Vessel for the generation of synthesis gas

A vessel for the generation of synthesis gas at a high pressure, using hydrocarbons, includes a catalytic endothermic reforming section with a plurality of reformer tubes heated externally and filled with a catalyst, and a mixture of hydrocarbons and steam entering the reformer tubes which are positioned by a common plate. The reforming gas generated in the tubes flows from the tubed section into a partial oxidation section which has a larger diameter than the tubed section and the shape of a pressure vessel closed at one end, the free ends of the reformer tubes penetrating into the partial oxidation section, and in which inlet gas such as additional hydrocarbons and oxygen or oxygen-rich gas are mixed with the reforming gas. A plurality of inlet devices for the inlet gas are positioned in the cylindrical shell of the partial oxidation section with the axes of the gas flow streams being inclined away from the radial. The inlet devices are spaced a predetermined distance from the outlet end of the reformer tubes such that a rotary gas vortex is produced and the product gas stream flows through the outer section of the chamber, heats the reformer tubes and leaves the reforming section via an outlet nozzle.

BACKGROUND OF THE INVENTION 
The invention relates to a vessel for the generation of synthesis gas at a 
high pressure (thirty bar or more), using hydrocarbons, particularly 
natural gas, naphtha and/or refinery gas in a catalytic endothermic 
reforming section with a cylindrical pressure vessel and a plurality of 
reformer tubes heated externally and filled with a catalyst, and a mixture 
of hydrocarbons and water vapor entering the reformer tubes which are 
positioned by means of a common plate. The reforming gas generated in said 
tubes flows from the tubed section into a partial oxidation section in 
which hydrocarbons and oxygen or oxygen-rich gas are admixed. The 
oxidation section has the shape of a pressure vessel closed at one end, 
with the reformer tubes penetrating into said section. 
The synthesis gas which mainly contains hydrogen and carbon monoxides is 
the raw material for a number of commercial-scale synthesis plants such as 
methanol or ammonia plants. It is also possible to produce pure hydrogen, 
provided the synthesis gas is subjected to an appropriate treatment. 
Vessels for synthesis gas generation are known, in which the following 
process steps are used: 
catalytic endothermic steam reforming (I) and 
partial autothermic oxidation (II) 
and in which the reformer tubes filled with a catalyst are heated with hot 
reaction gas generated in partial oxidation step II. 
West German Pat. No. 32 44 252, for example, describes a vessel in which a 
first stream of hydrocarbons is mixed with steam and subjected to the 
steam reforming reaction in the reformer tubes filled with a catalyst. The 
process gas generated in this reaction step leaves the reformer tubes 
suspended perpendicularly in a cylindrical brick-lined vessel and then 
enters an untubed chamber under the reformer tube ends which is referred 
to as the mixing chamber. The temperature of the gas leaving reaction step 
I is normally over 700.degree. C. The second stream of hydrocarbons, which 
need not have the parameters of the first stream (quantity, etc.), is fed 
to said chamber, thereby admixing oxygen or oxygen-rich gas. The gases 
react with each other (reaction step II). The gases in the immediate 
vicinity of the above mentioned reactants also take part in the step II 
reaction. 
The temperature of the gas generated in reaction step II is approximately 
1400.degree. to 2100.degree. C. and, consequently, it exceeds considerably 
the temperature of the gas generated in reaction step I. The gas streams 
from reaction steps I and II should be thoroughly mixed in the mixing 
chamber until the mixture has a uniform temperature. The equilibrium 
reactions taking place simultaneously are called reaction step III, the 
temperature being in excess of 950.degree. C., preferably 1100.degree. C., 
and governing the synthesis gas composition. This gas flows in a 
counter-current to the gases generated in reaction step I and enters the 
tubed part of the catalytic reforming section, the tubes of which are 
heated to the temperature required for reaction step I. 
The gas generated in reaction step I has a high residual methane content 
while the gas stream from step II contains only traces of methane. The gas 
stream from reaction step III has a target methane content which is 
compatible with the reaction temperature, for example less than 1%, 
preferably less than 0.5%. However, this reaction temperature and the gas 
composition which can be calculated on this basis can only be achieved if 
the gas streams from reaction steps I and II are completely mixed, i.e. 
leaving no gas striae. In order to ensure an optimum performance, it is 
imperative that the gases be completely mixed prior to entering the 
cooling section (tubed reforming section). The device described in patent 
No. 32 44 252 does not ensure an appropriate mixing of the gas streams. 
Another vessel is known from U.S. Reissue Pat. No. 24,311, in which the 
hydrocarbons are mixed with steam and then subjected to a limited 
catalytic endothermic steam reforming process which takes place in a 
cylindrical pressure vessel equipped with reformer tubes partly filled 
with a catalyst. Oxygen-carrying tubes are installed in the center of the 
reformer tubes. At the outlet of said tubes, the partly reformed 
hydrocarbons are mixed with heated oxygen and subjected to a simultaneous 
partial autothermic oxidation. The lower part of the cylindrical pressure 
vessel is an untubed reaction chamber in which the reaction gases return 
at the chamber bottom in order to flow upwards and to heat the reformer 
tubes. From the technological and metallurgical point of view, it is very 
difficult to mount the oxygen-carrying tubes in the center of the hot 
reformer tubes and, as a result, this device has never been constructed. 
Moreover, the design does not permit universal application for various raw 
materials and is not suitable for the treatment of hydrocarbons in two 
reaction steps. 
SUMMARY OF THE INVENTION 
An object of the present invention is to design a vessel which is suitable 
for the required thermal reactions, which provides reliable operation and 
complete reactions and which permits a control of the reaction steps such 
that synthesis gases having different compositions can be generated. 
The advantages of the invention are that the partial oxidation section, 
i.e. the mixing chamber, provides stable flow conditions. The reactants 
such as reforming gas, additional hydrocarbons and oxygen or oxygen-rich 
gas are injected in such a manner that a vortex generally coaxial with the 
vessel longitudinal axis is produced in the mixing chamber and that a 
low-pressure area forms in the center of said vortex, whereby the 
reforming gas is withdrawn from the reformer tubes and forced into the 
lower part of the mixing chamber. This configuration permits a thorough 
mixing of the reforming gas and gas stream from the partial oxidation 
section for the generation of synthesis gas, using special inlet devices. 
The main stream of the gas mixture or synthesis gas in the outer section 
of the vortex leaves the untubed space between the inlet devices in the 
partial oxidation section and enters the reforming section. The hot 
synthesis gas stream heats the reformer tubes and the mixture in the tubes 
to the temperature required for the endothermic reaction. 
The vessel described above operates properly, irrespective of the position 
of the reforming section which may be arranged upstream or downstream of 
the partial oxidation section. It is essential that certain technical 
requirements be met, taking into account the gas to be processed. The 
pitch "t" of the opening in the plane of the reformer tube outlets, for 
example, must comply with the following formula: 
EQU t is less than or equal to d+(0.317.times.h) 
Thus, the gas stream cannot return into the tubed section. The factors d 
and h are defined as follows: 
EQU h==(m.sub.1 /m.sub.o)(.rho..sub.o /.rho..sub.1) (d/0.32) 
where: 
m.sub.o is the mass of the steam from an opening in the plane of the 
reformer tube outlets. 
m.sub.1 is the mass of the gas stream produced with the aid of m.sub.o. 
.rho..sub.1 and .rho..sub.o are the densities of the steams involved. 
d is the diameter of the opening in the plane of the reformer tube outlets. 
The Reynolds numbers for the individual streams from the reformer tube 
outlets should be greater than 5.times.10.sup.3, preferably greater than 
5.times.10.sup.4. The impulses resulting from these flow conditions permit 
a penetration of the gas streams through the vortex into the lower part of 
the mixing chamber, producing a rotary vortex ring which is required for 
the spiral return flow of the gases in the outer section of the mixing 
chamber. 
The Reynolds numbers for the inlet devices (nozzle outlet) should be 
4.times.10.sup.3, preferably 4.times.10.sup.4. It is calculated on the 
basis of an assumed outlet velocity, an assumed diameter and the mean 
viscosity of the gases concerned, said numbers being based on the 
uniformity of impulses and streams and on the design of the nozzle ends of 
the inlet devices pointing towards the mixing chamber. 
The flow parameters of the injected fluids must always be stable. If the 
inlet flow rate is varied in this case (this function is indispensable for 
load variations and for the control of the product gas composition), the 
flow conditions in the mixing chamber are not changed and the mixing 
process is not affected. The plus sign in the above equation represents a 
deviation from the horizontal axis of the mixing chamber, i.e. the inlet 
devices are inclined towards the reformer tube sections. 
An adequate residence time of the reactants in the mixing chamber is 
required to ensure a close approach to the equilibrium of reaction step 
III. According to the invention, the depth of the chamber which has a 
given diameter is selected such that the minimum residence time is four 
seconds. The mixing chamber diameter should be 1.1 times the diameter of 
the enveloping circle of the tubed section, said diameter being reduced in 
the tubed part of the vessel. This configuration permits a radial upward 
product gas stream from reaction step III into the tubed section. Thus, 
the product gas does not come into contact with the gases generated in 
reaction step I. If the chamber diameter exceeds a certain limit, the flow 
pattern cannot be maintained. 
It is also known that the synthesis gas generated in reaction step III 
tends to change its composition when cooling slowly, i.e. the methane 
content increases as the equilibrium conditions change. The effect of this 
reforming step would partly be lost in such a case. Therefore, it is 
imperative that the product gas which has the required equilibrium be 
cooled as quickly as possible in order to preserve the state of the 
product gas. Experience has shown that said conditions can be stabilized 
at temperatures of less than 600.degree. C. 
In order to achieve a uniform and efficient heating of the reformer tubes 
with the aid of the hot synthesis gas, adequate gas cooling is provided. 
The formation of methane and carbon deposits is avoided. Therefore, the 
reformer tubes are jacketed at a certain distance from the outlet of the 
reformer tubes. The hot synthesis gas flows through the annular spaces 
between the tube jackets and the reformer tubes. 
Furthermore, the inventive vessel permits the application of a conventional 
process, using the catalytic reaction as the last step for the synthesis 
gas generation. The space between the outlet ends of the reformer tubes is 
filled with a catalyst such that the synthesis gas entering this section 
passes the catalyst bed. This downstream catalytic autothermic reaction 
step permits a closer approach to methane equilibrium, thus reducing the 
residual methane content of the synthesis gas, i.e. the synthesis gas 
stream from the upstream reaction steps has a lower temperature. 
A further advantage of the catalyst bed mentioned above is that it 
compensates for an insufficient mixture and/or reaction of the gas passing 
the catalyst bed. A section with an inert packing and a special supporting 
structure for the reformer tube jackets can be arranged downstream of the 
catalyst bed. 
The invention does not relate to the design of the outlet ends or nozzles 
of the reformer tubes. Any state-of-the-art configuration may be selected 
for this part.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The reactor in FIG. 1 consists of reforming section 1 and oxidation section 
2 for partial oxidation. The first stream of hydrocarbons mixed with steam 
enters chamber 4 of the reforming section 1 via inlet nozzle 3 and is 
distributed such that it flows through reformer tubes 6 filled with a 
catalyst 5. The tubes are heated and the catalytic steam reforming 
reaction takes place, i.e. reaction step I. The reforming gas 7 generated 
in reaction step I leaves the reformer tubes via nozzles 8 and enters 
mixing chamber 9 at a high flow rate. Said flow rate as well as the pitch, 
diameter and position of nozzles 8 are of major importance for the 
required distance between the position of the nozzles and the position of 
inlet devices 10. The outlet flow rate, the nozzle diameter and the 
position of inlet devices 10 in conjunction with the ratio of the diameter 
of mixing chamber 9 and the diameter of the enveloping circle 11 of 
reformer tubes 6 are crucial for the required flow conditions marked with 
arrows in FIGS. 1, 2, 3 and 4. An adequate axial size of mixing chamber 9 
ensures the required residence time of the reactants. 
The fluids such as oxidizer 12 and the second stream of hydrocarbons 13, 
which are injected via inlet devices 10 and which may also contain steam, 
react with each other and with the ambient gases in the form of a partial 
oxidation. The inlet parameters related to the fluids (i.e. direction, 
velocity and quantity) are such that a vertical vortex is produced in 
mixing chamber 9, said vortex having a low-pressure center. The defined 
positions of inlet devices 10 and nozzles 8 are crucial for the formation 
of a vortex which permits a permanent stream of reforming gas from nozzles 
8 to the lower part of the mixing chamber. Thus, reforming gas 7 and 
oxidation gas 14 are constantly mixed and react with each other. This gas 
mixture flows downwards in a spiral stream, returns at the bottom of the 
mixing chamber and is forced upwards in a spiral stream to the tubed 
reaction part. Synthesis gas forms in annular space 16 between the reactor 
wall and the tubed reforming section and flows in an upward radial pattern 
to the tubed section. 
Annular space 16 is tapered in the section adjacent the unjacketed reformer 
tubes and is designed such that gases 15 can enter this area without 
coming into contact with gases 7. In this area, the radiation heat of 
synthesis gas 15 is used for heating reformer tubes 6. When the gases have 
entered the reformer tube jackets 17, the heat is transferred onto the 
reformer tubes in a convective manner. Annular spaces 18 between tube 
jackets 17 and reformer tubes 6 are sized such that synthesis gas 15 is 
cooled in the shortest possible period. The selected velocity of the gas 
permits an adequate heat transfer onto the reformer tubes so that 
synthesis gas 15 leaves the vessel via nozzle 19 at the lowest possible 
temperature. The size of annular spaces 18 is adjusted by means of spacers 
20 such as helix components, rails parallel to the vessel axis, wires or 
cam rings. In order to achieve a uniform synthesis gas distribution for 
annular spaces 18, the external surfaces of the reformer tubes and the 
internal surfaces of the tube jackets 17 are smoothened to facilitate the 
flow in the annular spaces. Spacers 20 are designed such that the reformer 
tubes and the jackets can compensate for different thermal expansion. 
Moreover, said spacers permit the removal of individual tubes from the 
jackets after removing flanged head 21. 
The tube jackets 17 are jointly supported by means of spacers 22 mounted in 
one plane, said spacers permitting expansion of individual tube jackets. 
Tube jackets 17 are open at the end of partial oxidation section 2 or 
mixing chamber 9 and at the end of outlet chamber 23, thus reducing the 
pressure acting on partition plate 24. Partition wall 25 is the reformer 
tube sheet. 
Since the temperatures are very high in both reactor sections, said 
components have refractory lining 26. The liner surface which comes into 
contact with the hot gas should not contain SiO.sub.2 because of the 
reducing gas atmosphere. In order to protect the jackets against too high 
temperatures, for example in the event of an emergency, the vessel may be 
equipped with a conventional water-cooled jacket or sprinkler system (not 
shown). 
The vessel shown in FIG. 1 has suspended reformer tubes 6 and the partial 
oxidation section 2 is on the lower side. If the catalyst grid is arranged 
at the reformer tube inlet, it is possible to operate the vessel in a 
reversed mode. A further embodiment of the invention is shown in FIG. 2. 
In this case, the first stream of hydrocarbons mixed with steam enters 
chamber 4 via inlet nozzle 3 and is distributed such that it is forced 
into the tubes 6 filled with catalyst 5. The tubes are heated and the 
catalytic reforming reaction takes place, i.e. reaction step I. Gas 7 
generated in reaction step I enters mixing chamber 9 via nozzles 8 at a 
high velocity. Said outlet flow rate as well as the pitch, diameter and 
position of nozzles 8 are of major importance for the distance between the 
position of nozzle 8 and the positions of inlet devices 10. The outlet 
velocity, the nozzle diameter and position of inlet devices 10 in 
conjunction with the ratio of the diameter of mixing chamber 9 and the 
diameter of the enveloping circle of the reformer tubes 6 are crucial for 
the required flow conditions marked with arrows in FIGS. 2 and 3. An 
adequate axial size of the mixing chamber ensures the residence time 
required for the reactants. 
The fluids such as oxidizer 12 and the second stream of hydrocarbons 13, 
which are injected via inlet device 10 and which may also contain steam, 
react with each other and with the ambient gases, i.e. gas 14 forms in 
reaction step II. The inlet parameters for the fluids (i.e. direction, 
velocity and quantity) are such that a vertical vortex is produced in 
mixing chamber 9, said vortex having a low-pressure area in the center. 
The defined positions of inlet devices 10 and nozzles 8 are crucial for 
the formation of a vortex which permits a permanent stream of gas 7 from 
nozzles 8 to the lower part of the mixing chamber so that gases 7 and 14 
are constantly mixed and react with each other. This gas mixture returns 
in a spiral stream through the outer section of the mixing chamber to the 
tubed reactor part and is forced through the catalyst bed in annular space 
16 between the reactor wall and the tubed reactor section. 
The catalyst permits a closer approach to the methane equilibrium, thus 
reducing the residual methane content of the gas. In addition to the heat 
required for this reaction (IV), the gas also supplies the heat for 
reformer tubes 6 in the catalyst bed. The heat transferred onto the 
reformer tubes in this section may be generated to meet the requirement of 
reaction step IV., for example by providing an internal and external 
insulation and/or by reducing the tube diameter, by selecting an adequate 
reformer tube pitch, by adequately sizing the annular space 16 and/or the 
catalyst volume. The hot gas from catalyst bed 27 passes a layer of 
non-catalytic bulk material (packing 28) and dissipates further heat to 
the reformer tubes. The cooled product gas passes the perforated wall 29, 
enters outlet chamber 23 and is discharged via nozzle 19. By selecting an 
adequate shape and material for packing 28, it is possible to achieve the 
required heat transfer as well as the necessary cooling time. The means 
indicated below are also suitable for this objective, for example reformer 
tube pitch, use of large displacers, and use of reformer tubes with larger 
surfaces. 
Catalyst bed 27 is in the section above packing 28 supported by perforated 
plate 29. This plate is placed on the clips of reformer tubes 6 but it is 
also possible to attach the clips to partition wall 25 or to the reactor 
wall. Reformer tubes 6 are positioned by means of at least one perforated 
and sectionalized spacer plate 30 such that each tube has sufficient 
clearance for thermal expansion. Said plate is supported by packing 28. 
This vessel configuration requires no head flange 21 as in the case of the 
vessel in FIG. 1. Catalysts 5 and 27 and packing 28 can be withdrawn 
through a manhole 31. Catalyst 5 can also be removed through a manhole 
(not shown) in chamber 4 if the catalyst grid 32 is detachable. 
FIG. 3 shows a horizontal cross section of the vessel according to FIGS. 1 
and 2, along section line I--I. Six inlet devices 10 are equally spaced in 
the shell of mixing chamber 9 and are directed such that the gas streams 
from the inlet nozzles (marked as streams 14) and their center-lines or 
longitudinal axes deviate from a radial 33 of the chamber 9 to form angle 
alpha 34. The gas streams 14 generate the required vortex 35 marked with 
arrows. The angle 34 can be in the range of 1.degree. to 30.degree. but 
preferably is in the range of 5.degree. to 20.degree.. 
FIG. 4 is a vertical cross section of mixing chamber 9 of the vessel 
according to FIGS. 1 and 2. Gas streams 14 are inclined, i.e. angle beta 
36 indicates the inclination of the stream in relation to the horizontal 
plane of mixing chamber 9. Typically, angle 36 can be in the range of 
+5.degree. (toward the outlets 8) to -15.degree. (away from the outlets 8) 
and preferably in the range of 0.degree. to -10.degree.. The nozzles of 
inlet devices 10 form a plane related to all horizontal axes. The distance 
"h" between this plane and the plane related to the nozzles of the 
reformer tube outlets 8 is crucial for the flow pattern marked with arrows 
in the drawing, vortex 35 shown in FIG. 3 overlapping said pattern. 
Typically, the distance "h" is in the range of 0.15 to 1.0 times the 
diameter of the enveloping circle 11. If required, inlet devices 10 may be 
installed at different levels to form the necessary planes. 
FIG. 5 shows the components to the inlet device 10. Lines 38 for oxidizers 
12 are separately installed in inlet device 10 and connected to nozzles 
37. This applies also to line 39 for the second stream of hydrocarbons 13 
which is connected to nozzle 40. The lines 38 and 39 extend inside a 
tubular shell 44 and are welded to a head 41 with the nozzles 37 and 40 
respectively pointing towards mixing chamber 9. The lines 37 enter the 
shell 44 through and are welded to a head 42 and the line 39 enters the 
shell through and is welded to a head 43. The space between shell 44, said 
heads and the feed lines constitutes a chamber 45 cooled with water. The 
cooling water enters via a flange 46 and flows through a partition plate 
47 to the head 41, which has the high.RTM.st temperature, and is 
discharged via a flange 48. The partition plate 47 is tubular with an open 
end adjacent the head 41 and an opposite end closed by the head 43. The 
partition plate 47 is coaxial with and surrounds the line 39. A portion of 
the plate 47 which extends between the heads 42 and 43 is connected to the 
flange 46. The remainder of the plate 47 44 is connected to the flange 48. 
a vessel for the generation of synthesis gas according to the present 
invention, for example with a capacity of 6634 m.sup.3 /h of CO+H.sub.2 
has the following main dimensions: 
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Inside diameter of reformer section (1) 
800 mm 
Length of reformer section 
10,000 mm 
Number of reformer tubes (6) 
19 
Diameter of enveloping circle (11) 
750 mm 
Reynolds number for outlet 
97,000 
of reformer tubes 
Inside diameter of oxidation section (2) 
1,000 mm 
Length of mixing chamber (9) 
2,200 mm 
Distance h (reformer tube end to plane of 
600 mm 
inlet devices) 
Number of inlet devices 6 
Angle alpha (34) 15.degree. 
Angle beta (36) 0.degree. 
Reynolds number 260,000 
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Tables 1 and 2 show the operating data for the vessels according to FIGS. 1 
and 2. The columns are headed by the reference numbers used for the 
components in the figures. 
TABLE 1 
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3 7 12 13 23 
______________________________________ 
CO [Mol. %] 4.82 23.64 
CO.sub.2 [Mol. %] 10.07 6.93 
H.sub.2 [Mol. %] 54.75 67.33 
CH.sub.4 [Mol. %] 
96.74 28.88 96.74 0.96 
N.sub.2 [Mol. %] 
3.26 1.48 0.5 3.26 1.14 
O.sub.2 [Mol. %] 99.5 
##STR1## 63.66 140.68 51.192 42.44 325.5 
##STR2## 153.96 118.84 133.77 
Temperature [.degree.C.] 
370 730 200 370 613 
Pressure [bar] 
43 41 &gt;41 &gt;41 40 
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TABLE 2 
______________________________________ 
3 7 12 13 23 
______________________________________ 
CO [Mol. %] 4.82 23.83 
CO.sub.2 [Mol. %] 10.07 6.89 
H.sub.2 [Mol. %] 54.75 67.61 
CH.sub.4 [Mol. %] 
96.74 28.88 96.74 0.54 
N.sub.2 [Mol. %] 
3.26 1.48 0.5 3.26 1.13 
O.sub.2 [Mol. %] 99.5 
##STR3## 62.77 138.72 51.136 41.85 323.84 
##STR4## 151.81 117.18 131.79 
Temperature [.degree.C.] 
370 730 200 370 614 
Pressure [bar] 
43 41 &gt;41 &gt;41 40 
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In accordance with the provisions of the patent statutes, the present 
invention has been described in what is considered to represent its 
preferred embodiment. However, it should be noted that the invention can 
be practiced otherwise than as specifically illustrated and described 
without departing from its spirit or scope.