JPS6033421A - Air preheater - Google Patents

Abstract

PURPOSE:To provide the outer boundary film of heat transmission pipe with an increased coefficient of heat transfer for thereby improving its heat transfer, by improving the opening of buffle plate in its configuration and heat transmission pipes in their arraying structures. CONSTITUTION:A buffle plate 11 has an opening 34 formed at the center thereof for insertion of inner cylinder 5, and a through-hole 35 for the passage of heat transfer pipe 8 therethrough. The through-hole 35 is formed slightly larger in diameter than the outer diameter of heat transmission pipe 8 including a spiral fin 13, so that the heat transmission pipe 8 may be lightly engaged into the hole 35. The buffle plate 11 is inserted into and welded to an inner cylinder 5, engaging lightly with an outer cylinder 9. The spiral fin 13 of heat transfer pipe 8 is secured to the outer peripheral surface of heat transfer pipe 8 by a high frequency welding, but is not provided at the upper portion of heat transfer pipe 8, i.e., above the uppermost buffle plate 11 in order to prevent a low-temperature corrosion by sulfuric oxides contained in a combustion gas flowing through the heat transfer pipe 8.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an air preheater used in combustion equipment used in petroleum refining and petrochemical plants.

BACKGROUND OF THE INVENTION With the recent trend toward resource conservation and the dramatic rise in fuel costs, combustion equipment such as various industrial furnaces are required to improve their thermal efficiency to the limit.

In general, the use of a heat exchanger for heat recovery, that is, an air preheater, has been known as one of the means for improving the thermal efficiency of combustion equipment such as industrial furnaces.

This air preheater exchanges heat between the high-temperature combustion gas discharged from combustion equipment such as industrial furnaces and the combustion air sent to the furnace. In other words, it preheats the combustion air using the residual heat of the combustion gas.
There are various types depending on the shape of the heat transfer surface, such as Jungstrom type, shell and tube type, and plate type.

If such an air preheater is used, it is possible to reduce the heat loss of the combustion gas, raise the temperature of the combustion air to increase the combustion efficiency, reduce the amount of excess air, and improve the thermal efficiency of the entire industrial furnace.

However, in such a conventional air preheater,
There is a drawback that when the combustion gas flows through the heat transfer section, it encounters flow resistance and a large pressure loss occurs.

Therefore, it is necessary to provide a ventilation fan to forcibly suck in the combustion gas. The installation of such a ventilation fan usually requires duct construction to connect the air preheater installed on the ground with the industrial furnace and the ventilation fan, making the construction work related to the installation of the air preheater complicated. These construction costs alone typically account for a significant portion of the price of the entire industrial furnace system. Furthermore, the power cost for driving the combustion gas suction ventilation fan cannot be ignored.

Furthermore, in conventional air preheaters, the entire amount of combustion gas flows through a tube-shaped, plate-shaped heat transfer section, etc., so the design had to be made in accordance with the maximum load of the industrial furnace.

As a result, during most normal operations other than the maximum load, which is usually extremely short, the exhaust fan has an unreasonably large capacity together with the ventilation fan for sucking combustion gas and forcing air for combustion, which is extremely uneconomical.

In view of these circumstances, the air preheating section, which can adjust the flow rate of combustion gas to the heat transfer section of the air preheating chamber consisting of an annular space according to the load of the combustion equipment, has been organically combined with the combustion equipment main body. The air preheating section, which can suppress the pressure loss in the combustion air-combustion-combustion gas system of the combustion equipment system and generate less thermal stress, is installed in the normal flue duct or part of the chimney of the combustion equipment. An air preheater has been devised that is used as a combustion gas suction passage fan, eliminates the need for associated ductwork, and saves power.

This air preheater includes an inner cylinder through which combustion gas from a combustion device flows, and an outer cylinder disposed around the outer circumference of the inner cylinder and having an inlet and an outlet for combustion air to be supplied to the combustion device. , an air preheating chamber consisting of an annular space through which the combustion air flows, and a damper for regulating gas flow rate is provided in the inner cylinder, and a damper is provided in the air preheating chamber in the longitudinal direction of the outer periphery of the inner cylinder. Multiple lines are arranged around this along the
In addition, a heat transfer pipe having a large number of fins is provided on the outer circumferential surface of the cylinder, bypassing the damper and communicating the upstream and downstream parts of the damper in the cylinder.

Incidentally, the arrangement structure of heat transfer pipes in such a conventional air preheater is as shown in FIG. 1A1-(C).

In addition, in these figures, 35 is an inner cylinder, 36 is an outer cylinder, 3
7 is a damper, and 38 is a heat transfer pipe.

That is, the one shown in FIG. 1 IAI uses vertical fins 39 as the heat transfer pipe 38, and allows air to flow between the inner cylinder 35 and the outer cylinder 36 in the direction in which the heat transfer pipe 38 extends. This is what I did.

However, in this type of air preheater, when the heat transfer pipes 38 are arranged in multiple layers, the speed of the air flowing on the fin 39 side decreases, so the film heat transfer coefficient between the fins 39 and the air decreases significantly. There is a drawback that it does.

In addition, the one shown in FIG. 1 (Bl and +C1 is the inner cylinder 35
A plurality of baffle plates 41 are provided at predetermined intervals in the axial direction on a surface substantially perpendicular to the axis of the space between the outer cylinder 36 and the outer cylinder 36, and divide the space into a plurality of chambers in the axial direction. The openings 42 cut out based on the notch line on the outer periphery of the upper and lower adjacent panful plates 4 are respectively
The baffle plates 41 are arranged so that each baffle plate 41 is alternately located at opposite positions, and air is sequentially circulated through the chambers partitioned by the baffle plates 41. In the case of FIG. 1 IB), a heat transfer pipe 38 using spiral fins 40 is disposed throughout the space between the inner cylinder 35 and the outer cylinder 36, and the first
In the one shown in Fig. tel, a similar heat transfer pipe 38 is arranged in a part of the space that does not pass through any opening 42 of a panful plate 41.

By the way, as a result of the forced spiral movement of the air flowing between the inner cylinder 35 and the outer cylinder 36, if the heat transfer pipe 3B is not provided, the outer circumference of the space between the inner cylinder 35 and the outer cylinder 36 will change. The air flowing through this section has a high velocity, and the air flowing through the inner circumferential section has a low velocity. It is a well-known fact that the higher the air velocity, the better the heat transfer coefficient between the air and the heat transfer pipes 38. Therefore, in order to make the arranged heat transfer pipes 38 participate in heat transfer most effectively, It is desirable that the air velocity be equal in all parts of the outer circumferential portion and the inner circumferential portion.

However, in the case shown in FIG. 1cI, since the opening 42 of the baffle plate 41 is formed by a simple linear notch, the heat transfer pipes 38 can only be arranged in the same number on the outer circumference and the inner circumference. You cannot expect such an effect.

Furthermore, in the case shown in FIG. 1cI, if the openings 42 are made small in order to increase the number of heat transfer pipes 38 arranged, there is a disadvantage that the pressure loss on the air side becomes large. On the other hand, if the pressure loss is to be reduced, the opening 42 must be made larger, resulting in the inconvenience that a large number of heat transfer pipes 38 cannot be arranged.

Further, as shown in FIG. 1cI, when the heat transfer pipes 38 are also arranged in the opening 42 portion, the following problem occurs because the spiral fins 40 are adopted as the heat transfer pipes 38.

That is, the air flowing through the opening 42 does not flow across the heat transfer pipe 38, but flows along the heat transfer pipe 38. As is a well-known fact, in the case of spiral fin 40,
It acts effectively on heat transfer for cross-crossing airflow, but
It does not work effectively on parallel flows.

Since high-temperature combustion gas flows inside the heat transfer pipe 38, if the spiral fins 40 do not work effectively, the heat transfer pipe 38 will not be cooled and the heat transfer pipe will overheat and burn out. It turns out.

In view of the above-mentioned conventional circumstances, the present invention divides a space between an inner cylinder and an outer cylinder using a baffle plate, and connects a heat transfer pipe with a spiral fin to a pan full plate opening in the space. In an air preheater configured to be installed in a location where neither of them passes through, by improving the opening shape of the panful plate and the arrangement structure of the heat transfer pipes, the number of heat transfer pipes arranged in the outer circumference of the space is reduced compared to the inner circumference of the space. It is possible to effectively involve all the heat transfer pipes in the array in the transmission, and it is possible to have a large number of arrays while maintaining the opening area that minimizes the pressure loss on the air side. As a result, the present invention provides an air preheater that can improve heat transfer by increasing the heat transfer coefficient of the outer membrane of the heat transfer pipe.

Hereinafter, one embodiment of the present invention will be described based on FIGS. 2 to 7.

In Figure 2 (Al, (Bl, icl), 1 is attached to a conical flue duct and a conical chimney on the side of the furnace body (not shown), which constitutes a flue through which combustion gas from the furnace body (not shown) flows. 5 is an inner cylinder through which combustion gas flows, and 6 is a damper for adjusting the gas flow rate arranged approximately in the center of the flue 5A of the inner cylinder 5.This damper 6 is rotated as appropriate. This makes it possible to narrow down the flue 5A, and when the flue 5A is placed in a horizontal position, the flue 5A is blocked by a spiral 8 on the outer peripheral surface that bypasses the damper 6 and communicates the upstream and downstream sides of the damper 6. A heat transfer pipe 9 comprising fins 13 is arranged on the outer periphery of the inner cylinder 5 in which the heat transfer pipes 8 are arranged, and combustion air that reaches the combustion part of the furnace body flows between the outer periphery of the inner cylinder 5 and the outer periphery of the inner cylinder 5. This is an outer cylinder that constitutes an annular air preheating chamber 9A.

The outer cylinder 9 is provided with an air inlet 9a and an air outlet 9b at opposing positions on the outer periphery of the upper and lower ends in the figure, respectively, so that combustion air flows through the air preheating chamber 9A in a direction opposite to the flow of combustion gas in the flue 5A. It is now possible to distribute it. 10 is a heat insulating material fixed to the outer peripheral surface of the outer cylinder 9.

A ventilation duct from a ventilation fan (not shown) for sucking outside air is connected to the air introduction port 9a of the outer cylinder 9, and an air delivery duct (not shown) is connected to the air delivery port 9b. Connect to the combustion air supply of the

Reference numeral 11 denotes two or more baffle plates that are disposed at a predetermined interval in the axial direction on a surface substantially perpendicular to the axis in the air preheating chamber 9A to partition the air preheating chamber 9A into three or more chambers in the axial direction. In this case, three chambers are prepared and divided into four chambers 12A to 12D. 14 is formed by notching in each of the panful plates 11 based on a pair of notch lines extending from a point on the outer circumference of the inner cylinder 5 to the inner circumference of the outer cylinder 9 in a figure 7 shape with the normal line passing through the point as a line of symmetry. The openings are provided so as to be alternately located at opposite positions for each of the vertically adjacent baffle plates 11.

Here, the heat transfer pipe 8 is installed in a portion of the air 'P heat chamber 9A that does not pass through any of the baffle plate openings 14, so as to surround the inner cylinder 5 along the outer periphery in the longitudinal direction. A plurality of them are concentrically arranged so that the number gradually increases from the outer peripheral surface to the inner peripheral surface of the outer cylinder 9.

'Next, the detailed structure of each air preheater structure mentioned above will be explained.

In FIG. 2fA), IBI, an upper tube sheet 15 and a lower tube sheet 16 are provided at the upper and lower ends of the outer cylinder 9, respectively. Penetration fixing holes 17 and 18 for the inner cylinder 5 and each heat transfer pipe 8 are formed in these upper tube sheet 15 and lower tube sheet 16, and the upper end of these inner cylinder 5 and each heat transfer pipe 8 are penetrated and welded. Fixed.

The upper tube plate 15 is fixedly attached to the upper end surface of the outer cylinder 9. On the other hand, in order to absorb the difference between the elongation of the heat transfer pipe 8 and the elongation of the outer cylinder 9 due to heat, the lower tube plate 16 is not fixed to the outer cylinder 9 but is floated by sealing between the outer cylinder 9 and the outer cylinder 9 with a backing. It is supposed to be done.

This is shown in FIG. 3. In the figure, 19 is an annular banking case fixed to the lower surface of the outer periphery of the lower tube plate 16 with a fixing device such as a screw, and there is an annular space between it and the inner periphery of the outer cylinder 9. 2
Define 0. 21 is a banking that fills this annular space 20.

The support shaft 22 of the damper 6 is connected to a pipe body 2 provided in the diametrical direction of the damper 6, as shown in FIG.
3 and is fixedly attached to the pipe body 23 with a fixing tool such as a screw. Also, both sides of the support shaft 22 are formed into an inner cylinder 5.
It is rotatably fitted into a sleeve tube 24 supported by the outer cylinder 9, and this sleeve tube 24 is fixed by a sleeve support lug 25 on the outer peripheral wall of the outer cylinder 9. This is shown in Figure 5 (Al-(D
As shown in FIG.
One flange plate is fixed to the outer peripheral wall of the outer cylinder 9 by fixing devices such as screws or welding, and sleeve tube support holes provided in both flange plates 26 and 27. The sleeve tube 24 is fitted into 26A and 27A and fixed by welding.

In addition, in order to ensure that the sleeve tube 2A and the inner cylinder 5 are loosely fitted in the snow-covered state, a long through hole 29 is formed in the inner cylinder 5 as shown in FIG. 5(0). Asbestos 30 is interposed between the through hole 29 and the sleeve tube 24. Further, a bearing 31 is fixedly supported on the outer flange plate 27 of the anti-leave support lug 25 with a fixing device such as a screw, and the sleeve tube 24 is attached to this bearing 31.
The end portion of the support shaft 22 that has been inserted through the support shaft 22 is supported.゛Also, as shown in Fig. 4+AI and IBI, when the flue 5A in the inner cylinder 5 is closed by the damper 6, the pipe body 23 of the damper 6 is placed in each semicircular part between them. A pair of seal plates 32 each having a shape of a ring-shaped member divided into two are provided to ensure reliable sealing. This seal plate 32 is '+1' in Fig. 4? As shown in 1', they are fixed by welding to the opposing end faces of the semi-circumferential portion of the damper 6, so that when the damper 6 is in the closed state, they protrude to opposing positions on the circumferential wall of the inner cylinder 5. Next to the fixed valve seat 33, the baffle plate 11 has an opening 34 in the center to be fitted into the inner cylinder 5, as shown in FIG. The through hole 35 is formed to have a slightly larger diameter than the outer diameter of the heat transfer pipe 8 including the spiral fin 13, and the heat transfer pipe 8 is loosely fitted therein. The eye 1 is fitted into the inner cylinder 5 and fixed by welding, and is loosely fitted into the outer cylinder 9.
゛The spiral fins 13 of the heat transfer pipe 8 are fixed to the outer periphery of the heat transfer vibe 8 by high frequency welding. It is not provided in the upper part of the heat pipe 8, that is, in the part above the baffle plate 11 at the uppermost position.

Next, a procedure for assembling such an air preheater structure will be explained.

(1) The inner cylinder 5, upper and lower tube plates 15, 16, heat transfer pipe 8, and panful plate 11 are all welded and fixed to form an integral structure.

(2) As shown in FIG. 2 (C1 line C-C), cover the structure assembled in (1) with the outer cylinder 9, which has been divided into two in the vertical direction, from both sides. Flanges 9c and 9d formed on 9C and 9D are fixed to each other with bolts, and the upper tube plate 15 and the upper end of the outer cylinder 9 are fixed with bolts.

(3) Sleeve tube 24 and pipe body 2 for damper 6
3 is inserted into the inner cylinder 5 and outer cylinder 9, and the sleeve support lug 25 is inserted into the end of the pipe body protruding from the outer circumferential wall of the outer cylinder 9. The inner flange plate 26 is fixed to the outer circumferential wall of the outer cylinder 9 using a fixture.

(4) Weld and fix the sleeve support lug 5 and the outer cylinder 9 and the pipe body and the sleeve support lug 25.

(5) The pipe body 23 is cut from the inside of the inner cylinder 5 by the diameter length of the damper 6, and the pipe body 23 and the sleeve tube 24 are formed separately.

A pre-formed damper 6 with the pipe body 23 of +61 +51 as one of the components is placed in the inner cylinder 5, and the support shaft 22 is connected to the sleeve tube 24 and the pipe body 2 from the outside of the outer cylinder 9.
Insert into 3.

(7) Fix the damper 6 to the support shaft 22 with the pipe body 23 using a fixture, and attach the bearing 31 to the end of the support shaft 22.

(8) Fix the bearing 31 to the outer flange plate 27 of the filter support lug 25 using a fixture at a position where the support shaft 22 does not touch the sleeve tube 24.

Next, the operation of the air preheater having such a configuration will be explained.

Combustion gas supplied from the flue duct of the furnace body (approximately 200
℃) flows into the heat transfer pipe 8, the other part flows toward the damper 6, passes through the heat transfer pipe 8 and the flue 5A, and reaches the upper end of the heat transfer pipe 8 and the inner cylinder 5. , where they join together and are discharged to the outside through the chimney.

On the other hand, when the ventilation fan is activated, external air flows through the air duct into the air preheating chamber 9A through the air inlet 9a of the outer cylinder 9.
The liquid is forcibly introduced into the uppermost chamber 12A within the chamber. The room 12
The air introduced into A flows across the heat transfer pipe 8,
It is introduced into the second stage chamber 12B through the opening 14 of the uppermost pan full brake eye 1, and similarly flows across the heat transfer pipe 8, and similarly flows into the third stage chamber 12C and the lowermost chamber 12D.
During this time, heat exchange takes place between the air and the combustion gas flowing in the heat transfer pipe 8 and the flue 5A via the heat transfer pipe 8 and the outer wall of the inner cylinder 5. be exposed. Therefore, the air flowing through the air preheating chamber 9A is heated and becomes air for grilling at the optimum temperature, and is supplied from the air outlet 9b to the combustion air supply section of the furnace body, and the air to be heated is heated in the furnace body. While the purpose of the furnace, such as heating, is accomplished, combustion gases are exhausted from the furnace body and introduced into the air preheater.

Here, the action and effect of the damper 6 will be explained.

If the combustion gas circulation area in the flue 5A is changed by operating the damper 6 and changing its rotation angle,
The ratio of the flow rate of combustion gas flowing through the flue 5A and the heat transfer pipe 8 changes. In particular, if the damper 6 is positioned in the horizontal position shown by the two-dot chain line as described above, the flue 5A
is blocked, and the entire amount of combustion gas flows through the heat transfer pipe 8.

Therefore, during the extremely short maximum load of the furnace, the damper 6 is operated to open the flue 5A as appropriate and a portion of the combustion gas flows into the flue 5A.
By reducing the amount of combustion gas flowing through the heat transfer pipe 8, the pressure loss of the combustion gas in the air preheater can be kept small.

Also, during most normal operations other than when the Hibiki is at its maximum load, the damper 6 is operated to throttle the flue 5A.
By suppressing the amount of combustion gas flowing through the heat transfer pipe 8 and increasing the amount of combustion gas flowing inside the heat transfer pipe 8, effective heat recovery can be achieved.

According to the air preheater having such a configuration, the panful plate 1
A fan-shaped opening 14 is formed in the air preheating chamber 9A, and a fan-shaped opening 14 is formed in the area of the air preheating chamber 9A that does not pass through any of the openings. The structure in which a plurality of heat transfer pipes 8 having spiral fins 13 are arranged concentrically on the outer circumferential surface such that the number increases from the surface to the inner circumferential surface of the outer cylinder 9 has the following advantages. .

+11 As a result of being able to arrange as many heat transfer pipes 8 as possible in the outer circumferential portion and the inner circumferential portion of the air preheating chamber 9A, a large amount of resistance is provided to the air that attempts to flow at high speed in the outer circumferential portion due to forced spiral motion. Since the air velocity can be made substantially the same in the outer circumferential portion and the inner circumferential portion, all of the arranged heat transfer pipes 8 can be most effectively involved in heat transfer.

In this case, the larger the number of circumferences of the heat transfer pipes 8 arranged, the greater this effect becomes.

(2) Compared to the opening with the linear cutout shown in Figure 1 (Bl), the fan-shaped opening allows more heat transfer pipes 8 to be arranged for the same opening area. This has the advantage that a large number of heat transfer pipes 8 can be arranged while minimizing pressure loss on the air side.

The graph shown in FIG. 7 compares the performance of the air preheater according to the present invention and the air preheater shown in FIG. When the thermal coefficient is set to 100, it represents the change in the coefficient due to an increase in the number of arrays.

In addition, the number of heat transfer pipes in the air preheater being compared.

The heat transfer area and the shapes of the outer cylinder and inner cylinder are both the same. Further, the amount of air supplied to the air preheater and the temperature conditions are the same for each arrangement circumference.

As is clear from the graph, the air preheater according to the present invention has a larger value of the outer membrane heat transfer coefficient than the conventional one, and it is clear that efficient heat transfer can be performed.

As explained above, according to the present invention, the space between the inner cylinder and the outer cylinder is divided using a baffle plate, and the heat transfer pipe with spiral fins is connected to the opening of the pan full plate in the space. In an air preheater configured to be disposed in a part where the heat transfer pipes do not pass through, by improving the opening shape of the baffle plate and the arrangement structure of the heat transfer pipes, the number of heat transfer pipes arranged in the outer circumference part of the space can be greater than that in the inner circumference part, All the arranged heat transfer pipes can be effectively involved in the transfer, and the opening area can minimize the pressure loss on the air side while allowing for a large number of arrangements. It is possible to provide an air preheater that can improve heat transfer by increasing the heat transfer coefficient of the outer membrane of a heat transfer pipe.

[Brief explanation of the drawing]

FIG. 1 (Al-(C1 is a schematic cross-sectional view showing the pan-full plate shape and heat transfer pipe arrangement structure of a conventional air preheater; FIG. 2 is an air preheater according to the present invention. (Al is a front longitudinal sectional view, (Bl
Ic) is a plan view, Ic) is a sectional view taken along the arrow A-A in +Al, and Figure 3 (At is an enlarged view of part B in Figure 2 (Al);
4(A) is a plan view showing the structure of the damper, FIG. 5 (A) is a plan view showing the structure of the damper, FIG. Front sectional view, same figure (C1 is the same figure (Bl right side view, same figure (Di
is a left side view, Figure 6 is a plan view of the baffle plate, and Figure 7 is a left side view.
The figure is a graph explaining the effect of the device of the present invention, and shows the change in the outer membrane heat transfer coefficient as the number of arrays increases, assuming that the outer membrane heat transfer coefficient in the case of one round arrangement is 100. 1... Air preheater 5... Inner cylinder 5A... Flue 6... Damper 8... Heat transfer pipe 9... Outer cylinder 9A... Air preheating chamber 11... Baffle plate 1
3... Spiral fin 14... Opening patent applicant Niigata Iron Works Co., Ltd. Agent Patent attorney Fujio Sasashima\7 0 τ-1 Hinoki Figure 3 (A) Figure 2 (C,) 110-

Claims (1)

[Claims] Between an inner cylinder through which combustion gas of a combustion device flows, and an outer cylinder arranged on the outer periphery of the inner cylinder and having an inlet and an outlet for combustion air supplied to the combustion device on the outer peripheral wall. an air preheating chamber consisting of an annular space through which the combustion air flows, and a damper for regulating gas flow rate is provided in the inner cylinder, and a damper is provided in the inner cylinder at a predetermined interval in the axial direction on a surface substantially perpendicular to the axis of the air preheating chamber. Two or more baffle plates are arranged to divide the air preheating chamber into three or more chambers in the axial direction, and each of the baffle plates is symmetrical with respect to a normal line passing from a point on the outer circumference of the inner circular part to the cough point. Fan-shaped openings cut out based on a pair of notch lines extending in the shape of a letter ■ on the inner periphery of the outer cylinder are provided so as to be positioned alternately in opposite positions in each vertically adjacent panful plate. The number of baffle plates gradually increases from the outer circumferential surface of the inner cylinder to the inner circumferential surface of the outer cylinder so as to surround it along the circumferential direction of the inner cylinder in a portion that does not pass through any of the baffle plate notches. A plurality of heat transfer pipes are arranged in a concentric manner as shown in FIG. Air preheater.