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Performance test code on steam surface condenser
1 Scope
This standard specifies the basic principles and methods of instrument selection, test procedure and test data processing for performance test of steam surface condenser (herein after referred to as “condenser”).
This standard is applicable to the performance test of water-cooling and steam surface condenser operating in vacuum.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition (including any amendments) applies.
GB/T 8117 (all parts) Rules for steam turbine thermal acceptance tests
GB/T 13930 Methods for the measurement of volume flow of gas of water-ring vacuum pumps and compressors
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
condenser pressure
absolute static pressure maintained at the steam channel within 300 mm above the first row of condenser tube in the condenser shell
3.2
condenser heat load
heat transferred from steam to cooling water in condenser per unit time
3.3
overall heat-transfer coefficient
heat transfer quantity of condenser per unit time, unit surface area and unit temperature difference in consideration of comprehensive factors
3.4
cleanliness factor
ratio of the heat-transfer coefficient of the old condenser tube to that of the new condenser tube or the clean tube, under the same operating conditions
3.5
condensate subcooling
difference between the saturated temperature of steam under condenser pressure and the temperature of condensate
3.6
dissolved oxygen in the condensate
unit content of dissolved oxygen in the condensate
3.7
condenser circulating water pressure losses
difference of static pressure between inlet and outlet of cooling water
4 Symbols
This standard adopts the symbols, subscripts, superscripts and their definitions specified in Tables 1, 2 and 3, unless otherwise specified.
Table 1 Symbols and definitions of performance parameters
Symbol Name Definition Unit
A Condenser area Effective surface area of all cooling tubes in the condenser, plus the area of external air cooler if it is used, which excludes the area of tubes blocked
in the test m2
Cf Cleanliness factor Ratio of the heat-transfer coefficient of the old condenser tube to that of the new tube or the clean tube (almost new), under the same operating conditions —
cp Specific heat capacity at constant pressure Specific heat capacity of cooling water at average temperature and salt content measured during the test J/(kg·°C)
D Tube diameter Diameter of cooling tube m
DO Dissolved oxygen in the condensate Unit content of dissolved oxygen in condensate μg/L
F Fluorescence Concentration of indicator in the measured solution to determine the flow rate in the large-diameter pipe. —
g Gravitational acceleration Constant used in Nusselt equation m/s2
h Heat-transfer coefficient on the convection surface Heat transfer per unit time, unit surface area and unit temperature difference, deemed as the main performance parameter of condenser to be measured W/(m2·°C)
j Variable Summation —
k Thermal conductivity Heat transfer per unit length of material W/(m·°C)
L Length Length of cooling tube m
LMTD Logarithmic mean temperature difference Calculated logarithmic mean temperature difference between steam and cooling water in condenser °C
㏑ Natural logarithm — —
m Relative molecular mass Relative molecular mass —
N Tube number Number of cooling tube Pcs
NTU Number of transfer units — —
n Number of passes Number of cooling tube pass —
P Pressure Absolute pressure of fluid kPa
Pr Prandtl number Ratio of momentum diffusivity to thermal diffusivity —
Q Condenser heat load Heat transferred from steam to cooling water, usually regarded as an independent variable in any condenser test W
R Thermal resistance Heat transfer resistance m2·°C/W
Re Reynolds number Ratio of inertia per unit volume of fluid to viscosity per unit volume —
SCFM Air in-leakage rate Rate of standard air leakage into condenser (at 101.325kPa + 20°C） m2/s
T Temperature Temperature of cooling water, steam or condensate °C
△T Temperature difference Temperature difference between two points in the fluid °C
U Overall heat-transfer coefficient Heat transfer per unit time, unit surface area and unit temperature difference, deemed as the main performance parameter of condenser to be measured W/(m2·°C)
v Flow velocity of cooling water Average flow velocity of cooling water, which is the average flow velocity of each pass for multi-pass condenser due to its different number of cooling tubes in each pass m/s
ω Flow rate of cooling water Cooling water quantity passing through condenser per unit time kg/s
Ws Steam output Mass of steam entering condenser per unit time kg/s
△ Difference Difference between two measured values —
△H Differential pressure Difference of pressure on both sides of flow orifice plate kPa
△P Pressure drop Loss of pressure caused by friction between two points in fluid kPa
μ Dynamic viscosity Strength of viscous shear force in fluid kg/(m·s)
ρ Density Ratio of mass to volume of fluid or solid kg/m3
Table 2 Subscripted symbols and definitions of performance parameters
Symbol Definition Symbol Definition
B Capacity or volume t Tube side
c Cleanliness v Steam
DO Dissolved oxygen w Tube wall
F Film x Low pressure section
f Fouling factor y Medium pressure section
G Non-condensable gas z High pressure section
i Inside the tube 1 Inlet
m Metal 2 Outlet
o Outside the tube 3 Condensate
s Shell or steam △ Difference
sat Saturation condition — —
Table 3 Superscripted symbols and definitions of performance parameters
Symbol Definition
* Value derived from the design basis condition
+ Measured or calculated value under test conditions
0 Test value corrected to design condition
5 General provisions
5.1 Performance parameters
Main performance parameters of condenser are as follows:
a) condenser pressure;
b) condenser pressure corrected to the design conditions;
c) condensate subcooling
d) dissolved oxygen in the condensate;
e) condenser circulating water pressure losses.
5.2 Uncertainty
5.2.1 Uncertainty of test in the main performance parameter code
The requirements for uncertainty are as follows:
a) uncertainty of condenser test pressure: ±0.17 kPa;
b) total uncertainty of condenser pressure corrected to the design condition: ±0.51 kPa;
c) uncertainty of condensate subcooling: ±0.11°C;
d) uncertainty of dissolved oxygen in the condensate: ±4.0 μg/L;
e) uncertainty of condenser circulating water pressure losses: ±9%;
5.2.2 Uncertainty of main parameters in the condenser cleanliness factor comparison test
The requirements for uncertainty are as follows:
a) uncertainty of condenser test pressure: ±0.14 kPa;
b) total uncertainty of condenser pressure corrected to the design condition: ±0.41 kPa;
c) uncertainty of condensate subcooling: ±0.11°C;
d) uncertainty of dissolved oxygen in the condensate: ±4.0 μg/L;
e) relative uncertainty of condenser circulating water pressure losses: ±9%;
5.3 Test scheme
The following contents shall be considered for test scheme:
a) Test purpose (to measure the following parameters and performance, such as condenser pressure, design pressure, subcooling, dissolved oxygen in the condensate, water resistance, tube bank performance, cleanliness factor and fouling thermal resistance);
b) test scope;
c) test duration;
d) test conditions;
e) correction of deviation according to the requirements of this standard;
f) calculation method for overall heat-transfer factor;
g) method for determining the condenser pressure;
h) method for determining the temperature of cooling water;
i) method for determining the flow rate of cooling water;
j) method for determining the condenser fouling;
k) method for determining the uncertainty of dissolved oxygen in the condensate;
l) method for determining the uncertainty of condensate subcooling;
m) method for determining the condenser circulating water pressure losses;
n) measures in case of non-conforming condenser performance test conditions;
o) requirements for test instrument installation;
p) division of test units or systems.
5.4 Test preparation
Before the test, the following contents shall be determined:
a) measurement of test parameters used in calculation;
b) methods for maintaining stability or controlling test conditions;
c) number, location, type and calibration of instrument;
d) confirmation of the opening position of manual and automatic valves;
e) methods for testing leaked water or other inflow;
f) method for determining the conformity of non-condensable gas amount to the requirements;
g) test method for the dissolved oxygen in the condensate (operation instrument measurement and external laboratory test);
h) training on testers and data acquisition and processing personnel;
i) operating conditions during the test;
j) allowable deviation between design conditions, standards and test plan;
k) number of tests;
l) duration of each test;
m) stabilization time before the test;
n) method for determining the effectiveness of repeated tests;
o) measurement frequency;
p) analysis of the test process and factors and timely adjustment of the test parameters to meet the specified conditions. See Table 4;
q) determination of other correction methods not specified in this standard;
r) limitation of failure to meet the design conditions due to external reasons within the specified time, such as the unit can't take full load;
s) determination of the correction method of test results;
t) specific responsibilities of the test parties;
u) distribution of test reports;
v) acceptance criteria for blockage and fouling on the tube side.
5.5 Allowable deviation
The test is carried out under certain inlet temperature of cooling water, condenser heat load and flow rate of cooling water. See Table 4 for the allowable deviation.
Table 4 Allowable deviation of test conditions and specified conditions
Test parameter Allowable deviation of
specified test condition Stability requirement
for condition
Inlet temperature of cooling water ±6°C ±1°C
Condenser heat load ±5% ±2%
Flow rate of cooling water ±5% ±2%
5.6 Test preparation and requirements
5.6.1 System and equipment
5.6.1.1 Before the test, check the related equipment and pipelines connected with the condenser, and confirm the instrument to be used and instrument calibration results.
5.6.1.2 Data collection shall be carried out before the test to ensure that the instrument is connected normally and operating well.
5.6.1.3 Specify the method for measuring fluid flowing in and out of the system, and isolate all drainage or waste liquid related to the test results, including the replenished water that affects the dissolved oxygen in the condensate.
5.6.1.4 See Annex A for test process and precautions, and Annex B for operation performance test.
5.6.2 Non-condensable gas
5.6.2.1 The in-leakage rate of non-condensable gas shall meet those specified in Table 5.
5.6.2.2 Before the performance test, measure the volume of non-condensable gas to ensure that the performance of condenser is not affected.
5.6.2.3 See GB/T 13930 for the method for measuring the volume of non-condensable gas.
5.6.2.4 Before the performance test, check and ensure that all air extraction equipment is in good performance.
5.6.2.5 See Annex C for leakage detection of vacuum system, and Annexes D and E for the fault diagnosis of vacuum system or air extraction equipment.
Table 5 Limits of non-condensable gas volume (air in-leakage) in the condenser
5.6.3 Cleaning on the tube side
Check the blockage of tube sheet before and after the test. Before the test, clean the cooling tubes of condenser thoroughly. See 6.9 for quantitative analysis method of fouling on the tube side.
5.6.4 Dissolved oxygen in the condensate
5.6.4.1 When the dissolved oxygen in the condensate is 14 μg/L, the replenished water shall not be more than 5% of the condensate; when the dissolved oxygen in the condensate is 7 μg/L, the replenished water shall not be more than 3% of condensate.
5.6.4.2 When the tested dissolved oxygen in the condensate does not meet the requirements, the air in-leakage rate in Table 5 is not applicable, and the air in-leakage rate shown in Table F.1 in Annex F may be used.
5.6.4.3 In the test, if excessive water replenishment is required or the dissolved oxygen in the condensate exceeds the standard, the test shall be terminated.
5.6.5 Preparative test
Before the formal test, conduct a preparative test to comprehensively check and reasonably organize the whole test links, including data acquisition and result calculation. If the preparative test fully meets the requirements of this standard, the preparative test may be used as a working condition of the formal test.
5.6.6 Test duration
After reaching the stable condition, the data acquisition period of each test condition is not less than 1 h, the reading interval is not more than 5 min, and in the 1 h of test, the collection times of important parameters are not less than thirteen times.
5.6.7 Test data
Test data should be recorded by data acquisition system. At the end of the test, a complete set of test data shall be kept.
Inaccurate data shall be eliminated when sorting out test data. If abnormal data is found in the test, it shall be deleted. If the problem data only appears at the beginning or end of the test, the data will be deemed invalid.
5.7 Test report
The test data can only be deemed as valid if the measuring instrument passes the calibration. The deviated test conditions shall be corrected to the design conditions, and all test results shall be sorted out and included in the report.
6 Measuring instrument and method
6.1 Allowable error
See Table 6 for the maximum allowable error of condenser performance test instruments specified in this standard. The requirements do not exclude the use of advanced technologies and measurement methods not explicitly described in this document, provided that the accuracy requirements in Table 6 can be met.
Table 6 Maximum allowable error of instruments for measurements
Measurement Condenser performance test Cleanliness factor comparison test of condenser
Condenser pressure ±0.169 kPa ±0.135 kPa
Inlet temperature of cooling water ±0.056°C ±0.056°C
Outlet temperature of cooling water ±0.17°C ±0.11°C
Air leakage ±3.397 m3/h ±3.397 m3/h
Effect of cleanliness factor on inlet temperature of scaling tube N/A 0.06°C
Effect of cleanliness factor on inlet temperature of scaling tube N/A 0.42°C
Effect of cleanliness factor on inlet temperature of clean tube N/A 0.06°C
Effect of cleanliness factor on outlet temperature of clean tube N/A 0.42°C
Flow rate of cooling water ±3% ±3%
Condenser circulating water pressure losses ±2% ±2%
Dissolved oxygen ±2 μg/L ±2 μg/L
Note: The maximum allowable error is the uncertainty under the full scale of the instrument. For digital instruments, the full range is the previous order of magnitude corresponding to the data range measured by the instrument; for example, the measurement range of dissolved oxygen in the condensate is 5 μg/L ~ 8 μg/L, and the full range is 10 μg/L; the flow measurement range is 15 000 m3/h ~ 18 000 m3/h, and the full range is 1×105 m3/h.
6.2 Arrangement of measuring points
See Figure 1 for the measuring points of performance test of single-pass single-pressure condenser.
For multi-pass multi-pressure condensers, the positions of measuring points is similar to those shown in Figure 1, and the following points shall be noted:
a) For single-shell multi-backpressure condensers, pressure measuring points shall be added above each group of cooling tube banks in each back pressure condensation area, and the performance of each area may be evaluated with the method for measuring the final outlet water temperature described in 6.4.2 and the temperature rise of each area described in Clause 6.
b) For multi-shell multi-backpressure condensers, additional measuring points for pressure and temperature shall also be added at the cooling water inlet and outlet of each shell. There may be water temperature stratification in cooling water connecting tubes between multi-backpressure condenser shells, and the average inlet temperature of cooling water of medium-pressure or high-pressure shells shall be measured with the method given in 6.4.2.
c) The arrangement of measuring points for double-pass condensers is basically the same as that of single-pass condensers and single-backpressure condensers, and it is unnecessary to measure in the return water chamber.
Keys:
——dissolved oxygen measuring point;
——salinity measuring point;
——flow rate measuring point;
——temperature measuring point;
——pressure measuring point;
——water level measuring point.
Figure 1 Measuring points in the condenser test
6.3 Condenser pressure
6.3.1 Measuring position
6.3.1.1 The condenser pressure is measured 0.3 m ~ 0.91 m above the heat-transfer tube bank.
6.3.1.2 For single-shell or multi-shell condensers, at least three measuring points shall be arranged in each shell. For single-shell multi-backpressure condensers, at least two pressure measuring points shall be arranged in each pressure chamber.
6.3.1.3 When three measuring points are to be arranged, they shall be arranged at intervals of 1/4 of the tube bank length as shown in Figure 1; when two measuring points are to be arranged, they shall be arranged at intervals of 1/3 of the tube bank length. The lateral position of the measuring point shall be close to the lateral midpoint of the tube bank.
6.3.1.4 The area where measuring points are located shall avoid the effect of high-velocity steam flow area or local separation area caused by condenser throat interference.
6.3.2 Primary pressure transmission element
6.3.2.1 Static pressure measuring points on the wall surface
For the steam channel whose wall is parallel to the steam flow direction, according to the requirements of 6.3.1, the static pressure measuring points on the wall surface are longitudinally distributed in the steam channel and shall meet the requirements in this standard. There shall be no obstacles near the joint, and the joint shall be smooth and burr-free. When the static pressure measuring points are not applicable, a mesh cage probe or a baffle probe shall be set at the condenser throat.
6.3.2.2 Mesh cage probe
The typical pressure transmission element of condenser for large steam turbine unit is mesh cage probe. The cage probe has a structure shown in Figure 2, and shall be installed at an angle of 30° ~ 60° from the main flow direction. The structure of exhaust pressure probe of steam turbine given in GB/T 8117 is optional.
Foreword i
1 Scope
2 Normative references
3 Terms and definitions
4 Symbols
5 General provisions
6 Measuring instrument and method
7 Expression of results
8 Test report
Anne A (Informative) Test preparation and flow chart
Annex B (Informative) Operation performance monitoring
Annex C (Informative) Leakage detection of vacuum system
Annex D (Informative) Cause analysis of condenser air lock
Annex E (Informative) Performance analysis of air extraction equipment
Annex F (Informative) Cleanliness factor comparison test
Annex G (Informative) Physical properties of seawater
Annex H (Informative) Calculation example
Bibliography
