PROCESS AND APPARATUS FOR SEPARATING PARTICLES OF A CERTAIN ORDER OF MAGNITUDE FROM A SUSPENSION

Abstract

The disclosure includes a process and a plant for separating a suspension C from a suspension A, wherein the fraction of particles P.sub.C in the suspension C, which have a diameter smaller than a defined limit grain diameter, is greater than in the suspension A by at least the factor of 2. The suspension A is introduced into a container extending from the bottom to the top and a suspension B is withdrawn from the container, whose fraction of particles with a diameter greater than the defined limit grain diameter is increased with respect to suspension A. Due to the fact that suspension C is withdrawn from the container in a second partial stream above the first partial stream, in that the flow velocity of the suspension C is greater than the sinking velocity of the particles P.sub.C contained therein, an effective separation can be achieved.

Claims

1. A process for the separation of a suspension C from a suspension A, wherein the fraction of particles P.sub.C in the suspension C, which have a diameter smaller than a defined limit grain diameter, is greater than in the suspension A by at least the factor of 2, wherein the suspension A is introduced into a container extending from the bottom to the top and wherein a suspension B is withdrawn from the container, whose fraction of particles with a diameter greater than the defined limit grain diameter is increased with respect to suspension A, wherein the suspension C is withdrawn from the container in a second partial stream above the first partial stream due to the fact that the flow velocity of the suspension C is greater than the sinking velocity of the particles P.sub.C contained therein.

2. The process according to claim 1, wherein the process is carried out continuously and with stationary operating conditions.

3. The process according to claim 1, wherein the defined limit grain diameter has a value between 10 and 50 m.

4. The process according to claim 1, wherein the suspension A contains a gas.

5. The process according to claim 4, wherein the gas in the container is separated by outgassing and subsequently is withdrawn.

6. The process according to claim 1, wherein a pressure of more than 10 bar exists in the container.

7. The process according to claim 1, wherein suspension A flows into the container due to an applied or a hydrodynamic flow.

8. An apparatus for separating a suspension C from a suspension A, wherein the weight percentage of particles P.sub.C in the suspension, which are smaller than a defined limit grain diameter, is greater than in the suspension A by at least the factor of 2, comprising a container, at least one feed conduit for the suspension A into the container and at least one outlet for a suspension B, whose fraction of particles with a diameter greater than the defined limit grain diameter is increased with respect to suspension A, wherein a discharge conduit is provided for a suspension C, wherein by at least one device a flow is applied such that the flow velocity of the suspension C is greater than the sinking velocity of the particles P.sub.C contained therein, and wherein at least one discharge conduit for the suspension C is arranged above the outlet for the suspension B.

9. The apparatus according to claim 8, wherein the container with its entire height cylindrically extends from its bottom to the top.

10. The apparatus according to claim 8, wherein by at least one partition wall the container is divided into at least two chambers not completely separated from each other.

11. The apparatus according to claim 10, wherein the chambers are open in the lower region.

12. The apparatus according to claim 10, wherein the feed conduit opens into the first chamber in which gas escapes from the suspension by outgassing and can be withdrawn through a conduit and that at least one discharge conduit is provided for the suspension C in the region of at least one other chamber.

13. The apparatus according to claim 10, further comprising three chambers, wherein into one chamber of the three chambers the feed conduit for the suspension A opens and into the two other chambers of the three chambers discharge conduits for the suspension C are provided.

14. The apparatus according to claim 13, wherein the horizontal cross-sectional area of the second chamber relative to the horizontal cross-sectional area of the third chamber has a ratio of 2:3.

15. A use of the apparatus according to claim 8 for separating catalyst fine grain from a product stream of a Fischer-Tropsch synthesis.

16. A use of the apparatus according to claim 8 for separating deactivated catalyst from a product stream of a Fischer-Tropsch synthesis.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0054] In the drawing:

[0055] FIG. 1 shows a schematic representation of a plant according to the disclosure,

[0056] FIG. 2 shows a schematic representation of a Fischer-Tropsch process according to the prior art, and

[0057] FIG. 3 shows a schematic representation of a Fischer-Tropsch process according to the disclosure.

DETAILED DESCRIPTION

[0058] FIG. 1 schematically shows the apparatus according to the disclosure for separating fine particles from the entire stream.

[0059] The container 100 used here includes a feed conduit 110 via which a suspension A is introduced into the container. Through the partition walls 121 and 122, which do not extend down to the bottom, three chambers 101, 102 and 103 are obtained, wherein the feed conduit 110 opens into the chamber 101.

[0060] Process gas possibly contained in the suspension A here exits via the indicated surface of the suspension and can be discharged via conduit 111. The remaining suspension is backed up. Both downstream chambers 102 and 103 have two different sizes in which the ratio of the cross-sectional area of the chamber 102 relative to the cross-sectional area of the chamber 103 is 1:2.

[0061] Via the conduits 112 and 113, the suspension C which contains the particles P.sub.C, in which the weight percentage of particles which are smaller than a defined limit grain diameter is greater than in the suspension A by at least the factor of 2, can be withdrawn from the chambers 102 and 103. The flow rate of suspension C can be controlled via the control device 114 and the associated valve 114 or via the control device 116 and the associated valve 116. Via the withdrawal of the stream of suspension C a flow velocity in the chambers 102 and 103 can be applied. With increasing particle size the sinking velocity of particles increases. When the sinking velocity of the particle is greater than the flow velocity in the separation chambers 102 and 103, the particle is discharged via conduit 118 as suspension B which contains the particles P.sub.B by using the control device 119, in which suspension at least 80 wt-% of the particles have a diameter which is greater than a defined limit grain diameter. When the particle, however, is smaller and its sinking velocity therefore is smaller than the flow velocity obtained in the separation chambers 102 and 103 through the discharge conduits 112 and 113, the particle is discharged there via conduit 112 or 113.

[0062] With the selection of the used chambers for separation, namely only the smaller chamber, only the larger chamber or both chambers in parallel, the quantity of the discharged suspension can be varied without the flow velocity in the chamber and hence the size of the discharged particles being changed thereby. The constructional determination of the cross-sectional area for the chambers is effected corresponding to the targeted limit grain size, i.e. that particle size which is to be discharged. Further factors to be considered here are the density differences between the solids and the surrounding liquid.

[0063] According to the disclosure, the disclosed process proceeds with particular separation sharpness when a constant level of the liquid is ensured in the two chambers 102 and 103. This is the only way to ensure that the particles in the chambers 102 and 103 must pass a sufficiently quiet zone and thus sinking velocity and flow velocity actually compete with each other and there is no discharge of larger particles at individual points due to locally larger flow velocities.

[0064] According to the disclosure, the process can be operated both continuously and alternately. It can also be advantageous to multiply such plant, to use reactors operated in parallel for generating the suspension A, so that the apparatus according to the disclosure alternately is charged by several reactors. In principle, it also is conceivable that several streams jointly enter into the apparatus according to the disclosure.

[0065] It also can be expedient to control the pressure in the container by supplying nitrogen. This nitrogen, which for example can originate from a waste gas treatment, can then be discharged again via conduit 111.

[0066] FIG. 2 shows the integration of a plant known from the prior art in a Fischer-Tropsch synthesis.

[0067] From the two bubble column reactors 11 and 11 connected in parallel a continuous process stream is withdrawn and discharged via the conduits 2 and 2. The withdrawal of this stream can be metered via the control device 4 and 4, respectively. The conduits 2 and 2 then open into conduit 3, via which the collected stream is guided into a heat exchanger 5 and into a storage tank 14.

[0068] The heat exchanger medium is supplied and discharged again via the conduit 13, 13. In the storage tank 14, the pressure is controlled in a waste gas treatment by supplying nitrogen with elevated pressure and possibly by discharging nitrogen via conduit 6.

[0069] Via conduit 7, the suspension is supplied from the storage tank to a centrifuge 15 for separating the contained solids.

[0070] The light phase separated there is supplied to the treatment of the contained Fischer-Tropsch products by means of conduit 8. The light phase is supplied to a cooling device 16 via conduit 9. The suspension subsequently can be disposed of or be reprocessed in a non-illustrated way.

[0071] For a process management according to FIG. 2, Table 1 shows specific parameters of individual streams which are divided onto the two reactors 11 and 11 and each have a total mass flow of 3565 kg/h each. Particles with a grain size of 25 m are removed.

TABLE-US-00001 TABLE 1 Stream composition with a process design acc. to FIG. 2. 2, 2 3 7 9 8 Mass flow of all 1069.6 7130 7130 4750 2380 particles (kg/h) Temperature ( C.) 234 234 150 148 148 Pressure (bar(g)) 10 10 9.5 0.2 0.2 Mass flow of the 38.5 77 77 75.9 1.1 particles below the limit grain size (kg/h) Mass flow of the 1031 2062 2062 2061.9 0.1 particles above the limit grain size (kg/h)

[0072] FIG. 3 shows the integration of an apparatus according to the disclosure in a Fischer-Tropsch synthesis. The gaseous products obtained again are largely discharged from the bubble column reactors 11 and 11 via conduits 1 and 1.

[0073] Via conduits 110 and 110, a continuous product stream which contains liquid hydrocarbons, catalyst particles and in part also gaseous hydrocarbons is withdrawn and supplied to the container 100 and 100, respectively. This container 100, 100 is designed as shown in FIG. 1.

[0074] In the container 100 and 100 the gas contained in the inflowing product initially is separated and via conduits 111 and 111 combined with the waste gas from the bubble column reactor 11, 11 in conduit 1, 1 and discharged.

[0075] Via conduits 118 and 118, in which a non-illustrated control device 119, 119 is provided, the suspension B, which contains a particle fraction P.sub.B in which at least 80 wt-% of the particles have a diameter which is greater than a defined limit grain diameter, gets back into the bubble reactor 11, 11.

[0076] One or more partial streams with the suspension C, which contains a particle fraction P.sub.C in which the weight percentage of particles which are smaller than a defined limit grain diameter is greater than in the suspension A by at least the factor of 2, are discharged from the container 100, 100 in a controlled manner via conduit 112, 112 and/or 113, 113 and fed into the common conduit 3 via conduit 2, 2. The further configuration corresponds to the one explained in FIG. 2.

[0077] Table 2 describes the stream composition for the incorporation of the disclosure in a Fischer-Tropsch process as shown in FIG. 3. A total mass flow of wax and particles of 53526 kg/h each is charged to the two reactors 11 and 11, in order to remove particles with a grain size of 25 m and smaller from the system.

TABLE-US-00002 TABLE 2 Stream composition with a process design acc. to FIG. 3. 110, 110 113 2 3 7 9 8 Mass flow of all 16058 3509 5168 10336 10336 331 10005 particles (kg/h) Temperature ( C.) 234 234 234 234 150 148 148 Pressure (bar(g)) 32 10 10 10 9.5 0.2 0.2 Mass flow of the 578 26.1 38.5 77 77 72.3 4.7 particles below the limit grain size (kg/h) Mass flow of the 15480 26.1 38.5 77 77 72.3 4.7 particles above the limit grain size (kg/h)

LIST OF REFERENCE NUMERALS

[0078] 1-3 conduit [0079] 4, 4 control device [0080] 5 heat exchanger [0081] 6-9 conduit [0082] 11, 11 bubble column reactor [0083] 13 conduit [0084] 15 storage tank [0085] 15 centrifuge [0086] 16 cooling device [0087] 100, 100 container [0088] 101-103 chamber [0089] 104 lower region [0090] 110-113 conduit [0091] 114-114 control device [0092] 116-116 control device [0093] 117, 118 conduit [0094] 119 control device [0095] 121, 122 partition wall