CN113883916B - Air cooling island minimum antifreezing flow calculation method considering various influence factors - Google Patents
Air cooling island minimum antifreezing flow calculation method considering various influence factors Download PDFInfo
- Publication number
- CN113883916B CN113883916B CN202111065700.5A CN202111065700A CN113883916B CN 113883916 B CN113883916 B CN 113883916B CN 202111065700 A CN202111065700 A CN 202111065700A CN 113883916 B CN113883916 B CN 113883916B
- Authority
- CN
- China
- Prior art keywords
- formula
- air cooling
- air
- calculating
- heat exchange
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Active
Links
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F28—HEAT EXCHANGE IN GENERAL
- F28B—STEAM OR VAPOUR CONDENSERS
- F28B1/00—Condensers in which the steam or vapour is separate from the cooling medium by walls, e.g. surface condenser
- F28B1/06—Condensers in which the steam or vapour is separate from the cooling medium by walls, e.g. surface condenser using air or other gas as the cooling medium
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F28—HEAT EXCHANGE IN GENERAL
- F28B—STEAM OR VAPOUR CONDENSERS
- F28B9/00—Auxiliary systems, arrangements, or devices
- F28B9/08—Auxiliary systems, arrangements, or devices for collecting and removing condensate
Abstract
The invention provides a method for calculating the minimum anti-freezing flow of an air cooling island by considering various influencing factors, which considers the influences of steam discharge parameter change, uneven steam flow distribution and dirt thermal resistance, combines the analysis of heat exchange performance of an air cooling condenser with variable working condition calculation, obtains a guiding value of the minimum anti-freezing flow according to data acquired by unit operation measuring points through a series of calculation and correction, and ensures the accuracy and simultaneously gives consideration to the use convenience.
Description
Technical Field
The invention relates to a method for calculating the minimum anti-freezing flow of an air cooling island by considering various influencing factors.
Background
The direct air cooling unit in China is mainly located in arid areas of rich coal in north, and the ambient temperature in winter in the areas is relatively low, so that the freezing prevention of the unit is critical to the safe operation of the unit in winter, while so far, china uses some foreign design and operation experience and some specific operation experience accumulated by the unit, the freezing problem of the air cooling radiator tube bundles in winter can be solved to a large extent, but in the severe cold areas in China, the lowest low temperature in winter can reach about minus 50 ℃, and the freezing prevention in some severe cold areas is deficient, so that the safe, economical and stable operation of the direct air cooling unit is brought with great hidden trouble.
The steam in the single-row pipe air-cooled condenser pipe is subjected to heat exchange condensation with air outside the pipe through the heat exchange pipes and the fins, if the air flow outside the pipe is too large or the steam flow in the pipe is too small, most of the steam can be condensed into water in advance along the pipe side in the pipe bundle, and the steam can be continuously cooled when flowing downwards along the pipe wall, so that the condensed water is gradually changed into supercooled water from saturated water, and the supercooling degree is increased. The fluid slowly freezes when the temperature drops below 0 ℃. After the freezing phenomenon occurs, the steam flow channel becomes narrower, the phenomena of steam flow speed reduction, flow suspension and the like can occur, the freezing area is further increased, and even the tube bundles of the whole cooling unit are frozen down, so that the unit is stopped. Therefore, in order to ensure the safe and stable operation of the direct air cooling unit, the related research on the air cooling island antifreezing technology is significant.
For a typical direct air cooling unit, an air cooling condenser of the direct air cooling unit consists of a large number of single-row serpentine fin tubes. There are two cases of freezing of fluid in the tube:
(1) When the outside environment temperature is lower than 0 ℃, if the steam flow in the condenser tube bundle does not reach the minimum anti-freezing flow specified in the design within a limited time (generally 2 hours), the steam is condensed in the former section of the radiator tube bundle, the condensed water in the latter half section of the tube bundle is supercooled, the condensed water is gradually changed from saturated water into supercooled water, and the supercooling degree is increased until the condensed water is frozen;
(2) When the external environment temperature is lower than 0 ℃, the steam discharge pipeline and the steam distribution pipeline of the steam turbine are not tightly sealed or the steam flow is too low, so that a large amount of air exists in the fin tubes. The non-condensable gas in the fin tubes at the top end of the countercurrent unit is accumulated more and cannot be discharged in time, and the air-cooled condenser tube bundles at the top end of the countercurrent unit can be gradually blocked. The flow of fluid in the fin tube of the radiator is blocked, so that the flow speed is reduced, the fluid is condensed in the first half section of the single-row tube, and supercooling and even icing phenomena occur in the second half section.
From the above, the main reason for freezing the air cooling island is that the steam flow is too low. Therefore, ensuring enough steam in the air cooling island is a key for normal starting and running of the direct air cooling unit in winter. A minimum anti-freezing flow is required to be set, and the exhaust steam quantity of the unit is prevented from being smaller than the minimum anti-freezing flow.
The minimum anti-freezing flow of the current unit is a guiding value directly given by a design manufacturer, and is generally a flow value under given steam exhaust parameters and ambient temperature.
The existing method for determining the minimum anti-freezing flow of the air cooling island mainly has the following problems:
(1) The minimum antifreezing flow value directly provided by manufacturers has limited reference meaning and is inconvenient to use
The minimum antifreeze flow guide value given by the design manufacturer is generally a flow value given the exhaust gas parameters and the ambient temperature, and only represents a few typical working conditions, and the value is also discrete. In actual running of the unit, the working conditions often deviate from the typical working conditions, and the minimum antifreezing flow guiding value cannot be directly used. The minimum antifreeze flow is obtained by interpolation, so that extra errors can be brought, and the obtained value deviates from the true value. In particular, if the value is lower than the true value, the operator performs the operation in this way, which increases the risk of freezing the tube bundle. The minimum antifreezing flow value directly provided by a manufacturer has limited reference significance and is inconvenient to use.
(2) Irrespective of the influence of exhaust parameters
The minimum antifreeze flow guide value given by the design manufacturer is generally the flow value given the exhaust parameters, and the change of the exhaust parameters, namely the influence caused by the change of the exhaust pressure, the temperature and the humidity, is not considered. In actual operation of the unit, the steam exhaust parameters often deviate from given values, and the heat carried by the steam per unit mass is higher/lower than a design value. Moreover, the degree of deviation is large and cannot be ignored by simple calculation.
(3) Irrespective of the influence of uneven steam flow distribution
The design of the air cooling island of the direct air cooling unit is considered according to the steam load distribution of each air cooling unit. However, in actual operation, the pressure distribution of the steam distribution pipeline is very likely to be uneven, so that the steam flow entering the condenser is also unevenly distributed, and the steam flow deviation can reach about 5% during low-load operation of the unit. Particularly, the steam flow of the unit is low in the start-stop process, the heat load change is slow, and the steam flow distribution is uneven, so that the steam flow of part of the air cooling condenser is less, the steam is quickly condensed into water in the forward/backward flow condenser, and the condensed water is quickly condensed into ice in a low-temperature environment in winter, so that the fin tube bundles of the air cooling unit are easily frozen and cracked, the vacuum of the unit is damaged, and the normal operation of the unit is influenced. Therefore, if the problem of unreasonable steam distribution is not considered, even if the total amount of steam reaches the standard, too little steam may occur in some air-cooled condenser columns. At present, the minimum antifreezing flow guiding value given by the design manufacturer does not consider the factor, and is unfavorable for the antifreezing work of the unit.
(4) Irrespective of the influence of thermal resistance change of dirt
The direct air-cooling condenser adopts a finned tube structure, the arrangement of fins is compact, and the fin spacing is small. In the western region rich in coal and poor in water, the environment condition is relatively bad, the sand is large, and dust is more. Dust is thus liable to accumulate on the finned tubes and, in severe cases, to clog the cooling air passages. The heat transfer coefficient of the condenser is reduced due to the increase of the thermal resistance of dirt, the heat transfer performance is deteriorated, the exhaust pressure of the unit is increased, and the temperature of the condensed water is increased. In hot summer, the larger dirt thermal resistance can affect the output of the unit. However, in cold winter, the thermal resistance to fouling can have a positive effect on the freeze protection of the air condenser. This factor should also be considered.
In summary, the method for determining the minimum anti-freezing flow rate of the air cooling island by the guidance value provided by the design manufacturer ignores the influence caused by the change of various influencing factors, reduces the reference meaning, is inconvenient to use and is difficult to meet the needs of anti-freezing work of the air cooling island in winter.
Disclosure of Invention
The invention provides a method for calculating the minimum anti-freezing flow of an air cooling island by considering various influencing factors, which considers the influences of steam discharge parameter change, uneven steam flow distribution and dirt thermal resistance, combines the analysis of heat exchange performance of an air cooling condenser with variable working condition calculation, obtains a guiding value of the minimum anti-freezing flow according to data acquired by unit operation measuring points through a series of calculation and correction, and ensures the accuracy and simultaneously gives consideration to the use convenience.
A method for calculating the minimum anti-freezing flow of an air cooling island by considering various influencing factors comprises the following steps:
(1) Calculating the thermal resistance of dirt;
(2) Calculating the windspeed of the air-cooled condenser at the head-on under the natural ventilation state;
(3) Calculating the minimum anti-freezing flow under the target working condition;
(4) And (3) repeating the step, and calculating the lowest anti-freezing flow under different environment temperatures and exhaust parameters.
Further, the step (1) specifically includes the following steps:
the method comprises the steps of (1-1) searching historical data recorded by a unit to obtain operation data of all air-cooled condenser columns in a certain period of time after winter;
(1-2) calculating the number of heat transfer units based on the operation data;
(1-3) calculating the test heat exchange coefficient of the air cooling island in the selected time period;
(1-4) calculation of fouling thermal resistance Using equation (5)
In the formula (5), K is the test heat exchange coefficient of the air cooling island in the selected time period; k (K) 0 Designing a heat exchange coefficient for the air-cooled condenser; w/m 2 ·℃。
Further, the step (2) specifically includes the following steps:
(2-1) calculating the heat exchange coefficient of the air-cooled condenser in a natural ventilation state;
(2-2) searching parameters related to the calculation of the head-on wind speed by using the performance curve of the air cooling island;
and (2-3) calculating and solving the value of the face wind speed in the natural ventilation state by iteration.
Further, the step (3) specifically includes the following steps:
(3-1) calculating a target working condition heat exchange coefficient considering the influence of dirt thermal resistance;
(3-2) calculating the number of heat transfer units of the target working condition;
(3-3) calculating a target working condition heat exchange amount;
(3-4) calculating the minimum anti-freezing flow of the target working condition;
(3-5) correction of steam flow maldistribution.
When the historical data is obtained, the following requirements need to be met:
1) Before winter, the air-cooled condenser tube bundle is thoroughly and completely cleaned;
2) The selected time period is up to now, the inside and the outside of the air cooling island are not cleaned again;
3) In the selected time period, the operation measuring points of the required data work normally;
4) The length of the selected time period is 1 to 2 hours, each parameter in the time period is stable, no large fluctuation exists, and the data acquisition frequency is 20 seconds/time;
5) The unit load in the selected time period is as high as possible, and all air-cooled condenser rows are put into operation.
Wherein the number of heat transfer units is calculated by formula (1):
in the formula (1), Q p The heat is released for the steam of the air cooling island, and kW; t is t s1 Is the temperature of condensation water, and the temperature is lower than the temperature; t is t a1 The temperature of cold air at the inlet of the air cooling fan is expressed in DEG C；D a1 The inlet air quantity of the air cooling fan is m 3 /s；C pa1 The specific heat capacity is fixed for cold air, kJ/kg DEG C; ρ is the cold air density, kg/m 3 ；
In the formula (1), D a1 The calculation formula is as follows:
in the formula (2), D a For the air quantity of the air cooling fan at the rated rotating speed, m 3 /s；n a The rated rotation speed of the air cooling fan is r/min; n is n a1 The test working condition rotating speed of the air cooling fan is obtained through data acquisition, and the unit is r/min;
in the formula (1), Q p The calculation formula of (2) is as follows:
Q p ＝D p ·(h p -h s1 ) (3)
in the formula (3), D p T/h is the steam flow entering the air cooling island; h is a p Is the exhaust enthalpy value of the steam turbine, kJ/kg; h is a s1 For the condensation enthalpy, kJ/kg is obtained from the condensation temperature obtained by data acquisition.
The test heat exchange coefficient of the air cooling island in the selected time period is calculated by the formula (4):
in the formula (4), A is the heat exchange area of the air cooling island, m 2 。
The heat exchange coefficient of the air-cooled condenser in the natural ventilation state is calculated by the formula (6):
in the formula (6), alpha it W/m is the steam side heat exchange coefficient 2 DEG C; lambda is the coefficient of heat conductivity of the pipe wall, W/m 2 ·℃；α ot Heat exchange for air sideCoefficient, W/m 2 ·℃；A i 、A m 、A o The heat exchange areas of the steam side, the pipe wall and the air side are respectively m 2 ；η o The heat exchange efficiency is the fin;
in the formula (6), alpha ot The calculation formula of (2) is as follows:
in the formula (7), v t And v o The wind speed at the head-on of the air-cooled condenser under the natural ventilation working condition and the design working condition is m/s respectively; alpha o To design the air side convection heat transfer coefficient, W/m 2 ·℃。
The method comprises the following steps of (1) obtaining a face wind speed value in a natural ventilation state through iterative calculation of a formula (9):
in the formula (9), delta is a difference value; v t Is the head-on wind speed in a natural ventilation state, m/s; a is that y Is windward area, m 2 The method comprises the steps of carrying out a first treatment on the surface of the Give v t An extremely low initial value and increases in steps of 0.001 m/s; when the difference delta is lower than the preset absolute value or relative value, the iteration is ended, v t The value is the face wind speed in the natural ventilation state.
The target working condition heat exchange coefficient considering the influence of dirt thermal resistance is calculated by the formula (10):
the number of the heat transfer units in the target working condition is calculated by the formula (11);
the target working condition heat exchange amount is calculated by the formula (12):
Q pm ＝(t s1m -t a1m )A y ·v t ·C pa1tm ·ρ tm (1-exp(1-NTU m )) (12)
in the formula (12), t s1m The temperature of the condensed water is the minimum value defined by design;
the minimum antifreeze flow of the target working condition is calculated by the formula (13):
in the formula (13), h s1m Enthalpy value kJ/kg for minimum condensate temperature defined for the corresponding design; h is a pm And the exhaust enthalpy value is the target working condition.
Wherein, consider steam flow maldistribution, utilize formula (14) to revise the minimum anti-freezing flow of target operating mode:
in the method, in the process of the invention,the correction coefficient for uneven steam flow distribution is 1.05; d (D) pmx The target working condition minimum antifreezing flow value after comprehensively considering various influencing factors is obtained.
The invention has the beneficial effects that:
the invention can rapidly and accurately calculate the minimum anti-freezing flow rate in winter of the direct air cooling unit after comprehensively considering various influencing factors, is convenient for operators to evaluate the current freezing risk of the unit, further makes targeted adjustment, provides basis for starting/stopping of the direct air cooling unit in winter, selects proper starting/stopping parameters, and finally achieves the aim of improving the running safety of the direct air cooling unit in winter.
(1) Good accuracy and high practicability
The calculation method of the present invention considers a variety of influencing factors, including: the steam exhaust parameter change, uneven steam flow distribution, dirt thermal resistance and the like are calculated based on the real performance of the air cooling island, so that the method is more accurate than a method for directly using a design value, and the applicability is effectively improved.
(2) Simple implementation method
The invention does not need to use extra instruments, uses the self-carried operation measuring points of the machine set, has clear and clear calculation process, reasonably simplifies some complex factors, can be executed by a computer, and has simple implementation method.
(3) Improving the anti-freezing capacity of the direct air cooling unit in winter
The invention can help operators evaluate the current freezing risk of the unit, and further make targeted adjustment, thereby effectively avoiding the occurrence of freezing caused by insufficient steam flow of the air cooling island.
(4) Providing basis for starting/stopping the direct air cooling unit in winter
The low steam flow makes the start/stop of the direct air cooling unit difficult in winter, and the invention can provide basis for the start/stop in winter, is beneficial to operators to select proper start/stop parameters, and reduces the risk of freezing during the start/stop of the unit.
In a word, the invention overcomes some defects of the existing method, has obvious improvement in the aspects of accuracy, practicability and implementation convenience, and can provide assistance for normal operation and start/stop of the direct air cooling unit in winter.
Drawings
FIG. 1 provides a graph of performance for a design manufacturer.
FIG. 2 is a schematic diagram of an air cooling island system according to an embodiment.
In fig. 2: 1 is an air cooling island steam inlet pressure measuring point, 2 is an air cooling island steam inlet temperature measuring point, 3 is a steam isolation valve, 4 is each row of condensation water temperature measuring points, 5 is a condensation water tank, and 6 is an air cooling fan.
Fig. 3 is a flow chart of an embodiment of the invention.
Detailed Description
The present invention is further described with reference to specific embodiments thereof, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily think about variations or substitutions within the scope of the present invention.
The technical scheme provided by the invention is described in detail below in connection with specific embodiments.
Two 660MW ultra-supercritical direct air cooling units are built in the third period of Guohua jin, the whole high-level arrangement of the turbine generator set and the arrangement schematic diagram of the air cooling island are shown in figure 2.
Exhaust steam exhausted by the steam turbine is led out of the row A of the steam turbine room through a main exhaust steam pipeline by a flow guide tee joint and is divided into eight exhaust branch pipes to the top of the air-cooled condenser after passing through a section of horizontal straight pipe. Steam enters from a header at the upper part of the air-cooled condenser, and is condensed after surface heat exchange with air; condensed water is collected by a condensed water pipe and is discharged to a condensed water tank or is connected to a temporary system for discharging; the units adopt an 8 multiplied by 8 arrangement scheme (64 fans in total), namely each unit consists of 8 rows of air-cooling condensers, and each row of air-cooling condensers is provided with 8 air-cooling condenser units; the air-cooled condenser consists of a forward tube bundle and a reverse tube bundle.
The main design data are shown in Table 1.
TABLE 1
The minimum winter antifreeze flow provided by the design manufacturer is shown in Table 2.
TABLE 2
Note that: the exhaust parameters corresponding to the data in the table are exhaust pressure 15kPa (a), exhaust enthalpy 2382.2kJ/kg.
According to the method disclosed by the invention, the calculation of the dirt thermal resistance of the air-cooled condenser is firstly carried out.
Step 1, calculating the thermal resistance of dirt.
Step 1.1, searching historical data recorded by the unit, and selecting operation data of the unit in the latest time period after winter.
The following requirements need to be met:
1) Before winter, the air-cooled condenser tube bundle is thoroughly and completely cleaned;
2) The selected time period is up to now, the inside and the outside of the air cooling island are not cleaned again;
3) In the selected time period, the operation measuring points of the required data work normally;
4) The length of the selected time period is 1 to 2 hours, each parameter in the time period is stable, no large fluctuation exists, and the data acquisition frequency is 20 seconds/time;
5) The unit load in the selected time period is as high as possible, and all air-cooled condenser rows are put into operation.
The length of the selected time period of the embodiment is 1.5 hours, and the data acquisition frequency is 20 seconds/time; other aspects of the assembly meet the above requirements.
The main data obtained are shown in Table 3.
TABLE 3 Table 3
And 1.2, calculating the number of heat transfer units according to the acquired unit history data.
The following formula is used:
in the formula (1), Q p The heat is released for the steam of the air cooling island, and kW; t is t s1 Is the temperature of condensation water, and the temperature is lower than the temperature; t is t a1 The temperature of cold air at the inlet of the air cooling fan is DEG C; d (D) a1 The inlet air quantity of the air cooling fan is m 3 /s；C pa1 The specific heat capacity is fixed for cold air, kJ/kg DEG C; ρ is the cold air density, kg/m 3 ；
In the formula (1), D a1 The calculation formula is as follows:
in the formula (2), D a For the air quantity of the air cooling fan at the rated rotating speed, m 3 /s；n a R/min is the rated rotating speed of the air cooling fan; n is n a1 The rotating speed is the rotating speed of the air cooling fan under the test working condition, and is obtained through data acquisition, and r/min;
in the formula (1), Q p The calculation formula of (2) is as follows:
Q p ＝D p ·(h p -h s1 ) (3)
in the formula (3), D p T/h is the steam flow entering the air cooling island; h is a p Is the exhaust enthalpy value of the steam turbine, kJ/kg; h is a s1 Obtaining kJ/kg for condensate enthalpy through condensate temperature obtained through data acquisition;
in the formula (1), the steam turbine exhaust enthalpy h t The value of (2) is calculated by an energy balance method, and the actual power of the final stage group is obtained after the mechanical loss and the motor loss and the power generated by the previous stage groups calculated according to the steam flow and the actual enthalpy drop are subtracted according to the actual power generated by the unit in the selected time period, so that the actual enthalpy drop is obtained, and the exhaust steam enthalpy is obtained; specific procedures will not be described in detail herein.
The result obtained by calculation is: ntu= 1.812.
And 1.3, calculating the test heat exchange coefficient of the air cooling island in the selected time period.
Using equation (4),
in the formula (4), A is the heat exchange area of the air cooling island, m 2 ；
The calculation result is as follows: k=34.551W/(℃·m 2 )；
Step 1.4 calculation of fouling thermal resistance
The heat exchange coefficient of the air-cooled condenser is generally smaller than the design value, which is due to the influence of dirt thermal resistance; and comparing the test value and the design value of the heat exchange coefficient to obtain the dirt thermal resistance, wherein the formula is as follows:
in the formula (5), K 0 Design heat exchange coefficient, W/m for air-cooled condenser 2 ·℃；
Using equation (5), the result is: r is R f ＝0.00204(℃·m 2 )/W。
Step 2, calculating the head-on wind speed of the air-cooled condenser in a natural ventilation state
In winter, all air-cooled condenser rows with steam isolation valves are closed, only the starting row is reserved (no steam isolation valve is installed), and all fans stop running, so that the air-cooled condenser rows are in an optimal anti-freezing running state which can be adopted by a unit under normal conditions, and the minimum anti-freezing flow can ensure that the condensation water temperature of each row of the air-cooled island is not lower than a certain specified value.
Although the fans of all the air cooling units are closed, air still passes through the air cooling fin radiator, so that the fin pipes are cooled, namely natural ventilation heat exchange is used for replacing forced ventilation heat exchange; for simplifying analysis, the natural ventilation refers to the air quantity formed by air convection under the distribution effect of the temperature field of the radiator, and the influence of the natural wind under the atmospheric environment on the air cooling system is temporarily not considered.
The flow resistance and the heat exchange characteristic of the air-swept fin tube bundle are mainly influenced by the head-on wind speed, and are less influenced by the ambient temperature and the wall surface temperature of the fin tube bundle; therefore, the wind speed at the head-on of natural ventilation and heat exchange can take a fixed value; this value is calculated in steps as follows.
And 2.1, calculating the heat exchange coefficient of the air-cooled condenser in a natural ventilation state.
The basic theory of heat transfer theory shows that the total thermal resistance of the air-cooled condenser comprises condensation heat exchange thermal resistance of a steam side, heat conduction thermal resistance of a pipe wall, convection heat exchange thermal resistance of an air side and dirt thermal resistance; therefore, the calculation formula of the heat exchange coefficient of the air-cooled condenser is as follows:
in the formula (6), alpha it W/m is the steam side heat exchange coefficient 2 DEG C; lambda is the coefficient of heat conductivity of the pipe wall, W/m 2 ·℃；α ot Is the air side heat exchange coefficient, W/m 2 ·℃；A i 、A m 、A o The heat exchange areas of the steam side, the pipe wall and the air side are respectively m 2 ；η o Is fin heat exchange efficiency.
The single-row elliptical finned tube used for the air-cooled condenser affects the total heat exchange resistance mainly in the convective heat exchange resistance of the air side; the heat exchange resistance of the pipe wall and the steam side is small, and the change value under different working conditions is also small, so that the heat exchange resistance can be used as a constant value for treatment.
In the formula (6), alpha ot The calculation formula of (2) is as follows:
in the formula (7), v t And v o The wind speed at the head-on of the air-cooled condenser under the natural ventilation working condition and the design working condition is m/s respectively; alpha o To design the air side convection heat transfer coefficient, W/m 2 ·℃。
And 2.2, the relation between the head-on wind speed and parameters such as heat exchange quantity, condensation water temperature and the like.
Solving the head-on wind speed in the natural ventilation state, wherein a performance curve provided by an air cooling island designer is required to be used, and the performance curve is shown in fig. 1; in the figure, the relationship between different environmental temperatures, heat exchange amount and back pressure can be seen after the fans are completely stopped; from the graph, a group of data is selected, and the following relations exist among the data such as the head-on wind speed, the heat exchange amount, the condensation water temperature and the like according to the formulas (1) and (4):
in the formula (8), v t Is the head-on wind speed in a natural ventilation state, m/s; a is that y Is windward area, m 2 The method comprises the steps of carrying out a first treatment on the surface of the The other parameters are defined as before.
And 2.3, calculating the value of the head-on wind speed in an iterative manner.
From formulas (6) and (7), K t Can be expressed as v only t A function of a variable, i.e. K t ＝f(v t ) Thus, there is only one unknown v in equation (8) t The method comprises the steps of carrying out a first treatment on the surface of the Formula (8) cannot be reduced to v t The analytical formula of (2) cannot be directly obtained, and the method of the invention is obtained by carrying out iterative calculation, wherein the calculation formula is derived from formulas (6), (7) and (8), and is as follows:
in the formula (9), delta is a difference value; give v t An extremely low initial value, such as 0.01m/s, and increasing in steps of 0.001 m/s; when the difference delta is small enough (below a preset absolute or relative value), the iteration ends, v t The value is the face wind speed in the natural ventilation state.
Selecting data of the environmental temperature of 10 ℃ and the thermal load rate of 50% as the basis in the figure 1, and deriving the calculation formulas in the step 2.1 and the step 2.2 to obtain the calculation formula in the step 2.3; using equation (9), let v be t The initial value is 0.01m/s, the step length is 0.001, the iteration stop condition is set to be |delta| less than or equal to 0.005, and the result is that: face wind speed v in natural ventilation state t =0.394 m/s, heat exchange coefficient K t ＝8.945W/(℃·m 2 )。
Step 3, calculating the minimum anti-freezing flow under the target working condition
And calculating the lowest anti-freezing flow under the target working condition, namely calculating the lowest steam flow under the specified boundary condition.
The specified boundary conditions, namely specified ambient temperature and exhaust parameters, consider the influence caused by dirt thermal resistance and flow deviation, and stop the fan to meet the condition that the temperature of the condensed water is not lower than a limit value;
the specified boundary conditions are: ambient temperature t a1m = -20 ℃ and exhaust pressure P pm =15 kPa, minimum value of condensate temperature t defined in the operating protocol s1m Taking into account the effects of fouling resistance and flow bias, all fans were shut down, and the steam isolation valves in columns #1, #2, #7, #8 were closed, and only columns #3, #4, #5, #6 were put into operation.
And 3.1, calculating a target working condition heat exchange coefficient considering the influence of dirt thermal resistance.
As can be seen from step 2.1, the heat exchange coefficient is not affected by the ambient temperature, so the calculation formula of the target working condition heat exchange coefficient is:
the results were: target operating mode heat exchange coefficient K tm ＝8.785W/(℃·m 2 )。
And 3.2, calculating the number of the heat transfer units under the target working condition.
The definition of each parameter in the formula (11) is the same as the above.
Using equation (11), the result is; NTU (NTU) m ＝2.524。
Step 3.3 calculating the heat exchange amount of the target working condition
Q pm ＝(t s1m -t a1m )A y ·v t ·C pa1tm ·ρ tm (1-exp(1-NTU m )) (12)
In the formula (12), t s1m The temperature of the condensed water is the minimum value defined by design; the other parameters are defined as before.
Using equation (12), the result is: q (Q) pm ＝149.814MW。
Step 3.4 minimum anti-freezing flow calculation under target working condition
In the formula (13), h s1m Enthalpy value kJ/kg for minimum condensate temperature defined for the corresponding design; h is a pm And the exhaust enthalpy value is the target working condition.
Using equation (13), the result is: d (D) pm ＝238.445t/h。
The energy balance method mentioned in the step 1.2 is used for relatively complicated calculation, and most of steam turbine exhaust steam has certain humidity and is not saturated steam; the data show that the humidity of the final exhaust steam of the steam turbine is generally not more than 10 to 12 percent, and the humidity of the intermediate reheating unit is generally 5 to 8 percent; in order to facilitate calculation, the upper limit of the humidity of the exhaust steam is taken; the higher humidity means that the steam of unit mass carries less heat, so that the processing can avoid the situation that the calculated value is lower than the true value due to the fact that the humidity value is too small, and the calculation is convenient and quick.
And 3.5, correcting uneven steam flow distribution.
In actual operation, the pressure of the steam distribution pipeline is very likely to be unevenly distributed, so that the steam flow entering the condenser is unevenly distributed, and the steam flow deviation can reach about 5% during low-load operation of the unit; if not, D in step 3.4 pm The calculation result of (2) is corrected, and the freezing phenomenon of the individual air-cooled condenser rows and units can occur; the correction calculation formula is:
in the method, in the process of the invention,the correction coefficient for uneven steam flow distribution is 1.05; d (D) pmx I.e. comprehensively consider a plurality ofAnd the target working condition after the influence factors has the lowest antifreeze flow value.
Using equation (14), the result is: d (D) pmx ＝250.367t/h；
D pmx The minimum antifreeze flow value of the target working condition after comprehensively considering various influencing factors has a small phase difference with the reference value 249.0t/h provided by a design manufacturer under the working condition, and the accuracy of the method is verified.
Step 4, repeating the step 3, and calculating the lowest anti-freezing flow under different environment temperatures and exhaust parameters; and summarizing, listing or drawing curves of the lowest anti-freezing flow values of the target working conditions so as to facilitate use.
In summary, the invention relates to a method for calculating the minimum anti-freezing flow of an air cooling island by considering various influencing factors, which can be applied to direct air cooling units with different capacities, has obvious improvement in the aspects of accuracy, practicability and implementation convenience, can provide assistance for normal operation and start/stop of the direct air cooling units in winter, and has a certain application prospect.
The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, or alternatives falling within the spirit and principles of the invention.
Claims (8)
1. The air cooling island minimum antifreezing flow calculating method considering various influencing factors is characterized by comprising the following steps of:
(1) Calculating the thermal resistance of dirt;
(2) Calculating the windspeed of the air-cooled condenser at the head-on under the natural ventilation state;
(3) Calculating the minimum anti-freezing flow under the target working condition;
(3-1) calculating a target working condition heat exchange coefficient considering the influence of dirt thermal resistance;
the target working condition heat exchange coefficient considering the influence of the thermal resistance of dirt is calculated by the formula (10):
in the formula (10), K t The heat exchange coefficient of the air-cooled condenser in a natural ventilation state; k (K) tm The heat exchange coefficient of the air-cooled condenser under the target working condition; r is R f Dirt thermal resistance of the air-cooled condenser;
the number of the heat transfer units in the target working condition is calculated by the formula (11);
in the formula (11), A is the heat exchange area of the air cooling island; a is that y The windward area of the air cooling island; v t Is the head-on wind speed in the natural ventilation state; c (C) pa1tm The constant pressure specific heat capacity of the cold air under the target working condition; ρ tm The cold air density under the target working condition;
the target working condition heat exchange amount is calculated by the formula (12):
Q pm ＝(t s1m -t a1m )A y ·v t ·C pa1tm ·ρ tm (1-exp(1-NTU m )) (12)
in the formula (12), t s1m The temperature of the condensed water is the minimum value defined by design; t is t a1m The temperature of the cold air at the inlet of the air cooling fan under the target working condition is set;
the minimum antifreeze flow of the target working condition is calculated by the formula (13):
in the formula (13), h s1m Enthalpy of minimum condensate temperature defined for the corresponding design; h is a pm The exhaust enthalpy value is the target working condition;
(3-2) calculating the number of heat transfer units of the target working condition;
(3-3) calculating a target working condition heat exchange amount;
(3-4) calculating the minimum anti-freezing flow of the target working condition;
(3-5) correcting the steam flow maldistribution;
(4) And (3) repeating the step, and calculating the lowest anti-freezing flow under different environment temperatures and exhaust parameters.
2. The method for calculating the minimum antifreeze flow rate of the air cooling island taking into consideration the influence factors according to claim 1, wherein the step (1) specifically comprises the following steps:
the method comprises the steps of (1-1) searching historical data recorded by a unit to obtain operation data of all air-cooled condenser columns in a certain period of time after winter;
(1-2) calculating the number of heat transfer units based on the operation data;
(1-3) calculating the test heat exchange coefficient of the air cooling island in the selected time period;
(1-4) calculation of fouling thermal resistance Using equation (5)
In the formula (5), K is the test heat exchange coefficient of the air cooling island in the selected time period; k (K) 0 Designing a heat exchange coefficient for the air-cooled condenser; unit W/m 2 ·℃。
3. The method for calculating the minimum antifreeze flow rate of the air cooling island taking into consideration a plurality of influencing factors according to claim 2, wherein the number of the heat transfer units is calculated by the formula (1):
in the formula (1), Q p The heat is released for the steam of the air cooling island, and kW; t is t s1 Is the temperature of condensation water, and the temperature is lower than the temperature; t is t a1 The temperature of cold air at the inlet of the air cooling fan is DEG C; d (D) a1 The inlet air quantity of the air cooling fan is m 3 /s；C pa1 The specific heat capacity is fixed for cold air, kJ/kg DEG C; ρ is the cold air density, kg/m 3 ；
In the formula (1), D a1 The calculation formula is as follows:
in the formula (2), D a For the air quantity of the air cooling fan at the rated rotating speed, m 3 /s；n a R/min is the rated rotating speed of the air cooling fan; n is n a1 The rotating speed is the rotating speed of the air cooling fan under the test working condition, and is obtained through data acquisition, and r/min;
in the formula (1), Q p The calculation formula of (2) is as follows:
Q p ＝D p ·(h p -h s1 ) (3)
in the formula (3), D p T/h is the steam flow entering the air cooling island; h is a p Is the exhaust enthalpy value of the steam turbine, kJ/kg; h is a s1 For the condensation enthalpy, kJ/kg is obtained from the condensation temperature obtained by data acquisition.
4. The method for calculating the minimum antifreeze flow rate of the air cooling island taking into account a plurality of influence factors according to claim 3, wherein the test heat exchange coefficient of the air cooling island in the selected time period is calculated by the formula (4):
in the formula (4), A is the heat exchange area of the air cooling island, m 2 。
5. The method for calculating the minimum antifreeze flow rate of the air cooling island taking into consideration the influence factors according to claim 4, wherein the step (2) comprises the following steps:
(2-1) calculating the heat exchange coefficient of the air-cooled condenser in a natural ventilation state;
(2-2) searching parameters related to the calculation of the head-on wind speed by using the performance curve of the air cooling island;
and (2-3) calculating and solving the value of the face wind speed in the natural ventilation state by iteration.
6. The method for calculating the minimum antifreeze flow rate of the air cooling island taking into consideration various influence factors according to claim 5, wherein the heat exchange coefficient of the air cooling condenser in the natural ventilation state is calculated by the formula (6):
in the formula (6), alpha it W/m is the steam side heat exchange coefficient 2 DEG C; lambda is the coefficient of heat conductivity of the pipe wall, W/m 2 ·℃；α ot Is the air side heat exchange coefficient, unit W/m 2 ·℃；A i 、A m 、A o The heat exchange areas of the steam side, the pipe wall and the air side are respectively m 2 ；η o The heat exchange efficiency is the fin;
in the formula (6), alpha ot The calculation formula of (2) is as follows:
in the formula (7), v t And v o The wind speed at the head-on of the air-cooled condenser under the natural ventilation working condition and the design working condition is m/s respectively; alpha o To design the air side convection heat transfer coefficient, W/m 2 ·℃。
7. The method for calculating the minimum antifreezing flow rate of the air cooling island by considering various influence factors according to claim 6, wherein the value of the face wind speed in the natural ventilation state is calculated by iterative calculation of the formula (9):
in the formula (9), delta is the differenceA value; v t Is the head-on wind speed in a natural ventilation state, m/s; a is that y Is windward area, m 2 The method comprises the steps of carrying out a first treatment on the surface of the Give v t An extremely low initial value and increases in steps of 0.001 m/s; when the difference delta is lower than the preset absolute value or relative value, the iteration is ended, v t The value is the face wind speed in the natural ventilation state.
8. The method for calculating the minimum antifreeze flow rate of the air cooling island taking into consideration the plurality of influencing factors according to claim 7, wherein the minimum antifreeze flow rate of the target working condition is corrected by using the formula (14) in consideration of uneven steam flow distribution:
in the method, in the process of the invention,the correction coefficient for uneven steam flow distribution is 1.05; d (D) pmx The target working condition minimum antifreezing flow value after comprehensively considering various influencing factors is obtained.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202111065700.5A CN113883916B (en) | 2021-09-10 | 2021-09-10 | Air cooling island minimum antifreezing flow calculation method considering various influence factors |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202111065700.5A CN113883916B (en) | 2021-09-10 | 2021-09-10 | Air cooling island minimum antifreezing flow calculation method considering various influence factors |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN113883916A CN113883916A (en) | 2022-01-04 |
| CN113883916B true CN113883916B (en) | 2023-08-15 |
Family
ID=79008982
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN202111065700.5A Active CN113883916B (en) | 2021-09-10 | 2021-09-10 | Air cooling island minimum antifreezing flow calculation method considering various influence factors |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN113883916B (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114934823B (en) * | 2022-04-25 | 2024-02-13 | 国网河北能源技术服务有限公司 | Method for determining relation between heat supply steam extraction flow and minimum technical output characteristic of extraction condensing heat supply unit |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2312752A1 (en) * | 1975-05-27 | 1976-12-24 | Delas Condenseurs | Air:cooled heat exchanger insert - comprises box with internal baffles and external sheet metal fins |
| CN204705216U (en) * | 2015-06-01 | 2015-10-14 | 天津商业大学 | Leakage resistance vapour type shell-and-tube experiment condenser |
| CN106855365A (en) * | 2015-12-09 | 2017-06-16 | 乔治洛德方法研究和开发液化空气有限公司 | The air cooling tubes condenser unit of running optimizatin |
| WO2017185198A1 (en) * | 2016-04-25 | 2017-11-02 | 谭波 | Air cooler, air cooling island and operation method for air cooling island |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN104114954A (en) * | 2012-02-29 | 2014-10-22 | 吉坤日矿日石能源株式会社 | Method for controlling and device for controlling cogeneration system |
-
2021
- 2021-09-10 CN CN202111065700.5A patent/CN113883916B/en active Active
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2312752A1 (en) * | 1975-05-27 | 1976-12-24 | Delas Condenseurs | Air:cooled heat exchanger insert - comprises box with internal baffles and external sheet metal fins |
| CN204705216U (en) * | 2015-06-01 | 2015-10-14 | 天津商业大学 | Leakage resistance vapour type shell-and-tube experiment condenser |
| CN106855365A (en) * | 2015-12-09 | 2017-06-16 | 乔治洛德方法研究和开发液化空气有限公司 | The air cooling tubes condenser unit of running optimizatin |
| WO2017185198A1 (en) * | 2016-04-25 | 2017-11-02 | 谭波 | Air cooler, air cooling island and operation method for air cooling island |
Also Published As
| Publication number | Publication date |
|---|---|
| CN113883916A (en) | 2022-01-04 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CN103225521B (en) | Air cooling steam turbine cold end optimization method | |
| CN102831302B (en) | Performance calculating method of finned tube evaporator under frosting working condition | |
| CN113883916B (en) | Air cooling island minimum antifreezing flow calculation method considering various influence factors | |
| CN101526313B (en) | Freeze-prevention direct air cooling condenser | |
| EP0390990B1 (en) | Method of condensing steam and installation for use in such a method | |
| CN111879464A (en) | Condenser air leakage exceeding detection method | |
| CN201348447Y (en) | Anti-freezing direct air-cooled condenser | |
| CN113532188B (en) | Steam flow calculation method and device during hot flushing of air cooling island and terminal equipment | |
| CN1173148C (en) | Pressure control system improving power plant efficiency | |
| CN105674760A (en) | Joint air-cooling system and control method | |
| CN205025515U (en) | Condensing steam turbine system based on heat pump | |
| CN111914389B (en) | Cold end system operating point determining method based on curve fitting | |
| CN2924455Y (en) | Direct air-cooling condensator tube bundles | |
| Putman et al. | The cleaning of air cooled condensers to improve performance | |
| CN109783874B (en) | Marine hybrid regulation nuclear turbine unit coupling variable working condition calculation model | |
| CN2779074Y (en) | Modified contranatant steam condensation device of direct air cooling units | |
| CN114458397B (en) | Method for strengthening winter starting performance of small-machine direct-discharge air cooling unit | |
| CN115265221A (en) | Serial-type cooling regulation system, air cooling island system and cooling method | |
| CN114647937B (en) | Variable working condition performance calculation method for cold end system of combined cycle power station | |
| CN216594888U (en) | System for actually measuring running performance of buried pipe of middle-deep geothermal ground | |
| CN113701519B (en) | Method for optimizing circulating water system under condenser separately arranged on main turbine and small turbine | |
| CN214173013U (en) | Air cooling condenser temperature transition interface catching device | |
| CN111306955B (en) | Control system and method of direct air cooling system based on temperature and humidity of vacuumized pipeline | |
| CN113959237B (en) | Coupled steam refrigeration cooling operation optimization method for direct air cooling unit | |
| CN203310273U (en) | 1000MW stage air cooling generator set condenser temperature field monitoring device |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PB01 | Publication | ||
| PB01 | Publication | ||
| SE01 | Entry into force of request for substantive examination | ||
| SE01 | Entry into force of request for substantive examination | ||
| GR01 | Patent grant | ||
| GR01 | Patent grant |