WO2004053025A1

WO2004053025A1 - Transport conduit for solid particles in a gaseous transport medium

Info

Publication number: WO2004053025A1
Application number: PCT/EP2003/050965
Authority: WO
Inventors: Ye-Mon Chen; Rene Samson
Original assignee: Shell Internationale Research Maatschappij B.V.
Priority date: 2002-12-10
Filing date: 2003-12-09
Publication date: 2004-06-24
Also published as: AU2003298348A1; TW200415099A

Abstract

Process and apparatus to pass a mixture of solids and gas downwards through a downwardly positioned conduit (2), which conduit is internally provided with an obstruction (4) defining an opening, which opening has a smaller cross-sectional area than the cross-sectional area of the conduit (3), and wherein downstream of said obstruction gas is vented (7, 9) from the conduit (3).

Description

TRANSPORT CONDUIT FOR SOLID PARTICLES IN A GASEOUS TRANSPORT MEDIUM

The invention is directed to a process to pass a mixture of solids and gas downwards through a downwardly positioned conduit, which conduit is internally provided with an obstruction having an opening, which opening has a smaller cross-sectional area than the cross-sectional area of the conduit. The invention is also directed to a transport conduit for upward transport of solid particles in a gaseous transport medium provided at its lower end with means to add the gaseous transport medium and means to add the solid particles, wherein the means to add solid particles comprises of a downwardly directed supply conduit fluidly connected to said riser at its lower end, said supply conduit further provided with an obstruction, namely a means to control the flow of solid particles, at a higher position in said supply conduit.

Such a conduit is described in EP-A-309244. This publication describes a supply conduit provided with a control valve as part of a fluid catalytic cracking (FCC) reactor. The FCC reactor consists of a reactor riser terminating in a catalyst stripper vessel. The stripper vessel in turn is fluidly connected to a catalyst regenerator vessel. The regenerator vessel is provided with a supply conduit to supply regenerated catalyst by means of gravity to the lower end of the reactor riser. In this supply conduit a control valve is present to regulate the admission of catalyst to the reactor riser. At the lower end of the reactor riser regenerated catalyst particles are contacted with an evaporating hydrocarbon feed. The reactor riser can be considered to be a transport conduit for solid particles, catalyst, in a gaseous mixture, the hydrocarbon mixture.

A disadvantage of the FCC reactor as described in EP- A-309244 is that a uniform distribution of catalyst particles in the reactor riser is not always achieved. Furthermore an uniform flow of catalyst over time is not always achieved.

The object of the present invention is to provide a process for the uniform flow of solids and gas in a conduit provided with an obstruction. This object is achieved with the following process.

Process to pass a mixture of solids and gas downwards through a downwardly positioned conduit, which conduit is internally provided with an obstruction defining an opening, which opening has a smaller cross-sectional area than the cross-sectional area of the conduit, and wherein downstream of said obstruction gas is vented from the conduit .

The invention is also directed to the following apparatus for performing the above process.

Transport conduit for upward transport of solid particles in a gaseous transport medium provided at its lower end with means to add the gaseous transport medium and means to add the solid particles, wherein the means to add solid particles comprises of a downwardly directed supply conduit fluidly connected to said riser at its lower end, said supply conduit further provided with means to control the flow of solid particles at a higher position in said supply conduit, wherein a de-aeration tube is present connecting (a) the interior of the supply conduit between the flow control means and its lower end and (b) the transport conduit at a position above the means to add the solid particles.

Applicants found that downstream of the obstruction gas can accumulate and, when it has grown to a certain volume, form a gas bubble in the stream of gas and solids. For example in the supply conduit of a FCC reactor just downstream of the means to control the flow of solid particles some segregation of solids and gas takes place, wherein gas accumulates at the upper end of the supply conduit and solids accumulate at the lower end of the supply conduit. This non-uniform flow of solids in the supply conduit will result in a less favorable distribution of solids in the lower end of the transport conduit. Furthermore the accumulated gas will, when it has grown to a certain size, escape from the supply conduit into the transport conduit and rise as a bell through said transport conduit. Such a gas bubble results in a non-uniform flow of catalyst in time.

Gas is preferably vented from the area where the gas accumulates. This area is the area of the conduit where the flow of the gas-solids mixture is less strong as compared to the velocity of said mixture just downstream of the opening which is defined by the obstruction. The area or space from where the gas is vented is just downstream the obstruction and preferably within 2 times and more preferably within 1 times the diameter of the conduit downstream of the obstruction. In case of a tilted conduit the gas will accumulate in the upper part of the conduit and it is therefore preferred to vent the gas from the upper half of the conduit downstream the obstruction.

Applicants further found that by applying the above process to a supply conduit of a FCC reactor a more uniform distribution is achieved in the transport conduit as described above.

The invention is in particular directed to gas-solids mixtures wherein the solids have an average particle size, as defined by the so-called Sauter Mean Diameter of between 50 and 100 micron. The particle density of the solid particles is preferably between 1000 and 2000 kg/m^. The solids may suitably be catalyst particles, for example FCC catalyst particles, or any other particle. The gas may in principle be any gas, for example steam in case the invention is applied in a FCC reactor.

The invention will be illustrated by making use of the following Figure 1 and 2. Figure 1 shows the lower part of a transport conduit. Figure 2 shows how the invention can be applied to the lower end of a FCC reactor riser.

Figure 1 shows a, preferably vertical, transport conduit 1 provided at its lower end 2 with means to add the gaseous transport medium. These means comprise of a gas ring 5 and an injector 6. Figure 1 also shows means to add the solid particles, namely supply conduit 3 which is fluidly connected to the lower end 2 of the transport conduit. Supply conduit 3 is downwardly directed such that solid particles will flow by means of gravity to the transport conduit 1. Supply conduit 3 is further provided with a slide valve 4 to control the flow of solid particles. Figure 1 shows a de-aeration tube 7 connecting (a) the interior of the supply conduit 3 between the flow control means 4 and its lower end and (b) the interior of the transport conduit 1 at a position 9. Position 9 is at least higher that the location wherein solid particles enter the transport conduit 1 from the supply conduit 3. The gas inlet of de-aeration tube 7 is preferably positioned at the upper end of supply conduit 3 or said otherwise above axis 10 of supply conduit 3. De-aeration tube 7 is preferably provided with means 8 to supply a purge gas to de-aeration tube 7 such to increase the flow of segregated gas from the supply conduit 3 into tube 7. The choice of purge gas is will depend on the specific process. In a FCC process it is suitably steam.

Figure 2 shows a detail of the gas inlet opening of de-aeration tube 7 provided with purge gas means 8. Tube 7 will preferably the fixed to the walls of supply conduit 3 and transport conduit 1. Tube 7 may be positioned internally both said conduits. Optionally tube 7 may partly be positioned externally said conduits.

Transport gas may be any gas, for example steam, nitrogen or light hydrocarbons. The choice of transport gas is dependent on the type of process and the location of the device according to the invention in said process. For example in a FCC process the device according to the invention may be applied in the reactor riser and in a vertical riser terminating in the catalyst regenerator. An example of a vertical riser ("spent cat riser") terminating in a FCC regenerator is described in Figure 2 of the above referred to EP-A-309244. If the invention is applied to the spent cat riser the transport gas or lift gas will be suitably steam. If the invention is applied to a FCC reactor riser the lift gas may be steam, a light hydrocarbon or the hydrocarbon feedstock of the FCC process itself.

Figure 3 shows how the invention can be applied in a FCC reactor riser. The reference numbers of Figure 3 and 1 have the same meaning of not said otherwise. Additionally Figure 3 shows a hydrocarbon feed nozzle 12 from which a mixture of hydrocarbon droplets and steam is supplied to the interior of the reactor riser 1. Feed nozzle 12 is provided with means to supply hydrocarbon feed 13 and steam 14 to said nozzle 12. Examples of such side entry feed nozzles and nozzle arrangements are described in O-A-9627647, EP-A-717095 and EP-A-593171. Position 9 at which the gas is being discharged from tube 7 is preferably positioned above such hydrocarbon feed injection means (12, 13, 14) . It has been found that the invention can also be beneficial when the hydrocarbon feed is injected at the bottom of the reactor. Use may be made of the well know so-called bottom entry feed nozzles as for example described in US-A-6387247. These feednozzles inject the hydrocarbon feed in a substantially vertical direction into the vertical FCC reactor riser.

The invention is thus also directed to a reactor riser conduit wherein in use upward transport of solid catalyst particles in a gaseous hydrocarbon transport medium takes place, wherein the riser is provided at its lower end with means to add a hydrocarbon feed in a substantially vertical direction and means to add the solid catalyst particles, wherein the means to add solid catalyst particles comprises of a downwardly directed supply conduit fluidly connected to said reactor riser conduit, said supply conduit further provided with means to control the flow of solid particles at a higher position in said conduit, wherein a de-aeration tube is present connecting (a) the interior of the supply conduit between the flow control means and its lower end and (b) the transport conduit at a position above the means to add the solid particles. The invention is also directed to a method of transporting a solids-gaseous mixture upwardly in a vertical transport conduit by supplying solids to the lower end of the transport conduit via a downwardly positioned supply conduit at which lower end the solids are directed upwards into the transport conduit by contacting the solids with an upwardly moving gas. In the method of the invention the admission of solids to the transport conduit is regulated by a control valve in the supply conduit and gas which accumulates downstream of the control valve is discharged from the supply conduit to avoid the formation of large bubbles in the supply conduit. If no segregated gas was discharged from the supply conduit large bubbles could form and from time to time enter the transport conduit resulting in a non- uniform flow of solids in said transport conduit. The method is preferably applied to a FCC process in for example the spent cat riser and more preferably to the reactor riser.

A typical FCC process consists of a regenerator, a riser reactor and a stripper, such as that shown in US-A-5562818 to Hedrick which is incorporated herein by reference. In said process finely divided regenerated catalyst is drawn from the regenerator through the regenerator standpipe (supply conduit) and contacts with a hydrocarbon feedstock in a lower portion of a reactor riser. Hydrocarbon feedstock and steam enter the riser through feed nozzles. The mixture of feed, steam and regenerated catalyst, which has a temperature of from about 200 °C to about 700 ^CC, passes up through the riser reactor, converting the feed into lighter products while a coke layer deposits on the surface of the catalyst. The hydrocarbon vapors and catalyst from the top of the riser are then passed through cyclones to separate spent catalyst from the hydrocarbon vapor product stream. The spent catalyst enters the stripper where steam is introduced to remove hydrocarbon products from the catalyst. The spent catalyst containing coke then passes through a stripper standpipe (optionally via a spent cat riser) to enter the regenerator where, in the presence of air and at a temperature of from about 620 ^CC to about 760 °C, combustion of the coke layer produces regenerated catalyst and flue gas. The flue gas is separated from entrained catalyst in the upper region of the regenerator by cyclones and the regenerated catalyst is returned to the regenerator fluidized bed. The regenerated catalyst is then drawn from the regenerator fluidized bed through the regenerator standpipe and, in repetition of the previously mentioned cycle, contacts the feedstock in the lower riser.

Claims

C L A I S

1. Process to pass a mixture of solids and gas downwards through a downwardly positioned conduit, which conduit is internally provided with an obstruction defining an opening, which opening has a smaller cross-sectional area than the cross-sectional area of the conduit, and wherein downstream of said obstruction gas is vented from the conduit.

2. Process according to claim 1, wherein the gas is vented within a distance of 2 times the diameter of the conduit downstream of the obstruction.

3. Process according to any one of claims 1-2, wherein the conduit is tilted and the gas is vented from the upper half of the conduit.

4. Process according to any one of claims 1-3, wherein the average particle size of the solids , as defined by the Sauter Mean Diameter, of between 50 and 100 micron and the particle density of the solid particles is between 1000 and 2000 kg/m³.

5. Process according to any one of claims 1-4, wherein the mixture of gas and solids is a mixture of a fluid catalytic cracking catalyst and gas.

6. Transport conduit for upward transport of solid particles in a gaseous transport medium provided at its lower end with means to add the gaseous transport medium and means to add the solid particles, wherein the means to add solid particles comprises of a downwardly directed supply conduit fluidly connected to said riser at its lower end, said supply conduit further provided with means to control the flow of solid particles at a higher position in said supply conduit, wherein a de-aeration tube is present connecting (a) the interior of the supply conduit between the flow control means and its lower end and (b) the transport conduit at a position above the means to add the solid particles.

7. Reactor riser conduit wherein in use upward transport of solid catalyst particles in a gaseous hydrocarbon transport medium takes place, wherein the riser is provided at its lower end with means to add a hydrocarbon feed in a substantially vertical direction and means to add the solid catalyst particles, wherein the means to add solid catalyst particles comprises of a downwardly directed supply conduit fluidly connected to said reactor riser conduit, said supply conduit further provided with means to control the flow of solid particles at a higher position in said conduit, wherein a de-aeration tube is present connecting (a) the interior of the supply conduit between the flow control means and its lower end and (b) the transport conduit at a position above the means to add the solid particles.