JPS6252122B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to boiler operation technology, and specifically to a control method and apparatus for operating a variable pressure once-through boiler apparatus.

In variable pressure boiler systems, the throttling pressure changes with load. Ideally, the throttle valve on the turbine would be left wide open and the throttle pressure would vary directly with load. This type of variable pressure operation is desirable because it can increase the efficiency of the turbine. However, the primary incentive for variable pressure operation is the ability to increase the number of times the turbine can be loaded and unloaded. This is because the change in pressure temperature at the first stage steam outlet of the turbine is relatively small, minimizing thermal stress in the metals that make up the turbine. In contrast, in constant pressure type operation, the first steam outlet temperature is load dependent. This can cause large temperature changes in the turbine, which can cause excessive metal fatigue in the metal.

For the reasons stated above, it has become desirable to develop a control method and apparatus for controlling the operation of once-through boilers so as to utilize a variable throttle pressure type of operation over a very wide load range.

The present invention solves the above-mentioned and other problems associated with the prior art by providing a control method and apparatus that allows variable throttle pressure operation to be introduced at as low a load as possible and available over most load operating ranges. It is something. This involves opening the turbine valve to approximately 70% of its full open position as soon as possible when the boiler system is being loaded, utilizing the flush tank during this time until the load demand exceeds the required minimum feedwater flow rate, and then increasing the load. This is accomplished by causing the boiler system to enter a variable throttling pressure operating mode until the throttling pressure approaches the set operating pressure. Thus, at the point when the throttle pressure approaches the set operating pressure mentioned above, the turbine valve is adjusted to meet the load demand. Essentially, the control method and apparatus of the present invention provides approximately 20%
Enables variable pressure operation from to 75% load, and enables smooth transitions from low load operation to variable pressure mode of operation, and from variable pressure mode of operation to full pressure mode of operation. In addition, control regulators are provided to monitor and modify steam flow rate, combustion rate, and feed water flow rate during the variable pressure mode of operation. In this way, the present control method and device
Deviations of these parameters from the desired ones can be automatically adjusted and compensated for.

In view of the above points, one object of the present invention is to provide a control method and apparatus that allows variable throttling pressure operation of a once-through boiler.

Another object of the invention is to provide a control method and device that allows a once-through boiler to be operated in a variable pressure operating mode over a wide range.

Yet another object of the present invention is to provide a control method and apparatus for a once-through boiler that provides smooth transitions from a low load type of operation to a variable pressure mode of operation and from a variable pressure mode of operation to a full pressure mode of operation. That's true.

These and other objects and advantages of the invention will become apparent from the following description of a preferred embodiment, taken in conjunction with the drawings. The drawings are for the purpose of illustrating preferred embodiments and are not intended to limit the invention.

FIG. 1 is a schematic diagram of a boiler system 10 used by the control device of the present invention. The boiler system 10 mainly has an output of a primary superheater 14.
a furnace 12 connected to a flash tank 16, a secondary superheater 18 whose output is connected to the input of a turbine 20 via a turbine valve 22, a generator 23;
and a condenser 24. The condenser 24 includes a low pressure heater 26, an air separator 28, and a boiler feed water pump 3.
0 and to the input of the furnace 12 via a high pressure heater 32.

The primary superheater 14 is connected via a valve 34 to the input of the flash tank 16 and
6 is connected to the secondary superheater 18 via a valve 36. A pair of valves 38 and 40 are connected in parallel between the input of valve 34 and the output of valve 36. valve 42
is provided between the flash tank 16 and the condenser 24, and controls the flow of water from the flash tank 16 to the condenser 24. Secondary superheater 1
A superheated steam temperature reduction valve 44 is provided between the output of 8 and the flash tank 16.

The operating principle of this boiler system will be explained with reference to FIG. In FIG. 2, % pressure or valve opening is shown versus % load, and flash tank pressure, furnace pressure, turbine valve position and throttle pressure are illustrated. The purpose of the boiler system is to obtain variable throttling pressures at as low a load as possible, to allow a smooth transition from low load operation to once-through operation, and to maintain the function of the control regulator 50 shown in FIG. 3 during the variable throttling pressure mode of operation. It is to combine. This is done by operating the flash tank 16 until dry by opening the turbine valve 22 as soon as possible and by opening the valves 38 and 40 between the primary superheater 14 and the secondary superheater 18, as will be explained later. This is accomplished by using the as a throttle valve. A unique feature of this control method is that, except at minimum pressures, the throttle pressure is not directly controlled, but is allowed to float to the level required for the desired load. In this way, variable pressure operation is achieved over a significant portion of the load range.

In order to accomplish the above-mentioned objectives, an organic configuration of a boiler system is shown in FIG. In this figure, the incoming control signal is transmitted to the unit load request generator 5.
2, and the output of the device is supplied to a control regulator 50 and a turbine valve program 54, a steam flow modifier 56, a combustion rate modifier 58, a feed water flow modifier 60, and also controls valve 36. Masu. The turbine valve program 54 includes the turbine valve 2
2, and the steam flow rate changer 56 controls the operation of valve 3.
8 and 40, and the combustion rate changer 5
0 controls the mixing of fuel and air within the boiler system, and the water feed rate modifier 60 adjusts the feed water flow rate in the boiler system. A pressure transmitter 62 is connected to the control regulator 50 and the control valve 34; an electrical transmitter 64, a feed water temperature transmitter 66 and a superheater temperature transmitter 68 are also connected as inputs to the control regulator 50; The device 50 regulates the steam flow rate modifier 56, the combustion rate modifier 58, and the feed water flow rate modifier 60 by the generated control signals.

With this control method and device, there are basically three operating modes: low load operation, flow-through variable pressure operation and full pressure operation. Low load operation is
Occurs when the boiler feed water flow is limited to its minimum flow. Through-flow variable pressure operation occurs when the feed water flow rate exceeds its minimum flow rate and continues until the throttling pressure reaches the full set pressure or furnace pressure. Full pressure operation occurs when the throttle pressure reaches the full set pressure and continues until full load is reached.

During low load operating mode, i.e. 0 to about 25%
During loading, the throttle pressure is held constant and the turbine valve 22 is rapidly opened to about 70% of its full open position, as shown in FIG. In this mode of operation, valves 38 and 40 are closed and valve 3
4 and 36 are opened along with turbine valve 22. Valve 34 controls furnace pressure, while valve 36 controls throttle pressure. Valve 42 is also opened to regulate the water level in flush tank 16. During this mode of operation, all flow from the furnace 12 is delivered to the flash tank 16, starting as water and becoming steam as combustion is increased. Flash tank 16
acts as a steam and water separator, supplying water to condenser 24 and steam to turbine 20. By the time the steam flow supplied to the turbine 20 is equal to the minimum feedwater flow rate of approximately 25%, the flash tank 1
6 will be dry. At that time, valve 40 opens and valves 34 and 36 begin to close, stopping flow to flash tank 16. This occurs at approximately 25% of load and initiates the next operating mode: variable throttle pressure operating mode or flow-through variable pressure operating mode.

In the flow-through variable pressure mode of operation or the variable throttle pressure mode of operation, the turbine valve 22 is controlled by the turbine valve programmer 54 to approximately 70% of its full open position.
will be maintained. During this mode of operation, steam flow is regulated by valve 40, which essentially acts as a remote throttle valve. In this mode of operation, the feed water flow is responsible for controlling the steam temperature, while the combustion rate controls the load, and the throttling pressure is
It is allowed to float to the value necessary to meet the load requirements. Control regulator 50 performs an important function in this mode of operation. That is, the regulator generates error or correction signals to steam flow modifier 56, combustion rate modifier 58, and feedwater flow modifier 60. These error or correction signals operate as follows. The megawatt error minus the furnace pressure error controls the signal provided to the steam flow modifier 56, the megawatt error plus the furnace pressure error controls the signal provided to the combustion rate modifier 58, and the superheat temperature error plus the feedwater temperature controls the signal provided to the water supply flow rate modifier 60. In this manner, the feedwater flow rate can be adjusted to maintain steam temperature, while the steam flow and combustion rate can be modified to maintain proper furnace pressure and megawatts.

Once valve 40 reaches the fully open position, valve 38 begins to open and turbine valve 22 begins to open further from the 70% open position. This initiates the next mode of operation, the full pressure mode of operation.

In the full pressure operating mode, the throttle pressure reaches the full set pressure and the turbine valve 22 is opened further to maintain the required load. In this mode of operation, steam flow is controlled by turbine valve 22 rather than valve 40, and the combined capacity of valves 38 and 40 is greater than that required by turbine valve 22 as it opens further from the 70% open position. sufficient to provide steam flow. Note that in non-variable pressure once-through boiler systems, such as in the prior art, this is a one-time normal operating mode above the minimum feedwater flow rate, and thus a variable pressure operating mode is never introduced.

The control method and apparatus described above provides numerous benefits. For example, by using variable pressure,
The first stage steam temperature can be closely controlled, allowing rapid loading of the turbine without excessive thermal stress. In addition, the present control method and apparatus allows rapid achievement of variable pressure operation, temperature matching of the turbine metal and smooth conversion to flow-through operation. Finally, a control regulator controls the overall operation of the boiler system in the variable pressure mode of operation and adjusts the various elements of the boiler system to compensate for various operational deviations.

Those skilled in the art will be able to devise various modifications and improvements from the above description without departing from the scope of the claims.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a boiler system utilizing the present invention; FIG. 2 is a graph of % pressure or valve opening versus % load; a graph showing flush tank pressure, furnace pressure and turbine valve position and throttle pressure lines; FIG. 3 is a schematic diagram illustrating a complete boiler system utilized in accordance with the present invention. 10: Boiler system, 12: Furnace, 14: Primary superheater, 16: Flash tank, 18: Secondary superheater, 20: Turbine, 22: Turbine valve, 2
3: Generator, 24: Condenser, 26: Low pressure heater, 28: Air separator, 30: Boiler feed water pump, 32: High pressure heater, 34, 36, 42: Valve,
44: Superheated steam temperature reduction valve.

Claims (1)

[Claims] 1. A method for controlling a once-through boiler under a low-load operating mode and a once-through variable pressure operating mode and a full-pressure operating mode, comprising: directing the flow of steam from the means 14, 18 for generating steam to the turbine 20 via the tank 16, said means 14 for generating steam in response to a load demand during the once-through variable pressure mode of operation of the once-through boiler; ,18
during the once-through variable pressure operation mode and the full pressure operation mode of the once-through boiler, the steam generating means 14,1
A method for controlling a once-through boiler comprising directing a flow of steam from 8 to a turbine 20 and bypassing said flash tank 16. 2. A control device for a boiler 10 supplying steam to a load under various load conditions, comprising: means 14, 18 for generating steam; and connecting the steam generating means 14, 18 to the load;
Under all load conditions, said steam generating means 14,
connecting means comprising a first valve 22 for controlling the flow of steam from 18 to the load;
a flush tank 16 selectively interconnected with the steam generating means 14, 18 and the first valve 22 during a low load operating mode of the controller; a second valve 34, 36 operable to connect said steam generating means 14, 18 to said first valve 22 during full pressure and through variable pressure modes of operation of the controller; a third valve 40 operable to bypass the valves 34, 36 of the steam generating means; and during a full pressure operating mode of operation of the controller, the third valve 40 is flow-connected in parallel with the third valve 40 and is operable to bypass the valves 34, 36 of the steam generating means. 14 and 18 to said first valve 22. 3. Said first valve 22 opens to a predetermined position during the through-flow variable pressure mode of operation and during the low load mode of operation of the control device, and from this predetermined position during the full pressure mode of operation of the control device. A control device according to claim 2, which is further open.