JPS6127676B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for effectively recovering heat from combustion exhaust gas generated from various combustion furnaces.

More specifically, for example, a group of heat exchanger tubes with fixed vanes is installed in high-temperature combustion exhaust gas discharged from industrial heating furnaces, diesel engines, etc., and the retained heat of the high-temperature exhaust gas is transferred to hot water flowing inside the heat exchanger tubes. This relates to a waste heat boiler that supplies waste heat, heats it, and recovers it as high-pressure steam.

With the recent rise in energy costs and deterioration of the energy situation, various energy saving measures have been implemented and have achieved results. Although installing waste heat boilers has been widely adopted as one method, efforts are still needed to recover heat more effectively.

Therefore, in order to increase the heat recovery efficiency, the waste heat boiler in the heat recovery device of the present invention has a large number of heat transfer tubes arranged in a heat exchange chamber provided in a part of the flue, and fixed impellers are installed around the outer periphery of each tube. This has been improved to increase the heat transfer area and the amount of contact with exhaust gas. However, in this type of waste heat boiler, dust such as combustion residue that adheres to the fixed blades reduces the heat exchange efficiency, and also causes corrosion of the heat exchanger tubes, shortening their lifespan. Therefore, measures are taken to prevent the dust from adhering and to effectively remove the adhering materials, thereby reducing fluctuations in the pressure, temperature, and amount of generated steam and allowing stable, long-term continuous operation. It is necessary to do so.

Conventionally commonly used methods for removing deposits accumulated on the outer surface of heat transfer tubes in heat recovery equipment include blowing steam or air, washing with water, and increasing the temperature of the tubes by stopping the water supply.
It is known that this is caused by vibration of the pipe, but there are two types of deposits: dry and sticky, and there is no method that can effectively remove both types of deposits, so removal of deposits is often required. However, it was not possible to continuously generate steam.

For example, when using steam to remove combustion residue accumulated on fixed vanes, etc., blowing steam naturally lowers the ambient temperature around the vanes, generates sulfuric acid mist, and removes the residue from the outside surface of the heat exchanger tube. corrosion occurs, so the amount of steam used is limited,
Therefore, it is not possible to completely remove deposits, the removal effect period is short, cleaning is required frequently due to suspension of operation, the heat recovery efficiency tends to decrease, and the amount of steam generated becomes unstable. It wasn't always satisfying.

In view of the above-mentioned conventional defects, the present invention provides a waste heat recovery device equipped with a waste heat boiler.
By increasing the effect of removing deposits and prolonging the duration of the effect, stable high-pressure steam is generated continuously with almost no need to stop operation, and the efficiency of heat recovery from high-temperature exhaust gas is significantly increased. The present invention provides a heat recovery device as described above.

In other words, when removing the deposits on the fixed blades stuck to the outer surface of the heat transfer tube, a part of the circulating hot water from the steam/water separation drum is mixed with high-pressure steam, and the deposits are removed by blowing with the nozzle spray. It was designed to be removed.

The main components of the heavy oil combustion residue mixed in the exhaust gas are SO ₃ , Na ₂ O, and V ₂ O ₅ , and other components include SiO ₂ , CaO, Fe ₂ O ₃ , and
It is composed of NiO, etc. and becomes a corrosive solid substance, but when Na salt is present, it forms salts with a very low melting point and which tend to stick to heat transfer surfaces _.
It is known that it reacts with SO ₃ to form Na ₂ SO ₄ and is extremely corrosive in the presence of a reducing agent, and that V ₂ O ₅ acts on these to cause a synergistic corrosive effect. Furthermore, when the exhaust gas temperature is around 700°C, a large amount of sulfuric acid accumulates on the outer surface of the heat exchanger tube, while when the exhaust gas temperature is around 150°C, sulfuric acid condensation is known to occur. Among these,
Alkaline circulating water with a pH of about 10 to 12 is used as a measure to prevent scale adhesion on the inner surface of heat exchanger tubes.Using this circulating hot water, it is possible to overcome the various limitations mentioned above and achieve an excellent adhesion removal effect. In particular, it was found that when phosphate was added to the circulating hot water, the effect significantly increased.

These reasons are that the combustion residue contains substances that are easily soluble in alkali, and as a result of being sprayed with alkaline mist, the binding force of the combustion residue is reduced, the blowing effect of steam is promoted, and the This is thought to be because it also forms a protective film to prevent kimono, and furthermore, the special effect of phosphate is thought to be because it weakens the electrostatic bonding force, which is a major cause of combustion residue accumulation. In addition, in the conventional blowing method that generates steam, sulfuric acid mist is generated as the ambient temperature decreases, causing pipe corrosion problems, but by spraying an alkaline aqueous solution as in the present invention, Corrosion is completely preventable.

Hereinafter, one embodiment of the present invention will be described based on the drawings.

Reference numeral 1 denotes a waste heat boiler main body, which is provided with an exhaust gas inlet 2 and an exhaust gas outlet 3 at both ends, and inside the waste heat boiler main body, a large number of heat exchanger tubes 4 for heating circulating hot water are arranged in a group. Although not shown in the figure, each heat transfer tube 4 has a large number of fixed vanes fixed to the outer peripheral surface of the tube. These heat transfer tubes are connected to a steam/water separation drum 7 via an inlet pipe 5 and an outlet pipe 6 to the waste heat boiler main body, and circulating hot water pipes 13 and 13'. That is, the circulating hot water passes from the steam/water separation drum 7 through the piping 13, enters the heat transfer tube group from the inlet pipe 5 of the waste heat boiler main body using the circulation pump 8, becomes high-pressure steam, and passes from the outlet pipe 6 through the piping 13'. The water is then refluxed to the steam/water separation drum 7. This high-pressure steam is separated into circulating hot water and high-pressure steam in the steam-water separation drum 7, and the high-pressure steam is sent to other processes from piping 9, and a part of it passes through piping 10 as high-pressure steam for soot blowing. regulated by a control valve 12,
It is supplied from each soot blowing nozzle section 11 as necessary. On the other hand, a portion of the circulating hot water passes through the pipe 14, the amount of hot water is adjusted by the regulating valve 12', and is supplied to each soot blowing nozzle section 11 as required.

Regarding the water supply, the hard water softening device 20 and the chemical injection device 15 perform alkalinity treatment and addition of phosphoric acid, respectively, and the water supply water preheating steam piping 16
The resulting steam is heated in the water supply preheating section 18 and sent to the steam/water separation drum 7 by the water supply pump 19.

That is, a part of the circulating hot water extracted from the steam/water separation drum is passed through the pipe 14, and the exhaust gas temperature is measured at the exhaust gas inlet and outlet of the waste heat boiler main body, although not shown in the figure. When the exhaust gas temperature difference is detected and the detected value is smaller than the set value, it is assumed that the heat exchange efficiency has decreased due to the estimated combustion residue, and the amount of steam and circulating hot water are automatically reduced during operation. The control valves to be adjusted are opened, and the air is sprayed toward the outer surface of the heat exchanger tube with fixed vanes, thereby removing deposits. The water supply can also be automatically adjusted depending on the water level in the tank.

As is clear from the above description, according to the present invention, the alkaline high-pressure hot water mixed steam containing the phosphate solution is purged, and the combustion residue deposits accumulated on the fixed blades on the outer periphery of the heat transfer tube are extremely removed. It can be removed with a simple operation, and as mentioned above, it becomes difficult to estimate the amount of deposits themselves, which reduces the frequency of spraying on the fixed blades, and makes it easier to disassemble and clean the waste heat boiler by shutting down the operation. The number of times of purging is drastically reduced, making long-term continuous operation possible, reducing fluctuations in operating conditions even during purging, and significantly increasing waste heat recovery efficiency. Furthermore, by spraying an alkaline aqueous solution, even if sulfuric acid mist is generated, it can be neutralized, which not only improves the operating rate and thermal efficiency, but also prevents corrosion of the outer peripheral surface of the heat exchanger tube and fixed blades. This has achieved a number of excellent early effects, such as reducing waste heat boiler repair costs and extending the life of the waste heat boiler.

[Brief explanation of the drawing]

The drawing is an explanatory diagram showing an implementation outline of the waste heat recovery device of the present invention. 1 ...Waste heat boiler body, 2...Combustion exhaust gas inlet, 3...Combustion exhaust gas outlet, 4...Heat transfer tube for heating circulating hot water, 5...Circulating hot water inlet pipe, 6...Circulating hot water outlet Pipe, 7... Steam/water separation drum, 8... Circulation pump, 9... High pressure steam pipe, 10... Steam piping for soot blow, 11... Nozzle part for soot blow, 12... Soot blow steam control valve, 12'...
...Soot blow hot water control valve, 13... Circulating hot water piping, 13'... Returning high pressure steam pipe, 14... Ring hot water pipe, 15... Chemical injection device, 16... Steam piping for preheating feed water, 17... Safety valve, 18...Water preheating section, 19...Water pump, 20...Water softening device, 21...Water supply control valve, 22...Drain drain.

Claims (1)

[Scope of Claims] 1. A heat exchange chamber provided in a flow path of combustion exhaust gas generated from a combustion furnace, and a heat exchange tube group in which heat exchange tubes each having a large number of fixed blades fixed to the outer peripheral surface are disposed within the heat exchange chamber. , a steam-water separation drum that separates circulating hot water and steam, a pipe in which the steam-water separation drum and the heat transfer tube are connected via a circulation pump, and a water softening device and a water softener in the pipe that supplies water to the steam-water separation drum. A water supply regulator and a water supply pump disposed before and after the water softening device, a water supply preheating heater and a chemical injection device provided on the piping on the discharge port side of the water supply pump, and a water supply system that supplies water from the steam separation drum to the heat exchange chamber. The waste heat is characterized by comprising a pipe for mixing the high-pressure steam produced and a part of the circulating hot water, and a blowing nozzle provided at the tip of the pipe toward the outer surface of the heat exchanger tube with fixed vanes. Collection device. 2. The waste heat recovery device according to claim 1, characterized in that phosphate is added to the circulating hot water.