Patent Application
20180372417
The present disclosure relates to a heat exchanger for heating or cooling bulk solids.
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.
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.
Improvements to heat exchangers for high temperature applications is desirable.
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. The heat exchanger also includes a plurality of spaced apart heat transfer tubes supported within the housing, between the inlet and the outlet, and extending through the heat exchange chamber, 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, and through the heat transfer tubes, toward the outlet. The heat transfer tubes include a first end for receiving the bulk solids into the heat transfer tubes, and a second end for release of bulk solids flowing by the force of gravity, out of the heat transfer tubes. At least one of the first end and the second end is moveable relative to the housing to accommodate thermal expansion or contraction.
The housing may include a top plate and a bottom plate enclosing the heat exchange chamber within the housing. The heat transfer tubes may be supported by the top plate, for example, by welding. The top plate may be shaped to facilitate flow of the bulk solids into the heat exchange tubes.
The heat transfer tubes may extend through apertures in the bottom plate and may extend below the bottom plate. Bellows may be coupled to the second end of the heat transfer tubes and to the bottom plate such that the heat transfer tubes extend through the tube bellows.
Embodiments of the present invention will be described, by way of example, with reference to the drawings and to the following description, in which:
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.
Referring to
The tube size and spacing between tubes may differ from the tube size and spacing illustrated in the figures, depending on the desired heat exchange, the volume of bulk solids and the pressure drop across the gaseous heat exchange medium.
In the example shown in
The entry hopper 116 is separated from the heat exchange chamber 108 by a top plate 120 that is coupled to the inside wall of the heat exchange chamber 108 section of the housing 102 to form a seal. For example, the top plate 120 may be welded to the inside wall of the housing 102. The top plate 120 provides a seal between the entry hopper 116 and the heat exchange chamber 108.
The discharge hopper 118 is separated from the heat exchange chamber 108 by a bottom plate 132 that is coupled, for example, by welding, to the inside wall of the housing 102 to form a seal. The bottom plate 132 provides a seal between the heat exchange chamber 108 and the discharge hopper 118.
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 stainless steel, such as Type 304L stainless steel. In this example, the heat transfer tubes 110 extend generally linearly and vertically. The heat transfer tubes 110 may have a circular cross-section or may have an oval shaped cross-section. In one example, the ends of the heat transfer tubes 110 have a circular cross-section and the center portion or majority of the body of the heat transfer tubes 110 have an oval cross-section. Alternatively, the heat transfer tubes 110 may have any other suitable shape.
The heat transfer tubes 110 are coupled to the top plate 120, at apertures that extend through the top plate 120. Thus, the heat transfer tubes 110 are supported by the top plate 120. Each heat transfer tube 110 is coupled at a first end 112, to the top plate 120 at a respective aperture such that the respective aperture provides an opening for the flow of bulk solids into the heat transfer tube 110. The heat transfer tube 110 is coupled to the top plate 120, for example, by welding thereto, to maintain the seal between the entry hopper 116 and the heat exchange chamber 108. Thus, the first end 112 of each of the heat transfer tubes 110 is isolated from the heat exchange chamber 108.
The bottom plate 132 also includes a plurality of apertures. The heat transfer tubes 110 extend through the apertures in the bottom plate 132 such that each heat transfer tube 110 extends through a respective aperture in the bottom plate 132. The apertures are sized to provide a clearance fit for the heat transfer tubes 110 to facilitate thermal expansion and contraction of the heat transfer tubes 110. Thus, the heat transfer tubes 110 extend through and below the bottom plate 132.
A second end 114 of each of the heat transfer tubes 110 is coupled to a respective tube bellows 134. The tube bellows 134 is a metal tube bellows, is coupled at a bottom end 136 thereof to the second end 114 of the respective heat transfer tube 110, and is coupled at a top end 138 thereof to the bottom plate 132, around the respective one of the apertures through which the respective heat transfer tube 110 extends. Thus, the heat transfer tube 110 extends through the respective tube bellows 134. The top end 138 of the tube bellows 134 may be, for example, welded to the bottom plate 132 to provide a seal between the heat exchange chamber 108 and the discharge hopper 118. Thus, the second end 114 of each of the heat transfer tubes 110 is isolated from the heat exchange chamber 108.
By coupling the second end 114 of each of the heat transfer tubes 110 to a bottom end 136 of the respective tube bellows 134 and coupling the top end 138 of the tube bellows 134 to the bottom plate 132, the heat transfer tubes 110 are supported by the bottom plate 132 while facilitating thermal expansion and contraction of the heat transfer tubes 110. Thus, the second ends 114 of the heat transfer tubes 110 are movable relative to the housing 102 to accommodate thermal expansion and contraction of the heat transfer tubes 110. Additionally, the tube bellows 134 provide a seal around the apertures in the bottom plate 132 to isolate the second ends of the heat transfer tubes 110 from the heat exchange chamber.
Alternatively, the heat transfer tubes 110 may be coupled to the bottom plate 132 by welding directly to the bottom plate 132 and tube bellows may be utilized to couple the heat transfer tubes 110 to the top plate 120.
The inlet 104 is disposed in the top of the housing 102 and is sufficiently spaced from the top plate 120 to provide the entry hopper 116. The entry hopper 116 facilitates distribution of bulk solids that flow from the inlet 104, as a result of the force of gravity, over the top plate 120, thus disbursing the bulk solids over the top plate 120 as bulk solids flow from the inlet 104 into the housing 102. Optionally, the top plate 120 may be shaped to facilitate flow of the bulk solids into the heat transfer tubes 110. For example, the top plate 120 may include ridges between the apertures in the top plate 120 and valleys surrounding the apertures to direct the flow of bulk solids into the heat transfer tubes 110.
The bottom plate 132 and the send ends 114 of the heat transfer tubes 110 are spaced from the outlet 106 for the flow of bulk solids through the outlet and out of the housing 102. In this example, the discharge hopper 118 includes a generally conical section 140 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.
The heat exchange chamber 108 includes a gas inlet 142 for the flow of a gaseous heat exchange medium into the heat exchange chamber 108, and a gas outlet 144 for the flow of the gaseous heat exchange medium out of the heat exchange chamber 108. Thus, in this embodiment, the gaseous heat exchange medium flows generally upwardly in the heat exchange chamber 108. Alternatively, the gas inlet and gas outlet may be reversed to flow downwardly, or co-current, in the heat exchange chamber. Optionally, baffles may extend into the heat exchange chamber to facilitate circuitous flow of the gaseous heat exchange medium through the heat exchange chamber 108.
The housing may be made from any suitable material, such as Type 314L stainless steel or Type 316L stainless steel. Optionally, all or part of the housing may be lined with a heat resistant lining. Examples of materials for the heat resistant lining include graphite or any other suitable insulating material, such as a refractory board or other fibrous or foam type board.
The additional flanges and openings illustrated in
In use, bulk solids are introduced into the heat exchanger 100 through the inlet 104. The entry hopper 116 facilitates the distribution of the bulk solids into the first 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 second ends 114 of the heat transfer tubes 110, into the discharge hopper 118. The discharge hopper 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 are atmospherically isolated from the heat exchange medium in the heat exchange chamber 108.
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.
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.
In the above-described embodiment, tube bellows are utilized to couple the heat transfer tubes 110 to the bottom plate 132, or, alternatively, to the top plate 120, as described. In another embodiment, the heat transfer tubes 120 may be coupled to one of the top plate 120 or the bottom plate 132 and may extend through the other of the top plate 120 and the bottom plate 132, in a sliding fit. For example, the heat transfer tubes 120 may be welded to the top plate 120 to support the heat transfer tubes 120, and may extend through apertures in the bottom plate 132, in a sliding fit. In this example, a small volume of the gaseous heat exchange medium may exit the heat exchange chamber 108. Thus, in this embodiment, tube bellows are not utilized, resulting a lower manufacturing cost for the heat exchanger.
Referring now to
Referring to
The first heat exchange chamber 608 and the second heat exchange chamber 609 are separated by an intermediate plate 660. The heat transfer tubes 610 in the present example extend from the top plate 620, through apertures in the intermediate plate 660, and through the apertures in the bottom plate 632. In this example, the apertures in the intermediate plate 660 are sized to provide a clearance fit for the heat transfer tubes 610 and thus, no seal is provided between the first heat exchange chamber 608 and the second heat exchange chamber 609. Alternatively, the apertures in the intermediate plate 660 may be sized to provide a tight fit through which expansion and contraction of the heat exchange tubes 610 may occur.
The first heat exchange chamber 608 includes a gas inlet 642 for the flow of a gaseous heat exchange medium into the first heat exchange chamber 608, and a gas outlet 644 for the flow of the gaseous heat exchange medium out of the first heat exchange chamber 608. The second heat exchange chamber 609 includes a gas inlet 662 and a gas outlet 664. The gas outlet 664 of the second heat exchange chamber 609 is coupled to the gas inlet 642 of the first heat exchange chamber 608 such that the gaseous heat exchange medium flows from the second heat exchange chamber 609 into the first heat exchange chamber 608. Thus, the first heat exchange chamber 608 is not atmospherically isolated from the second heat exchange chamber 609.
In this example, the intermediate plate 660 is utilized as a baffle to facilitate circuitous flow of the gaseous heat exchange medium in the heat exchanger 600. Further heat exchange chambers may also be employed.
Alternatively, multiple banks of heat exchange tubes may be utilized such that bulk solids flow through a first bank of heat exchange tubes, exit the first bank of heat exchange tubes and enter a second bank of heat exchange tubes. Optionally, each bank of heat exchange tubes may utilize separate tube bellows.
Reference is now made to
The first heat exchange chamber 708 and the second heat exchange chamber 709 are separated by an intermediate plenum 754 in which the bulk solids from the heat transfer tubes 710 of the first bank 750 collect and are distributed into the heat transfer tubes 711 of the second bank 752.
The heat transfer tubes 710 of the first bank 750 are coupled to a first top plate 720 at aperatures that extend through the first top plate 720 and extend through apertures in the first bottom plate 732. First tube bellows (not shown) may be utilized to couple the heat transfer tubes 710 to the first bottom plate 732, as described above with reference to
The heat transfer tubes 711 of the second bank 752 are coupled to a second top plate 721 at aperatures that extend through the second top plate 721 and extend through apertures in the second bottom plate 733. Second tube bellows (not shown) may be utilized to couple the heat transfer tubes 711 to the second bottom plate 733.
The intermediate plenum 754 referred to above is formed by the spacing between the first bottom plate 732 and second top plate 721. Bulk solids that exit from the heat transfer tubes 710 of the first bank 750 are received in the intermediate plenum 754 and are distributed into the heat transfer tubes 711 of the second bank 752. The intermediate plenum 754 may also include a vent or outlet (not shown) for exit of gasses from the bulk solids.
The first heat exchange chamber 708 includes a gas inlet 742 for the flow of a gaseous heat exchange medium into the first heat exchange chamber 708, and a gas outlet 744 for the flow of the gaseous heat exchange medium out of the first heat exchange chamber 708. The second heat exchange chamber 709 includes a gas inlet 762 and a gas outlet 764. In this example, the gas outlet 764 of the second heat exchange chamber 709 is coupled to the gas inlet 742 of the first heat exchange chamber 708 such that the gaseous heat exchange medium flows from the second heat exchange chamber 709 into the first heat exchange chamber 608.
Advantageously, 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.
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 500° C. or greater. In addition, the bulk solids flowing through the heat transfer tubes may be atmospherically isolated from the heat exchange medium in the heat exchange chamber.
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.
