JPS6224681B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a boiler apparatus for preventing cavitation of a boiler recirculation pump.

When the temperature of the water supplied to the boiler economizer is low, moisture condenses around the economizer pipe wall, and the sulfur content in the combustion gas produces sulfuric acid, which causes low-temperature corrosion that corrodes the pipe body. There is a problem. For this reason, a method has been adopted in which the hot water in the boiler drum is extracted and mixed with the feed water at the inlet of the economizer to increase the temperature of the water supplied to the economizer. In addition, in the case of a boiler having a circulation pump 6, it is necessary to supply the water in the drum, which has been heated by absorbing heat in the evaporator 4, to the water supply pipe from the viewpoint of rapid startup of the boiler. be. FIG. 1 specifically shows this method. In the figure, the water supply W ₁ passes through the water supply pump 1, the water supply heater 2, and then the water supply pipe 21 to the energy saver 3.
However, because the level of temperature rise in the heater 2 is insufficient to prevent low-temperature corrosion of the economizer 3 and because of the rapid start-up, the hot water supply pipe 15
The hot water _W2 in the boiler drum 5 is supplied by this. 6 is a recirculation pump that supplies hot water _W2 . In this boiler device, when the boiler load suddenly decreases, the hot water W ₂ in the hot water supply pipe 15 partially evaporates on the upstream side of the circulation pump 6 due to the sudden pressure drop. Therefore, there is a risk that cavitation may occur in the circulation pump 6 and the pump may be damaged. Second
The figure shows the relationship between boiler pressure and enthalpy of saturated water in hot water _W2 . If the boiler was operating at pressure P ₂ and is now lowered to P ₁ , if the pressure drop is gradual, the temperature of hot water W ₂ will also drop from T ₂ to T ₁ in response to the pressure drop. As it gradually descends, the hot water maintains a saturated state. On the other hand, when the pressure drop is rapid, the temperature drop of the hot water near the inlet of the circulation pump 6 cannot correspond to the pressure drop, and the pressure drops to _P1 while being close to the temperature _T2 . In other words, in the figure, the hot water descends to the temperature T ₁ via point A, and the enthalpy Q ₂ of the hot water is greater than the enthalpy Q ₁ for pressure P ₁ , so there is no steam in the hot water. Bubbles are generated and the circulation pump 6 causes cavitation.

In addition to the above reasons, near the inlet of the circulation pump, there is a pressure drop in the hot water in the suction side pipe line due to the suction force of the circulation pump, which promotes steam generation in the hot water on the pump suction side. For these reasons, a method has been implemented in which a cooling water supply conduit 16 is provided on the inlet side of the circulation pump 6 and the feed water on the upstream side of the feed water heater 2 is injected to prevent cavitation. However, in reality, the amount of cooling water injected is more than twice the theoretical value that can prevent cavitation for safety reasons. For this reason, the capacity of the circulation pump must be increased unnecessarily, resulting in high equipment and operating costs.
Furthermore, since a large amount of cooling water is supplied, a problem arises in that the efficiency of the entire boiler is reduced.

An object of the present invention is to eliminate the above-mentioned problems and provide a boiler device that supplies the minimum amount of cooling water necessary to prevent cavitation of the boiler.

In short, this invention focuses on the fact that the pressure change in the boiler drum occurs before reaching the circulation pump, and controls the amount of cooling water supplied in response to the pressure change in the boiler drum, thereby achieving cavitation with the minimum amount of cooling water necessary. It is designed to prevent this.

Examples of the present invention will be described below.

In FIG. 3, reference numeral 9 is a pressure detector that detects the pressure within the boiler drum 5, 17 is a control box that stores and issues command signals, and 18 is a flow control valve provided in the cooling water supply pipe 16. Among boiler load controls, rapid load fluctuations are normally handled by the valve 20 of the steam pipe 19 connected to the superheater 8, but the pressure change caused by the adjustment of this valve 20 is controlled by the superheater 8 and the boiler drum. 5. The hot water is transmitted to the circulation pump 6 via the hot water supply pipe 15a. Therefore, by detecting the pressure change inside the boiler drum 5 and adjusting the amount of cooling water supplied, the hot water near the inlet of the circulation pump 6 will be subcooled, making it possible to control the hot water before it starts to evaporate. . The control method will be specifically explained below.

First, the pressure detector 9 detects the pressure within the boiler drum 5, and inputs this as a signal to the differential circuit 10 of the control box 17. The differentiating circuit 10 calculates the rate of change in pressure based on this signal, and inputs this rate of change to the flow rate adjustment circuit 11 . The flow rate adjustment circuit 11 stores in advance the amount of cooling water supplied corresponding to the rate of change in pressure, and calculates the amount of cooling water to be injected.
In this case, since cavitation also occurs due to a pressure drop based on the suction force of the circulation pump 6, this pressure drop is also included in the calculation. However, since this pressure drop can be quantitatively determined by the operating state of the circulation pump 6, this pressure drop is also stored in the control box in advance. Once the supply amount of cooling water has been determined through the above process, the valve 18 is adjusted to supply a predetermined amount of cooling water to the hot water supply pipe 15 upstream of the circulation pump 6, and cavitation is applied to the circulation pump 6. prevent the occurrence of Next, the hot water in the hot water supply pipe 15 joins the water supply W ₁ in the water supply pipe 21 , and if necessary, after raising the water supply W ₁ to a predetermined temperature, it passes through the energy saver 3 and the evaporator 4 . It flows into the boiler drum 5. The steam in the drum is transferred to superheater 8
After being superheated at , it is passed through a steam pipe 19 and used in a predetermined device.

By carrying out this invention, the minimum amount of cooling water necessary to prevent cavitation of the circulation pump is supplied, so the capacity of the circulation pump is not unnecessarily increased, which is economical.

Furthermore, since a large amount of cooling water is not supplied, the thermal efficiency of the entire boiler can be increased.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing a conventional boiler water circulation state, FIG. 2 is a line diagram showing the relationship between pressure and hot water saturation temperature, and FIG. 3 is a system diagram of a boiler apparatus according to the present invention. 3... Energy saver, 5... Boiler drum, 6... Circulation pump, 9... Pressure detector, 15... Hot water supply pipe, 16... Cooling water supply pipe, 18... Flow rate control valve, 21 ...Water supply pipe.

Claims (1)

[Claims] 1. Connect the boiler drum and the water supply pipe that supplies water to the economizer with a hot water supply pipe that has a circulation pump, and connect the cooling water supply pipe to the upstream side of the circulation pump of the hot water supply pipe to create a circulation pump. In order to prevent cavitation in the boiler drum, a pressure detector is installed in the boiler drum, and the pressure detector and the flow control valve of the cooling water supply pipe are connected to a control box that emits memory and command signals through a signal circuit. A boiler device that prevents cavitation of a circulation pump and is characterized by controlling the amount of cooling water injected in response to pressure changes.