JPS5837405A - Method of controlling once-through boiler with circulator - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] The present invention relates to a method for controlling a once-through boiler with a circulation device.

In the evaporator of a once-through boiler, when the load is low and the amount of water flowing through decreases, flow imbalance and flow vibration occur. This is because when the flow rate in one tube of an evaporator consisting of parallel tubes decreases, evaporation becomes more active, so the flow resistance in that tube increases and the flow rate decreases even more. Since this phenomenon occurs at a low load below the normal shaft load, when the boiler 2 is used at this low load, a circulation device is provided to set the amount of water flowing through the evaporator to a flow rate corresponding to the false load or higher. The circulation system consists of a steam/water separator, a separation tank, a circulation pump, etc. At a low load below the i load, the water level appears in the separation tank and the circulation pump operates, and at a high load exceeding the false load, the water level in the separation tank rises. disappears and the circulation pump stops.

However, the characteristics of the water level in the separation tank are static characteristics when the load on the boiler does not change, and when the load changes rapidly, the water level in the separation tank may not appear or disappear depending on the load. . For example, when a high load that exceeds the false load suddenly changes to a low load that is below the light load, the water level in the separation tank does not appear immediately due to the heat capacity of the evaporator, and therefore the circulation pump cannot be operated, and the water supply t is reduced due to the reasons mentioned above. Therefore, the load cannot be lowered below the i load equivalent amount.

However, in conventional boiler control methods, the amount of water and fuel are always supplied at a constant ratio, so in this case, the amount of fuel also becomes a value equivalent to the same false load as the amount of water, and therefore the load range This situation will continue until the water level reaches the separation tank and the circulation pump starts operating.

The present invention was made in order to solve the problems of the conventional boiler control method, and it changes the water supply amount at the time of load change so that the sum of the circulating water amount becomes a predetermined value, and controls the fuel amount depending on the load. It is an object of the present invention to provide a method for controlling a once-through boiler with a circulation device, which controls the main steam pressure drop to a predetermined value, which is determined by the opening degree of the main steam valve.

An embodiment of the method for controlling a once-through boiler with a circulation device according to the present invention will be described in detail below. The figure shows a once-through boiler with a circulation device and its control device, which implements the main function. It consists of a desuperheater 5 between the superheaters 4 and 4', a separation tank 6 provided in the path from the steam separator 8 to near the inlet of the evaporator 2, and a circulation charge including a microvolume bombeuf. There is. This once-through boiler with a circulation device is provided with a control device, and the control device is installed on the outlet side of the water supply pump 1, and includes a special water supply control valve 8 and a water supply amount regulator 9 that controls this, and a fuel supply path 10. the main steam valve 14 installed in the main steam pipe 115 and the steam amount regulator IIs that controls it, the evaporator sudden inlet (water supply and circulation (on the evaporator 2 side rather than the water confluence point) K equipped with a feedwater flow meter 16, a selector 1f that selects the larger of the load signal and the dynamic load signal, a boiler outlet pressure gauge 18, and the outlet side of the circulation pump 7. A circulating water regulator that controls the pressure so that the water level of the circulating water regulating valve 19 and separation tank 6 provided in the is constant! It is composed of IO.

Note that although the actual control device is complicated as it includes various correction circuits, feed forwards, etc., parts that are less relevant to the present invention have been omitted.

Now, in the once-through boiler with a circulation device and its control device configured as described above, when it is desired to lower the load from a high load exceeding the expected load to a low load below the light load, the required load signal is sent to the steam amount controller 15. When the main steam valve 14t is opened to the required degree, the output of the turbine becomes a value commensurate with the required load.

However, since the amount of steam generated by the boiler does not decrease, the steam pressure at the inlet of the main steam valve 14 (boiler outlet) becomes too high. Therefore, this pressure is measured by the boiler outlet pressure needle 18, and the opening degree of the fuel control valve 11 is controlled by the fuel amount regulator 1z so that this pressure becomes a predetermined value (constant or a function of load), thereby reducing the fuel amount. The amount of water supplied at this time has been controlled so far to match the load signal, but when the required load becomes the shaft load Klk, the separator 17 operates and picks up the almost load signal and sends it to the evaporator 2.
The water supply control valve 8 is activated by the signals from the water supply flow meter 16 and the water supply amount regulator 9 so that the water supply amount at the 0 inlet becomes the amount corresponding to the i load.
operate. The circulation pump 7 does not operate until the water level appears in the separation tank 6, and starts operating once the water level appears, and the circulating water control valve 19 is controlled so that the water level in the separation tank 6 is constant. As the amount of circulating water increases, the water supply flow rate decreases. Since the amount of fuel is once rapidly reduced as described above, the amount of steam generated by the evaporator B is small, and therefore the amount of water entering the separation tank 6 is increased, so that the water level appears rapidly. At this time, the inlet steam pressure of the main steam valve 14 decreases, so the amount of fuel increases, and eventually the amount of water and the amount of water supplied are reduced to match the load.

Prize: In the control method of the present invention, the amount of generated steam is temporarily large (the amount of generated steam does not decrease due to the heat capacity of the evaporator 2),
Although the amount of fuel may decrease and the superheated steam temperature may decrease,
In such a case, by adjusting control variables such as the proportional band of the fuel amount regulator 1z, it is possible to easily limit the amount and speed of decrease in the fuel amount. Similarly, if it is desirable to set a lower limit on the amount of fuel, it can be easily controlled using the 4-hour control mechanism.

As described in detail above, the control method for a once-through boiler with a circulation device according to the present invention changes the water supply amount at the time of load change so that the sum of the circulating water amount becomes a predetermined value, and the fuel amount is controlled by the main steam valve controlled by the load. Since the main steam pressure, which is determined by the opening of can. Therefore, there is no flow imbalance or vibration in the evaporator, no drop in steam temperature at any part of the boiler, and no troubles.

[Brief explanation of the drawing]

The figure is a system diagram of a once-through boiler with circulation system equipped with a control system [i]. 1... Water supply pump 2... Evaporator 8... Steam/water separator 4.4'... Superheater 5... Superheat reducer 6.
...Separation tank? ...Circulation pump 8...Water supply control valve 9...Water supply amount regulator 10...Fuel supply path
11...Fuel control valve 12...Fuel amount regulator 18
...Main steam pipe 14...Main steam valve 16...Steam t
a moderator 16...water supply flowmeter 17...selector 1
8... Boiler outlet pressure gauge 19... Circulating water control valve
20...Circulating water regulator

Claims (1)

[Claims] In a once-through boiler with circulating capacity, the amount of water supplied at the time of load change is changed so that the sum of the amount of circulating water becomes a predetermined value, and one fuel amount is changed to the main amount determined by the opening degree of the main steam valve controlled by the load. A method for controlling a once-through boiler with a circulation device, characterized in that the steam pressure is controlled to a predetermined value.