AU471237B2

AU471237B2 - Process forthe separation of soot'particles froman aqueous slurry

Info

Publication number: AU471237B2
Application number: AU58138/73A
Authority: AU
Inventors: PETRUS MARIA VAN SWAAN and PIETER VISSER WILLIBRORDUS
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 1972-07-18
Filing date: 1973-07-16
Publication date: 1976-04-15
Also published as: FR2192877A1; IT998242B; FR2192877B1; ZA734800B; CA999986A; NL7209891A; GB1436464A; AU5813873A; IN139765B; BE802398A

Description

58.13 8 n3 The invention relates to a process for the sep.:ration of soot particles from an aqueous suspension of soot produced by water-washing soot- containing gases obtained in the partial combustion of hydrocarbons, by means of flotation with a gas. The gas is passed upwardly through the suspension in a finely divided fom in a flotation zone, the soot particles being entrained and removed from the top of the flotation zone by suitable means such as a stream of gas or a&worm screw. A common method of carrying out the .flotation consists of dissolving the flotation gas in the suspension, or in a stream of water which is then added to the suspension, under pressure. The mixture is then passed to a flotation zone where a lower pressure is maintained causing at least part of the gas to be released in a very finely divided form resulting in the upward entrainment of the soot particles. Many gases are suitable for this purpose as, for example, air, nitrogen, gaseous hydrocarbons and carbon dioxide.

A disadvantage of the above-mentioned process is that flotation is not always complete. The present invention provides an improvement in this respect.

The invention therefore relates to a process for the separation of soot particles from an aqueous suspension of soot, produced by water- washing soot-containing gases obtained in the partial combustion of hydrocarbons, by means of gas flotation, in which the Soot particles in the suspension are

58.1 3 8 n3 rendered water-repellent prior to flotation by the

addition ofa -light-liquid hydroarbonv or-Lqud-

mixture of hydrocarbona-

By means of this invention the separation process takes place more rapidly and completely. The flotation zone of a new flotation plant is smaller for the same capacity and, of course, the capacity of an existing zone is increased. The water leaving the flotation zone is clean and may be discharged or re-used.

quid hdroarbo (or the mixture f The light

.Ughtliquid hyfrocarbon^s preferentially wets the

surface of the soot particles, rendering the soot particles water-repellent. Once on the surface of the water, these particles can be ,removed more easily than

when noi i huiroeearbon is added. The removed

particles are also drier. The use of a1light-hyd4o-

4arbe* has a further advantage in that the addition can.

be made at ambient temperature since thethdroarben

is then sufficiently liquid. The wetting of the soot particles by the takes place quickly

owing to its low viscosity.

It is advantageous to add the naphtha in an.amount of between 0.01 parts and 3 parts by weight per part by weight of soot since greater amounts tend to impede the flotation due to theformaton of soot agglomerates. With regard to the amount of naphtha which is suitably

5813 8n3 A4a added the following considerations apply.14ght- l1qidO4on&rb~f 8-&dhe'rO-to the surface of the soot particles. If their surface area is large, i.e. if the particles are highly porous, the effect of the added Was a water repellant only becomes clearly apparent when the pores are largely filled with the /birroasrbons- Since the soot particles originating from a gas preparation process by incomplete combustion of a feedstock which contain hydrocarbons have a high porosity and therefore a high surface area it is therefore necessary to add a minimum amount of naphtha to the aqueous suspension of the soot particles in order to achieve the water repellent effect. Accordingly it has been found that the naphtha is preferably added in an amount between 0.3 parts and 3 parts by weight to 1 part by weight of soot particles. An elegant process is achieved if the flotation e gas for example air and the -light hydre

for-exmalemphtha are added to the suspension under low pressure, the mixture obtained subsequently being pressurized by a pump and passed to a flotation zone where the gas is at least partially released by reducing the pressure. The pressure is preferably between 10 and 50 kg/cm In order to give the gas 2

sufficient time to dissolve in the suspension, a buffer vessel, which is also under pressure, is suitably included between the pump and the flotation vessel. A suitable pump for this process is a kneader-type pump

58.13 8 73 such as a gear pump.

The soot particles separated in the flotation zone are conveniently collected and freed of the

y aroabon by application of heat, after which the

soot particles are available for further use, such

as the preparation of active charcoal. 4par-t f4v

naphtha, othor light hydroparbon such a benene.-

according to the present.invention

In a further embodiment of the invention the soot particles separated in the flotation zone are passed to a contact zone and brought into oontact with

warm oil, from which contact zone thelight-hyd--

-oarbon()- are withdrawn as. vapour and after condensation

re-used in the process, a suspension of soot particles

in oil being obtained. The transport of, the separated

soot particles from the flotation zone to the contact

zone is suitably effected by a stream of gas. This may

be the flotation gas, to which may be added if necessary

a gas jet directed to blow the soot particles away. A

warm screw.may also be used to transport the soot

particles. In addition to the -hydocarbon-vapours,

flotation gas and, possibly, transport as also are liberated from the contact zone. TheJhydroc&rbn- separated from the gas in a hydrocarbon condenser.

.In another embodiment of the invention the suspension of soot in oil obtained by the method

58.13 8 3 described above is at least partially used or,

feedstock for the partial combustion process from

which the soot-containing gases originate. The soot in oil is preferably completely recycled and a continuously operating soot separation process in a completely closed system is achieved. The auxiliary naphtha is recycled.

The invention will now be illustrated in more detail with reference to the Figures. Figure 1 is a diagrammatic representation of a soot separation process according to the present invention and Figure 2 is a diagrammatic representation of such a soot separation process integrated in a gas preparation process.

In Figure 1 a stream of an aqueous soot suspension is designated.by 1. This suspension is pumpable and cortains,.for example, 4% by weight'soot in water.;Under low pressure a stream 2 of qgh-.&qu

hVadroarbn fr -e rm ple naphtha, and a stream 3 of a gas, for example air, are added to this suspension. By.

means of a pump 4 this mixture is put under pressure,

which pressure is partly controlled by a valve

In a flotation vessel 6 the sspension, in which gas is now dissoved, and the soot particles 'which have absorbedi hydra n and thus become

water-repellent are subjected to low pressure. The emulsion now develops gas bubbles so that a layer 8

58.1 38 n3 of suspension with free gas bubbles, which rise and

entrain the soot particles, is produced. Beneath .the

layer 8 a layer 7 of clean water develops. This gives

rise to a layer 9 consisting of the soot particles separated from the water with a gas cap 10 above it. A stream of soot particles 11 is obtained, transported by the gas out of the vessel 6. A gas stream 12 blown in from the side may also be used to remove the soot particles. Water is discharged as a stream 13.

In Figure 2 the numerals 1 to 13 indicate the same process features as in Figure 1.

In this case a buffer vessel 14 is situated between the pump 4 and th valve 5 in which the mixture of emulsion, gas andjhydroarbons remains under pressure for a short period. This enables the taking-up of arbene by the soot particles and the dissolution of gas in the suspension to be achieved more completely.

The stream of soot particles passes to a contact column 15 through which a stream of warm oil 16 is circulating This causes the soot particles to be freed of the light hydr. arb- which leave the column

as a vapour stream 17. Gas originating from the

flotation process also accompanies the stream 17. In a

condenser 18 the/r liquefied and re-

introduced to the slurry as the stream 2. Gas is

removed via a line 19.

7 471.237

58.1 3 8 n3 From the column 15 a stream 20 consisting of a suspension of soot particles in oil is obtained.

A stream 21 of warm oil is added to the stream of the suspension of soot particles in oil which is recycled to the column 15. The stream 20 suitably serves as feedstock for a gasification process as described above, from which the aqueous soot suspension stream 1 is obtained.

58.1 3 8 n3 THE CIADIS DEFINING THE INVENTION ARE AS FOLLOWS

1. A process for the separation of soot particles by water- from an aqueous suspension of soot, produced the partial washing soot-containing gases obtained in flotation, combuation of hydrocarbons, by means of gas are in which the soot particles in the suspension by the rendered water-rpellent prior to flotation addition of-ight liquid hydrocarbon r liquid

mixture of hrdrociaf

A prc e au cc.imcd in claim q light liquid hydr"carbon i naphthat_

A process as claimed in claime, characterized 2L.

in that the naphtha is added in an amount of between by weight 0.01 parts and 3 parts by weight to 1 .part of soot. 3 2 the 3 4. A process as claimed in claimL3, in which and 3 naphtha is added in an amount between 0.3 parts particles. parts by weight to 1 part by Weight of soot

S A process as claimed in any one of claims 1- a are in which the flotation gas and oligh-hy droar.n(. the added to the suspension under low pressure, by a mixture obtained subsequently, being pressurized the gas is pump and passed to a flotation zohe where the pressure. at least partially released by reducing

6. A process as claimed in claim 9, in which the 2 pressure is between 10 and 50 kg/cm

Claims

58.13 8n3Y JJI- A process as claimed in any one of claims 1-16, in which the soot particles separated during flotation are passed to a contact zone and brougt acntc

with~oil from which contact zone the1gt -Yr-- earbon(9) i4 (re withdrawn as vapour and after condensation re-used in the process, a suspension of soot particles in oil thus being obtained. 6 74. A process as'claimed in claimj'F in w1*ch the suspension of soot particles in oil is at least partially used as feedstock for the partial combustion process from which the soot-containing gases originate.

A process as claimed in claim 1 substantially

as hereinbefore described and with particular reference to thie Figures.

Soot particles- whenever obtained with-the aid- of the process as claimd'inlarny one or more of alaii

DATED this TWENTY-NINTE day of MAY, 1973 SHELL INTERNATIONALE RESEARCH MAATSCBAPPLY B.V.

Patent Attorneys for the Applicant SPRUSON PEMUSOE

10.