GB2303377A

GB2303377A - Treatment of petrochemical residues

Info

Publication number: GB2303377A
Application number: GB9514475A
Authority: GB
Inventors: Anthony Bennett; Robert Charles Eddolls
Original assignee: Individual
Current assignee: Individual
Priority date: 1995-07-14
Filing date: 1995-07-14
Publication date: 1997-02-19
Also published as: GB9514475D0

Description

TREATMENT OF PETROCHEMICAL RESIDUES This invention relates to treatment of heavy petrochemical residues (which will be referred to for convenience as "sludge"), recovered from a source which may typically (but without limitation) be a crude oil storage tank or a lagoon or the like. In this specification, for simplicity, the invention will be explained with reference to sludge recovered from a crude oil storage tank.

The normal method of removing residue from a crude oil storage tank is by collecting it together, for example using a specially adapted bulldozer, and then taking it out of the tank, for example using a suitable lobe pump, the sludge so recovered being dumped in another tank for disposal. It used to be common to dispose of the sludge on landfill sites. This is no longer permitted in the United Kingdom, and recourse has had to be had to incineration, which is expensive, hazardous, and environmentally highly undesirable.

In any case, both the simple dumping and the destruction of the sludge in the state in which it has been recovered from the crude oil storage tank (or from whatever source) is wasteful, because it does contain a substantial amount of reusable product, typically in the form of the lighter fractions of the sludge which, if recovered, constitute refinable oil. It is known to be perfectly feasible to separate this oil out from the sludge, thus substantially reducing the latter to solid constituents of the sludge, which are much more easily disposed of, and which can represent only a relatively small proportion of the original volume and mass of the sludge.Such separation is achieved using application of heat and/or suitable additives, in the form of aqueous solutions and/or suspensions of chemical reagents, followed by physical separation of the reusable product using a centrifuge or other suitable equipment (which will be referred to in general terms as decanting apparatus).

Quite apart from the foregoing considerations, current methods of recovering the residue from stored locations tend to be slow, expensive and cumbersome. In this connection, in order to assist the disposal of sludge, and also (where some refinable oil is in fact recovered from the sludge) in order to improve the recovery process itself, use is increasingly being made of diluents and/or carrier fluids referred to in general terms in the industry as "cutter", consisting typically of light oils such as diesel oil.

The comparatively high cost of "cutter" is a major factor militating against the cost-effectiveness of currently known methods of recovering refinable oil from heavy residues.

According to the invention in a first aspect, equipment for treatment of heavy petrochemical residues ("sludge") comprises: a plurality of process tanks, at least one of which has a raw sludge inlet; decanting apparatus for receiving processed sludge from at least one of the process tanks and for physically separating a reusable fraction, such as refinable oil, from the remainder of the processed sludge; ductwork connecting process tanks with each other and with the decanting apparatus; and control means for controlling flow through the tanks and ductwork.

Preferably, the ductwork interconnects at least two of the process tanks in series and/or in parallel with each other. The control means are then preferably arranged to enable sludge to be processed in two or more of the process tanks in succession; and/or in at least two process tanks simultaneously; and/or in a plurality of stages using two process tanks, with sludge being transferred between the two tanks between each stage and the next.

The residue recovered from the crude oil storage tank is processed, i.e. subjected to the desired chemical and/or heat treatment, in the process tanks, with addition of any additives necessary as mentioned above.

For this purpose, at least one of the process tanks contains a mixer for mixing fluids in the tank (and in this connection, the term "fluid" in this document is to be taken to mean whatever flowable substance, whether or not containing solid matter, is implied by the context).

Heating means are also preferably provided, so that the process takes place at a predetermined temperature. In addition, at least one of the process tanks preferably has an internal pump circulation system for keeping fluids in circulation within the tank.

The additives are preferably supplied from a plurality of dosing tanks connected to at least one of the process tanks, for supplying at least one additive in fluid form to sludge being processed. Preferably, the dosing tanks comprise at least one pair, interconnected for alternate operation of the two dosing tanks of the pair.

According to the invention in a second aspect, a method of treating heavy petrochemical residues ("sludge"), using the apparatus of the invention, comprises feeding raw sludge to at least one process tank; processing raw sludge by introducing additives to the tank for enabling a reusable fraction, such as refinable oil, to be separated from the remainder of the sludge, mixing the sludge and additives and heating the mixture in the process tank or tanks; and subsequently separating the reusable fraction physically from the remainder in the decanting apparatus.

According to an important and preferred feature of the invention, after the decanting apparatus has removed solids from the reusable fraction, some of the latter is fed back to the raw sludge inlet or inlets, and/or to at least one process tank (or indeed to any other location that may be desirable) in order to serve as "cutter". Thus, the benefits of using "cutter" are available using the product of the process itself rather than using expensive supplies bought in for the purpose. Furthermore, the "cutter" used in this way is of course then recycled, very little of it being lost in the process, so that any "cutter" introduced from an external source need only be that required for "topping-up" purposes.

The equipment according to the invention is extremely versatile, and using standard components it can be designed so as to be very flexible in operation. Thus, the various process tanks can be operated in parallel, either simultaneously or one after the other; or in series; or with, say, two tanks operated in tandem and each feeding into a common third tank, which is preferably a holding tank (whether or not part of the process takes place in it), from which the decanting apparatus can be continuously fed.

The term "ductwork" is to be understood to include pipes, channels or any other form of duct along which a flowable substance can travel. It includes appropriate pumps.

The control means comprises appropriate valves, on the tanks and pumps and in the ductwork as required, together with controls for the various pumps, valves and other controllable elements of the equipment, to enable the desired flow circuits to be established, and changed as necessary, including making transfers between different stages of the process, in order to produce the maximum effect and overall optimum performance. The dosing tank system in accordance with the invention also allows chemicals, and other additives as required, to be introduced at different stages of the process, again for maximum effect and overall optimum performance.

The equipment can be installed together on a single site close to the source of the residue, e.g. next to a crude oil storage tank or in the middle of a group of such tanks, so as to be very compact, and all on one level.

A preferred embodiment of the invention will now be described, by way of example only and with reference to the accompanying drawings, in which: Figure 1 is a simplified block diagram showing the main components and fluid circuitry of the equipment; and Figure 2 is a simplified site plan showing a typical layout of the equipment on the ground, in association with a crude oil storage tank.

The equipment shown in the drawings comprises a pair of substantially identical primary process tanks 10, 12, and a third process tank 14. Each of these three tanks contains a steam heating coil 16, supplied with steam from a suitable external source not shown, via a steam inlet 80. Condensate is removed via an outlet 82.

Each process tank also contains a mixer shown diagrammatically at 18, for ensuring that the contents of the tank are properly mixed. In the case of the tanks 10 and 12, the mixer is incorporated in an internal pumping system, indicated purely diagrammatically at 20, which keeps the solids in continuous suspension. The tank 14 may if desired also have such a system.

Residue in the form of sludge is collected in the usual way within a crude oil storage tank 22, Figure 2, and pumped by a lobe pump 24 to a sludge inlet 26 which is connected via a main inlet valve 84 in a main feed line 27, to sludge inlets 28 of the process tanks. Each tank 10, 12 has an outlet 30, connected to a common feed pump 32 for the tank 14. The tank 14 has an outlet 34 connected through a decanter feed pump 36 to an inlet of a decanter 38, which is typically in the form of a conventional centrifuge but which may take any suitable form.

The equipment also includes two pairs of dosing tanks 40 and 42, with a common water supply 44 to which each of the four tanks 40, 42 is connected through a respective stop valve 46. The outlets of the two tanks 40 are connected through further stop valves to a pump 48 in a polymer feed line 50, which delivers suitable polymer, mixed with water, from each tank 40, operated alternately by means of the associated stop valves, to the centrifuge 38, in order to assist separation of usable oil from solid matter in the centrifuge. Each tank 40 is refilled with polymer while the other is discharging.

The chemicals required for the process in the tanks 10, 12 and 14 are placed in the tanks 42, which are again operated in alternation in the same way as the tanks 40, by means of their inlet valves 46 and outlet valves 47, the outlets of which are both connected, via a delivery pump 52, to dosing inlets 54 of the process tanks, via a dosing main 56. Each dosing tank contains a mixer 45, for mixing the additive placed in the tank with the water from the supply 44.

It will be noted from Figure 1 that every inlet and every outlet of each process tank 10, 12, 14 has a control valve. The equipment includes control means which includes these and other valves, including the remaining valves shown in Figure 1 and not necessarily mentioned individually in this description. It will be realised that any of the various valves may be operated, manually or otherwise, in order to provide a wide variety of flow circuits for.the sludge received from the inlet 26, and the additives received from the dosing tanks 42, operated as described above.

Thus, for example, if the valves on both inlets 28 of the tanks 10 and 12 are open, and the valve on the inlet 28 of tank 14 closed but its main inlet valve 33 open, then with all three outlet valves 30, 34 open, sludge supplied from the inlet 26 is fed in parallel into the tanks 10 and 12, heated in those tanks and mixed with the appropriate chemicals supplied from the dosing main 56, and discharged by the pump 32 into the tank 14.

The latter serves as a holding tank, the mixer 18 in the tank 14 keeping the mixture in suspension until it is delivered by the pump 36 to the centrifuge 38, which physically separates solid matter from the remainder of the sludge which has been processed in the process tanks. This solid matter is discharged at 60 (Figure 2), for example to a skip, while refinable oil from which it has been separated is delivered to a storage tank 62 for subsequent removal in any convenient way.

It may be desired to use a process consisting of two or more stages, in which, for example, a different chemical reagent is used in each stage. In that event, the tanks 10 and 12 can be used alternately with a first reagent from one of the dosing tanks 42 being introduced into the tank 10 in one stage, and a second, from the other tank 42, into the tank 12 in the next stage. In order to permit such a mode of operation of the tanks 10 and 12, there is a transfer network 64 of pipes with their associated inlet and outlet valves, containing a circulation pump 66. It can be seen that by appropriate adjustment of the valves in the network 64, not only can the tanks 10 and 12 be connected in series with flow from tank 10 to tank 12, but flow can also be obtained from tank 12 to tank 10. In this way, any number of process stages can be employed using just two process tanks.

A feedback line 68, containing a pump 69, is arranged to take a fraction of the oil from the storage tank 62 to any of the process tanks 10, 12, 14 that may be desired, under the control of inlet valves 70. The line 68 is also connected through a further valve 72 to the main feed line 27. An external "cutter" inlet 74 is also provided, so that in the event of "cutter" fluid from an external source being required, e.g. for topping-up purposes, this can be supplied through the inlet 74.

Finally, a bypass line 76 may be provided if necessary so that sludge 26 can be passed direct to the centrifuge 38.

Claims

1. Equipment for treatment of heavy petrochemical residues (referred to as sludge), comprising: a plurality of process tanks, at least one of which has a raw sludge inlet; decanting apparatus for receiving processed sludge from at least one of the process tanks and for physically separating a reusable fraction, such as refinable oil, from the remainder of the processed sludge; ductwork connecting process tanks with each other and with the decanting apparatus; and control means for controlling flow through the tanks and ductwork.

2. Equipment according to Claim 1, wherein the ductwork interconnects at least two of the process tanks in series and/or in parallel with each other.

3. Equipment according to Claim 2, wherein the control means are arranged to enable sludge to be processed in two or more process tanks in succession.

4. Equipment according to Claim 2 or Claim 3, wherein the control means are arranged to enable sludge to be processed in at least two process tanks simultaneously.

5. Equipment according to any one of Claims 2 to 4, wherein the control means are arranged to enable sludge to be processed in a plurality of stages using two process tanks, with sludge being transferred between the two tanks between each stage and the next.

6. Equipment according to any one of the preceding Claims, wherein the process tanks comprise at least two primary process tanks and a holding tank downstream of the primary tanks, the holding tank having an outlet for delivery of processed sludge to the decanting apparatus.

7. Equipment according to any one of the preceding Claims, wherein at least one of the process tanks contains a mixer for mixing fluids in the tank.

8. Equipment according to any one of the preceding Claims, wherein at least one of the process tanks has an internal pump circulation system for keeping fluids in circulation within the tank.

9. Equipment according to any one of the preceding Claims, wherein at least one of the process tanks contains means for heating contents of the tank.

10. Equipment according to any one of the preceding Claims, further including a plurality of dosing tanks connected to at least one of the process tanks, for supplying at least one additive in fluid form to sludge being processed.

11. Equipment according to Claim 10, wherein the dosing tanks comprise at least one pair, interconnected for alternate operation of the two dosing tanks of the pair.

12. Equipment for the treatment of petrochemical sludge, substantially as described in the foregoing description with reference to the accompanying drawings.

13. A method of treating heavy petrochemical residues ("sludge") using apparatus according to any one of the preceding Claims, comprising feeding raw sludge to at least one process tank; processing the sludge by introducing additives to the tank for enabling a reusable fraction, such as refinable oil, to be separated from the remainder of the sludge, mixing the sludge and additives and heating the mixture in the process tank or tanks; and subsequently separating the reusable fraction physically from the remainder in the decanting apparatus.

14. A method according to Claim 13, including feeding sludge to at least one primary process tank, discharging the sludge processed in the primary process tank or tanks to a holding tank, and keeping it in a mixed state in the latter until it is fed to the decanting apparatus.

15. A method according to Claim 13, wherein the processing step comprises at least two stages, including feeding sludge to a process tank, performing the first stage, transferring the sludge processed in the latter into another process tank for the next stage, and so on as required, before delivering the fully processed sludge to the decanting equipment.

16. A method according to Claim 15, including discharging fully or partially processed sludge from a preceding process tank into a holding tank, and keeping it in a mixed state in the latter until it is delivered to the decanting apparatus.

17. A method according to any one of Claims 13 to 16, including feeding some of the recovered reusable fraction back to the raw sludge inlet or inlets, and/or to at least one process tank, for use as "cutter".

18. A method of treating heavy petrochemical residues, substantially as described in the foregoing description with reference to the accompanying drawings.