The present invention relates to the loading of catalyst particles in reactor tubes. In particular, the invention relates to a method and apparatus for the uniform loading of catalyst particles in heat exchange reactors used for carrying out non-adiabatic catalytic reactions. More particularly, the invention relates to a method for the uniform loading of catalyst particles in catalyst tubes having annular spaces adapted to accommodate said particles, and especially for the uniform loading of catalyst particles in bayonet tubes of heat exchange reactors used for the reforming of hydrocarbon feedstocks.

Non-adiabatic catalytic reactions such as the endothermic steam reforming of hydrocarbons are often conducted in heat exchange reactors. A particular type of heat exchange reactor is the bayonet tube reactor. The bayonet tubes are tubes in which the catalyst is placed in the annular space between an outer and inner tube, and in which the hydrocarbon feed first passes through the catalyst-containing annular space in one direction, and then through the inner, empty (catalyst-free) tube in the opposite direction. Apart from the heat provided for the endothermic steam reaction by the flue gas flowing outside the bayonet tube, additional heat is supplied by the reformed gas flowing upwardly through the inner tube. Typically, the outer diameter of the outer tube is about 125 mm, the wall thickness about 5 mm, while the outer diameter of the inner tube is about 50 mm with a wall thickness of about 5 mm. The length of the outer and inner tubes is normally about 7 m, but can be higher for instance about 10 m. The number of bayonet

tubes in a heat exchange reactor for steam reforming processes varies from 1 to about 30. One particular embodiment of a bayonet tube heat exchange reactor is for instance disclosed in EP-A-O, 535, 505.

Loading of catalyst particles in reformer tubes has previously been conducted according to the so-called sock- method, by which an elongated hose is attached in one end to a hopper containing the catalyst to be loaded. The hose, being a sock-like member, is charged with catalyst and the particles are released at the opposite end of the hose by raising the hose, for instance by jerking the line to which the hose is attached. It is well known that this loading method results in uneven and inhomogeneous loading of the reactor, as cones and voids in the catalyst bed are created during the loading.

Recent developments include the application of mechanical devices having fixed parts. For example, when loading with the loading apparatus described in EP-A-1, 283, 070 a loading tube is introduced into the reactor tube to be loaded with catalyst. The loading tube has a diameter smaller than that of the reactor tube and a tube length substantially corresponding to the length of the reactor tube. The loading tube consists of separate tube sections provided with a spirally formed body on the inner wall so as to decelerate the catalyst particles. The loading tube is then successively withdrawn from the bayonet tube in a length corresponding to the loaded height of catalyst particles. This provides normally an even and gentle loading of the catalyst particles in conventional straight reformer tubes and

eliminates the risk of crushing particles as they fill the reactor tube.

However, because the annular space of bayonet tubes is small, normally in the range of only 70-80 mm, the loading of catalyst by means of mechanical devices having fixed parts is often inexpedient. For example, when loading with the loading apparatus of EP-A-I, 283, 070 a loading tube having a diameter lower than for example 70 mm and a tube length substantially corresponding to the length of the bayonet tube (about 10 m) is introduced into the annular space of the bayonet tubes. Although the inner tube of the bayonet tube runs substantially coaxially with the outer tube, said inner tube is often not fully straight along its length so that its wall often bends slightly outwardly. On the other hand, the loading tube is substantially straight along its whole length. Thus, in the confined region provided by the annular space of the bayonet tube the introduction of the loading tube results in an undesired colli- sion with the inner wall of the bayonet tube at a certain height, normally in its middle region for instance in the region corresponding to 30% to 70% of the length of the bayonet tube. This impedes further penetration of the loading tube and as a result there is higher propensity of crushing catalyst particles as they are forced to be loaded into the catalyst tube from a high dropping height. Moreover, almost regardless of how gentle the particles are loaded, the density of particles at the bottom of the tube is higher than at any other height, thus further increasing the risk of breakage of particles, particularly at the bottom of the catalyst tube. Some bayonet tubes disposed in a heat exchange reactor may have inner tubes which are fully

straight along their length, while others may have inner tubes that bend slightly outwardly. As a consequence, apart from the unwanted increase in the pressure drop due to differences in density along the length of each bayonet tube, the bending of the inner tube in some bayonet tubes conveys the attendant problem of uneven loading of catalysts across the different bayonet tubes. This in turn creates uneven flow conditions in the reactor so that non-uniform temperatures prevail. Poor control of the conversion of reactants and/or undesired side reactions may thus occur.

It is therefore an object of the invention to provide a method and apparatus for the uniform loading of catalyst particles in reactor tubes having an annular space adapted to receive solid catalyst particles. By the term uniform loading is meant a loading in which the density of the catalyst particles along the whole length of the reactor tubes is substantially equal or within a narrow range of density values for instance within the range 800-820 kg/m ³ .

It is another object of the invention to provide a method and apparatus, whereby the time required for the loading of catalyst tubes is significantly reduced with respect to known methods .

It is a further object of the invention to provide a method and apparatus, whereby the loading of the catalyst particles occurs gently so as to avoid crushing the particles as they fall and fill the reactor tubes.

We have now found that by properly using a loading hose and varying the initial drop height (IDH) of the particles de-

pending on the loaded height of the reactor tube, a uniform loading of the particles is obtained, that is a substantially equal density of particles along the length of catalyst tube or densities within a narrow range are obtained. An attendant benefit is the achievement of an even pressure drop in the catalyst-filled tubes. Thus, the value of the pressure drop from top to bottom in the tubes can be kept substantially equal or within a narrow range, for instance about 10% preferably about 5% from the average pressure drop.

By the term initial dropping height (IDH) is meant the distance from the open end of the hose where the particles are first discharged to the surface of the underlying catalyst bed.

By the term loaded height is meant the distance from the bottom of the catalyst tube to the catalyst surface at the top of the particle bed.

The term catalyst tube encompasses in its broadest scope tubes having an annular space adapted to receive solid catalyst particles, such as bayonet tubes as described above and also so-called double-tubes, as for instance de- scribed in EP-A-I, 106, 570.

According to the invention we provide a method for the uniform loading of one or more catalyst tubes in a heat exchange reactor, in which the one or more catalyst tubes consist of an inner tube arranged substantially coaxially with an outer tube and in which the walls of the inner and outer tube define an annular space adapted to receive solid

catalyst particles, the method comprising stages (a) and (b) :

(a) introducing a loading hose into the annular space of the tube to be filled with catalyst so that the distance from the discharging end of the loading hose to the bottom of the tube defines a first initial drop height IDH, and filling in one or more steps the annular space of the tube with catalyst up to a loaded height, the level of said loaded height corresponding to the level of the discharging end of the loading hose or below, whilst at the same time maintaining said first initial drop height constant by raising the loading hose after each catalyst filling step;

(b) raising the loading hose so that the distance from the discharging end of the loading hose to the catalyst surface defines a subsequent initial drop height IDH which is higher or lower than the initial drop height of the previous stage and filling in one or more steps the annular space of the tube with catalyst up to a subsequent loaded height, said subsequent loaded height having a value greater than the loaded height of the previous stage but not above the total length of the catalyst tube, the level of said loaded height corresponding to the level of the discharging end of the loading hose or below, whilst at the same time maintaining said subsequent initial drop height constant by raising the loading hose after each filling step; in which said stage (b) is conducted at least once.

Hence, in the broadest scope of the invention the IDH may be adjusted at any stage to a value which may be higher or lower than the IDH of the previous stage. If the catalyst tubes are filled at a given initial drop height regardless

of the loading position in the catalyst tube, the density of particles will decrease with the loaded height, i.e. with the highest density at the bottom of the catalyst tube and lowest density at the top. By varying the initial drop- ping height as the loading position in the catalyst tube increases, the density of particles is kept at substantially the same value as at the bottom of the catalyst tube or within a narrow range of density values. Further, the loading time of the catalyst tubes is significantly reduced with respect to known methods.

Clearly, the loading position in the catalyst tube is governed by the position of the discharge end of the loading hose, and each stage corresponds to IDH being adjusted to the required level.

Before raising the loading hose to the next upper level, the flow of catalysts into the hose from a catalyst box lying above the reactor tube or reactor tube assembly may be slowed down or optionally completely stopped. When such next upper level in the tube is found the flow of particles may then be resumed. This enables better control of the loading procedure.

According to the invention it is possible to conduct a loading of solid catalyst particles in a 10 m long catalyst tube as follows. In the first stage, i.e. stage (a) at a loaded height of 0 to 0.5 m, the IDH may conveniently be set at about 0.8 m. In the second stage, from e.g. 0.5 to 1.0 m, the IDH may then be adjusted to about 1.1 m. In the third stage, covering a loaded height of 1.0 to about 3 m, the IDH may be adjusted to 1.6 m. Finally, in the fourth

and last stage, from 3 m to 10 m, the IDH is adjusted to a lower level of 1.3 m. This enables the density to be kept within a narrow range along the length of the tube.

At a given loaded height, the initial drop height (IDH) should not be too small because the packing of the particles and thereby the density may be too low. On the other hand the IDH should not be too high since the catalyst particles may break. Accordingly, the IDH may be increased up to the maximum level IDH _max , which provides the highest density at any given loaded height. Increase of IDH above IDH _max will result in a decrease in density. We have found that best results in terms of even density in the tubes and loading time are obtained by gradually increasing IDH after each stage. Thus, in a preferred embodiment of the invention the IDH is adjusted at any stage to a value which is higher than the IDH of the previous stage but not above IDH _max .

Accordingly, the invention provides also a method for the uniform loading of one or more catalyst tubes as described above, wherein in stage (b) said subsequent initial drop height IDH is higher than the initial drop height of the previous stage but not above a threshold value IDH _max .

Hence, if the catalyst tubes are filled at a given initial drop height regardless of the loading position in the catalyst tube, the density of particles will decrease with the loaded height, i.e. with the highest density at the bottom of the catalyst tube and lowest density at the top. By increasing the initial dropping height up to a maximum value IDH _max as the loading position in the catalyst tube in-

creases, the density of particles is kept at substantially the same value as at the bottom of the catalyst tube or within a narrow range of density values. Further, the loading time of the catalyst tubes is also significantly re- duced with respect to known methods.

Preferably, IDH at the bottom of the catalyst tube, for example at a loaded height between 0 and 1 m (first 10% of tube's length from the bottom in a 10 m long tube), is in the range 0.4 to 0.9 m; the subsequent IDH at a loaded height of up to 4 or 5 m is preferably in the range 1.0 to 1.2 m, while up to a loaded height of 10 m, i.e. up to the top of the tube, the initial drop height may correspond to IDH _max having values of 1.3 to 1.5 m.

An IDH of for example 0.8 m gives a low density value and is thus more convenient to apply near the bottom of a 10 m catalyst tube. A lower value of IDH can be used at the bottom, for example 0.6 or 0.5 m or even lower, such as 0.4 m. In the upper part of the tube, for example from bottom to the middle of the catalyst tube, for example up to 4 or 5 m, a value of IDH of 1.0-1.2 m may be applied. From about 4 or 5 m up to the top of the catalyst tube an IDH of 1.3 to 1.4 m (IDH _max ) may be used. Further increasing IDH above IDH _max to for instance 1.6 m results in a decrease of density with loaded height, which normally is undesired.

The catalyst tubes in the heat exchange reactor are selected from the group of bayonet tubes and double tubes. Preferably the catalyst tubes are bayonet tubes. In a particular embodiment the catalyst tubes are bayonet tubes having a length about 10 m and the loading of the catalyst

along the whole length of the tube is conducted in three stages, wherein the initial drop height up is about 0.8 m up to a loaded height of 0.5, the subsequent initial drop height is about 1.1 m up to a loaded height of 4 m and the subsequent initial drop height is 1.3, which corresponds to IDH _max and is used up to a loaded height of 10 m.

Preferably, the filling of catalyst is effected so that an amount of catalyst corresponding to 0.2 to 0.7 m, most preferably 0.5 m loaded height is introduced in each filling step once the IDH has been adjusted to the required level. In this manner the annular space of the catalyst tube is filled after each filling step with particles up to a level of about 0.1 to 0.8 m below the level corresponding to the discharging end of the loading hose (i.e. distance between catalyst surface and discharging end of loading hose after each filling) . This enables a reasonable dropping height for all the particles while being loaded.

Accordingly, when 0.5 m loaded height is introduced in each filling step once the IDH has been adjusted to the required level, at the bottom of the tube for instance up to a height load of 0.5 m in a 10 m long tube, and where the initial dropping height is only 0.6 m, the distance between catalyst surface and discharging end of loading hose after each filling, in this case only one filling, is about 0.1 m. In the next stage with the subsequent adjustment of the initial dropping height to a value of 1.1, which may be applied up to a loaded height of 4 m, the distance between the catalyst surface and discharging end of loading hose after each filling is about 0.6 m. From a load height of 4 m and above, corresponding to the third stage in which the

initial dropping height is adjusted to 1.3 (IDH _max ) the distance between the catalyst surface and discharging end of loading hose after each filling reaches a value of about 0.8 m.

The loading of the annular space of the catalyst tube may also be effected by simultaneously filling particles with additional loading hoses introduced at different positions along the annular space. This enables more even packing and thereby even density at any position in the annular space of the catalyst tube. Alternatively, a single loading hose can be shifted from one side to the opposite side in the annular region.

The invention provides also a loading apparatus for use in the loading method described above. The loading apparatus comprises a flexible loading hose adapted to be introduced into the annular space of the tube, said loading hose having a first end which is connected to a catalyst box con- taining the solid particles to be charged into the annular space of the tube and a discharging end, said loading hose further having an internal coating so as to provide for inner friction of the solid catalyst particles as they fall within the hose.

The catalyst box is preferably a hopper having a conical end to which the first end of the loading hose is attached. It would also be understood that the discharging end of the hose is the open end of the loading hose from where cata- lyst particles travelling within the hose are discharged.

By the term flexible hose is meant that the hose is bend- able and therefore it can easily be adapted within the annular space of the catalyst tubes. The flexible loading hose enables the operator to lower the hose easily and rap- idly into the catalyst tube and at any position without bothering about the hose colliding with the outer wall of the catalyst tube.

The inner side of the loading hose which is in contact with the solid particles has to comply with the requirements of having a sufficiently high friction so as to decrease the speed of the particles in order to prevent particle breakage. At the same time, the friction has to be sufficiently low so as to avoid blockage of particles. The hose is therefore provided with an internal coating that provides for inner friction of the particles so these decelerate during their passage through the loading hose. Preferably, the hose is made of polyester with an internal coating of ethylenpropylenpolymer rubber. Particular benefits are ob- tained with this internal coating, since it enables the loading of the catalyst particles to occur gently. Normally the diameter of the hose is about 50 mm, depending naturally on the size of the annular space to be filled. Obviously, the diameter of the hose is such that it can be in- troduced easily in the annular space along the length of the catalyst tube.

The invention encompasses also a heat exchange reactor for carrying out non-adiabatic catalytic reactions comprising at least one catalyst tube filled with solid catalyst particles according to the method above. Preferably, the heat exchange reactor is a bayonet tube reactor comprising one

or more catalyst tubes used for the reforming of hydrocarbon feedstocks. A particularly preferred type of reactor is the so-called HTCR heat exchange reformer, as for instance disclosed in EP-O, 983, 963.

The invention is further illustrated by reference to the accompanying drawings in which Figure 1 shows a simplified longitudinal section of a bayonet tube catalyst tube and Figure 2 shows the trendlines of density of the catalyst particles as a function of the loaded height and initial drop height (IDH) in a bayonet tube.

In Figure 1 bayonet tube 1 consists of an outer tube 2 having an open inlet 3 for the passage of unconverted process gas and closed outlet 4. Within the outer tube 2 an inner tube 5 open at both ends is arranged substantially coaxi- ally with said outer tube 2. Converted process gas enters through perforated bottom of inner tube 5 and leaves at its top. The perforated bottom of inner tube 5 is fixed at the closed outlet 4 of the outer tube 2. The outer and inner tubes define an annular space 6 adapted to receive and accommodate the solid catalyst particles 7 so as to form a catalyst bed 8. The bayonet tube is provided with a sleeve 9 which defines a space 10 for the passage of a heat con- ducting medium, such as flue gas. A loading hose 11 is introduced into the annular space 6 in one side of the bayonet tube 1, said hose 11 has a discharge end 12 where solid catalyst particles eject onto catalyst surface 13. The distance from the bottom of the bayonet tube 1 to the catalyst surface 13 represents the loaded height, while the distance from the discharge end of the hose 12 (where the particles are discharged for the first time once the loading hose has

been positioned) to the catalyst surface represents the initial drop height (IDH) .

Figure 2 shows the trendlines of obtained densities of par- tides. The densities are higher at the bottom of the catalyst tube than in the top. This indicates that the particles, despite the inner coating of the loading hose, still accelerate significantly. At a given IDH the density of particles decreases with loaded height. However, by in- creasing the IDH it is possible to jump into another density vs. loaded height trendline that enables to maintain the density at a substantially equal value, for instance 0.81 kg/L (810 kg/m ³ ) or within a narrow range of densities along the whole range of loaded height values, for instance 800-820 kg/m ³ along the tube's 10 m. A maximum in density at a given loaded height is obtained with an IDH of 1.3 m; further increasing IDH to for instance 1.6 m may result in a decrease of density as illustrated by the density vs. loaded height trendline for IDH of 1.6 m of Figure 2.

Example :

Bayonet tubes having the following dimensions were tested:

Inner diameter of outer tube: 125 mm Outer diameter of inner tube: 50 mm Tube height: 6 m

The catalyst material is a steam reforming catalyst with particles of size 16 x 11 mm, but which are not impregnated with nickel, which is the active catalyst component in steam reforming. It is expected that nickel increases the strength of the particles. In order to feed material and

control the loading speed a catalyst box (loader) was used. A flexible hose was attached to the exit of the loader. Because the diameter of this standard hose was too big, a smaller hose was put inside. Since the diameter of this hose still was too big a slid was made to decrease the diameter. The loading hose was lowered into the catalyst tube.

Loading hoses of various lengths were made to vary the drop height. The loading hoses were made varying the length with 0.5 m. During loading it was thus aimed at loading particles corresponding to 0.5 m of tube at a time.

The loading density may vary as a function of the loading speed. If the loading speed is too high then the density will decrease. The loading speed was independent of the reformer tube diameter. The minimum loading speed for loading 0.5 m in a 120 mm tube is thus the same as when loading a 72 mm tube. In regular reformer tubes the minimum loading speed was found to be 20 seconds for loading of 0.8 meter of tube. Assuming the principle also was valid for bayonet tubes then the minimum loading time for loading 0.5 m was expected to be 12.5 seconds. However, the area in a bayonet tube is distributed differently than in a regular tube and the particles will typically drop in one side of the tube and then roll to the other side. Therefore, the minimum loading speed required in a bayonet tube may be higher than in a regular reformer. In the tests a loading rate of around 2 minutes (standard deviation of 0.5 minute) for a 6 m long bayonet tube was used. This loading speed was significantly above 12.5 seconds for loading 0.5 m as described above, and a variation of loading density as a

function of loading speed was unlikely. Consequently, the loading speed was not varied.

The loading of a 10 m bayonet tube according to the invention can be conducted as follows:

After loading the annular space of the tube with catalyst particles from the bottom to 0.5 m, the catalyst surface reaches a level of about 0.1 below the level of the discharging end of the loading hose. The loading hose is then raised 1 m to provide for a new IDH of 1.1 m. The catalyst tube is further filled with catalyst particles corresponding to 0.5 m so that the loaded height is now 1 m and reaches a level of 0.6 m below the discharging end of the hose i.e. distance between catalyst surface and discharging end of loading hose after each filling. The loading hose is raised 0.5 m to provide again for an IDH of 1.1 m. The procedure is repeated after reaching a loaded height of 4 m. It would be understood that in this stage (loaded height: 0.5 - 4 m) the IDH is constant at 1.1 m and the distance between the discharging end of the hose and the catalyst surface after each 0.5 m filling is kept at 0.6 m. After reaching a loaded height of 4 m the hose is raised 0.7 m to provide for a new IDH of 1.3 m (IDH _max ), which is kept for the rest of the loading. Again the catalyst tube is filled

with catalyst corresponding to 0.5 m loaded height, thus resulting in a distance between the discharging end of the hose and the catalyst surface after each 0.5 m filling of 0.8 m. The procedure is repeated until the catalyst mate- rial reaches a loaded height of 10 m. Hence, in this stage (loaded height: 4-10 m) the IDH is constant at 1.3 m and the distance between the discharging end of the hose and the catalyst surface after each 0.5 m filling is kept at 0.8 m.

The loading according to the inventive method provides a loading time of 1 hour per tube, which is a significant reduction in loading time compared with the use of the loading apparatus described in EP-A-I, 283, 070, where the time required for conducting the loading of one bayonet tube is 6-7 hours per tube. Reactors used for the reforming of hydrocarbons contain normally about 30 bayonet tubes.