JPS6119919B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for periodically decoking coking incidentally generated during heat recovery of coke oven gas.

Conventionally, crude coke oven gas (hereinafter referred to as crude COG) generated from a coke oven is directly cooled by ammonium water flushing as soon as it leaves the coke oven. There is a movement to recover the sensible heat (outlet temperature of approximately 700℃).

The present inventors have already proposed a heat recovery method using a spouted bed cooler and a wet wall cooler (patent application
55-111196), crude COG contains many high-boiling substances such as benzols and tars, water, and other soluble substances. It was discovered that a so-called coking phenomenon occurs, which causes the pipes to become clogged and the heat recovery equipment to be shut down.

Therefore, in order to continue stable heat recovery of crude COG, it is necessary to perform decoking.

In the case of crude COG, coking is mainly carbonized tar, and burning it off is the safest and cleanest method. However, when decoking by combustion, it is necessary to control the combustion temperature. That is, if a sufficient amount of oxygen is present, the surface temperature of the equipment and piping may rise, causing deformation due to thermal stress or impairing the functionality of the equipment.

Therefore, decoking must be performed according to the suitability of the equipment and the characteristics of the processing gas, but
In the case of COG heat recovery systems, no decoking method that takes these into consideration has been shown to date.

The present inventors have arrived at the present invention as a result of intensive research to understand the properties and characteristics of coking materials in terms of the heat recovery rate of crude COG, and to establish the safest and most effective decoking method.

That is, the present invention is a method for periodically decoking coking incidentally generated during heat recovery of crude COG, in which hot air for decoking is created and gas is revealed during decoking by the hot air. The present invention relates to a decoking method characterized in that heat is recovered as steam in this heat recovery system, and the O ₂ concentration of the hot air is adjusted using the steam and decoking exhaust gas.

In addition, in the method of the present invention, when a spouted bed cooler is used as one of the heat recovery devices, mechanical decoking using spouted bed heat transfer medium particles can also be used for decoking the crude COG introduction pipe.
This combination can shorten the decoking time.

Hereinafter, the method of the present invention will be explained in detail with reference to the accompanying drawings.

The attached drawing is a diagram for explaining one embodiment of the method of the present invention, and shows the case where the method of the present invention is applied to a system using a combination of a spouted bed cooler and a wet wall cooler as a heat recovery device for crude COG. It is a figure which shows an example.

In the figure, in the conventional case without heat recovery,
Crude COG generated in the coke oven 1 passes through a line 21, enters the dry main 2, is directly cooled by ammonium water flushing, and is suctioned and pressure-fed to a refining process (not shown).

When performing heat recovery, the crude COG generated in the coke oven 1 enters the air collecting pipe 3 through the line 20 and then enters the spouted bed cooler 5, which is the first stage heat recovery device, through the line 24. Here, the crude COG is first cooled (about 450 to 400 degrees Celsius), and then enters the wet wall cooler 8, which is the second stage heat recovery device, through lines 29 and 31, where it is secondarily cooled (to about 250 to 300 degrees Celsius). . Then, it enters the ammonium water spray tank 9 from line 33, is directly cooled by the ammonium water supplied from line 35, enters the gas-liquid separation drum 10 from line 34,
The blower 16 sends it through lines 36 and 43 to a purification step (not shown).

The locations where coking occurs during the above heat recovery process are the lines 20, 24, 29, the air collection pipe 3, the heat transfer tube in the spouted bed cooler 5, the heat medium particles circulating in the spouted bed cooler 5, the lines 20, 24, 29, measurement terminals (for example, thermocouples), etc.

To begin decoking according to the method of the present invention, the crude COG closes the edge valve 101 in line 20 to change to the conventional flow described above. Next, hot air (approximately 500 to 800° C.) is generated in the hot air generating furnace 7 using the fuel from the line 39 and the air from the line 40, and the hot air is sent from the line 23 to the line 20, the air collection pipe 3, and the line 24. At that time, gas was sampled from line 23, and steam from line ₂₈ and decoking exhaust gas, which will be described later, were transferred to line 38 so that the O ₂ concentration was 3 to 10% as determined by the O ₂ concentration meter O 2 I.
The O ₂ concentration is controlled by recycling from the

The steam from this line 28 is used to operate the spouted bed cooler 5 in the same manner as during heat recovery of crude COG, and the sensible heat of the hot air and the combustion heat generated by decoking are transferred to the boiler water circulated by the pump 14 and line 26. The steam is recovered as steam, passed through the gas-liquid separation drum 11, line 27, and accumulator 12, and then used.

The hot air leaving the spouted bed cooler 5 enters the line 29, and after decoking the inside of the line 29,
The ammonium water enters the spray tank 9 from the line 30, is cooled by the ammonium water injected from the line 35, and is sent to the gas-liquid separation drum 10 from the line 34, as in the case of heat recovery of the crude COG. The drum 10
The gas and ammonium water are separated, and the gas is sent out of the system via the lines 36 and 43 by the blower 16, or is recycled from the line 38 as described above and becomes O ₂
It is sent to the hot air generating furnace 7 for concentration adjustment. On the other hand, the liquid is discharged out of the system from the line 37 by the pump 15, normally enters the dry main 2, and only ammonium water is recycled to the line 35.

By the way, line 24 is heavily caulked, so decoking takes a long time. Therefore, in the present invention, a storage tank 4 for heat medium particles used in the spouted bed cooler 5 is provided at the inlet of the line 24, and a fixed amount (solid-air ratio of 10 to 30 kg particles/kg hot air is preferable) is introduced at a time during decoking. Mechanical decoking can also be used to shorten decoking time. When this mechanical decoking is used in combination, the number of heat medium particles increases in the spouted bed cooler 5, so particles corresponding to the amount input from the storage tank 4 are transferred from the line 25 to the tank 6.

During the above decoking, if hot air is sent to the wet wall cooler 8, there is a risk that the tar condensed during the recovery of crude COG heat in the cooler 8 will ignite, so the valves 102 and 103 of the lines 31 and 33 should be closed. Also, in order to prevent the tar from solidifying during decoking, the tar is circulated through the line 32 and the pump 13. If necessary, equipment for externally heating the tar piping can be provided.

Note that line 31 has a minimum piping length (300 mm at most).
degree), or the line 3
Lines 1 and 33 are both lines where caulking troubles are rare, so there is no need to decolk them together with the overall decoking.

Furthermore, in order to recover heat from the crude COG, the wet wall cooler 8 may be omitted, and in this case, decoking can be performed in exactly the same manner.

Next, examples of the method of the present invention will be given.

Example: In a crude COG heat recovery test plant with a capacity of 300Nm ³ /h, a hot air generating furnace using COG as fuel was installed.
COG29Nm ³ /h, combustion air 160Nm ³ /h, steam
Hot air with an O ₂ concentration of 8% and a temperature of 700°C was generated at a rate of 108 Kg/h and a recycled gas (decoking exhaust gas) of 280 Nm ³ /h, and a portion of it was used for decoking.

As a result, decoking was completed after 5 hours,
The amount of heat recovered in the spouted bed cooler is 12000Kca.
It was l/h.

In addition, alumina particles of 2 to 4 mmφ, which are heat transfer medium particles of the spouted bed cooler, were added to the crude COG introduction pipe (6 ^B × 20 m) of the heat recovery test plant.
When decoking was carried out in the same manner as above while introducing Kg hot air at a solid-gas ratio, decoking was almost completed after 2 hours. Note that the pipe pressure loss in this case was 500 mmAg → 50 mmAg.

The effects of the method of the present invention detailed above are summarized as follows.

(1) Because steam and recycled gas are used to control the O ₂ concentration of hot air for decoking, there is no need to adjust the air ratio of the hot air generator (therefore, there is no need to adjust the air ratio of the hot air generator (therefore, the hot air generator may blow out or cause incomplete combustion). ) You can easily control the O ₂ concentration.

(2) Decoking time can be shortened by injecting heat carrier particles for a spouted bed cooler into the crude COG introduction pipe and using mechanical decoking together.

(3) A spouted bed cooler is operated during decoking to recover heat, and the resulting steam is used to control the O ₂ concentration of the hot air for decoking, resulting in an energy saving effect.

(4) Safe and effective decoking is possible;
The crude COG heat recovery system can be operated safely and effectively.

[Brief explanation of the drawing]

The accompanying drawings are explanatory diagrams showing one embodiment of the method of the present invention.

Claims (1)

[Claims] 1 In a method of periodically decoking the coking incidentally generated during heat recovery of coke oven gas, hot air for decoking is created, and the sensible heat of the gas during decoking by the hot air is absorbed by this method. A decoking method, which comprises recovering steam in a heat recovery system, and adjusting the O ₂ concentration of the hot air using the steam and decoking exhaust gas.