CA1107943A

CA1107943A - Process for the preparation of dry soot

Info

Publication number: CA1107943A
Application number: CA270,555A
Authority: CA
Inventors: Berend P. Ter Meulen; Bernardus H. Mink
Original assignee: Shell Canada Ltd
Current assignee: Shell Canada Ltd
Priority date: 1976-03-08
Filing date: 1977-01-27
Publication date: 1981-09-01
Also published as: DE2709882C2; JPS52108394A; DE2709882A1; AU2297677A; NL182486C; AU513581B2; IT1076179B; ZA771359B; FR2343803B1; CS203998B2; IN143874B; FR2343803A1; BR7700747A; BE851943A; GB1564782A; NL182486B; NL7602388A

Abstract

ABSTRACT OF THE DISCLOSURE
The invention relates to a process for the preparation of dry soot from a suspension with a soot content of from 0.5 to 1.5%w of soot particles in water as obtained when washing gases originating from a process for the preparation of gas by partial combustion of a carbon-containing feed, the suspension being brought to turbulence in an agglomeration zone with addition of a liquid light hydrocarbon or mixture of hydro-carbons, characterized in that the mixture of liquid and agglom-erates leaving the agglomeration zone is passed through the drum of a rotary sieve, in which sieve drum the mixture is filtered, the agglomerates leaving the sieve drum having a water content of from 4-5%w and a light hydrocarbon(s) content of from 300-800%w, and the agglomerates are de-watered while being trans-ported to the outlet of the drum, after which the light hydro-carbon(s) is (are) recovered by evaporation and condensation.

Description

11~7~3 The invention relates to a process for the preparation of dry soot from a suspenslon of soot particles in water~ A
suspension of soot particles in water is obtained for example when washing gases ori~inat;ng from a process ~or the preparation of gas by partial combustion of a carbon-containing feed. A
carbon-containing feed may be a mineral oil or a fracti~on there-of, varying from methane to a heavy asphalt. It also includes coal or a suspension of coal fines in a liquid oil or oil fraction.
lQ The crude product gas contains very fine soot, the quantity of which is dependent on various- factors such as compo-sition of t~e feed, the fuel-oxygen ratio during t~e com~ustion, temperature, pressure. A frequently occurring soot content of the gas is 2-4%w. The soot can be removed from the gas by wash-~;~ ing with water, which yi~elds an aqueous suspension of soot part-icles The soot content of this suspension is 0.5~1.5%w. It is in general necessaxy to work up th~s suspensi~on to soot-free water. A convent~onal and effectlve method of do~ng this is to bring the suspension to turbulence in an agglomeration zone with addition of a liquid light hydrocar~on or mixture of hydrocarbons. The soot particles will then agglomerate to form lumps some mi~llimetres in dLameter which can be separated from the water. Conventional methods here are the use of a settling vesselr a vibrating screen or a sieve plate~
It has now-been found that when applied on a large scale it is precisely this separation of liquid and agglomerates that causes dif~iculties arising mainly from transport problems and the invention indicates ho~ this pro~lem can be solved.
According to the present inventi~on there is provided a process for the preparation of dry soot from a suspension with a soot content of from 0 5 to 1.5%w of soot particles in water as obtained when washing gases originating from a process for the preparation of gas ~y partial combustion of a carbon-containing feed, the suspension being hrought to turbulence in an agglomer-ation zone with addition of a liquid light hydrocarbon or mix-ture of hydrocarbons, characterized in that the mixture of liquid and agglomerates leaving the agglomeration zone is passed through the drum of a rotary sieve, in which sieve drum the mixture is filtered, the agglomerates leaving the sieve drum having a water content of from 4-5~w and a light hydrocarbon(s) a content of from 3ao-800%w-, and the agglomerates are de-watered ~hile being transported to the outlet of the drum, after which the light hydrocarbon(s~ ;~s (are) recovered by evaporation and condensation.
According to the invention the mixture of liquid and ; agglomerates leaving the agglomeration zone is passed through the drum of a rotary s~eve, in which sieve drum the mixture is fi~ltered and the agglomerates are de-watered while being trans-ported to the outlet of the drum, after which the light hydro-- carbon(s~ is ~are) recovered from the agglomerates by evaporation 2Q and condensation.
The mixture of l~quid - as a rule water - and agglomer-ates should be handled w~th particular care. Agglomerates of soot particles with ligHt hydrocarbons as the binder, for in-stance naphtha or gasoline, are not strong. If agglomerates should already disintegrate during the separation of agglomer-ates and liquid, no clean liquid - 2a -~B79~3 i~ obtained. Agglomeration with a light hydrocarbon or a mixture of light hydrocsrbons is attractive, because the relatively expensive binder can ea~ily be recovered and recirculated. The a~glomerates are passed through the drum by the rotation of the sieve. This can be done with a helical ribbon that is perpendicular to the sieve wall, A slight inclination of the drum, combined with the rotation, may likewise effect transportation of the agglomerates through the drum. It has been found that no trsnsport difficultics occur in the sieve drum, irrespective of the residence time of the agglomerates~ There is no attrition and no agglomeration.
It has further been found that the water content of the agglomerates leaving the sieve drum is very low, viz. 4-5 %w. Sur~risingly, this water content even proves to be the theoreticsl minimum. The a~glomerates in question have dimensions Or a few millimetresO
They come from an aqueous medium and because of their small d;mensions much water adheres to the surface snd i5 present in the voids between the agglomeratesO Filtration, also in this rotary sieve, occurs as a result of gravity. For, the rotational speed Or the sieve i~ very low~ 5-10 rev/min, With conventional separation methods much water still adheres to and is held between the agglomerates.
In the rotary sieve the agglomerates are constantly tumbling one over another. Every droplet of water gets a chsnce of contacting the sie~e surface and thus being removedO This means that all the adhering and enclosed water is removedO Only the water trapped within the agglomerste~ fails to be removed in the rotary sieve.
Another important advantage of the process according to the invention is thst it is technically no problem to enclose the rotary sieve drum ~ithin an impervious, stationary wall, permitting operat;on under pressure. This is important because sgglomeration is usually carried out under pressure. As a rule, the soot suspension introduced has a temperature upwards Or 10GCo There can then be sn open connection from the scrubbine tower ~or the crude product gas to the agglomeration zone and to the sieve drum, ~hich is a great advantage. For, it is technically a complicated matter to pass dispersions with larger particles through locks.
Finally, it has been found that the process according to the invention can be carried out in continuous operation on any scale.
Apart from the aforementioned small quantity of water, the soot agglomerates obtained in this way still contain the light hydrocarbon(s).
This quantity may be 300-~00 %w calculated on soot. It can be expelled by hc;ltillg alld be recoverecl by condellsation. This is preferably done by bringing the agglomerates leaving tlle sieve drum to a fluidized state with superlleated vapour o~ hydrocarbon~s) as used for the agglomeration as the fluidizillg gas, after which the vapour rising from the fluidized bed is con-densed. This process can be carried out in a vessel in which the same pres-sure prevails as in the sieve drum. The use of vapour of ligllt hydrocarbon-(s), for instance naphtha vapour, has the great advantage that the liquid or-ganic product obtained by condensation can be used again for the agglomeration and fluidization without any intermediate step. During the fluidization water that was trapped in the agglomerates will also be removed, which water will segregate from the hydrocarbon(s) after condensation. Obviously, also another gas such as nitrogen may be used as the fluidizing gas. The agglomerates re-main intact.
The agglomerates obtained in this way consist almost entirely of soot and can be used for many purposes. As an example its use as an absorbent may be mentioned here.
Theprocess according to the invention further creates the possibil-ity of introducing the agglomerates leaving the sieve drum by means of a pump into the feed for the process for the preparation of gas by partial combustion.
As a rule, this feed has a temperature upwards of 100C to have a viscosity low enough to permit pumping and atomization in the burner. When under these conditions water-containing soot is added, foaming will occur due to escaping water vapour. It has now been found that the soot as obtained from the sieve drum has already such a low water content that no foaming occurs. The binder ~ - light hydrocarbon(s) - can be removed from the fuel by flash evaporation and ; be recovered by condensation. A suitable pump for the introduction into the fuel is an extrusion pump. This pump can introduce the agglomerates straight-away into the hot and pressurized fuel, while at the same time the agglomer-ates are ground. If desired, the agglomerates leaving the sieve drum can first be incorporated into hydrocarbon(s) as used for the agglomeration, and .

~7~43 tl~cn be pullll)ed illtO tlle fuel. It w:ill then be possib:le to use, for instance, a sliding vanc pu~p. A disudvalltage is that more hydrocarbon(s) has(have) to be recovered.
As a rule, the agglomerates will be transported from the agglomer-ation zone to the sieve drum by a stream of water. However, it is also pos-sible to pass the mixture of water and agglomerates after leaving the agglomeration zone to a separator containing a bottom layer , - 4a -79~3 Or water and a top layer Or liquid light hydrocarbon(s) as used for the agglomeration, from which unit ~urplus water is discharged and the top lqyer with the agglomerates in it i~ pa~sed to the sieve drum. The aeglomerates ~re thus taken up in the light hydro-carbon(s) before they are filtered. The advantage is that practically no adhering water enters the sieve drum with the agglomerates, ~o that further de-watering is accelerated.
The invention will now be elucidated Wittl reference to some figures and examples.
Fig. 1 shows a scheme of the process for the preparation of dry soot according to the invention.
Fig. 2 shows a scheme of the integrntion of the process according to the invention for the preparation of dry soot with a gas preparation process 0 In Fie. 1 10 is the stream of aqueous soot suspension entering ~he agglomeration apparatus 11. This apparatus is provided with a stirrer 12 with motor 13. A stream of binder 14, for instance naphtha or gasoline, is also passed into apparatus 11~ The turbulence gives rise to the formation of soot agglomerates, which leave the apparatus together with water as stream 15 and are introduced into sieve drum 16. Drum 16 is slowly rotated by A motor 170 The cylindrical wall of the drum has holes of about 200 ~m. The drum is internally provided with a ver~ical helical ribbon. The rotation, e.g. 6-10 rev/min, and the pitch Or the ribbon cause the agglomerates to move towards outlet 18. Water is discharged at 19. A housing 20 encloses drum 16. A sprinkler 21 may be present to deal with possible blockage~ in the sieve wall of the drum, which may occur for instance a~ a result of a maloperation.
The agglomerates freed from adhering water go to a drier 22~ In this drier they are brought to a M uidized stQte by means of a hot gas issuine from nozzles 23. The binder, e.g. naphtha, evaporates in this process and is dischar6ed, together with the fluidizing gas~ at 24. The fluidizing gas is here superheated vspour o~ the hydrocarbons that have been used as the binder. Vapour 24 passes through a conden~er 250 Thus a liquid binder is formed, indicated earlier as stream 14, A side stream is evaporated in heat exchanger 26 and supplies the fluidizing gas. Possible binder losses are compensated for by stream 27. The dry agglomerates are discharged as stream 280 In Fig. 2 30 i9 a reactor for the incomplete combustion Or a carbon-containing feed 31 by reaction with oxygen or an o~ygerl~con-taining gas 32 with addition of steam 330 The gas is cooled in cooler 35. In scrubber 37 the gas is treated with WQter 38 BS a result of which gas 39, which contains no 900t anymore, und an aqueous soot suspension 40 are obtained. This soot suspension is brought to turbulence in an agglomeration spparatus 41 provided with stirrer and motor 42, together with a liquid light hydrocarbon 43, eOg. naphth~. The agglomerates formed go with water as stream 44 to the rotary sieve apparatus 45 designated by numerals 45, 46, 47, 48 and 49, which numerals have the same meaning as 16, 17, 18, 19 and 20, respectively, in Fig. 1.
The dried agglomerates are taken up here into feed stream 51 with an extrusion pump. The agglomerates still contain the binder, which is removed in flash evaporator 52. In condenser 53 the vapour is condensed and used again as binder 43, replenished, if required, with fresh material 54 to compensate for losses. the soot-enriched feed stream, which is freed from binder, goes as feed 31 to reactor 30.
Several variations on this scheme are possible. ~o foaming occurs in evaporator 52.
EXAMPLES
The suspension of soot particles in water contained 1.14 %w sootO This suspension originated from a process for the preparation of ~as by partial combustion Or a residual mineral oil. A stream of this suspension was pas~ed through an agglomeration apparatus at a rate of 1.12 m3/h. The stirrer rotated Qt a rate of 1000 rev/min.
A stream of naphtha of 58.8 kg/h was added aimultaneously. A quantity of 12.77 kg/h of dry soot was thus introduced and the naphtha/soot ratio was 406.
The stream leaving the agglomeration apparatus was passed to a rota~y ~ieve~ The drum was 30 cm in diameter and 150 cm long.
helical, vertical ribbon against the inner wall of the sieve wall (hole~ of 200 um) had a height of 2.5 cm and a pitch of 3 cm. The drum rotated at a rate of 6 rev/min.
The agglomerates leavine the drum were passed to a fluidized bed. The fluidizing gas was naphtha vapour having a temperature of 180C. This vapour was introduced at the rate of 340 kg/h. The superficial gas rate was 0.16 m/~.

_ 7 _ ~7943 From this drier emerged a stream Or dry soot of 12.04 ke~h in the form of agglomerates. A further quantity of O.29 kg/h dry soot WBS separated ~rom the stream of naphtha vapour by means of Q cyclone.
The experiment lasted 8 hours and no bre~kdowns or blockages were obser~ed. The agglomerates were externally completely dryo They contained about 3 %w water1 The following table gives conditions and results of a series of experiments with aeglomerates obtained as described hereinbefore without application of a fluidized bed. The a~glomeration and sieve conditions were vsried.
_______~_________________~_______________________________________________________ Supply rate of soot suspension, l/h 810 810 olO 810 8101200 olO 860 1200 Soot content in suspension, ~w 1.16 1.00 t.O2 o.98 o.87 o.89 0.94 0.85 o~88 Naphtha/soot ratio 4.1 5,1 5.2 5.0 5.6 6.o 9.7 4.7 4.B
Stirrer speed, rev/min 900 900 900 800 900 900 900 900 900 ____________________________________________ _______________________. ___________ Sieve drum speed, re~/~ni~ 6 6 6 6 10 10 10 10 10 Inclination of sieve drum, degrees 0 0 O O O O 0 10 10 ____________________________~_______________---___________________________________ Water content of ~gglomerates, %w 19.9 5.2 5.2 7.2 4,1 4.7 202 5.7 2.3 Water/soot ratio 1.27 0.34 0.34 o.46 0.28 0.34 0.24 0.36 0.13 At the optimum naphtha/soot wei~lt ratio for agglomeration of 5.6_6.o, the uater content of the agglomerates was 4-5 %w. At the very hig~l naphtha/soot ratia Or 9.7, the water conteat was lower. At a low naphtha/soot ratio smaller pellets are obtaiaed.
These pellets bind more water to their surfaces, becsuse Or the larger surface area per unit weight. It has beea found that by increasing the residence time in the rotary sieve, by giving it an upward inclination, better dry;ng is achieved again.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for the preparation of dry soot from a sus-pension with a soot content of from 0.5 to 1.5%w of soot part-icles in water as obtained when washing gases originating from a process for the preparation of gas by partial combustion of a carbon-containing feed, the suspension being brought to turbu-lence in an agglomeration zone with addition of a liquid light hydrocarbon or mixture of hydrocarbons, characterized in that the mixture of liquid and agglomerates leaving the agglomeration zone is passed through the drum of a rotary sieve, in which sieve drum the mixture is filtered, the agglomerates leaving the sieve drum having a water content of from 4-5%w and a light hydrocarbon(s) content of from 300-800%w, and the agglomerates are de-watered while being transported to the outlet of the drum, after which the light hydrocarbon(s) is (are) recovered by evaporation and condensation.

2. A process according to claim 1 characterized in that the agglomerates leaving the sieve drum are brought to a fluid-ized state with superheated vapour of hydrocarbon(s) used for the agglomeration as the fluidizing medium, after which the vapour leaving the fluidized bed is condensed.

3. A process according to claim 1 characterized in that the agglomerates leaving the sieve drum are introduced by means of a pump into the feed for a process for the preparation of gas by partial combustion of a carbon-containing feed.

4. A process according to claim 1 characterized in that the agglomerates issuing from the sieve drum are first taken up in hydrocarbon(s) as used for the agglomeration, and are then pumped into the feed for the process for the preparation of gas by partial combustion of a carbon-containing feed.

5. A process according to claim 1, 2 or 3 characterized in that the mixture of water and agglomerates, after leaving the agglomeration zone, is passed to a separator containing a bottom layer of water and a top layer of liquid light hydro-carbon(s) as used for the agglomeration, from which unit surplus water is discharged and the top layer with the agglomerates in it is passed to the sieve drum.

6. A process according to claim 4 characterized in that the mixture of water and agglomerates, after leaving the agglom-eration zone, is passed to a separator containing a bottom layer of water and a top layer of liquid light hydrocarbon(s) as used for the agglomeration, from which unit surplus water is discharged and the top layer with the agglomerates in it is passed to the sieve drum.