GB1591658A

GB1591658A - Gravity settling

Info

Publication number: GB1591658A
Application number: GB36855/77A
Authority: GB
Original assignee: Lummus Co
Current assignee: CB&I Technology Inc
Priority date: 1976-09-07
Filing date: 1977-09-02
Publication date: 1981-06-24
Also published as: DE2740079A1; CA1097574A; ZA775127B; JPS5732603B2; FR2363353B1; IT1091406B; AU512559B2; AU2843077A; FR2363353A1; JPS5344971A

Description

(54) IMPROVEMENTS IN OR RELATING TO GRAVITY SETTLING (71) We, THE LUMMUS COMPANY, a Corporation organised and existing under the Laws of the State of Delaware, United States of America of 1515 Broad Street, Bloomfield, New Jersey, 07003, United States of America, 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: This invention relates to a liquid-solid separation, and more particularly, to liquidsolid separation by gravity settling.

In many operations, there is a need for effecting the separation of solids from a liquid. Thus, for example, in U.S. Patent Specification No. 3,856,675 there is dis closed a process for separating insoluble material from a coal liquefaction product wherein such insoluble material is separated by gravity settling in the presence of a promoter liquid having specific characteristics. In such a process, and similar processes, there is a need for improved apparatus for effecting such gravity settling.

The present invention seeks to provide an improved process for the separation of insoluble material from a coal liquefaction product by gravity settling.

According to one aspect of this invention, there is provided a process for separating solids from a liquid by gravity settling, the process comprising the steps of: introducing a feed of combined solids and liquid into a gravity settler vessel at multiple locations; intercepting the settling path of the solids below each of the feed locations by bringing the solids into contact with inclined intercepting surfaces thereby to coalesce the solids and increase the solids settling rate, each inclined intercepting surface being a plate in the form of an inverted "V" vertically spaced from an adjacent one of said surfaces and formed from first and second downwardly inclined, upwardly curved, intersecting sections, each section being a part of the bounding surface of a notional cone, so that an apex of each section is at the vessel wall, there being a substantially enclosed separation zone defined between adjacent plates; said process further comprising recovering a solids-containing underflow from the separate separation zones; and recovering substantially solids free overflow from the separation zones.

The feed may be a coal liquefaction product and preferably includes a promoter liquid which promotes and enhances the separation of solids.

Conveniently, the apparatus for the process additionally comprises a vessel; underflow outlet means for withdrawing underflow from a lower portion of each of the separation chambers; overflow outlet means for withdrawing overflow from an upper portion ob each of the separation chambers; and a fresh feed inlet means for separately introducing said feed into at least two of the separation chambers The terms "overflow" and "underflow" are used herein to mean the liquid and solids, respectively after separation from the mixture thereof.

Suitably, at least one of the underflow outlet means comprises first and second outlet pipes adjacent the lower of the plates defining the respective chamber, and advantageously at least one of the inlet means in the apparatus comprises first and second inlet pipes for introducing feed into first and second portions of the respective chamber.

Preferably, the apices of the said sections are spaced diametrically opposite one another on the vessel wall, and most preferably the sections of each plate are inclined to the horizontal at an angle of between 45" and 75".

It is convenient if the said plates, in addition to being shaped like an inverted "V" are substantially in the form of a saddle wih the line of intersection of the two sections being an upwardly concave curve.

Advantageously the plates are corrugated.

According to another aspect of this invention there is provided a gravity settler for effecting solid-liquid separation, comprising: a vessel, at least two vertically spaced inverted V-shaped plates within the vessel, each of said V-shaped plates comprising first and second downwardly oppositely inclined sections which extend from the apex of the inverted V-shaped plate to adjacent the vessel wall, there being a substantially enclosed liquid-solid separating chamber defined between the said two V-shaped plates; inlet means for introducing a liquidsolid feed into the said chamber; first and second underflow outlet means positioned above and adjacent to the lower portions of said first and second sections of the lower of the said two inverted V-shaped plates; and overflow outlet means below and adjacent to the apex of the higher of the said two inverted V-shaped plates for withdrawing clarified liquid from said chamber.

The invention encompasses a product of the said process.

In order that the invention may be more readily understood and so that further features thereof may be appreciated, the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a simplified schematic drawing of an embodiment of the gravity settler for carrying out a gravity settling process in accordance with the present invention; Figure 2 is a simplified drawing of another embodiment of a gravity settler for carrying out a gravity settling process in accordance with the present invention; and Figure 3 is a detailed view of a pipe connection for the settler illustrated in Figure 2.

An embodiment of the present invention --is illustrated in Figure 1. A gravity settling vessel l01, having a cylindrical upper portion 102 and a conically shaped lower portion 103, is divided into a plurality of separate liquid-solid separation surfaces in the form of inverted V-shaped plates 104 having oppositely slanted portions 105 and 106, with each of the oppositely slanted portions being sloped at an angle with respect to hori zonal sof between 450 and 75 . The Ashaped plates 11)4 define therebetween two liquidzsolid separation chambers 107 and 108.Each of the separate solid separation chambers 107 and 108 is provided with an underflow outlet 109 and 110, respectively, w h a combined overflow being withdrawn from the upper portion of each of the chambers 107 and 108, such overflow with drawl means being schematically indicated as :111. 'The -outlet withdrawal means 111 comprises a plurality of riser pipes. Each riser pipe discharges into the next higher riser pipe; the highest riser pipe discharges into the top separation zone, wherein sub stantially solid-free overflow is withdrawn through the overflow outlet.Each of the separate chambers 107 and 108 is provided with fresh feed inlet for introducing a liquid-solid feed, with such feed inlets being .schemaficallly Tepresented as 112 and 113.

In operation, liquid-solid feed is introduced into the chamber 107 through inlet 112, and the solids which settle are intercepted by the plate 105 for utilmate withdrawal through underflow outlet 109.

Similarly, liquid-solid feed introduced through inlet 113 is separated in chamber 108, with settled solids being intercepted by plate 106 for ultimate withdrawal through outlet 110.

Although the embodiment has been particularly described with respect to separate underflow withdrawal from each of the chambers, it is to be understood that underflow withdrawal may be effected in a com twined manner, or by using a plurality of downcomer pipes operating in a similar fashion to the said plurality of riser pipes.

Similarly, overflow withdrawal can be effected other than as particularly described.

As a further modification, the intercepting surfaces may take the form of plates having a configuration such that the intercepting surfaces are in the form of superimposed cones, and thus the plates can be considered to be of inverted V-shape in section.

Figure 2 shows a gravity settler comprising a vessel, schematically indicated by the dash-dotted line. Within the vessel are a plurality of vertically spaced plates, each formed from two inclined sections 301 and 302. The sections each form part of the bounding surface of a notional cone, and the respective apices 303 and 304 of the sections 301, 302 are positioned at the vessel wall.

The sections 301 and 302 are so arranged that they intersect with each other in the interior of the vessel above the apices 303, -304 to form a curved or saddle-like intersection 305, with the apices 303 and 304 of the respective sections 301 and 302 being spaced diametrically opposite one another on the vessel wall. Thus, the intemal plates are defined by the intersection of two inclined sections with one another and with the vessel which is preferably cylindrical.

The sections 301, 302 incline to the horizontal at an angle of between 45" and 75 , and are preferably corrugated, and the corrugations provide additional surface for coalescing of solids and provide additional strength to the plates.

A liquid-solid separation compartment or chamber 307 is defined between .each pair of adjacent 'plates. Each chamber 307 has two portions 307a and 307b defined between the sections 301 and 302, respectively, and the vessel wall.

Each of the portions 307a and 307b is provided with an underflow outlet, 309 and 311 respectively, positioned at the apex of the respective section, with a combined overflow being withdrawn through an apertured overflow outlet pipe 312 which extends across the vessel and is positioned immediately below the saddle-like intersection of the plate defining the top of the respective chamber.

Each of the portions 307a and 307b is provided with a feed inlet in the form of an apertured inlet pipe, 314 and 315 respectively, which extend across the vessel at an intermediate portion of the respective portion.

Each of the inlet pipes and outlet pipes may be connected to the vessel wall through a suitable bayonet type connection, as shown in Figure 3.

In operation, a liquid-solid feed is introduced into the gravity settler through fresh feed inlets 314, 315 into portions 307a and 307b, respectively, and as the solids settle they strike the slanted plates which thereby intercept their settling path forcing them to coalesce and separate more quickly. The agglomerated particles, as a result of the inclined surfaces of the plates, move to the underflow outlets 309, 311 for withdrawal.

The substantially solid-free liquid is withdrawn through the overflow outlet pipe 312 from the upper portions of the separation chambers 307.

The use of conically shaped sections 301 and 302 offers the advantage that the intercepting surfaces are sloping towards the underflow withdrawal at the section apex, thus minimising solid hangup. In addition, the curved shape provides additional mechanical strength, which should eliminate the need for stiffening members.

The gravity settlers described above are particularly suitable for separating insoluble material from a coal liquefaction product wherein the gravity settling is effected in the presence of a promoter liquid.

The coal liquefaction product is preferably introduced into the gravity settler in admixture wih a promoter liquid, as net feed, with the promoter liquid having the properties -described in U.S. Patent Specification No. 3,856,675. As described in the aforementioned patent specification, the promotor liquid is one that has an aromaticity less than that of the liquefaction solvent and is generally a hydrocarbon liquid having a characterisation factor (K) of at least about 9;75 -and preferably at least about 11.0, with such characterisation factor being an index of the aromaticity/paraflinicity of hydrocarbons -and petroleum fractions as disclosed by Watson and Nelson, Ind.Eng. Chef. 25 "880 (1933). The liquid which is used to enhance and promote the separation of in soluble material is fu-rther -characterised by a 5 volume percent distillation temperature of at least 250"F and a 95 volume percent dis tillation temperature of at least 8500F and no greater than 750 F. The promotor liquid preferably has a 5 volume percent distillation temperature of at least 310 F and most pre Iferably of at least 400"F.'The 95 volume percent distillation temperature is preferably no greater than 600 1F. The most preferred promoter liquid has a 5 volume percent distillation temperature of at least 4250F and a 95 volume percent distillation temperature of no greater than 500"F.

As representative examples of such liquids, there may be mentioned: kerosene or kerosene fraction from paraffinic or mixed base crude oils; middle distillates, light gas oils and gas oil fractions from paraffinic or mixed based crude oils; alkyl benzenes with side chains containing 10 or more carbon atoms; paraffinic hydrocarbons containing more than 12 carbon atoms; fully hydrogenated naphthalenes and substituted naphthalenes; propylene oligomers Wenta- mer and higher); tetrahydronaphthalene, heavy naphtha fractions, etc. The most preferred liquids are kerosene fractions; white oils; fully hydrogenated naphthalenes and substituted naphthalenes.

The amount of liquid promoter used for enhancing and promoting the separation of insoluble matter from the coal liquefaction product will vary with the particular liquid employed, the coal liquefaction solvent, the coal used as starting material and the manner in which the liquefaction is effected. As should be apparent to those skilled in the art, the amount of liquid promoter used should be minimised in order to reduce the overall costs of the process. It has been found that by using the liquid of controlled aromaticity, the desired separation of insoluble material may be effected with modest amount of liquid promoter. In general, the weight ratio of liquid promoter to coal solution may range from 0;2:1 to 3.0:1, preferably from 0.3:1 to 1.5:1.In using the preferred promoter liquid, which is a kerosene fraction having 5 percent and 95 percent volume distillation temperatures of 4250F and 5000F respectively, promoter liquid to coal solution weight ratios in the order of 0.4:1 to 0.6:1 have been particularly successful. It is to be understood, however, that greater amounts of liquid promoter may be employed, but the use of such greater amounts is uneconomical. In addition the use of an excess of liquid promoter may result in the precipitation or separation of an excessive amount of desired coal-derived products from the coal extract. More particularly, as the amount of liquid promoter employed is increased, a greater amount -of ash is separated from the coal solution, but such an increased separation is accompanied by an increased separation of desired -coal-derived products from the coal solution.

The net coal product (the extracted carbonaceous matter, -excluding the promoter liquid, liquefaction solvent and gas make) contains less han about i'% insoluble material, generally less than 0.1% insoluble material, and most preferably less than 0.05% insoluble material, all by weight.

The gravity settling is generally effected at temperatures from 300"F to 6000F, preferably from 350"F to 500"F, and a pressure from 0 psig to 500 psig, preferably at a pressure from 0 psig to 300 psig. It is to be understood, however, that higher pressures could be employed, but as should be apparent to those skilled in the art, lower pressures are preferred.

Although the present invention is particularly suitable for effecting liquid-solid separation of solid particulate material from a coal liquefaction product, it is to be understood that the present invention is suitable for separating any one of a wide variety of liquid-solid mixtures by gravity settling.

Thus, for example, a gravity settler as described above may also be employed for the removal of char fines from oils produced from pyrolysis of coals; finely dispersed solid particles in kerogen retorted from shale, tar sands, oil shale, and the like. The use of gravity settling in accordance with the invention for the these applications and others should be apparent to those skilled in the art from the teachings herein.

WHAT WE CLAIM IS:- 1. A process for separating solids from a liquid by gravity settling, the process comprising the steps of: introducing a feed of combined solids and liquid into a gravity settler vessel at multiple locations; intercepting the settling path of the solids below each of the feed locations by bringing the solids into contact with inclined intercepting surfaces thereby to coalesce the solids and increase the solids settling rate, each inclined intercepting surface being a plate in the form of an inverted "V" vertic ally spaced from an adjacent one of said surfaces and formed from first and second downwardly inclined, upwardly curved, intersecting sections, each section being a part of the bounding surface of a notional cone, so that an apex of each section is at the vessel wall, there being a substantially en closed separation zone defined between adjacent plates; said process further comprising recovering a solids-containing underflow from the separate separation zones; and recover ing substantially solids free overflow from the separation zones.

2. A process according to claim 1, wherein said feed comprises a coal liquefaction product.

3. A process according to claim 2, wherein the coal liquefaction product includes a promoter liquid which promotes and enhances the separation of solids.

4. A process according to any one of the preceding claims wherein the gravity settling apparatus for effecting solid-liquid separation comprises, underflow outlet means for withdrawing underflow from a lower portion of each of the separation chambers; an overflow outlet means for withdrawing overflow from an upper portion of each of the separation chambers; and a fresh feed inlet means for separately introducing said feed into at least two of the separation chambers.

5. A process according to claim 4 wherein at least one of the underflow outlet means comprises first and second outlet pipes adjacent the lower of the plates defining the respective chamber.

6. A process according to claim 4 or claim 5, wherein at least one of the inlet means in the apparatus comprises first and second inlet pipes for introducing feed into first and second portions of the respective chamber.

7. A process according to any one of the preceding claims wherein the apices of the said sections are spaced diametrically opposite one another on the vessel wall.

8. A process according to any one of the preceding claims wherein the sections of each plate are inclined to the horizontal at an angle of between 45" and 75".

9. A process according to any one of the preceding claims wherein the said plates, in addition to being shaped like an inverted "V" are substantially in the form of a saddle, with the line of intersection of the two sections being an upwardly concave curve.

10. A process according to any one of the preceding claims wherein the plates are corrugated.

11. A gravity settler for effecting solid-liquid separation, comprising: a vessel, at least two vertically spaced inverted V-shaped plates within the vessel, each of said V-shaped plates comprising first and second downwardly oppositely inclined sections which extend from the apex of the inverted V-shaped plate to adjacent the vessel wall, there being a substantially enclosed liquid-solid separating chamber defined between the said two V-shaped plates; inlet means for introducing a liquidsolid feed into the said chamber; first and second underflow outlet means positioned above and adjacent to the lower portions of said first and second sections of the lower of the said two inverted V-shaped plates; and overflow outlet means below and adjacent to the apex of the higher of the said two inverted V-shaped plates for withdrawing clarified liquid from said chamber.

12. A gravity settler according to claim 10 wherein the inlet means comprises first and second inlet pipes for introducing feed into first and second portions of the chamber above the first and second sections of the lower inverted V-shaped plate.

13. A gravity settler according to claim

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. most preferably less than 0.05% insoluble material, all by weight. The gravity settling is generally effected at temperatures from 300"F to 6000F, preferably from 350"F to 500"F, and a pressure from 0 psig to 500 psig, preferably at a pressure from 0 psig to 300 psig. It is to be understood, however, that higher pressures could be employed, but as should be apparent to those skilled in the art, lower pressures are preferred. Although the present invention is particularly suitable for effecting liquid-solid separation of solid particulate material from a coal liquefaction product, it is to be understood that the present invention is suitable for separating any one of a wide variety of liquid-solid mixtures by gravity settling. Thus, for example, a gravity settler as described above may also be employed for the removal of char fines from oils produced from pyrolysis of coals; finely dispersed solid particles in kerogen retorted from shale, tar sands, oil shale, and the like. The use of gravity settling in accordance with the invention for the these applications and others should be apparent to those skilled in the art from the teachings herein. WHAT WE CLAIM IS:-

1. A process for separating solids from a liquid by gravity settling, the process comprising the steps of: introducing a feed of combined solids and liquid into a gravity settler vessel at multiple locations; intercepting the settling path of the solids below each of the feed locations by bringing the solids into contact with inclined intercepting surfaces thereby to coalesce the solids and increase the solids settling rate, each inclined intercepting surface being a plate in the form of an inverted "V" vertic ally spaced from an adjacent one of said surfaces and formed from first and second downwardly inclined, upwardly curved, intersecting sections, each section being a part of the bounding surface of a notional cone, so that an apex of each section is at the vessel wall, there being a substantially en closed separation zone defined between adjacent plates; said process further comprising recovering a solids-containing underflow from the separate separation zones; and recover ing substantially solids free overflow from the separation zones.

13. A gravity settler according to claim

10 or claim 11 wherein said first and second sections are inclined at an angle of from 45 to 75 with respect to horizontal.

14. A gravity settler according to any one of claims 11 to 13 comprising more than two of said inverted V-shaped plates defining a plurality of said chambers, each provided with respective said inlet means, underflow outlet means and overflow outlet means.

15. A process for separating solids from liquid substantially as herein described with reference to, and as shown in, Figure 1 of the accompanying drawings.

16. A process for separating solids from liquid substantially as herein described with reference to, and as shown in, Figures 2 and 3 of the accompanying drawings.

17. A gravity settler substantially as herein described with reference to, and as shown in, Figure 1 of the accompanying drawings.

18. A gravity settler substantially as herein described with reference to, and as shown in, Figures 2 and 3 of the accompanying drawings.

19. A product of a process according to any one of claims 1 to 10, 14 and 15.