JPS608320Y2 - Shell-and-tube heat exchanger - Google Patents

Description

[Detailed explanation of the idea] The present invention relates to a shell-and-tube heat exchanger.

Shell-and-tube heat exchangers, which preheat air, etc. using the latent heat of combustion waste gas in industrial furnaces, have tended to become larger in recent years, and because they are used in the high temperature range of the heat source and preheating medium, There are many accidents caused by thermal deformation, oxidation thinning, and corrosion caused by high temperatures in steel pipes, which are the lifeblood of steel pipes, and the stability of operations is significantly deteriorated.

Figure 1 shows a generally known multi-tubular heat exchanger.
The steel pipe groups 4 and 6 provided in the flue 1 are arranged in a lattice or staggered pattern, and both ends thereof are attached to end plates, respectively.

On the one hand, the heat source medium flows between the steel pipe groups from a to b, and on the other hand, the preheating medium flows from the nozzle 2 through the cold air distribution surface 3 and down the inside of the steel pipe group 4, changes direction in the lower conversion box 5, and flows inside the steel pipe group 6. The structure is such that the flow collects in a flow distribution channel 7 and reaches a nozzle 8.

The main cause of deformation, oxidation, and corrosion thinning of the steel pipes in the heat exchanger is due to an abnormal rise in the wall temperature of the steel pipes.

The causes of the abnormal rise in temperature of the steel pipes are local insufficient cooling due to non-uniform flow within each pipe caused by fluctuations in the flow rate of the preheating medium, and overheating due to non-uniformity in the heat receiving temperature of each pipe.

The reason for this will be explained below with reference to FIGS. 1 and 2.

In the case of FIG. 1, the heat source medium radiates heat from point a to point b, and the temperature gradually decreases.

On the other hand, the pipe wall temperature of the steel pipe is shown in Figure 2 in rows 41 and 42.
...4□□□[It will follow and decrease similarly.

Here, as an actual value, the internal resistance ΔP when flowing in a steel pipe is L /d12" x 10 f'mm water column according to the following formula, where W: flow velocity, T: fluid temperature, P: pressure, L: Pipe length, d: Pipe diameter (written by Corona Corporation Applied Heat Transfer A/5CHACK)
According to the above formula, if the temperature difference between the 41st row steel pipe and the 4th row steel pipe is 300°C and 100°C, the pipe diameter is 6h.
Assuming a pipe length of 300 mm and a flow rate of 20 m/s, the internal resistance of both pipes is 68 rrrm water column and 40 TIr! There is a large difference in the water column, which naturally indicates that it is difficult for the flow rate to flow in the direction of greater resistance.

When the flow rate fluctuates, the preheating medium is evenly distributed from the nozzle 2 to the cold air distribution pipe 3 to the container pipes as shown in FIG. 1, but in reality, the following events occur.

Assuming that the pipe diameter is 60 m, the pipe length is 3000 mm, the flow rate of the preheating medium (air) is 20 m/s, and the average temperature is 300°C, the pressure loss according to the above equation is 68 normal water columns.

If the flow rate is reduced by half, the flow rate will be torn/s and the pressure loss will be 18 columns of water.

Furthermore, when the flow rate is reduced to one-fifth, the pressure loss drastically decreases to 5 mm of water column.

In particular, as shown in Figure 2, when the number of tube rows in the flow direction of the heat source medium is larger than the number of tube rows 412 to 418, the difference in tube wall temperature between the inlet side and the outlet side of the heat source medium steel pipe becomes large, and the tube row 41
The flow rate through ~49 becomes significantly non-uniform.

This invention solves the non-uniformity of temperature in the tube group by dividing the cold air distribution section into multiple sections and controlling the amount of preheating medium sent into these distribution sections. The purpose is to provide a multi-tubular heat exchanger that protects steel pipes.

Hereinafter, the present invention will be explained with reference to an illustrated embodiment.

In FIG. 3, reference numeral 52 indicates a cold air main pipe for a preheating medium, such as air, which is connected to a pump (not shown).

This cold air pipe 52 is connected to one end of branch pipes 53 and 54, respectively.

The other ends of the branch pipes 53 and 54 are connected to cold air distribution boxes 57, respectively.
．． 58 nozzles 55 and 56, and one branch pipe 54 is provided with a flow rate control medium 15.

The cold air distribution section 57 is arranged on the upstream side in the flow of the heat source medium of the flue 1, and the air inflow side of the heat transfer tube group 59 is connected to the end plate 57a of this.

In addition, a cold air distribution box 5 located on the downstream side in the above flow
The air inflow side of the heat exchanger tube group 60 is connected to the end plate 58a of No. 8.

The other sides of the heat exchanger tube groups 59 and 60 are connected to the lower air conversion box 61, respectively.

The lower end of a heat exchanger tube group 62 located further downstream of the heat exchanger tube group 60 is connected to the lower air conversion box 61, and the upper end of the tube group is connected to a hot air header 63.

A hot air pipe (not shown) is connected to the hot air header 63 via a nozzle 64.

Further, the flow rate control medium 1 disposed in the branch pipe 54
5 detects the temperature of the tube wall of the heat transfer tube group 59, 60 or the temperature of the air at the outlet of the tube group 59, 60, and operates based on this to control the amount of air flowing into the cold air distribution arrangement i57, 58. Control.

Now, the air press-injected into the cold air main pipe 52 is transferred to the branch pipe 5.
3. The cold air is distributed by branching into preset amounts at 3 and 54.
57 and 58 to the heat exchanger tube group 59 and 60, and as they flow down the heat exchanger tubes heated by the heat source medium flowing around the tube group, they absorb heat and merge at the lower conversion box 61, and the heat exchanger tube group 62 The hot air header 63 is reached through the hot air header 63.

When the above air flows down the heat transfer tube group 59.60, if the amount of air sent to the cold air distribution arrangement f157.58 is the same, the resistance inside the tube changes due to the temperature drop of the heat source medium as described above, and the flow rate increases. Although it becomes non-uniform, since the flow rate to the upstream heat exchanger tube 59 and the downstream side heat exchanger tube group 60 is controlled by the medium 15, that is, the internal resistance of the heat exchanger tube is forcibly changed by adjusting the flow rate. Even the upstream heat exchanger tube group 59, which was severely damaged, is now supplied with enough air to sufficiently cool it.

Therefore, overheating of the upstream heat exchanger tube group 59 and accompanying deformation are prevented.

Further, the flow rate adjustment medium 15 may of course be configured to operate automatically in accordance with the temperature detection. The distribution section may be multi-divided to change the resistance inside the tube in accordance with the temperature drop of the heat source medium.

As explained above, according to the multi-tube heat exchanger of the present invention, which divides the cold air distribution box into a plurality of parts and controls the flow rate of the preheating medium sent into the boxes, a group of heat transfer tubes located upstream of the heat source material Since the flow rate of the preheating material flowing through the heat exchanger tube group located downstream of this is controlled, the former heat exchanger tube group is sufficiently cooled, and in other words, the heat exchanger tube group is protected and has a long service life. A shell-and-tube heat exchanger can be provided.

[Brief explanation of drawings]

Fig. 1 is a side sectional view showing a conventional shell-and-tube heat exchanger, Fig. 2 is an enlarged plan sectional view of the same, and Fig. 3 is a side sectional view showing an embodiment of the shell-and-tube heat exchanger of the present invention. It is a diagram. 15...Bata valve for flow rate control, 52...
Cold air main piping, 53.54...Branch piping, 57.
58... Cold air distribution box, 59.60 Bent/heat transfer tube group, 61... Lower air conversion inside.

Claims (1)

[Scope of utility model registration request] In a multi-tube heat exchanger that is used by being suspended in a flue and in which a preheating medium flows perpendicularly to the flow of the heat source medium, a heat exchanger connected to the preheating medium inflow side of a group of heat transfer tubes located upstream of the flow of the heat source medium. A multi-tubular heat exchanger comprising: a distribution box divided into a plurality of sections perpendicular to the flow; and a mechanism for controlling the flow rate of a preheating medium to the distribution box divided into the plurality of sections.