GB2183169A - Process for replacing particulate solids from a reaction zone - Google Patents

Abstract

A process for replacing particulate solids (e.g. hydroconversion catalyst) from a reaction zone at an elevated temperature and pressure comprising the following steps: (a) removing solids from the reaction zone(s); (b) introducing into the reaction zone(s) an intermediate liquid (e.g. a hydrocarbons-containing hydroconversion product) which is substantially inert with respect to fresh solids at the prevailing temperature and pressure; (c) loading the reaction zone(s) at least partly with fresh particulate solids which are brought into contact with intermediate liquid, and (d) removing intermediate liquid from the solids-containing zone(s) by means of a gas (e.g. a hydroconversion product- or feed gas). n

Description

SPECIFICATION Process for replacing particulate solids from a reaction zone The invention relates to a process for replacing particulate solids from a reaction zone.

It is known to replace solids, such as catalyst particles which gradually become deactivated during operation of the processes in which they are employed, by stopping the (conversion) process which is carried out in a reaction zone and decreasing the temperature and pressure in said zone substantially (e.g.

by means of a liquid) before unloading deactivated solids and loading fresh solids.

The substantial temperature- and pressure variations which occur during such an (un)loading procedure will cause undesirable stresses and other material problems with respect to the reactor vessel(s), valves and the solid particles. Moreover, a substantial amount of time will be required to carry out such an (un)loading operation, during which time no products according to specification will be obtained from the reaction zone(s). Furthermore, the aforementioned liquid, in particular when feed to be catalytically treated is to be used, will in some cases react with the, initially hot, solids to be replaced which may cause undesirable heat generation and formation by-products.

When the reaction zone(s) have been loaded with fresh solids the cooling liquid is usually replaced by fresh feed (e.g. liquid and substantial amounts of gas) without further precautions, which may lead to an undesirably high pressure drop over the reaction zone(s).

It has now been found that the aforementioned disadvantages can be largely overcome by carrying out a four-step process in which particulate solids are replaced at an elevated temperature and pressure.

Accordingly, the present invention provides a process for replacing particulate solids from a reaction zone which comprises the following steps carried out at an elevated temperature and pressure: a) removing solids from the reaction zone(s); b) introducing into the reaction zone(s) an intermediate liquid which is substantially inert with respect to fresh solids at the prevailing temperature and pressure; c) loading the reaction zone(s) at least partly with fresh particulate solids which are brought into contact with intermediate liquid, and removing intermediate liquid from the solids-containing zone(s) by means of a gas.

Suitably, the process according to the present invention is carried out at a pressure substantially equal to the operating pressure for conversion processes carried out in the reaction zone(s); the pressure may vary within a wide range, however, depending on the type of process to be carried out in the reaction zone(s). For (hydro)conversion processes the pressures are suitably from 5-250 bar, and preferably from 25-200 bar, whereas the temperatures are suitably from 200-450 "C, and preferably from 250-435 "C.

In the event that the process according to the present invention is carried out at the temperatures at which the conversion processes are carried out, care should be taken that the temperature in the reaction zone(s) does not increase to unacceptable high values during periods when insufficient or no heat carrying medium (e.g. liquid or gaseous feed) flows through said zone(s) in which exothermic reactions may continue after the appropriate zone(s) has (have) been shut off from normal operation. Therefore, at least steps (a)-(c) of the present process are preferably carried out at temperatures from 30-200 "C, and preferably from 50-150 "C below the normal operating temperatures of conversion processes carried out in the reaction zone(s) whilst the pressure is substantially maintained.

The process according to the present invention is advantageously carried out in conjunction with conversion processes in which catalysts particles are employed which relatively quickly become deactivated, such as hydroconversion processes (including hydrocrackingand hydrodemetallization processes). In the latter processes heavy hydrocarbonaceous feeds (e.g. atmospheric- and/or vacuum residues of crude oils or shale oil) are catalytically upgraded in the presence of hydrogen, leaving carbonaceous and/or metal-containing deposits on the catalyst. particles. Such processes are suitably carried out in a hydroconversion unit normally comprising a series of reactors, each having one or more reaction zones.When the catalyst particles in one reactor become deactivated to an unacceptable degree and have to be replaced, this can be attained with the process according to the present invention without shutting down the whole hydroconversion unit.

Suitably, only the reactor in which solids are to be replaced is shut off from feed (e.g.

liquid hydrocarbons and a hydrogencontaining gas) and preferably filled at least partly with a cooling fluid before carrying out step (a) of the present process. Preferably, a liquid product obtained by carrying out such a conversion process is used as cooling fluid, and in particular liquid products are preferred which have been obtained after separating gaseous products in a separation zone at an elevated temperature and pressure from the total effluent withdrawn from the furthest downstream reactor of a hydroconversion unit.Preferably, the cooling fluid (which, of course, must have a lower temperature than temperature prevailing in the reaction zone(s) wherein the replacement is to be carried out) is circulated from the separation zone via the reaction zone(s) in which catalyst is to be replaced back to said separation zone until the desired temperature decrease in the appropriate reaction zone(s)- is attained.

In some cases particulate solids (e.g. catalyst particles) can be removed in step (a) of the present process while a liquid flow (circulating cooling fluid or even hydrocarbonaceous feed) is maintained in the reaction zone, depending on the type of solids and solid/liquid separation means present in the reaction zone(s). However, it is preferred to carry out step (a) of the process according to the invention substantially in the absence of liquid flow in the reaction zorte(s) in question, in particular when solids/fluid separation openings are present in the bottom section of the reaction zone(s).Therefore, the circulation of cooling fluid is suitably stopped after attaining the desired temperature in the reaction zone(s) and remaining cooling fluid is at least partly (and preferably substantially completely) removed from said zone(s) by introducing a relatively small stream of purge gas therein before carrying out step (a) of the present process.

The main advantages of the use of a liquid product as cooling liquid in the process according to the invention are: (i) the high (conversion) pressure separation vessel in which gaseous- and liquid (hydro)conversion products are separated at a temperature of e.g. 50-150 "C below the conversion temperature is employed as buffer vessel, thereby eliminating the need for an additional vessel, and (ii) recycling of purge gas is substantially reduced in comparison with processes in which purge gas instead of cooling liquid is employed to reduce the temperature in the reaction zone(s).

Preferably, a feed gas (e.g. a hydrogen-containing gas) or a product gas (comprising e.g.

hydrogen and hydrocarbons containing molecules having 1-4 C-atoms) of the hydroconversion process is used as purge gas, thus avoiding introduction of non-process related compounds and additional separation steps; the resulting mixture of liquid and gaseous hydroconversion products (and in some cases additional hydrogen) can be led directly to the separation zone mentioned hereinbefore.

The main advantage of carrying out step (a) of the process according to the invention in the presence of a small, preferably downwardly directed stream of purge gas, without substantial amounts of liquid being present in the reaction zone(s) from which solids are removed, is that the forces applied on the solid particles are similar to those applied during an unloading operation carried out at atmospheric pressure; consequently less fines (i.e. particles of a substantially smaller size than fresh particulate solids) are produced, and less "pinning" of solids in the aforementioned solid/fluid separation openings will occur, compared with unloading under liquid flow conditions.

The intermediate liquid which is introduced in step (b) of the process according to the present invention in the reaction zone(s) is preferably a similar liquid as the cooling liquid mentioned hereinbefore. Liquid hydroconversion product is the preferred intermediate liquid because it is usually substantially inert with respect to at least partially deactivated catalyst particles at temperatures of e.g. 50150 "C below the hydroconversion temperatures. Preferably, step (b) is carried out by filling the reaction zone(s) (from which solids have been removed) substantially completely (up to the solids inlet means which are preferably located in the top of the reactor) with intermediate liquid and subsequently stopping the liquid flow.

Loading of the reaction zone(s) with solids is carried out according to the present invention while the solids are brought in contact with intermediate liquid, i.e. solids are introduced into a reaction zone which is at least partly, and preferably substantially completely, filled with intermediate liquid, thus wetting the solids completely and avoiding free fall of the solids which could lead to breakage of solids (in particular for reactors having a substantial height and for solids with a relatively low strength such as extrudates of e.g. alumina).

Moreover, by dropping solids in intermediate liquid a better oriented packing is attained, compared with "dry" loading, thus attaining a relatively high solids filling density (kg solids/m3 reaction zone). Furthermore, the present loading method is particularly suitable for reactors comprising more than one reaction zone defined by internal supporting means provided with various openings for liquid, gas and solids.

Solid particles are suitably introduced in (and removed from) the reaction zone(s) as a slurry with a liquid, e.g. liquid feed and/or product of the conversion process. Preferably, liquid hydrocarbons substantially boiling above the temperature prevailing in the reaction zone(s) are used in said slurry, in particular (heavy) gas oil.

Step (c) of the process according to the present invention is preferably carried out by withdrawing intermediate liquid at substantially the same rate (expressed in m3/h) from the reaction zone(s) as fresh solids are introduced therein, in order to maintain the level of the intermediate liquid near the solids (slurry) inlet means.

When the desired amount of solids has been introduced into the reaction zone(s), the intermediate liquid is removed in step (d) of the present process by means of a gas, preferably again a feed- or product gas of the conversion process (in particular a hydrogencontaining gas). The intermediate liquid thus removed from the reaction zone(s) loaded with fresh solids is suitably directed to the aforementioned separation zone. In this manner mixing of liquid (hydro)conversion feed with intermediate liquid is avoided. Moreover, when the reaction zone(s) are subsequently taken back into normal operation, liquid and gaseous feed streams are introduced into reaction zone(s) which are not substantially filled with liquid, thus avoiding start-up problems which would otherwise occur due to an excessive pressure drop over a liquid-full reactor.

The process according to the present invention is suitable for replacing particulate solids having various shapes (e.g. pellets, spheres, cylinders, trilobes or quadrulobes) and compositions. The advantages of the present process are most apparent when relatively fragile particles such as extrudates or trilobes, in particular alumina-containing extrudates are to be replaced.

The process according to the present invention will be further elucidated by means of the following Example.

EXAMPLE A feed stream containing heavy hydrocarbons, lighter hydrocarbons and hydrogen enters reactor (1) of the flow scheme as depicted in the Figure (in which no ancillary equipment such as pumps and valves is shown) at a temperature of 420 "C and a pressure of 150 bar abs. through line (2) and is subjected to hydroconversion therein in the presence of alumina-containing extruded catalyst particles. Hydrogen-rich gas is introduced into the reactor through line (3) for temperature regulation purposes. (Partially) hydrncon- verted product is transferred through line (4) to reactor (2) wherein the product is further processed. Hydrogen-rich gas is introduced through line (5) under similar conditions as in reactor (1).Hydroconverted product is transferred through line (6) to separator (7) operating at a temperature of 350 "C and a pressure of 150 bar abs. Relatively low-boiling products are removed from separator (7) through line (8), whereas relatively high-boiling products are removed through line (9).

When the catalyst in reactor (1) becomes substantially deactivated, reactor (1) is taken out of normal operation by closing lines (2) and (4) and introducing the heavy hydrocarbon-containing feed stream through line (10) directly into reactor (2). Subsequently cooled hydroconversion product is led via line (9) to reactor (1) and recirculated to separator (7) via lines (4) and (11) until the temperature inside reactor (1) is at a substantially uniform level of 350 "C; the pressure in reactor (1) is meanwhile maintained at 150 bar abs. The hydroconversion product circulation is then stopped and said product is removed from reactor (1) by using hydrogen-containing gas introduced through line (3).

Next, the catalyst particles are removed (step (a)) from reactor (1) through line (12) by means of a rotary star valve or by other means (not indicated in the Figure). In the following step (b) reactor (1) is again filled through line (9) with liquid hydroconversion product up to the catalyst inlet means (not shown) in the top of reactor (1).

Subsequently, fresh catalyst particles are introduced (step (c)) through line (13) as a slurry with gas oil into liquid-filled reactor (1), while liquid is removed through line (4) to maintain its level (similarly, catalyst can be introduced through line (14) into reactor (2) during its turn of solids replacement). After the desired amount of catalyst has been loaded, the liquid hydroconversion product is substantially removed (step (d)) by again introducing hydrogen-containing gas through line (3) into reactor (1). When the liquid has been removed, reactor (1) is taken back into normal operation by introducing heavy hydrocarbon feed through line (2) and closing line (10); the temperature in reactor (1) is gradually increased to the normal operating temperature of 420 "C, whereas the pressure remains 150 bar abs.

Claims (14)

1. A process for replacing particulate solids from a reaction zone which comprises the following steps carried out at an elevated temperature and pressure: a) removing solids from the reaction zone(s); b) introducing into the reaction zone(s) an intermediate liquid which is substantially inert with respect to fresh solids at the prevailing temperature and pressure; c) loading the reaction zone(s) at least partly with fresh particulate solids which are brought into contact with intermediate liquid, and d) removing intermediate liquid from the solids-containing zone(s) by means of a gas.

2. A process according to claim 1 which is carried out at a pressure substantially equal to the operating pressure for conversion processes carried out in the reaction zone(s).

3. A process according to claim 1 or 2 which is carried out at temperatures from 200-450 "C, preferably from 250-435 "C, and pressures from 5-250 bar, preferably from 25200 bar.

4. A process according to any of the preceding claims wherein at least steps (a)-(c) are carried out at temperatures from 30-200 "C, and preferably from 50-150 "C below operating temperatures for conversion processes carried out in the reaction zone(s).

5. A process according to any of the preceding claims wherein the reaction zone(s) in which solids are to be replaced are shut off from feed for a conversion process and filled at least partly with a cooling fluid before carrying out step (a).

6. A process according to claim 5 wherein cooling fluid is at least partly removed by introducing a purge gas in said reaction zone(s) before carrying out step (a).

7. A process according to any of the preceding claims wherein step (a) is carried out substantially in the absence of liquid flow in the reaction zone(s).

8. A process according to any of the preceding claims wherein step (b) is carried out by filling the reaction zone(s) substantially completely with intermediate liquid and subsequently stopping the liquid flow.

9. A process according to any of the preceding claims wherein step (c) is carried out by withdrawing intermediate liquid at substantially the same rate (expressed in m3/h) from the reaction zone(s) as fresh solids are introduced therein

10. A process according to any of the preceding claims wherein the intermediate liquid and/or the cooling liquid comprises a liquid product obtained by carrying out a conversion process in the reaction zone(s).

11. A process according to any of the preceding claims wherein the gas applied in step (d) comprises feed- and/or product-gas of the conversion process carried out in the reaction zone(s).

12. A process according to any of the preceding claims wherein the particulate solids comprise particles having catalytic activity for hydroconversion of hydrocarbon-containing feeds in the presence of hydrogen.

13. A process according to claim 12 wherein the particulate solids comprise alumina-containing extrudates.

14. A process substantially as described hereinbefore with reference to the Example.