GB2127800A - Process for pearling sulfur - Google Patents

Abstract

Liquid lambda-sulfur is added to water in constant movement to produce pearls of sulphur. On entering the water the sulfur separates into particles which assume a spherical form and solidify producing pearls. The granulation of these pearls can be controlled during the pearling process. Cylindrical vessels or channels with rectangular section are preferred for said process.

Description

SPECIFICATION Process for pearling sulfur The present invention relates to a process for pearling sulfur and, as shown hereinafter, features simplicity, small investment costs and production of substantially perfectly spherical and homogeneous sulfur pearls affording also the possibility of granulometric control of the product.

The handling of sulfur has always implied serious problems related to safety, pollution and contamination of adjacent areas.

The problems of handling sulfur commence at the site where sulfur is mined. In mines using the FRASCH process liquid sulfur is pumped through pipes to solidify into enormous blocks of product.

When commercialized, the sulfur must be broken away from these enormous blocks with heavy machinery and prepared by grinding in order to exhibit better homogeneity and be more acceptable to clients.

In practice the grinding of sulfur has always presented a big problem.

Because of the numerous safety problems involved and a strong propensity for incipient fusion grinding operations are an almost exclusive attribution of the big producers.

The difficulties inherent to the grinding of sulfur have induced producers to do research with the object of developing safer and more efficient equipments.

The Freeport Sulfur Company in the U.S.A. developed a mill according to the U.S. Patent 2656123.

In reality, sulfur producers generally do not guarantee the granulometry of the product and having accompanied said problem for many years we are in a position to say that commercial sulfur displays a great variety of granulometry.

The grinding of sulfur as well as the heterogeneity of the product imply a series of disadvantages: - The dust generated during the grinding process and transportation.

Like all poor conductors of electricity sulfur rapidly accumulates static electricity.

For these reasons the system must be provided with the necessary protection, e.g. by adopting a confined system.

- Ground sulfur is generally corrosive, particularly when it is not very dry, which implies using compatible construction material.

- The system calls for additional safety measures such as constant flow of steam at sites of greater incidence of dust in order to prevent explosions.

- All metallic equipment must be buried to prevent accumulation of static electricity.

- Maintenance operations involving welding or use of manual tools can only be carried out after all the sulfur has been removed from the area.

- Use of tractors and loading shovels for the sole purpose of this operation and consequently additional consumption of fuel.

- Heterogeneous granulometry.

The product displays a granulometry varying from fine powder to lumps of 1 5 (fifteen) cms, aggravated by the fact that a reduction of the granulometry implies a substantial increase of fines.

- The grinding operation calls for great care and attention on the part of the operator.

-And lastly, the make-up of the products makes marketing more difficult.

The producers of sulfur recovered from petrochemical sources are using various methods to get rid of the problem caused by the big blocks of sulfur.

Sulfur scalers of different types and capacities perform satisfactorily but require substantial investments as well as permanent maintenance.

Sulfur pearlers in pearling towers where the sulfur falls through nozzles at a certain height, usually with air in counter-current, are sometimes used with satisfactory results, but the cost is considerable.

Processes based on fragmentation in strong water jets with fall from a certain height, making the product fall on rotating obstacles to prevent agglomeration, were developed. However, notwithstanding that the continuous operation of these fragmentation devices is reliable and the investment substantially small, the process exhibits the disadvantage of an excessively fine granulometry and the retention of a very great amount of water in the sulfur octained because of the great number of recesses formed in the fragmented product. The extremely fine granulometry of the product as well as the porosity and the excessive retention of water make commercialization more difficult and raise the cost of transportation.

It is, therefore, of vital importance that the processing of sulfur originating in conventional methods be carried out in such a way as not only to eliminate or reduce the above mentioned problems, i.e., handling, safety, maintenance of equipment, granulometry and product marketing etc., but also to provide a system which is simple and economically viable.

Therefore, one of the objects of the present invention is to provide a process for pearling sulfur originating in conventional methods of obtaining sulfur which overcomes the above mentioned inconveniences and renders a pearled sulfur product with the desired improved characteristics. By the terms "pearling" and "pearled" are meant "formation into substantially spherical particles" and "in the form of substantially spherical particles" respectively. These terms are concerned solely with the outward appearance (form) of the sulfur.

Therefore, one of the objects of the present invention is to provide a process for pearling sulfur originating in conventional methods of obtaining sulfur which overcomes the above mentioned inconveniences and renders a pearled sulfur product with the desired improved characteristics.

Particulariy, the process according to the present invention affords a pearled sulfur product whose granulometry (particle size distribution) can be adequately controlled during the process.

The symbols used in this description are the following ones: Sa = Rhombic sulfur = = Monoclinic sulfur SA = Liquid free-flowing pale-yellow sulfur predominent at low temperatures = = Liquid viscous dark brown sulfur predominant at high temperatures Sy = Plastic sulfur Note: 1-When SA solidifies, it changes into SP and Sa, both of which are crystalline and soluble in carbon sulfide.

2 - When Sy solidifies, it changes into Sy, i.e., plastic, amorphous and insoluble in carbon sulfide.

3 - Therefore, the proportion of sulfur soluble and insoluble in carbon sulfide in solidified sulfur depends on the relative quantities of SA and S present in the liquid at the moment of solidification and is a function of the temperature of liquid sulfur.

The process in accordance with the present invention is based on the characteristic that the sulfur in the lambda-formed (SA) solidifies passing through the forms of Sa and Sp.

In the present invention the sulfur in the lambda-form is defined as sulfur whose temperature is comprised between the sulfur melting temperature and a temperature of approximately 1 570C. The temperature of the sulfur should not exceed 1 570C.

At temperatures above 1 570C significant amounts of sulfur are formed in the y form which upon solidifying form Sy. The y form of sulfur, which is predominant at the above mentioned temperatures, affects not only the pearling process preventing the formation of sulfur pearls due to the plastic nature of Sy and possibly causing obstruction, but also the pumping operation, since the viscosity of sulfur at high temperatures is not suitable for operations of this kind.

On the other hand, it was established that a liquid charge of sulfur of the specific type SA when added to water in constant movement affords the formation of solid sulfur pearls with satisfactory sphericity and homogeneity. It was also established that the granulometry of the pearls thus obtained can be adequately controlled during the pearling process by adjusting the velocity of the water flow established during the process and/or adjusting the water level in the vessel where the charges of sulfur in the A form and of water come into contact, and/or adjusting the variation of the size of the openings for introducing the sulfur charge.

The process for pearling sulfur in accordance with the present invention comprises the following steps: a) providing a charge or liquid sulfur in the form of lambda-sulfur; b) adding said sulfur charge to water in constant movement, thereby forming sulfur pearls; and c) recovering and drying said pearls.

The liquid sulfur charge from step a) can be obtained by heating a liquid or solid sulfur charge to a maximum temperature of about 1 570C. However, a sulfur charge in a liquid state is preferred.

The addition of sulfur to water described in step b) is normally carried out by means of devices comprising openings localized in a position and at a water level previously established. Preferred devices and arrangements of this step of the present invention are shown in the examples.

Step c), related to recovering and drying the pearls, consists in recovering the pearls by means of different forms, depending on the type of equipment that is used for pearling, and then drying the recovered pearls, generally by exposing them to air.

The equipment for carrying out the pearling process in accordance with the present invention can be of different geometrical forms, the preferred types being those in the shape of cylindrical vessels or channels with rectangular section. The preferred equipment as well as dispositions and auxiliary devices particularly suitable for use in the process of the invention are shown in the accompanying drawings, which are given by way of example only, and which illustrate the invention.

Figure 1 is a schematic view of the basic initial system of the sulfur pearling process in accordance with the invention; Figure 2 is a graph showing the variation of the increase of the temperature of water in the process, with relation to the inlet water temperature and the proportion of the feeding charged of sulfur and water; Figures 3A, 3B and 3C show a sulfur pearling system of the channel type with a rectangular crosssection; Figure 4 shows another sulfur pearling system of the type that uses an eievation device for transporting the pearled product; Figure 5 shows a section of the portions of a nozzle which can be used in the process of the invention; Figure 6 shows another sulfur pearling system, and Figure 7 shows a lay-out of the latter system.

These figures will be more fully defined in the illustrative examples of the invention.

As already cited, the granulometry of the sulfur pearls can be adequately controlled during the pearling process. This control can be carried out by controlling the velocity of the water flow established in the process. The intensity of the induced water flow is essentiaily a function of either the degree of water movement generated by devices such as agitator, flow homogenizer and similar types, or of the degree of movement generated by the inlet velocity of the water charge and/or the outlet velocity thereof, or is a function of both. By adjusting the velocity prevalent at these points a controlled ganulometry is obtained for the formed pearled product.

Moreover, the granulometry control can be also carried out by adequate adjustment of the water level in the vessel where the sulfur and water charges come into contact and/or by varying the size of the openings through which the sulfur charge is fed in the process.

In the specific embodiment shown in Figures 6 and 7 the feeding and outlet water charge itself establishes a desired water flow by forming a vortex, induced by tangential inlet of water and by the outlet thereof. Variations of these velocities as well as adequate adjustment of the water level afford the necessary alteration of the established water flow and the adjustment of the water level, thereby obtaining the desired control of the granulometry of the formed pearled product.

Besides exhibiting evident advantages such as, on the one hand, the simplicity of the process and of the equipment used for carrying it out, and, on the other hand, the reduced cost of the material used for pearling, i.e.: water, the pearling process in accordance with the present invention imparts to the pearled sulfur product satisfactory properties such as substantially perfect sphericity and homgeneity, controlled granulometric range, excellent resistance, quick drying etc., without displaying the inconveniences inherent to the conventional methods of sulfur processing.

The sequence of experiments which gave origin to the pearling process of the present invention will now be described in the form of illustrative examples.

The initial tests which led to the development of the present process consisted in adding SA to water under mechanical agitation and consequent establishment of the SA property of producing particles in water, giving origin to SP which in a few hours changes into Sa.

The property of SA to produce sulfur pearls was then studied and the test was repeated numerous times in many different ways. The basic experiment is described hereinafter and is followed by other examples describing various alternatives as well as the industrially tested process put into continuous operation.

The following examples are illustrative of the invention but not limitative.

The basic experiment of sulfur pearling as shown in Figure 1, consisted in adding sulfur in the A form (from a vessel (1), through an opening (2) having a diameter of 2 mm placed in the bottom of said vessel and at a height of 10 cm from the water level, directly on the half the radius of a Becker cup (3) having a capacity of 2.5 litres and a diameter of 19 cm. The water level in the Becker cup was twothirds of the height of said Becker cup.

2.0 litres of water at room temperature were added to the Becker cup and an agitator system (4) with 4 (four) 5 cm long, turbine-shaped stainless steel blades (5) connected thereto. The blades entered two-thirds of the height of the water column.

The addition of SA was initiated at an agitation of 100 rpm, obtaining a pearled, perfectly spherical material with satisfactory granulometry, 100% of the product being comprised in the range of 0.25 mm to 4.0 mm.

The product was submitted to friability tests showing excellent resistance moments after production (sup) as well as two days after production (Sa).

The amount of water necessary for cooling the S was then verified and it was established that even under adiabatic conditions there could be various recirculations, evidencing that in practice the increase of the water temperature does not constitute a limiting factor for the process because it is not necessary to use very expensive cooling systems.

Assuming an adiabatic system, i.e. under the worst conditions, and using a proportion of six kilos of water at 200C for each kilo of sulfur, the resulting temperature will be approximately 490C, as shown in Figure 2 for adiabatic conditions. In Figure 2, the written information on the right hand portion of the graph refers to the illustrative calculation of final temperatures (T) of the mixture for the specific case of SA and water at an entry temperature of 1 20 C (3930K) and 200C (2930K) respectively (second curve of the graph). The equation presented there is derived from the thermal balance of the system. In the equation, n is in the number of moles, Cp is specific temperature, dt is temperature differential, and T is the final temperature of the mixture.

It is seen that the amount and temperature of water do not constitute obstacles for the present invention.

EXAMPLE 1 By using a sulfur pearling system as shown in Figures 3A, 3C and 3B sulfur was added through six openings (8) having a diameter of 3 mm, from a height of 30 cm direct to the central part of the water level of a channel (6) with a flow homogenizer (7). The water level was adjusted to 4 cm by a set of gates held by laths (9). The set of laths (9) and gates is shown with greater details in Figures 3B and 3C.

Figure 3B shows a side view of the lower part of said pearling system which comprises 8 sets of laths (9) for mounting the gates spaced from each other by 25 cm. The height of said channel is 32 cm and the length 5.9 cm. Figure 3C shows a section of the lower part of said pearling system which evidences the disposition of the gate-holding laths (9) in the channel (6). The system also comprises a water inlet (10) and a steam input coil device (11), as shown in Figure 3A.

The product obtained was well pearled. Because of its granulometry it afforded rapid water drainage and rapid loss of the residual free moisture, displaying a good grade of dryness.

The granulometry of the product obtained was as follows: Tyler Mesh Opening (mm) % Retained % Accumulated 5 4,00 33,19 33,19 6 3,36 16,22 49,41 7 2,83 7,40 56,81 8 2,38 15,65 72,46 9 2,00 9,99 82,45 10 1,68 5,95 88,40 12 1,41 2,06 90,46 14 1,19 4,10 94,56 16 1,00 1,48 96,04 32 0,50 2,60 98,64 60 0,25 0,64 99,28 > 60 < 0,25 0,72 100,00 EXAMPLE 2 Sulfurs was added through six openings having a diameter of 2 mm, at a height of 10 cm above the water level of a system mounted in accordance with Figures 3A, 3B and 3C, but the height of the water level was adjusted to 2 cm.

The addition of SA was made in the manner described in the foregoing example. The product obtained was well pearled, with a good flow-off of free residual moisture, drying rapidly.

The granulometry of the product obtained was as follows: Tyler Mesh Opening (mm) % Retained % Accumulated 5 4,00 28,08 28,08 6 3,36 18,78 46,81 7 2,83 8,21 55,07 8 2,38 17,51 72,58 9 2,00 12,28 84,86 10 1,68 5,56 90,42 12 1,41 1,53 91,95 14 1,19 3,88 95,83 16 1,00 1,21 97,04 32 0,50 2,21 99,25 60 0,25 0,48 99,73 > 60 < 0.25 0,27 100,00 EXAMPLE 3(1) By using a sulfur pearling system as shown in Figure 4, sulfurS was added through a nozzle (12) having 4 openings with a diameter of 2 mm, from a height of 40 cm from the water level, on half the radius of a water-containing cylindrical vessel (13). The system was worked at 70 rpm by means of a mechanical agitator device (14) with turbine-shaped blades (15).The product was discharged by an elevation device (16) driven by a driving mechanism (17) installed on the conical bottom of the vessel (13) and stored in a container (18). The water drained from the product in said container (18) was transferred to a water receiving container (20) through line 1 9 and recirculated through lines (21) and (23) to a cylindrical vessel (13) by means of a pump (22). The lower section (24) of the nozzle (12) as well as the cross section (25) thereof is shown in Figure 5. Said nozzle (12) is made of stainless steel 304 with a thickness in excess of 1 mm, having 4 openings (26) for sulfur input as well as an inlet (27) and outlet (28) for steam.

The product obtained was very well pearled, with excellent drainage of residual free moisture, drying rapidly when stockpiled.

The granulometry of the product was as follows: Tyler Mesh Opening (mm) % Retained % Accumulated 3,5 5,66 0,85 5 4,00 3,05 3,90 6 3,36 11,25 15,15 7 2,83 8,75 23,90 8 2,38 35,66 59,56 9 2,00 18,89 78,45 10 1,68 8,09 86,54 12 1,41 3,05 89,59 14 1,19 4,71 94,30 16 1,00 1,63 95,93 32 0,50 2,55 98,48 60 0,25 0,30 98,73 > 60 < 0,25 1,21 100,00 EXAMPLE 3(2) Sulfurs was added to the same system as described in Example 3(1), but in order to change the granulometry, the velocity of the agitator was changed to 100 rpm, obtained a finer product, as it is seen in the granulometry analysis:: Tyler Mesh Opening (mm) % Retained % Accumulated 3,5 5,66 5 4,00 6 3,36 5,20 5,20 7 2,83 10,30 15,50 8 2,38 30,20 45,70 9 2,00 45,00 90,70 10 1,68 3,70 94,40 12 1,41 1,05 95,45 14 1,19 1,30 96,75 16 1,00 1,83 98,58 32 0,50 0,22 98,80 60 0,25 0,87 99,67 > 60 < 0,25 0,33 100,00 EXAMPLE 4(1) By using a sulfur pearling system as shown in Figure 6, sulfurA was added through a nozzle shown in Figure 5, but having 8 openings with a diameter of 3 mm each, on half the radius of a cylindrical vessel (29). The cylindrical vessel (29) is provided with a tangential water inlet (30) and has a lower conical portion (31). The vessel (29) has further a bottom-valve with a 2-inch opening mounted in the lower portion (31) thereof.Said system also comprises a channel (33) for receiving pearled material and water, situated below said valve (32) and a movable trough (34) which transports the product coming from the channel (33) for an appropriate site.

The process was started by adding water to the vessel (29), in sufficient amounts for operating the system with a vortex induced by tangential entrance of water (30) and so that the height and the velocity of the water flow in the vessel (29) would be controlled by opening the bottom valve (32).

The vortices in the southern hemisphere were given a clockwise direction.

The SA was added giving origin to a pearling similar to the pearling described in Examples 3(1) and 3(2), the pearled product being automatically removed with the water by the valve (32) of the vessel (29) and arranged in the best way at the storage site with the help of a moving conveyor (34) trough. The lay-out of the above system is shown in Figure 7, in which the sulfur is introduced through line (35) through the nozzle (12) direct into said cylindrical vessel (29). The system has a base portion (36) for supporting the equipments and indicates the range of said movable trough (34). The other references shown in this figure are as already defined in this example.

The pearled product displayed excellent granulometry as well as very good conditions for draining the residual free moisture affording natural drying to the stocked product.

The granulometry of the product obtained was as follows: Tyler Mesh Opening (mm) % Retained % Accumulated 5 4,00 10,97 10,97 6 3,36 10,05 21,02 7 2,83 2,26 23,28 8 2,38 4,81 48,09 9 2,00 24,03 72,12 10 1,68 12,51 84,63 12 1,41 2,96 87,59 14 1,19 6,16 93,75 16 1,00 1,62 95,37 32 0,50 2,88 98,25 60 0,25 0,77 99,02 > 60 < 0,25 0,98 100,00 EXAMPLE 4(2) SulfurS was added to the same system as in Example 4(1) but adjusting the water level of the vortex induced by the bottom valve so as to maintain the water level at a distance of 1 5 cm from the nozzle with the object of obtaining a product with coarser granulometry. As seen in the granulometric analysis this object was fully achieved and as expected the product having coarser granulometry dried more quickly than the products with finer granulometry.

The granulometry of the product obtained was as follows: Tyler Mesh Opening (mm) % Retained % Accumulated 3,5 5,66 8,75 8,75 5 4,00 30,59 39,34 6 3,36 12,68 52,02 7 2,83 3,67 55,69 8 2,38 19,24 74,93 9 2,00 10,52 85,17 10 1,68 6,39 91,56 12 1,41 2,09 93,65 14 1,19 1,90 95,55 16 1,00 0,49 96,04 32 0,50 0,61 96,65 60 0,25 2,21 98,86 > 60 < 0,25 1,14 100,00 The experiment described in Examples 4(1) and 4(2) was texted to an industrial scale and put into operation in a petrochemical sulfur recovery unit (Claus process) with a production capacity of 57 t/d.

Claims (12)

1. Process for pearling sulfur, characterized in that it comprises the steps of: a) providing a charge of liquid sulfur in the form of lambda sulfur, b) adding said sulfur charge to water in constant movement, thereby forming sulfur pearls, and c) recovering and drying said pearls.

2. Process in accordance with claim 1, characterized in that said liquid sulfur charge from step a) is obtained by heating a liquid of solid sulfur charge to a maximum temperature of about 1 570C.

3. Process in accordance with claim 2, characterized in that said sulfur charge to be heated is in a liquid state.

4. Process in accordance with claim 1, characterized in that the granulometry of said sulfur pearls is controlled by varying the velocity of the water flow established in the process and which results from the movement thereof.

5. Process in accordance with claim 1 or 4, characterized in that the movement of water is afforded either by devices such as agitator, flow homogenizer and similar types, or by the inlet velocity of the water charger and/or the outlet velocity thereof, or by both.

6. Process in accordance with claim 5, characterized in that the granulometry is controlled by adjusting the velocity at the points which provide the water movement.

7. Process in accordance with claim 4 or 6, characterized in that the granulometry is further controlled by adequate adjustment of the water level in the vessel in which the sulfur charge comes into contact with the vessel.

8. Process in accordance with claim 5, characterized in that a vortex is formed, induced by tangential introduction of water and by the outlet thereof, and in that the granulometry of the pearls is controlled by adjusting the inlet and outlet velocities of the water and by adjustment of the water level in the vessel where said charges come into contact.

9. A process as claimed in claim 1 carried out substantially as described herein with reference to, and as illustrated by, any of the figures of the accompanying drawings.

10. A process as claimed in claim 1 carried out substantially as described in any of the Examples herein.

11. Pearled sulphur whenever obtained by a process as claimed in any one of claims 1 to 10.

12. Any new and novel feature described herein.