WO2024168425A1

WO2024168425A1 - Heat exchanger for heating or cooling bulk solids

Info

Publication number: WO2024168425A1
Application number: PCT/CA2024/050179
Authority: WO
Inventors: Gerald Marinitsch; David Moon; Ashley Byman; Jason Gass
Original assignee: Solex Thermal Science Inc
Current assignee: Solex Thermal Science Inc
Priority date: 2023-02-17
Filing date: 2024-02-12
Publication date: 2024-08-22
Anticipated expiration: 2025-08-17

Abstract

A heat exchanger for bulk solids, includes a housing including an inlet, an outlet, and a heat exchange chamber therebetween. Heat transfer tubes include an inlet end and an outlet end, and in the heat exchange chamber for indirect heat exchange of a heat exchange medium with the bulk solids that flow through the heat transfer tubes. Upper and lower tube plates are coupled to the housing and include upper tube plate holes in which the heat transfer tubes are disposed and lower tube plate holes in which the heat transfer tubes are supported. Stepped inserts in the lower tube plate holes are sized to provide a clearance fit in the lower tube plate holes. Each heat transfer tube is supported on an inner step of a stepped insert, and forms a clearance fit therewith. The heat transfer tubes stand loosely on the stepped inserts.

Description

HEAT EXCHANGER FOR HEATING OR COOLING BULK SOLIDS

FIELD OF THE INVENTION

[0001] The present disclosure relates to a high temperature heat exchanger for heating bulk solids to a temperature above 400°C or cooling bulk solids from a temperature above 400°C.

BACKGROUND

[0002] Heat exchangers may be used to heat or cool bulk solids. The solids may flow through the heat exchanger by the force of gravity as heat is exchanged with a heat exchange medium.

[0003] The temperature of the bulk solids being cooled or the temperature to which the bulk solids are heated is typically limited because of the effects of thermal expansion and contraction of the elements of the heat exchanger, wear on elements of the heat exchanger, and thus the reduced operational life of the heat exchanger. In addition materials that may be utilized to withstand high temperature applications exhibit reduced wear properties and reduced strength.

[0004] Improvements to heat exchangers for high temperature applications is desirable.

SUMMARY

[0005] According to an aspect of an embodiment, a heat exchanger for heating or cooling bulk solids, includes a housing including an inlet for receiving the bulk solids into the housing, an outlet for discharging the bulk solids from the housing, and a heat exchange chamber disposed between the inlet and the outlet. A plurality of spaced apart heat transfer tubes include an inlet end for receiving the bulk solids and an outlet end for discharging the bulk solids from the heat transfer tubes. The heat transfer tubes extend generally vertically along the heat exchange chamber of the housing, for indirect heat exchange of a heat exchange medium in the heat exchange chamber with the bulk solids that flow by gravity from the inlet end and through the heat transfer tubes, toward the outlet end. An upper tube plate and a lower tube plate are coupled to the housing, between the inlet and the outlet of the housing, the upper tube plate including upper tube plate holes in which the heat transfer tubes are disposed and the lower tube plate including lower tube plate holes in which the heat transfer tubes are supported.

Stepped inserts are each disposed in a respective one of the lower tube plate holes and sized to provide a clearance fit in the respective one of the lower tube plate holes. Each heat transfer tube of the plurality of spaced apart heat transfer tubes is disposed in and supported on an inner step of a respective one of the stepped inserts, and forms a clearance fit with the respective one of the stepped inserts. The heat transfer tubes stand loosely on the stepped inserts in the lower tube plate, accommodating thermal expansion or contraction.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Embodiments of the present invention will be described, by way of example, with reference to the drawings and to the following description, in which:

[0007] FIG. 1 is a perspective view of a heat exchanger in accordance with an embodiment;

[0008] FIG. 2 is a side view of the heat exchanger of FIG. 1;

[0009] FIG. 3 is a sectional side view of the heat exchanger, taken along the line 3-3 of FIG. 2;

[0010] FIG. 4 is a sectional side view of a part of the heat exchanger of FIG. 1, showing a heat transfer tube and an upper tube plate in accordance with one embodiment;

[0011] FIG. 5 is a sectional side view of a part of the heat exchanger of FIG. 1, showing a heat transfer tube and a lower tube plate according to an embodiment; and [0012] FIG. 6 is simplified sectional side view of a part of the heat exchanger of FIG. 1, showing a heat transfer tube and an upper tube plate according to another embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] For simplicity and clarity of illustration, reference numerals may be repeated among the figures to indicate corresponding or analogous elements. Numerous details are set forth to provide an understanding of the embodiments described herein. The embodiments may be practiced without these details. In other instances, known methods, procedures, and components have not been described in detail to avoid obscuring the embodiments described. The description is not to be considered as limited to the scope of the embodiments described herein.

[0014] As indicated above, improvements to heat exchangers for high temperature applications is desirable. PCT patent application publication WO 2019/000079 assigned to Solex Thermal Science Inc. discloses a heat exchanger suitable for high temperature applications. The heat exchanger includes heat transfer tubes that are connected to an upper or lower tube plate by bellows to facilitate expansion and contraction of the heat transfer tubes. Maintenance and replacement of heat transfer tubes may be time consuming and somewhat cumbersome, however for attachment of the heat transfer tubes to the upper and lower tube plates.

[0015] The heat exchanger described herein is suitable for use at high temperatures and includes heat transfer tubes that are supported on one or both of the upper tube plate and the lower tube plate with the heat transfer tubes sized to provide a clearance fit with respective holes in the tube plates. The heat transfer tubes are removable by lifting the heat transfer tubes out of the tube plates, facilitating maintenance or replacement. Furthermore, expansion and contraction of the heat transfer tubes and the upper and lower tube plates is accommodated.

[0016] Referring to FIG. 1 through FIG. 5, the disclosure generally relates to a heat exchanger 100 for heating or cooling bulk solids. The heat exchanger 100, includes a housing 102 that has an inlet 104 for receiving the bulk solids into the housing 102, an outlet 106 for discharging the bulk solids from the housing 102, and a heat exchange chamber 108 disposed between the inlet 104 and the outlet 106. The heat exchanger 100 also includes a plurality of spaced apart heat transfer tubes 110 that include an inlet end 112 for receiving the bulk solids and an outlet end 114 for discharging the bulk solids from the heat transfer tubes 110, the heat transfer tubes 110 extending generally vertically along the heat exchange chamber 108 of the housing 102, for indirect heat exchange of a heat exchange medium in the heat exchange chamber 108 with the bulk solids that flow by gravity from the inlet end 112 and through the heat transfer tubes 110, toward the outlet end 114. The heat exchanger 100 also includes an upper tube plate 116 and a lower tube plate 118 coupled to the housing 102, between the inlet 104 and the outlet 106 of the housing 102. The upper tube plate 116 includes upper tube plate holes in which the heat transfer tubes 110 are disposed and the lower tube 118 plate includes lower tube plate holes in which the heat transfer tubes 110 are support in the housing 102. The heat exchanger 100 also includes stepped inserts 508. Each stepped insert 508 is disposed in a respective one of the lower tube plate holes and sized to provide a clearance fit in the respective one of the lower tube plate holes. Each heat transfer tube 110 of the plurality of spaced apart heat transfer tubes 110 is disposed in and supported on an inner step 514 of a respective one of the stepped inserts 508, and forms a clearance fit with the respective one of the stepped inserts 508. The heat transfer tubes 110 stand loosely in the lower tube plate 118 to accommodate thermal expansion or contraction.

[0017] The size of the heat transfer tubes 110 and spacing between the heat transfer tubes 110 may differ from the size and spacing illustrated in the figures, depending on the application, the volume of bulk solids, and the pressure drop across the gaseous heat exchange medium.

[0018] In the example shown in FIG. 1 through FIG. 5, the housing 102 is generally cylindrical in shape and includes three sections, including an entry hopper 120, the heat exchange chamber 108, and a discharge hopper 122. In this example, the sections of the housing 102 are coupled together, for example, by bolting the sections together. An entry hopper flange 124 is coupled to an upper heat exchange chamber flange 126. A lower heat exchange chamber flange 128 is coupled to a discharge hopper flange 130.

[0019] The entry hopper 120 is separated from the heat exchange chamber 108 by the upper tube plate 116. The upper tube plate 116 in this example is a generally circular plate that is larger in diameter than the internal diameter of the heat exchange chamber 108 or the entry hopper 120. The upper tube plate 116 extends outwardly and is clamped between the entry hopper flange 124 and the upper heat exchange chamber flange 126. By clamping the upper tube plate 116 between the entry hopper flange 124 and the upper heat exchange chamber flange 126, some radial expansion of the upper tube plate 116 is accommodated when the heat exchanger 102 is in use.

[0020] The discharge hopper 122 is separated from the heat exchange chamber 108 by the lower tube plate 118. The lower tube plate 118 in this example is a generally circular plate that is larger in diameter than the internal diameter of the heat exchange chamber 108 or the discharge hopper 122. The lower tube plate 118 extends outwardly and is clamped between the lower heat exchange chamber flange 128 and the discharge hopper flange 130. Thus, some radial expansion of the lower tube plate 118 is accommodated when the heat exchanger 102 is in use.

[0021] A plurality of spaced apart heat transfer tubes 110 are disposed within the housing 102 and extend generally vertically through the heat exchange chamber 108. The heat transfer tubes 110 may be ceramic heat transfer tubes, such as silicon carbide heat transfer tubes. Other heat transfer tube materials may be successfully implemented, however. For example, stainless steel, such as Type 304L stainless steel, heat transfer tubes may be successfully implemented. Alternatively, the heat transfer tubes 110 may be a nickel based alloy such as Inconel™. The heat transfer tubes 110 may be made of a different material than the upper tube plate 116 or the lower tube plate 118.

[0022] In this example, the heat transfer tubes 110 extend generally linearly and vertically. The heat transfer tubes 110 may have a circular crosssection or may have an oval shaped cross-section.

[0023] The heat transfer tubes 110 are supported in the housing 102 by the upper tube plate 116 and the lower tube plate 118. The upper tube plate 116 includes a plurality of holes such that, for each heat transfer tube 110, there is a corresponding hole in the upper tube plate 116. Similarly, the lower tube plate 118 includes a plurality of holes such that, for each heat transfer tube 110, there is a corresponding hole in the lower tube plate 118.

[0024] Each of the heat transfer tubes 110 extend into respective holes in the upper tube plate 116 and the lower tube plate 118. The holes are sized to provide a clearance fit for the heat transfer tubes 110 extending therethrough such that the heat transfer tubes 110 hang loosely from the upper tube plate 116 or stand loosely in the lower tube plate 118 to accommodate thermal expansion or contraction.

[0025] Reference is now made to FIG. 4 which shows one example of a heat transfer tube 110 and the upper tube plate 116. The upper tube plate 116 may be a metal plate of, for example, stainless steel. The metal plate may be coated with a ceramic coating to inhibit corrosion. In this example, the upper tube plate 116 is insulated on a bottom side thereof by a layer of insulation 402, which may be refractory material. A hole into which the heat transfer tube 110 is inserted, extends through the upper tube plate 116 and the layer of insulation 402. In this example, the diameter of the hole through the upper tube plate 116 is the same as the diameter of the hole through the layer of insulation 402 to provide a continuous hole of constant diameter. [0026] A packing material 404 lines the edges of the upper tube plate 116 and the layer of insulation 402 inside the hole and provides protection for the edge 406 of the upper tube plate 116 and the edge 408 of the layer of insulation 402 that define the hole, while also reducing the escape of gasses from the heat exchanger chamber 108, through the hole and into the entry hopper. The heat transfer tube 110 is inserted into the hole such that the packing material 404 is seated between the heat transfer tube 110 and the edge 406 of the upper tube plate 116 and between the heat transfer tube 110 and the edge 408 of the layer of insulation. The inlet end 112 of the heat transfer tube 110 is spaced from a top side 410 of the upper tube plate 410. Thus, the heat transfer tube 110 extends only partly into the hole.

[0027] A tube protector 412, which includes a tube insert 414 with a flanged end 416 is inserted into the hole such that the tube insert 414 extends into an upper portion of the heat transfer tube 110. The outer diameter of the tube insert 414 is smaller than the inner diameter of the heat transfer tube 110. Thus, the outside of the tube insert 414 is spaced from the outside of the heat transfer tube 110, providing a clearance fit. The flanged end 416 of the tube protector 412 is seated on the top side 410 of the upper tube plate 116, around a margin of the hole. The tube protector 412 protects the inlet end 112 of the heat transfer tube 110. The inlet end 112 of the heat transfer tube 110 is spaced from the flanged end 416 of the tube protector to accommodate thermal expansion and contraction. The heat transfer tube 110 is held loosely by the upper tube plate 116.

[0028] The remaining heat transfer tubes 110 and upper tube plate 116 are similarly constructed and arranged and are also similarly held in the upper tube plate 116.

[0029] Reference is now made to FIG. 5 which shows one example of a heat transfer tube 110 and the lower tube plate 118. Similar to the upper tube plate 116, the lower tube plate 118 may be a metal plate of, for example, stainless steel. The metal plate may be coated with a ceramic coating to inhibit corrosion. The lower tube plate 118 is insulated on a top side thereof by a layer of insulation 502, which may be refractory material. A hole into which the heat transfer tube 110 is inserted, extends through the layer of insulation 502 and through the lower tube plate 118. In this example, the diameter of the hole steps down as the diameter of the hole through the layer of insulation 502 is larger than the diameter of the hole through the lower tube plate 118. The change in diameter of the hole results in a step 504 on an upper surface 506 of the lower tube plate 118, from the layer of insulation 502 to the lower tube plate 118.

[0030] A stepped insert 508, which may be a ceramic insert, includes a generally tubular first section 510 and a generally tubular second section 512. The first section 510 has an inner diameter that is larger than an outer diameter of the heat transfer tube 110 and an outer diameter that is smaller than the diameter of the portion of the hole that extends through the layer of insulation. The second section 512 has an inner diameter that is less than the inner diameter of the first section and less than the outer diameter of the heat transfer tube 110.

[0031] The second section 512 also has an outer diameter that is less than the diameter of the portion of the hole that extends through the layer of insulation 502. Thus, the inner diameter of the stepped insert 508 steps down from the first section 510 to the second section 512, resulting in an inner step 514. The inner step 514 may be non-flat or include rounded edges. For example, the inner step may be rounded from the internal tube surface 518 of the first diameter to the internal tube surface 520 of the second diameter. Similarly, the outer diameter steps down from the first section 510 to the second section 512, resulting in an outer step 516. The outer step 516 provides a generally flat step surface.

[0032] The stepped insert 508 is disposed in the hole that extends through the layer of insulation 502 and through the lower tube plate 118 with the outer step 516 of the stepped insert seated on the step 504 on the lower tube plate 118. The second section 512 of the stepped insert 508 extends through the portion of the hole that extends through the lower tube plate 118. The first section 510 of the stepped insert 508 is disposed in the portion of the hole that extends through the layer of insulation 502. The stepped insert 508 lines the hole through the layer of insulation 502 and the lower plate 118.

The first section 510 of the stepped insert 508 is sized to provide a clearance fit between the stepped insert 508 and the layer of insulation 502. The second section 512 of the stepped insert 508 is sized to provide a clearance fit between the stepped insert 508 and the lower tube plate 118.

[0033] The heat transfer tube 110 is inserted into the first section 510 of the stepped insert 508 and forms a clearance fit with the first section 510. The outlet end 114 of the heat transfer tube 110 rests on the rounded inner step 514. The outlet end 114 of the heat transfer tube 110 may also include rounded edges or may be rounded to complement the rounded inner step 514. The rounded inner step 514 and rounded outlet end 114 facilitate rotation of the stepped insert 508 that may result from bowing of the lower tube plate 118 during use and to accommodate misalignment.

[0034] Thus, the heat transfer tube 110 stands on and is supported by the lower tube plate 118 to accommodate thermal expansion or contraction. The construction is similar for others of the plurality of heat transfer tubes 110, which are also maintained in place by the upper tube plate 116 and the lower tube plate 118 while standing loosely in the lower tube plate 118. By supporting the heat transfer tubes 110 on the lower tube plate 118, the heat transfer tubes 110 are removable by lifting the heat transfer tubes 110 out of the lower tube plate 118.

[0035] The remaining heat transfer tubes 110 and lower tube plate 118 are similarly constructed and arranged and are also similarly supported on the lower tube plate 118.

[0036] An alternative example of a heat transfer tube 110 and the upper tube plate 116 is illustrated in FIG. 6. As in the example described with reference to FIG. 4, the upper tube plate 116 may be a metal plate of, for example, stainless steel. The metal plate may be coated with a ceramic coating to inhibit corrosion. In the present example, a layer of insulation 602, such as a refractory material, is disposed on an upper surface 606 of the upper tube plate 116. The layer of insulation may be disposed on the upper surface 606 of the upper tube plate 116, for example, in a cooling application in which hot bulk solids are introduced into the entry hopper 120.

[0037] A hole extends through the layer of insulation 602 and the upper tube plate 116. The diameter of the hole that extends through the layer of insulation 602 and through the upper tube plate 116 steps down as the diameter of the portion of the hole through the layer of insulation 602 is larger than the diameter of the portion of the hole through upper tube plate 116. Thus, a step 604 on the upper surface 606 of the upper tube plate 116 is provided.

[0038] A collar 608 is located along the heat transfer tube 110, near but spaced from the inlet end 112 of the heat transfer tube 110. The collar 608 may be fitted onto the heat transfer tube 110 and coupled to the heat transfer tube 110, for example, by diffusion bonding or any other suitable method. Alternatively, the heat transfer tube 110 may be molded, machined, or formed with an integrated collar, i.e., formed of a single piece rather than joining a collar to a separate tube.

[0039] The portion of the hole through the layer of insulation 602 is larger in diameter than the outer diameter of the collar 608. The portion of the hole through the upper tube plate 116 is larger in diameter than the outer diameter of the remainder of the heat transfer tube 110.

[0040] With the heat transfer tube 110 inserted into the upper tube plate 116, the collar 608 is seated on the step 604, which is part of the upper surface 606 of the upper tube plate 116. The heat transfer tube 110 is supported on the upper tube plate 116 by the collar 608 seated on the upper surface 606 of the upper tube plate 116. The heat transfer tube 110 hangs loosely in the upper tube plate 116, facilitating thermal expansion or contraction. [0041] In this example, the remaining heat transfer tubes 110 and upper tube plate 116 are similarly constructed and arranged and the heat transfer tubes 110 are similarly supported on the upper tube plate 116.

[0042] Referring again to FIG. 1 through FIG. 3, the inlet 104 is disposed in the top of the housing 102 and is sufficiently spaced from the upper tube plate 116 to provide the entry hopper 120. The entry hopper 120 facilitates distribution of bulk solids that flow from the inlet 104, as a result of the force of gravity, over the upper tube plate 116, thus disbursing the bulk solids over the upper tube plate 116 as bulk solids flow from the inlet 104 into the housing 102.

[0043] The lower tube plate 118 and the outlet ends 114 of the heat transfer tubes 110 are spaced from the outlet 106 for the flow of bulk solids through the outlet 106 and out of the housing 102. In this example, the discharge hopper 122 includes a generally conical section 132 utilized to create a mass flow or "choked flow" of bulk solids and to regulate the flow rate of the bulk solids out of the heat exchanger 100. The term "choked flow" is utilized herein to refer to a flow other than a free fall of the bulk solids as a result of the force of gravity.

[0044] The heat exchange chamber 108 includes a gas inlet 134 for the flow of a gaseous heat exchange medium into the heat exchange chamber 108, and a gas outlet 136 for the flow of the gaseous heat exchange medium out of the heat exchange chamber 108. The gaseous heat exchange medium flows generally upwardly in the heat exchange chamber 108 in the present example. Alternatively, the gas inlet and gas outlet may be reversed such that the gaseous heat exchange medium flows generally downwardly, or cocurrent, in the heat exchange chamber 108.

[0045] In the present example, baffles 138 extend into the heat exchange chamber 108, to facilitate circuitous flow of the gaseous heat exchange medium through the heat exchange chamber 108. The baffles 138 may be semi-circular baffles that force the gaseous heat exchange medium to flow in a non-linear path from the gas inlet 134 to the gas outlet 136. [0046] The housing may be made from any suitable material, such as Type 304L stainless steel or Type 316L stainless steel. Optionally, all or part of the housing may be lined with an insulator or heat resistant lining. Examples of materials for the heat resistant lining include graphite or any other suitable insulating material, such as a refractory material or board, or other fibrous or foam type board.

[0047] Additional flanges and openings may be utilized as inspection or cleanout ports as well as instrumentation and spare ports.

[0048] In the above-described examples, collars may be added or formed on the heat exchange tubes. Optionally, the heat exchange tubes may be rolled before insertion into the tube plates or in place in the tube plates to provide the collar.

[0049] In use, bulk solids are introduced into the heat exchanger 100 through the inlet 104. The entry hopper 120 facilitates the distribution of the bulk solids into the inlet ends 112 of the heat transfer tubes 110. The bulk solids flow through the heat transfer tubes 110, by the force of gravity, thus passing through the heat exchange chamber 108. The bulk solids are heated or cooled by indirect heat exchange with the gaseous heat exchange medium flowing around the heat transfer tubes 110 that extend through the heat exchange chamber 108. The bulk solids then exit the outlet ends 114 of the heat transfer tubes 110, into the discharge hopper 122. The discharge hopper 122 is utilized to create a choked flow of the bulk solids out of the heat exchanger 100 and thereby control residence time of the bulk solids in the heat exchanger 100. The bulk solids are contained in the heat transfer tubes 110 as they flow through the heat exchange chamber 108. As a result, the bulk solids indirectly exchange heat with the gaseous heat exchange medium in the heat exchange chamber 108.

[0050] In a particular example application, the bulk solids may be introduced into the heat exchanger 100 at temperature of, for example, about 500°C and cooled to a temperature of about 100°C. The gaseous heat transfer medium, which may be air, may be introduced to the heat exchange chamber 108 at a temperature of about 50°C and may exit the heat exchange chamber 108 at a temperature of about 145°C.

[0051] In another example application, bulk solids may be introduced into the heat exchanger at a temperature below 500°C and heated to a temperature above 500°C. The gaseous heat transfer medium may be heated air, introduced at a temperature in excess of 900°C.

[0052] Utilizing tubes through which the solids flow, a greater volume of gaseous heat exchange medium may be utilized at lower pressure than, for example, utilizing tubes for the flow of heat exchange fluid therethrough. As a result, the velocity of the gaseous heat exchange medium are also lower. The velocity and lower pressure results in a reduced cost of operation.

[0053] The heat transfer tubes of the heat exchanger are supported within the heat exchanger and extend through the heat exchange chamber while thermal expansion and contraction of the heat transfer tubes is facilitated. Thus, the heat exchanger is suitable for use in relatively high temperature applications, such as cooling of bulk solids from a temperature of 400 °C or greater or heating bulk solids to a temperature above 400 °C. In addition, the bulk solids flowing through the heat transfer tubes may be atmospherically separated from the heat exchange medium in the heat exchange chamber.

[0054] The use of the ceramic inserts facilitates movement of the heat transfer tubes relative to the tube plates as a result of thermal expansion and contraction. Buckling of the lower tube plate may occur as a result of thermal expansion that occurs when the heat exchanger is utilized for high temperature applications. The buckling is accommodated by the use of the ceramic inserts with clearance fits with the lower tube plate and with the heat transfer tubes. Thus, additional forces on the heat transfer tubes that result from the buckling, may be reduced or even eliminated as movement and rotation of the heat transfer tubes relative to the lower tube plate is accommodated by the ceramic inserts. [0055] The heat transfer tubes are supported on the lower tube plate such that the heat transfer tubes are removable by lifting the heat transfer tubes out of the tube plates, facilitating maintenance or replacement.

[0056] The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the claims should not be limited by the preferred embodiments set forth in the examples but should be given the broadest interpretation consistent with the description as a whole. All changes that come with meaning and range of equivalency of the claims are to be embraced within their scope.

Claims

Claims:

1. A heat exchanger for heating or cooling bulk solids, the heat exchanger comprising: a housing including an inlet for receiving the bulk solids into the housing, an outlet for discharging the bulk solids from the housing, and a heat exchange chamber disposed between the inlet and the outlet; a plurality of spaced apart heat transfer tubes including an inlet end for receiving the bulk solids and an outlet end for discharging the bulk solids from the heat transfer tubes, the heat transfer tubes extending generally vertically along the heat exchange chamber of the housing, for indirect heat exchange of a heat exchange medium in the heat exchange chamber with the bulk solids that flow by gravity from the inlet end and through the heat transfer tubes, toward the outlet end, an upper tube plate and a lower tube plate coupled to the housing, between the inlet and the outlet of the housing, the upper tube plate including upper tube plate holes in which the heat transfer tubes are disposed and the lower tube plate including lower tube plate holes in which the heat transfer tubes are supported; stepped inserts, each stepped insert disposed in a respective one of the lower tube plate holes and sized to provide a clearance fit in the respective one of the lower tube plate holes, each heat transfer tube of the plurality of spaced apart heat transfer tubes disposed in and supported on an inner step of a respective one of the stepped inserts, and forming a clearance fit with the respective one of the stepped inserts, wherein the heat transfer tubes stand loosely on the stepped inserts in the lower tube plate, accommodating thermal expansion or contraction.

2. The heat exchanger according to claim 1, wherein the heat transfer tubes are supported on the upper tube plate or the lower tube plate such that the heat transfer tubes are removable by lifting the heat transfer tubes out of the tube plates.

3. The heat exchanger according to claim 1, comprising a packing material disposed between the heat transfer tubes and the upper tube plate.

4. The heat exchanger according to claim 1, comprising flanged tube protectors disposed on the upper tube plate, each of the flanged tube protectors including a flange portion and a neck extending from the flange portion into a respective one of the holes of the upper tube plate and into an upper portion of a respective one of the heat transfer tubes.

5. The heat exchanger according to claim 4, wherein a top of each heat transfer tube is spaced from the flange portion of the respective flanged tube protectors.

6. The heat exchanger according to claim 1, wherein the stepped inserts comprise ceramic inserts.

7. The heat exchanger according to claim 1, comprising insulation disposed on the tube plates.

8. The heat exchanger according to claim 1, comprising insulation on a bottom side of the upper tube plate and insulation on a top side of the lower tube plate.

9. The heat exchanger according to claim 1, wherein the upper tube plate and the lower tube plate are comprised of a different material than the heat transfer tubes.

10. The heat exchanger according to claim 1, wherein the heat transfer tubes comprise ceramic heat transfer tubes.

11. The heat exchanger according to claim 1, wherein the upper tube plate is disposed between upper flanges of the housing to facilitate radial expansion of the upper tube plate.

12. The heat exchanger according to claim 1, wherein the lower tube plate is disposed between lower flanges of the housing to facilitate radial expansion of the lower tube plate.

13. The heat exchanger according to claim 1, wherein the upper tube plate includes a ceramic coating to inhibit corrosion.

14. The heat exchanger according to claim 1, wherein the lower tube plate includes a ceramic coating.

15. The heat exchanger according to claim 1, wherein the stepped inserts each include a generally tubular first section and a generally tubular second section, the generally tubular second section disposed in a forming a clearance fit with the lower tube plate.

16. The heat exchanger according to claim 15, wherein the generally tubular first section is disposed in and forms a clearance fit with insulation on a top side of the lower tube plate.

17. The heat exchanger according to claim 15, wherein an outer diameter of each of the stepped inserts steps down from the first section to the second section and an inner diameter of each of the stepped inserts steps down from the first section to the second section, providing the inner step and an outer step.

18. The heat exchanger according to claim 17, wherein the inner step includes a rounded surface.

19. The heat exchanger according to claim 18, wherein the outlet ends of the heat exchange tubes are rounded.