HOT WATER BOILER
M. Ye. Baibalinova
3. RESULTS AND DISCUSSION
Analysis of thermographic images (Figures 1, 2) showed that on the contaminated heating AH surface in comparison with the cleaned one there are deposits of combustion products with a sufficiently high temperature after the boiler is shut down. Therefore, in the actual operation of the boiler unit, the fuel burn-out areas can be formed, leading to damage to the AH and to a decrease in the cooling of exhaust gases, which ultimately affects the efficiency of the boiler.
Thus, the timely cleaning of the exhaust duct from the deposits equalizes the temperatures along its surface.
In order to determine the nature of the temperature change in the contaminated and cleaned AH surface, an analysis area was selected on the thermographic image, which is marked by the line I-I passing along the central part of the gas pipeline (Figures 1, 2).
The nature of the temperature change along the control line I-I is shown in the graphs (Figures 3, 4).
The Study of Heat Transfer Processes in the Tail Heating Surfaces of the Hot Water Boiler
http://www.iaeme.com/IJCIET/index.asp 968 [email protected] Figure 3 Graph of temperature changes in the contaminated AH surface
Figure 4 Graph of temperature changes in the cleaned AH surface
Analysis of the graphs of temperature changes in the contaminated and cleaned AH surfaces showed that the presence of deposits leads to a sharp temperature change from the maximum value of 46.77°C in the deposit zone and the flue gas inlet to the minimum value of 40.03°C on the tube surface. After blasting and cleaning the AH from the deposits, the temperature in the section of the flue gas inlet decreased to 44.37°C, and the temperature of the tube surface increased to 41°C. This resulted in the equalization of the temperatures over the surface of the heat exchanger.
The simulation of processes in the AH was carried out to determine:
- the speed of movement of the heated air for the contaminated and cleaned AH surfaces;
- the temperature of the heated air at the outlet from the contaminated and cleaned surfaces.
For simulation, the initial and final values of the heat carriers at the AH inlet and outlet (the temperature of the heated and heating media, the mass flow, the velocity of flue gases, depending on the capacity) are taken from the data of the boiler’s standard readings.
Based on the obtained data, a two-dimensional model of the AH tuberows was constructed. In order to determine the nature of temperature and velocity changes for the contaminated and cleaned AH surfaces, the coordinate of the analysis was selected, passing along the exhaust duct height marked by the line II-II (Figure 5).
A. R. Khazhidinova, O. A. Stepanova, M. V. Yermolenko, S. L. Elistratov, M. Ye. Baibalinova
http://www.iaeme.com/IJCIET/index.asp 969 [email protected] Figure 5 The model of the AH tube rows
The distribution of the heated air velocity at a heat output of 50 Gcal/h for the contaminated and cleaned surface in the obtained AH model is shown in Figure 6. In the narrow sections of the model, the maximum air velocity was 9.0 and 9.3 m/s, respectively.
According to the boiler's standard readings, the flue gas velocity is 8.2 m/s, and the required average velocity of the heated air is 4.1 m/s.
(a) (b)
Figure 6 Distribution of the heated air velocity at a heat output of 50 Gcal/h on the contaminated (a) and cleaned (b) AH surface
The distribution of the heated air velocity at a heat output of 100 Gcal/h for the contaminated and cleaned surface in the obtained AH model is shown in Figure 7. In the narrow sections of the model, the maximum air velocity was 9.8 and 10.1 m/s, respectively.
According to the boiler's standard readings, the flue gas velocity is 10.4 m/s, and the required average velocity of the heated air is 5.2 m/s.
The Study of Heat Transfer Processes in the Tail Heating Surfaces of the Hot Water Boiler
http://www.iaeme.com/IJCIET/index.asp 970 [email protected]
(a) (b)
Figure 7 Distribution of the heated air velocity at a heat output of 100 Gcal/h on the contaminated (a) and cleaned (b) AH surface
The average velocity magnitudes, obtained in the simulation process, for the contaminated and cleaned AH surfaces along the line II-II at the minimum and nominal heat output are shown in Figure 8 and Figure 9.
Figure 8 The average velocity for the contaminated and cleaned AH surface at a heat output of 50 Gcal/h
Analysis of the obtained data (Figures 8 and 9) for the contaminated AH surface showed that the average velocity of the heated air is 4.62 and 3.69 m/s, which is much less than the required value. For the cleaned AH surface, there is an increase in the average velocity of the heated air to the required values at these capacities.
3.69 4.1
0.501 1.52 2.53 3.54 4.55 5.56 6.57 7.58 8.59 9.5
0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045
Velocity, m/s
Coordinate along II - II, m
A. R. Khazhidinova, O. A. Stepanova, M. V. Yermolenko, S. L. Elistratov, M. Ye. Baibalinova
http://www.iaeme.com/IJCIET/index.asp 971 [email protected] Figure 9 The average velocity for the contaminated and cleaned AH surface at a heat output of 100 Gcal/h
The distribution of the heated air temperatures at the outlet from the contaminated and cleaned AH surfaces at the minimum and nominal heat output is shown in Figures 10 and 11.
(а) (b)
Figure 10 Distribution of the heated air temperatures at the outlet from the contaminated (a) and cleaned (b) AH surface at a heat output of 50 Gcal/h
4.62 5.2
0.501 1.52 2.53 3.54 4.55 5.56 6.57 7.58 8.59 9.510 10.5
0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045
Velocity, m/s
Coordinate along II - II, m
The Study of Heat Transfer Processes in the Tail Heating Surfaces of the Hot Water Boiler
http://www.iaeme.com/IJCIET/index.asp 972 [email protected]
(a) (b)
Figure 11 Distribution of the heated air temperatures at the outlet from the contaminated (a) and cleaned (b) AH surface at a heat output of 100 Gcal/h
The heated air temperatures, obtained in the simulation process, at the outlet from the contaminated and cleaned AH surface along the line II-II at the minimum and nominal heat output are shown in Figures 12 and 13.
Figure 12 The heated air temperature at the outlet from the contaminated and cleaned AH surface at a heat output of 50 Gcal/h
The heated air temperatures, obtained in the simulation process, at the outlet from the contaminated AH surface at the nominal and minimum capacities were 535 and 537 K, respectively. For the cleaned AH surface, at the nominal and minimum capacities, there was an increase in the heated air temperature to 540 and 543 K (Figures 12, 13).
535 540
470 480 490 500 510 520 530 540 550
0 0.01 0.02 0.03 0.04 0.05
Temperature, К
Coordinate along II - II, m
A. R. Khazhidinova, O. A. Stepanova, M. V. Yermolenko, S. L. Elistratov, M. Ye. Baibalinova
http://www.iaeme.com/IJCIET/index.asp 973 [email protected] Figure 13 The heated air temperature at the outlet from the contaminated and cleaned AH surface at a
heat output of 100 Gcal/h
Based on the obtained data, nomograms were constructed that relate the efficiency factor, the heated air velocity, the temperature of outgoing flue gases, and the performance of the boiler unit for the contaminated and cleaned AH surfaces (Figures 14 and 15). In constructing the nomogram, the quantity of heat losses due to emitted combustibles remained constant.
The efficiency factor к.браwas determined using the inverse balance method:
пот
бр а
к. 100 q
, (1)
where
qпотis the loss amount of the boiler unit [1].Figure 14 Nomogram for the determination of the efficiency factor for the contaminated AH surface 543
537
470 480 490 500 510 520 530 540 550
0 0.01 0.02 0.03 0.04 0.05
Temperature, К
Coordinate along II - II, m
144 145 146
t = 152°C 3,69
3,91 4,1 v = 4,62 м/с
87.7 87.8 87.9 88 88.1 88.2 88.3 88.4 88.5 88.6 88.7
50 60 70 80 90 100
Efficiency factor, %
Heat output, Gcal/h
The Study of Heat Transfer Processes in the Tail Heating Surfaces of the Hot Water Boiler
http://www.iaeme.com/IJCIET/index.asp 974 [email protected] Figure 15 Nomogram for the determination of the efficiency factor for the cleaned AH surface Analysis of the obtained data showed a decrease in the amount of heat losses with outgoing gases and losses to the environment through the enclosing AH surfaces after cleaning the heating surfaces, which contributes to an increase in the efficiency of the boiler unit. When the boiler was operated at the minimum performance for the contaminated and cleaned AH surfaces the efficiency factor was 87.7 and 88.2%, with a nominal performance of 88.7 and 89.6%, respectively.
The obtained results testify to a uniform increase in the heated air velocity with an increase in the boiler’s heat output from the minimum to the nominal value after cleaning the AH surface. The temperature of outgoing flue gases after cleaning the surface of the heat exchanger uniformly increases depending on the heat output, hence the amount of heat that goes to heat the air in the AH increases. Flue gas deposits create additional thermal resistance, which significantly affects the efficiency of heat exchange and reduces the heat transfer from flue gases. As a result of this, the regular cleaning of the exhaust duct heating surface leads to an increase in the efficiency factor.