|
(11) | EP 0 885 365 B1 |
| (12) | EUROPEAN PATENT SPECIFICATION |
|
|
| (54) |
METHOD IN THE UTILIZATION OF BOIL-OFF FROM LIQUID GAS AND APPARATUS FOR CARRYING OUT THE METHOD METHODE ZUR VERWENDUNG DES VERDAMPFTEN ANTEILS VON FLÜSSIGGAS UND VORRICHTUNG ZUR DURCHFÜHRUNG DER METHODE PROCEDE D'UTILISATION DE GAZ EVAPORES PROVENANT DE GAZ LIQUIDES ET APPAREIL DE MISE EN OEUVRE DE CE PROCEDE |
|
|
|||||||||||||||||||||||||||||||
| Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). |
[0001] The invention relates to a method of utilising boil-off from liquefied gas as fuel gas in combination with gas produced by vaporising the liquefied gas.
[0002] The invention also relates to a plant for carrying out said method, wherein boil-off and vaporised liquefied gas are transported together to a consumer, comprising a storage tank for liquefied gas, a draw-off line for boil-off from the storage tank, a pump with attached draw-off line for liquefied gas from the storage tank, and a combined heat exchanger having two separate flow banks in a common surrounding shell, where one bank is connected to the draw-off line for liquefied gas for vaporisation thereof and the other bank is connected to the draw-off line for boil-off, which banks open into a common mixing chamber, which is connected to a flowline leading to the consumer.
[0003] WO 94 17 325 makes known a method for utilising boil-off from liquefied gas as fuel gas in combination with gas produced by vaporising the liquefied gas, wherein boil-off and vaporised gas are brought together and compressed, and where the boil-off and the liquefied gas prior to compression are superheated and vaporised, respectively, each in its respective section in a combined heat exchanger, and brought together in a common mixing chamber.
[0004] The same publication also makes known a plant wherein boil-off and vaporised gas are brought together and compressed. The plant comprises a storage tank for liquefied gas, draw-off lines for boil-off and liquefied gas, respectively, from the storage tank, and a combined heat exchanger having two separate flow banks in a common surrounding shell. One of the flow banks is connected to the liquefied gas draw-off line, whilst the other flow pipe bank is connected to the boil-off draw-off line. The flow banks open into a common mixing chamber, which is connected to a flowline leading to a consumer.
[0005] One advantage obtained with the above-mentioned known art is that both the method and the plant are simplified, it being possible to dispense with an otherwise customarily used separator, because the suction temperature of the compressor will be considerably higher, and nor does the compressor need to be cryogenic. A disadvantage of this prior art is that the compressor must necessarily carry the total volume of gas, i.e., both the natural boil-off and vaporised gas.
[0006] The objective of the present invention is to provide a method and a plant as mentioned by way of introduction, wherein the advantages of the prior art from WO 94 17 325 are retained, whilst simplifying the plant even further.
[0007] This is achieved according to the invention by a method as mentioned above, wherein the boil-off is compressed and passed to heat exchange with the liquefied gas, and is subsequently mixed with the liquefied gas vaporised during the heat exchange.
[0008] By virtue of the fact that the compression takes place prior to the heat exchange and that only the boil-off is compressed, the advantage is obtained that the compression applies only to the volume of boil-off and not the total volume of gas. This results in reduced power requirements and simpler capacity control.
[0009] According to the invention, a plant is also proposed as mentioned above, which plant is characterised in that a compressor is provided in the boil-off draw-off line before the combined heat exchanger.
[0010] By placing the compressor in the boil-off line upstream of the heat exchanger, the compressor only needs to carry the boil-off volume and not the total volume of gas. The compressor will have to be constructed to work with gas at temperatures as low as - 140°C when LNG is involved, but this disadvantage will be more than compensated for by the advantages obtained, namely that the compressor in terms of size will be more compact, have reduced power requirements, a smaller working area and simpler capacity control. An additional advantage is that the combined heat exchanger will be capable of being dimensioned for a higher pressure drop, which will result in reduced shell dimensions and lower production costs. It is thus only the choice of material for the compressor which tends to be unfavourable, but as mentioned this disadvantage is cancelled out as a result of the compressor being made more compact.
[0011] The invention will now be explained in more detail with reference to the drawing which is a schematic illustration of a plant according to the invention.
[0012] On the figure the reference numeral 1 denotes a storage tank for liquefied gas, for example, an LNG tank on board a LNG ship. As a result of heat penetration from the surroundings, so-called boil-off will be produced. This accumulates in the dome 2 of the storage tank 1 and can be withdrawn through a boil-off draw-off line 3. This draw-off line 3 runs to a compressor 4. In the compressor 4 the boil-off is compressed, with attendant rise in temperature. From the compressor, the compressed boil-off passes to a combined heat exchanger 9.
[0013] The boil-off is used as fuel gas in the propulsion engine of the ship. The plant is such that if the boil-off is not sufficient, i.e., larger amounts of fuel gas are required than the boil-off can supply, liquefied natural gas is withdrawn with the aid of a pump 11, and led through a draw-off line 10 to the combined heat exchanger 9.
[0014] The combined heat exchanger 9 has separate flow banks 7 and 8 for liquefied gas and boil-off, respectively. The liquefied gas and the boil-off are heat exchanged with an external hot flow, indicated by mean of the arrow in the figure. This flow, which in most cases will be vapour, is conducted from the shell side of the heat exchanger.
1. A method for utilising boil-off from liquified gas as fuel gas in combination with
gas produced by vaporising the liquified gas, wherein the boil-off is passed to heat
exchange with an external hot medium flow together with the liquified gas, said boil-off
and said liquified gas vaporised during said heat exhange thereafter being mixed to
form fuel gas, characterised in that the bail-off is compressed before being heated and mixed with the vaporised liquefied
gas.
2. A plant for carrying out the method according to claim 1, wherein boil-off and vaporised
liquefied gas are transported together to a consumer, comprising a storage tank (1)
for liquefied gas, a draw-off line (3) for boil-off from the storage tank (1), a pump
(11) with draw-off line (10) attached thereto for liquefied gas from the storage tank
(1), and a combined heat exchanger (9) having two separate flow banks (7, 8) in a
common surrounding shell, where one flow bank (7) is connected to the liquefied gas
draw-off line (10) and the second flow-through unit (8) is connected to the boil-off
draw-off line (3), which flow banks open into a common mixing chamber (6) which is
connected to a flowline (5) to the consumer, said combined heat exchanger (9) having
flow connection with a supply of hot flow medium for conducting said hot flow medium
on the shell side of said heat exchanger (9), characterized in that a compressor (4) is provided in the boil-off draw-off line (3) before the combined
heat exchanger (9).
1. Verfahren zur Verwendung von Abdampf aus Flüssiggas als Brenngas in Kombination mit
Gas, das durch Verdampfen des Flüssiggases erzeugt wurde, wobei der Abdampf zum Wärmetausch
mit einer externen Heißmediumströmung zusammen mit dem Flüssiggas geführt wird und
der Abdampf und das Flüssiggas, das während dem Wärmetausch verdampft wurde, danach
gemischt werden, um das Brenngas zu bilden, dadurch gekennzeichnet, dass der Abdampf, bevor er erwärmt wird und mit dem verdampften Flüssiggas gemischt wird,
komprimiert wird.
2. Anlage zum Ausführen des Verfahrens nach Anspruch 1, wobei Abdampf und verdampftes
Flüssiggas zusammen zu einem Verbraucher gefördert werden, umfassend einen Speicherbehälter
(1) für das Flüssiggas, eine Absaugleitung (3) für Abdampf aus dem Speicherbehälter
(1), eine Pumpe (11) mit einer Absaugleitung (10) für das Flüssiggas aus dem Speicherbehälter
(1), die daran angebracht ist, und einen kombinierten Wärmetauscher (9) mit zwei separaten
Strömungskrümmungen (7, 8) in einer gemeinsamen umgebenden Hülle, wobei eine Strömungskrümmung
(7) mit der Flüssiggasabsaugleitung (10) verbunden ist und die zweite Durchströmeinheit
(8) mit der Abdampfabsaugleitung (3) verbunden ist, wobei die Strömungskrümmungen
sich in eine gemeinsame Mischkammer (6) öffnen, die mit einer Strömungsleitung (5)
zu dem Verbraucher verbunden ist, wobei der kombinierte Wärmetauscher (9) eine Strömungsverbindung
mit einer Zufuhr eines heißen Strömungsmediums zum Leiten des heißen Strömungsmediums
auf die Umhüllungsseite des Wärmetauschers (9) aufweist, dadurch gekennzeichnet, dass in der Abdampfabsaugleitung (3) vor dem kombinierten Wärmetauscher (9) ein Kompressor
(4) vorgesehen ist.
1. Procédé pour utiliser le gaz d'évaporation d'un gaz liquide comme gaz combustible
en combinaison avec le gaz produit par vaporisation du gaz liquide, dans lequel le
gaz d'évaporation est passé pour échanger de la chaleur avec un courant d'un milieu
extérieur chaud ensemble avec le gaz liquéfié, ledit gaz d'évaporation et ledit gaz
liquéfié vaporisé durant ledit échange étant ensuite mélangés pour former le gaz combustible,
caractérisé en ce que le gaz d'évaporation est comprimé avant d'être chauffé et mélangé avec le gaz liquide
vaporisé.
2. Installation pour mettre en oeuvre le procédé selon la revendication 1, dans laquelle
le gaz d'évaporation et le gaz liquide vaporisé sont transportés ensembles vers un
utilisateur, comprenant un réservoir de stockage (1) pour gaz liquéfié, une conduite
de soutirage (3) pour le gaz d'évaporation à partir du réservoir de stockage (1),
une pompe (11) avec une conduite de soutirage (10) reliée à celle-ci pour soutirer
le gaz liquéfié à partir du réservoir de stockage (1) et un échangeur thermique combiné
(9) ayant deux faisceaux de circulation séparés (7, 8) contenus dans une enveloppe
commune, dans laquelle l'un des faisceaux de circulation (7) est connecté à la conduite
de soutirage du gaz liquéfié (10) et la deuxième faisceau de circulation (8) est connectée
à la conduite de soutirage du gaz d'évaporation (3), lesquels faisceaux de circulation
débouchent dans une chambre de mélange commune (6) qui est connectée à une conduite
(5) de distribution à l'utilisateur, ledit échangeur thermique combiné (9) étant connecté
à une alimentation en un courant d'un milieu chaud pour conduire ledit courant de
milieu chaud sur l'enveloppe dudit échangeur de chaleur (9), caractérisé en ce qu'un compresseur (4) est disposé sur la ligne de soutirage du gaz évaporé (3) avant
l'échangeur thermique combiné (9).