Waste heat boiler for cooling a process gas stream

Abstract

The invention relates to a waste heat boiler for cooling a process gas stream that flows through a plurality of heat exchange tubes, having a heat exchange chamber for accommodating a liquid cooling medium surrounding the heat exchange tubes; at least one tube sheet in order to form an impervious dividing wall between the heat exchange chamber and an inlet chamber for the process gas to be cooled, wherein the tube sheet for each heat exchange tube has a continuous opening which is connected in a fluid-tight manner to a first end of the respective heat exchange tube. The invention comprises a seal having lower thermal conductivity than a ferrule disposed in the opening and / or the tube sheet and having a gas permeability lower than that of the first and / or of the second section of a thermal insulation.

Description

[0001] WASTE HEAT BOILER FOR COOLING A PROCESS GAS STREAM

[0002] TECHNICAL FIELD

[0003] The invention relates to a waste heat boiler for cooling a process gas stream that flows through a plurality of heat exchange tubes from a reforming process and is formed in a chemical process plant. The invention further relates to the use of a waste heat boiler for cooling a process gas stream from a reforming process and to a reforming plant.

[0004] BACKGROUND OF THE INVENTION

[0005] In chemical process plants, in particular in reforming processes such as steam methane reforming (SMR), autothermal reforming (ATR) and partial oxidation (POx), and ammonia cracking processes, waste heat boilers are of central importance. These processes generate synthesis gas from light hydrocarbons and at the same time produce high temperatures which require efficient cooling and heat recovery.

[0006] Waste heat boilers utilize the thermal energy from the hot process gases that arise in these reforming processes. The hot synthesis gas or process gas is passed through heat exchange tubes which are arranged in a heat exchange chamber, for example a steam chamber, also called a steam generation chamber. Steam is generated in a steam chamber by heat transfer from the process gas to water. The steam may be utilized in other processes as heating medium or as process steam.

[0007] The reforming processes are characterized by high temperatures, and there is therefore a requirement for efficient heat removal and utilization of the waste heat. In the case of steam methane reforming (SMR), methane is converted to synthesis gas together with water vapour and a catalyst within a temperature range from 700°C to 1000°C. The resulting high temperature of the synthesis gas requires effective cooling in order to prepare the gas for further processing. The autothermal reforming (ATR) process reforms methane in a reactor at temperatures between 900°C and 1200°C, with addition of oxygen and water vapor. This process combines exothermic and endothermic reactions, which leads to a complex heat balance. Here too, the waste heat boiler is crucial for the regulation of the high temperatures of the synthesis gas and ensures that the gas is cooled to a safe temperature. In the partial oxidation (POx), methane is reacted with a substoichiometric amount of oxygen to produce synthesis gas, with the temperatures likewise between 800°C and 1200°C. The waste heat boiler takes up the excess heat from the synthesis gas and ensures that the gas is brought to

[0008] 2022P00459WO a safe temperature before being processed further. Industrial ammonia cracking typically involves temperatures ranging from 600 °C to 900 °C.

[0009] The process in the waste heat boiler begins in the inlet chamber into which the hot process gas is introduced from a transfer conduit. The process gas flows through a system of heat exchange tubes in the steam chamber formed between a first tube sheet and a second tube sheet. The tube sheets constitute dividing walls that separate the vapor chamber from the inlet chamber and the outlet chamber. The heat exchange tubes extend between the tube sheets and are connected to openings therein. In the steam chamber, the cooling medium, usually water, surrounds the heat exchange tubes and cools them while the water evaporates. The cooled process gas is then passed into the outlet chamber, whence it is transferred onward. The pressure ranges for the synthesis gas which is guided into a waste heat boiler vary depending on the type of reforming process, but are typically between 15 and 60 bar. These pressure ranges ensure that the synthesis gas can be passed effectively through the waste heat boiler before it is processed further or used in other applications.

[0010] A significant problem in reforming processes and synthesis gas is a corrosion effect known by the name of "metal dusting". Metal dusting is a phenomenon in which metals in a carbon monoxide-containing gas atmosphere are significantly degraded as a result of the formation and inward diffusion of carbon by the Boudouard reaction. This process leads to drastic decomposition of the metal surfaces and can considerably shorten the lifetime of fittings owing to significant loss of material. Metal dusting typically occurs at temperatures between 450°C and 750°C. The main cause of metal dusting is the interaction between metal and carbon formed on the surface from the gas phase, which leads to formation of graphite and metal carbides in the microstructure after inward diffusion and supersaturation of the material with carbon. The internal pressure caused thereby, in the affected region, leads to destruction of the material with leaching of metal particles. In reforming processes such as steam reforming (SMR), autothermal reforming (ATR) and partial oxidation (POx), the prevailing conditions are particularly favourable for metal dusting, since the process gases contain high amounts of carbon monoxide that can be converted to elemental carbon under the abovementioned conditions. If these gases come into contact with the metal surfaces under the aforementioned conditions, carbon formed can penetrate into and destabilize the metal. As a result of the high temperatures in reforming processes, the synthesis gas, in the course of cooling, has to pass through the temperature range between about 450°C

[0011] 2022P00459WO and 750°C which is of relevance for metal dusting. This harbours the risk that metal surfaces are attacked by metal dusting in this temperature range. In order to prevent this, all metallic surfaces that come into contact with synthesis gas must be either colder than 450°C (e.g. the water-cooled heat exchanger tubes) or hotter than 750°C. If this is not possible, materials with high stability can slow or delay attack and hence prolong lifetime, but attack cannot be permanently prevented.

[0012] A further challenge in the case of waste heat boilers for reforming gases relates to the necessary thermal insulation. Owing to the high temperatures of the process gas conducted into the waste heat boiler, comprehensive thermal insulation is required. Therefore, transfer conduits, inlet chamber and tube sheets are frequently insulated with refractory material. Particularly critical connections are those between the tube sheet at the inlet chamber and the heat exchange tubes, since the process gas here can come directly into contact with barely cooled or uncooled metal surfaces and the formation of carbon in this region is particularly promoted owing to the prevailing conditions. In order to withstand these conditions, sleeve-shaped tube protection devices, known as "ferrules", are used. These ferrules are placed in the openings of the tube sheets and partly inserted into the heat exchange tubes, and project from the tube sheet insulated with refractory concrete. Insulation between the ferrule and the inner surface of the heat exchange tube or the tube sheet serves to reduce heat transfer from ferrule to heat exchange tube or tube sheet and to ensure that the ferrule does not cool down too much, such that the temperature of the ferrule is above the temperatures that promote metal dusting. At the same time, the insulation is intended to avoid excessive heating of the heat exchange tubes and of the tube sheet in the inlet region, such that the temperature thereof does not rise into the temperature range that promotes metal dusting.

[0013] The insulation between the ferrule and the heat exchange tube has to be renewed at certain time intervals, since it no longer exists after a period of operation. This increases the risk of corrosion, such as the elucidated metal dusting. The renewal of the insulation is costly and involves high technical outlay.

[0014] It is therefore an object of the invention to develop a solution that reduces the need for frequent renewal of the insulation and counteracts the occurrence of corrosion.

[0015] 2022P00459WO SUMMARY OF THE INVENTION

[0016] The invention is based on the recognition of the problem as follows: Owing to the significantly higher gas velocity in the heat exchange tubes compared to the inlet chamber, the static pressure in the heat exchange tubes is lower than in the inlet chamber (Bernoulli effect). This pressure differential gives rise to a driving force that pushes the hot process gas across the outer diameter of the ferrules placed in the heat exchange tubes. This bypass gas stream can push the insulation out of its seat and lead to metal dusting on tube sheet and tubes. After thorough examination, this problem was attributable in particular to the fact that no decomposition residues of the seal were found.

[0017] The problem underlying the invention is solved by a waste heat boiler for a process gas stream from a reforming process according to Claim 1. Further and preferred embodiments of the invention are disclosed in the description that follows and in the dependent claims. The features illustrated in the claims and in the description are combinable with one another in any technologically meaningful manner.

[0018] In a first aspect of the invention, a waste heat boiler is proposed for cooling a process gas stream that flows through a plurality of heat exchange tubes from a reforming process or ammonia cracking process and is formed in a chemical process plant. The waste heat boiler comprises a heat exchange chamber, for example a steam chamber, for accommodating a liquid cooling medium, such as water in particular, that surrounds the heat exchange tubes. The waste heat boiler further comprises at least one tube sheet in order to form an impervious dividing wall between the heat exchange chamber and an inlet chamber for the process gas to be cooled, where the tube sheet for each heat exchange tube has a continuous opening which is connected in a fluid-tight manner to a first end of the respective heat exchange tube. This serves to seal the interior of the heat exchange chamber with respect to the process gas stream and to establish a fluid connection between the heat exchange tubes and the inlet chamber. The waste heat boiler further comprises a ferrule which is disposed in the opening and projects from the tube sheet on the inlet chamber side and on the heat exchange chamber side, where the ferrule is embedded into a refractory lining on the inlet chamber side, wherein the ferrule is partly accommodated in the first end of the heat exchange tube and a first portion of a thermal insulation is disposed between the ferrule and the heat exchange tube, where a clearance in which a second portion of a thermal insulation is

[0019] 2022P00459WO disposed is formed between an inner circumferential surface of the opening of the tube sheet and the ferrule extending through the opening. Also provided is a seal which seals the clearance with respect to the inlet chamber, wherein the seal has a lower thermal conductivity than the ferrule and / or the tube sheet and a gas permeability lower than that of the first and / or the second portion of the thermal insulation.

[0020] The seal effectively seals the gap between the tube sheet and the ferrule and can bear against the tube sheet and the ferrule. The waste heat boiler may comprise a main body in which the heat exchange chamber is formed.

[0021] The seal prevents the above-described gas flows through the clearance, which allows prevention of expulsion of the insulation. This also considerably reduces the risk of metal dusting. In addition, the seal functions as an insulator which minimizes heat transfer from the ferrule to the tube sheet, as a result of which unwanted heat transfer is reduced, and the tube sheet, heat exchange tube and ferrule components are kept outside the temperature range which is favourable for development of metal dusting.

[0022] The ferrule can be produced from ceramic or metal. However, metal is preferred since it is better suited to the mechanical stresses that occur in a generic waste heat boiler. Effective control of the temperature of the ferrule outside the range for metal dusting makes it possible to use metal ferrules in an effective manner.

[0023] In a further embodiment of the invention, the seal seals the clearance directly with respect to the refractory lining. Although the ferrule is embedded in the refractory lining, the refractory lining is not gas-impermeable. A ferrule arrangement that exposes the clearance structurally to the refractory lining, meaning that the clearance would directly adjoin the refractory lining, can be effectively protected from ingress of gas by use of the seal.

[0024] In a further embodiment of the invention, the waste heat boiler further comprises an outlet chamber which is fluidically connected to a second end of the heat exchange tubes and is intended for collecting and discharging the cooled process gas stream passed through the heat exchange tubes, wherein a second tube sheet is provided in order to provide a fluid-tight dividing wall between the heat exchange chamber and the outlet chamber, wherein the second tube sheet for each heat exchange tube has a continuous opening which is connected in a fluid-tight manner to the second end of the respective heat exchange tube.

[0025] 2022P00459WO In a further embodiment of the invention, the first portion and the second portion of a thermal insulation are fluidically connected.

[0026] In a further embodiment of the invention, the first and second portions of the thermal insulation are portions of a common insulation, i.e. are formed in one piece.

[0027] In a further embodiment of the invention, the first portion of the thermal insulation is provided as a layer on the ferrule.

[0028] In a further embodiment of the invention, the second portion of the thermal insulation is designed as a ferrule body which is pushed onto the ferrule or into an end of the heat exchange tube.

[0029] In a further embodiment of the invention, a collar formed transversely to an axis of the ferrule is provided, wherein the seal is arranged between the collar and a surface of the tube sheet on the inlet chamber side. In a further embodiment of the invention, the collar is mounted on the ferrule, preferably in a fluid-tight manner, or formed in one piece with the ferrule.

[0030] In a further embodiment of the invention, the seal is an annular seal with a central opening through which the ferrule extends. The ring seal preferably rests on the tube sheet on the inlet chamber side.

[0031] In a further embodiment of the invention, the seal is positioned by a holder, in particular a metal ring, mounted on the tube sheet.

[0032] In a further embodiment of the invention, the seal is positioned by the refractory lining.

[0033] In a further embodiment of the invention, the second portion of the thermal insulation has a sealing effect, and in particular has a gas permeability lower than that of the first portion of a thermal insulation. In a development of this concept of the invention, in a further embodiment of the invention, the seal and the second portion of a thermal insulation are formed in one piece.

[0034] The heat exchange tube may extend into the opening of the tube sheet such that the first end is positioned in the opening. The clearance may be on the outside of the ferrule between heat exchange tube and inner surface of the opening. The heat exchange tube may be mounted by the first end on the surface of the tube sheet on the heat exchange chamber side or may extend partly into the opening. In a further embodiment of

[0035] 2022P00459WO the invention, a ferrule section of the ferrule proceeds from the first end of the heat exchange tube and extends along an inner circumferential surface of the opening of the tube sheet, such that the clearance is formed between an outer circumference of the ferrule section and an inner circumferential surface of the opening. The first end of the heat exchange tube ends upstream of the edge of the opening on the inlet side, which gives rise to an annular clearance with an axial length. In this embodiment, the first portion and the second portion of a thermal insulation may be immediately adjacent to each other.

[0036] In a further embodiment of the invention, the seal is positioned by the refractory lining. The refractory lining may be mounted on the tube sheet in such a way that it exerts a prestress on the seal, such that the interfaces of the seal are sealed, for example toward the tube sheet and toward the ferrule or toward the collar. Moreover, the pressure prevailing in the inlet chamber can contribute to the prestress force.

[0037] In a further embodiment of the invention, the refractory lining extends over the entire area of the tube sheet present in the inlet chamber, or at least 80% of it. This excludes the end sections of the ferrules or the openings thereof.

[0038] The refractory lining may comprise materials such as, in particular, high-alumina refractory concrete, high-alumina refractory bricks or high-alumina fibre materials.

[0039] The refractory lining may have a porosity of about 15% up to 95%. The porosity is expressed in per cent and describes how much of the volume of a material consists of open or closed pores.

[0040] The insulation may in particular comprise the following materials: ceramic alumina fibre mats, for example RHI Pyrostop LD 1600 mat or Unifrax Safil mat, and ceramic paper made of alumina fibres, for example RHI Pyrostop 1600 paper.

[0041] Suitable sealing materials include products based on graphite and / or high-alumina fibres, for example ceramic sealing cords. However, a seal may also have metallic or metal oxide constituents.

[0042] In a further embodiment of the invention, the refractory lining has a thermal conductivity in the range from 10% to 100% of the thermal conductivity of the seal.

[0043] In a further embodiment of the invention, the seal has ceramic constituents, in particular ceramic paper and / or ceramic fibres based on alumina or zirconia.

[0044] 2022P00459WO In a further embodiment of the invention, the heat transfer chamber is designed as a steam generator chamber in which water is provided as cooling medium.

[0045] It has been found to be particularly advantageous when the ferrule has an insertion length of 100-250 mm into the first end of the heat exchange tube. The insulation between the ferrule and the heat exchange tube has a layer thickness of preferably 2- 6 mm. The seal preferably has a thickness of 2-12 mm between the surfaces to be sealed.

[0046] In a further embodiment of the invention, the waste heat boiler is designed for the process gas from steam reforming (steam methane reforming, SMR), autothermal reforming (ATR), partial oxidation (POx) or ammonia cracking.

[0047] A further aspect of the invention relates to a reforming plant comprising a reactor for generating synthesis gas from a feed gas stream and a waste heat boiler downstream of the reactor, as described herein. The waste heat boiler described herein is of optimal suitability for such plants in particular because of its corrosion-preventing properties and effective temperature control.

[0048] A further aspect of the invention relates to the use of a waste heat boiler as described herein for cooling a process gas stream from a reforming process, in particular from steam reforming (steam methane reforming, SMR), autothermal reforming (ATR) or partial oxidation (POx).

[0049] A further aspect of the invention relates to an ammonia cracker comprising a reactor for generating a mixture of nitrogen and hydrogen and a waste heat boiler downstream of the reactor, as described herein. The waste heat boiler described herein is of optimal suitability for such plants in particular because of its corrosion-preventing properties and effective temperature control.

[0050] A further aspect of the invention relates to the use of a waste heat boiler as described herein for cooling a process gas stream from an ammonia cracking process.

[0051] DESCRIPTION OF FIGURES

[0052] The invention is elucidated in detail hereinafter with reference to figures. The figures show a preferred working example, but the invention is not limited thereto. The figures and the relative sizes shown therein are merely schematic. The figures show:

[0053] 2022P00459WO FIG. 1 a schematic, in a lateral sectional view, of a waste heat boiler in a first embodiment of the invention; and

[0054] FIG. 2 details of the waste heat boiler from FIG. 1.

[0055] FIG. 1 shows a schematic diagram of a waste heat boiler 1 in a lateral section view. The waste heat boiler 1 comprises a heat exchange chamber 2 in the form of a steam chamber. An inlet chamber 3 establishes a fluid connection between a first tube sheet 4 on the inlet side and a transfer conduit 5 which supplies hot synthesis gas from a reforming process. A plurality of heat exchange tubes 6 extend parallel between the tube sheet 4 on the inlet side and a second tube sheet 7. The heat exchange tubes 6 are each connected to openings in the tube sheets 4 and 7 and establish a fluid connection between the inlet chamber 3 and an outlet chamber 8. The tube sheets 4 and 7 form a sealing dividing wall between the heat exchange chamber 2 and the inlet chamber 3 or the outlet chamber 8. The tube sheet 4 is provided with a refractory lining 9 on the inlet chamber side. As shown, such a lining 10 can also be provided on the surface on the outlet side of the second tube sheet 7. The cooled synthesis gas leaves the outlet chamber 8 via a further transfer conduit 24.

[0056] In use, the hot synthesis gas originating from a chemical process is fed into the inlet chamber 3 via the transfer conduit 5. During operation, the heat exchange tubes 6 in the heat exchange chamber 2 are surrounded by a cooling medium 11 , cooling water here, which is fed into the heat exchange chamber 2. From the inlet chamber 3, the synthesis gas flows through the openings in the tube sheet 4 on the inlet side and the heat exchange tubes 6. As it flows through the heat exchange tubes 6, the synthesis gas is cooled by the cooling water 11 . At the same time, the cooling water is heated and water vapor 12 is generated. A water / steam mixture is then present in the heat exchange chamber 2. The water vapour or the water-steam mixture is passed out of the heat exchange chamber 2 for further use. The cooled synthesis gas leaves the heat exchange tubes 6 at the second tube sheet 7 and enters the outlet chamber 8. From the outlet chamber 8, the synthesis gas can be subjected either to a further processing cycle or an additional cooling process.

[0057] FIG. 2 shows details of the tube sheet 4 on the inlet chamber side, in particular the connection between heat exchange chamber 2 and inlet chamber 3. The tube sheet 4 has a multitude of through-openings, of which one opening 13 is illustrated in FIG. 2. The heat exchange tube 6 is connected to the opening 13 in a fluid-tight manner on the

[0058] 2022P00459WO heat exchange chamber side by means of a weld bond 15 to a first end 14 of the heat exchange tube 6. A metal ferrule 17 extending along a ferrule axis 16 has been partly introduced into the first end 14 of the heat exchange tube 6 via the introduction section X and projects from the first end 14. The ferrule 17 projects from the tube sheet 4 on the inlet chamber side and on the heat exchange chamber side along the ferrule axis 16. On the inlet chamber side, the portion of the ferrule projecting from the tube sheet 4 is embedded in the refractory lining 9. The end thereof on the inlet chamber side opens into the inlet chamber 3. The ferrule 17 thus provides fluid connection between the inlet chamber 3 and the heat exchange tube 6.

[0059] In the section X along which the ferrule 17 extends into the heat exchange tube 6, a first portion 18 of a thermal insulation 19 is disposed on the outer circumference of the ferrule 17 between the ferrule 17 and the inner surface of the heat exchange tube 6. This has thickness Y. The first portion 18 extends from the back end as far as the weld bond 15.

[0060] Between the outer surface of the ferrule 17 and the inner surface of the through-opening 13, an annular gap or clearance 20 is formed, which is delimited on the heat exchange chamber side by the first end 14 of the heat exchange tube 6 and the first portion 18 of the thermal insulation 19. A second portion 21 of the thermal insulation 19 is disposed in the clearance 2. The first portion 18 of the thermal insulation 19 is fluidi- cally connected to the second portion 21 of the thermal insulation.

[0061] The clearance 20 is at first open with respect to the refractory lining 9. Since the refractory lining 9 is gas-permeable, a gas stream can enter the clearance 20 and push the thermal insulation 19 out of position, in particular the first portion 18. In order to counteract this, a seal 22 in the form of an annular disk or sealing cord in the form of a ring is provided.

[0062] The seal 22 has a central opening through which the ferrule 17 extends. On the inlet chamber side, the ferrule 17 has a circumferential collar 23 which extends perpendicularly to the ferrule axis 16 and which is likewise embedded in the refractory lining 9. In axial direction of the ferrule axis 16, the seal 22 bears against the surface of the tube sheet 4 on the inlet chamber side around the opening 13 and against the axially directed surface of the collar 23, and hence seals the clearance 20. This prevents the gas from penetrating into the clearance 20 and the thermal insulation 19 from being pushed out of its seat.

[0063] 2022P00459WO The seal 22 consists of ceramic materials having lower thermal conductivity than the ferrule 17 and the tube sheet 4. In operation, the ferrule 17 is heated up by the incoming synthesis gas to a temperature above the critical range for metal dusting. The thermal insulation 19 ensures that the heat exchange tube 6 and the tube sheet 4 do not heat up excessively, in particular into the range of relevance for metal dusting. At the same time, the thermal insulation 19 prevents cooling of the ferrule 17. The seal 22 additionally prevents heat transfer from the ferrule 17 and its collar 23 into the tube sheet 4.

[0064] 2022P00459WO List of reference numerals

[0065] 1 waste heat boiler

[0066] 2 heat exchange chamber

[0067] 3 inlet chamber

[0068] 4 tube sheet

[0069] 5 transfer conduit for process gas

[0070] 6 heat exchange tube

[0071] 7 second tube sheet

[0072] 8 outlet chamber

[0073] 9 refractory lining

[0074] 10 refractory lining

[0075] 11 cooling medium (water)

[0076] 12 water vapour

[0077] 13 opening in tube sheet

[0078] 14 first end of the heat exchange tube

[0079] 15 weld bond

[0080] 16 ferrule axis

[0081] 17 ferrule

[0082] 18 first portion of the thermal insulation

[0083] 19 thermal insulation

[0084] 20 clearance

[0085] 21 second portion of the thermal insulation

[0086] 22 seal

[0087] 23 collar

[0088] 24 transfer conduit

[0089] X introduction section of ferrule into heat exchange tube

[0090] Y thick thermal insulation of first portion

[0091] 2022P00459WO

Claims

Claims1 . Waste heat boiler (1) for cooling a process gas stream from a reforming process or ammonia cracking process that flows through a plurality of heat exchange tubes (6) and is formed in a chemical process plant, comprising: a heat exchange chamber (2) for accommodating a liquid cooling medium surrounding the heat exchange tubes (6); at least one tube sheet (4) in order to form an impervious dividing wall between the heat exchange chamber (2) and an inlet chamber (3) for the process gas to be cooled, wherein the tube sheet (4) for each heat exchange tube (6) has a continuous opening (13) which is connected in a fluid-tight manner to a first end (14) of the respective heat exchange tube (6); a ferrule (17) which is disposed in the opening (13) and projects from the tube sheet (4) on the inlet chamber side and on the heat exchange chamber side, wherein, on the inlet chamber side, the ferrule (17) is embedded in a refractory lining (9), wherein the ferrule (17) is partly accommodated in the first end (14) of the heat exchange tube (6) and a first portion (18) of a thermal insulation (19) is disposed between the ferrule (17) and the heat exchange tube (6), wherein a clearance (20) in which a second portion (21) of the thermal insulation (19) is disposed is formed between an inner circumferential surface of the opening (13) of the tube sheet (4) and the ferrule (17) extending through the opening (13); and a seal (22) which seals the clearance (20) with respect to the inlet chamber (3), wherein the seal (22) has a lower thermal conductivity than the ferrule (17) and / or the tube sheet (4) and a gas permeability lower than that of the first and / or the second section (18, 21) of the thermal insulation (19).

2. Waste heat boiler (1) according to Claim 1 , wherein a ferrule section of the ferrule (17) proceeds from the first end (14) of the heat exchange tube (6) and extends along an inner circumferential surface of the opening (13) of the tube2022P00459WOsheet (4), such that the clearance (20) is formed between an outer circumference of the ferrule section and an inner circumferential surface of the opening (13).

3. Waste heat boiler (1) according to Claim 1 or 2, wherein the first section (18) and the second section (21) of the thermal insulation (19) are fluidically connected.

4. Waste heat boiler (1) according to any of the preceding claims, comprising a collar (23) formed transversely with respect to a ferrule axis (16) of the ferrule (17), wherein the seal (22) is disposed between the collar (23) and a surface on the inlet chamber side of the tube sheet (4).

5. Waste heat boiler (1) according to any of the preceding claims, wherein the seal (22) is positioned by a holder, in particular a metal ring, mounted on the tube sheet (4).

6. Waste heat boiler (1) according to any of the preceding claims, wherein the seal (22) is positioned by the refractory lining (9).

7. Waste heat boiler (1) according to any of the preceding claims, wherein the refractory lining (9) extends over the entire area of the tube sheet (4) present in the inlet chamber, or at least 80% of it.

8. Waste heat boiler (1) according to any of the preceding claims, wherein the refractory lining (9) has a thermal conductivity in the range from 10% to 100% of the thermal conductivity of the seal (22).

9. Waste heat boiler (1) according to any of the preceding claims, wherein the seal (22) includes ceramic constituents, especially ceramic paper and / or ceramic fibres.

10. Waste heat boiler (1) according to any of the preceding claims, wherein the heat exchange chamber (2) is in the form of a steam generator space in which the cooling medium provided is water.11 . Waste heat boiler (1) according to any of the preceding claims, wherein the waste heat boiler is designed for the process gas from steam reforming (steam methane reforming, SMR), autothermal reforming (ATR), partial oxidation (POx) or ammonia cracking.2022P00459WO- 15 -12. Waste heat boiler (1) according to any of the preceding claims, wherein the ferrule (17) is made of metal or ceramic.

13. Reforming plant comprising a reactor for generating synthesis gas from a feed gas stream and, downstream of the reactor, a waste heat boiler (1) according to any of the preceding claims.

14. Use of a waste heat boiler (1) according to any of Claims 1 to 12 for cooling a process gas stream from a reforming process, in particular from steam reforming (steam methane reforming, SMR), autothermal reforming (ATR) or partial oxidation (POx).

15. Ammonia cracker comprising a reactor for generating a mixture of nitrogen and hydrogen and, downstream of the reactor, a waste heat boiler (1) according to any of claims 1 to 12.

16. Use of a waste heat boiler (1) according to any of Claims 1 to 12 for cooling a process gas stream from an ammonia cracking process.2022P00459WO

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