GB1564782A

GB1564782A - Process for the preparation of de-watered carbonaceous particles

Info

Publication number: GB1564782A
Application number: GB9467/77A
Authority: GB
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 1976-03-08
Filing date: 1977-03-07
Publication date: 1980-04-16
Also published as: FR2343803A1; FR2343803B1; NL7602388A; JPS52108394A; ZA771359B; IN143874B; DE2709882C2; IT1076179B; BR7700747A; NL182486B; AU2297677A; NL182486C; DE2709882A1; AU513581B2; CS203998B2; CA1107943A; BE851943A

Description

(54) PROCESS FOR THE PREPARATION OF DE-WATERED CARBONACEOUS PARTICLES (71) We, SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V., a company organised under the laws of the Netherlands, of 30 Carel van Bylandtlaan, the Hague, The Netherlands, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The invention relates to a process for the preparation of de-watered carbonaceous particles from a suspension of carbonaceous material in water. Examples of carbonaceous material are soot and mined coal. The suspension of soot in water is obtained for example when washing gases originating from a process for the preparation of gas by partial combustion of a carbon-containing feed. A suspension of mined coal may be prepared from coal fines for transport by pipeline or for working-up processes. For mined coal deashing is often as important as de-watering.

A carbon-containing feed for a partial combustion process indicated above may be a mineral oi or a fraction thereof, varying from methane to a heavy asphalt. It also includes coal or a suspension of coal fines in a liquid oil or oil fraction.

The crude product gas contains very fine soot, the quantity of which is dependent on various factors such as composition of the feed, the fuel-oxygen ratio during the combustion, temperature, pressure. A frequently occurring soot content of the gas is 2A %w. The soot can be removed from the gas by washing with water, which yields an aqueous suspension of soot particles. The soot content of this suspension is 0.5-1.5 %w. It is in general necessary to work up this suspension to soot-free water. A conventional and effective method of doing this is to bring the suspension to turbulence in an agglomeration zone, with addition of a liquid light hydrocarbon or mixture of hydrocarbons. The soot particles will then agglomerate to form lumps some millimetres in diameter which can be separated from the water. In the case of ashcontaining material deashing and dewatering are carried out simultaneously with this process, the ash being removed with the water in non-agglomerated form.

Conventional methods for the separation of lumps and water-possibly with ash - are the use of a settling vessel, 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 difficulties arising mainly from transport problems and the invention indicates now this problem can be solved.

According to the invention 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 and the agglomerates are de-watered while being transported to the outlet of the drum, after which the light hydrocarbon(s) is(are) recovered from the agglomerates by evaporation and condensation.

The mixture of liquid - as a rule water or ash-containing water - and agglomerates should be handled with particular care..

Agglomerates of soot or coal particles with light hydrocarbons as the binder, for instance naphtha or gasoline, are not strong. If agglomerates should disintegrate during the separation of agglomerates and liquid, no clean liquid is obtained. Agglomeration with a light hydrocarbon or a mixture of light hydrocarbons is attractive, because the relatively expensive binder can easily be recovered and recirculated. The agglomerates 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 transport difficulties occur in the sieve drum, irrespective of the residence time of the agglomerates. There is hardly any attrition or agglomeration.

It has further been found that the water content of the agglomerates leaving the sieve drum is very low, viz. 4-5 "bw for agglomerates of soot, for agglomerates of coal much lower. Surprisingly, this water content even proves to be the theoretical minimum. The agglomerates in question have dimensions of a few millimetres. They come from an aqueous medium and because of their small diniensions much water adheres to the surface and is present in the voids between the agglomerates. Filtration, also in this rotary sieve, occurs as a result of gravity. For, the rotational speed of the sieve is very low, 5-25 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 chance of contacting the sieve surface and thus being removed. This means that all the adhering and enclosed water is removed.

Only the water trapped within the agglomerates fails to be removed in the rotary sieve.

Another important advantage of the process according to the invention is that it is technically no problem to enclose the rotary sieve drum within an impervious, stationary wall, permitting operation under pressure. This is important because agglomeration is usually carried out under pressure. As a rule, the soot suspension introduced has a temperature upwards of 100"C. There can then be an open connection from the scrubbing tower for the crude product gas to the agglomeration zone and to the sieve drum, which 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 aformentioned small quantity of water, the soot or coal agglomerates obtained in this way still contain the light hydrocarbon(s). This quantity may be 300800 O,w calculated on soot. It can be expelled by heating and be recovered by condensation. This is preferably done by bringing the agglomerates leaving the sieve drum to a fluidized state with superheated vapour of hydrocarbon(s) as used for the agglomeration as the fluidizing gas, after which the vapour rising from the fluidized bed is condensed. This process can be carried out in a vessel in which the same pressure prevails as in the sieve drum. The use of vapour of light hydrocarbon(s). for instance naphtha vapour, has the great advantage that the liquid organic 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 remain intact.

The soot agglomerates obtained in this way consist almost entirely of soot and can be used for many purposes. As an example its use as an adsorbent may be mentioned here.

The process according to the invention further creates the possibility of introducing the agglomerates leaving the sieve drum by means of a pump into the feed for a process for the preparation of gas by partial combustion of a carbon-containing feed. As a rule, this feed has a temperature upwards of 100"C to have a viscosity low enough to permit pumping and atomization in the burner. When under these conditions watercontaining 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 straightaway into the hot and pressurized fuel, while at the same time the agglomerates are ground. If desired, the agglomerates leaving the sieve drum can first be incorporated into hydrocarbon(s) as used for the agglomeration, and then be pumped into the fuel. It will then be possible to use, for instance, a sliding vane pump. A disadvantage is that more hydrocarbon(s) has(have) to be recovered.

As a rule, the agglomerates will be transported from the agglomeration zone to the sieve drum by a stream of water.

However, it is also possible to pass the mixture of water and agglomerates after leaving the agglomeration zone 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. The agglomerates are thus taken up in the light hydrocarbon(s) before they are filtered. The advantage is that practically no adhering water enters the sieve drum with agglomerates, so that further de-watering is accelerated.

The invention will now be elucidated with reference to some figures and examples.

Fig. 1 shows a scheme of the process for the preparation of dry soot or coal according to the invention.

Fig. 2 shows a scheme of the integration of the process according to the invention for the preparation of dry soot with a gas preparation process.

In Fig. 1 10 is the stream of the aqueous suspension entering the 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 or coal 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 17.

The cylindrical wall of the drum has holes of of about 200 m. The drum is internally provided with a vertical helical ribbon. The rotation, e.g. 6-10 rev/min, and the pitch of 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 blockages in the sieve wall of the drum, which may occur for instance as a result of a maloperation.

The agglomerates freed from adhering water go to a drier 22. In this drier they are brought to a fluidized state by means of a hot gas issuing from nozzles 23. The binder, e.g. naphtha, evaporates in this process and is discharged, together with the fluidizing gas, at 24. The fluidizing gas is here superheated vapour of the hydrocarbons that have been used as the binder. Vapour 24 passes through a condenser 5. 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 28.

In Fig. 2 30 is a reactor for the incomplete combustion of a carbon-containing feed 31 by reaction with oxygen or an oxygencontaining gas 32 with addition of steam 33.

The gas is cooled in cooler 35. In scrubber 37 the gas is treated with water 38 as a result of which gas 39, which contains no soot anymore, and an aqueous soot suspension 40 are obtained. This soot suspension is brought to turbulence in an agglomeration apparatus 41 provided with stirrer and motor 42, together with a liquid light hydrocarbon 43, e.g. naphtha. 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 sootenriched feed stream, which is freed from binder, goes as feed 31 to reactor 30.

Several variations on this scheme are possible. No foaming occurs in evaporator 52.

Example I.

A suspension of soot particles in water contained 1.14 %w soot. This suspension originated from a process for the preparation of gas by partial combustion of a residual mineral oil. A stream of this suspension was passed through an agglomeration apparatus at a rate of 1.12 m3/h. The stirrer rotated at a rate of 1000 rev/min. A stream or naphtha of 58.8 kglli was added simultaneously. A quantity of 12.77 kgIli of dry soot was thus introduced and the naphtha/soot ratio was 4.6 The stream leaving the agglomeration apparatus was passed to a rotary sieve. The drum was 30 cm in diameter and 150 cm long. A helical, vertical ribbon against the inner wall of the sieve wall (holes 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 leaving the drum were passed to a fluidizing bed. The fluidizing gas was naphtha vapour having a temperature of 180"C. This vapour was introduced at the rate of 340 kg/h. The superficial gas rate was 0.16 m/s.

From this drier emerged a stream of dry. soot of 12.04 kg/h in the form of agglomerates. A further quantity of 0.29 kg/h dry soot was separated from the stream. of naphtha vapour by means of a cyclone.

The experiment lasted 8 hours and no breakdowns or blockages were observed.

The agglomerates were externally completely dry. They contained about 3 %2 water.

The following table gives conditions and results of a series of experiments with agglomerates obtained as described hereinbefore without application of a fluidized bed. The agglomeration and sieve conditions were varied.

Supply rate of soot suspension, l/h 810 810 810 810 810 1200 810 860 1200 Soot content in suspension, % w 1.16 1.00 1.02 0.98 0.87 0.89 0.94 0.85 0.88 Naphtha/soot ratio 4.1 5.1 5.2 5.0 5.6 6.0 9.7 4.7 4.8 Stirrer speed, rev/min 900 900 900 800 900 900 900 900 900 Sieve drum speed, rev/min 6 6 6 6 10 10 10 10 10 Inclination of sieve drum, degrees 0 0 0 0 0 0 0 10 10 Water content of agglomerates, % w 19.9 5.2 5.2 7.2 4.1 4.7 2.2 5.7 2.3 Water/ soot ratio 1.27 0.34 0.34 0.46 0.28 0.34 0.24 0.36 0.13 At the optimum naphtha/soot weight ratio for agglomeration of 5.6-6.0, the water content of the agglomerates was 4-5 %w.

At the very high naphtha/soot ratio of 9.7, the water content was lower. At a low naphtha/soot ratio smaller pellets are obtained. These pellets bind more water to their surfaces, because of the larger surface area per unit weight. It has been found that by increasing the residence time in the rotary sieve, by giving it an upward inclination, better drying is achieved again.

Example II.

A suspension of mined coal fines in water contained 13 %w coal. The ash content of the coal was 25-30 %w. A stream of this suspension was passed through an agglomeration apparatus at a rate of 20 l/h.

The stirrer rotated at a rate of 1400 rev/min.

A stream of naphtha of 0.41 kg/h was added simultaneously.

The stream leaving the agglomeration apparatus was passed to a rotary sieve of the same type as in Example I.

The agglomerates leaving the drum were passed to a fluidized bed. The fluidizing gas was N2 having a temperature of 150-160 C, introduced with a superficial rate of 0.20 m/s.

From this drier emerged a stream of aglomerates with an ash content of 5 %w and a water content of 0 %w. The coal recovery was 85-90 %w, the ramaining coal left the agglomerator with the water as tailings containing 70-80 %w wash.

The N2 in the fluidized bed may be replaced by naphtha vapour.

Claims

WHAT WE CLAIM IS:1. A process for the preparation of dewatered carbonaceous particles from a suspension of carbonaceous fines in water, the suspension being brought to turbulence 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 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 fluidized state with superheated vapour of hydrocarbon(s) as 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 3, 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 carboncontaining feed, after which the hydrocarbon(s) is(are) recovered by evaporation and condensation.
5. A process according to any one of claims 1, 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 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.
6. A process according to claim 1 as described hereinbefore with reference to the examples.
7. Soot agglomerates prepared according to claim 1, 2 5 or 6.