JPS584241B2 - Nenshiyou Higas Karano Netsukaishyuhouhouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION As a method for removing ammonia from coke oven gas, a method of cleaning and removing ammonia has conventionally been adopted.

The washing water here is then led to an ammonia stripper, and the ammonia stripper top steam has traditionally been combusted with heavy oil or other appropriate combustion aids, and then released directly into the atmosphere. It was dissipating into

However, the combustion waste gas produced by burning such ammonia column vapor in a combustion furnace has an extremely high temperature.
It is extremely uneconomical to dissipate this into the atmosphere as it is, and for this reason various attempts have been made to recover heat from this combustion waste gas.

However, since the overhead steam of an ammonia stripper itself contains ammonia, H2S, etc. in addition to water vapor, unburned ammonia and H2S are also included in the combustion waste gas obtained by combusting this. It contains SO2 and SO3 produced by the combustion of H2S and H2S, which causes various problems.

That is, unburned ammonia in the combustion waste gas and the above-mentioned H
SO2 and SO3 produced by the combustion of 2S react and form NH4HSO4 or (NH4)3Fe(SO4).
3 and other salts precipitate significantly, and this adheres to the heat exchanger tubes of the heat recovery boiler, clogging the pipes, and also causes water vapor and SO
There was a problem that the waste heat recovery boiler tube and other parts were immediately corroded due to the synergistic corrosion effect with H2SO4, which is the reaction product of step 3.

For this reason, in the past, the high energy contained in the combustion waste gas had no choice but to be dissipated into the atmosphere without being recovered.

The inventor of the present application focused on this conventional situation and researched corrosion prevention measures for heat recovery equipment when recovering heat from the waste gas mentioned above, and as a result, unexpectedly, the above-mentioned heat We have come to the conclusion that prevention of corrosion in recovery equipment can be achieved by limiting the operating conditions.

The present inventors attempted various experiments in completing this invention, and through a series of experiments, it was possible to specify the ratio of NH3/H2O in the vapor composition fed to the combustion furnace. This is important, and they discovered that it would be good to regulate the temperature on the water side of the waste heat recovery boiler and the temperature at the exhaust gas outlet of the waste heat recovery boiler, and finally completed this invention.

The details of this invention will be explained below.

In order to find heat recovery conditions for combustion waste gas according to this invention, the inventors
A waste heat recovery experimental boiler with a steam generation rate of 20 kg/h as shown in Fig. 1 was installed on the machine side of a 3/H model ammonia stripper tower top gas combustion furnace, and various experiments were conducted.

In the figure, reference numeral 1 denotes an existing combustion furnace, into which ammonia stripper top steam, combustion improver, air, etc. are fed together and burned.

The composition of the combustion waste gas in this case is as shown in FIG. 1, but what is particularly problematic here are unburned ammonia, SO2, SO3, and the like.

Conventionally, this waste gas was released into the atmosphere without any heat recovery, but in this invention, it is released into the outlet pipe 2.
It is introduced into the experimental boiler 3 through.

The experimental boiler 3 is a smoke tube boiler, and the high-temperature combustion gas passes through the boiler tube side and imparts sensible heat to the boiler canned water on the shell side, and is then sucked out by the exhaust fan 4.

Since the exhaust fan 4 is usually made of mild steel (SS41), the exhaust fan 4 sucks in air as shown in the figure to lower the temperature.

The waste gas exiting the exhaust fan 4 is mixed with the main stream of combustion furnace waste gas in the existing waste gas duct 5 and released into the atmosphere.

On the other hand, the boiler supply water supplied to the experimental boiler 3K is introduced into the air-water drum 10 from the soft water tank 6 through the soft water pump 7, the water supply tank 8, and the water supply pump 9.

The canned water is naturally circulated between the air-water drum 10 and the experimental boiler 3 as shown in the figure.

After the steam is separated in an air-water drum 10, it is discharged into the atmosphere through a steam pipe 11.

The supply of boiler feed water is controlled by a level indicating control and alarm device 12 attached to the steam drum 10, and the steam pressure is controlled to be constant by a pressure indicating control and alarm device 13 provided in the steam line.

The specifications of the main equipment used in this experimental equipment are as follows.

(1) Boiler type Type Fire tube type vertical boiler Dimensions Shell inner diameter 600mm x length 3594mm Material SS41 Tube outer diameter 38.1mm x wall thickness 4.5mm x length 34
00mm x 9 pieces Material STB35 Transmission surface 3.0m2 Internal volume 1m3 Maximum working pressure 22kg/cm2G Regular pressure 20kg/cm2G (2) Air/water drum type Cylindrical vertical type Dimensions Inner diameter 600mm x Length 1400mm Internal volume 0.4m3 Max. Working pressure 22kg/cm2G Regular pressure 20kg/cm2G (3) Water suction pump type Plunger pump capacity 70l/H x 300m Electric motor 0.75kW x 4P x 3φ x 60Hz (4
) Exhaust fan type Turbo fan capacity 200Nm3/H x 500mmAqat1
50° C. Electric motor 3.7 kW×4 PV belt (fan rotation speed 2900/min) The flow rate and temperature pressure of each fluid in illustrations A to F are as follows.

Using the above device, a portion of the waste gas from the combustion furnace was introduced into the experimental boiler to obtain results under various conditions.

The weight ratio of NH3/H2O in the vapor composition can be adjusted by adjusting the temperature at the top of the ammonia stripper and the flow rate of the cooling water of the vapor condenser installed at the top of the ammonia stripper in a conventional manner. This was done by adjusting the ammonia-steam vapor temperature.

The results were as shown in Table 2.

As is clear from this table, in Experiment 1, in which the present invention was not applied, the amount of adhering salts was 295 g/piece for 20 days, and 148 g/piece for 1 day, but in Experiment 2, also in which the present invention was not applied. Cumulative amount of adhesion is 338g/piece, new amount of adhesion is 43g/
This is gradually decreasing to 1.8g/day.

This was NH3/H2O < 0.16, which was outside the conditions of the present invention, but in Experiment 1, the tube was new and its surface properties made it easy for salts to adhere, so a large amount of salt adhered to it, but in Experiment 2, the tube was The surface of the test tube was covered with a film of salts, and when the salts became too large, the excess salts were blown away from the surface along with the waste gas, and the amount of accumulated salts decreased compared to the 10th period of the experiment.

Next, looking at the cases of Experiments 3 and 4 using the method of the present invention, N
o. In No. 3, the cumulative amount of attached salt was 324 g/piece, a real decrease of 14 g/piece, that is, a decrease of 0.6 g/piece/day.

This shows that because the method of the present invention was carried out, no salt accumulation occurred, and on the contrary, the amount blown away by the waste gas was considerably larger.

Experiment no. 4, it can be seen that this tendency is even more pronounced.

These conditions can be explained by the relationship between the vapor composition of NH3/H2O fed to the combustion furnace shown in Figure 2 and the concentration of unburned ammonia contained in the combustion waste gas. The unburned ammonia concentration is closely related to the vapor composition, especially NH3/H2O, and NH3
/H2O (kg/kg) increases, the unburned ammonia concentration in the combustion waste gas decreases, and approximately NH3/H
This is because when 2O>0.16, the ammonia concentration becomes 40 ppm or less.

As the unburned ammonia concentration decreases, ammonia and S
Precipitation of salt due to the reaction of O3 is inhibited, and a phenomenon in which salt adheres to and blocks the boiler heat exchanger tubes is no longer observed.

This is clearly shown in the section for boiler tube deposit weight in Table 2 above.

Although the inventor continued the above experiment, the amount of attached salt remained almost the same even after 90 days had passed, and there was no particular increase.

Furthermore, in this invention, in order to avoid corrosion of the boiler tube, the temperature on the water side of the waste heat recovery boiler can is set to be higher than the acid dew point (150 to 170°C in the case of this waste gas), and the molten salt corrosion temperature is set to about 400°C. Keep the exhaust gas duct below,
In order to prevent salts from adhering to the exhaust fan, the exhaust gas outlet temperature of the waste heat recovery boiler is also regulated to 200°C or higher.

By doing so, it has become possible to recover heat from the combustion waste gas without causing corrosion of the waste heat recovery boiler tube or precipitation of salts as in the past.

Therefore, according to this invention, if a waste heat recovery boiler is attached to a coke oven gas 100,000Nm3/H scale ammonia combustion furnace, the recovery of about 8T of high pressure steam (20kg/cm2G) per hour will reduce the corrosion of the equipment. This will become possible without much effort, and its benefits will be enormous.

Furthermore, in order to release combustion waste gas directly into the atmosphere through the stack as in the past, it is necessary to mix a large amount of air to lower the temperature in order to protect the flue and stack (for example, coke oven gas of 40,000 Nm3/H on a scale of 100,000 Nm3/H). ~5
0,000Nm3/H of air), the installation and operating costs of blowers and ducts were not negligible.
According to this invention, it is possible to minimize these costs.

Furthermore, when performing SO2 removal treatment in which the combustion gas is directly released into the atmosphere, the waste gas, which previously had a temperature of approximately 1100°C, must be cooled all at once to 50 to 80°C, which is the normal inlet temperature of the desulfurization equipment. First, the cost was large,
According to this invention, since cooling is performed from about 300° C., there is an advantage that the cost of cooling equipment for this purpose can be significantly reduced.

In the above explanation, the heat recovery from the combustion waste gas of the vapor at the top of the ammonia stopper of coke oven gas purification equipment was described, but the present invention is not limited to the above, and the present invention is not limited to the above. It can be widely applied to heat recovery from liquid or gaseous combustion waste gas in which unburned ammonia, SO3, and water vapor coexist.

[Brief explanation of drawings]

FIG. 1 is a flow sheet for waste heat recovery from the steam at the top of the ammonia stripper tower, and FIG. 2 is a diagram showing the relationship between the ammonia concentration at the inlet of the combustion furnace and the unburned ammonia concentration. 1... Combustion furnace, 3... Experimental boiler, 8... Water supply tank, 9... Water supply pump, 10... Air water drum, 1
1...Steam pipe.

Claims (1)

[Claims] 1. In recovering heat from the combustion waste gas, the top steam containing water vapor, ammonia, and hydrogen sulfide, which is obtained by washing coke oven gas and evaporating this washing water using an ammonia stripper, is combusted in a combustion furnace. The vapor composition fed to the furnace is set to a weight ratio of NH3/H2O>0.16,
Heat recovery from combustion waste gas, characterized in that the temperature on the water side of the heat recovery boiler is set to be above the acid dew point of the waste gas and below 400°C, and further the temperature at the exhaust gas outlet of the heat recovery boiler is set to 200°C or above. Method.