WO1985003922A1 - Procedure for preventing hydrocarbon emission from rock cisterns - Google Patents

Procedure for preventing hydrocarbon emission from rock cisterns Download PDF

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Publication number
WO1985003922A1
WO1985003922A1 PCT/FI1984/000022 FI8400022W WO8503922A1 WO 1985003922 A1 WO1985003922 A1 WO 1985003922A1 FI 8400022 W FI8400022 W FI 8400022W WO 8503922 A1 WO8503922 A1 WO 8503922A1
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WO
WIPO (PCT)
Prior art keywords
cistern
rock
heated
liquid
conducted
Prior art date
Application number
PCT/FI1984/000022
Other languages
French (fr)
Inventor
Juha Jakkula
Markku Hurme
Esko Koskinen
Original Assignee
Neste Oy
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Neste Oy filed Critical Neste Oy
Priority to PCT/FI1984/000022 priority Critical patent/WO1985003922A1/en
Publication of WO1985003922A1 publication Critical patent/WO1985003922A1/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
    • B65G—TRANSPORT OR STORAGE DEVICES, e.g. CONVEYORS FOR LOADING OR TIPPING, SHOP CONVEYOR SYSTEMS OR PNEUMATIC TUBE CONVEYORS
    • B65G5/00—Storing fluids in natural or artificial cavities or chambers in the earth
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
    • B65D—CONTAINERS FOR STORAGE OR TRANSPORT OF ARTICLES OR MATERIALS, e.g. BAGS, BARRELS, BOTTLES, BOXES, CANS, CARTONS, CRATES, DRUMS, JARS, TANKS, HOPPERS, FORWARDING CONTAINERS; ACCESSORIES, CLOSURES, OR FITTINGS THEREFOR; PACKAGING ELEMENTS; PACKAGES
    • B65D90/00—Component parts, details or accessories for large containers
    • B65D90/22—Safety features
    • B65D90/30—Recovery of escaped vapours

Definitions

  • the present invention concerns a procedure for inhibiting hydrocarbon emission when liquid hydrocarbons with high vapour pressure are stored in rock cisterns.
  • Rock cisterns have been used for storing, for instance, crude oil, heavy fuel oil, middle fractions, petrol and LP gas. From the increasing difficulties in obtaining crude oil and from its price increase has resulted a need to increase the storage facilities. Rock cisterns are eminently suited for storing large quantities of liquids, and among their advantages may be mentioned their favourable price, safety, environment-benignity and unobtrusiveness.
  • rock cisterns have a fixed roof
  • the methods applied to counteract losses in conventional tanks or cisterns, such as floating roofs cannot be used.
  • the evaporating hydrocarbons constitute the lightest and most valuable part of the crude oil.
  • the air conservation legislation in some countries restricts emissions of hydrocarbons into the atmosphere and implies the use either of a floating roof or a vent gas processing plant.
  • the hydrocarbons in the vent gases may form explosive mixtures with air and thereby give rise to a safety hazard.
  • the invention concerns the storing of liquid hydrocarbons at the normal operating temperature of the cistern. If no emissions at all are permitted, the valves of the cistern could be kept completely closed. In that case, however, the cistern cannot be filled to capacity because the pressure in the air space of the cistern would become too high. The cistern would thus contain "empty" non-disposable space, which increases the construction costs.
  • the present invention concerns a procedure by the aid of which liquid hydrocarbons with high vapour pressure can be stored In rock cisterns without incurring hydrocarbon emissions during the filling or emptying of the cisterns. Hereby, no vent gas recovery or burning installations are required either.
  • One object of the invention is to achieve a procedure in which the whole capacity of the cistern can be made usable.
  • the procedure of the invention for preventing hydrocarbon emissions when liquids with high vapour pressure are stored in rock cisterns is characterized in that the rock cistern is kept completely closed both during withdrawal and during filling, and that when emptying the cistern the pressure in the gas space is elevated by heating.
  • the cistern is kept entirely airless. It is then possible to fill the cistern to capacity, as all vapour condenses to liquid. In this way, the procedure of the invention also improves the safety of storing because no explosive hydrocarbon mixtures occur.
  • the air can be best evacuated from the cistern for instance in connection with the first filling by filling the cistern to its complete capacity with the liquid to be stored.
  • the requirements imposed by a rock cistern imply that at least 50 kPa pressure is maintained in the cistern.
  • the vapour pressure at normal storing temperature (about 20oC) of the liquids being stored is, however, lower than this value. Therefore, the surface interacting with the gas space has to be heated to a temperature at which its vapour pressure is at least 50 kPa.
  • the gas space also has to be kept at this temperature so that condensation might not reduce the vapour pressure.
  • the pressurizing by heating according to the invention is suitable for liquids with high vapour pressure. The heating requirements and the temperature of the gas space are reasonable with such liquids.
  • Crude oil is a typical liquid to be stored in rock cisterns having high vapour pressure and which is stored in great quantities in rock cisterns. At the same time, even great variations in quantity may occur when big tankers unload their cargo into the rock cistern.
  • Petrol is another typical liquid with high vapour pressure, for the storing of which In a rock cistern the invention Is appropriate.
  • the heating during emptying of the cistern may be carried out in various ways. It is possible to heat the surface layer of the cistern in the cistern itself or outside the cistern. In the first case, one or several means or members have to be disposed in the cistern which heat the surface layer in the cistern.
  • a means of such kind may, for instance, be an electric heater or a pipe coil containing a heated fluid.
  • Another method, and which is easier to provide is to conduct a small part of the liquid being discharged from the cistern to be heated outside the cistern and to be returned into the upper part of the cistern.
  • the heating is carried out advantageously utilizing conventional heat exchanger elements.
  • the heated liquid is preferably returned into the air space of the top part of the cistern by means of injection pipes.
  • Fig. 1 presents schematically the rock cistern used for storing crude oil in an advantageous embodiment of the procedure of the Invention.
  • Fig. 2 presents schematically the rock cistern used for storing crude oil in another embodiment of the procedure of the invention.
  • crude oil is continuously pumped through the pump 12 and pipe 13 into a feed tank (not depicted). Part of this flow is circulated through the pipe 14 and the heat exchanger 15 back to the rock cistern 11.
  • the hot crude oil is injected into the rock cistern 11 through injection pipes 16 in the roof, whereat part of the liquid evaporates.
  • hydrocarbons may also be conducted by the pipe 18 into the rock cistern 11 from another cistern (not depicted).
  • hydrocarbons are conducted from the other cistern along a pipeline 18 through the heat exchanger 15 into the rock cistern 11.
  • heated hydrocarbons from another cistern may be conducted by a pipeline 18' directly into the rock cistern 11.
  • FIG. 2 The embodiment shown in Fig. 2 is otherwise the same as the embodiment of Fig. 1, except that in the embodiment of Fig. 2 a second pump 19 has been disposed to pump a liquid flow from the surface layer by the pipeline 20 to the heat exchanger 15, and from the heat exchanger 15 by the pipeline 14 back into the rock cistern 11.
  • the pipeline 20 may, of course, lead to a heat exchanger 15 other than the heat exchanger 15 shown in Figs 1 and 2, and this liquid flow may accordingly have its own return line to the rock cistern 11.
  • the cistern 11 is filled to capacity, whereby the air departs from the cistern.
  • the air valves are then closed and one starts to heat the surface, at the same time circulating crude oil through the heat exchanger 15 in the manner just described while crude oil is being pumped out from the cistern 11.
  • a layer of light hydrocarbons is established on the surface of the crude oil.

Landscapes

  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Environmental & Geological Engineering (AREA)
  • General Life Sciences & Earth Sciences (AREA)
  • Geology (AREA)
  • Filling Or Discharging Of Gas Storage Vessels (AREA)

Abstract

A procedure for preventing hydrocarbon emissions when liquid hydrocarbons with high vapour pressure are stored in rock cisterns (11). The rock cistern (11) is kept completely closed during withdrawal as well as filling. When the cistern (11) is emptied, the pressure in the gas space is elevated by heating. The surface layer of the liquid in the cistern (11) is heated, and heated hydrocarbons are conducted into the cistern (11). When the cistern is emptied, part of the liquid flow is conducted to a heat exchanger (15), in which it is heated, and conducted back into the cistern (11). From the surface layer of the liquid in the cistern (11) a liquid flow is pumped to the heat exchanger (15), where it is heated, and conducted back into the gas space (17) of the cistern (11).

Description

Procedure for preventing hydrocarbon emission from rock cisterns
The present invention concerns a procedure for inhibiting hydrocarbon emission when liquid hydrocarbons with high vapour pressure are stored in rock cisterns.
Rock cisterns have been used for storing, for instance, crude oil, heavy fuel oil, middle fractions, petrol and LP gas. From the increasing difficulties in obtaining crude oil and from its price increase has resulted a need to increase the storage facilities. Rock cisterns are eminently suited for storing large quantities of liquids, and among their advantages may be mentioned their favourable price, safety, environment-benignity and unobtrusiveness.
Since, rock cisterns have a fixed roof, the methods applied to counteract losses in conventional tanks or cisterns, such as floating roofs, cannot be used. There are many reasons for the efforts at loss prevention. First may be mentioned the economic losses from incurred hydrocarbon evaporation losses. In addition, the evaporating hydrocarbons constitute the lightest and most valuable part of the crude oil. Secondly, the air conservation legislation in some countries restricts emissions of hydrocarbons into the atmosphere and implies the use either of a floating roof or a vent gas processing plant. Thirdly, the hydrocarbons in the vent gases may form explosive mixtures with air and thereby give rise to a safety hazard.
It is impossible to construct a floating roof in rock cisterns, and therefore the elimination of losses has made it necessary to resort to vent gas processing. No recovery equipment with adequate capacity has been available; the other processing alternative, i.e., burning involves rather foolish use of a valuable raw material. In the storing of hydrocarbons, emissions from the cistern can be prevented by keeping the air valves closed. When the cistern is being filled, the pressure increases and the vapour in the air condenses, thereby counteracting the increase of overall pressure. When the cistern is emptied, the pressure correspondingly goes down, and evaporation ensues. This penomenon counteracts the decrease of overall pressure.
The storing of hydrocarbons under pressure in an enclosed volume is known in itself in prior art in connection with storing LP gases. In that case the storing of gaseous hydrocarbons at the normal operating temperature of the cistern under a pressure of such height is concerned that the greater part of the gas remains in liquid form. No heating is used.
The invention concerns the storing of liquid hydrocarbons at the normal operating temperature of the cistern. If no emissions at all are permitted, the valves of the cistern could be kept completely closed. In that case, however, the cistern cannot be filled to capacity because the pressure in the air space of the cistern would become too high. The cistern would thus contain "empty" non-disposable space, which increases the construction costs.
If minor emissions are allowed, air could be let out of the cistern towards the end of the filling process, and similarly air could be let in when the cistern is completely emptied, in order to keep the pressure within allowable limits. The advantage is that the cistern can be utilized to capacity, while drawbacks are the increased hydrocarbon emissions or the compulsory use of recovery or burning equipment.
The present invention concerns a procedure by the aid of which liquid hydrocarbons with high vapour pressure can be stored In rock cisterns without incurring hydrocarbon emissions during the filling or emptying of the cisterns. Hereby, no vent gas recovery or burning installations are required either. One object of the invention is to achieve a procedure in which the whole capacity of the cistern can be made usable.
The procedure of the invention for preventing hydrocarbon emissions when liquids with high vapour pressure are stored in rock cisterns is characterized in that the rock cistern is kept completely closed both during withdrawal and during filling, and that when emptying the cistern the pressure in the gas space is elevated by heating.
By the procedure of the invention, the advantages of full pressurizing are achieved without the drawbacks normally associated therewith when the level in the cistern varies. When withdrawing, the gas volume in the cistern is heated, whereby the pressure increases, making up for the loss of pressure caused by the falling of the level. When the cistern is being filled, the vapours in the gas space will condense, thus counteracting the pressure increase caused by the rising of the level.
As taught by an advantageous embodiment of the invention, the cistern is kept entirely airless. It is then possible to fill the cistern to capacity, as all vapour condenses to liquid. In this way, the procedure of the invention also improves the safety of storing because no explosive hydrocarbon mixtures occur. The air can be best evacuated from the cistern for instance in connection with the first filling by filling the cistern to its complete capacity with the liquid to be stored.
The requirements imposed by a rock cistern imply that at least 50 kPa pressure is maintained in the cistern. The vapour pressure at normal storing temperature (about 20ºC) of the liquids being stored is, however, lower than this value. Therefore, the surface interacting with the gas space has to be heated to a temperature at which its vapour pressure is at least 50 kPa. The gas space also has to be kept at this temperature so that condensation might not reduce the vapour pressure. The pressurizing by heating according to the invention is suitable for liquids with high vapour pressure. The heating requirements and the temperature of the gas space are reasonable with such liquids. Crude oil is a typical liquid to be stored in rock cisterns having high vapour pressure and which is stored in great quantities in rock cisterns. At the same time, even great variations in quantity may occur when big tankers unload their cargo into the rock cistern. Petrol is another typical liquid with high vapour pressure, for the storing of which In a rock cistern the invention Is appropriate.
The heating during emptying of the cistern may be carried out in various ways. It is possible to heat the surface layer of the cistern in the cistern itself or outside the cistern. In the first case, one or several means or members have to be disposed in the cistern which heat the surface layer in the cistern. A means of such kind may, for instance, be an electric heater or a pipe coil containing a heated fluid. Another method, and which is easier to provide, is to conduct a small part of the liquid being discharged from the cistern to be heated outside the cistern and to be returned into the upper part of the cistern. The heating is carried out advantageously utilizing conventional heat exchanger elements. The heated liquid is preferably returned into the air space of the top part of the cistern by means of injection pipes.
The invention is described in detail, referring to certain advantageous embodiments of the invention, presented in the figures of the drawing attached, but to which the invention is not meant to be exclusively confined.
Fig. 1 presents schematically the rock cistern used for storing crude oil in an advantageous embodiment of the procedure of the Invention.
Fig. 2 presents schematically the rock cistern used for storing crude oil in another embodiment of the procedure of the invention. From the rock cistern 11 of Fig. 1, crude oil is continuously pumped through the pump 12 and pipe 13 into a feed tank (not depicted). Part of this flow is circulated through the pipe 14 and the heat exchanger 15 back to the rock cistern 11. The hot crude oil is injected into the rock cistern 11 through injection pipes 16 in the roof, whereat part of the liquid evaporates.
In the procedure of the invention, hydrocarbons may also be conducted by the pipe 18 into the rock cistern 11 from another cistern (not depicted). In this embodiment, hydrocarbons are conducted from the other cistern along a pipeline 18 through the heat exchanger 15 into the rock cistern 11. Alternatively, heated hydrocarbons from another cistern may be conducted by a pipeline 18' directly into the rock cistern 11.
The embodiment shown in Fig. 2 is otherwise the same as the embodiment of Fig. 1, except that in the embodiment of Fig. 2 a second pump 19 has been disposed to pump a liquid flow from the surface layer by the pipeline 20 to the heat exchanger 15, and from the heat exchanger 15 by the pipeline 14 back into the rock cistern 11. The pipeline 20 may, of course, lead to a heat exchanger 15 other than the heat exchanger 15 shown in Figs 1 and 2, and this liquid flow may accordingly have its own return line to the rock cistern 11.
At first filling, the cistern 11 is filled to capacity, whereby the air departs from the cistern. The air valves are then closed and one starts to heat the surface, at the same time circulating crude oil through the heat exchanger 15 in the manner just described while crude oil is being pumped out from the cistern 11. Hereby a layer of light hydrocarbons is established on the surface of the crude oil.

Claims

Claims
1. A procedure for preventing hydrocarbon emissions when liquid hydrocarbons with high vapour pressure are stored in rock cisterns (11), characterized in that the rock cistern (11) is kept completely closed during both withdrawing and filling, and that when cistern (11) is emptied, the pressure in the gas space is elevated by heating.
2. A procedure according to claim 1, characterized in that the surface layer of the liquid in the cistern (11) is heated.
3. A procedure according to claim 1, characterized in that heated hydrocarbons are conducted into the cistern (11).
4. A procedure according to claim 1,2 or 3, characterized in that when the cistern (11) Is emptied part of the liquid flow is conducted to a heat exchanger (15), In which it is heated, and conducted back into the cistern (11).
5. A procedure according to claim 3 or 4, characterized in that the heated hydrocarbons are conducted into the gas space (17) of the cistern (11).
6. A procedure according to claim 1,2 or 3, characterized in that from the surface layer of the liquid in the cistern (11) a liquid flow is pumped to the heat exchanger (15), where it is heated, and conducted back into the gas space (17) of the cistern. (11).
7. A procedure according to claim 1 or 2, characterized in that heating Is carried out by the aid of a heating coil placed in the cistern (11).
8. A procedure according to any one of the preceding claims, characterized in that the gas space (17) of the cistern (11) is maintained airless.
9. A procedure according to any one of the preceding claims, characterized in that when the cistern (11) is taken into use it is filled to capacity, whereby the air is removed.
PCT/FI1984/000022 1984-03-06 1984-03-06 Procedure for preventing hydrocarbon emission from rock cisterns WO1985003922A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
PCT/FI1984/000022 WO1985003922A1 (en) 1984-03-06 1984-03-06 Procedure for preventing hydrocarbon emission from rock cisterns

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/FI1984/000022 WO1985003922A1 (en) 1984-03-06 1984-03-06 Procedure for preventing hydrocarbon emission from rock cisterns

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WO1985003922A1 true WO1985003922A1 (en) 1985-09-12

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0609696A1 (en) * 1993-01-30 1994-08-10 SOLVAY SALZ GmbH Method of discharging brine with simultaneous pneumatic support of salt caverns

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR846543A (en) * 1938-05-27 1939-09-19 Thermal process to reduce losses, by evaporation, of volatile liquids in storage
DE685425C (en) * 1936-09-08 1939-12-18 August Spannagel Dipl Ing Process for storing volatile and / or flammable liquids in tanks
SE302141B (en) * 1964-03-02 1968-07-08 Conch Int Methane Ltd
DK113202B (en) * 1965-03-10 1969-02-24 Shell Int Research Method for underground storage of a liquid medium in an underground container as well as underground plant for use in this method.
SE318527B (en) * 1967-06-30 1969-12-08 Skanska Cementgjuteriet Ab
SE339659B (en) * 1969-11-14 1971-10-11 Skanska Cementgiuteriet Ab
DE2734428C2 (en) * 1976-07-30 1984-03-22 Gosudarstvennyj proektno-konstruktorskij institut po proektirovaniju technologii montaža legkoj i piščevoj promyšlennosti, Moskva Containers for storing liquids

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE685425C (en) * 1936-09-08 1939-12-18 August Spannagel Dipl Ing Process for storing volatile and / or flammable liquids in tanks
FR846543A (en) * 1938-05-27 1939-09-19 Thermal process to reduce losses, by evaporation, of volatile liquids in storage
SE302141B (en) * 1964-03-02 1968-07-08 Conch Int Methane Ltd
DK113202B (en) * 1965-03-10 1969-02-24 Shell Int Research Method for underground storage of a liquid medium in an underground container as well as underground plant for use in this method.
SE318527B (en) * 1967-06-30 1969-12-08 Skanska Cementgjuteriet Ab
SE339659B (en) * 1969-11-14 1971-10-11 Skanska Cementgiuteriet Ab
DE2734428C2 (en) * 1976-07-30 1984-03-22 Gosudarstvennyj proektno-konstruktorskij institut po proektirovaniju technologii montaža legkoj i piščevoj promyšlennosti, Moskva Containers for storing liquids

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0609696A1 (en) * 1993-01-30 1994-08-10 SOLVAY SALZ GmbH Method of discharging brine with simultaneous pneumatic support of salt caverns

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