EP4675167A1

EP4675167A1 - Apparatus and method for evaporating cryogenic fluids

Info

Publication number: EP4675167A1
Application number: EP24020226.7A
Authority: EP
Inventors: Fokke Bokker; Martin Murer
Original assignee: Selas Linde GmbH
Current assignee: Selas Linde GmbH
Priority date: 2024-07-04
Filing date: 2024-07-04
Publication date: 2026-01-07

Abstract

The present invention relates to an apparatus (100) for evaporating cryogenic fluids comprising a heat exchanger (105) at least partly immersed in a bath (140) of heat transfer medium, the heat exchanger being configured for conducting a cryogenic fluid therethrough, a burner system (104) for combustion of a fuel by means of an oxidizing agent, said burner system comprising at least one fuel supply line (102) and at least one oxidizing agent supply line (101) for supplying the fuel and the oxidizing agent to a combustion chamber (114), the combustion chamber configured for the combustion of the fuel by the oxidizing agent, a flue gas distributor and sparger system (103) for conducting the flue gas downstream away from the combustion chamber and for ejecting the flue gas into the bath of heat transfer medium underneath the heat exchanger, wherein the apparatus further comprises a bypass oxidizing agent line (111), the bypass oxidizing agent line branching off from the at least one oxidizing agent supply line (101) at a position upstream the combustion chamber (114) for bypassing the combustion chamber and being configured to return a bypassed part of oxidizing agent into the flue gas distributor and sparger system (103) and/or into the bath (140) of heat transfer medium.

Description

The present invention relates to an apparatus and a method for evaporating or vaporizing cryogenic fluids using a bath of heat transfer medium, which heat transfer medium itself is heated by flue gas from a combustion process.

Background of the invention

Such apparatuses are known as submerged combustion vaporisers (SCVs), for example. SCVs are usually used to vaporise (evaporate) cryogenic liquids such as LNG (liquefied natural gas), for which a water bath (bath of heat transfer medium) with typical temperatures between 10 and 50°C is used. The cryogenic liquid to be vaporised is passed through a heat exchanger located in this water bath. The water bath itself is heated by flue gas streams from a burner whose burner flame has a temperature of over 1000°C. For example, the combustion chamber of the burner can be located completely or partially in the water bath and the burner exhaust gas or flue gas can be injected into the water bath via appropriately distributed flue gas outlets. Overall, the water bath can nevertheless be understood as an isothermal heat source to a good approximation, which means that the vaporised cryogenic fluid cannot easily be heated above the water bath temperature.
WO 2011/066939 A1 proposes a two-stage combustion process for vaporising a cryogenic fluid and then further heating or superheating it, using a first heat exchanger, which is designed as an SCV, and a second heat exchanger, which is also heated with flue gas.

Disclosure of the invention

In a SCV, the water is circulated through the heat exchanger, which typically comprises a bundle of tubes, by means of the flue gas injected into the water resulting in flue gas bubbles rising up in the water (principle of an air lift pump). The two-phase flow regime results in a highly turbulent flow which ensures high heat transfer rates. Typically, the flue gas is distributed beneath the heat exchanger using a distributor and sparger system. The flue gas is generated in an upstream burner and provides the heat input. Such fired SCVs are operated with excess oxygen concentrations of typically 3 to 7 vol. % at full load. During part load, the excess oxygen concentration is significantly increased to levels typically up to 18 vol. %. The high excess air operation is necessary to keep up the water circulation through the heat exchanger, while the necessary heat generated by combustion is correspondingly lower. Generally, air is used as an oxidizing agent for the combustion process. The high excess air rate during part load, especially at turn-down of the SCV, reduces the average combustion temperature. On the other hand, the core of the flame remains at a high temperature, which results in high NOx emissions. Due to a reduced average combustion temperature, however, CO emissions are raising caused by a reduced reaction rate of CO at lower temperatures. This problem can be avoided by operating a plurality of SCVs installed on a single site. This allows for an operation of some of the SCVs at higher loads, while other SCVs are switched off in order to avoid part load operation. This mode of operation results in lower CO emissions.
As an increasing size of single SCVs, resulting in fewer SCVs per site, is desired and stricter emission regulations are in force, an improvement of CO and NOx emissions also at low or part load operation of a single SCV is required.
The present invention provides an apparatus and a method for evaporating cryogenic fluids according to the independent claims. Embodiments are the subject-matter of the respective dependent claims. Further, embodiments and advantages are described in the description below.
An apparatus for vaporizing or evaporating cryogenic fluids according to the present invention comprises a heat exchanger at least partly immersed or located in a bath of heat transfer medium, typically water, the heat exchanger being configured for conducting a cryogenic fluid therethrough. The heat exchanger typically comprises a bundle of tubes for conducting a cryogenic fluid through these tubes. The apparatus further comprises a burner system for combustion of a fuel by means of an oxidizing agent, said burner system comprising at least one fuel supply line and at least one oxidizing agent supply line for supplying the fuel and the oxidizing agent to a combustion chamber. Typically, air is used as the oxidizing agent. The burner system further comprises the combustion chamber configured for the combustion of the fuel by the oxidizing agent, and a flue gas distributor and sparger system for conducting the flue gas downstream away from the combustion chamber and for ejecting the flue gas into the bath of heat transfer medium underneath the heat exchanger.
The apparatus further comprises a bypass oxidizing agent line, the bypass oxidizing agent line branching off from the at least one oxidizing agent supply line at a position upstream the combustion chamber for bypassing the combustion chamber and being configured to return a bypassed part of oxidizing agent into the flue gas distributor and sparger system and/or into the bath of heat transfer medium. The bypass oxidizing agent line bypasses the combustion chamber in order to inject a bypassed part of oxidizing agent downstream the combustion into the flue gas and/or into the bath of heat transfer medium. By bypassing a part of the oxidizing agent, which would otherwise be led into the combustion chamber, the temperature is only reduced downstream of the combustion chamber. Thus, the reaction rate of CO in the combustion chamber is not reduced resulting in lower CO emissions. At the same time, as the oxygen excess in the combustion chamber is lowered, NOx emissions are reduced and can further be controlled by water injection due to the higher temperature in the combustion chamber. The apparatus according to the present invention thus lowers CO and NOx emissions also at low or part load operation, especially of a SCV.
Typically, the combustion in a SCV burner is a staged and superstoichiometric combustion. At least two oxidizing agent (air) supply lines supply primary and secondary oxidizing agent (air), primary air being used for the combustion, while secondary air is used for post-combustion usually in an area at the end of the burner flame. Depending on the burner design, post-combustion by secondary air may also take place in the upper part of the burner if primary air and fuel are injected into the burner against the main flow direction. According to the present invention, another oxidizing agent line branching off from a main oxidizing agent supply line and/or from any one of the existing oxidizing agent supply lines for the staged combustion, is used to bypass the combustion chamber and to gradually inject a bypassed part of oxidizing agent into the flue gas distributor and sparger system and/or into the heat transfer medium bath.
The present invention ensures proper agitation of the heat transfer medium as the total amount of gas used for the airlift pump as described above is at least the same as in an apparatus not implementing the present invention and therefore heat transfer at the heat exchanger during turn-down or part load is guaranteed while keeping the temperature in the burner high for good CO conversion and keeping the amount of oxygen low for lower NOx emissions. In general, there is a narrow temperature window at which both, CO and NOx emissions are low. With the oxidizing agent bypass according to the present invention, additional flexibility is gained to operate the burner system in this temperature window.
In an embodiment, the bypass oxidizing agent line comprises one or more injection lines for injecting the bypassed part of oxidizing agent into the flue gas distributor and sparger system and/or into the bath of heat transfer medium. The bypass oxidizing agent line may thus comprise a main bypass oxidizing agent line and one or more injection lines branching off the main bypass oxidizing agent line. The injection lines comprise one or more gas outlets, orifices, or nozzles. Such outlets may be provided over a predetermined length of the circumferential surface of an injection line and/or at the end of an injection line.
In an embodiment, the flue gas distributor and sparger system comprises a main distributor line having a plurality of branch tubes, the branch tubes being at least in part provided with ejection openings for ejecting flue gas underneath the heat exchanger. In such a system, the flue gas generated in the combustion chamber, is conducted downstream in the main distributor line and from there distributed into the plurality of branch tubes, which branch tubes are provided with ejection openings or orifices or nozzles through which the flue gas is injected or sprayed in the area underneath the heat exchanger resulting in a highly turbulent flow as described above to ensure high heat transfer rates between the hot flue gas and the heat transfer medium (water). Typically, the branch tubes have such ejection openings over a predetermined length of their circumferential surface, which part is typically provided underneath the heat exchanger.
With such a construction of the flue gas distributor and sparger system, there are the following preferred options of injecting bypassed oxidizing agent into the system.
First, one or more of the injection lines may be arranged along the longitudinal axis of the main distributor line and configured to inject oxidizing agent particularly radially into the main distributor line. In such an embodiment, the main bypass oxidizing agent line may extend parallel to the main axis of the main distributor line, for instance, above or laterally next to the main distributor line, and a number of injection lines branching off the main bypass oxidizing agent line extend to the circumferential surface of the main distributor line and are configured to inject oxidizing agent into the main distributor line where the oxidizing agent is mixed with the flue gas. The direction of injection of the oxidizing agent may be radial.
In an alternative or additional option, one or more of the injection lines are arranged and configured to inject oxidizing agent axially into the main distributor line. In this embodiment, it might be sufficient to only have one single injection line, which may be identical to the main bypass oxidizing agent line, and which extends to the surface of the main distributor line of the distributor and sparger system and which is configured to inject the bypassed part of oxidizing agent in an axial direction into the main distributor line. A preferred location for such an injection is the transition region between the combustion chamber and the main distributor line, particularly the outlet part of the burner bottom volute.
In the above described two options, the oxidizing agent (air) bypass injection into the main distributor line can be implemented as a high velocity injection using the available pressure drop. This results in an improved mixing of the bypassed part of the oxidizing agent with the hot flue gas from the burner and thus in a more homogeneous temperature distribution.
In another option, which still can be implemented alternatively or additionally, one or more of the injection lines are arranged and configured to inject oxidizing agent at and/or below and/or above the ejection openings of the plurality of branch tubes such that ejected flue gas is mixed with the oxidizing agent injected by the one or more injection lines into the bath of heat transfer medium. In this embodiment, the one or more injection lines may comprise injection openings or orifices or nozzles particularly over a predetermined length along their circumferential surfaces for injecting the bypassed part of oxidizing agent into the bath of heat transfer medium (water). These injection openings are arranged and/or configured to inject the oxidizing agent at/below/above the ejection openings for ejecting the flue gas such that the hot flue gas is thoroughly mixed with the injected oxidizing agent.
In a possible implementation of this embodiment, the plurality of branch tubes is arranged parallel to each other, and a plurality of the injection lines is also arranged parallel to each other, the distance between two adjacent injection lines being essentially the same as the distance between two adjacent branch tubes. With such an implementation, the array of parallel injection lines may be arranged into the interspaces of the array of parallel branch tubes such that the ejection openings of the branch tubes are as close as possible to the injection openings of the injection lines resulting in an improved mixing. In an embodiment, the plurality of parallel injection lines is arranged in a first plane, and the plurality of parallel branch tubes is arranged in a second plane, the first plane being identical or parallel to the second plane. In this embodiment, it is preferred if - in a projection view onto the first or second plane - the injection lines are located between the branch tubes. The injection lines may also be arranged above or below the branch tubes as the resulting bubbles of flue gas and oxidizing agent rise upwards in the bath of heat transfer medium and mix with each other on their way upwards.
In another aspect, the present invention relates to a method for vaporizing or evaporating cryogenic fluids. The method comprises the steps of conducting a cryogenic fluid through a heat exchanger, the heat exchanger being at least partly immersed in a bath of heat transfer medium; heating the heat transfer medium by flue gas generated by combustion of a fuel and an oxidizing agent, the flue gas being ejected into the bath of heat transfer medium underneath the heat exchanger; wherein at least a part of the oxidizing agent (originally supplied for the combustion with the fuel) is branched off before combustion and the branched-off or bypassed part of the oxidizing agent is returned to the flue gas and/or to the bath of heat transfer medium. Regarding the embodiments and advantages of the method according to the present invention, reference is made to the above discussion of the apparatus according to the present invention, which can be applied to the method accordingly.
In an embodiment, the branched-off part of the oxidizing agent is returned to the flue gas by injecting the branched-off part of oxidizing agent axially and/or radially into a main stream of flue gas.
In an embodiment, the branched-off part or bypassed part of oxidizing agent is returned to the bath of heat transfer medium by injecting the branched-off part of oxidizing agent into the bath of heat transfer medium at predetermined locations where the flue gas is ejected into the bath of heat transfer medium such that the ejected flue gas is mixed with the oxidizing agent injected into the bath of heat transfer medium.
In an embodiment, the amount of the branched-off part of oxidizing agent is determined dependent on a load range of the vaporizing operation, particularly on a load range of the apparatus according to the present invention. In a part-load range, particularly during turn-down, the part of branched-off oxidizing agent is increased. To this end, a valve is arranged in the bypass oxidizing agent line, which valve is controlled by a controller depending on the load range of the apparatus. The load range of the apparatus is in the range of 10 to 100 %. The amount of bypassed air can be indirectly proportionally increased with the load. As an example, at 10 % load up to about 90 % of the air can be bypassed, at 20 % load up to about 80 % of the air can be bypassed, and so on, while at 100 % load only a small amount of air for purging the bypass system may be applied.

Detailed description

In the following, the invention and the embodiments and advantages are further described in connection with the appended figures, wherein

Figure 1 schematically shows an apparatus according to an embodiment of the invention;
Figure 2 schematically shows an apparatus according to another embodiment of the invention; and
Figure 3 schematically shows an apparatus according to still another embodiment of the invention.

The figures are described comprehensively; identical reference signs denote identical or functionally identical elements. Although Figures 1 to 3 illustrate three different possible options for implementing the invention, it should be noted that various combinations of the options shown are possible. In principle, all options can also be realised together. Even if individual combinations of the following embodiments are not explicitly described, they are nevertheless intended to form part of the disclosure of the present patent application.
Figure 1 shows an embodiment of the present invention. A SCV, Submerged Combustion Vaporiser, serves as an example of the claimed apparatus. The SCV 100 shown here comprises a water bath 140 in a tank 130. The water bath 140 is heated by a burner system 104. The burner system 104 is supplied with combustion air as oxidizing agent via an oxidizing agent supply line 101 and a combustion gas via a fuel supply line 102. A part of the combustion air is fed via a valve through a primary oxidizing agent line 112 and mixed with combustion gas in the lower part of the burner to be combusted in the combustion chamber 114. Also, a part of the combustion air is supplied via a valve through a secondary oxidizing agent line 113 to the upper part of the burner system 104, where it is forced downwards towards the combustion chamber 114 by means of a pressure gradient. The flue gas produced by the combustion is fed into the flue gas distributor and sparger system 103 which is submerged into the waterbath 140 and which has outlet openings (not shown) through which flue gas exits to spread inside the tank 130 and heat the water bath 140.
A liquefied or liquid cryogenic medium or fluid is fed via a cryogenic fluid supply line 107 into a heat exchanger 105, which is located in the water bath 140. By exchanging heat between the liquid cryogenic medium and the water bath 140, the liquid cryogenic medium is vaporised and may additionally be superheated. The vaporised cryogenic medium is discharged from the heat exchanger 105 via an evaporated cryogenic fluid line 109.
The cryogenic medium enters the heat exchanger 105 in order to absorb heat via the heat transfer medium (water) in the water bath 140. The water bath 140 itself is heated by the flue gas distributed by the flue gas distributor and sparger system 103 particularly in an area beneath the heat exchanger 105 as will become clear from Figure 2 showing a schematic top view on the SCV 100. The flue gas ejected into the bath 140 of water results in a highly turbulent flow which ensures high heat transfer rates. Typically, the SCV 100 is operated with excess oxygen concentrations of about 3 to 7 vol. % at full load, increasing up to a range of 10 to 20, particularly about 18 vol. %, at part load operation down to turn-down of the SCV 100. This high excess air operation is necessary for keeping up a sufficient water circulation through the heat exchanger, while the heat necessary for part load operation generated by the combustion is correspondingly lower. According to the present invention, particularly at part load operation of the SCV 100, a predetermined part of the combustion air is bypassed the combustion chamber and fed downstream the combustion chamber 114 into the flue gas distributor and sparger system 103 and/or into the bath 140 of water. As already discussed above, this measure reduces CO and NOx emissions simultaneously by keeping the temperature in the combustion area sufficiently high for a good CO conversion and, at the same time, keeping the amount of oxygen low for lower NOx emissions. To this end, the SCV 100 comprises a bypass oxidizing agent line 111 branching off from the oxidizing agent supply line 101 at a position upstream the combustion chamber 114 for bypassing the combustion chamber 114. By means of valve 121 in the bypass oxidizing agent line 111, which valve 121 is controlled by a controller (not shown), an amount of oxidizing agent/combustion air to be branched-off can be determined dependent on a load range of the vaporizing operation of the SCV 100. In a part-load range, particularly during turn-down, the part of branched-off oxidizing agent/combustion air is increased.
According to the embodiment shown in Figure 1, the bypass oxidizing agent line 111 comprises a plurality of injection lines 111' for injecting the bypassed part of oxidizing agent at different positions into the flue gas distributor and sparger system 103. According to the same principles, the part of bypassed oxidizing agent can alternatively or additionally be injected into the bath 140 of water in the tank 130. In the embodiment of Figure 1, the injection lines 111' are arranged perpendicularly to and along the longitudinal axis of the main distributor line 123 of the flue gas distributor and sparger system 103 and configured to inject oxidizing agent/combustion air particularly radially into the main distributor line 123.
The flue gas distributor and sparger system 103 is shown in Figures 2 and 3 in a top view on the tank 130 of Figure 1. As can be seen from Figures 2 and 3, the flue gas distributor and sparger system 103 comprises a main distributor line 123 extending through a part of the tank 130 particularly below the heat exchanger 105 (not shown), and further comprises a plurality of branch tubes 123', at least a part of the branch tubes 123' being arranged underneath the heat exchanger 105 and being at least in part provided with ejection openings for ejecting flue gas into the water bath 140.
It should be noted that, in the embodiment of Figure 1, injection lines 111' may extend to such a flue gas distributor and sparger system 103 at any positions. Thus, injection lines can be arranged above, next to and/or below the flue gas distributor and sparger system 103.
In another embodiment shown in Figure 2, a plurality of injection lines 111' is arranged particularly parallel to each other, more particularly in a first plane. The flue gas distributor and sparger system 103 also comprises a plurality of branch lines 123', particularly arranged parallel to each other, more particularly in a second plane. In such an embodiment, the injection lines 111' are arranged and configured to inject oxidizing agent/combustion air at and/or below and/or above the ejection openings of the plurality of branch tubes such that ejected flue gas is mixed with the oxidizing agent injected by the injection lines 111' into the water bath 140. To this end, each injection line 111' may be arranged between two branch lines 123'. In the embodiment of Figure 2 where the injection lines 111' are arranged in a first plane, while the branch lines 123' are arranged in a second plane, it is expedient if the first plane being identical or parallel to the second plane, i.e., in a projection view onto the first or second plane, the injection lines 111' are located between the branch tubes 123'. The injection lines 111' may be arranged in the same plane but also above or below the second plane of branch tubes 123' as the resulting bubbles of flue gas and of oxidizing agent rise upwardly in the water bath 140 and mix with each other on their way upwards around the heat exchanger 105.
In still another embodiment shown in Figure 3, one or more of the injection lines 111' are arranged and configured to inject oxidizing agent/combustion air axially into the main distributor line 123 of the flue gas distributor and sparger system 103. In this embodiment, the injection line 111' is identical to the main bypass oxidizing agent line 111, which extends to the transition region between the combustion chamber 114 and the main distributor line 123, particularly at the outlet part of the burner bottom volute.
In the above described embodiments according to Figures 1 and 3, the combustion air bypass injection into the main distributor line 123 can be implemented as a high velocity injection using the available pressure drop for an improved mixing of the bypassed combustion air with the hot flue gasses.

Claims

An apparatus (100) for evaporating cryogenic fluids comprising a heat exchanger (105) at least partly immersed in a bath (140) of heat transfer medium, the heat exchanger being configured for conducting a cryogenic fluid therethrough,
a burner system (104) for combustion of a fuel by means of an oxidizing agent, said burner system comprising

at least one fuel supply line (102) and at least one oxidizing agent supply line (101) for supplying the fuel and the oxidizing agent to a combustion chamber (114),

the combustion chamber configured for the combustion of the fuel by the oxidizing agent,

a flue gas distributor and sparger system (103) for conducting the flue gas downstream away from the combustion chamber and for ejecting the flue gas into the bath of heat transfer medium underneath the heat exchanger,

wherein the apparatus further comprises

a bypass oxidizing agent line (111), the bypass oxidizing agent line branching off from the at least one oxidizing agent supply line (101) at a position upstream the combustion chamber (114) for bypassing the combustion chamber and being configured to return a bypassed part of oxidizing agent into the flue gas distributor and sparger system (103) and/or into the bath (140) of heat transfer medium.
The apparatus of claim 1, wherein the bypass oxidizing agent line (111) comprises one or more injection lines (111') for injecting the bypassed part of oxidizing agent into the flue gas distributor and sparger system and/or into the bath of heat transfer medium.
The apparatus of claim 2, wherein the flue gas distributor and sparger system (103) comprises a main distributor line (123) having a plurality of branch tubes (123'), the branch tubes being at least in part provided with ejection openings for ejecting flue gas underneath the heat exchanger (105).
The apparatus of claims 2 and 3, wherein one or more of the injection lines (111') are arranged along the longitudinal axis of the main distributor line (123) and configured to inject oxidizing agent particularly radially into the main distributor line.
The apparatus according to claims 2 and 3 or according to claim 4, wherein one or more of the injection lines (111') are arranged and configured to inject oxidizing agent axially into the main distributor line (123).
The apparatus according to claims 2 and 3 or according to claim 4 or 5, wherein one or more of the injection lines (111') are arranged and configured to inject oxidizing agent at and/or below and/or above the ejection openings of the plurality of branch tubes (123') such that ejected flue gas is mixed with oxidizing agent injected by the one or more injection lines into the bath of heat transfer medium.
The apparatus of claim 6, wherein the plurality of branch tubes (123') is arranged parallel to each other and wherein a plurality of the injection lines (111') is arranged parallel to each other, the distance between two adjacent injection lines being essentially the same as the distance between two adjacent branch tubes.
The apparatus of claim 7, wherein the plurality of parallel injection lines (111') defines a first plane and the plurality of parallel branch tubes (123') defines a second plane, the first plane being the same plane as or parallel to the second plane.
The apparatus of any one of the preceding claims, further comprising a valve (121) arranged in the bypass oxidizing agent line (111), the valve being controlled by a controller, said controller being configured to control the amount of the bypassed part of oxidizing agent dependent on a load range of the apparatus.
A method for evaporating cryogenic fluids comprising the steps of conducting a cryogenic fluid through a heat exchanger (105), the heat exchanger being at least partly immersed in a bath (140) of heat transfer medium,
heating the heat transfer medium by flue gas generated by combustion of a fuel and an oxidizing agent,

the flue gas being ejected into the bath of heat transfer medium underneath the heat exchanger,

wherein at least a part of the oxidizing agent is branched off before combustion and the branch-off part of the oxidizing agent is returned to the flue gas and/or to the bath of heat transfer medium.
The method of claim 10, wherein the branched-off part of oxidizing agent is returned to the flue gas by injection of the branched-off part of oxidizing agent axially and/or radially into a main stream of flue gas.
The method of claim 10 or claim 11, wherein the branched-off part of oxidizing agent is returned to the bath of heat transfer medium by injection of the branched-off part of oxidizing agent into the bath of heat transfer medium at predetermined locations where the flue gas is ejected into the bath of heat transfer medium such that the ejected flue gas is mixed with the oxidizing agent injected into the bath of heat transfer medium.
The method of any one of claims 10 to 12, wherein a water bath is used as the bath of heat transfer medium.