WO2013002637A1

WO2013002637A1 - Method and apparatus for cleaning tanks

Info

Publication number: WO2013002637A1
Application number: PCT/NL2012/050452
Authority: WO
Inventors: Perry Van Der Bogt
Original assignee: VCS Global Systems BV
Current assignee: VCS Global Systems BV
Priority date: 2011-06-28
Filing date: 2012-06-27
Publication date: 2013-01-03
Anticipated expiration: 2013-12-28
Also published as: NL2007010C2

Abstract

Described are a method and an apparatus for removing hazardous materials from a tank, wherein vapour is passed out of the tank and hazardous materials are condensed and collected. An inert gas or inert gas mixture is supplied to the residual vapour. The obtained mixture of inert gas and residual vapour is heated and passed back to the tank. The cycle is repeated until a desirable level of hazardous material in the tank has been reached. The apparatus comprises a pipe (2) provided with a pump (3), which pipe is connected to a tank (1) and leads to a cooler (4), from the cooler (4) to an inertising system (13) from where the vapour is passed to the tank (1) via a heating system (19), wherein hazardous material condensed from the vapour is passed out of the cooler (4) via a pipe (11) to a reservoir (12).

Description

Method and apparatus for cleaning tanks

The invention relates to a method and an apparatus for cleaning tanks such as storage tanks and ship's tanks, and particularly for removing vapours present in the tank. Usually said tanks are ventilated, especially if hazardous materials, such as benzene, have been present in the tank. Said ventilating is a time-consuming procedure producing vapours that are potentially dangerous to the environment. The emitted gasses are combusted in an incinerator or discharged into the outside air. Said methods are both expensive and detrimental to the environment.

In PCT WO2010/052020 Al an alternative method is described with which vapours of hazardous materials can be removed from a tank. In said method vapour present in a tank is heated. Subsequently the vapour is sucked out of the tank using a pump. Said vapour is subsequently cooled by means of a cooling system. The materials condensed as a result of this cooling down are collected in a reservoir for liquids and the residual vapour is passed back again into the tank. This cycle is then repeated until an acceptable or desired residual level of hazardous material in the tank has been reached. The method described in PCT WO2010/052020 Al is an improvement on previous methods of cleaning and ventilating tanks but nonetheless it has its limitations. Many of the hazardous materials transported in tanks namely are highly flammable. As a result heating the tank often is impossible and/or not allowed. Heating the vapours present entails the risk of ignition and thus an increased risk of explosion. Moreover this method uses relatively much external energy when heating the tank.

The invention described herein avoids the risk of ignition and reduces the required external energy required for cleaning tanks by cleaning a tank in an energy-saving manner and by degassing and inertising a tank in one combined process during the cleaning procedure .

In the method described herein residual material is passed out of a tank in the form of vapour. The vapour is subsequently cooled down. Due to cooling down, a part of the vapour condenses. The liquid components are then collected. An inertising system supplies an inert gas or inert gas mixture to the residual vapour and the overall gas mixture is heated and passed back into the tank. The cycle is repeated until an acceptable or desired residual level of material in the tank has been reached.

This invention thus relates to a method for removing residues of hazardous materials from a tank, wherein

(i) a vapour containing hazardous materials that is present in a tank, is passed out of the tank to a collection unit,

(ii) the vapour in the collection unit is cooled down to a temperature of at least 5°C below the initial temperature and above the melting point or melting range of the hazardous materials to be removed, wherein condensed hazardous materials of the vapour are collected, (iii) an inert gas or inert gas mixture is supplied to the residual vapour,

(iv) the obtained mixture of inert gas and residual vapour is heated to a temperature of at least 5°C above the melting point or melting range of the hazardous materials to be removed,

(v) the heated gas mixture is passed back to the tank, and

(vi) the cycle is repeated and recycling is continued until a desired level of hazardous material in the tank has been reached, and clean vapour is blown off.

In this method it is also possible to supply an inert gas or inert gas mixture to the vapour containing hazardous materials that comes from the tank, prior to it being passed to the collection unit in step (i) .

As heating of vapours present in a tank entails the risk of ignition and thus an increased risk of explosion, heating of vapour takes place as from the end of the first vapour circulation, when the vapour mixture is inert.

Heating the inert residual vapours may take place

(a) immediately after condensation and therefore prior to supply of an inert gas or inert gas mixture to the residual vapour,

(b) after supply of an inert gas or inert gas mixture to the residual vapour, but prior to the inert residual vapour being passed into the tank,

(c) after the inert residual vapour has been passed into the tank.

Preferably heating the inert residual vapours takes place immediately after condensation and therefore prior to supply of an inert gas or inert gas mixture to the residual vapour.

In one embodiment of the method described herein the temperature at which the vapour is cooled down preferably is below the condensation point or condensation range of the hazardous materials to be removed and approximates the condensation point or condensation range of the hazardous materials to be removed as close as possible. The temperature at which the vapour is heated preferably is above the condensation point or condensation range of the hazardous materials to be removed and approximates the condensation point or condensation range of the hazardous materials to be removed as close as possible. This results in the saving of energy. By keeping the difference between the temperature used to condense the vapour and the temperature used to heat the vapour as small as possible, the energy reguired to condense the vapour and to heat the vapour in the tank is limited to a minimum.

It is also possible to apply a second type of energy saving in this method by using the energy released when the vapour cools down in heating the vapour mixture.

In this method a cooling medium such as water or another coolant may be used for cooling the vapour. This medium may also be used for heating the vapour mixture. For these purposes bilge water may for instance be used. Water from the sea or a river may also be pumped up in order to be used as a cooling medium.

In this method, after condensation, the vapour may be passed to a collection unit by using a pump.

In order to prevent that the pressure in the apparatus used in this method becomes too high, residual vapour may be passed out of the system after condensation of the hazardous materials. In order to prevent that this will lead to emission of hazardous materials, the last residues of the hazardous materials may be filtered out of the non-inert residual vapour.

This method renders it possible to remove hazardous materials from a tank to a desired level of hazardous material in one cycle and that in said cycle the tank is also inertised to a desired level. This results in saving time and therefore economic advantage .

The inert gas used in the method according to the invention may be nitrogen, carbon dioxide, helium, neon, argon, krypton, xenon, sulphur hexafluoride , radon or another inert gas, or an inert gas mixture. The inert gas or inert gas mixture is supplied to the above-mentioned residual vapour which after adding the inert gas or inert gas mixture, results in the creation of a gas mixture containing an oxygen content of 5% or less based on volume, wherein the inert gas is the main component. This result is already achieved after one cycle.

In this method it is preferred to use nitrogen as inert gas. Nitrogen is often used in inertising industrial systems and is both harmless and cheap.

In this method the source of the inert gas or inert gas mixture may be a pure or purified gas.

The invention thus also relates to a method wherein the inert gas or inert gas mixture is a purified gas, generated by inertising gas mixtures, particularly air or mixtures with air, present in the tank or pipes. In case of a purified gas it is preferred that the purified gas is generated within the apparatus used in this method. Preferably it is inertised by extracting oxygen by means of for instance an inertising system such as a filter system. In case gas suppletion is desired, the same inertising system may extract oxygen from air supplied from the outside and the resulting inert gas mixture may be introduced into the apparatus used in this method. Adding an external inert gas as described above will not be necessary then.

Another possibility is that the inert gas or inert gas mixture is extracted from the air or from heating systems and cooling systems by inert-gas- generators .

An inertising system, supplying an inert gas or inert gas mixture to the residual vapour may comprise a flue gas installation, a combustion engine, a liquid-nitrogen system, a gas-nitrogen system, an argon system or another system capable of supplying inert gas or an inert gas mixture to the residual vapour in order to inertise the tank.

The invention also relates to an apparatus for removing residues of hazardous materials from a tank, comprising a pipe (2) provided with a pump (3), which pipe is connected to a tank and leads to a cooler (4), from the cooler (4) to a inertising system (13) from where the vapour is passed to the tank (1) via a heating system (19), wherein hazardous material condensed from the vapour may be passed out of the cooler (4) via a pipe (11) to a reservoir (12) . The cooler (4) is suitably provided with a cooling jacket (10) or internally placed cooling radiator, spiral or heat exchanger, in which cooling medium circulates through a pipe (5) via a reservoir (6) for cooling medium and a pipe (7) via a cooling unit (8) and a pipe (9) .

A schematic view of an apparatus of the invention described herein is shown in figure 1, wherein the hazardous vapour described above is sucked out of a tank (1) via a pipe (2) by means of a pump (3) and passed to a cooler (4) . For this cooling system a cooling jacket cooling device could be used. The vapour condensed by the cooling device is passed to a reservoir (12) via a pipe (11) . A cooling unit (8) supplies coolant to a cooling jacket (10) of the cooler (4) via pipe (9), wherein the coolant is passed back via a pipe (5), a coolant reservoir (6) and a pipe (7), to the cooling unit (8) . The residual vapour in the cooler (4) is passed onwards via the pipe (2) to an inertising system (13) as described above, where from an external source (14) via a pipe (15) an inertising gas from the group described above is supplied to the residual vapour. The system offers the possibility to blow vapour to the outside, optionally after filtering, via at least one pipe (16) . Said at least one pipe (16) may be connected to the inertising system (13) and/or pipe (2) and/or be located elsewhere in the apparatus.

There is the possibility to place the inertising system after the tank (1), but before the pump-and-cooling system (3-12).

It is possible to place a filter before, between or after the inertising system for removing the last residues of hazardous materials that are in the residual vapour. Possible residues from the vapour coming from the tank may be removed by placing filter systems such as for instance membrane filter systems (17) before, between or after the inertising system. The inert vapour is subsequently heated by a heating system (19) and passed back to the tank (1) via the pipe ( 2 ) .

There is the possibility to build in a pressure system (18) into the system, which offers the possibility of effecting the supply of inert gas and in that way supplying energy to the pump-and-cooling system (3-12) and the inertising system (13) using one energy source.

The heating system may be placed after the cooler (4) but before the inertising system (13), after the inertising system but before the tank (1), be connected to the tank (1), or be located elsewhere in the apparatus. Preferably the heating system is placed after the cooler (4) but before the inertising system (13) .

The apparatus according to the invention forms a closed system. That means that hazardous materials from the tank cannot leave the apparatus, except when this is desirable, such as when the hazardous materials have to be removed from the reservoir (12) . A "closed system" should furthermore be understood to mean that in such a system supply and discharge of gasses or gas mixtures only takes place when this is desirable.

In order to make the tank suitable for further use, optionally undesirable material may be removed using a scrubber or in another suitable manner.

The method and apparatus according to the invention may be used for cleaning tanks that for instance transport aromatic substances such as benzene, ethanol or other solvents or petroleum or petroleum products, such as gasoline, or palm oil or olive oil.

The method and apparatus according to the invention furthermore offer the possibility of cleaning tanks in a mobile manner at any desired location, without hazardous substances being emitted into the environment. In a preferred embodiment of the invention the apparatus namely is a mobile apparatus comprised in a mobile container, such as a standard shipping container. This may for instance be a 40-foot container. This renders it possible to move the apparatus to the location where a tank needs to be degassed. Such an apparatus may furthermore easily be placed on board a ship such as an oil tanker.

The method according to the invention furthermore offers the advantage that removed hazardous substances that end up in the reservoir (12) may easily be recycled.

The method may also be used in the reduction of odour emission by the vapours present in the tank, which vapours come from materials such as for instance di-hydrogen sulphide and mercaptans.

The invention described herein offers possibilities of variations in and adaptations of the embodiment described above without deviating from the spirit and scope of action and range of application of the invention.

The method described herein works best when for passing the vapour out of the tank a suction pressure or outlet pressure of between 100 and 250 hPa, preferably a suction pressure of 190-210 hPa or an outlet pressure of 140-160 hPa, is set to suck or press, respectively, the vapour out of the tank. The vapour in step (ii) preferably is cooled down to between -10°C and 10°C and the method preferably is carried out at an outside air temperature of -20°C to 40°C and at a controllable gas suction temperature of 0-30°C.

By means of the method and apparatus according to the invention a ventilation capacity of 3000-4000 m³ per hour can be easily be achieved.

Apart from the method and apparatus according to the invention relating to cleaning tanks such as storage tanks and ship's tanks, the invention may also be used in the emission-free transfer of hazardous substances from a tank on a ship to a tank on another ship, transferring hazardous substances from the quayside into a tank of a ship and degassing tank lorries, airplanes or tank wagons.

The invention described herein particularly applies to substances having a melting point that is lower than 6°C, a boiling point that is above 30°C, a self-combustion temperature that is higher than 200 °C and a viscosity that is lower than 5 mPa.s.

The invention described herein among others applies to the removal of the hazardous substances benzene and ethanol. Preferably the initial vapour temperature is between 11 °C and 30°C for benzene and between 9°C and 30°C for ethanol. Benzene preferably is cooled down to a temperature above 6°C, or ethanol is cooled down to a temperature above 4°C. Water may be used as a cooling medium here. Hazardous material condenses in the cooler and is passed to a reservoir. Residual vapour is passed to the inertising system, where an inert gas or an inert gas mixture is supplied. Before, during or after inertising, residual benzene or ethanol may be removed from the residual vapour by a filter system. Inert gas and optionally gas purified from residual benzene or ethanol may be passed back into the tank. The tank is heated using energy released in the cooling process. Water, for instance bilge water, may be used here as heating medium. Recycling is repeated until a desirable level of benzene or ethanol has been reached.

Claims

1. Method for removing residues of hazardous materials from a tank, wherein

(ii) the vapour in the collection unit is cooled down to a temperature of at least 5°C below the initial temperature and above the melting point or melting range of the hazardous materials to be removed, wherein condensed hazardous materials of the vapour are collected,

(iii) an inert gas or inert gas mixture is supplied to the residual vapour,

(iv) the obtained mixture of inert gas and residual vapour is heated to a temperature of at least

5°C above the melting point or melting range of the hazardous materials to be removed,

(v) the heated gas mixture is passed back to the tank, and

2. Method according to claim 1, wherein in one cycle, the hazardous materials are removed from the tank to a desired level of hazardous material and the tank is inertised to a desired level.

3. Method according to claim 1 or 2, wherein the residual vapour, after the supply of the inert gas or the inert gas mixture, after one cycle contains an oxygen content of 5% or less based on volume.

4. Method according to any one of the claims

1-3, wherein the temperature in step (ii) is below the condensation point or condensation range of the hazardous materials to be removed and approximates the condensation point or condensation range of the hazardous materials to be removed as close as possible.

5. Method according to any one of the claims 1-4, wherein heating in step (iv) takes place immediately after condensation and therefore prior to supplying an inert gas or inert gas mixture to the residual vapour.

6. Method according to any one of the claims 1-5, wherein the temperature in step (iv) is above the condensation point or condensation range of the hazardous materials to be removed and approximates the condensation point or condensation range of the hazardous materials to be removed as close as possible.

7. Method according to any one of the claims 1-6, wherein, in order to pass the vapour out of the tank in step (i) , a suction pressure or outlet pressure of between 100 and 250 hPa, preferably a suction pressure of 190-210 hPa or an outlet pressure of 140- 160 hPa, is set to suck or press, respectively, the vapour out of the tank, and wherein the vapour in step (ii) is cooled down to between -10°C and 10°C, wherein the method is carried out at an outside air temperature of -20°C to 40°C and at a controllable gas suction temperature of 0-30°C.

8. Method according to any one of the claims 1-7, wherein the vapour comprises one or several of the substances from the following group: benzene, ethanol, a solvent, one or several components of petroleum or petroleum products such as gasoline, one or several components of palm oil, one or several components of olive oil, di-hydrogen sulphide, mercaptans .

9. Method according to any one of the claims 1-8, wherein the vapour contains benzene.

10. Method according to claim 9, wherein the vapour in step (ii) is cooled down to a temperature above 6°C.

11. Method according to any one of the claims 9 and 10, wherein the vapour in step (iv) is heated to between 11°C and 30°C.

12. Method according to any one of the claims 1-8, wherein the vapour contains ethanol.

13. Method according to claim 12, wherein the vapour in step (ii) is cooled down to a temperature above 4°C.

14. Method according to any one of the claims 12-13, wherein the vapour in step (iv) is heated to between 9°C and 30°C.

15. Method according to any one of the claims 1-14, wherein the inert gas or inert gas mixture is a purified gas, generated by inertising gas mixtures, particularly air or mixtures with air, present in the tank or pipes.

16. Method according to claim 15, wherein the inertising takes place by extracting oxygen.

17. Method according to claim 1-14, wherein the inert gas or inert gas mixture that is supplied to the residual vapour is selected from the group consisting of nitrogen, carbon dioxide, helium, neon, argon, krypton, sulphur hexafluoride , radon or another inert gas .

18. Method according to claim 17, wherein the inert gas is nitrogen.

19. Method according to any one of the claims 1-18, wherein the vapour in step (iv) is heated using energy that is released at cooling down the vapour in step ( ii ) .

20. Method according to any one of the claims 1-19, wherein after condensation of the hazardous materials residual vapour is passed out of the system.

21. Method according to claim 20, wherein last residues of the hazardous materials are filtered out of the residual vapour.

22. Apparatus for removing residues of hazardous materials from a tank, comprising a pipe (2) provided with a pump (3), which pipe is connected to a tank and leads to a cooler (4), from the cooler (4) to a inertising system (13) from where the vapour is passed to the tank (1) via a heating system (19), wherein hazardous material condensed from the vapour is passed out of the cooler (4) via a pipe (11) to a reservoir (12) .

23. Apparatus according to claim 22, wherein the heating system is placed after the cooler (4) but before the inertising system (13) .

24. Apparatus according to claim 22 and 23, wherein the cooler (4) is provided with a cooling jacket (10) in which cooling medium circulates through a pipe (5) via a reservoir (6) for cooling medium and a pipe (7) via a cooling unit (8) and a pipe (9) .

25. Apparatus according to any one of the claims 22-24, wherein the inertising system (13) is selected from the group of: a flue gas installation, a combustion engine, a liquid-nitrogen system, a gas- nitrogen system, an argon system or another system capable of supplying inert gas or an inert gas mixture to the residual vapour, and wherein the inert gas source is air out of which inert gas is produced, or another medium out of which inert gas is delivered.

26. Apparatus according to any one of the claims 22-25, wherein a filter system (17) is placed before, between or after the inertising system (13) .

27. Apparatus according to any one of the claims 22-26, wherein the filter system (17) is a membrane system.

28. Apparatus according to any one of the claims 22-27, wherein the inertising system (13) comprises the possibility of blowing vapour to the outside via at least one pipe (16) .

29. Apparatus according to any one of the claims 22-28, wherein a pressure system is placed after the pump (3) and before the inertising system (13) .

30. Apparatus according to any one of the claims 22-29, wherein the pressure system makes it possible to let the pump-and-cooling system (3-12) and the inertising system (13) function on one energy source, wherein the energy source provides the pump- and-cooling system (3-12) and the pressure system (18) with energy and wherein the pressure differences created by the pressure system drive the inertising system ( 13 ) .

31. Apparatus according to any one of the claims 22-30, wherein the apparatus is a mobile apparatus .

32. Apparatus according to any one of the claims 22-31, wherein the apparatus forms a closed system.