JPS5935712A - Method of preventing corrosion of combustion device - Google Patents

Abstract

PURPOSE:To prevent the lowering of pH of ash treating water by transferring a part of scattered coal ashes arrested by a coal ash arrester provided in a flue or the like to a water-immersion type ash hopper, upon driving a coal-burning combustion device having at the furnace bottom the water-immersion type ash hopper in which ash treating water circulates. CONSTITUTION:In order to cause the device to carry out the pH adjusting operation of ash treating water due to the injection of scattered coal ashes and an operation to prevent contact with circulated combustion waste gas due to suspention in correspondence to the pH of the ash treating water, it is advisable to provide a pH meter 20 concurrently used for a ash water transfer control valve 21 in the water-immersion type ash hopper 2 and an ash water transfer pipe 25, respectively and connect them to each other, and further an ash air transfer control valve 23 in an ash air transfer pipe 24. For instance, if the ash water transfer control valve 21 is set to operate when the pH is lowered to a predetermined value, and the ash air transfer control valve 23 is set to operated at every predetermined time, the lowering of the pH of the ash treating water can be prevented constantly, automatically and stably.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for preventing corrosion of a combustion device, and particularly to a method of preventing corrosion of a coal-fired combustion device in which measures are taken to reduce nitrogen oxides.

Conventionally, in the operation of a coal-fired combustion device, such as a pulverized coal-fired boiler, a portion of the ash in the combusted coal (e.g., 0 to 15% of the total ash amount) is generally absorbed into the water-immersed filter bottom. The ash is dropped into an ash hopper, and other ash is drawn into the flue along with the exhaust gas and collected in various coal ash collectors, and these coal ash are combined and disposed of.

An example of such a conventional ash collection process will be explained in detail with reference to FIG. A portion of the high-temperature coal ash generated in the combustion chamber is transferred to a water-immersed ash hopper 2 installed at the bottom of the furnace 1.
It falls into water and is rapidly cooled to form clinker, a very brittle tissue. This clinker-like coal ash is discharged from the ash gate to the outside of the hopper 2 together with water by a jet nozzle 11 through which high-pressure water is passed from time to time (for example, once every 8 hours), and then crushed by a clinker crusher 3. The pulverized coal ash generated in this way is transferred to a high ejector 4 using high-pressure water, and then sent to a dehydration tank 6 via an ash transfer pipe 5 to be dehydrated, and then transported to an ash dump site by a transport truck 12. Ru. The wastewater separated in the dewatering tank 6 is transferred to the sedimentation tank 8 via the separated water pipe 7, where the remaining coal ash is sedimented and separated, and the water is made into high pressure water by the high pressure water pump 9 at any time.
The water is circulated through the high-pressure water pipe 10 to each of the above locations. In addition, a part of the circulating water is also used as seal water 14 that seals the connection between the furnace bottom 1 and the water-immersed ash hopper 2, and the seal water 14 that flows through the seal part is
It joins the circulating water through the overflow pipe 15 and is circulated. In addition, after the clinker-like coal ash in the water-immersed ash hopper 2 is crushed by the clinker crusher 3,
In addition to transporting the ash from the ash ejector 4 through the above-mentioned route, it is also possible to transport the ash directly from the ash ejector 4 to the ash disposal site via the ash disposal plumber 3. [7] However, in recent years, from the viewpoint of efficient use of water resources and prevention of water pollution, the above-mentioned circulation method, which uses a small amount of wastewater, has become mainstream.

On the other hand, the coal ash that has not fallen into the water-immersed ash pipe 2 enters the flue along with the exhaust gas (hereinafter, such coal ash may be referred to as scattered coal ash). A coal economizer, a dust collector (multi-cyclone, Cottrell), an air preheater, etc. are installed in sequence, and the scattered coal ash in the exhaust gas is collected or separated by each of these devices, for example, a coal economizer hopper 17. , falls into the dust collector hotsunoku 18 and air preheater hopper 19 and is stored],
Ru. The amount of ash collected by the economizer and the air preheater is, for example, about 6 to 10% of the total ash amount, and most of the remaining amount is collected by the dust collector. The scattered coal ash stored in each of the above-mentioned hoppers l'i', 1B, and 19 is transferred to the dehydration tank 6 by the Hydrobear exhauster 16 operated by circulating high-pressure water at appropriate times, and is treated in the same way as the crushed coal ash. It is processed. As mentioned above, a series of water used for processing coal ash, such as cooling and transporting it, is sometimes referred to as ash treatment water.

This method of treating coal ash produces nitrogen oxides (NO
X) Similar reduction measures have been implemented in combustion equipment that partially recirculates combustion exhaust gas and adjusts the air ratio, but recently, combustion equipment, especially combustion equipment that implements measures to reduce NOx, have recently been implemented. The ash transfer pipe 5, the overflow pipe 15 of the seal water 14, the sill box trough, the outside of the hopper seal pipe, and the parts that come into contact with the ash treatment water during the coal ash treatment process were corroded and thinned, and the combustion equipment was installed to repair them. It became necessary to stop driving. The inventor of the present invention investigated the cause and found the following.

In other words, due to NOx reduction measures that have been implemented in recent years to purify the environment, the flame temperature downstream of the burner in the combustion device has decreased, resulting in a decrease in the heat load capacity of the combustion chamber. The amount of clinker-like coal ash that adheres to the ice wall of the combustion chamber has been reduced, and the amount of clinker-like coal ash that falls from the combustion chamber to the water-immersed combustion chamber has been significantly reduced. Since a part of the gas is circulated to the combustion chamber via the bottom of the furnace, acidic components such as Box contained in the combustion exhaust gas are absorbed into the ash treatment water of the water-immersed ash hopper, reducing 1) H. It is made and used as such. This pH lowering effect is caused by the fact that acidic components are significantly accumulated and strengthened by recycling the ash-treated water, and by the fact that a small amount of clinker-like coal ash falls from the combustion chamber. It was found that the balance between the pH lowering effect of coal ash and the neutralizing effect of coal ash was no longer maintained, and the pH of the ash treated water was lowered, causing corrosion phenomena.

The use of drugs to neutralize such acidity imposes a heavy economic burden on the wrestlers due to the large consumption of drugs.

In view of the above-mentioned prior art, an object of the present invention is to provide a method for preventing corrosion of combustion equipment, which can prevent corrosion of various equipment caused by treated coal ash water without using special chemicals.

The present invention provides for scattered coal ash that is collected by a coal ash collector installed in a flue or the like when operating a coal-fired combustion device that has a water-immersed ash hopper at the bottom of the furnace through which ash treatment water circulates. By transferring a portion of the ash to the water-immersed ash hopper, a decrease in the pH of the ash treatment water is prevented.

In the method of the present invention, a portion of the scattered coal ash collected in the flue is transferred to a water-immersed ash hopper in response to a decrease in the pH of the ash treatment water, thereby preventing a decrease in the pH of the ash treatment water. .

One of the effects of the scattered coal ash transferred to the water-immersed ash hopper is that the carbon contained in the ash, 01Mg01Fe203
The purpose is to shift the pH of the ash treatment water to the neutral or alkaline side by using alkaline components such as. To achieve this effect, scattered coal ash may be injected into the ash treatment water in the submerged ash hopper. Another function of the coal ash is to suspend the scattered coal ash on the surface of the ash treatment water in the submerged ash hopper, thereby preventing it from coming into contact with the circulating combustion exhaust gas, which has the effect of lowering the p. As for the properties of the above-mentioned transported coal ash, it is necessary to be scattering in order to prevent contact with circulating combustion exhaust gas, but in order to adjust the pH, even if it is scattering, it must be mixed with water. There may be. The above two effects do not necessarily have to be simultaneous, and the p
Coal ash may be injected or suspended at appropriate times depending on H.

Hereinafter, the present invention will be explained in more detail with reference to the drawings. Second
The figure is a system diagram for explaining one embodiment of the corrosion prevention method of the present invention. In Fig. 2, clinker-like coal ash falls into the ash treatment water of the water-immersed hopper 2, is crushed by the clinker crusher 3, is transferred to the dehydration tank 6 via the ash transfer pipe 5 by the high ejector 4, and is dehydrated. The separated coal ash is transported to the ash dump, and the separated water is pressurized and circulated from the settling tank 8 to various locations as ash treatment water, and a portion of it is returned to the circulation path as seal water 14 via the overflow pipe 15. is the same as in FIG. As schematically shown in FIG. 3, a combustion exhaust gas furnace bottom duct 26 is opened near the furnace bottom 1 of the combustion device, so that the flue gas that has been circulated and the water-immersed ash hopper 2 are opened. is always in gas-liquid contact with the ash-treated water, and the pJ of the ash-treated water gradually decreases for the reasons described above.

When the pJ (pJ) decreases, the scattered coal ash concentrated in the economizer hopper 17, dust collector hopper 18, air preheater hopper 19, etc., enters the water together with high-pressure water by the Hydrobear exhauster 16. The ash is injected into the ash treatment water of the water immersion type ash hopper 2 through the transfer pipe 25.This inlet water transfer pipe 25 is connected to the Hydrobear exhauster 1 explained in FIG.
6 to the dewatering tank. The above hoppers]-tsu, 1
The scattered coal from B, 19 is transported through the ash air transfer pipe 24 without using the hydrobear exhauster 16, and is transported from the ash blowing pipe 22 into the ash treatment water of the water-immersed ash hopper 2. May be injected. In this way, the pH of the ash treatment water is adjusted and corrosion of each device is prevented. On the other hand, scattered coal ash is blown out from the ash blowing pipe 22 onto the ash treatment water surface of the water-immersed ash hopper 2 by adjusting the blowing speed and angle, forming an ash floating layer 2'y on the surface of the ash treatment water. This prevents the ash treatment water from coming into contact with the circulating combustion exhaust gas, thereby preventing its acidification as much as possible. In this way, 1-p of the ash treated water is
A decrease in H is prevented.

To automatically and timely perform the above-mentioned effects of adjusting the pH of ash treated water by injecting scattered coal ash and preventing contact with circulating combustion exhaust gas by floating the ash, depending on the pH of the ash treated water. , as shown in FIG.
and connected to the inlet water transfer pipe 25, and the ash air transfer pipe 2
4 may be provided with an ash air transfer control valve 23. For example, if the inlet water transfer control valve 31 is set to operate when the pH drops to a certain value, and the ash air transfer control valve 23 is set to operate at fixed intervals, the valve will always operate automatically and stably. This can prevent the pH of the ash treatment water from decreasing.

As described above, according to the present invention, it is possible to prevent the pH of the ash treatment water from decreasing and to prevent corrosion of the combustion device without using any special chemicals. Therefore, even with measures to reduce NOx that are expected to become more advanced in the future, maintenance of combustion equipment for corrosion becomes easier and stable operation becomes possible. Also,
Operating costs are also lower due to no use of chemicals and lower maintenance costs.

[Brief explanation of drawings]

FIG. 1 is a conventional ash collection and treatment system diagram, FIG. 2 is a system diagram showing one embodiment of the corrosion prevention method of the present invention, and FIG. 3 is a schematic diagram of the vicinity of the bottom of a combustion apparatus. l... Furnace, Wm, 2... Water immersion type Atsushiko 4 hopper, '3... Clinker crusher, 4... Ejector, 5...・・・
...Ash transfer pipe, 6...Dehydration tank, Fu...
Separation ・Water piping, 8... Sedimentation tank, 9...
・High pressure water pump, 10... High pressure water pipe, 11...
... Jet nozzle, 12 ... Truck,
13...Ash disposal pipe, 14...Seal water, 15...Overflow pipe, 16...
・Hydrobear exhauster, 17...--Energy saver hopper, 18...Dust collector hopper, 19...
... Air preheater hopper, 20 ... pH meter and controller, 21 ... Rainwater transfer control valve, 22 ...
...Ash blow-off pipe, 23...Ash air transfer control valve,
24... Ash air transfer pipe, 25... Return water transfer pipe, 26... Combustion exhaust gas furnace bottom duct, 27
...Floating ash layer. Agent Patent Attorney Takenaga Kawakita Figure 1

Claims (1)

[Claims] (1) When operating a coal-fired combustion equipment that has a water-immersed ash hopper at the bottom of the furnace where ash treatment water circulates, scattered coal ash is collected by a coal ash collector installed in the flue, etc. A method for preventing corrosion of combustion equipment, characterized in that a portion of the ash treated water is transferred to the water-immersed ash hopper to prevent a decrease in P and H of the ash treated water.