JPH09133308A - Preheating apparatus for feed water of boiler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To always keep feed water temperature to a feed water preheating apparatus not lower than an acid dew point by allowing feed water to bypass the feed water preheating apparatus and directing extracted water from a boiler feed pump to an inlet of a feed water preheating apparatus. SOLUTION: A bypass valve 12 is opened, an Open/Close valve 15 is closed and a water feed valve 14 is switched to an open position. Feed water through an outlet of a deaerator feed water pump 8 bypasses a gas type feed water preheating apparatus (feed water preheating apparatus) 1 and is mixed with feed water from an outlet of the feed water preheating apparatus before being directed into a deaerator 6. Preheated feed water extracted from an intermediate stage of the boiler feed water pump 7 is guided through a feed water pipe 13 into the preheating apparatus 1 to be preheated. Temperature of the feed water mixed at the outlet of the feed water preheating apparatus 1 with the feed water which has passed through the bypass pipe 11 is lower than that in the case of black liquor mono-fuel combustion, but because internal pressure within the deaerator 6 is kept constant by heating vapor, temperature of the feed water at the outlet of the deaerator 6 becomes equal to that in the case of the black liquor mono-fuel combustion. Water extracted from the intermediate stage of the boiler feed water pump 7 and introduced into the feed water preheating apparatus 1 always has a temperature not lower than an acid dew point.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a feed water preheating device for a recovery boiler or the like.

[0002]

2. Description of the Related Art FIG. 2 shows a conventional example of a feed water preheating system in a recovery boiler. In FIG.
Reference numeral 2 is a boiler, 7 is a boiler feed pump for feeding water to the boiler 2, 1 is a gas type water preheater for preheating the feed water, 6 is a deaerator for deaerating the feed water, Reference numeral 8 is a deaerator water supply pump, 5 is a chimney, 3 is a dust collector for purifying exhaust gas from the boiler 2, and 4 is a ventilator.

In the water supply preheating system, the water supplied from the deaerator water supply pump 8 is supplied by the gas type water preheater 1.
Is preheated by the exhaust gas from the boiler 2, degassed by the deaerator 6, and then sent to the boiler 2 by the boiler feed pump 7. In the boiler 2, the heavy oil is exclusively burned only for a short time at the time of starting / stopping.

[0004]

In the recovery boiler equipped with the conventional feed water preheating system as shown in FIG. 2, the heavy oil is burned only for a short time such as when starting / stopping. This is because when switching from black liquor combustion to heavy oil combustion, the sulfur content in the heavy oil combustion gas is higher than the sulfur content in the black liquor combustion gas, so the temperature of the water supply to the water supply preheater 1 is below the acid dew point. Due to the problem that the heat transfer tube in the preheater 1 is corroded.

An object of the present invention is to keep the feed water temperature always above the acid dew point to prevent corrosion of the heat transfer tube of the feed water preheater,
An object of the present invention is to provide a feed water preheating system that enables long-time heavy oil burning operation of a recovery boiler.

[0006]

Means for Solving the Problems The present invention solves the above problems, and the gist of the means is to supply water to a boiler equipped with a water supply preheater for preheating the water supplied to the boiler by the exhaust gas from the boiler. In the preheating system, a bypass pipe line connecting the feed water inlet pipe and the feed water outlet pipe of the feed water preheater by bypassing the feed water preheater, a bypass valve for opening and closing the bypass pipe line, and the feed water preheater. A water supply pipe that connects a water extraction pipe from a boiler water supply pump that supplies the supplied water to the boiler to a water supply inlet pipe to the water supply preheater, and a water supply valve that opens and closes the water supply pipe. It is in the boiler water supply preheater.

According to the above means, when the heavy oil is exclusively burned, the bypass pipe is opened to bypass the feed water preheater to feed the feed water, and when the water extracted from the boiler feed pump is guided to the feed water preheater inlet, the feed water preheater outlet is provided. The temperature of the feed water mixed with the feed water from the bypass pipe passes through the deaerator, so that the feed water temperature at the deaerator outlet and the water extraction temperature of the boiler feed water pump, that is, the feed water temperature sent to the feed water preheater, are exclusively black liquor. It will be equal to the time, will always be kept above the acid dew point, and it will be possible to operate heavy oil burning for a long time.

[0008]

DETAILED DESCRIPTION OF THE INVENTION An embodiment of the present invention will be described in detail below with reference to FIG. FIG. 1 shows a system diagram of a feedwater preheating system for a recovery boiler according to an embodiment of the present invention.

In FIG. 1, 2 is a recovery boiler, 1 is a gas type water preheater for preheating the water supply to the boiler 2 with exhaust gas from the boiler, 7 is a boiler water supply pump for supplying water to the boiler, and 6 is A deaerator, 8 is a deaerator water supply pump, 5 is a chimney, 3 is an electrostatic precipitator, and 4 is a draft fan. The above construction is similar to the conventional one shown in FIG.

Reference numeral 16 is a water extraction pipe for feeding water extracted from the intermediate stage of the boiler water supply pump 7 to a desuperheater (not shown), and a water supply pipe 13 branched from the water extraction pipe 16 is provided.
Is connected to the water supply inlet pipe 17 between the deaerator water supply pump 8 and the gas type water preheater 1, and the water supply pipe 13 is also provided.
A water supply valve 14 for opening and closing is provided.

Further, the bypass pipe 11 is branched from the water supply inlet pipe 17 at the outlet of the deaerator water supply pump 8 and connected to the water supply outlet pipe 18 at the outlet of the gas type water preheater 1, and the bypass pipe 11 is also provided. There is provided a bypass valve for opening and closing and a shutoff valve 15 for opening and closing the feed water inlet pipe line 17 downstream of the branch portion of the bypass pipe line 11.

In the recovery boiler having the water supply preheating system configured as described above, when heavy oil is exclusively burned, the bypass valve 12 of the bypass pipe 11 is opened, the opening / closing valve of the water supply inlet pipe 17 is closed, and the water supply valve of the water supply pipe 13 is closed. Switch 14 to open. As a result, the feed water at the outlet of the deaerator feed pump 8 bypasses the feed water preheater 1 and is mixed with the feed water at the outlet of the feed water preheater to be guided to the deaerator 6.

On the other hand, the preheated feedwater extracted from the intermediate stage of the boiler feedwater pump 7 is guided to the feedwater preheater 1 through the feedwater pipe 13 and preheated by the preheater 1. In this case, the temperature of the feed water mixed with the feed water passing through the bypass pipe 11 at the outlet of the gas-type feed water preheater 1 is lower than that during black liquor firing (when the bypass pipe 11 is closed), but degassing is performed. Since the internal pressure of the vessel 6 is kept constant by the heating steam, the feed water temperature at the outlet of the deaerator 6 becomes the same during the black liquor exclusive firing. This allows
The boiler feed water pump 7 intermediate stage drawing water temperature introduced into the gas feed water preheater 1 via the feed water pipe 13 is always maintained at the acid dew point or higher, and the heavy oil exclusive firing operation can be performed for a long time.

[0014]

The present invention is configured as described above.
According to the present invention, the feedwater temperature from the boiler feedwater pump that is guided to the feedwater preheater is always maintained at the acid dew point or higher even during the heavy oil burning operation, so that the occurrence of corrosion of the heat transfer pipe of the feedwater preheater is prevented. Therefore, it becomes possible to perform a heavy oil burning operation for a long time.

[Brief description of the drawings]

FIG. 1 is a system diagram of a feedwater preheating system for a recovery boiler according to an embodiment of the present invention.

FIG. 2 is a system diagram of a conventional water supply preheating system.

[Explanation of symbols]

 1 Gas Type Water Supply Preheater 2 Boiler 6 Deaerator 7 Boiler Water Supply Pump 8 Deaerator Water Supply Pump 11 Bypass Pipe 12 Bypass Valve 13 Water Supply Pipe 14 Water Supply Valve 15 Open / Close Valve 16 Water Extraction Pipe 17 Water Supply Inlet Pipe 18 Water Supply Outlet Pipe

Claims (1)

[Claims] 1. A water supply preheating system for a boiler, comprising a water supply preheater for preheating water supply to the boiler by exhaust gas from the boiler, wherein a water supply inlet pipe and a water supply outlet pipe of the water supply preheater are provided with the same water supply preheater. Bypass pipes that connect by-pass, bypass valves that open and close the bypass pipes, and extraction pipes from the boiler feed pump that feeds the water that has passed through the water supply preheater to the water supply preheater. A water supply preheating device for a boiler, comprising: a water supply pipe connected to a water supply inlet pipe; and a water supply valve for opening and closing the water supply pipe.