JPS6115007A - Method of controlling boiler - 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 Field of the Invention The present invention relates to a method for controlling a boiler, and more particularly to a method for controlling a once-through boiler with a steam-water separator.

Conventional technology A once-through boiler with a steam-water separator is a once-through type boiler with a steam-water separator installed between the evaporating section and the superheating section. The remaining 1 in the separator
Since all the moisture is removed and only dry steam enters the superheater, the length of the superheater is always constant (it is not affected by the movement of the evaporation end point).

However, since the starting point of evaporation depends on the feedwater/fuel ratio, if this ratio is not maintained correctly, the dryness of the steam entering the steam separator will change.

If the dryness is low, the flow rate of steam going to the superheater will decrease, and the amount of blow water will increase, reducing efficiency.
If the degree of dryness exceeds 100 degrees, overheating will occur within the evaporator tube and the evaporator tube will be damaged.

For this purpose, conventionally, as shown in Fig. 4, the evaporator tube 1 was constructed with a plurality of parallel structures, and only one of them was equipped with a throttle to reduce the flow rate to a smaller amount than the others. The steam dryness of other steam pipes is estimated based on the degree of overheating, and the amount of water supplied is controlled based on the steam dryness.

Specifically, the steam dryness is estimated by installing a multi-thermostat 3 and detecting the degree of overheating. 4 in Figure 10
5 is a preheating section, and 5 is an evaporation section.

Problems to be Solved by the Invention Since the evaporator tubes 1 need to be constructed in parallel, the installation space is large (cannot be used with the Natsuko Koban boiler).

Since the aperture is provided, the characteristics may change significantly due to the influence of dust or the like or changes over time.

Means and action for solving the problem The amount of water supplied is controlled based on the intermediate temperature of the preheating section to maintain a constant degree of dryness.

Embodiment FIG. 1 shows the relationship between steam temperature and boiler length, and what was the formula (feed water temperature) at the preheating section 100 inlet +08 rises to Ic'I'' until it reaches the outlet 10bK, and the evaporating section 11
The water then flows to the steam separator 12.

Then, the temperature T at one location 10' of the preheating section 10 is measured, and the overall dryness is estimated based on that temperature, and the water supply amount is automatically controlled.

Note that the temperature T11 is the temperature at a position 10' which is sufficiently far away from the preheating section outlet 10b to prevent evaporation.

Here, assuming that the heat transfer in the evaporator tube is uniform, the relationship between the amount of heat transfer and the heat transfer area is (('II-Tl) Cp+xh) : (Th-T
L) Cp=(4+4):L...(1).

From equation (1) becomes.

However, T is the preheating section inlet water supply temperature, T is the measured temperature, T
IS is the evaporation temperature, Cp is the specific heat of the feed water, X is the dryness, h is the latent heat of evaporation, t is the heat transfer area ratio to the T3 temperature measurement point, tl
is the heat transfer area ratio of the preheating section, and 4 is the heat transfer area ratio of the evaporation section, so that 4+4 equals 1.

Since T1 and T5 are usually constant, cp-h is also constant, and in equation (2), measured temperature T2 and dryness xl
i has a constant relationship (Ta = Cz x + CI). However, q and Cg are constants.

Therefore, by measuring T1, Ta= CIX + Q+
By automatically controlling the amount of water supplied so that the dryness level is maintained constant.・Specifically, as shown in Figure 2, the set temperature Tx and the measured temperature T are compared and calculated, and the value is sent to the PiD controller 13.
The water is then sent to the water supply amount controller 14 of the water supply pump to control the amount of water supplied to the boiler 15.

In addition, if the feed water temperature fluctuates, the preheating section inlet temperature Tx
You can correct the amount of water supplied.

In other words, the above formula (2)... (3) Since Tstj is constant and cp-h is also constant, Ts+T1(t-1) = CIX+04 =
(4) becomes. However, C1 and C11 are constants.

Therefore, if T1 and - are measured and the amount of water supplied is automatically controlled to satisfy equation (4), the degree of dryness can be maintained constant.

Alternatively, as shown in FIG. 3, the preheating section inlet temperature (feed water temperature) Tl is sent to the ratio calculator 16 and Tx (4-1)
What is necessary is to calculate, compare the value with the measured temperature -, and calculate the value with the measured temperature Tx.

Effects of the invention: It is compact because there is no need to install evaporation tubes in parallel. [Can also be used in a shed boiler.

Since there is no need to provide a diaphragm, stable control can be achieved without significant changes in characteristics due to the influence of dust or changes over time.

[Brief explanation of the drawing]

Figures 1 to 3 show examples of the present invention; Figure 1 is a table showing the relationship between steam temperature and boiler length; Figures 2 and 3 are diagrams showing the relationship between steam temperature and boiler length;
4 is a block explanatory diagram showing specific examples of different control methods, and FIG. 4 is an explanatory diagram of a conventional example. +oh preheating section, 11 evaporation section, 12 company steam water separator.

Claims (1)

[Claims] In a once-through boiler with a steam/water separator that sends steam to a steam/water separator 12 via a preheating section 10 and an evaporation section 11, the amount of water supplied is controlled based on the temperature at an intermediate position 10' of the preheating section 10. A boiler control method characterized by: