JPS6017968B2 - Decoking method for heat exchanger tubes - Google Patents

Description

[Detailed Description of the Invention] The present invention is applicable to a wide range of industries such as oil refining, petrochemistry, fertilizer chemistry, and synthetic chemistry, in addition to rapid cooling heat exchangers for olefin production or waste heat boilers after partial oxidation reactions of coal and heavy trade oil. This invention relates to a decoking method for heat exchanger tubes used in waste heat boilers for cooling high-temperature gas.

A process for producing olefins by thermal decomposition of hydrocarbons such as ethane, naphtha, kerosene, and light oil; a process for producing SNG by partial oxidation and hydrocracking of petroleum heavy oil and coal; and a process for producing SNG by steam reforming of natural gas and naphtha. In the production process of hydrogen or synthesis gas, the produced crude gas (750-1400%) exiting a cracking furnace, gasifier, reformer, etc. is rapidly cooled for reaction freezing and scarlet heat recovery. - ``Conventionally, there are two methods for rapid cooling and heat recovery: recovery of high-pressure steam from the source using a shell-and-tube heat exchanger, and direct cooling using water or oil mist, but each method has the following drawbacks. There is a.
Multi-alarm heat exchanger method - Contamination of the heating tubes, especially caulking Tube burnout and burnout due to local overheating Increased cost due to the use of high-quality materials (b) Direct cooling method - Low steam recovery efficiency (b) Contamination of process gas Of these, coking (a) is especially effective against created carbon and high boiling point substances (
This is a phenomenon in which tar-like substances (tar-like substances) settle on the heat transfer tubes and then grow into a coke laminate, which leads to a decrease in heat transfer performance and an increase in pressure loss, so the operation must be stopped at regular intervals to remove the coke. This is a major hindrance to the continuous operation of the process and causes a decrease in productivity.

Methods for removing coke include a mechanical decoking method, which mechanically removes coke, and a steam, air, and decoking method.

The mechanical decoking method requires a long stoppage period, and
There are many expenses such as personnel expenses, which increases the cost.

On the other hand, the steam, air, and decoking methods (in which a mixed gas of steam and air is passed through a pipe and the coke is combusted with oxygen in the air) require complicated equipment structures and require strict operation to protect the tubes. It is necessary to maintain the conditions.

It is thought that the above-mentioned coking phenomenon becomes more severe as the raw materials become more militarized, and the cost for decoking becomes greater.

The present invention has been made in view of the above-mentioned drawbacks of the related art.
In the NG production process, high-temperature crude gas containing rutted carbon and high-boiling components is rapidly cooled, and both reaction freezing to prevent secondary reactions and heat recovery to recover the head heat of the crude gas as high-pressure steam are performed. In carrying out the action, a fluidized bed type was used, as already described in Hakama-gao Sho 51-31 Sono. A rapid cooling heat exchanger (with a built-in boiler water pipe for recovering high-pressure steam) has been proposed, but
The present invention solves the drawbacks of these existing types, such as increased size of the device,
The purpose is to eliminate drawbacks such as a decrease in olefin yield.

The present invention is designed to cool and recover heat from high-temperature gas (750-1400 am) containing created carbon and high boiling point components produced by thermal decomposition of vehicle hydrocarbons, partial oxidation of coal, and hydrocracking. In order to rapidly cool the sea bream heat possessed by the high-temperature gas and recover it as high-pressure steam, a fluidized bed or warm bed heat exchange section having a group of heat transfer tubes through which water or steam flows and a shell-and-tube heat exchange section are used. In a rapid cooling heat exchanger consisting of two parts, by supplying fine particles to the fluidized bed section (including the spouted bed), the fine particles fly to the water tube group above the fluidized bed, where they condense and settle on the tube wall surface. Coke is prevented by blasting condensate consisting of high boiling components.

Next, one embodiment of the present invention will be described with reference to FIG. In the figure, 1 is a gas supply port, 2 is a fluidized bed heat exchange section, 3 is a water supply port, 4 is a steam outlet, 5 is a heat exchanger tube, 6 is a lees extraction port, 7 is a solid particle, and 8 is a solid particle supply 1 is a gas outlet, 12 is a high-pressure steam drum, 13 is a water or steam supply port, 14 is a high-pressure steam outlet, 15 16 is a switching valve, 17 is a cyclone for collecting pongee grains, 18 is a bag for removing pongee grains, 19 is a gas outlet pipe, and 2 rivers are fine grain outlets.

High-temperature gas (flammable) generated by thermal decomposition or partial oxidation enters the spouted bed heat exchange section 2 from the gas supply port 1, gives heat to the fluidized bed, and the fluidized bed is cooled by exchanging heat with the heat exchanger tubes 5. Ru. The gas is introduced into the upper shell-and-tube heat exchange section 9. The heat exchanger tube 5 consists of one or more tubes having a water or steam outlet 3 at one end and a steam outlet 4 at the other end, and the water or steam inside the heat exchanger tube 5 receives the sensible heat of the gas. The gas that has entered the multi-tubular heat exchanger section 9 exchanges heat with a plurality of double-tube heat exchanger tubes 10, and then is passed from the gas outlet 11 through the flap valve 15 to the gas outlet piping 19. be led out of the system.

In the double-pipe heat transfer tube 10, water or steam entering from the water or steam outlet 13 descends inside the inner tube.
This is to convert the gas into high-pressure steam by the sensible heat of the gas while it is reversed and ascends between the outer tube and the inner tube, and the generated steam is separated into gas and liquid in the high-pressure steam drum 12 and sent to the high-pressure steam outlet 14. more will be recovered. If the normal operation described above continues for a certain period of time, the solid particles flowing in the spouted bed heat exchange section 2 will become large particles as the tidal carbon brought in by the high temperature gas adheres to their surroundings, causing the fluid state to deteriorate. In addition, high boiling point components in the high temperature gas condense and deposit on the outer wall surface of the outer tube of the double tube type low heat tube 10 to form coke.
In order to avoid such a situation where heat transfer is inhibited, new solid particles (recycled solid particles may also be used) are supplied from the solid particle supply port 7 to the solid particle supply device 8 at regular intervals. ) is supplied to the fluidized bed heat exchange section 2.

The supplied solid particles are adjusted in advance to a certain ratio of lees grains and pongee grains, and the mixed grains are mixed with the already flowing solid particles and then extracted to the outside from the coarse grain extraction port 6. The recorded data is then reproduced using a suitable reproduction device. On the other hand, the supplied fine grains are
It flies to the multi-tube heat exchange section 9, peels off the liquid that is condensing and depositing on the outer wall surface of the outer tube of the double-tube heat exchanger tube 10, captures it on the surface of the pongee grains, and then removes it together with the gas. Switching valve 16
The pongee grains enter the cyclone 17 for collecting fine grains, where the pongee grains are separated into gas and solids. Reprocessed.

The gas separated by the fine particle collecting cyclone 17 exits to an outlet pipe 19. As mentioned above, the external cyclone 17 is used only when replenishing solid particles, that is, replacing the fluidized medium and decoking the double-head heating tube 10, and during other normal operations, the external cyclone 17 is switched to shortcut and bypass. Carry out driving. According to the present invention, the following effects can be expected by replenishing string grains.
a The coking thickness of the double-tube heat exchanger tubes in the multi-tube heat exchange section is suppressed to a certain value, and stable heat exchanger tube performance and pressure loss are maintained.

b) There is no need to stop the furnace operation and perform the decoking operation as in the conventional method, which greatly improves productivity and greatly simplifies maintenance.

Note that the cyclone can be omitted and the fine particles can be captured by a reservoir wall type heat exchanger installed downstream of the quenching heat exchanger. In the above case, fine particles can also be combined continuously. Further, at the same time as coarse sand is replenished (continuously in most cases), lees grains may be added together with it. Next, test results of the present invention will be explained.

As the cooling test continued, the system became inoperable at about 5 mph, and as a result of opening the equipment and inspecting it, caulking about 3 sides thick was found around the outer pipe of the straight double pipe.

Next, we continued the test by replenishing fine particles once in each of the two pans.As a result, the coking thickness did not grow beyond the first side, and no erosion was observed, and the operation continued without any problems for over 40 days. I was able to do that. In the above tests, the amount of fine particles supplied per time was 20, 7F150, 225K9 (solid-air ratio 0.0
27, 1.0, 2.0, 3.0), the relationship between pressure loss and solidification in the multi-tubular heat exchange section is as shown in Figure 2. In FIG. 2, the curve in the direction of arrow a shows the effect of increasing caulking, and the curve in the direction of arrow b shows the effect of increasing coking ratio. As a result, the appropriate ratio is around 1.0k9 (particles)/k9 (gas), and if it exceeds this, the pressure loss will increase and the ethylene yield will decrease.

Moreover, below this range, the pressure loss tended to gradually increase, probably because the decoking effect was insufficient. In addition, Figure 3 shows the change over time in the temperature of the recovered steam when the multi-layer heat exchanger was sandblasted using fine-grained sand for each divalent r.
It can be seen that these also exert a sufficient decoking effect.

In the figure, arrows a and b indicate the blast direction.
As described above, by intermittently replenishing fine-grained sand in the form of solid particles, a remarkable effect was confirmed in that continuous operation could be extended to over 40 days instead of only 2 days without replenishment.

[Brief explanation of the drawing]

Fig. 1 is a system diagram showing an embodiment of the present invention, Fig. 2 is a chart showing the effect of the intermittent blasting method on pressure loss, and Fig. 3 is a chart showing the effect of the intermittent blasting method on steam recovery temperature. be. 1... Gas supply port, 2... Fluidized bed heat exchange section, 3, 13...
...Water or steam supply port, 4...Steam outlet, 5
... Heat exchanger tube, 6 ... Phase particle extraction port, 7 ... Solid particle child general port, 8 ... Solid particle child V feeding device,
9...Multi-tube heat exchange section, 10...Double tube heat exchanger tube, 11...Gas outlet, 12...High pressure steam drum, 14... ...High pressure steam outlet,
15, 16...Switching valve, 17...Cyclone for collecting pongee grains, 18...Pongee grain extraction device, 1
9...Gas outlet piping, 20...Fine particle outlet. Figure 1 Sakai Z drawing powder figure 3

Claims (1)

[Claims] 1 High-temperature gas containing by-product carbon and high-boiling components produced by thermal decomposition or partial oxidation of heavy hydrocarbons is rapidly cooled in this order by a fluidized bed exchange section and a multi-tubular heat exchange section above the exchange section. A method for decoking heat exchanger tubes, characterized by supplying fine particles for blasting a multi-tubular heat exchanger section that are scattered along with the gas when recovering the sensible heat held by the gas.