JPH027352B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tube heating furnace that mainly utilizes radiation heat transfer.

As this type of heating furnace, a coal slurry heating furnace used, for example, in a preheating step of coal slurry in a coal liquefaction process is known.

A typical coal liquefaction process is shown in Figure 1, and the main processes include adding hydrogen and removing impurities such as sulfur, nitrogen, and ash. In this process, coal slurry is made by mixing pulverized coal with a solvent containing a large amount of aromatic compounds, and then adding mainly hydrogen gas and light hydrocarbon gas, which is then heated in the preheating step. A tube-type heating furnace that heats the coal slurry used in the process is essential in the coal liquefaction process, and a tube-type heating furnace that uses radiant heat transfer is used.

This tube heating furnace has a combustion chamber equipped with a burner,
The main part is a heat exchanger tube of about 11/2 ^B to 6 ^B installed in the combustion chamber, and the heated fluid circulating inside the heat exchanger tube is heated using flame as a radiant heat source or high temperature gas from combustion as a heat source. When used as a tube heating furnace for heating coal slurry, the following specifications are required.

(1) Coal slurry consists of gas (mainly hydrogen gas and light hydrocarbon gas), liquid (solvent), and solid (coal).
It is a three-phase fluid, and in order to react with the hydrogen gas, high pressure (50 to 300 kg/1 cm ² G) is required.
However, if the fluid flow rate is high, the heat transfer tube will be pressurized.
When using a 180゜u bend, centrifugal force acts on the bend, making it easier for the solids to separate from the liquid.
There is a risk that the inner wall of the bend will be scraped off due to erosion, resulting in holes or other damage to the bend. On the other hand, if the fluid flow rate is low, solids (coal) suspended in the liquid may precipitate and clog the heat exchanger tube, which is particularly noticeable in the 180° u bend.

Therefore, in heat transfer tubes, it is necessary to maintain an appropriate fluid flow rate and to prevent separation, precipitation, etc.
It is recommended to avoid the use of 180°u bends.

(2) Since solvents are generally used that contain large amounts of aromatic compounds with large molecular weights, if heating is not done uniformly and localized overheating occurs, the coal slurry decomposes and causes coking (carbonization), resulting in the formation of Objects may adhere to the inner walls of the heat exchanger tubes, clogging the tubes, inhibiting fluid flow, and causing localized overheating. Therefore, it is necessary to heat the heat exchanger tube as uniformly as possible.

(3) The coal slurry inside the heat transfer tube can be gas, liquid,
Since it is a three-phase solid, if there is a part of the flow that changes from an upward flow to a downward flow, or conversely from a downward flow to an upward flow, there is a risk that the pipe will vibrate.

Therefore, it is desirable that the fluid in the heat transfer tube be kept in either an upward flow or a downward flow as much as possible.

Here, the structure of a conventionally used heating furnace is shown in FIGS. 2 and 3.

The one shown in FIGS. 2A and 2B is a substantially vertical circular spiral wound inside a cylindrical combustion chamber 1 lined with a heat insulating material so as to include the vertical axis along the inner wall of the combustion chamber 1. Heat exchanger tubes 2 are arranged in the furnace, and the heat exchanger tubes 2 are heated from the center of the furnace by a burner 3 installed in the center of the hearth.

This type of heating furnace does not have a 180° u bend that can cause fluid erosion or clogging, and because the slurry flow direction is constant from top to bottom, pipe vibration is less likely to occur. On the other hand, it is difficult to build a large heating furnace due to the structural limitations of the circular spiral heat exchanger tube. In other words, the winding diameter of the heat transfer tube exceeds approximately 8 m and the height
If the length exceeds 12 m, the heat from the burner will not be distributed evenly, causing local overheating, and the structure of the furnace body will also make it difficult to manufacture. In addition, because the heat transfer tube is heated on one side only by the burner in the center, the radiant heat is not spread evenly, and only the side facing the burner flame is heated strongly, causing the slurry to decompose and cause coking (carbonization), which is transferred. It adheres to the inner wall of the heat tube, narrowing the flow path and creating a risk of extremely high tube surface temperature.

3A and 3B, a meandering heat exchanger tube 2' extending laterally is disposed along opposite side walls in a box-shaped combustion chamber 1', and this heat exchanger tube 2'
is heated by burners 3' arranged in a row in the center of the hearth.

In the case of this type of heating furnace, since the heat transfer tube 2' is relatively free from structural restrictions, it is possible to easily increase the size of the furnace, but on the other hand, there are the following drawbacks.

That is, since heat exchanger tubes use 180°u bends with short curvature radius of less than twice the inner diameter of the tube to connect straight sections, the bends are prone to damage due to erosion, and clogging occurs at these bends. In addition, similar to the heating furnace shown in FIG. 2, the heat exchanger tube is heated on one side, and the slurry tends to cause coking, causing local overheating and clogging.

Furthermore, in the case where the heat transfer tubes shown in FIG. 3 are formed in a meandering shape extending in the vertical direction, the fluid flow in the tubes flows from upward flow to downward flow or vice versa, and the flow direction cannot be maintained in one direction. The disadvantage is that the heat exchanger tubes vibrate.

Note that the problems shown in FIGS. 2A and 2B and 3A and 3B are not limited to the case where a three-phase fluid to be heated consisting of solid, liquid, and gas is heated.

For example, in a heating furnace that heats the feed (atmospheric residual oil) of a vacuum distillation column in petroleum refining, even if it is supplied in the liquid phase, it becomes a gas-liquid mixture by heating and flows through the heat transfer tube at a speed close to the speed of sound. In addition, erosion occurs due to the accompanying liquid. Furthermore, vibrations due to multiphase are not limited to three phases consisting of solid, liquid, and gas, but naturally occur in gas-liquid mixed phases. Furthermore, hydrocarbons such as petroleum naturally cause coking.

Therefore, the present invention solves the above-mentioned problems in heating furnaces all at once, and also solves the problem of heating the liquid phase of the organic hydrocarbon and the solid phase of the catalyst, which is a common practice in the chemical field. Furthermore, the present invention provides a tube-type heating furnace that is capable of heating three-phase fluids to be heated, including solid, liquid, and gas, in the heating furnace.

That is, the tube heating furnace of the present invention uses a spiral heat exchanger tube consisting of a straight section and a central curvature radius section that is 5 times or more the inner diameter of the tube, and is configured to heat both sides of the spiral heat exchanger tube. As a result, the heating furnace satisfies all the specifications desired for the heating furnace, can efficiently heat the fluid to be heated, has a high degree of safety, has excellent durability, and can easily be made larger.

Embodiments of the present invention will be described below with reference to FIGS. 4 to 6.

In FIGS. 4A and 4B, 10 is a heating furnace main body casing constructed on a foundation 11, and 12 is a furnace wall made of heat-resistant brick castable refractory or mortar, forming a combustion chamber 13 inside. The main casing 10 has an octagonal box shape with a cross section elongated in one direction, and the furnace wall 12 is also formed in this shape. 1
Reference numeral 4 denotes an oval spiral heat exchanger tube arranged at the center of the combustion chamber 13 and wound (approximately in the vertical direction) to include the vertical axis. Center curvature radius r more than 7.5 times
It consists of a music part 14B having the following. Note that the center radius of curvature used here is a radius of curvature based on the center of the heat exchanger tube 14, and is not based on the outer curve or inner curve of the heat exchanger tube 14.

The oval spiral heat transfer tube 14 has a configuration in which the tube is wound into two threads so that the flow of the fluid to be heated becomes two passes.
When passing, there are three strips, and the number of strips is determined depending on the number of passes required. Moreover, the arrangement interval between the oval spiral heat exchanger tubes 14 is 1.2 to 1.2 to the outer diameter of the heat exchanger tubes 14.
A three-fold pitch is preferred, and a two-fold pitch is more preferred.

The upper and lower ends of the heat transfer tube 14 serve as an inlet 14a and an outlet 14b for the fluid to be heated, respectively, and the inlet 14a penetrates the furnace wall 12 on one side and is led out of the casing 10. , the outlet part 14b is the hearth 1
2A. 15 is a tube support made of heat-resistant cast steel that supports the heat exchanger tube 14 in the furnace, and as shown in FIG. Support claws 1 that protrude in multiple steps in the direction
5b, and the lower ends of the heat transfer tubes 14 arranged in multiple stages are supported on the support claws 15b in a sword-like manner.

This tube support 15 has a lower end that is connected to the hearth 1.
2A, and is supported with its upper end passing through a through hole 12a in the furnace wall 12 in the ceiling, so that thermal expansion when exposed to high temperature in the furnace is released through the through hole 12a. There is.

Reference numeral 16 denotes heat exchanger tubes 14 arranged with a floor burner serving as a first heat source that heats the inner circumferential outer surface of the heat exchanger tubes 14.
A plurality of them are arranged in a row at regular intervals in the center of the hearth 12A, facing the inner surface, so as to generate flame upward. 17 is heat exchanger tube 1
4. A plurality of linear wall burners are provided as a second heat source for heating the outer periphery of the outer surface of the furnace wall 12 and are spaced apart from each other at regular intervals in the circumferential direction at the lowest end position of the inner periphery of the furnace wall 12.

This wall burner 17 consists of a burner part 17a bent upward from the furnace wall 12 and a burner tile block part 17b bent in the same direction. It is configured to heat the furnace wall 12 by forming a flame, and the outer periphery and outer surface of the heat transfer tube 14 is heated by radiation heat from the furnace wall 12. Reference numerals 18 and 19 are window boxes for the two types of floor burners 16 and wall burners 17, respectively, and serve as mufflers to reduce noise generated from each burner 16, 17.

In addition, in this embodiment, the above floor burner 1
6 and 12 wall burners 17 are provided, but the number can be freely set depending on the size of the furnace. In this case, the shortest burner center distance c between the floor burners 16 and the wall burner 17
It is preferable that the shortest distance d between the burner centers satisfies the following formula in order to prevent incomplete combustion caused by interference between the flames of the individual burners.

c≧k+0.1 [m] d≧f+0.1 [m] where k is the maximum diameter of the flame of the floor burner 16 [m], and f is the maximum width of the block portion 17b of the wall burner 17 [m].

On the other hand, 30 is a chimney for discharging combustion exhaust gas, which is installed on the furnace wall 12 in the ceiling and communicates with the inside of the combustion chamber 13.
It is lined with a heat insulating material 30a. 31 is chimney 3
The combustion exhaust gas draft adjustment damper installed in the combustion exhaust gas draft is manually controlled and set as appropriate.

In the heating furnace configured as described above, the fluid to be heated is introduced from the inlet portion 14a of the heat exchanger tube 14, flows downward from the top to the bottom within the heat exchanger tube 14, and reaches the outlet portion 14b. It is heated by radiant heat transfer from the outer surface.

It goes without saying that the heat transfer tube 14 is given some convective heat transfer due to the flow of combustion exhaust gas in the combustion chamber 13 by the burners 16 and 17.

If the central radius of curvature r of the curved portion 14B of the spiral heat transfer tube 14 is at least 5 times or more preferably 7.5 times or more the inner diameter h of the tube, damage such as abrasion in the curved portion 14B and solids in the slurry may settle and transfer. There is no possibility that the heat pipe 14 will become clogged. This will be described in more detail, including the results of a study on a heating furnace with an inner diameter of 4 inches in which coal slurry was used as the fluid to be heated.

When the slurry flow velocity is in the range of 1.2 to 3.2 m/sec.
The ratio η between the amount of thinning due to erosion in the curved portion of the heat transfer tube and the amount of thinning due to erosion in the straight portion of the heat transfer tube is as shown in FIG. Note that r/h and η in FIG. 7 are as shown below.

r/h = center radius of curvature of heat exchanger tube [m] / inner diameter of heat exchanger tube [m] η = amount of thinning of curved part of heat exchanger tube [mm/day] / amount of thinning of straight part of heat exchanger tube [mm/ On the other hand, in the case of slurry such as cole slurry,
In the vicinity of the inlet of the heat exchanger tube, the coal grains contained in the fluid have not yet begun to dissolve, so there is a particularly large amount of solid phase consisting of coal grains. If the radius of curvature of the bent portion (bent) of the heat transfer tube, which uses slurry as the heated fluid, is not appropriate,
This part of the song will cause plugging. According to a study using a 4-inch tube,
The speed at which blockage occurs in this curved portion is shown in FIG. Incidentally, μ and v _c in FIG. 8 are as shown below.

μ: Average particle size of coal [MESH] v _c : Minimum flow velocity that does not cause clogging [m/S] Also, r/h is the same as in Fig. 7. As is clear from FIGS. 7 and 8, in the range of r/h≧5, preferably r/h≧7.5, there is little adverse effect especially in the curved portion of the heat exchanger tube, and it can be designed almost equivalently to a straight portion. I understand.

Furthermore, in order to prevent local heating in the vertical direction of the spiral shape of the heat transfer tube 14, the center radius of curvature r and the distance a from the surface of the furnace wall 12 to the center of the heat transfer tube 14 should further satisfy the following formula. is preferable.

That is, it is preferable that the center radius of curvature r [unit: m] satisfies the following three equations at the same time.

r≧5×h (preferably r≧7.5×h) …(1) r≧0.28×g+0.20 …(2) r≧0.13×b …(3) However, g: Floor burner 16 Heat amount per unit [×
10 ⁶ Kcal/Hr] h: Pipe diameter of the heat exchanger tube 14 [m] b: Vertical length of the spiral shape of the heat exchanger tube 14, that is, the distance between the centers of the top and bottom heat exchanger tubes 14 [m] (2) above The formula means the minimum distance that the heat transfer tubes 14 must be from the floor burner 16,
The above equation (3) means the minimum value that needs to be maintained in order to make the heat absorption distribution in the vertical direction of the spiral heat exchanger tube 14 uniform by the floor burner 16.

The distance a [unit: m] from the surface of the furnace wall 12 to the center of the heat exchanger tube 14 is preferably a value that satisfies the following formula.

Vertical length b of the spiral shape of the heat exchanger tube 14
is less than 11.2 m, 0.848≦a...(4) More preferably, 0.848≦a<1.272...(4)' The vertical length b of the spiral shape of the heat exchanger tube 14 is
In the case of 11.2 m or more, 0.0757×b≦a ...(5) More preferably, 0.0757×b≦a<0.1135×b ...(5)' The above equations (4) and (5) are It means the minimum value that needs to be maintained in order to make the heat absorption distribution in the vertical direction of the spiral shape of the heat tube 14 uniform.

When the heating furnace of the above embodiment is used as a coal slurry heating furnace in a coal liquefaction plant, for example, an elliptical spiral heat exchanger tube having a curved portion 14B with a center radius of curvature in the longitudinal direction of 5 times or more the inner diameter of the heat exchanger tube. 14 and that the heat exchanger tube 14 is heated on both sides by a floor burner 16 and a wall burner 17, the following advantages are obtained.

(1) We did not use a short 180°u bend with a diameter less than twice the inner diameter of the tube, but instead installed an oval spiral heat exchanger tube with a central radius of curvature that was five times the inner diameter of the tube. No erosion occurs,
Damage such as wear of the tube is less likely to occur. In addition, there is no possibility that solids (coal) in the slurry will settle and clog the heat exchanger tubes.

(2) The heat transfer tubes are heated evenly from the inner and outer surfaces of the loop-shaped piping array, making it difficult for localized overheated areas to occur and for the fluid to be less prone to caulking, which prevents clogging of the pipes. do not have.

For example, if heat exchanger tubes are arranged at a pitch twice the outer diameter of the heat exchanger tubes, and the heat flux (heat absorption amount per unit surface area of the heat exchanger tubes) is the same, double-sided heating will be different from conventional single-sided heating. The maximum heat flux generated on the side facing the flame is 1.5 times lower than in the case of heating.

(3) Because the fluid always flows downward and is held in one direction, the heat transfer tubes are less likely to vibrate.

(4) Heat transfer tubes can be easily made larger by forming long straight sections and long diameter sections, and are not subject to structural constraints like conventional circular spiral heat transfer tubes. The double-sided heating structure makes it possible to maintain a uniform heating state.

Therefore, large furnaces can be manufactured without any restrictions.

Next, another embodiment of the present invention will be described based on FIGS. 6A and 6B.

This shows an example in which the heating furnace structure shown in Fig. 5 is applied to large-scale equipment, and the heating furnace main body casing 20 is wound so as to include the vertical axis, similar to the furnace internal structure shown in Fig. 4. an oval spiral heat exchanger tube 24, a floor burner 26 and a wall burner 27.
and a heat recovery section 20A that extends vertically in the center between these radiant chambers 23 and recovers heat from the combustion exhaust gas mainly by convective heat transfer. It is. The heat exchanger tubes 24 are enlarged by forming their linear portions to be longer in the longitudinal direction, and the number of floor burners 26 and wall burners 27 is increased along with this enlargement. In addition, when the wall burner 27 is formed to be long in the height direction of the spiral shape of the heat exchanger tube 24, as shown in FIG. They are wound around the vertical axis and arranged in two horizontal rows on the inner periphery of the furnace wall as shown in the figure. In this case, when the vertical length b of the spiral shape of the heat transfer tube 24 is b≦5.6 m, the number of rows of the wall burner 27 is one, and when b>5.6 m, the number of rows is two. I like it. Of course, depending on the size of the heat exchanger tubes 24, they can be arranged in multiple rows and stages. Furthermore, the effect of providing the heat recovery section 20A is that high-temperature combustion exhaust gas can be used to heat other process fluids that require heating, or when a suitable process fluid is not available, a waste heat boiler can be installed. By generating steam, heat is recovered and the thermal efficiency of the entire heating furnace can be improved.

Furthermore, the effects of providing a plurality of radiant chambers 23, ie, furnaces, are as follows.

In a coal slurry heating furnace, no matter how it is designed, the coal slurry will more or less cause coking within the heat transfer tubes.

Therefore, it is customary to periodically perform a decoking operation in which steam and air are fed into the heat transfer tubes to remove coke adhering to the inner walls of the tubes. In such a case, if the decoking operation is performed one after another by using one furnace as a preliminary furnace, there is no need to stop the operation of the heating furnace itself, which has the effect of preventing a decrease in operating efficiency.

As explained above, the tube heating furnace of the present invention uses a vertical spiral heat transfer tube consisting of a straight section and a curved section having a center radius of curvature of 5 times or more the inner diameter of the tube. By adopting a double-sided heating structure for the inner and outer periphery of the heat transfer tube, the fluid to be heated can be heated gently and uniformly, and localized overheating in the heat transfer tube can be prevented as much as possible, and the temperature of 180゜u Since the structure eliminates the use of bends, it is possible to prevent as much as possible the inner wall of the curved portion from being worn out and damaged by erosion, and the solids in the fluid from settling and clogging the pipe.

In addition, the flow direction of the fluid can be maintained in either a downward flow or an upward flow, thereby suppressing the occurrence of vibrations in the heat exchanger tubes. Furthermore, there is an advantage that the heat exchanger tube can be designed to be large in structure, and the heating furnace can be easily enlarged.

The tubular heating furnace of the present invention can heat various heating fluids without any problems, but in particular, the heating furnace of the present invention can be used to heat coal slurry used in the coal slurry preheating process in a coal liquefaction plant. When used as a tube heating furnace, it can handle gases (mainly hydrogen gas), liquids (solvents), and solids (coal).
It has a great effect in that it can technically solve problems such as durability against erosion, coking, etc., and life span when heating a three-phase coal slurry.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the coal liquefaction process, FIGS. 2 and 3 are diagrams showing the structure of a conventional tube heating furnace, and FIGS. 2A and 3A are front longitudinal sectional views, respectively. Fig. 2B is a plan cross-sectional view, Fig. 3B is a side longitudinal sectional view, and Fig. 4 is a diagram showing the structure of the tube heating furnace according to the present invention, where A is a front longitudinal sectional view and B is a longitudinal sectional view of A. A
5 is a partial view showing the heat exchanger tube support structure in the above furnace, and FIG. 6 is a view showing another embodiment of the present invention, A is a front longitudinal sectional view, and B is a sectional view taken from the direction of arrow A'. A cross-sectional plan view, Figure 7 is a graph showing the ratio of the amount of thinning due to erosion in the curved portion of the heat exchanger tube to the amount of thinning due to erosion in the straight portion of the heat exchanger tube, and Figure 8 is a graph showing the amount of wall thinning due to erosion in the curved portion of the heat exchanger tube. This is a graph explaining the speed of slurry that causes . 10, 20... Main body casing, 12... Furnace wall, 13, 23... Combustion chamber, 14, 24... Heat exchanger tube, 14A... Straight section, 14B... Curved section, 1
6, 26...floor burner (first heat source), 17,
27... Wall burner (second heat source).

Claims (1)

[Scope of Claims] 1. A tube-type heating furnace that heats a fluid to be heated in the tube by heating a heat transfer tube, which consists of a straight section and a curved section having a center radius of curvature that is 5 times or more the inner diameter of the tube. A first heat source that heats the inner peripheral outer surface of the spiral heat exchanger tube and a second heat source that heats the outer peripheral outer surface of the spiral heat exchanger tube is provided in the furnace. A tube heating furnace characterized by comprising: 2. The tube heating furnace according to claim 1, wherein the spiral heat exchanger tube has a curved portion having a center radius of curvature that is 7.5 times or more the inner diameter of the tube. 3. The heating furnace is characterized by having a plurality of radiant chambers each equipped with a heat source consisting of a heat transfer tube and a burner, and a heat recovery section provided between the radiant chambers and recovering heat of combustion exhaust gas in the chamber. A tube heating furnace according to claim 1 or 2. 4. Claim 1, characterized in that the spiral heat transfer tube is supported by a tube support supported on a furnace wall, and the furnace wall is provided with a relief portion when the tube support thermally expands. - The tube heating furnace according to any one of Items 3 to 3. 5. Claims characterized in that a plurality of first heat sources are arranged in a row at a central position in the lower part of the furnace, and a plurality of second heat sources are arranged in multiple rows and stages along the peripheral wall of the furnace. The tubular heating furnace according to any one of Items 1 to 4.