WO2021081985A1

WO2021081985A1 - Vaporizer for vaporization of liquefied gases and method of vaporizing liquefied gas

Info

Publication number: WO2021081985A1
Application number: PCT/CN2019/115021
Authority: WO
Inventors: David De Nardis; Neil Wilson
Original assignee: Cryostar Sas
Priority date: 2019-11-01
Filing date: 2019-11-01
Publication date: 2021-05-06
Also published as: EP4051947A1; KR20220087405A; CN113924438A; WO2021083547A1; WO2021083547A9

Abstract

A vaporizer unit (200) for vaporizing a liquefied gas comprising a plurality of inlet compartments (211, 213), separated from each other, each inlet compartment (211, 213) being in fluid connection with a plurality of conduits (211a-f; 213a-d) for conducting liquefied gas through the vaporizer (200) for vaporization, a common discharge compartment (220), said discharge compartment (220) being in fluid connection with the conduits (211a-f; 213a-d) of said plurality of inlet compartments (211, 213) for discharging vaporized liquefied gas, and an inner vaporizer unit space (230), wherein the conduits (211a-f; 213a-d) are at least partly arranged, the inner vaporizer unit space (230) being configured to effect heat transfer to the liquefied gas in the conduits (211a-f; 213a-d).

Description

Vaporizer for vaporization of liquefied gases and method of vaporizing liquefied gas

Description

The present invention relates to a vaporizer unit for vaporizing a liquefied gas and a corresponding method of vaporizing a liquefied gas. More particularly, the present invention is related to vaporizing a liquefied gas like liquefied natural gas (LNG) or other cryogenic liquids, like Liquid Nitrogen, or liquid mixtures.

Related Prior Art

While natural gas (NG) is conveniently stored and transported in liquid state, it is generally used, however, in the gaseous state, e.g. for propulsion of ocean-going tankers or other on shore applications this end, a flow of LNG can be vaporized and/or boil-off gas, i.e. evaporated LNG from the ullage space of the container can be used. Typically, such vaporized gas is supplied from the source of liquefied gas through a main input line to a compressor for pressurising the vaporized gas.

LNG carriers require a capability to vaporize a part of the cargo or to vaporize liquid LNG from shore side for the following purposes: (1) vaporizing liquid LNG provided from shore, when commissioning an LNG cargo tank for operation, by cooling the tank interior with cold vaporized natural gas (NG Vapour) . This is called "Gassing-up" ; (2) vaporizing a part of the cargo during unloading of the vessel, in case there is no supply of NG Vapour from the receiving vessel or terminal to replace the volume of LNG Liquid being pumped out, in order to create the necessary NG Vapour volume. The NG Vapour is required to maintain the pressure required for safe operation of the cargo tank. This is called "Emergency Unloading" mode; (3) vaporizing a part of the LNG cargo to provide NG Vapour to supplement the natural boil-off when the fuel gas required is greater than the amount of natural boil-off. This is called "Forcing" mode; (4) in some instances, another operating case is identified for vaporization of Liquid Nitrogen, which is used in the absence of LNG during commissioning to provide suitable cold conditions, e.g. for tank maintenance or testing operations.

Frequently, two separate vaporizer units of different capacities are installed on board, one vaporizer unit for purposes (1) , (2) and (4) (the so-called "LNG Vaporizer" ) and another vaporizer unit for purpose (3) (the so-called "Forcing Vaporizer" ) . They are frequently arranged and connected in a way that the LNG Vaporizer can be used as a back-up for purpose (3) in the event of malfunction of the Forcing Vaporizer.

Typically, on LNG carriers, the heating medium is steam, but other heating media, for example thermal oil or glycol water could be used. It is also possible that the heat could be generated electrically either within the unit or remotely to heat an intermediate heating fluid.

Known vaporizer units for one or more of the above purposes (1) , (2) , (3) and (4) are described in connection with Figure 1. Figure 1 schematically shows a vaporizer unit 100 having a head 170 permanently connected to a tubesheet 160. The head 170 has an internal divider plate 180 to separate the inlet compartment 110 from the discharge compartment 120. The inlet compartment 110 has an inlet nozzle 140 for LNG entry; the outlet compartment 120 has an outlet nozzle 150 for gas discharge. A number n of u-tubes 110x, x = 1, …, n, is connected to the tubesheet 160 to provide a path for LNG between the inlet compartment 110 and the outlet compartment 120, a path along which LNG is vaporized.

In the inner space 130 of the vaporizer unit 100 commonly steam is used as a heat source for effecting a heat transfer to the LNG in the u-tubes 110x. The steam is introduced through nozzle 191 into the vaporizer unit shell 190, where it condenses as a result of the cold LNG entering the tubes, and the condensate is collected and removed via nozzle 193 fitted at the lowest point of the shell 190.

Typically two such vaporizer units 100 are installed, one operating as the Forcing Vaporizer, the other one working as the LNG Vaporizer. The LNG Vaporizer is infrequently used and is at the same time a large costly item. Compared to the LNG Vaporizer, the Forcing Vaporizer is a smaller unit and more frequently operated.

From GB 18670, priority date 19 August 1911, a u-tube cooler for multi-stage gas compressors is known, the cooler having two nests of cooling tubes, one nest being perpendicular to the set of cooling tubes of the other nest. Gas from a first compression stage reaches a first inlet chamber of the cooler and passes through the first nest of cooling tubes to exit the cooler via a first outlet chamber. The cooled gas then passes a second compression stage, whereafter it is fed into a second inlet cavity of the same cooler to enter the second nest of cooling tubes. After passing through the second nest of cooling tubes, the cooled gas is discharged from a second outlet cavity and fed into a third compression stage. Thus, in this known cooler, series streams of gas at different compression stages are passed through two different bundles of u-tubes arranged in the same cooling unit. Such a cooler, however, can not be adapted to the requirements of an LNG vaporizer being suited for the above purposes (1) to (4) .

It is therefore an object of the present invention to reduce costs and space for vaporizing liquefied gas where the vaporized liquefied gas needs to be provided at different levels of flow rate and/or operating pressure.

Summary of the present invention

The present invention provides a vaporizer unit for vaporizing a liquefied gas and a corresponding method of vaporizing liquefied gas according to the independent claims. Embodiments and advantages of the present invention are given in the respective dependent claims and in the following description.

The present invention provides in a first aspect a vaporizer unit for vaporizing a liquefied gas comprising a plurality of inlet compartments, separated from each other, each inlet compartment being in fluid connection with a plurality of conduits for conducting liquefied gas through the vaporizer for vaporization, further comprising a common discharge compartment, said discharge compartment being in fluid connection with all of the conduits of said plurality of inlet compartments for discharging vaporized liquefied gas, and an inner vaporizer unit space, wherein the conduits are at least partly arranged, the inner vaporizer unit space being configured to effect heat transfer to the liquefied gas in the conduits.

According to another aspect of the present invention, a method of vaporizing liquefied gas is provided, wherein the vaporized liquefied gas is supplied at at least two different levels of demand by using a single vaporizer unit according to the first aspect of the present invention, wherein, depending on the level of demand, liquefied gas is supplied to one or more of the plurality of the inlet compartments, a heating medium is supplied to the inner vaporizer unit space and/or an electrical heating unit is operated to effect heat transfer to the liquefied gas in the conduits of the vaporizer unit, and the vaporized liquefied gas is discharged from the common discharge compartment of the vaporizer unit.

The vaporizer unit according to the present invention reduces costs and space by proposing a combined unit making it possible to use one or more sets of conduits by separating the inlet chamber into multiple inlet compartments to be used either individually or simultaneously. The sets of conduits of each of the inlet compartments are joined into the single discharge compartment. The two or more inlet compartments are configured to receive liquefied gas and distribute the liquefied gas into a number of conduits assigned to the respective inlet compartment. Through heat transfer in the conduits, the liquefied gas is vaporized on its path through the conduits. The common discharge compartment is configured to receive the vaporized liquefied gas from the respective conduits and to discharge the vaporized liquefied gas for further use.

By using one or more inlet compartments, different levels of demand of vaporized gas can be satisfied. Typically, the number of conduits and their flow rate capacity determine the maximum flow rate capacity of such an inlet compartment. The flow rate capacity of a conduit typically depends on the conduit diameter.

By arranging, for example, two inlet compartments of the same flow rate capacity, a 50%and a combined 100%capacity can be provided. By arranging a first inlet compartment of e.g. 40%capacity and a second inlet compartment of 60%capacity in the vaporizer unit according to the present invention, three different levels of demand can be met, namely a 40%, a 60%and a combined 100%capacity by using only the first inlet compartment, only the second inlet compartment or both inlet compartments. By this measure, the operational range is widened and different modes can be realised by using a single vaporizer unit.

In a preferred embodiment, each of the inlet compartments is connected to a respective inlet nozzle for supplying liquefied gas into the vaporizer unit. In a similar way, the common discharge compartment is preferably connected to an outlet nozzle for discharging vaporized liquefied gas.

In another preferred embodiment, the conduits are connected to at least one tubesheet. It is preferred if the conduits are designed as u-tubes. In this case, only one tubesheet is necessary for connecting both ends of the u-tubes. Further, the use of u-tubes makes it possible to arrange the inlet compartments and the common discharge compartment in a head of the vaporizer unit. This further reduces the size of the vaporizer unit and allows a compact construction.

The inlet compartments are preferably separated from each other and from the common outlet compartment by two or more respective divider plates. This avoids any possible carryover between adjacent inlet compartments and/or between an inlet compartment and the outlet compartment.

In another preferred embodiment, the vaporizer unit comprises a vaporizer unit shell comprising the inner vaporizer unit space, wherein the conduits/u-tubes are at least partly arranged. The inner vaporizer unit space is configured to effect heat transfer to the liquefied gas in the conduits. To this end, the vaporizer unit shell may comprise a heating medium inlet for supplying heating medium into the inner vaporizer unit space. The vaporizer unit shell should then also comprise a heating medium outlet for discharging heating medium after heat transfer out of the inner vaporizer unit space. The heating medium can be steam, but also other heating media, for example, thermal oil or a glycol-water mix or other media, or also mixtures thereof, can be used.

On the other hand, the vaporizer unit may comprise an electrical heating unit to effect heat transfer to the liquefied gas in the conduits. The electrical heating unit can either be arranged inside the inner vaporizer unit space or remotely to heat an intermediate heating fluid which heats another heating fluid inside the vaporizer unit space.

As already discussed above, in a particularly preferred embodiment, at least two inlet compartments are configured to have different flow rate capacities. Particularly, the number and/or the flow rate capacity of the respective conduits connected to each inlet compartment is different in respect of at least two inlet compartments. This makes it possible to satisfy three or more different levels of demand of vaporized liquefied gas.

The temperature of the discharged vaporized liquefied gas depends on the massflow of the liquefied gas at the inlet and on the amount of heat transfer in the vaporizer unit and thus mainly on the temperature of the heating medium passing the inner space of the vaporizer or of the heat generated by an electrical heating unit inside the vaporizer unit space. Additionally, it is preferred to control the temperature of discharged vaporized gas by injecting preferably a part of the inlet flow of liquefied gas into a stream of discharged vaporized liquefied gas to adjust the temperature of the resulting mixture. This embodiment allows lowering the temperature of the discharged vaporized gas by injecting corresponding amounts of liquefied gas. With this so-called split-range temperature control, for a specific target flow, the inlet flow will be divided with one part entering the vaporizer and exiting at an uncontrolled temperature, resulting from a certain massflow/exchange surface and heating medium temperature. The second part is injected after the vessel to moderate the temperature to the desired level.

Regarding further explanation as to other embodiments and advantageous of the method according to the second aspect of the invention reference is explicitly made to the statements in connection with the vaporizer according to the first aspect of the present invention.

Further advantageous and preferred embodiments of the invention are disclosed in the following description and figures.

It is understood by a person skilled in the art that the preceding and the following features are not only disclosed in the detailed combinations as discussed or shown in the figure, but that also other combinations of the features can be used without exceeding the scope of the present invention.

The invention will now be further described with reference to the accompanying drawings showing preferred embodiments.

Brief description of the drawings

Figure 1 schematically shows a vaporizer unit according to the Prior Art.

Figure 2 schematically shows an embodiment of a vaporizer unit according to the first aspect of the present invention for inplementing the method according to the second aspect of the present invention, wherein Figure 2A shows a longitudinal cross section of the vaporizer unit and Figure 2B shows a section along the line AA of Figure 2A.

Detailed description of the drawings

The vaporizer unit according to Figure 1 has already been discussed in the introductory part of the description.

Figure 2 schematically shows an embodiment of a vaporizer unit 200 according to the present invention for vaporizing a liquefied gas like LNG. The vaporizer unit 200 comprises a plurality of inlet compartments, in these embodiment two

inlet compartments

211 and 213. The inlet compartments 212 and 213 are separated from each other by a divider plate 281. Each inlet compartment is in fluid connection with a plurality of conduits for conducting LNG through the vaporizer 200 for vaporization. In the embodiment shown, inlet compartment 211 is in fluid connection with a first set of

conduits

211a, 211b, 211c, 211d, 211e and 211f. Inlet compartment 213 is in fluid connection with a second set of

conduits

213a, 213b, 213c and 213d. It is noted that the number of conduits is only an exemplary number and that the number of conduits can be the same in each inlet compartment. Also, more than two inlet compartments can be realised. In the present embodiment, the conduits are designed as u-tubes. The u-tubes 211a –211f and 213a –213d are connected to a tubesheet 260 as shown in Figure 2A. While the first ends of the u-tubes are connected to the tubesheet 260 such that they end in the

respective inlet compartment

211 or 213, the second ends of the u-tubes are connected to the tubesheet 260 such that they end in the common discharge compartment 220.

Each of the inlet compartments 211 and 213 is connected to a

respective inlet nozzle

241 and 243, respectively, for supplying LNG into the vaporizer unit 200. The common discharge compartment 220 is connected to an outlet nozzle 250 for discharging vaporized LNG. The inlet compartments 211 and 213 and the common discharge compartment 220 are arranged in a head 270 of the vaporizer unit 200. The inlet compartments 211 and 213 are separated from the common discharge compartment 220 by a divider plate 283.

As shown in Figure 2A, the vaporizer unit 200 comprises a vaporizer unit shell 290 comprising the inner vaporizer unit space 230 in which the u-tubes are arranged. The vaporizer unit shell 290 comprises a heating medium inlet 291 and a heating medium outlet 293. For sake of intelligibility, only one u-tube 213d is shown in Figure 2A. The heating medium flowing through the inner vaporizer unit space 230 effects heat transfer to the LNG passing the u-tubes.

In the following, reference is made to the different modes of operation discussed in the introductory part of the description namely (1) gassing-up mode, (2) emergency unloading mode, (3) forcing mode, and (4) other operating modes especially for tank maintenance or testing operations. The modes 1, 2 and 4 require outlet pressures below 1barg, while mode 3 may, according to the vessel system design, require pressures in the range of below 1barg and up to 17barg. Hitherto, in cases where the required operating pressure of one vaporizer unit is higher than the other, the second one may not be able to be used as a back-up for the first vaporizer unit. The combined design according to the present invention rated at the higher of the pressures can avoid this.

Typically liquefied gas, such as LNG at a temperature of about -163 degC at between 3 and 20 barg depending on the fuel gas requirements, will enter one or more inlet nozzles and fill the inlet compartment (s) . The heating medium is introduced into the shell 290 of the unit and it provides a heat source on the outer diameter of the tube bundle tubes. Frequently saturated steam is used in a range of 5 to 9 bar gauge.

In the case of steam being used as a heating medium, the heat warms the tubes on their outside surface and vaporizes the liquid LNG entering the tubes. This causes part of the steam to condense and the condensate is collected in the lower part of the shell 290 for removal. The amount of steam condensed in this way is directly related to the flow of liquid LNG and the outlet temperature of the vapourized NG.

The discharge NG vapour is temperature controlled using a by-passed stream of liquid LNG which is injected downstream the vaporizer to adjust the temperature to the required level in a dedicated mixing device.

The number of u-tubes connected to each inlet compartment may be different to provide for example a 40%, 60%and combined 100%capacity, each with a turndown capability, thus widening the temperature controlled operational range.

A similar design could also be contemplated with other heating media such as glycol-water mix or thermal oil or other means.

Typical operation modes may be:

Additional compartments may be considered if more operating cases would justify it. Discharge pressures and temperature may vary, as the above is only an exemplary indication.

To summarize, the following advantages and improvements are achieved by the present invention.

- An overall reduction in footprint

- A simpler overall arrangement

- A better coverage of the Forcing Vaporizer duty during back-up (when problem due to sensors/control components) mode

- Equipment Costs will be lower due to a small mass of materials for construction,

- Redundancy benefits will be retained

- Customer installation costs (process & heating medium line + for local control panel installation & cabling) will be lower.

- A more compact Cargo Machinery room could be considered

- Control for both units may be incorporated into a single Local Control Panel

- In the case of a steam heated vaporizer, a single steam trap and drain system may be utilized.

List of reference signs

100 vaporizer unit

110 inlet compartment/110x u-tube

120 discharge compartment

130 inner space

140 inlet nozzle

150 outlet nozzle

160 tubesheet

170 head

180 divider plate

190 vaporizer unit shell

191 nozzle

193 nozzle

200 vaporizer unit

211 first inlet compartment

211 a –f first set of conduits

213 second inlet compartment

213 a –d second set of conduits

220 common discharge compartment

230 inner space

241, 243 inlet nozzle

250 outlet nozzle

260 tubesheet

270 head

281, 283 divider plate

290 shell

291 heating medium inlet

293 heating medium outlet

Claims

A vaporizer unit (200) for vaporizing a liquefied gas comprising

a plurality of inlet compartments (211, 213) , separated from each other, each inlet compartment (211, 213) being in fluid connection with a plurality of conduits (211 a –f; 213 a –d) for conducting liquefied gas through the vaporizer (200) for vaporization,

a common discharge compartment (220) , said discharge compartment (220) being in fluid connection with the conduits (211 a –f; 213 a –d) of said plurality of inlet compartments (211, 213) for discharging vaporized liquefied gas, and

an inner vaporizer unit space (230) , wherein the conduits are at least partly arranged, the inner vaporizer unit space being configured to effect heat transfer to the liquefied gas in the conduits.
The vaporizer unit (200) of claim 1, wherein each of the inlet compartments (211, 213) is connected to a respective inlet nozzle (241, 243) for supplying liquefied gas into the vaporizer unit.
The vaporizer unit (200) of claim 1 or claim 2, wherein the common discharge compartment (220) is connected to an outlet nozzle (250) for discharging vaporized liquefied gas.
The vaporizer unit (200) according to any one of claims 1 to 3, wherein the conduits are connected to at least one tubesheet (260) .
The vaporizer unit (200) of any one of claims 1 to 4, wherein the conduits for conducting liquefied gas are designed as u-tubes.
The vaporizer unit (200) of claim 5, wherein the inlet compartments and the common discharge compartment are arranged in a head (270) of the vaporizer unit.
The vaporizer unit (200) of claim 6, wherein the inlet compartments are separated from each other and from the common outlet compartment by respective divider plates (281, 283) .
The vaporizer unit (200) according to any one of claims 1 to 7, wherein the vaporizer unit comprises a vaporizer unit shell (290) comprising the inner vaporizer unit space (230) .
The vaporizer unit (200) of claim 8, wherein the vaporizer unit shell (290) comprises a heating medium inlet (291) for supplying a heating medium into the inner vaporizer unit space to effect heat transfer to the liquefied gas in the conduits.
The vaporizer unit (200) of claim 9, wherein the vaporizer unit shell (290) comprises a heating medium outlet (293) for discharging the heating medium out of the inner vaporizer unit space.
The vaporizer unit (200) according to any one of claims 1 to 10, wherein the vaporizer unit comprises an electrical heating unit to effect heat transfer to the liquefied gas in the conduits.
The vaporizer unit (200) according to any one of claims 1 to 11, wherein at least two inlet compartments (211, 213) are configured to have different flow rate capacities, particularly wherein the number and/or the flow rate capacity of conduits connected to each inlet compartment is different in respect of at least two inlet compartments.
A method of vaporizing liquefied gas, wherein the vaporized liquefied gas is supplied at at least two different levels of demand by using a single vaporizer unit (200) of any one of the claims 1 to 12, wherein,

depending on the level of demand, liquefied gas is supplied to one or more of the plurality of the inlet compartments,

a heating medium is supplied to the inner vaporizer unit space (230) and/or an electrical heating unit is operated to effect heat transfer to the liquefied gas in the conduits of the vaporizer unit,

and the vaporized liquefied gas is discharged from the common discharge compartment (220) .
The method of claim 13, wherein a temperature of discharged vaporized liquefied gas is controlled by injecting liquefied gas into a stream of discharged vaporized liquefied gas to adjust the temperature of the resulting mixture.
The method of claim 13 or claim 14, wherein three different levels of demand are realised by using a vaporizer unit (200) with two inlet compartments of different flow rate capacity.