JPS5927609B2 - Rapid heating method for fluids - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to combustion heaters, and more particularly to a new and improved combustion heater for rapidly heating process fluids.

Furthermore, the present invention provides flow. A new and improved method for rapidly heating the body. In recent years, a number of heaters have been developed for rapidly heating process fluids, for example in the pyrolysis of hydrocarbons, particularly in the production of ethylene.

Generally, such heaters are designed for intense decomposition with short residence times, and a particularly effective heater for such purposes is that of U.S. Pat. No. 274,978.
The present invention relates to a new and improved heater for intense and short residence time heating of process fluids, which may be used for purposes other than thermal cracking of hydrocarbons. The method of the present invention is a method for heating fluids that have been generally thought to cause serious coking problems to high temperatures in a short period of time without causing coking. The mixture can be used to reform hydrocarbons to produce fluids containing hydrogen and carbon monoxide, to reform carbon monoxide-rich hydrocarbon feedstocks such as ethane, propane, naphtha, or iron ore. It is effectively used when rapidly heating the regenerated reducing gas from the reduction process to the ore reduction temperature. That is, the method of the present invention is a method of heating a carbon monoxide-containing gas in a radiant heating zone of a combustion heater, in which (a) the gas is heated in a first radiant heating zone for a heating residence time of 0.20.
648-760℃ (1200℃)
(b) directing hot gas from a first radiant heating zone in said combustion heater into a second radiant heating zone; (c) directing said gas in said second radiant heating zone to a temperature of
An improved process comprises heating to a temperature of -9720C (1400-1700F) and heating at a rate such that the total residence time is less than 0.4 seconds.

The reducing gas containing carbon monoxide and hydrogen is generally about 4
26 to about 538°C (about 800 to about 1000°F), preferably about 454 to 483°C (about 850 to 900'F)
is introduced into the first radiant zone of the heater at a temperature of about 648 to about 760C (about 1200 to 1
It is rapidly heated to a first radiant zone exit temperature of 40'F.

The reducing gas is then pumped into the second radiant zone of the heater at about 760
It is further heated to a second radiant zone exit temperature of about 1400 to about 17000F. Accordingly, reducing gas is introduced into the radiant area of the heater at a temperature of about 800 to about 1000 F, and at a temperature of about 760 to about 1000 F.
At least 50%, preferably about 60-80%, of the total temperature raised from the inlet temperature of the heater to the outlet temperature during removal from the heater at a temperature of about 927°C (about 1400° to about 1700°F) In one zone, a higher heating rate is heated in the first radiant zone of the heater. The total residence time for heating is generally less than 1 second, and the residence time in the first radiant zone is less than 70% of the total residence time, preferably from about 30 to about 60% of the total residence time.

Generally, the total residence time will be in the range of about 0.02 to about 0.40 seconds, so the residence time in the first radiation zone will generally be in the range of about 0.01 to about 0.20 seconds. Rapid heating of the reducing gas containing hydrogen and carbon monoxide in the radiant heating zone reduces or essentially eliminates coking problems by using a high heating rate at the inlet end of the first radiant heating zone. Then it becomes possible. The process of the invention may also be used for the pyrolysis of hydrocarbon feedstocks, such as ethane, propane, naphtha, gas oil and similar feedstocks, in particular for the production of ethylene, in which case two radiant zones are used. Separately controlled heating of the ingredients in the first zone is rapid, followed by slow heating in the second zone.

Thus, for example, pyrolysis takes less than 1 second, preferably 0.
The total residence time is in the range of 2 to 0.9 seconds, with the fluid not exceeding 70% of the total residence time, preferably 50 to 50% of the total residence time.
65% is done while in the first zone. The hydrocarbon feedstock is generally preheated to about its initial decomposition temperature, generally no more than about 100'F below the initial decomposition temperature. Initial decomposition temperatures vary depending on each feedstock, but are generally between 482 and 677 C (900 and 125
Temperatures range from 0 to 0 F). The preheated feedstock is introduced into a first radiant heating zone where it is heated to a temperature in the preferred decomposition temperature range, generally about 732 to 76°C (about 135°C).
0-14000F). The feedstock is then heated to approximately 8150C (approximately 150°C) in a second radiant heating zone.
F), generally from about 1500 to about 16,258F, preferably from about 815 to about 855C (
further heated to an exit temperature of about 1500 to about 1570 degrees Fahrenheit. Thermal cracking is generally carried out in the presence of steam to reduce the partial pressure of the hydrocarbon, and the steam is used in an amount ranging from 0.3 to about 1.0 kg per kg of hydrocarbon feed.
The total inlet pressure for the heating tube is generally about 3.15 to about 1.
75k9/CTi gauge (40 to about 25PS1g) and the pressure drop from inlet pressure to outlet pressure is generally about 0.
．． 7 to about 2.1kg/Cd gauge (about 10 to about 30p
sig) range.

Thus, in the method of the present invention, the fluid to be pyrolyzed is rapidly heated from just below its initial decomposition temperature to a temperature within the preferred decomposition temperature range, thus reducing the overall residence time.

The method of the invention also includes the steps of: reforming hydrocarbons using an oxidized substrate and either steam, carbon dioxide, or mixtures thereof, preferably steam, to produce an effluent containing hydrogen and carbon monoxide; It is particularly used in the steam reforming of gaseous by-products containing methane, hydrogen and carbon monoxide produced during the reforming of carbon monoxide-rich hydrocarbon feedstocks such as ethane, propane, naphtha and similar feedstocks.

The carbon monoxide-rich hydrocarbon feed gas and steam (which steam is used in amounts ranging from 0.1 to about 25%) are present in the first radiant heating zone for a residence time of less than 0.25 seconds, generally about 0. About 426 to about 5 with a residence time of .01 to about 0.15 seconds
From an inlet temperature of 100C (about 800 to about 95'F) about 7
04°C (about 1300°P) or higher, preferably to a temperature of about 704°C to about 760°C (about 1300°F to about 14000°F). The reforming mixture is then applied at a temperature of about 815 to about 955 g C (about 1500 to about 1
Further heated to an exit temperature of 75'F) with a total residence time of 0
．． 50 seconds or less, generally about 0.10 to 0.25 seconds. The inlet pressure of the mixture is generally about 3.5 to about 9.8 k9/
? gauge (approximately 50 to approximately 140 psig) and the pressure drop from inlet pressure to outlet pressure is typically 0.7 to
2.1k9/Cd (10-30 psig).

By rapidly heating the feedstock in the first zone to temperatures above 704 dC (13000 F), coke formation is greatly reduced. Heating in the first radiant heating zone is preferably carried out without a catalyst, whereas heating in the second radiant heating zone is carried out in the presence of a suitable reforming catalyst such as nickel. Thus, the raw material that is steam reformed in the method of the present invention is heated through the critical temperature range where coking is likely to occur, thereby reducing coking. Various objects of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.

The method of the present invention is broadly accomplished by utilizing a heater that includes two radiant zones, the radiant zones being substantially completely separated from each other. Each radiant zone has a single row of vertical process tubes that are combustion heated on both sides, and the fluid to be heated is passed successively through both radiant heating zones. The combustion rate in each radiant zone is controlled separately to provide a heating intensity in each zone that is most suitable for the desired fluid process conditions. As a result of the radiant heating zones being substantially completely separated from each other, the combustion rate used in one has no significant effect on the combustion rate in the other. The present invention,
The description will now be described in more detail in conjunction with the accompanying drawings, which illustrate aspects of the invention.

However, it should be understood that the scope of the invention is not limited thereby. Referring to FIG. 1, it is supported on a structural steel frame, generally indicated as 10, rests on piers, and has exterior walls 11 and 1.
2, a vertical tube heater consisting of inner walls 13 and 14, end walls 15 and floors 16 and 17 is shown.

The outer walls 11 and 12 are substantially parallel to the inner walls 13 and 14 such that the highest portions of the outer walls 11 and 12 are parallel to the inner wall 13.
and extending over the highest portion of 14. A plurality of vertical rows of intense radiant burners, generally shown as 18, are located in the outer walls 11 and 12 and the inner walls 13 and 14. Floors 16 and 17 are connected to exterior walls 11 and 12, respectively.
and between the inner walls 13 and 14. Beds 16 and 17 have floor burners, generally designated 19, and preferably of the flame type. The outer wall 11, the inner wall 13 and the floor 16 together with the end wall 15 form a first radiant heating zone, generally designated 20, while the outer wall 12. Internal wall 14 and floor 17 together with end wall 15 form a second radiant heating zone, generally designated 21 .

The end wall 15 has an inverted U shape. It forms an open area 22, allowing entry to the burner 18 located in the inner walls 13 and 14. An internal roof 25 is placed horizontally over the internal walls 13 and 14.

Upper roof 26 placed on the outer wall 11 and end wall 15
is located horizontally and extends inward from the outer wall 11. Meanwhile, the upper roof 27 is similarly located, with the outer wall 12 and the end wall 15
placed on top. The upper walls 28 and 29 are the upper roof 2
6 and 27 which together with the upper extension of the end wall 15 form a convection zone, generally indicated as 30. Horizontal passageway 33 is positioned such that radiant chambers 20 and 21 are in fluid communication with convection area 30. All walls, floors and roofs have suitable fireproofing. The convection zone 30 has a plurality of horizontal convection tubes, schematically shown as 35, which include the convection tubes and the radiant heating zone 20.
and 21 are located in the convection area so that they cannot be seen directly. Within the radiant heating zone 20 is a single row of vertical process tubes 31 extending in a plane parallel to and equidistant from the inner and outer walls 13 and 11, the bottom of each tube 31 extending into the radiant chamber 20. The inlet manifold 36 is connected in fluid flow communication to an inlet manifold 36 located in the bed 16 of the inlet manifold 36 .

Similarly, there is a single row of vertical process tubes 32 extending in a plane parallel to and equidistant from the inner and outer walls 14 and 12, with the bottom of each tube 32 located in the floor 17 of the radiation chamber 21. The outlet manifold 37 is connected in fluid flow communication to the outlet manifold 37 . A plurality of parallel horizontal spanner tubes 38 are located in the horizontal passageway 33 and interconnected such that the process tubes 31 of the radiant heating zone 20 are in fluid flow communication with the process tubes 32 of the radiant heating zone 21. The fluid to be processed moves upwardly through vertical process tubes 31 in radiant zone 20, horizontally through straddle tubes 38 in horizontal passages 33, and downwardly through process tubes 32 in radiant zone 21. through the heater as multiple separate streams through channels consisting of:

Vertical tubes 31 and 32 in radiant heating zones 20 and 21
is supported from the frame 10 by a hanger 39,
The horizontal tube 38 rests on a spring support 40;
This spring support prevents horizontal tube 38 from sagging, but allows it to expand at high operating temperatures.
The burners 18 are arranged in a plurality of regularly spaced vertical rows over the entire depth of the inner walls 13 and 14 and the outer walls 11 and 12, so that the tube rows 31 and 32 in the radiating areas 20 and 21 are arranged in each row. is heated by combustion from both sides along its entire length, and each tube in each row is heated by combustion from both sides along substantially its entire vertical length.

Each vertical row of burners is supplied with fuel through a separate manifold 41, and each burner 18 in the vertical row has a valve 43 and is supplied with fuel through a manifold 42 for that row.
In this method, each row of burners 18 and each burner 18 in each row is individually adjusted to control the rate of combustion.To simplify the description of the overall manner, the manifold 41 is connected to the outer wall 12.
Although only internal burners 18 have been described, it should be understood that burners in the internal walls are similarly provided.
Another aspect of the invention is illustrated in FIG.

Since this is similar to the embodiment of FIG. 1, equal parts are indicated by equal numbers with a prime 5 in the figure. Referring to FIG. 2, it is supported on a structural steel frame, generally shown as 10'', rests on piers, and includes end walls 15'', outer walls 11' and 127, and inner wall 13'.
A vertical tube heater is shown extending both above and below the inner walls 13' and 14' to the outer walls 11' and 12t. The horizontal internal floor 102 is the end wall 1
5'' and connected to the inner walls 13' and 14',
A horizontally extending external floor 101 parallel to the internal floor 102 is connected to the end wall 15' and the external walls 11' and 1γ, such that the internal floor 102 and the external floor 101 together with the end wall 15' form a substantially horizontal lower part. It defines a passageway 103 which communicates with a pair of radiant heating zones 20'' and 2''.

The radiant heating zone 20'' has a lower floor 101, an outer wall 11', and an inner wall 1.
3' and end wall 15 curves, radiant heating zone 2'
are the lower floor 101, the outer wall 12'', the inner wall 14' and the end wall 1.
5'. A plurality of vertical rows of radiant burners 185 are located in the inner walls 13'' and 14'' and the outer walls 1'' and 12'. A horizontal inner roof 25'' connects the end wall 15' and the inner walls 13' and 14'. and l pairs of horizontal external roofs 26' and 2r each extend from the end wall 1.
5", each extending inwardly in the same plane from the outer walls 11' and 12" and substantially parallel to the inner roof 25' and extending inwardly from the outer roofs 26" and 27'0) The ends are kept at a constant distance from each other and rest on the inner internal roof 25' (7).

A pair of parallel side walls 28' and 29'' each extend to the exterior roof 2.
6'' and 2r'', extending vertically upwardly from the inner ends of the convection area 30' and connecting with the upper extension of the end wall 15'.
, which is completely off-stage from both radiating areas 20'' and 21'', and has an end wall 15'', an internal roof 2
5'' and a horizontal passageway 33' defined by external roofs 26' and 2r in gas tube communication with the radiant areas 20' and 212.

The convection zone 30'' includes a plurality of horizontal convection tubes, schematically shown as 355, which tubes are connected to the radiant heating zone 2.
It is located where it cannot be seen directly from 0' and 2'. Since the end wall 15 corresponds to the entire contour of the heater, the inner wall 13
2 and 14", low root 25" and upper floor 102 to provide an open area 22" to allow entry of burner 18k. The floor and roof are constructed with suitable fireproofing materials known in the art. In the radiant heating zone 20'', the inner wall 13
There is a single row of vertical process tubes 31' extending in a plane parallel to and equidistant from the outer walls 11'' and 11'', with the upper portion of each tube located in the roof 26' of the radiant chamber 20'0). The inlet manifold 104 is in fluid flow communication with the inlet manifold 104 .

Similarly, there is a single row of vertical process tubes 322 extending in a plane parallel to and equidistant from the inner and outer walls 14'' and 12', with the top of each tube extending toward the roof 27 of the radiant chamber 21'. a plurality of parallel horizontal straddles 106 .
are located in the horizontal passageway 103 and interconnect to provide fluid flow connection of the radiant heating zone 20'0) process tube 31' with the radiant heating zone 21'0 process tube 32' so that the process The fluid is transported downwardly through vertical process tube 31'' in radiant zone 20', horizontally through straddle tube 106 in horizontal passageway 103, and upwardly through process tube 32' in radiant zone 21'. is passed through the heater as multiple separate streams through channels consisting of the movement of .

The lower floor 101 has supports 107 and supports 10
7 is the midpoint of the horizontal straddle pipe 106 and extends beyond its depth just below. At the high operating temperatures encountered during operation of the heater, the straddle tube 106 is connected to the lower support 1.
07, but its support 107 is horizontal tube 106
to prevent it from deflecting at high operating temperatures. It is noted that more than one support may be used, or the support may be connected to the horizontal tube 106.
It is also clear that it may be located at a point other than the midpoint of .

The burner 18 is connected to the inner walls 135 and 14' and to the outer wall 1.
1' and 12' as a plurality of regularly spaced verticals, so that the radiating area 2
Tube rows 31'' and 3γ in 0'' and 2'', respectively, are combustion heated from both sides along the entire length of each row, with each tube in each row being combustion heated from both sides along substantially its entire length.

Each vertical row of burners 18'' is supplied with fuel through a separate manifold 4'', and each burner 18' in the vertical row is supplied with fuel through a separate manifold 4''.
A pipe 42 having a valve 43'' and connected to a manifold for the row.
Fuel is supplied through '. In this method, the bar
18b Each row and each burner 18" in each row is adjusted separately to control the combustion rate. To simplify the description and drawings of the invention, manifold 41" is used for only burner 18' in outer wall 1γ. Although described, it should be understood that the burners in the inner walls 13'' and 14'' and the outer wall 11'' are similarly supplied. Obviously, many modifications and variations of the preferred embodiments described above are possible within the spirit and scope of the invention. For example, the convection zone tube of the embodiment described above can be described as being used to heat a fluid other than the fluid passing through the radiant zone. Convection tubes may be used for preheating the fluid passing through the radiant heating zone, with the outlet of the convection tube being connected to the inlet manifold of the radiant heating zone using a suitable straddle tube, or the inlet manifold It is clear that instead of using tubes, a plurality of straddle tubes may be arranged such that the convection tube is in direct fluid flow connection with several vertical process tubes in the inlet radiant heating zone. Alternatively, the convection area can be staggered at one end of the heater instead of being staggered in the middle, as specifically shown in the figures. Similarly, the convection zone may be arranged such that the convection zone is not on a level with the radiant heating zone and the convection tubes are not maintained outside of direct line of sight from the radiant zone; Such an arrangement is not preferred since it limits the heater capacity. In other embodiments, several process tubes in a single row of each radiant zone may be interconnected to provide multiple process stream passages therethrough for more than one pass (as specifically noted). can be made. For example, two adjacent tubes can be interconnected with a fold joint in a first radiant zone, whereby the fluid to be processed can be interconnected in the first radiant zone before being routed to a horizontal straddle tube for introduction into the second radiant zone. Two passes through the radiation area shall be made. Similar to the first radiation area, 2
Two adjacent tubes may also be interconnected with a fold joint to provide two passes of the fluid being processed through the second radiant heating zone. In this way, each fluid stream processed in the heater may make two passes through each of the first and second radiant heating zones. In such modifications, the inlet and outlet manifolds are repositioned to create such a flow pattern. Similarly, more than two tubes in each row can be interconnected for more than two passes in each radiant heating zone, so that the number of passes made in each radiant zone is equal to each other. It should be understood that this may be the same or different. In still other embodiments, the tubes located in a single row of each radiant heating zone may be of different diameters and may be interconnected to reduce the number of parallel flows through the heater between the inlet and outlet manifolds. May be connected.

For example, the first radial area has a single row of 24 tubes, 16 of which have an internal diameter of 5.08-7, 8 tubes have an internal diameter of 7.62-32, and the second radial The area has a single row of 6 tubes, 4 of which have an inner diameter of 10.1
60frL4, two tubes have an inner diameter of 15.24cTn6″
It is. The fluid to be processed is made into 16 parallel flows,
Inner diameter 5.080! N2" tubes for a first passage through the first radiant heating zone, each pair of tubes having an inner diameter of 7.
62crrL3I tube to provide a second passage through the first radiant heating zone. Each pair of 7.62 ID Tr L30 tubes is interconnected to one 10.16 cfr L4" ID horizontal straddle tube, and each horizontal straddle tube is connected to one 10.16 cfr L4" ID tube in the second radial area. let me,
A first path for fluid therethrough to a second radiant area. Each pair of tubes with an inner diameter of 10.16 cm 4" and one inner diameter 15"
．． 24CTIL6" tube to provide a second passageway through which fluid is conveyed through the second radial area and to the outlet. Process fluid flow is controlled at the inlet by using a plurality of small diameter tubes as the inlet section. Rapid heating, more gradual heating at the outlet is facilitated. It is also contemplated within the spirit and scope of the invention to reduce the diameter of the tube from inlet to outlet without reducing the number of parallel process streams. These and other modifications will be apparent to those skilled in the art from the description herein.

The above-described heater for use in the method of the invention is particularly advantageous where the overall design allows combustion at different heating rates in two separate zones.

As such, the two radiant heating zones are substantially completely separated from each other, i.e., the vertical process tube in one radiant zone along substantially its entire length is substantially out of direct view from the other radiant zone. In this way, the two radiant heating zones are substantially completely separated from each other, and each radiant heating zone is separately controlled to provide two different heating rates. Generally, the heater is operated to provide a substantially equal tube metal temperature over the length of each tube;
Achieving that result is facilitated by firing and heating the tubes on both sides in a plane perpendicular to the tube row, and the burners in each vertical row are generally separated over the length of each row of burners. Controlled to reduce the combustion rate in the direction of process fluid flow. Generally, each vertical process tube of the burner is fired in the same manner to create the same temperature, so each stream of process fluid is subjected to the same conditions. As such, the radiant heating zone into which the fluid is initially introduced is operated at a high heating rate to quickly bring the temperature of the fluid to be processed to a specific desired temperature in a minimum amount of time; The outlet is operated at a low heating rate. In that way, the temperature of the tube metal is generally controlled so that it does not rise below the higher temperature of the radiant heating zone outlet. Like that, 2
By providing two separate radiant heating zones and passing the fluid to be processed through both zones, a higher heating rate is used to initially heat the fluid to quickly bring the temperature of the fluid to a specific temperature range. and then use a lower heating rate to further heat the fluid to a generally less critical critical temperature range at the desired higher exit temperature. In the absence of two separate radiant heating zones, the maximum heating rate of the outlet end of the tube placed within a single radiant heating zone is the metallurgical limit of the outlet end tubing material.

The separation of the two radiant zones thus provides a higher combustion rate at the inlet end of the process stream than would be achieved by passing the process stream through a single radiant heating zone.
In other words, the process fluid in each tube in each zone is heated by combustion from both sides in each zone, establishing an essentially equal temperature over the length of the tube. The fluid may be heated in the tube to the highest temperature allowed by valid metallurgy, and as a result of the fluid passing through two separate radiant zones, the fluid is heated to the desired higher temperature in a shorter time. In particular, more rapid heating occurs at the inlet end than when the fluid is passed through one radiant heating zone. The convection section of the heater, as mentioned above, is preferably completely flush with both radiant sections, and the convection tubes are not directly visible from the radiant chamber. In this case, the convection tubes are not a limiting factor in the operation of the radiant zone, since cooling the tubes in the convection zone is not expected to warm the radiant zone. The method of the present invention is used in a wide variety of processes because it rapidly heats a fluid from an inlet temperature to a temperature intermediate between the inlet and outlet process temperatures.

Thus, for example, gaseous mixtures containing high contents of carbon monoxide and hydrogen, such as those obtained by steam reforming of hydrocarbons, may be recycled before being used in foreign processes such as the reduction of iron ore. must be heated, and such reheating generally presents significant coking problems as a result of containing carbon monoxide. In the iron ore reduction process, carbon monoxide in the reducing gas is partially oxidized to carbon dioxide, and the reducing gas removed from the reduction process is regenerated by removing its carbon dioxide portion.
Generally, about 40 to about 80 mole%, preferably about 40 to about 60 mole% hydrogen, about 10 to about 30 mole%, preferably about 15 to about 25 mole% carbon monoxide, and up to about 5 mole, preferably The regenerated reduction gas containing less than about 1 mole percent carbon dioxide must also be reheated and recycled to ore reduction. In accordance with the present invention, the heater described above is used to rapidly heat such reducing gas, ie, the effluent from the reformer or the regenerated reducing gas from the iron ore reduction process, to the ore reduction temperature. Aspects of the present invention are as follows.

(1) (a) introducing a carbon monoxide-containing gas into a first radiant heating zone of a combustion heater; (b) introducing the gas within said first radiant heating zone for a heating residence time of 0.20 seconds or less; At a certain rate, about 648 to about 76 'C (about 1200 to about 140
(c) directing the hot gas from the first radiant zone to a second radiant heating zone of the combustion heater; (d) directing the gas in the second radiant heating zone to a temperature of about 927 air C (about 1400 to about 17007F
) heating the carbon monoxide-containing gas at a rate such that the total residence time is not more than 0.4 seconds; and (e) withdrawing the hot gas from the second radiant heating zone. heating method.

(2) The mixture is about 426 to about 51"C (about 800 to
A first radiant heating zone is introduced into the first radiant heating zone at a temperature of 950 degrees Fahrenheit.
The method described in section 1).

(3) Residence time in the first radiant heating zone is about 0.01~
about 0.20 seconds, and the total residence time is about 0.02 to about 0.2 seconds.
The method according to item (2), wherein the square circle (4) according to item (1) is 40 seconds, and the gas is a reducing gas, and further contains hydrogen.

[Brief explanation of drawings]

FIG. 1 is a cutaway elevational view showing one embodiment of the heater used in the method of the present invention, and FIG. 2 is a cutaway elevational view showing another embodiment of the heater used in the method of the present invention.

Claims (1)

[Claims] 1 A method of heating a carbon monoxide-containing gas in a radiant heating zone of a combustion heater, comprising: (a) heating said gas in a first radiant heating zone at a rate such that the heating residence time is not more than 0.20 seconds; 648-760°C (1200-1400°F)
(b) directing hot gas from a first radiant heating zone into a second radiant heating zone in the combustion heater; (c)
The gas is heated in a second radiant heating zone at 760-927°C (14
00 to 1700 degrees Fahrenheit) and heating at a rate such that the total residence time is 0.4 seconds or less.