Direct air cooling unit low-pressure cylinder no-load heat supply method and heat supply system

Abstract

The invention discloses a direct air cooling unit low-pressure cylinder no-load heat supply method and a heat supply system, the minimum safe steam admission amount and the maximum heat supply steam amount of a low-pressure cylinder under different operation back pressures are determined, the optimal operation back pressure under the current heat supply working condition is given through optimization calculation, and the maximum heat supply capacity of a unit is achieved under the optimal operation back pressure. The steam inlet share of the low-pressure cylinder is reduced by reducing the operation back pressure of the unit, so that the steam exhaust and heat supply share of the medium-pressure cylinder is increased, and the maximum heat supply capacity and peak regulation capacity of the unit are improved; in addition, the optimal operation back pressure of the current heat supply working condition is given through cold end optimization calculation, and effective guidance is provided for economical operation of the unit.

Description

Technical Field

[0001] The invention belongs to the technical field of cogeneration, and in particular relates to a no-load heating method and a heating system for a low-pressure cylinder of a direct air-cooling unit. Background Art

[0002] At present, the main heating method in winter in my country is centralized heating from thermal power plants. Due to its outstanding water-saving advantages, direct air-cooled thermal power generating units are widely used in northern my country, especially in areas with abundant coal resources and scarce water resources, and their share in the power industry is increasing.

[0003] Common heating technologies for air-cooled units are high back pressure heating and steam extraction heating. Under rated conditions, the heating capacity of direct air-cooled units can meet the requirements of peak heating loads. However, due to the rapid development of new energy power and the country's restrictions on "wind and solar abandonment", the power load of thermal power plants is relatively small, thus limiting the heating output of the units. This thermoelectric coupling phenomenon has brought great trouble to winter heating.

[0004] Therefore, conducting research on adaptive heat and power regulation technology for cogeneration units and further exploring the heating and peak-shaving potential of the units have important engineering application value and social significance. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a no-load heating method and a heating system for a low-pressure cylinder of a direct air-cooling unit, so as to achieve the purpose of improving the heating capacity of the air-cooling unit.

[0006] In order to solve the above technical problems, according to one aspect of the present invention, a method for heating a low-pressure cylinder of a direct air-cooling unit without load is provided, comprising the following steps:

[0007] Step 1: determine the minimum safe steam inlet and maximum heating steam volume of the low-pressure cylinder under different operating back pressures;

[0008] Determine the minimum volume flow of the low-pressure cylinder according to the original maximum heating condition of the unit, and quantitatively calculate the minimum safe steam inlet volume of the low-pressure cylinder under different back pressures according to the following:

[0009]

[0010] Among them, G min V is the minimum safe steam intake of the low pressure cylinder. min is the minimum volume flow of the low-pressure cylinder, v c (p c ) is the current back pressure p c The corresponding exhaust steam specific volume;

[0011] The maximum heating steam volume is obtained by subtracting the minimum safe steam volume of the low-pressure cylinder from the steam exhaust volume of the intermediate-pressure cylinder.

[0012] Step 2: The optimal operating back pressure under the current heating condition is given by optimization calculation, and the maximum heating capacity of the unit is achieved by operating under the optimal operating back pressure;

[0013] When the main steam flow of the unit is constant, the minimum safe steam intake of the low-pressure cylinder decreases as the back pressure decreases. By reducing the operating back pressure of the unit, the steam intake share of the low-pressure cylinder is reduced, thereby increasing the exhaust steam heating share of the medium-pressure cylinder.

[0014] As a preferred implementation, the operating back pressure of the unit is reduced by increasing the fan speed.

[0015] As a preferred implementation, the headwind speed after back pressure adjustment is obtained by a back pressure calculation formula, and the fan speed after back pressure adjustment is obtained according to the rated fan speed and the headwind speed.

[0016] As a preferred embodiment, the back pressure p is calculated according to the following formula: c :

[0017] where t s is the condensation temperature.

[0018] As a preferred implementation, when the heating load is constant, within the range of ±5kPa of the current operating back pressure, the unit's power generation increment and the air-cooling fan's power consumption increment are calculated every 0.1kPa. When the difference between the two is the largest, the corresponding back pressure is the optimal operating back pressure of the unit under the current heating condition.

[0019] According to another aspect of the present invention, there is provided a no-load heating system for a low-pressure cylinder of a direct air-cooled unit, comprising a medium-pressure cylinder, a low-pressure cylinder, a heat network heater, a first control valve and a second control valve; the exhaust pipe of the medium-pressure cylinder is connected to a first branch and a second branch respectively, wherein the first branch is connected to an air intake end of the low-pressure cylinder and a first control valve is arranged on the first branch; the second branch is connected to the heat network heater and a second control valve is arranged on the second branch.

[0020] As a preferred embodiment, an air cooling island is further included, and the exhaust end of the low-pressure cylinder is connected to the air cooling island.

[0021] The no-load heating method and heating system for the low-pressure cylinder of a direct air-cooled unit provided by the present invention reduce the steam intake share of the low-pressure cylinder by lowering the operating back pressure of the unit, thereby increasing the exhaust steam heating share of the medium-pressure cylinder, thereby achieving an improvement in the maximum heating capacity and peak-shaving capacity of the unit; in addition, the optimal operating back pressure of the current heating condition is given through cold-end optimization calculation, providing effective guidance for the economical operation of the unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The drawings herein are used to provide further explanation of the present invention and constitute a part of this application. The illustrative embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0023] Figure 1 It is a schematic diagram of the no-load heating system for the low-pressure cylinder of the direct air-cooling unit provided by the present invention;

[0024] Figure 2 It is the minimum steam inlet flow and back pressure curve of the low-pressure cylinder of a direct air-cooled unit;

[0025] Figure 3 It is an iterative flow chart for calculating the power consumption of air-cooling fans.

[0026] In the figure, 1-medium pressure cylinder; 2-low pressure cylinder; 3-air cooling island; 4-heating network heater; 5-first control valve; 6-second control valve. DETAILED DESCRIPTION

[0027] The basic concept of the present invention is that when the main steam flow of the unit is constant, the minimum safe steam intake of the low-pressure cylinder decreases as the back pressure decreases. By reducing the operating back pressure of the unit, the steam intake share of the low-pressure cylinder is reduced, thereby increasing the exhaust steam heating share of the medium-pressure cylinder.

[0028] Based on this, a typical embodiment of the present invention provides a direct air-cooling unit low-pressure cylinder no-load heating method, comprising the following steps:

[0029] Step 1: determine the minimum safe steam inlet and maximum heating steam volume of the low-pressure cylinder under different operating back pressures;

[0030] Determine the minimum volume flow of the low-pressure cylinder according to the original maximum heating condition of the unit, and quantitatively calculate the minimum safe steam inlet volume of the low-pressure cylinder under different back pressures according to the following:

[0031]

[0032] Among them, G min V is the minimum safe steam intake of the low pressure cylinder. min is the minimum volume flow of the low-pressure cylinder, v c (p c ) is the current back pressure p c The corresponding exhaust steam specific volume;

[0033] The maximum heating steam volume is obtained by subtracting the minimum safe steam volume of the low-pressure cylinder from the steam exhaust volume of the intermediate-pressure cylinder.

[0034] Step 2: The optimal operating back pressure under the current heating condition is given by optimization calculation, and the maximum heating capacity of the unit is achieved by operating under the optimal operating back pressure;

[0035] When the main steam flow of the unit is constant, the minimum safe steam intake of the low-pressure cylinder decreases as the back pressure decreases. By reducing the operating back pressure of the unit, the steam intake share of the low-pressure cylinder is reduced, thereby increasing the exhaust steam heating share of the medium-pressure cylinder.

[0036] like Figure 1 As shown, the above method is implemented based on a direct air-cooled unit low-pressure cylinder no-load heating system. The direct air-cooled unit low-pressure cylinder no-load heating system includes a medium-pressure cylinder 1, a low-pressure cylinder 2, an air-cooled island 3, a heat network heater 4, a first control valve 5 and a second control valve 6. The exhaust pipeline of the medium-pressure cylinder 1 is connected to the first branch and the second branch respectively, wherein the first branch is connected to the intake end of the low-pressure cylinder and the first control valve 5 is arranged on the first branch; the second branch is connected to the heat network heater and the second control valve 6 is arranged on the second branch, and the exhaust end of the low-pressure cylinder 2 is connected to the air-cooled island 3.

[0037] Taking a direct air-cooled unit as an example, the minimum safe steam inlet flow and back pressure curve of its low-pressure cylinder is calculated as follows: Figure 2 .according to Figure 2 When the main steam flow of the unit is constant, the minimum safe steam intake of the low-pressure cylinder decreases as the back pressure decreases. Therefore, the low-pressure cylinder steam intake share can be reduced and the medium-pressure cylinder exhaust steam heating share can be increased by reducing the operating back pressure of the unit, thereby improving the unit's maximum heating capacity and peak-shaving capacity.

[0038] Furthermore, the back pressure of the unit can be reduced by increasing the fan speed. The headwind speed after back pressure adjustment can be obtained from the back pressure calculation formula. Since the headwind speed is proportional to the fan speed, the fan speed after back pressure adjustment can be obtained based on the rated fan speed and the headwind speed. The back pressure can be adjusted by adjusting the air cooling fan to operate at this speed. The back pressure calculation process is as follows.

[0039] Calculate the inlet and outlet air temperature difference Δt according to formula (1) a ,

[0040] Δt a =t a2 -t a1 =Q n / A F v F ρc p , formula (1)

[0041] Among them, t a1 ,t a2 are the inlet and outlet air temperatures, Q n A is the heat released by exhaust steam condensation. F is the frontal area, v F is the headwind speed, ρ is the air density, c p is the specific heat capacity of air at constant pressure.

[0042] Calculate the variable operating heat transfer coefficient K' of the air-cooled condenser according to formula (2);

[0043]

[0044] Where K0 is the heat transfer coefficient under design conditions, v F 、v' F are the headwind speeds under design conditions and variable conditions, respectively.

[0045] According to formula (3), the air condenser end difference δ is calculated:

[0046]

[0047] Where A is the outer surface area of ​​the air-cooled condenser fin tube.

[0048] According to formula (4), the condensation temperature t s ,

[0049] t s =t a1 +Δt a +δ, formula (4)

[0050] Calculate the back pressure p according to formula (5): c ,

[0051]

[0052] After adjusting the operating back pressure, the minimum safe steam inlet and maximum heating steam volume of the low-pressure cylinder are calculated. The steam inlet of the low-pressure cylinder 2 is adjusted to the minimum safe value through the first control valve 5, and the heating steam volume is increased to the maximum value through the second control valve 6. The steam inlet of the low-pressure cylinder 2 is mainly to prevent the last-stage blades from blasting and fluttering, etc., to ensure the safe operation of the unit. The exhaust steam of the low-pressure cylinder 2 flows into the air-cooling island 3 to be cooled, and the heating steam flows into the heating network heater 4 through the second branch to heat the heating network return water.

[0053] When the heating load is constant, the unit's operating back pressure and the amount of steam entering the low-pressure cylinder are determined, then the optimal operating back pressure can be given through cold-end optimization calculation to guide the unit's economical operation.

[0054] Within the range of ±5kPa of the current operating back pressure, the unit's power generation increment and the air-cooling fan's power consumption increment are calculated every 0.1kPa. When the difference between the two is the largest, the corresponding back pressure is the optimal operating back pressure of the unit under the current heating condition. At the same time, the air-cooling fan frequency modulation range and the anti-freezing of the air-cooling condenser tube bundle in winter need to be considered.

[0055] According to formula (6), the power generation increment ΔP of the computer group is e ,

[0056] ΔP e =Δhi Gη m η g , formula (6)

[0057] Where Δh i is the effective enthalpy drop increment, G is the exhaust volume of the low-pressure cylinder, η m is the mechanical efficiency of the steam turbine, η g is the generator efficiency.

[0058] The calculation method of the power consumption increment of the air cooling fan is as follows:

[0059] Calculate the exhaust steam condensation heat Q according to formula (7): n ,

[0060] Q n =G(h ev -h ew ), formula (7), where h ev is the exhaust enthalpy; h ew is the enthalpy of condensation.

[0061] Calculate the air heat absorption Q according to formula (8): a , Q a =A F v F ρc p (t a2 -t a1 ), formula (8).

[0062] According to formula (9), the heat transfer capacity Q of the air condenser is calculated as follows:

[0063] Q=(t s -t a1 )A F v F ρc p (1-e -NTU ), formula (9)

[0064] Where NTU is the number of heat transfer units, and the calculation formula is NTU = KA / A F v F ρc p .

[0065] According to formula (10), the power consumption N of the air cooling fan under different wind speeds is calculated.

[0066]

[0067] Among them, N0, N i are the fan power consumption under current working condition and variable working condition, ρ0, ρ i are the air densities under current and variable conditions, q0, q iare the cooling air volumes under current working condition and variable working condition, v0, v i are the headwind speeds under current working condition and variable working condition respectively.

[0068] like Figure 3 The calculation process of air cooling fan power consumption is shown in the figure. Assuming that the air temperature at the outlet of the air condenser is Q n =Q a =Q is the judgment standard, and the outlet air temperature and headwind speed are obtained by iterative calculation, so as to obtain the power consumption increment of the air-cooling fan.

[0069] The scope of protection claimed by the present invention is not limited to the above specific embodiments. For those skilled in the art, the present invention may have various deformations and changes. Any modifications, improvements and equivalent substitutions made within the concept and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A direct air-cooling unit low-pressure cylinder no-load heating method, characterized in that: The following steps are involved: Step 1: determine the minimum safe steam inlet and maximum heating steam volume of the low-pressure cylinder under different operating back pressures; Determine the minimum volume flow of the low-pressure cylinder according to the original maximum heating condition of the unit, and quantitatively calculate the minimum safe steam inlet volume of the low-pressure cylinder under different back pressures according to the following: Among them, G min V is the minimum safe steam intake of the low pressure cylinder. min is the minimum volume flow of the low-pressure cylinder, v c (p c ) is the exhaust steam specific volume corresponding to the current back pressure pc; The maximum heating steam volume is obtained by subtracting the minimum safe steam volume of the low-pressure cylinder from the steam exhaust volume of the intermediate-pressure cylinder. Step 2: The optimal operating back pressure under the current heating condition is given by optimization calculation, and the maximum heating capacity of the unit is achieved by operating under the optimal operating back pressure; When the main steam flow of the unit is constant, the minimum safe steam intake of the low-pressure cylinder decreases as the back pressure decreases. By reducing the operating back pressure of the unit, the steam intake share of the low-pressure cylinder is reduced, thereby increasing the exhaust steam heating share of the medium-pressure cylinder.

2. The method for providing heat to the low-pressure cylinder of a direct air-cooling unit without load according to claim 1 is characterized in that: The operating back pressure of the unit can be reduced by increasing the fan speed.

3. The method for providing heat to the low-pressure cylinder of a direct air-cooling unit without load according to claim 2 is characterized in that: The headwind speed after back pressure adjustment is obtained from the back pressure calculation formula, and the fan speed after back pressure adjustment is obtained according to the rated fan speed and the headwind speed.

4. The direct air-cooling unit low-pressure cylinder no-load heating method according to claim 2 or 3 is characterized in that: The back pressure pc is calculated according to the following formula: where t s is the condensation temperature.

5. The no-load heating method for low-pressure cylinders of direct air-cooling units according to claim 1 is characterized in that: When the heating load is constant, within the range of ±5kPa of the current operating back pressure, the unit's power generation increment and the air-cooling fan power consumption increment are calculated every 0.1kPa. When the difference between the two is the largest, the corresponding back pressure is the optimal operating back pressure of the unit under the current heating condition.

6. A direct air-cooling unit low-pressure cylinder no-load heating system, characterized in that: It includes a medium-pressure cylinder, a low-pressure cylinder, a heat network heater, a first control valve and a second control valve; the exhaust pipeline of the medium-pressure cylinder is connected to a first branch and a second branch respectively, wherein the first branch is connected to the air intake end of the low-pressure cylinder and a first control valve is arranged on the first branch; the second branch is connected to the heat network heater and a second control valve is arranged on the second branch.

7. The direct air-cooling unit low-pressure cylinder no-load heating system according to claim 6 is characterized in that: An air cooling island is included, and the exhaust end of the low-pressure cylinder is connected to the air cooling island.

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