarded as
gray body, Area method is used to study heat transfer in
the furnace.
 Water wall is diaphragm wall, and the unilateral
surface gets different flame radiation.
 The flux of working medium in tube is homogene-
ous, and the boiler operation belongs to the supercritical
area; the coefficient of heat transfer in the tube is se-
lected according to working state (pressure, flow, heat
load), the physical properties of working medium and
experience parameters.
2.2. Mathematical Model
In this paper, two-dimensional area simplified furnace
water wall heat transfer model is established through
regional method. Area division is shown as Figure 1.
Yellow circle area represents fireball, and white area
represents flue gas around the fireball. We will take one
small area among the divisions into consid eration an d the
radiation heat from this area is transferred to the sur-
rounding water surface.
Figure 1. Furance partition figure.
Division calculation area of the object of study:
 Each layer is divided into regions on the basis of the
one-dimensional model of 18 layer partition, that is,
fireball center and fireball outside.
 Each layer of the wall was divided into 40 areas;
each side wall has ten regions.
The diameter of the fireball D can be calculated by the
following formal:
 
0.56 0.87 0.7
0.25
00
1.45 dl Ddmd Dhbsb 
We calculate the radiation characteristic parameters of
flame and flue gas through the real furnace operating
parameters, and radiation projection received by water
wall can be calculated by the following formal:
44
iijgiijsi
ii
GGST SST
si

 


Radiation heat transfer area can be expressed as:
/cos 32
22
22
22
cos cos
cos coscos cos
i
Ks KB
iij i
ij
ijij ij
ij
KeV A2
K
eb
GS sB
AA bh
SS ss



 






hR
3. Water Wall Tube Heat Transfer
Calculation Model
The heat transfer calculation of membrane type water
wall is on the basis of calculating heating load and me-
dium enthalpy value in each section by energy equation.
Then metal wall temperature and fouling wall tempera-
ture can be calculated:

, 1
2
2
,,
21
()
1
21
()
1
li iiii
gzgz gzgz
ii
js gzi
ii
hw gzi
qdl
hfpthh m
tt q
tt q

 






 




As the physical properties of working medium change
dramatically under ultra-supercritical pressure condition,
the selection of heat transfer coefficient can be fitted by
reference [8]. According to the measured date [8], the
calculation condition in this paper is given in Table 3.
Table 3. Calculation condition.
ConditionBoiler load/MWSteam pressure/MPa Steam flow/t·h-1
1 970 27.85 2869
2 662 19.64 1980
3 507 14.82 1477

Y. TENG ET AL. 313
4. Results and Discussions
The distributions of calculated value and measured data
on three conditions are shown as Figure 2. It did not
consider the influence of flame migration on the heat
load on water wall in calculation, so there is a certain
error compared to the measured values. However, it still
can show the same change tendency, and calculated val-
ues and measured values have better alignment. Two-
dimensional area model can reflect the basic change rule
of one-dimensional model, and it can give better features
of flue gas temperature, as well as heat load on water
wall after adjusting some parameters. However, more
factors will produce more errors which have more im-
pacts on the calculation results.
It can be concluded that the average heat load and
temperature on water wall surface along the furnace
height by one-dimension calculation model. But for real
boiler, the heat load distribution on water wall is not
uniform along the furnace width direction. The distribu-
tion of tangential firing boiler is generally high in the
middle and low on both sides.
Two representative cross-sections were selected in order
to compare the calculated value and measured data. The
two cross-sections are 34 m elevation (main burner cen-
ter section) and 54 m elevation (SOFA burner center sec-
tion). The fo rmer is located in burning area, and the latter
is located in burnout area. The distribution of heat load
along the width direction in 34 m elevation is shown as
Figure 3. The distribution of heat load along the width
direction in 54 m elevation is shown as Figure 4.
As shown in Figure 3 and Figure 4, along the water
wall width direction, both calculated values and meas-
ured data on back wall show the same distribution fea-
tures. The heat load on water wall surface is high in the
middle and low on both sides on these three conditions in
Figure 2. Heat load on water w al l on back wall .
Figure 3. Distribution of heat load along width direction in
34 m elevation.
Figure 4. Distribution of heat load along width direction in
54 m elevation.
34 m elevation, so it is on left wall. By contrast, the arc
in 34 m elevation is more apparent, but in 54 m elevation,
such law is not obvious, especially on the low load con-
dition 3. This means that the heat load on water wall sur-
face in 34 m elevation is more significantly than that in
54 m elevation along the furnace width direction. The
highest heat load on water wall on condition 1 is 501
kW/m2; 356 kW/m2 on condition 2 and 332 kW/m2 on
condition 3 in 34 m elevation. It agrees with the meas-
ured data. In 54 m elevation, the highest heat load on
water wall surface decreases obviously which shows the
unsatisfied agreement between the calculated values and
measured data.

Y. TENG ET AL.
314
Figure 5. Curve for heat load on water wall.
The expected highest position of heat load is generally
in the same height in the middle of each side wall in de-
sign, and the heat load of the four corners is low. Fig-
ure 3 reflects this rule, but Figure 4 does not. The main
reason is that 54 m elevation is at the SOFA wind vents
and the air temperature is only 334℃ in SOFA burner,
but its air volume accounts for 23% of the total air vol-
ume. Thus it will produce a certain cooling to the flue
gas of high temperature in furnace. As a result, it reduces
the heat load in this area.
Figure 5 shows the heat load distribution of water wall
surface on condition 1. The heat load distribution of the
four walls is the same when the flame center does not
deflect. The highest head load appears in the center of
each side wall which agrees with the design intention.
5. Conclusions
The complicated calculation model can reflect the calcu-
lation results of simple model. This strategy is closer to
the actual situation in terms of predicting larger variation
range and furnace area. However, there are some aspects
that can influence the precise calculation. The value and
distribution are reasonable by calculating the
two-dimensional area model of 1000 MW USC tower
boiler.
In the same height, the maximum value of heat load on
water wall surface appears in the central position which
shows radial distribution. Of all the calculation condi-
tions, the most dramatic change of heat load appears in
34 m elevation, and it gives a range from 237 kW/m2 to
501 kW/m2 which is 264 kW/m2 in difference.
USC boilers need to avoid heat transfer deterioration
in large specific heat region. The calculation results of
flue gas temperature show that the highest flue gas tem-
perature and heat load occur in the combustion area. The
phase transition point of working medium should be con-
trolled to be away from these areas under the supercriti-
cal pressure.
Calculation results show that the highest heat load on
water wall surface occurs in 34 m elevation. The maxi-
mum value of heat load on water wall surface is 501
kW/m2 on 970 MW condition. The maximum value of
heat load decreases with the decrease of boiler load. The
value becomes 332 kW/m2 on 507 MW condition.
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