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Method of monitoring and measuring seal clearances in a rotary heat exchanger
Heat Recovery Systems & ClIP Vol. 8, No. 5, pp. 469-473, 1988 Printed in Great Britain
0890-4332/88 $3.00 + .00 Pergamon Press plc
METHOD OF MONITORING AND MEASURING SEAL CLEARANCES IN A ROTARY HEAT EXCHANGER T. SKIEPKO* Department of Heat Engineering, Technical University of Bialystok, ul. Wiejska 45A, 15-351 Bialystok, Poland (Received 20 April 1988)
Almraet--A new method of measuring and monitoring seal clearances in a rotary heat exchanger is presented. The measuring and monitoring system consists of: a special instrument; linear displacement transducer; digitial display unit and loop oscillograph. The method proposed is described and illustrated by the results obtained during hot and cold rotation. The procedure was carried out for two rotary regenerators, 5.3 and 9.4 m in diameter.
1. INTRODUCTION The significant advantage of rotary heat exchangers applied as thermal regenerators for steam boilers, gas turbine installations or ventilation and air conditioning systems, is generally known. This is due to the larger and inexpensive heat transfer area per unit volume in rotary heat exchangers, in comparison to conventional shell and tube or plate-fin surface types. On the other hand, it is known that the rotary gas-to-gas heat exchangers have a general fault, called leakage, in which part of one gas stream passes into the other gas stream. For this reason performance of a plant with a rotary heat exchanger must include both temperature effectiveness and a leakage loss parameter [1]. The leakage can be defined as a quantity of gas flux flowing through the seal clearances as a result of the static pressure difference between the two gas streams [2]. The leakage primarily affects the energy consumption necessary for forcing the gases through a rotary heat exchanger. The leakages also affect gas and matrix temperature distributions, particularly in the radial direction and hand of rotation. The quantity of the leakage is dependent on seal clearance area and static pressure difference between the stream gases flowing through the rotary heat exchanger. In Fig. 1 possible leakage paths are shown. The static pressure difference results from the operating conditions of a plant. Therefore, the quantity of the leakage across the sealing system is directly dependent on the seal clearance area. This area and also its shape, are different at the hot rotor in comparison to the cold state. The difference in shape is due to thermal distortions of the rotor, its housing and sealing plates in the rotary heat exchanger [2-4]. Thus, an assurance of a long term reliability and effectiveness of the sealing system requires preventative monitoring and measurement of the seal clearance and their adjustment on the basis of the results obtained. The purpose of this paper is the presentation of a monitoring and measurement method for seal clearances in rotary heat exchangers. 2. THE METHOD 2.1. Apparatus The seal clearance is that distance c between the face of the sealing plate (4) and seal sheets (1) attached on the rotor (see Fig. 2). The instrument presented in Fig. 2 was employed for the measurement of seal clearances in rotary heat exchangers. Since the instrument operates at high temperatures, particularly on the hot side, and in a dust polluted medium, it was made as a mechanical meter. Whereas, on the outside of the heat exchanger an inductive linear displacement transducer has been mounted to the instrument. The complete measuring system is shown in *Home address: ul. Kalinowa 9 m.6, 15-809 Bialystok, Poland. T. Skiepko is Assistant Professor. 469
470
T. SKIEPKO
I.ok~....~ J
a
ill;"
t
Ilil
Fig. I. Possible leakage paths in rotary heat exchanger.
[XX]
t
Fig. 3. Block diagram of measuring circuit: (1) seal plate, (2) housing of rotary heat exchanger, (3) measuring instrument, (4) linear displacement transducer, (5) digital display unit, (6) loop oscillograph.
Fig. 2. View and details of the measuring instrument: (I) seal sheet, (2) hall, (3) inner sleeve, (4) seal piate, (5) flange homing, (6) spring, (7) screw, (8) spiine shaft, (9) pilot sleeve, (10) housing of rotary heat exchanger, (I 1) seal, (12) seal housing, (13) scale under zero setting and hand*held operation, (14) linear displacement transducer.
Fig. 3 and consists of the instrument (3), linear displacement transducer (4), digital display unit (5) and loop oscillograph (6). Signals from the displacement transducer (4) were passed through the digital display unit (5) and recorded on light-sensitive paper by means of loop oscillograph (6). The instrument (3) attached to the rotary heat exchanger is presented in Fig. 4. 2.2. Procedure Dimension d is the distance from zero setting (see Fig. 2) to the position of the ball (2) in contact with all the seal sheets (1). Then the seal clearance c~ (for seal sheet number i) is determined by
Monitoring and measuring seal clearances
471
Fig. 4. The measuring instrument attached to a rotary heat exchanger.
the equation: c, = d -f~,
(1)
where f~ is the travel of the spline shaft (8) which is due to seal sheet number i. The measurement of the seal clearances are carried as follows: (a) we turn (see Fig. 2) the adjusting spline shaft (8) and with the help of scale (13) we set up the ball (2) at zero setting, this is recorded on the light-sensitive paper by means of the loop oscillograph; (b) then by further turning (8) we set up the ball (2) to a position in contact with all the seal sheets; (c) the consecutive pushes of the spline shaft (8) caused by the seal sheets are recorded on the light-sensitive paper by means of the loop oscillograph (recording d and f); (d) on the basis of the scale of the displacement transducer the seal clearances resulting from equation (1) are read as recorded on light-sensitive paper. 2.3. Illustrative results The seal clearance measurements were carried out in two rotary regenerators applied to pulverized coal fired boilers [5, 6]. The sizes of the regenerators were, in the former case, 1.8 m height by 5.3 m diameter and in the other, 1.8 m height by 9.4 m diameter. In Figs 5 and 6 the results for the hot and cold states of the rotor are presented. 3. C O N C L U D I N G R E M A R K S The control of the quantity of leakages in rotary heat exchangers at a minimum level requires information about seal clearances in hot operating conditions and cold conditions. This information makes it possible to undertake an adequate adjustment of the seal clearance. Thus, following the above method we can ensure that: the quantity of leakage of one gas stream into the other will be as little as possible; there will be no risk of destruction of the seal system or rotor by external adjustment of radial and axial sealing plates; the effectiveness of a plant with a rotary heat
472
T. SKIEPKO
F
Scale 1.7:1
If
4.8:1
IIIItlllllll
-1
d
Cord state
Ha,_ ~ I .
J
7-
]
I !o!,o,
Hot state
1.7;I
L_
4.8:1
_J
Fig. 5. Seal clearance results for rotary heat exchanger 1.8 m height by 5.3 m diameter at inlet combustion gas temperature 339.3°C and inlet air temperature 28.7°C.
exchanger will n o t be excessively reduced on a c c o u n t o f the leakages; the process o f heat transport in a r o t a r y heat exchanger will take place according to generally accepted model assumptions, disregarding the effect o f the leakages on gas and matrix temperature distributions.
REFERENCES 1. D. B. Harper and W. M. Rohsenow, Effect of rotary regenerator performance on gas turbine plant performance, Trans. A S M E 75, 759-765 (1953). 2. E. J. MacDuff and N. D. Clark, Ljungstrom air preheater design and operation, part I: sealing and leakage, Combust. 47, 7-11 (1976). 3. L. Chiang and J. A. Cunningham, Ljungstrom air preheater, new design features and operating experience, Combust. 42, 28-35 (1970).
Monitoring and measuring seal clearances
473
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4.5:1 CoLd state
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,
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__lk_ Fig. 6. Seal clearance results for rotary heat exchanger 1.8 m height by 9.4 m diameter at inlet combustion gas temperature 353.8°C and inlet air temperature 51.3°C. 4. V. K. Migai, Regenerative Rotary Air Preheaters (in Ku,~an), Energiya, Leningrad (1971). 5. T. Skiepko, Investigations of regenerative rotary air preheater BD-22 type (in Polish), Rcp. of ITC L6di (unpublished), No. 3934 PP (1978). 6. T. Skiepko, Investigations of regenerative rotary air preheater BD-28 type (in Polish), Rep. of ITC L6d~ (unpublished), No. 4114 PP (1980).
0890-4332/88 $3.00 + .00 Pergamon Press plc
METHOD OF MONITORING AND MEASURING SEAL CLEARANCES IN A ROTARY HEAT EXCHANGER T. SKIEPKO* Department of Heat Engineering, Technical University of Bialystok, ul. Wiejska 45A, 15-351 Bialystok, Poland (Received 20 April 1988)
Almraet--A new method of measuring and monitoring seal clearances in a rotary heat exchanger is presented. The measuring and monitoring system consists of: a special instrument; linear displacement transducer; digitial display unit and loop oscillograph. The method proposed is described and illustrated by the results obtained during hot and cold rotation. The procedure was carried out for two rotary regenerators, 5.3 and 9.4 m in diameter.
1. INTRODUCTION The significant advantage of rotary heat exchangers applied as thermal regenerators for steam boilers, gas turbine installations or ventilation and air conditioning systems, is generally known. This is due to the larger and inexpensive heat transfer area per unit volume in rotary heat exchangers, in comparison to conventional shell and tube or plate-fin surface types. On the other hand, it is known that the rotary gas-to-gas heat exchangers have a general fault, called leakage, in which part of one gas stream passes into the other gas stream. For this reason performance of a plant with a rotary heat exchanger must include both temperature effectiveness and a leakage loss parameter [1]. The leakage can be defined as a quantity of gas flux flowing through the seal clearances as a result of the static pressure difference between the two gas streams [2]. The leakage primarily affects the energy consumption necessary for forcing the gases through a rotary heat exchanger. The leakages also affect gas and matrix temperature distributions, particularly in the radial direction and hand of rotation. The quantity of the leakage is dependent on seal clearance area and static pressure difference between the stream gases flowing through the rotary heat exchanger. In Fig. 1 possible leakage paths are shown. The static pressure difference results from the operating conditions of a plant. Therefore, the quantity of the leakage across the sealing system is directly dependent on the seal clearance area. This area and also its shape, are different at the hot rotor in comparison to the cold state. The difference in shape is due to thermal distortions of the rotor, its housing and sealing plates in the rotary heat exchanger [2-4]. Thus, an assurance of a long term reliability and effectiveness of the sealing system requires preventative monitoring and measurement of the seal clearance and their adjustment on the basis of the results obtained. The purpose of this paper is the presentation of a monitoring and measurement method for seal clearances in rotary heat exchangers. 2. THE METHOD 2.1. Apparatus The seal clearance is that distance c between the face of the sealing plate (4) and seal sheets (1) attached on the rotor (see Fig. 2). The instrument presented in Fig. 2 was employed for the measurement of seal clearances in rotary heat exchangers. Since the instrument operates at high temperatures, particularly on the hot side, and in a dust polluted medium, it was made as a mechanical meter. Whereas, on the outside of the heat exchanger an inductive linear displacement transducer has been mounted to the instrument. The complete measuring system is shown in *Home address: ul. Kalinowa 9 m.6, 15-809 Bialystok, Poland. T. Skiepko is Assistant Professor. 469
470
T. SKIEPKO
I.ok~....~ J
a
ill;"
t
Ilil
Fig. I. Possible leakage paths in rotary heat exchanger.
[XX]
t
Fig. 3. Block diagram of measuring circuit: (1) seal plate, (2) housing of rotary heat exchanger, (3) measuring instrument, (4) linear displacement transducer, (5) digital display unit, (6) loop oscillograph.
Fig. 2. View and details of the measuring instrument: (I) seal sheet, (2) hall, (3) inner sleeve, (4) seal piate, (5) flange homing, (6) spring, (7) screw, (8) spiine shaft, (9) pilot sleeve, (10) housing of rotary heat exchanger, (I 1) seal, (12) seal housing, (13) scale under zero setting and hand*held operation, (14) linear displacement transducer.
Fig. 3 and consists of the instrument (3), linear displacement transducer (4), digital display unit (5) and loop oscillograph (6). Signals from the displacement transducer (4) were passed through the digital display unit (5) and recorded on light-sensitive paper by means of loop oscillograph (6). The instrument (3) attached to the rotary heat exchanger is presented in Fig. 4. 2.2. Procedure Dimension d is the distance from zero setting (see Fig. 2) to the position of the ball (2) in contact with all the seal sheets (1). Then the seal clearance c~ (for seal sheet number i) is determined by
Monitoring and measuring seal clearances
471
Fig. 4. The measuring instrument attached to a rotary heat exchanger.
the equation: c, = d -f~,
(1)
where f~ is the travel of the spline shaft (8) which is due to seal sheet number i. The measurement of the seal clearances are carried as follows: (a) we turn (see Fig. 2) the adjusting spline shaft (8) and with the help of scale (13) we set up the ball (2) at zero setting, this is recorded on the light-sensitive paper by means of the loop oscillograph; (b) then by further turning (8) we set up the ball (2) to a position in contact with all the seal sheets; (c) the consecutive pushes of the spline shaft (8) caused by the seal sheets are recorded on the light-sensitive paper by means of the loop oscillograph (recording d and f); (d) on the basis of the scale of the displacement transducer the seal clearances resulting from equation (1) are read as recorded on light-sensitive paper. 2.3. Illustrative results The seal clearance measurements were carried out in two rotary regenerators applied to pulverized coal fired boilers [5, 6]. The sizes of the regenerators were, in the former case, 1.8 m height by 5.3 m diameter and in the other, 1.8 m height by 9.4 m diameter. In Figs 5 and 6 the results for the hot and cold states of the rotor are presented. 3. C O N C L U D I N G R E M A R K S The control of the quantity of leakages in rotary heat exchangers at a minimum level requires information about seal clearances in hot operating conditions and cold conditions. This information makes it possible to undertake an adequate adjustment of the seal clearance. Thus, following the above method we can ensure that: the quantity of leakage of one gas stream into the other will be as little as possible; there will be no risk of destruction of the seal system or rotor by external adjustment of radial and axial sealing plates; the effectiveness of a plant with a rotary heat
472
T. SKIEPKO
F
Scale 1.7:1
If
4.8:1
IIIItlllllll
-1
d
Cord state
Ha,_ ~ I .
J
7-
]
I !o!,o,
Hot state
1.7;I
L_
4.8:1
_J
Fig. 5. Seal clearance results for rotary heat exchanger 1.8 m height by 5.3 m diameter at inlet combustion gas temperature 339.3°C and inlet air temperature 28.7°C.
exchanger will n o t be excessively reduced on a c c o u n t o f the leakages; the process o f heat transport in a r o t a r y heat exchanger will take place according to generally accepted model assumptions, disregarding the effect o f the leakages on gas and matrix temperature distributions.
REFERENCES 1. D. B. Harper and W. M. Rohsenow, Effect of rotary regenerator performance on gas turbine plant performance, Trans. A S M E 75, 759-765 (1953). 2. E. J. MacDuff and N. D. Clark, Ljungstrom air preheater design and operation, part I: sealing and leakage, Combust. 47, 7-11 (1976). 3. L. Chiang and J. A. Cunningham, Ljungstrom air preheater, new design features and operating experience, Combust. 42, 28-35 (1970).
Monitoring and measuring seal clearances
473
ScoLe 4.5:1
4.5:1 CoLd state
Hot store
~,,,
II
,
kI
I "ll"lii
lilill l i ~
I
~Sm
~--------~A,~-~
F ~fJllrliil ll[ililJ'~
CoLd store u-
Hot store
4.5:1
4.5:1
__lk_ Fig. 6. Seal clearance results for rotary heat exchanger 1.8 m height by 9.4 m diameter at inlet combustion gas temperature 353.8°C and inlet air temperature 51.3°C. 4. V. K. Migai, Regenerative Rotary Air Preheaters (in Ku,~an), Energiya, Leningrad (1971). 5. T. Skiepko, Investigations of regenerative rotary air preheater BD-22 type (in Polish), Rcp. of ITC L6di (unpublished), No. 3934 PP (1978). 6. T. Skiepko, Investigations of regenerative rotary air preheater BD-28 type (in Polish), Rep. of ITC L6d~ (unpublished), No. 4114 PP (1980).