CA1172982A - Tubular furnace - Google Patents
Tubular furnaceInfo
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- CA1172982A CA1172982A CA000404824A CA404824A CA1172982A CA 1172982 A CA1172982 A CA 1172982A CA 000404824 A CA000404824 A CA 000404824A CA 404824 A CA404824 A CA 404824A CA 1172982 A CA1172982 A CA 1172982A
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- tube
- furnace
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- Production Of Liquid Hydrocarbon Mixture For Refining Petroleum (AREA)
- Muffle Furnaces And Rotary Kilns (AREA)
- Combustion Of Fluid Fuel (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
In a tubular furnace in which a heating tube is heated by radiation to thereby heat fluid within the tube, a tubular furnace characterized in that a heat transmission tube of spiral shape in a longitudinal direction is installed within the furnace, the heat transmission tube comprising linear portions and curved portions each having a center curvature radius of five times as large as a tube internal diameter or more, and a first heat source for heating inner circumferential surface of the heat transmission tube of spiral shape and a second heat source for heating outer circumferential surface of the tube are also installed within the heating furnace.
In a tubular furnace in which a heating tube is heated by radiation to thereby heat fluid within the tube, a tubular furnace characterized in that a heat transmission tube of spiral shape in a longitudinal direction is installed within the furnace, the heat transmission tube comprising linear portions and curved portions each having a center curvature radius of five times as large as a tube internal diameter or more, and a first heat source for heating inner circumferential surface of the heat transmission tube of spiral shape and a second heat source for heating outer circumferential surface of the tube are also installed within the heating furnace.
Description
i 172~2 The present invention relates to tubular furnaces utilizing radiation heat transmission.
Under world-wide shortage of crude petroleum in recent years, coal is being noticed as substitution energy since coal can be supplied relatively eas~ly. Establishment of techniques to liquefy coal and produce fuels such as kerosence or light oil and pe-trochemical raw material has been demanded.
Fig. 1 is a block diagram illust,rating the coal liquify-ing process;
Figs. 2 and 3 show structure of a tubular furnace in the prior art; Figs. 2(Al and 3(A) are front longitudinal section-al views; Fig. 2~) is a transverse sectional view; Fig. 3(B~ is a sectional side v:iew;
Fig. 4 shows structure of a tubular furnace according to the present invention; (A~ is a front longitudinal sectional view; (Bl is a sectional view taken along line A-A';
Fig. 5 is a segmentary view illustrating support struc-ture of heating tube of the furnace;
Fig. 6 shows another embodiment of the invention (A) isa front longitudinal sectional view; (B~ is a transverse sectional view; and (C), is a side cross-sectional view; and Figs. 7 to 11 are ~arious graphs illustrating the con-diti~ns (1) to ~5) according to the present invention, A general coal llquefying process is shown in Fig.`l, which comprises the steps of liquefying coal by adding a hydrogen gas and the solvent into the coal, and removing impurities such as sulfur content, nitrogen content, ash content from the lique-fied coal. The solvent used in a coal liquefaction process (coal ~0 slurry) is that of consisting mainly of an aromatic compound '~
: 172~
and/or an aliphatic compound, and the hydrogen gas is a hydrogen rich gas consisting mainly of a hydrogen gas and containing a light hydrocarbon gas and/or carbon monoxide or is simple sub-stance of hydrogen gas. (These gas being hereinafter simply referred to as "hydrogen gas".) In such process, a coal slurry is obtained through mix-ing said solvent in a pulverized coal, adding said hydrogen gas thereto and then the slurry is heated at a preheating process of Fig. 1. Therefore the coal slurry furnace used for preheating is indispensable for coal liquefaction process, and a tubular furnace utilizing radiation heat transfer is generally used therefor.
The tubular furnace is constituted principally of a b~r~ rj combustion chamber equipped with-a burnor-as a source for heat generation and heating tubes 1-1/2~ - 6B (size of the tube defined ~IjS ~`
by, for example, ~H~ 3467/19781. The tube are arranged in the com~ustion chamber and are heated with a high-temperature gas or flame as radiation sources, so that the "fluid" within the tube is heated, In vario~ls coal li~uefying processes, although it is dif~icult to specify a diameter of the pulverized coal due to various limitations of hardness, reaction property of coal and slurr~ transportation means used in the processes, it is general that 70~ of coal particles has 200 Mesh (0.074 mm in diameter) and the upper limit thereof is about 2 to 3 mm. Furthermore, in general, a weight ratio between coal and solvent is selected in the range of 25:75 to 75:25, and a ratio between the hydrogen gas and coal is preferably 0.5 to20 Nm3 H2/Kg coal. However, these ratios are suitably determined according to a property of products to be obtained and a quality of coal to be processed. Incident-3~ ally, part of the hydrogen gas may be heated in another preheating if 29~ ~
1 process. Therefore, there is a possibility that slurry containinga small amount of the hydrogen gas may be heated. When the tubula furnace is used as the coal slurry furnace, the following specif-ications are required.
(1) A coal slurry is fluid of three phases, i.e. a yas phase (mainly hydrogen gas and light hydrocarbon gas), a liquid phase (solvent) and a solid phase (coal). The coal slurry is pressurized at a high pressure of 50 - 300 Kg/cm2 G for reaction with the hydrogen gas. When the fluid flows at a high rate and 180 U-shaped bends are used in the heating tubes, centrifugal forces are applied to the bent portions and solid constituents are liable to be separated from liquid constituents so that lnner walls of the bent portions are abraded by the erosion and are damaged, for example, to form a hole. Inversely when the fluid flows slowly, solid constituents such as coal suspended in the fluid are precipitated or settled, thereby allowing the heat transmission tube to be clogged or plugged. This is remarkable in the 180 U-shaped bends.
Accordingly, it is preferably that in the heating tubes the fluid be held at a suitable flow rate and a usage of 1~0 U-shaped bends causing the separation and deposit be avoided.
Under world-wide shortage of crude petroleum in recent years, coal is being noticed as substitution energy since coal can be supplied relatively eas~ly. Establishment of techniques to liquefy coal and produce fuels such as kerosence or light oil and pe-trochemical raw material has been demanded.
Fig. 1 is a block diagram illust,rating the coal liquify-ing process;
Figs. 2 and 3 show structure of a tubular furnace in the prior art; Figs. 2(Al and 3(A) are front longitudinal section-al views; Fig. 2~) is a transverse sectional view; Fig. 3(B~ is a sectional side v:iew;
Fig. 4 shows structure of a tubular furnace according to the present invention; (A~ is a front longitudinal sectional view; (Bl is a sectional view taken along line A-A';
Fig. 5 is a segmentary view illustrating support struc-ture of heating tube of the furnace;
Fig. 6 shows another embodiment of the invention (A) isa front longitudinal sectional view; (B~ is a transverse sectional view; and (C), is a side cross-sectional view; and Figs. 7 to 11 are ~arious graphs illustrating the con-diti~ns (1) to ~5) according to the present invention, A general coal llquefying process is shown in Fig.`l, which comprises the steps of liquefying coal by adding a hydrogen gas and the solvent into the coal, and removing impurities such as sulfur content, nitrogen content, ash content from the lique-fied coal. The solvent used in a coal liquefaction process (coal ~0 slurry) is that of consisting mainly of an aromatic compound '~
: 172~
and/or an aliphatic compound, and the hydrogen gas is a hydrogen rich gas consisting mainly of a hydrogen gas and containing a light hydrocarbon gas and/or carbon monoxide or is simple sub-stance of hydrogen gas. (These gas being hereinafter simply referred to as "hydrogen gas".) In such process, a coal slurry is obtained through mix-ing said solvent in a pulverized coal, adding said hydrogen gas thereto and then the slurry is heated at a preheating process of Fig. 1. Therefore the coal slurry furnace used for preheating is indispensable for coal liquefaction process, and a tubular furnace utilizing radiation heat transfer is generally used therefor.
The tubular furnace is constituted principally of a b~r~ rj combustion chamber equipped with-a burnor-as a source for heat generation and heating tubes 1-1/2~ - 6B (size of the tube defined ~IjS ~`
by, for example, ~H~ 3467/19781. The tube are arranged in the com~ustion chamber and are heated with a high-temperature gas or flame as radiation sources, so that the "fluid" within the tube is heated, In vario~ls coal li~uefying processes, although it is dif~icult to specify a diameter of the pulverized coal due to various limitations of hardness, reaction property of coal and slurr~ transportation means used in the processes, it is general that 70~ of coal particles has 200 Mesh (0.074 mm in diameter) and the upper limit thereof is about 2 to 3 mm. Furthermore, in general, a weight ratio between coal and solvent is selected in the range of 25:75 to 75:25, and a ratio between the hydrogen gas and coal is preferably 0.5 to20 Nm3 H2/Kg coal. However, these ratios are suitably determined according to a property of products to be obtained and a quality of coal to be processed. Incident-3~ ally, part of the hydrogen gas may be heated in another preheating if 29~ ~
1 process. Therefore, there is a possibility that slurry containinga small amount of the hydrogen gas may be heated. When the tubula furnace is used as the coal slurry furnace, the following specif-ications are required.
(1) A coal slurry is fluid of three phases, i.e. a yas phase (mainly hydrogen gas and light hydrocarbon gas), a liquid phase (solvent) and a solid phase (coal). The coal slurry is pressurized at a high pressure of 50 - 300 Kg/cm2 G for reaction with the hydrogen gas. When the fluid flows at a high rate and 180 U-shaped bends are used in the heating tubes, centrifugal forces are applied to the bent portions and solid constituents are liable to be separated from liquid constituents so that lnner walls of the bent portions are abraded by the erosion and are damaged, for example, to form a hole. Inversely when the fluid flows slowly, solid constituents such as coal suspended in the fluid are precipitated or settled, thereby allowing the heat transmission tube to be clogged or plugged. This is remarkable in the 180 U-shaped bends.
Accordingly, it is preferably that in the heating tubes the fluid be held at a suitable flow rate and a usage of 1~0 U-shaped bends causing the separation and deposit be avoided.
(2) Since a solvent including a large amount of aromatic compounds and having high molecular weight is generally used, heating must be uniformly performed. When a local over-heating takes place, the coal slurry is decomposed and coked or carb~nized. The product is deposited to inner walls of the heat-ing tubes, causing the pluqging of the heating tubes while pre-venting the fluid from flowing resulting in a further local over-heating. Accordingly, heating of the heating tubes must be pe~-formed as uniformly as possible.
; 1729~
1 (3) Since the coal slurry within the heating tube exists in a three-phase, i.e. gas phase, liquid phase and solid phase, if there is a portion, of the tube, where the flow is changed from a descending stream to an ascending stream and vice versa, the tube is subjected to vibrations or fluctuations.
Accordingly, it is preferably that fluid within the heating tube be held either in a descending flow or in an ascend-ing flow.
Structures of con~entional heating furnaces are shown in Figs. 2 and 3.
Referring now to Figs, 2(A) and (B), a heat insulating material is lined on an inner wall of a cylindrical combustion chamber 1, a heating tube 2 of circular spiral form is arranged in a longitudinal direction along the inner wall of the combustion chamber 1, and the heating tube 2 is heated from the center of the furnaces using a burner 3 arranged at the center of a hearth.
The furnace of this type is advantageous in that 180 U-shaped bend causing erosion or clogging are not used. Further-more~ the slurry flows in one direction from an upper portion to a lower porition, thereby preventing the tube from vibrating ~owever, such a furnace has disadvantages in that it is difficult t~ construct a furnace large in size on account of structural limitations of the heating tube of circular spiral shape, Namely, if the heating tube becomes larger than 8 m in turn diameter and then 12 m in height, heat from the burner is not distributed uniformly so as to cause a local overheating and construction thereof is difficult also in vieW of the structure of the furnace.
Since the heating tube is heated at one side only using the burner at the center, a radiation heat is not distributed uniformly and the side facing the flame of the burner is heated strongly, so ; i729~2 1 that the slurry is decomposed and coked or carbonized and the product is deposited to the inner walls of the heating tube. As a result, an effective flow path thereof is narrowed and a surface temperature of the tube becomes extremely high.
Referring to Figs. 3(A) and (B~, along opposed inner side walls of a combustion chamber 1' of box type is disposed a serpentine heating tube 2' extending in a lateral direction. The heating tube 2' is heated by burners 3' arranged in a line at the center of a hearth.
In the tubular furnace of this type, since the heat transmission tube 2' is not restricted comparatively in structure, the furnace large in size is readily constructed. ~owever, such furnace has disadvantages as described below.
Since the heating tube has 180 U-bend with a short radius of curvature being twice as large as the tube inner dia-meter or less for connecting linear portions, bend is damaged by erosion or clogging. Also the heating tube is heated on one side as in the furnace shown in Figs. 2 (A) and (Bl, thereby coking the slurry resulting in local overheating or clogging.
If the heat transmission tube shown in Figs. 3(A) and (B~ is modified in a serpentine form extending in the vertical direction along opposed inner side walls, the flow cannot be held in one direction hereby the heating tube is subjected to vibration.
In view of above noted defects inherent to the prior art, the present invention provides as an object a tubular furnace in which a heating tube of spiral and oval shape has lin-ear portiors and curved portions each having a curvature radius of five times as large as a tube inner diameter or more, the heating tube is heated on both sides by radiation, whereby specifications required as the tubular furnace are completely met ~ :~729~2 1 and the fluid can be efficiently heated, the furnace having high safety degree and excellent durability, and the furnace large in size can readily be constructed.
The present invention will now be described referring to Figs. 4 to 6.
In Figs. 4(A) and (B), a heating furnace body casing 10 is constructed on a foundation base 11, and a furnace wall 12 is made of heat-resistant material such as fire bricks, castable refractories or mortars, and a combustion or burning chamber 13 is defined by the furnace wall 12. The body casing 10 is formed in a box shape with transverse sections of a octagon being longer in one direction than in the other, and the furnace wall 12 also has a shape in conformity therewith, A heating tube 14 of oval spiral shape in the longitudinal direction is arranged in a center portion of the combustion chamber 13. The heating tube 14 is composed of linear portions 14A and curved portlons 14B, each of the curved portions having a center curvature radius r of five times as large as a tube internal diameter h or more and prefer-ably 7,5 times or more, In addition, the center curvature radius used here means a curvature radius with respect to center of the heating tube 14 and not outer curve or inner curve of the heating tube 14.
The heating tube 14 of oval spiral shape is formed along two lines of wound tubes so that fluid to be heated flows through two path. The number of lines is determined correspond-ing to that of required paths, for example, one line for one path and three lines for three paths. A distance between the adjacent tubes 14 of oval spiral shape is preferably pitch of 1.2 - 3 times as large as the tube outer diameter and more preferably pitch of twice, ; i 7 2 9 ~ ?
1 Upper and lower ends of the heating tube 14 are formed respecti.vely as inlets 14a and outlets 14b for the fluid to be heat.ed. The inlets 14a pass throush one side of the furnace wall 12 and are led out of the body casing 10, and the outlets 14b are led out of the hearth 12A. A tube support 15 made of heat-resist-ant cast steel is adapted to support the heating tube 14 in the urnace. As best shown in Fig, 5, the tube support 15 is com-posed of a support pole 15a extending in a vertical direction inside of an inner circumference of the heating tube 14 and support pawls l5b projecting outwardly in multiple stages from the support pole 15a, so that a bottom of each tube the heat tran~-m~ssion tube 14 arranged in multiple stages is supported by the pawl 15b, ,~ ~t~f ~ / fs Each of the tube support 15 has a lower end fixedly held to the hearth 12A and an upper end held while passing through a through-hole 12a of the furnace wall 12 at a ceiling portion so that the~rmal expansion of the tube support 15 heated at a high temperature within the furnace i.s allowed to escape in the through-hole 12a, Floor burners 16 are used as a first heat source to heat ins.ide circumferential surface of the heat trar.s-mission tube 14. A plurality of the floor burners 16 are spaced at a constant intervalti~ are arranged in a line at the center portion of the hearth 12AJand confronted with the inside surface c~76~ ar,,~
of the heating tube 14~arranged so as to yenerate flames upwardly.
W~ll burners 17 of linear shape are used as a second heat sou,rce to heat an outside circumferential surface of the heating tube 14, A plurality of wall burners 17 are spaced at a suitab.le interval in a circumferential direction at the bottom portion inside the furnace wall 12.
Each of the wall burners 17 is composed of a burner gun 17a bent upwardly along the furance wall 12 and a block 17b 1 of burner tile bent in the same direction as the burner gun 17a.
The wall burner 17 generates flat flame upwards along inner sur-face of the surface wall 12, thereby heating the furnace wall 12.
The outside circumferential surface of the heating tube 14 is heated by radiation heat from the furnace wall 12. Wind-boxes 18 and 19 for two types of burners, i.e. the floor burner 16 and the wall burners 17, serve as mufflers to reduce noise made by the burners 16 and 17.
In this embodiment, there are installed four floor burners 16 and twelve wall burners 17. The number of burners may be set freely corresponding to the size of the furnace. In order to prevent incomplete combustion or burning caused by inter-ference of the flame between adjacent burners in this case, a minimum burner center distance c between floor burners 16 and a ~minimum burner centers distance d between wall burners 17 prefer-ably meet the following relationships.
c > k + 0.1 (m) d > f + 0.1 (m) wherein k is the maximum diameter ~m) of flame of floor burner 16;
and f is the maxirnum width (m) of block 17b of wall burner 17.
A stack 30 for discharging flue gas is installed at the ceiling and a heat insulating material 3Qa is lined on an inner surface of the funnel 30~ A damper 31 for adjusting draft force of flue gas is disposed in the stack 30 and may be manually set suitably.
With such a constitution, the fluid to be heated is introduced in the inlets 14a of the heating tube 14 and is allowed to flow from the upper portion to the lower portion through the heating tube 14 and then flows to the outlets 14b. During the above mentioned process it is heated by radiant heat txansmission ; ~l 7 2 9 `~ '~
1 of the heating tube 14.
Of course, the heating tube 14 is slightly heated by convectionfromthe high temperature flue gas flowing in the com-bustion chamber 13.
If the center curvature radius r of the curved portion 14B of the heating tube 14 of spiral shape is five times, prefer-ably, 7,5 times as large as the tube inner diameter h or more, the curved portion 14B is not subjected to the damage such as abrasion, and the heating tube 14 îs not clogged by the deposit of solid constituents contained in slurry. In order to prevent the local overheating in the vertical direction of the heating tube 14 of spiral shape, it is found preferable from the follow-ing studies that the center curvature radius r and distance a from surface of the furnace wall 12 to the center of the heating tube 14 should meet the following conditions, It is preferable that center curvature radius r (unit:
m) meet the following conditions simultaneously.
r _ 5 x h (more preferably, r > 7.5 x h) (1 r _ 0.28 ~ g + 0.20 (2~
r _ 0,13 x b (31 wherein y is the firing rate per one floor burner 16 ~x 106 Kcal/
Hr); h is the tube inner diameter of heating tube 14 ~mi; and b is the longitudinal length of spiral shape of heating tube 14, i.e,, the center distance between uppermost and lowermost stages of heat transmission tube 14 ~m~.
The above condition ~22 means the minimum distance to separate the heating tube 14 from the floor burners 16, and the condition ~3~ means the minimum value required to make the uni-form distribution of heat absorption in the vertical direction of the heating tube 14 of spiral shape by the floor burners 16, ; :i72~
1 It is preferable that the distance a (unit : m~ from surface of the furnace wall 12 to the center of the heat trans-mission tube 14 meet the following conditions.
I1 When the longitudinal length b of spiral shape of the heating tube 14 is less than ll.2 ~:
0,848 c a (41 II~ When the longitudinal length b of spiral shape of the heating tube 14 is equal to or greater than ll,2 m:
O.Q757 x b < a (5~
The above conditions (4~ and (5) means the minimum value required to make uniform the distribution of heat absorp-tion in the vertical direction of the heating tube 14 of spiral shape by the wall burners 17.
The above described conditions Cl) to 15~ will now be explained in more detail. Various studies have been made as to the coal slurry furnace using four-inch inner diameter tubes or pipes in accordance with the present invention.
Condition (ll: r ~ 5 x h (preferably, r 7,5 x hl When the flow speed of the slurry is in the range of l.2 to 3.2 m/s, a ratio ~ of an erosion rate of the linear portion of tube to an erosion rate of a curvilinear or bent portion of tube ~s shown in Fig. 7 where the ratio ~ is represented by the expression ~ =
erosion rate of the bent portion (mm/day) erosion rate of the straight portion (mm/day~
On the other hand, since at an inlet portion of the heating tube coal perticles contained in the slurry fluid are not yet soluted therein, unless the radius of curvature is suitably selected, there would be caused a plugging or clogging in the-bent portion. In case of the studies using the four-inch inner diameter pipes, the flow speed at which the plugging will occur i `~72~2 1 is represented by Fig. 8 in which is the mean perticle degree ~mesh), and Vc is a minimum flow speed (m/s~ at which the plugging does not occur.
As has been apparent from Figs, 7 and 8, there is no fear that the erosion and plugging may occur significantly at the bent portion in the range of r/h > 5, preferably r/h > 7.5. Thus, it is understood that the bent portion may be designed in the same manner as in the straight portion.
C dition 12): r - 0.28 x g + 0.20 If during the operation of the heating furnace, the flame of burners impinges against the heating tube or pipes, the heating tubes or pipes are remarkably locally heated to thereby cause co~ing of fluid and damage of heating tubes, Therefore, the heating tubes must keep a distance from the flame suitable.
It is experienced that if the following lower limit is exceeded, the coking of fluid take place.
di > 0.107 x g + 0.113 where: di is the distance ~ml between the surface of flame and the heating tube center, The diameter of a flame produced by burners which produce r~,latively thin flame compared with their capacity is represented in Fig. 9 inwhich a first solid line on the left side denotes a diameter of flame, a second solid line on the right side denotes a center position of the heating tube nearest to the burner defined by di and a dotted line shows a straight line in-dicating the equation r = 0,28 x g + 0.20, It will readily be understood that as far as the rela-tionship r > 0.28 x g + 0.20, is gi~en, the heating tube may be protected against the excessive burner heating at a safety distance, , 1729~
1 Condit_on (3): r - 0.13 x b In general, difficulties have been experienced in determininy a distribution of a thermal absorptivity, per unit surface area q (kcal/m~ hr) of the heating tube because it re-markably depends upon types of burner, configuration of flame, con~iguration of furnace,.kind of fuel and the like. However, in case where two heat absorbing planes composed of a row of heating tubes are arranged to be confronted with each other in a vertical and parallel relationship and the up-firing burners are disposed at the center of the absorbing planes the relationship between the geometrical relation of the two heat absorbing planes yb and the non-uni~ormity of heat absorption max on the heating tubes is shown in Fig. 1.0 by using natural gas as a fuel, in which qav is the average heat absorption per unit surface area of heating tube by the floor burner (kcal/m2hrl and qmax is the maximum heat absorption per unit surface area of heating tube by the floor burner ~kcal/m2hr). As is apparent from Fig. 10, at a posi.tion represented by r = 0.13 x b, the relationship of qmax/qav - 1,6 is establi.shed; namely, heat absorbing rat~ per unit surface at the maximum heat absorbing portion of the heatiny tube is 1.6 times o~ the average thermal absorptive portion in heat ahsorption.
It is experienced that if non-uniformity in thermal absorption mvre remarkable than this expression occurs, the portion in which the maximum absorption takes place, is heated to a high temperature and the liquid cokiny may be caused.
Condi.tivns ~4) and ~5): 0~848 ~i a and 0,0757 x b - a ~i In general, a wall used for heatiny the heati.ng tube by radiation emitted from insulating materials or heat re-sistant material such.as fire brick which are heated by the wall i ~729~2 1 burners is r~ferre~ to as a radiatio1- wall. l~1hen the distance between the radiation wall and the heatiny tube is too short, since the temperature of the radiation wall is not uniform, the heatin~ tube is subjected to a non-uniform heating so that the coal slurry is coked at the portion at which the temperature is highest. Inversely, when the distance between the radiation wall and the heating tube is too long, the tubular furnace becomes uneconomically large in size, and the thermal efficiency of the wall burners is markedly reduced. Therefore, the suitable distance must be chosen.
The relationship in distance will now be explained with reference to Fig. ll.
(a) In the case where the longitudinal length b of the spiral shape of the heating tubes is equal to or greater than ll.2: In Fig. ll, q' v is the average heat absorption rate per unit surface area of the heating tube by means of the wall burners (kcal/m2hr) and q'max is the maximum heat absorption rate per unit surface area of the heating tube by the wall burners (kcal/m2hr).
As is apparent from Fig. ll, if the ratio a/b becomes smaller than 0.0757, the ratio q'ma /q' exceeds l.6 thereby making the local heating of the tube remarkable and causing a coking in coal slurry. Therefore, the condition (5):
0.0757 _ a must be given.
^ ~729~
1 (b) In the case where the longitu~ al length b of the spiral shape of the heating tubes is less than 11.2:
By substituting b in the condition (5) with 11.2, the relationship of 0.848 _ a is given, which is the same as condition (4). The condition (4) means that even if the value of b is small, it is prohibited to be smaller than 0.848 m as a minimum distance.
It is experienced that if the distance between the center of the heating tube and the radiation wall is smaller than - 13a -i ~729~2 1 ~.848, the following disadvantages are noticed. (i) It is difficult to construct the furnace. (ii~ It is difficult to carry out the maintenance works in the furnace for inspection.
(iii) The flame of the wall burners will impinge against the tube supports thereby causing the excessive heating. Therefore, it is highly desired that the sufficient distance must be kept with in the condition (4), It is therefore necessary that if the value of b is less than 11.2 m, the value of a be defined by the relationship of 0.848 = a.
In the case that the size of the furnace is increased resulting in increase of the height b while increasing the dis-tance a in accordance with the above described condition (5) to thereby increase the construction costs, the wall burners 27 may be provided in a two-stage manner as shown in Fig~ 6(a) in the vertical direction. In this case, a height of the spiral tube to be heated by each one of the double-stage wall burners may be reduced to halr the height of the single stage wall burners. Thus the distance a may be also reduced in accordance with the con-dition (5~ reducing the construction costs.
The above described conditions are generally used forthe tubular furnaces for three-phase fluids which are not limited to the coal slurry of three-phases. Incidentally/ f~o~ the ~oregoing descri`ption the center curvature rad~us r in the con-ditions (2) and (3) is expressed as a minimum necessary distance Q
(unit: meter~ from the center of the first heat source, i,e., floor burner 16 to the heating tube 14.
When the tubular furnace in the embodiment shown in Figs. 4A and B is used as, for example, a coal slurry heating furnace in a coal liquefying plant, the features that the heat transmission tube 14 of oval spiral shape has the curved portions 14B with center curvature radius in the longitudinal diréction ~ 172982 1 being five times as large as the heat transmission tube inner diameter or more and that the heat transmission tube 14 is heated on both sides by the floor burners 16 and the wall burner~ 17 offers the following advantages.
(1) Since the 180 U-bend of short diameter being twice as large as the tube inner diameter or less is not used but the heat transmission tube of oval spiral shape having the center curvature radius being five times as large as the tube inner dia-meter or more is provided, the excessive erosion of fluid does not occur at the curved portion which is the most critical portion of heating tube. The curved portion is also free from clogging by precipitation of solid material due to its curvedness.
(21 The heating tube is uniformly heated on inner and outer circumferential surfaces of the loop-shaped tube arrange-ment and the local overheating does not occur ~hile fluid is not coked, and therefore tube clogging due to the coking is not caused, Fox example, when the same average heat flux (heat absorption rate per unit area surface of the heating tube~ is applied, if the heat transmission tube is arranged in pitch being t~ice as large as the tube outer diameter, the maximum heat flux produced at the side faced to the flame in double-side heating becomes 1/1.5 in comparison with one-side heating.
(3~ The fluid always flow downwardly, namely flowing is held in one direction, and therefore the heat transmission tube is not subjected to vibration, ~ 4) If the linear portion of the heat transmission tube is lengthened there~y e~tending the long diameter portion, the furnace large in size can readily be constituted, Therefore, there is no restriction in structure as in the conventional heating tube of simple circular spiral shape, and uniform heating is obtained in the furnace large in size by means af the double-side heating.
l ~72g82 1 Accordingly, the furnace large in size can be construc-ted without any restrictions~
Another embodiment of the present invention will now be described referring to Figs, 6 (A~ and ~B).
This is an example of the large size heating furnace structure of Fig. 4, The radiant section of the furnace is divided into two chambers. Similarly to the furnace shown in Fig. 4, each chamber 23 having heating tubes 24, Therefore, the numbers of flower burners 26 and wall burners are increased. A
common heat recovery section 20A is proYided at the top of the two radiant sections, and recovers heat from flue gas mainly by convection. Linear portions of the heat transmission tube 24 are extended namely the long diameter direction is made long, thereby forming the furnace large in size. As the furance becomes large, the numbers of.the floor burners 26 and the wall burners 27 ~re increased. When the height of the heating tube 24 of spiral shape is increased, a uniform heating is not effected which the wall burners 17 which are mounted in single stage at the lower portion of the furnace wall as shown in Eig, 4(A~, Therefore, the arrangement in two lateral stages at the inner circumference of the furnace wall is effected as shown in Fig, 6 (B~. In this case, it is preferably that when the height b of spiral shape of the heat transmission tube 2~ be b - 5.6 m, the number of lateral stages of the wall burner 27 be one stage, and when b > 5.6 m, the number of lateral stages be two stages. Of course, multiple lateral stages more than double stages may be effected correspond-ing to the height of the heating tube 24 of spiral shape, Effect of installation of the heat recoYery section 2QA is that the waste flue gas of high temperature i5 used to heat other process fluids requiring heating, or if there is no suitable process i 1729`~2 1 fluid, a waste heat boiler is installed to generate steam. ~eat recovery is therefore effected and a thermal efficiency of the heating furnace as a whole is improved, Effect of installation of a plurality of the radiation chambers 23, is as follows;
In the tubular heating furnaces designed in any manner, the fluid is more or less coked within the heating tube.
Accordingly, in usual, decoking operation to introduce stea~ and air in the heating tube and to remove coke adhered to the inner wall of the tube is performed regularly. During the decoklng operation the furnace cannot serve as a coal slurry heater, When a plurality of the radiant chamber are installed as in this embodiment, the furnace can consequently serve as a coal slurry heater by means of alternate decoking operation between the two radiant chambers, If plural furnaces having two radiant chambers are each installed, decoking operation will be conducted more easily.
~ s described above, a tubular furnace of the present invention is constructed so that a heat transmission tube of spiral shape i.s composed of linear portions and curved portions, each.having the center curvature radius of five times as large as the tube inner diameter or more, the heat transmission tube is heated on both sides from the inner and outer circumferences, whereby fluid can be heated uniformly and smoothly, and local overheating in the heat transmission tube is prevented signif-icantly, the elimination of use of 180 U-bend prevents damage such as abrasion of inner wall of the curved position caused by erosion or clogging of the tube due to the deposit of solid constituents. contained in the slurry.
The flow of fluid is held in one direction either downwardly or upwardly, whereby the heat transmission tube is t 1729~2 1 prevented from vibrating. Tubular furnaces large in size can readily be constructed employing the oval heating tube.
When the heating furnace according to the present in-vention is used as coal slurry heating furnace in the preheating process of the coal slurry composed of a three-phases, i.e.
vapour ~hydrogen gas), liquid ~solvent) and solid (coal) in the coal liquefying processr technical problems such as erosion, durability for coking and service life of heating tubes can be improved.
; 1729~
1 (3) Since the coal slurry within the heating tube exists in a three-phase, i.e. gas phase, liquid phase and solid phase, if there is a portion, of the tube, where the flow is changed from a descending stream to an ascending stream and vice versa, the tube is subjected to vibrations or fluctuations.
Accordingly, it is preferably that fluid within the heating tube be held either in a descending flow or in an ascend-ing flow.
Structures of con~entional heating furnaces are shown in Figs. 2 and 3.
Referring now to Figs, 2(A) and (B), a heat insulating material is lined on an inner wall of a cylindrical combustion chamber 1, a heating tube 2 of circular spiral form is arranged in a longitudinal direction along the inner wall of the combustion chamber 1, and the heating tube 2 is heated from the center of the furnaces using a burner 3 arranged at the center of a hearth.
The furnace of this type is advantageous in that 180 U-shaped bend causing erosion or clogging are not used. Further-more~ the slurry flows in one direction from an upper portion to a lower porition, thereby preventing the tube from vibrating ~owever, such a furnace has disadvantages in that it is difficult t~ construct a furnace large in size on account of structural limitations of the heating tube of circular spiral shape, Namely, if the heating tube becomes larger than 8 m in turn diameter and then 12 m in height, heat from the burner is not distributed uniformly so as to cause a local overheating and construction thereof is difficult also in vieW of the structure of the furnace.
Since the heating tube is heated at one side only using the burner at the center, a radiation heat is not distributed uniformly and the side facing the flame of the burner is heated strongly, so ; i729~2 1 that the slurry is decomposed and coked or carbonized and the product is deposited to the inner walls of the heating tube. As a result, an effective flow path thereof is narrowed and a surface temperature of the tube becomes extremely high.
Referring to Figs. 3(A) and (B~, along opposed inner side walls of a combustion chamber 1' of box type is disposed a serpentine heating tube 2' extending in a lateral direction. The heating tube 2' is heated by burners 3' arranged in a line at the center of a hearth.
In the tubular furnace of this type, since the heat transmission tube 2' is not restricted comparatively in structure, the furnace large in size is readily constructed. ~owever, such furnace has disadvantages as described below.
Since the heating tube has 180 U-bend with a short radius of curvature being twice as large as the tube inner dia-meter or less for connecting linear portions, bend is damaged by erosion or clogging. Also the heating tube is heated on one side as in the furnace shown in Figs. 2 (A) and (Bl, thereby coking the slurry resulting in local overheating or clogging.
If the heat transmission tube shown in Figs. 3(A) and (B~ is modified in a serpentine form extending in the vertical direction along opposed inner side walls, the flow cannot be held in one direction hereby the heating tube is subjected to vibration.
In view of above noted defects inherent to the prior art, the present invention provides as an object a tubular furnace in which a heating tube of spiral and oval shape has lin-ear portiors and curved portions each having a curvature radius of five times as large as a tube inner diameter or more, the heating tube is heated on both sides by radiation, whereby specifications required as the tubular furnace are completely met ~ :~729~2 1 and the fluid can be efficiently heated, the furnace having high safety degree and excellent durability, and the furnace large in size can readily be constructed.
The present invention will now be described referring to Figs. 4 to 6.
In Figs. 4(A) and (B), a heating furnace body casing 10 is constructed on a foundation base 11, and a furnace wall 12 is made of heat-resistant material such as fire bricks, castable refractories or mortars, and a combustion or burning chamber 13 is defined by the furnace wall 12. The body casing 10 is formed in a box shape with transverse sections of a octagon being longer in one direction than in the other, and the furnace wall 12 also has a shape in conformity therewith, A heating tube 14 of oval spiral shape in the longitudinal direction is arranged in a center portion of the combustion chamber 13. The heating tube 14 is composed of linear portions 14A and curved portlons 14B, each of the curved portions having a center curvature radius r of five times as large as a tube internal diameter h or more and prefer-ably 7,5 times or more, In addition, the center curvature radius used here means a curvature radius with respect to center of the heating tube 14 and not outer curve or inner curve of the heating tube 14.
The heating tube 14 of oval spiral shape is formed along two lines of wound tubes so that fluid to be heated flows through two path. The number of lines is determined correspond-ing to that of required paths, for example, one line for one path and three lines for three paths. A distance between the adjacent tubes 14 of oval spiral shape is preferably pitch of 1.2 - 3 times as large as the tube outer diameter and more preferably pitch of twice, ; i 7 2 9 ~ ?
1 Upper and lower ends of the heating tube 14 are formed respecti.vely as inlets 14a and outlets 14b for the fluid to be heat.ed. The inlets 14a pass throush one side of the furnace wall 12 and are led out of the body casing 10, and the outlets 14b are led out of the hearth 12A. A tube support 15 made of heat-resist-ant cast steel is adapted to support the heating tube 14 in the urnace. As best shown in Fig, 5, the tube support 15 is com-posed of a support pole 15a extending in a vertical direction inside of an inner circumference of the heating tube 14 and support pawls l5b projecting outwardly in multiple stages from the support pole 15a, so that a bottom of each tube the heat tran~-m~ssion tube 14 arranged in multiple stages is supported by the pawl 15b, ,~ ~t~f ~ / fs Each of the tube support 15 has a lower end fixedly held to the hearth 12A and an upper end held while passing through a through-hole 12a of the furnace wall 12 at a ceiling portion so that the~rmal expansion of the tube support 15 heated at a high temperature within the furnace i.s allowed to escape in the through-hole 12a, Floor burners 16 are used as a first heat source to heat ins.ide circumferential surface of the heat trar.s-mission tube 14. A plurality of the floor burners 16 are spaced at a constant intervalti~ are arranged in a line at the center portion of the hearth 12AJand confronted with the inside surface c~76~ ar,,~
of the heating tube 14~arranged so as to yenerate flames upwardly.
W~ll burners 17 of linear shape are used as a second heat sou,rce to heat an outside circumferential surface of the heating tube 14, A plurality of wall burners 17 are spaced at a suitab.le interval in a circumferential direction at the bottom portion inside the furnace wall 12.
Each of the wall burners 17 is composed of a burner gun 17a bent upwardly along the furance wall 12 and a block 17b 1 of burner tile bent in the same direction as the burner gun 17a.
The wall burner 17 generates flat flame upwards along inner sur-face of the surface wall 12, thereby heating the furnace wall 12.
The outside circumferential surface of the heating tube 14 is heated by radiation heat from the furnace wall 12. Wind-boxes 18 and 19 for two types of burners, i.e. the floor burner 16 and the wall burners 17, serve as mufflers to reduce noise made by the burners 16 and 17.
In this embodiment, there are installed four floor burners 16 and twelve wall burners 17. The number of burners may be set freely corresponding to the size of the furnace. In order to prevent incomplete combustion or burning caused by inter-ference of the flame between adjacent burners in this case, a minimum burner center distance c between floor burners 16 and a ~minimum burner centers distance d between wall burners 17 prefer-ably meet the following relationships.
c > k + 0.1 (m) d > f + 0.1 (m) wherein k is the maximum diameter ~m) of flame of floor burner 16;
and f is the maxirnum width (m) of block 17b of wall burner 17.
A stack 30 for discharging flue gas is installed at the ceiling and a heat insulating material 3Qa is lined on an inner surface of the funnel 30~ A damper 31 for adjusting draft force of flue gas is disposed in the stack 30 and may be manually set suitably.
With such a constitution, the fluid to be heated is introduced in the inlets 14a of the heating tube 14 and is allowed to flow from the upper portion to the lower portion through the heating tube 14 and then flows to the outlets 14b. During the above mentioned process it is heated by radiant heat txansmission ; ~l 7 2 9 `~ '~
1 of the heating tube 14.
Of course, the heating tube 14 is slightly heated by convectionfromthe high temperature flue gas flowing in the com-bustion chamber 13.
If the center curvature radius r of the curved portion 14B of the heating tube 14 of spiral shape is five times, prefer-ably, 7,5 times as large as the tube inner diameter h or more, the curved portion 14B is not subjected to the damage such as abrasion, and the heating tube 14 îs not clogged by the deposit of solid constituents contained in slurry. In order to prevent the local overheating in the vertical direction of the heating tube 14 of spiral shape, it is found preferable from the follow-ing studies that the center curvature radius r and distance a from surface of the furnace wall 12 to the center of the heating tube 14 should meet the following conditions, It is preferable that center curvature radius r (unit:
m) meet the following conditions simultaneously.
r _ 5 x h (more preferably, r > 7.5 x h) (1 r _ 0.28 ~ g + 0.20 (2~
r _ 0,13 x b (31 wherein y is the firing rate per one floor burner 16 ~x 106 Kcal/
Hr); h is the tube inner diameter of heating tube 14 ~mi; and b is the longitudinal length of spiral shape of heating tube 14, i.e,, the center distance between uppermost and lowermost stages of heat transmission tube 14 ~m~.
The above condition ~22 means the minimum distance to separate the heating tube 14 from the floor burners 16, and the condition ~3~ means the minimum value required to make the uni-form distribution of heat absorption in the vertical direction of the heating tube 14 of spiral shape by the floor burners 16, ; :i72~
1 It is preferable that the distance a (unit : m~ from surface of the furnace wall 12 to the center of the heat trans-mission tube 14 meet the following conditions.
I1 When the longitudinal length b of spiral shape of the heating tube 14 is less than ll.2 ~:
0,848 c a (41 II~ When the longitudinal length b of spiral shape of the heating tube 14 is equal to or greater than ll,2 m:
O.Q757 x b < a (5~
The above conditions (4~ and (5) means the minimum value required to make uniform the distribution of heat absorp-tion in the vertical direction of the heating tube 14 of spiral shape by the wall burners 17.
The above described conditions Cl) to 15~ will now be explained in more detail. Various studies have been made as to the coal slurry furnace using four-inch inner diameter tubes or pipes in accordance with the present invention.
Condition (ll: r ~ 5 x h (preferably, r 7,5 x hl When the flow speed of the slurry is in the range of l.2 to 3.2 m/s, a ratio ~ of an erosion rate of the linear portion of tube to an erosion rate of a curvilinear or bent portion of tube ~s shown in Fig. 7 where the ratio ~ is represented by the expression ~ =
erosion rate of the bent portion (mm/day) erosion rate of the straight portion (mm/day~
On the other hand, since at an inlet portion of the heating tube coal perticles contained in the slurry fluid are not yet soluted therein, unless the radius of curvature is suitably selected, there would be caused a plugging or clogging in the-bent portion. In case of the studies using the four-inch inner diameter pipes, the flow speed at which the plugging will occur i `~72~2 1 is represented by Fig. 8 in which is the mean perticle degree ~mesh), and Vc is a minimum flow speed (m/s~ at which the plugging does not occur.
As has been apparent from Figs, 7 and 8, there is no fear that the erosion and plugging may occur significantly at the bent portion in the range of r/h > 5, preferably r/h > 7.5. Thus, it is understood that the bent portion may be designed in the same manner as in the straight portion.
C dition 12): r - 0.28 x g + 0.20 If during the operation of the heating furnace, the flame of burners impinges against the heating tube or pipes, the heating tubes or pipes are remarkably locally heated to thereby cause co~ing of fluid and damage of heating tubes, Therefore, the heating tubes must keep a distance from the flame suitable.
It is experienced that if the following lower limit is exceeded, the coking of fluid take place.
di > 0.107 x g + 0.113 where: di is the distance ~ml between the surface of flame and the heating tube center, The diameter of a flame produced by burners which produce r~,latively thin flame compared with their capacity is represented in Fig. 9 inwhich a first solid line on the left side denotes a diameter of flame, a second solid line on the right side denotes a center position of the heating tube nearest to the burner defined by di and a dotted line shows a straight line in-dicating the equation r = 0,28 x g + 0.20, It will readily be understood that as far as the rela-tionship r > 0.28 x g + 0.20, is gi~en, the heating tube may be protected against the excessive burner heating at a safety distance, , 1729~
1 Condit_on (3): r - 0.13 x b In general, difficulties have been experienced in determininy a distribution of a thermal absorptivity, per unit surface area q (kcal/m~ hr) of the heating tube because it re-markably depends upon types of burner, configuration of flame, con~iguration of furnace,.kind of fuel and the like. However, in case where two heat absorbing planes composed of a row of heating tubes are arranged to be confronted with each other in a vertical and parallel relationship and the up-firing burners are disposed at the center of the absorbing planes the relationship between the geometrical relation of the two heat absorbing planes yb and the non-uni~ormity of heat absorption max on the heating tubes is shown in Fig. 1.0 by using natural gas as a fuel, in which qav is the average heat absorption per unit surface area of heating tube by the floor burner (kcal/m2hrl and qmax is the maximum heat absorption per unit surface area of heating tube by the floor burner ~kcal/m2hr). As is apparent from Fig. 10, at a posi.tion represented by r = 0.13 x b, the relationship of qmax/qav - 1,6 is establi.shed; namely, heat absorbing rat~ per unit surface at the maximum heat absorbing portion of the heatiny tube is 1.6 times o~ the average thermal absorptive portion in heat ahsorption.
It is experienced that if non-uniformity in thermal absorption mvre remarkable than this expression occurs, the portion in which the maximum absorption takes place, is heated to a high temperature and the liquid cokiny may be caused.
Condi.tivns ~4) and ~5): 0~848 ~i a and 0,0757 x b - a ~i In general, a wall used for heatiny the heati.ng tube by radiation emitted from insulating materials or heat re-sistant material such.as fire brick which are heated by the wall i ~729~2 1 burners is r~ferre~ to as a radiatio1- wall. l~1hen the distance between the radiation wall and the heatiny tube is too short, since the temperature of the radiation wall is not uniform, the heatin~ tube is subjected to a non-uniform heating so that the coal slurry is coked at the portion at which the temperature is highest. Inversely, when the distance between the radiation wall and the heating tube is too long, the tubular furnace becomes uneconomically large in size, and the thermal efficiency of the wall burners is markedly reduced. Therefore, the suitable distance must be chosen.
The relationship in distance will now be explained with reference to Fig. ll.
(a) In the case where the longitudinal length b of the spiral shape of the heating tubes is equal to or greater than ll.2: In Fig. ll, q' v is the average heat absorption rate per unit surface area of the heating tube by means of the wall burners (kcal/m2hr) and q'max is the maximum heat absorption rate per unit surface area of the heating tube by the wall burners (kcal/m2hr).
As is apparent from Fig. ll, if the ratio a/b becomes smaller than 0.0757, the ratio q'ma /q' exceeds l.6 thereby making the local heating of the tube remarkable and causing a coking in coal slurry. Therefore, the condition (5):
0.0757 _ a must be given.
^ ~729~
1 (b) In the case where the longitu~ al length b of the spiral shape of the heating tubes is less than 11.2:
By substituting b in the condition (5) with 11.2, the relationship of 0.848 _ a is given, which is the same as condition (4). The condition (4) means that even if the value of b is small, it is prohibited to be smaller than 0.848 m as a minimum distance.
It is experienced that if the distance between the center of the heating tube and the radiation wall is smaller than - 13a -i ~729~2 1 ~.848, the following disadvantages are noticed. (i) It is difficult to construct the furnace. (ii~ It is difficult to carry out the maintenance works in the furnace for inspection.
(iii) The flame of the wall burners will impinge against the tube supports thereby causing the excessive heating. Therefore, it is highly desired that the sufficient distance must be kept with in the condition (4), It is therefore necessary that if the value of b is less than 11.2 m, the value of a be defined by the relationship of 0.848 = a.
In the case that the size of the furnace is increased resulting in increase of the height b while increasing the dis-tance a in accordance with the above described condition (5) to thereby increase the construction costs, the wall burners 27 may be provided in a two-stage manner as shown in Fig~ 6(a) in the vertical direction. In this case, a height of the spiral tube to be heated by each one of the double-stage wall burners may be reduced to halr the height of the single stage wall burners. Thus the distance a may be also reduced in accordance with the con-dition (5~ reducing the construction costs.
The above described conditions are generally used forthe tubular furnaces for three-phase fluids which are not limited to the coal slurry of three-phases. Incidentally/ f~o~ the ~oregoing descri`ption the center curvature rad~us r in the con-ditions (2) and (3) is expressed as a minimum necessary distance Q
(unit: meter~ from the center of the first heat source, i,e., floor burner 16 to the heating tube 14.
When the tubular furnace in the embodiment shown in Figs. 4A and B is used as, for example, a coal slurry heating furnace in a coal liquefying plant, the features that the heat transmission tube 14 of oval spiral shape has the curved portions 14B with center curvature radius in the longitudinal diréction ~ 172982 1 being five times as large as the heat transmission tube inner diameter or more and that the heat transmission tube 14 is heated on both sides by the floor burners 16 and the wall burner~ 17 offers the following advantages.
(1) Since the 180 U-bend of short diameter being twice as large as the tube inner diameter or less is not used but the heat transmission tube of oval spiral shape having the center curvature radius being five times as large as the tube inner dia-meter or more is provided, the excessive erosion of fluid does not occur at the curved portion which is the most critical portion of heating tube. The curved portion is also free from clogging by precipitation of solid material due to its curvedness.
(21 The heating tube is uniformly heated on inner and outer circumferential surfaces of the loop-shaped tube arrange-ment and the local overheating does not occur ~hile fluid is not coked, and therefore tube clogging due to the coking is not caused, Fox example, when the same average heat flux (heat absorption rate per unit area surface of the heating tube~ is applied, if the heat transmission tube is arranged in pitch being t~ice as large as the tube outer diameter, the maximum heat flux produced at the side faced to the flame in double-side heating becomes 1/1.5 in comparison with one-side heating.
(3~ The fluid always flow downwardly, namely flowing is held in one direction, and therefore the heat transmission tube is not subjected to vibration, ~ 4) If the linear portion of the heat transmission tube is lengthened there~y e~tending the long diameter portion, the furnace large in size can readily be constituted, Therefore, there is no restriction in structure as in the conventional heating tube of simple circular spiral shape, and uniform heating is obtained in the furnace large in size by means af the double-side heating.
l ~72g82 1 Accordingly, the furnace large in size can be construc-ted without any restrictions~
Another embodiment of the present invention will now be described referring to Figs, 6 (A~ and ~B).
This is an example of the large size heating furnace structure of Fig. 4, The radiant section of the furnace is divided into two chambers. Similarly to the furnace shown in Fig. 4, each chamber 23 having heating tubes 24, Therefore, the numbers of flower burners 26 and wall burners are increased. A
common heat recovery section 20A is proYided at the top of the two radiant sections, and recovers heat from flue gas mainly by convection. Linear portions of the heat transmission tube 24 are extended namely the long diameter direction is made long, thereby forming the furnace large in size. As the furance becomes large, the numbers of.the floor burners 26 and the wall burners 27 ~re increased. When the height of the heating tube 24 of spiral shape is increased, a uniform heating is not effected which the wall burners 17 which are mounted in single stage at the lower portion of the furnace wall as shown in Eig, 4(A~, Therefore, the arrangement in two lateral stages at the inner circumference of the furnace wall is effected as shown in Fig, 6 (B~. In this case, it is preferably that when the height b of spiral shape of the heat transmission tube 2~ be b - 5.6 m, the number of lateral stages of the wall burner 27 be one stage, and when b > 5.6 m, the number of lateral stages be two stages. Of course, multiple lateral stages more than double stages may be effected correspond-ing to the height of the heating tube 24 of spiral shape, Effect of installation of the heat recoYery section 2QA is that the waste flue gas of high temperature i5 used to heat other process fluids requiring heating, or if there is no suitable process i 1729`~2 1 fluid, a waste heat boiler is installed to generate steam. ~eat recovery is therefore effected and a thermal efficiency of the heating furnace as a whole is improved, Effect of installation of a plurality of the radiation chambers 23, is as follows;
In the tubular heating furnaces designed in any manner, the fluid is more or less coked within the heating tube.
Accordingly, in usual, decoking operation to introduce stea~ and air in the heating tube and to remove coke adhered to the inner wall of the tube is performed regularly. During the decoklng operation the furnace cannot serve as a coal slurry heater, When a plurality of the radiant chamber are installed as in this embodiment, the furnace can consequently serve as a coal slurry heater by means of alternate decoking operation between the two radiant chambers, If plural furnaces having two radiant chambers are each installed, decoking operation will be conducted more easily.
~ s described above, a tubular furnace of the present invention is constructed so that a heat transmission tube of spiral shape i.s composed of linear portions and curved portions, each.having the center curvature radius of five times as large as the tube inner diameter or more, the heat transmission tube is heated on both sides from the inner and outer circumferences, whereby fluid can be heated uniformly and smoothly, and local overheating in the heat transmission tube is prevented signif-icantly, the elimination of use of 180 U-bend prevents damage such as abrasion of inner wall of the curved position caused by erosion or clogging of the tube due to the deposit of solid constituents. contained in the slurry.
The flow of fluid is held in one direction either downwardly or upwardly, whereby the heat transmission tube is t 1729~2 1 prevented from vibrating. Tubular furnaces large in size can readily be constructed employing the oval heating tube.
When the heating furnace according to the present in-vention is used as coal slurry heating furnace in the preheating process of the coal slurry composed of a three-phases, i.e.
vapour ~hydrogen gas), liquid ~solvent) and solid (coal) in the coal liquefying processr technical problems such as erosion, durability for coking and service life of heating tubes can be improved.
Claims (11)
1. A tubular furnace wherein a heating tube is heated by radiation, thereby heating fluid within the tube, characterized in that a heat transmission tube of spiral shape in a longitudinal direction is installed within the heating furnace, said heating tube comprising linear portions and curved portions each having a center curvature radius of five times as large as a tube internal diameter or more, and a first heat source for heating inner cir-cumferential surface of the heat transmission tube of spiral shape and a second heat source for heating outer circumferential sur-face of the tube are also installed within the furnace.
2. A tubular furnace according to claim 1, wherein a plur-ality of first heat sources are arranged in a line at the center of lower portion of the furnace, and a plurality of second heat sources are arranged in lateral multiple stages along circumfer-ential wall within the furnace.
3. A tubular furnace according to claim 1 or 2, wherein the heating furnace comprises a plurality of radiation chambers, each having the heating tube and heat source means including burners, and heating recovery section installed at the top of the radiation chambers for recovering heat of high temperature waste gas within the chambers.
4. A tubular furnace according to claim 1, wherein individ-ual tubes of the heating tube of spiral shape are supported by a tube support held on furnace wall, and an escape portion of the tube support during thermal expansion is provided on the furnace wall.
5. A tubular furnace according to claim 1, wherein ? and a meet the following relationships:
? ? 0.28 x g + 0.20 ? ? 0.13 x b when b < 11.2, 0.848 ? a and when b ? 11.2, 0.0757 x b ? a where ? (unit:meter) is the minimum distance from the first heat source to the center of the heat transmission tube;
a (unit: meter) is the minimum distance from the surface of the furnace to the center of the heat transmission tube;
g is the heat quantity per one floor burner of the first heat source [x 10-6 Kcal/Hr]: and b (unit: meter) is the height of the heat transmission tube of spiral shape.
? ? 0.28 x g + 0.20 ? ? 0.13 x b when b < 11.2, 0.848 ? a and when b ? 11.2, 0.0757 x b ? a where ? (unit:meter) is the minimum distance from the first heat source to the center of the heat transmission tube;
a (unit: meter) is the minimum distance from the surface of the furnace to the center of the heat transmission tube;
g is the heat quantity per one floor burner of the first heat source [x 10-6 Kcal/Hr]: and b (unit: meter) is the height of the heat transmission tube of spiral shape.
6. A tubular furnace according to claim 5, wherein a plur-ality of first heat sources are arranged in a line at the center of lower portion of the furnace, and a plurality of second heat sources are arranged in lateral multiple stages along circumferent-ial wall within the furnace.
7. A tubular furnace according to claim 1, wherein the heat transmission tube of spiral shape comprises a curved portion with a center curvature radius of 7.5 times as large as the tube inter-nal diameter or more,
8. A tubular furnace according to claim 7, wherein a plur-ality of first heat sources are arranged in a line at the center of lower portion of the furnace, and a plurality of second heat sources are arranged in lateral multiple stages along circumferent-ial wall within the furnace.
9. A tubular furnace according to claim 7, wherein ? and a meet the following relationships:
? ? 0.28 x g + 0.20 ? ? 0.13 x b when b < 11.2, 0.848 ? a and when b ? 11.2, 0.0757 x b ? a where ? (unit: meter) is the minimum distance from the first heat source to the center of the heat transmission tube;
a (unit: meter) is the minimum distance from the surface of the furnace to the center of the heat transmission tube;
g is the heat quantity per one floor burner of the first heat source [x 10-6 Kcal/Hr]; and b (unit: meter) is the height of the heat transmission tube of spiral shape.
? ? 0.28 x g + 0.20 ? ? 0.13 x b when b < 11.2, 0.848 ? a and when b ? 11.2, 0.0757 x b ? a where ? (unit: meter) is the minimum distance from the first heat source to the center of the heat transmission tube;
a (unit: meter) is the minimum distance from the surface of the furnace to the center of the heat transmission tube;
g is the heat quantity per one floor burner of the first heat source [x 10-6 Kcal/Hr]; and b (unit: meter) is the height of the heat transmission tube of spiral shape.
10. A tubular furnace according to claim 9, wherein a plur-ality of first heat sources are arranged in a line at the center of lower portion of the furnace, and a plurality of second heat sources are arranged in lateral multiple stages along circumferent-ial wall within the furnace.
11. A tubular furnace according to claim 6, 8 or 10, wherein the heating furnace comprises a plurality of radiation chambers, each having the heating tube and heat source means including burners, and heating recovery section installed at the top of the radiation chambers for recovering heat of high temperature waste gas within the chambers.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP8744281A JPS57202380A (en) | 1981-06-09 | 1981-06-09 | Tubular heating furnace |
| JP87442/81 | 1981-06-09 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1172982A true CA1172982A (en) | 1984-08-21 |
Family
ID=13914966
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000404824A Expired CA1172982A (en) | 1981-06-09 | 1982-06-09 | Tubular furnace |
Country Status (3)
| Country | Link |
|---|---|
| JP (1) | JPS57202380A (en) |
| AU (1) | AU549829B2 (en) |
| CA (1) | CA1172982A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110878218A (en) * | 2018-09-06 | 2020-03-13 | 中国石化工程建设有限公司 | Method for heating delayed coking raw material |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB0604895D0 (en) * | 2006-03-10 | 2006-04-19 | Heliswirl Technologies Ltd | Piping |
| CN102925195B (en) * | 2012-10-12 | 2014-09-03 | 中国石油化工股份有限公司 | Ethylene cracking furnace combustion system taking water-coal-slurry as fuel |
-
1981
- 1981-06-09 JP JP8744281A patent/JPS57202380A/en active Granted
-
1982
- 1982-06-09 CA CA000404824A patent/CA1172982A/en not_active Expired
- 1982-06-09 AU AU84708/82A patent/AU549829B2/en not_active Ceased
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110878218A (en) * | 2018-09-06 | 2020-03-13 | 中国石化工程建设有限公司 | Method for heating delayed coking raw material |
Also Published As
| Publication number | Publication date |
|---|---|
| AU549829B2 (en) | 1986-02-13 |
| AU8470882A (en) | 1982-12-16 |
| JPH027352B2 (en) | 1990-02-16 |
| JPS57202380A (en) | 1982-12-11 |
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| MKEX | Expiry |