GB2584443A

GB2584443A - Vacuum insulated equipment

Info

Publication number: GB2584443A
Application number: GB1907837.7A
Authority: GB
Inventors: Georg Ebner; Hildenbeutel Jan; Soika Rainer
Original assignee: Linde Kryotechnik AG
Current assignee: Linde Kryotechnik AG
Priority date: 2019-06-03
Filing date: 2019-06-03
Publication date: 2020-12-09
Also published as: GB201907837D0

Abstract

A cyrogenic structure such as a vacuum insulated cyrogenic cylinder, comprising an inner structure 2, an outer structure 6, an interspace 8 between the two filled with a vacuum, where a thermal insulation layer 10, such as a multi-layer insulation of 5 layers of foils, so that no air gaps are present between the thermal insulation layer and the outer surface of the inner structure.

Description

VACUUM INSULATED EQUIPMENT

Field of Invention

The present invention relates to the field of vacuum insulated equipment. In particular, the invention relates to a vacuum insulated cryogenic equipment and a method of producing the same.

Background of Invention

Vacuum insulated equipment is used for the handling of cold fluids, and includes but is not limited to tanks, pipes, storage vessels, heat exchangers. The term "cold fluids" is understood to means fluids below -180°C (93 K; -292°F).

Vacuum insulated equipment is used for the storage, handling and processing or transport of liquefied gases for a wide range of applications, including metal processing, medical technology, electronics, water treatment, energy generation and the food industry. Cryogenic equipment is used for the handling of cryogenic liquids, such as but not limited to: liquid hydrogen (LH2), liquid helium, Liquid nitrogen (LIN), Liquid argon (LAR), Liquid oxygen (LOX), Liquid carbon dioxide (LCO2), Liquid natural gas (LNG), and Liquid nitrous oxide (LN2O).

The term "cryogenic equipment" can also be used, and is also understood to mean tanks, pipes, storage vessels etc, suitable for storing a liquified gas (and gas mixtures) at temperatures below approximately -180°C (93 K; -292°F).

Cryogenic tanks are generally vacuum-insulated and can be delivered as a vertical or horizontal installation. The inner vessels and piping are made of stainless steel to ensure high-grade cleanliness -particularly important for the food and electronics industry. Stainless steel is also a requirement due to the low temperatures.

Various insulation arrangements for cryogenic equipment are known. One insulation arrangement is known as the evacuated Multi-Layer Insulation (MLI). MLI is understood to mean multiple layers of thin sheets and is often used on spacecraft. It is designed to reduce heat loss by thermal radiation. The layers are generally formed of thin plastic and coated with metal. The layers are generally arranged as close together as possible without significant touching. Layers may be embossed or crinkled, so they only touch at a few points, or held apart by a thin cloth mesh. For some applications, stronger outermost layers are provided. These are often thicker and stronger plastic, reinforced with a stronger mesh material such as fiberglass.

An evacuated MLI arrangement comprises multiple layers of insulation provided within a vacuum. The vacuum ensures no heat transfer through convection. This is used in space applications, but the benefits of providing a vacuum can also be realised in atmospheric conditions. An evacuated MLI arrangement provides one of the lowest known effective thermal conductivities. In cryogenic applications at temperatures below the boiling point of liquid nitrogen (LN2) i.e. -196°C (77K) evacuated MLI is the most commonly used type of thermal insulation.

Evacuated MLI arrangements are proven to have superior insulation properties, exhibiting heat loads as low as 1 W/m2 at ambient temperatures to -266°C (4K), this being the temperature of cryogenically stored liquid helium. However, the sudden loss of insulating vacuum can lead to extremely high heat loads. Peak loads as high as 40 W/m2 into cryogenic containers containing liquid helium at -266°C (4K) have been reported. This is caused by the condensation of the nitrogen from the ambient air on the cold surface of the cryogenic equipment.

The sudden loss of insulating vacuum leads to a pressure increase in the system which has to be limited by relieving fluid via a pressure relief device. At a first approximation, the mass flow rate to be relieved increases linearly with the heat load. The volume flow may increase even faster in situations in which the temperature of the fluid to be discharged is increase. The volume flow rate must be used to determine a suitable relief device for a given application in order to comply with safety regulations.

Another type of insulation is polyurethane, and specifically polyurethane foam insulation (also known as SOFI, Spray On Foam Insulation). However, this has historically not been considered suitable for use in vacuum insulation systems.

Embodiments of the invention seek to provide improved tanks which may overcome some, or all of these problems.

Summary of Invention

According to the first aspect of the present invention there is provided a cryogenic apparatus comprising: an inner structure, an outer structure, an interspace between the inner structure and outer structure; and a vacuum provided in the interspace; wherein a thermal insulation layer is provided directly on an outer surface of the inner structure such that substantially no air gaps are present between the thermal insulation layer and the outer surface of the inner structure.

The thermal insulation layer is provided with substantially no air gaps between it and the outer surface of the inner structure to ensure that essentially no condensation occurs on the outer surface of the inner structure. Instead, any condensation will be formed on an outer surface of the thermal insulation layer.

The thermal insulation layer may have a minimum thickness of 2mm.

The thermal insulation layer may have a minimum thickness of 5mm. The thermal insulation layer may have a thickness of between 2mm and 10mm. The thermal insulation layer may have a thickness of between 4mm and 8mm.

The thermal layer may have a maximum thermal conductivity of 2W/mK at temperatures below -173 C (100K).

In other words, the thermal insulation layer may have a thermal conductivity below2 W/mK at temperatures below -173 C (100K). For a typical layer thickness of approximately 4mm, this equates to a heat load of 40 kW/m2. It will be appreciated that these values are quoted with a reference temperature since thermal conductivity is temperature dependent.

The thermal insulation layer may have a maximum thermal conductivity of 1.5 W/mK at temperatures below -173 C. The thermal insulation layer may have a maximum thermal conductivity of 1 W/mK at temperatures below -173 C. The thermal insulation layer may have a thermal conductivity between 0.5 W/mK and 2 W/mK at temperatures below -173 C. The thermal layer may comprise at least one of: a polyurethane foam, polyethylene (PE), Polyurethane (PUR), Polyethylene terephthalate (PET), Polytetrafluoroethylene (PTFE).

The thermal layer may comprise any suitable low conductivity material.

A multi-layer insulation may be provided in the interspace between the thermal insulation layer and the outer structure.

The multi-layer insulation may comprise at least 5 layers of foils. The multi-layer insulation may comprise at least 7 layers of foils. The multi-layer insulation may comprise at least 9 layers of foils. The multi-layer insulation may comprise at least 10 layers of foils. The multi-layer insulation may comprise 10 layers of foils.

The foils may be metallic. The multi-layer insulation may comprise metal coated thin plastic layers.

The layers may comprise spray-on foam. The layers may be applied using a spray technique. The layers may be applied using vapour deposition.

The cryogenic apparatus may be a tank, a cold box, a storage vessel, a container or a pipeline.

According to a further aspect of the invention, there is provided a method for manufacturing an insulated cryogenic apparatus comprising, Providing an inner structure, Providing an outer structure, thereby defining an interspace between the inner structure and outer structure; and evacuating the gases from the interspace to provide an interspace vacuum, wherein the method includes applying a thermal insulation layer directly on an outer surface of the inner structure such that substantially no air gaps are present between the thermal insulation layer and the outer surface of the inner structure.

The step of providing the thermal insulation layer may be achieved by spraying or vapour deposition. The step of providing the thermal insulation layer may comprise providing a layer at least 2mm thick. The step of providing the thermal insulation layer may comprise providing a layer at least 5mm thick. The step of providing the thermal insulation layer may comprise providing a layer having a thickness of between 2mm and 10mm. The step of providing the thermal insulation layer may comprise providing a layer having thickness of between 4mm and 8mm. The step of providing the thermal insulation layer may comprise providing a layer having a maximum thermal conductivity of 2W/mK at temperatures below -173 C (100K). In other words, the thermal insulation layer may have a thermal conductivity below2 W/m K at temperatures below -173 C (100K). For a typical layer thickness of approximately 4mm, this equates to a heat load of 40 kW/m2. It will be appreciated that these values are quoted with a reference temperature since thermal conductivity is temperature dependent.

The method may further include: providing a multi-layer insulation in the interspace between the thermal insulation layer and the outer structure.

The step of providing a multi-insulation layer may comprises at providing least 5 layers.

The layers may be foils. The layers may comprise metal coated thin plastic layers.

Since the thermal insulation layer is applied to the outer surface of the inner structure, condensation is essentially prevented from forming on this surface. Instead, condensation will form on the outer surface of the insulation layer.

The insulation of the invention can be used in any apparatus in which potential heat load transfer into a cold fluid can result in an increase volume flow (discharge), which therefore gives rise to the need for larger relief devices to ensure safety requirements are met.

The invention, as described, can be applied to existing cryogenic apparatus, such as cryogenic cold boxes, tanks, containers or pipes. Bu applying a thermal insulation layer as described (and optionally a Multi-layer insulation) the heat load in a vacuum loss scenario is significantly reduced. This is particularly advantageous in applications where additional sources of fluid flow, such as retro-fitted containers or pipes, have been added to an existing system and the existing relief system is too small for the new, higher volume flow requirements.

A further advantage of the invention is that the reduction in size of relief devices and associated relief piping typically leads to a reduced heat load into the cryogenic process. This leads to an increase in process efficiency.

Whilst the invention has been described above, it extends to any inventive combination of features set out above or in the following description or drawings.

Brief Description of the Drawings

Figure 1 is a schematic of a first embodiment of the invention; Figure 2 is a schematic of a second embodiment of the invention; Figure 3a is a schematic of a third embodiment of the invention; Figure 3b is a schematic of a fourth embodiment of the invention; and Figure 4 is a schematic of a fifth embodiment of the invention.

Specific embodiments of the invention will now be described in detail by way of example only and with reference to the accompanying drawings.

Detailed description

Figure 1 shows a first embodiment of the invention, comprising a cryogenic storage tank 1. The cryogenic tank 1 comprises an inner tank 2 and an outer tank 6. The inner tank 2 defines an internal chamber (or storage chamber) 4, which in use is used to store cryogenic liquid (not shown). Between the outer tank 2 and the inner tank 4 is provided a cavity which is referred to as an insulation interspace 8. The insulation interspace 8 is essential a vacuum. A thermal insulation layer is provided 10 on an outer surface 2a of the inner tank 2.

Figure 2 shows a second embodiment of the invention, comprising a cryogenic pipeline 101. The cryogenic pipeline 101 comprises an inner pipe 102 and an outer pipe 106. Within the inner pipe 102 there is a conduit 104, which in use is used to transport store cryogenic liquid (not shown). Between the outer pipe 102 and the inner pipe 104 is provided a cavity which is referred to as an insulation interspace 108. The insulation interspace 108 is essential a vacuum. A thermal insulation layer 110 is provided on an outer surface 102a of the inner pipe 102.

Figure 3a shows a third embodiment of the invention, comprising a cryogenic storage tank 201. The cryogenic tank 201 comprises an inner tank 202 and an outer tank 306. The inner tank 202 defines an internal chamber (or storage chamber) 204, which in use is used to store cryogenic liquid (not shown). Between the outer tank 202 and the inner tank 204 is provided a cavity which is referred to as an insulation interspace 208. The insulation interspace 208 is essential a vacuum. A thermal insulation layer is provided 210 on an outer surface 202a of the inner tank 202. A multi-layer insulation (MLI) 212 is provided in the insulation interspace 208, between the thermal insulation layer 210 and the outer tank 206.

Figure 3b shows an embodiment which is similar to that described and shown with reference to Figure 3a. This embodiment differs in that the insulation (MLI) 212' does not extend completely around the inner tank 202.

Figure 4 shows a fifth embodiment of the invention, comprising a cryogenic pipeline 301. The cryogenic pipeline 301 comprises an inner pipe 302 and an outer pipe 306. Within the inner tank 302 there is a conduit 304, which in use is used to transport store cryogenic liquid (not shown). Between the outer pipe 302 and the inner pipe 304 is provided a cavity which is referred to as an insulation interspace 308. The insulation interspace 308 is essential a vacuum. A thermal insulation layer is provided 310 on an outer surface 302a of the inner pipe 302.

In all the embodiments described above, the thermal insulation layer (10, 110, 210, 310) is applied directly to the outer surface of the tank or pipe (more generally referred to as an inner structure). The thermal insulation layer (10, 110, 210, 310) is applied in such a way as to avoid or minimise the presence of air gaps between thermal insulation layer and the outer surface of the inner structure to ensure that essentially no condensation occurs on the outer surface of the inner structure.

The thermal insulation layer (10, 110, 210, 310) comprises one of more of the following insulating materials: a polyurethane foam, polyethylene (PE), Polyurethane (PUR), Polyethylene terephthalate (PET), Polytetrafluoroethylene (PTFE).

The third and fourth embodiments show MLI arrangements provided within the vacuum. In the embodiments shown, the MLI arrangement extends around the entire covered inner structure, or alternatively the MLI arrangement has an opening at an upper section. It will be appreciated that in other embodiments of the invention (not shown), a MLI arrangement can be provided in any configuration within the insulation interspace.

Since the invention relates to the insulation of cryogenic apparatus, components of cryogenic apparatus such as tanks (inlets, outlet, control systems etc) are not shown in the figures or described here. It will be appreciated that the insulation of the invention can be implemented in cryogenic apparatus irrespective of the other components. It will be appreciated that the ceramic foam insulation of the invention can be used in any double walled cryogenic apparatus, regardless of size, shape or configuration.

Furthermore, the insulation of the invention can be used to reduce the heating of fluid in any uninsulated relief pipeline subject to below optimum ambient temperatures. In lower ambient temperatures, the temperature of the fluid in the pipe is lower, which results in a higher mass flow through a given cross-section of pipe, due to the higher density of the lower temperature fluid. By applying the insulation as described above, the temperature in the pipeline can be maintained at or closer to the optimum operating level.

The insulation as defined above can be applied or retrofitted to existing cryogenic equipment. This may be particularly advantageous in the situation where additional sources of fluid flow (such as retrofitted containers or piping) are added to a system, which can mean that the equipment as originally installed is insufficient for the new, higher volume flow requirements.

Cryogenic equipment must be fitted with safety devices to relieve excess pressure. The temperature of the fluid relieved increases in the equipment up-and downstream of any safety device, for example pressure relief valves provided in pipelines. Due to the lower fluid density at higher temperatures the volume flow increases and larger safety equipment is required to meet the stringent safety requirements. By implementing the insulation as described above, this temperature increase is reduced. This means that the size of the safety equipment required can be reduced.

All of the invention has been described above with reference to one or more preferred embodiments. It will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims.

Claims

Claims 1. A cryogenic apparatus comprising an inner structure, an outer structure, an interspace between the inner structure and outer structure; and a vacuum provided in the interspace; wherein a thermal insulation layer is provided directly on an outer surface of the inner structure such that substantially no air gaps are present between the thermal insulation layer and the outer surface of the inner structure.
2. Apparatus according to claim 1, wherein the thermal insulation layer has a minimum thickness of 2mm.
3. Apparatus according to claim 1 or 2, wherein the thermal insulation layer has a maximum thermal conductivity of 2W/mK at temperatures below -173 C (100K).
4. Apparatus according to any one of the preceding claims, wherein the thermal layer comprises at least one of: a polyurethane foam, polyethylene (PE), Polyurethane (PUR), Polyethylene terephthalate (PET), Polytetrafluoroethylene (PTFE).
5. Apparatus according to any one of the preceding claims, wherein a multi-layer insulation is provided in the interspace between the thermal insulation layer and the outer structure.
6. Apparatus according to claim 5, wherein the multi-layer insulation comprises at least layers of foils.
7. Apparatus according to any one of the previous claims, wherein the layers comprise metal coated thin plastic layers.
8. Apparatus according to any one of the previous claims, wherein the cryogenic apparatus is a tank, a cold box, a storage vessel, a container or a pipeline.
9. Method for manufacturing an insulated cryogenic apparatus comprising, Providing an inner structure, Providing an outer structure, thereby defining an interspace between the inner structure and outer structure; and evacuating the gases from the interspace to provide an interspace vacuum, wherein the method includes applying a thermal insulation layer directly on an outer surface of the inner structure such that substantially no air gaps are present between the thermal insulation layer and the outer surface of the inner structure.
10. Method according to claim 9, wherein the step of providing the thermal insulation layer is achieved by spraying or vapour deposition.
11. Method according to claim 9 or claim 10, wherein the step of providing the thermal insulation layer comprises providing a layer at least 2mm thick.
12. Method according to any one of claims 9 to 11, wherein the thermal layer comprises at least one of: a polyurethane foam, polyethylene (PE), Polyurethane (PUR), Polyethylene terephthalate (PET), Polytetrafluoroethylene (PTFE).
13. Method according to any one of claims 9 to 12, wherein the method further includes providing a multi-layer insulation in the interspace between the thermal insulation layer and the outer structure.
14. Method according to claims 13, wherein the step of providing a multi-layer insulation comprises providing at least 5 layers.
15. Method according to any of claims 9 to 14, wherein the cryogenic apparatus is a tank, a cold box, a storage vessel, a container or a pipeline.