HEAT STORE COMPONENT AND HEAT EXCHANGERS FITTED THEREWITH, IN PARTICULAR FOR FLUE GAS CLEANING SYSTEMS OF POWER PLANTS
A heat store component for passage of a gas flow, in particular, in heat exchangers of flue gas cleaning systems, is provided, including: a mounting forming an inlet and an outlet side of the heat store component for the gas flow fed therethrough; and a first and a second heat storage medium arranged one behind the other in the gas flow direction and each including a plurality of substantially parallel flow channels. The second heat storage medium is formed from one or more honeycomb blocks, which include a body made in one-piece manner of a plastics material and incorporating a plurality of parallel flow channels separated by channel walls, wherein the plastics material includes a plastic containing virgin polytetrafluoroethylene (PTFE) as a fraction of ca. 80% by weight or more and optionally a high performance polymer differing from the PTFE as a fraction of ca. 20% by weight or less.
This patent application is a continuation of International patent application No. PCT/EP2015/071855 filed on Sep. 23, 2015 and claims the benefit of German patent application No. 10 2014 114 050.8, filed on Sep. 26, 2014, which are incorporated herein by reference in their entirety and for all purposes.
FIELD OF THE INVENTIONThe invention relates to a heat store component, in particular for the fitting of heat exchangers which can be employed in flue gas cleaning systems of power plants for example. The heat store component comprises heat storage media having a plurality of parallel flow channels through which a gas flow can be fed, e.g., a flue gas which delivers heat to the heat storage media or a clean gas which absorbs heat.
BACKGROUND OF THE INVENTIONSuch heat store components are known from so-called Ljungström heat exchangers. When these are employed in flue gas desulphurizing plants (REA), raw and clean gas streams that are spatially-separated and moving in opposite directions are fed through a rotor which is equipped with the heat store components. Apart from their employment in the REA, Ljungström heat exchangers are also used in power plants for preheating the combustion air (LUVO) or for the provision of additional heat to the flue gases for optional reaction conditions in the modules of the selective, catalytic denitrification process (SCR).
In the region in which a raw or flue gas flows through the rotor, the heat storage media of the heat store components are heated whilst the raw or flue gas is cooled down. In the region in which a clean gas flows through the rotor, usually in the reverse direction of flow, the heat storage media deliver energy to the clean gas so that the temperature thereof thereby rises, whereas the heat storage media cool down again.
In the process of cooling the raw or flue gases, they can reach a temperature below the so-called dew point (TD) at which the water vapour contained in the raw or flue gas condenses and precipitates together with fractions of SO3, HF and HCl onto the surfaces of the heat storage media in the form of a highly-corrosive mixture. The location within a heat exchanger rotor in which the dew point TD is not reached under the usual operating conditions is referred to as the cold end position.
Consequently, apart from the temperature resistance demanded of the heat storage media that are used within this region of the rotor, there is also a need for very high corrosion resistance. Since the highly-corrosive precipitation that is typically mixed with ash residues has to be regularly removed from the heat storage media, a simple process for handling the heat store components and an efficient method of cleaning the heat storage media are likewise of great economic importance.
Stacks of corrugated steel or stainless steel sheets have been used until now as the heat storage media, whilst enameled steel sheets have already been used as the heat storage medium within the particularly critical region of the heat store components in which the dew point TD is reached.
In addition, so-called honeycomb blocks which consist of a body of a plastics material which is made in one-piece manner and comprises a plurality of mutually parallel flow channels that are separated from each other by channel walls have also been proposed as heat storage media. The German patent specification DE 195 12 351 C1 recommends such heat storage media in the form of honeycomb blocks manufactured from regenerated polytetrafluoroethylene alone or in the form of a mixture with another plastics material whereby fillers can be mixed with the plastics material or the plastics materials if so required.
These honeycomb blocks are of course sufficiently heat resistant and resistant in relation to the corrosively effective components contained in the flue gases and are thus, in principle, also usable in the cold end position, but the mechanical load-bearing capacity thereof is generally too low however for enabling them to be used economically in heat store components. Moreover, in the production process, certain operating conditions are necessitated which make the production process as such expensive.
As an alternative, plate-like elements which are built up on plate-like ceramic components that are provided with a coating of polytetrafluoroethylene were proposed as a heat storage medium in DE 84 19 655 U1.
Due to the ceramic components, these heat storage media only have a limited breaking strength and thus too are of little practical utility.
When using different heat storage media for the high temperature region and the cold end position, the problem frequently arises that the heat exchanger media are displaced and possibly jam up, in particular during a cleaning process where, for example, compressed air at 4 to 5 bar and/or water at a pressure of 80 to 100 bar is employed, so that in some cases, there is a malfunction in the operational sequence which makes it necessary to immediately switch off the entire flue gas cleaning system.
BRIEF SUMMARY OF THE INVENTIONThe object of the invention is to propose a heat store component which can be manufactured economically in a simple manner and handled securely as well as having sufficiently good mechanical properties.
In accordance with the invention, this object is achieved by a heat store component having the features of Claim 1.
Due to the placement of the first and second heat storage media in a common mounting fixture, they are easy to handle, whether it is during the assembly of the heat exchangers, during the replacement process or upon the temporary removal thereof for an external cleaning process.
Furthermore, the mounting accommodates the heat storage media in a defined position relative to each other so that the gas flow can be passed efficiently from the inlet side to the outlet side. In accordance with the invention, the first heat storage medium can be selected independently of the second heat storage medium so that the heat store component is specifically equippable for the particular purpose and with an optimal cost/use ratio. Moreover, trouble-free cleaning of the heat storage media is made possible.
Furthermore, the processes of inserting and dismantling the heat storage media are realizable in a simpler and in particular automated manner due to the common mounting for the heat store components in accordance with the invention.
In accordance with the invention, the second heat storage medium is optimized in such a way that it can be utilised in the so-called cold end position of the rotor.
When the uncleansed raw gas flows through the rotor equipped with the heat store components in accordance with the invention, it is the first heat storage medium that initially comes into contact therewith. In accordance with the invention, the second heat storage medium is arranged on the outflow side of the rotor (this is also referred to as the cold end position in the description) where the raw gas is at a lower temperature which mostly lies in a temperature range below the dew point TD of the chemical mixture contained in the raw gas.
The first heat storage medium can also be made of the same material as the second heat storage medium and in particular too have the same geometrical structure in the form of honeycomb blocks. This includes the option that the first and the second heat storage medium are manufactured as a whole in one-piece manner.
Due to the selection of the plastics material for the honeycomb blocks of the second heat storage medium which comprises a plastics material that contains virgin polytetrafluoroethylene (PTFE) at a fraction of ca. 80% by weight or more and, if so required, a high performance polymer differing from the PTFE and forming a fraction of ca. 20% by weight or less, one is additionally and surprisingly able to manufacture the honeycomb blocks for the second heat storage medium not only under significantly less demanding production conditions than the honeycomb blocks described in DE 195 12 351 C1, but furthermore the honeycomb blocks used in accordance with the invention for the second heat storage medium also exhibit mechanical strength properties and in particular tear resistant and elongation at break properties which are significantly better than those of the conventionally manufactured honeycomb blocks.
DETAILED DESCRIPTION OF THE INVENTIONPreferably, the second heat storage medium extends over ca. 10% to ca. 60% of the flow path of the gas flow from the inlet side to the outlet side of the heat store component. Even more preferably, the second heat storage medium extends over ca. 25% to ca. 60% and in particular to over ca. 30% to ca. 50% of the flow path.
The first and, if so required, a further heat storage medium form the remaining part of the flow path, wherein the first and the further heat storage medium can be formed from a material which is selected from steel, stainless steel, Cortén, enameled steel, steel covered with an epoxy resin corrosion protector and highly corrosion resistant nickel-chromium-molybdenum alloys. Examples of these materials are CRL steel as well as low C—P—Cu—Ni steel and in particular the materials bearing the numbers 1.4539, 2.4605 and 2.4610.
In accordance with a variant of the heat store component in accordance with the invention, the mounting thereof for the heat storage media is formed of two parts, wherein a first part of the mounting comprises the inlet side of the heat store component and a second part the outlet side of the heat store component. Preferably, the first and the second part of the mounting are connectable directly to one another.
This two-piece design of the mounting makes the process of equipping one of the two parts with the heat storage media simpler and in particular too, in an automatable manner, and also simplifies the subsequent completion of the assembly process when mounting the other part, preferably, by means of a direct connection of the parts to one another.
The mounting of the heat store component in accordance with the invention is preferably designed as a kind of basket structure, wherein a bottom side and an upper side of the basket structure preferably comprise mutually spaced struts and preferably form the inlet and outlet sides of the heat store component at the same time.
It is preferred that each of the struts extend substantially over the entire surface of the bottom side and the upper side of the heat store component at which the flow channels of the heat storage media end.
The mounting of the heat store component in accordance with the invention preferably comprises four side walls of which two, and more if so required, can be in the form of closed surfaces.
Alternatively, all of the side walls of the mounting can be open.
The heat store components in accordance with the invention are commonly formed in block-like manner, wherein for the purposes of being equipped with heat exchangers in the form of rotors, they are preferably trapezoidal in plan view and comprise a radially inwardly located side wall and a radially outwardly located side wall, wherein the radially inwardly located side wall has a smaller extent. The two lateral side walls are then of substantially the same size.
It is preferred that the mounting be formed in such a way that at least one of the laterally located side walls of the heat store component is open so that the heat storage media can be inserted without hindrance into the mounting or extracted therefrom through this side wall/side walls.
If necessary, the heat storage media can be fixed in the mounting with retaining elements, for example by using bolts.
It is further preferred that the mounting comprise bars which connect two oppositely located side walls such as to form a framework, wherein the frameworks are connected to each other and held mutually spaced at the bottom side and at the upper side of the heat store component by means of struts. Preferably, the frameworks are arranged on the radially inwardly located side wall and on the radially outwardly located side wall of the heat store component.
The mounting is preferably produced from structural steel, stainless steel, Cortén, enameled steel, steel covered with epoxy resin corrosion protector or a highly corrosion resistant stainless steel as well as special materials made from highly corrosion resistant nickel-chromium-molybdenum alloys (for example, materials bearing the numbers 1.4539, 2.4605 and 2.4610).
A virgin PTFE having an enthalpy of fusion of ca. 40 J/g or more is preferably used as the plastics material.
The density of preferred PTFE materials amounts to ca. 2.1 g/cm3 or more.
The virgin PTFE to be used in accordance with the invention can comprise a co-monomer fraction of ca. 1% or less by weight, preferably ca. 0.1% by weight or less. Typically, virgin PTFE materials incorporating such a co-monomer fraction are weldable without the addition of extraneous materials (e.g., PFA). Typical co-monomers are hexafluoropropylene, perfluoralkyl vinyl ether, perfluor (2.2-dimethyl-1.3-dioxol) and chlorotrifluoroethylene.
In accordance with the invention, it is preferred that use be made of virgin PTFE and optionally the high performance polymer differing from the PTFE, having an average primary particle size D50 of ca. 10 μm to ca. 200 μm, preferably ca. 10 μm to ca. 100 μm. By virtue of these particle sizes, the following effects in particular can be achieved for the production of the honeycomb blocks
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- good surface properties, in particular a low surface roughness and easy cleanability,
- homogeneous distributions of the fillers being optionally processed therewith,
- good mechanical properties with high tear resistance and elongation at break,
- good mechanical properties even when using low to medium pressures.
Sintered PTFE, and regenerated PTFE can also be counted as this, having only particle sizes of ca. 400 μm or more can be obtained due to the lower crystallinity thereof compared with virgin PTFE.
Reference is made hereinabove to the primary particle size since particulate agglomerates of virgin PTFE having considerably larger particle sizes are also process sable, assuming that the particulate agglomerates disintegrate into their primary particles under the processing conditions. For example, particulate agglomerates having particle sizes of 100 μm to 3000 μm can be employed if they disintegrate into the primary particles at ca. 150 bar or less.
Suitable fillers contain both non-metallic and metallic fillers which can also be used in a mixture. Coming into question as fillers are not only particulate fillers, but also fibre-like fillers. In particular, both the thermal conductivity and the thermal capacity of the plastics materials that are to be used in accordance with the invention and also, if so required, the mechanical properties of the honeycomb block in accordance with the invention can be optimized with the aid of the fillers.
It is preferred that the plastics material contain a non-metallic filler and/or a metallic filler wherein the mean particle size D50 of the respective filler preferably amounts to ca. 100 μm or less.
In regard to the preferred selection of the primary particle size of the plastics material that is to be used in accordance with the invention, the particle size of the fillers as regards the sought for uniform distribution thereof in the plastics material amounts to ca. 2 μm to ca. 300 μm, preferably ca. 2 μm to ca. 150 μm.
The proportion of the mean particle size D50 of the primary particles of the plastics material or the plastics materials to the mean particle size D50 of the fillers preferably lies in a range of from ca. 1:2 to ca. 2:1.
It is preferred that the non-metallic filler be contained in the plastics material as a fraction of up to ca. 80% by weight, more preferably of up to ca. 40% by weight and most preferably of up to ca. 35% by weight. Due to its greater density, the metallic filler can be contained in the plastics material as a fraction of up to ca. 90% by weight, preferably ca. 60% by weight.
The entire volumetric fraction of the fillers in the plastics material can amount to a maximum of ca. 90% by volume, but preferably should amount to ca. 50% or less by volume and more preferably to ca. 40% or less by volume.
It is preferred that the plastics material that has been processed into the form of a honeycomb block has a tear resistance of ca. 10 N/mm2 or more as measured in accord with ISO 12086-2 on the basis of a strip-like test piece having a cross section of 1×5 mm2. In the case of this strip-like test piece, the tear resistance of the plastics material of the honeycomb block preferably amounts to ca. 15 N/mm2 or more, more preferably to ca. 20 N/mm2 or more, and even more preferably to ca. 25 N/mm2 or more. Typically however, the tear resistance amounts to ca. 35 N/mm2 or less. Within the ranges of tear resistances defined hereinabove, the higher values are achieved by plastics materials which do not contain a filler, whereas the lower values are achieved by plastics materials which do contain a filler.
It is preferred that the elongation at break of the plastics material that has been processed into the honeycomb block, as measured in accord with ISO 12086-2 on the basis of a strip-like test piece having a cross section of 1×5 mm2, amount to ca. 80% or more, in particular ca. 100% or more, more preferably ca. 150% or more, and most preferably ca. 200% or more.
In accordance with the invention, honeycomb blocks having very easily cleanable surfaces are obtainable, wherein for this purpose, the average roughness value Ra of the surfaces of the honeycomb block amounts to ca. 10 μm or less, preferably to ca. 5 μm or less as measured in accord with DIN EN ISO 1302 in the longitudinal direction of the honeycomb block channels.
Preferably in regard to the cleanability thereof, the surface roughness Rz of the surfaces of the honeycomb block as measured in accord with DIN EN ISO 1302 in the longitudinal direction of the flow channels of the honeycomb body amounts to ca. 50 μm or less, in particular ca. 40 μm or less, preferably ca. 30 μm or less, and most preferably ca. 20 μm or less.
The honeycomb blocks in accordance with the invention preferably comprise a plastics material having a thermal conductivity of ca. 0.3 W (m·K) or more.
The honeycomb blocks in accordance with the invention preferably consist of a plastics material having a thermal capacity of ca. 0.9 J/(g·K) or more.
The values recommended above for the thermal conductivity and the thermal capacity are beneficial in providing effective heat exchange between the heat exchanger elements in the form of the honeycomb block and the flue gas flowing therethrough as well as the storage capacity of the heat exchanger element.
A multiplicity of arrangements are possible for the geometry of the honeycomb blocks in accordance with the invention.
In accordance with one preferred geometry, the flow channels have a polygonal and in particular a square or a hexagonal cross section.
Preferably, the channel walls of the flow channels of the honeycomb block are ca. 0.8 mm to ca. 2 mm thick, preferably up to ca. 1.6 mm thick.
The open cross-sectional area of the flow channels of a honeycomb block preferably adds up to ca. 75% or more of the basal area of the honeycomb block.
The honeycomb blocks of the present invention can be employed as heat exchanger elements either as such or by appropriately customising the geometry thereof by cutting.
The heat exchanger elements which serve for the equipping of a rotor are typically needed with basal areas of numerous differing dimensions.
The honeycomb blocks can be manufactured economically as units having a basal area of 440 mm×450 mm and a height (corresponding to the length of the flow channels) of 150 mm for example. In another configuration, the dimensions of the basal area amount to 510 mm×525 mm with a height of 250 mm for example. The geometry of the flow channels may, for example, be a hexagonal cross section having an edge length of ca. 7.2 mm.
If heat exchanger elements of greater dimensions are needed, a heat exchanger element having the requisite geometry can be manufactured in a simple manner by using two or more honeycomb blocks in accordance with the invention.
To this end, the two or more honeycomb blocks can be connected one behind the other in the longitudinal direction of the flow channels for the purposes of varying the length of the flow channel. Hereby, the flow channels of the honeycomb blocks are preferably in alignment.
If an enlargement of the basal area is sought, the honeycomb blocks are connected with the flow channels thereof oriented in parallel next to each other to form one heat exchanger element.
Of course, the process of connecting a plurality of honeycomb blocks could also be effected cumulatively for the purposes of enlarging the basal area and for lengthening the flow channels.
The process of connecting the honeycomb blocks to form a complete easily-manageable heat exchanger element can be effected mechanically, for example, by means of a positively-locking or force-locking connection, or by means of a substance-to-substance bond such as by adhesion or welding for example.
In this case, the geometry of the heat exchanger element could also be adapted to the particular requirements by cutting or sawing them to size and in particular, they can be formed such as to be wedge-shaped in a plane perpendicular to the longitudinal direction of the flow channels.
For the purposes of producing further heat exchanger elements, the parts of the honeycomb structures that have been detached by cutting the honeycomb blocks or honeycomb body to size can easily be connected to a honeycomb block in the way that has already been described above.
Finally, the invention also relates to a heat exchanger which is fittable with the heat store components in accordance with the invention.
Preferably, the heat store components in accordance with the invention are placeable in the heat exchanger in exchangeable manner.
It is preferred that the heat exchanger be in the form of a rotor, wherein the rotor preferably comprises chambers for accommodating individual ones or a plurality of the heat store components in accordance with the invention.
These and further advantageous embodiments of the invention are explained in more detail hereinafter taken in conjunction with the drawing.
In detail:
Before being fed into the combustion chamber 18 of the boiler 16, the combustion air is fed via the feed line 22 through a heat exchanger 30 and heated up therein by the flue gas being fed in via the flue gas line 28. The heat exchanger comprises a supply air region 32 and a flue gas region 34. A plurality of temperature zones are present in the heat exchanger 30 as viewed in the vertical direction, wherein the zone in which the temperature of the flue gas sinks below the condensation temperature (the dew point TD) is particularly prone to corrosion due to the condensation products then occurring.
In the heat exchanger 30, there is provided a rotor 36 that is equipped with a heat store and a heat transmission medium which absorbs heat from the flue gas being fed therethrough in the flue gas region 34 and delivers the heat to the combustion air flowing therethrough during its passage through the oppositely located supply air region 32. During its passage through the heat exchanger 30, the temperature of the flue gas sinks from ca. 250° C. to ca. 160° C. for example whereas the temperature of the air supply rises from the ambient temperature to ca. 150° C. for example.
The cooled flue gas is supplied for the purposes of removing dust therefrom via the line 29 to an electrostatic particle separator which is referred to hereinafter as an ESP unit 44 for short.
After the ESP unit 44, the treated (mostly dust-free) flue gas is supplied via a line 48 to a regenerative heat exchanger 50, referred to as a REGAVO for short, in which the treated flue gas is further cooled from ca. 160° C. to a temperature of ca. 90° C. or less for example.
The heat exchanger 50 contains a rotor 52 which is equipped with a heat store and a heat transmission medium which absorbs the heat that is being emitted by the dust-freed flue gas which is being fed through a first region 54 of the heat exchanger 50 for this purpose, the gas then being supplied via the line 62 to a flue gas desulphurizing plant 64.
The temperature of the dust-freed flue gas sinks from ca. 150° C. to ca. 85 to ca. 90° C. for example in the course of its passage through the first region 54 of the heat exchanger 50.
The desulphurized flue gas coming from the flue gas desulphurizing plant 64 still has a temperature in the range of ca. 40° C. to ca. 50° C. for example and is fed via the line 66 through a second region 56 of the heat exchanger 50 in the opposite direction to the still undesulphurized flue gas and thereby heated to ca. 90° C. to ca. 100° C.
The reheated desulphurized flue gas is fed from the heat exchanger 50 via a line 68 to the chimney 70. Due to the renewed heating to ca. 90° C. to ca. 100° C., the flue gas has a sufficiently high pressure to allow it to flow out of the chimney into the atmosphere.
Optionally, a further module (not shown) can be integrated into the flue gas stream between the flue gas desulphurizing plant (REA) 64 and the chimney 70 for the purposes of catalytic denitrification (SCR) of the flue gas. In like manner to the REA, this too can be fitted with a Ljungström heat exchanger in order to increase the effect of the catalyst.
Heat exchangers in the form of so-called Ljungström gas pre-heaters are used for the purposes of heating the supply air and also in flue gas desulphurizing plants in the illustrated and in a plurality of other concepts, these being equipped with a rotor 36 or 52 which caters for the transportation of heat from the flue gas region to the supply air region or from the first into the second region of the respective heat exchanger 30 or 50.
The chambers 104, 105, 106, 107, 108, 109 can be equipped with exchangeable heat store components in accordance with the invention 120 that are of appropriate size and contain a first and a second heat storage medium. A plurality of flow channels which run parallel to the axial direction of the rotor 100 pass through such heat storage media.
One of the possibilities for mounting the heat store components 120 in a chamber 104, 105, 106, 107, 108, 109 consists in arranging supporting strips 103 on the bottom of the respective chamber as is exemplarily depicted in
In addition or else as an alternative, retaining elements 169 can be fixed to walls of the chambers 104, 105, 106, 107, 108, 109, said elements holding and/or centering the heat store components 120 in the chambers. This is likewise shown in exemplary manner for one chamber 104 in
The heat store component 120 consists substantially of a mounting 136 as well as heat storage media placed in the mounting, wherein, of the latter, only the second heat storage medium 138 (in this connection, see also
The mounting 136 comprises bars 144, 145, 146 and 147, 148 and 150, 151, 152, 153, 154 which are connected to the radially inwardly and outwardly located side walls 126 and 128 to form a framework.
The two frameworks 140 and 142 are connected to each other and held spaced apart from one another by struts 160, 161, 162 and 164, 165, 166 which extend substantially completely over the surface of the bottom and the upper sides 122, 124.
This basket-like or cage-like structure of the mounting 136 can then be comfortably equipped with the heat storage media, e.g., the second heat storage medium 138 from the direction of the lateral side walls 130, 132.
If so required, the heat storage media can be fixed in the mounting 136 after being placed therein, for example, by inserting bolts (not shown).
In the exemplary embodiment shown in
The direction of flow through the heat store component 120 is from the bottom side 122 to the upper side 124 or vice versa. The flow channels of the heat storage media run correspondingly and in each case end at the bottom side or the upper side 122 or 124.
The two frameworks 140, 142 preferably comprise recesses 168 at the corners thereof, at least in the region of the bottom side 122, complementarily shaped retaining elements 169 being fixed to the rotor chamber wall. When inserting the heat store components into the respective rotor chamber, the frameworks 140, 142 are then seated at the bottom with their corners on the mountings and, due to the engagement of the mountings in the recesses of the frameworks 140, 142, are fixed in a predetermined exact position at the same time.
The recesses could also be provided at the upper side of the frameworks 140, 142, as shown in
The recesses 168 in the frameworks 140, 142 can be obtained in a simple way, for example, in that the horizontally extending bars 145 and 151 (or 147 and 153) are not flush with the vertically extending bars 144, 146 or 150, 152 but are connected offset.
It is preferred that the heat store component 120 preferably comprise narrow strips 137 which are mounted externally on the mounting 136 and serve to secure the heat storage media 138 inserted into the mounting 136. As shown in
If so required, supporting strips 103 can be provided in the bottom region of the rotor chambers, said strips alternatively or else in addition to the retaining elements 169 supporting the heat store component 120 in the position occupied thereby in the rotor 100 (c.f.
The mounting 136 is constructed in two-pieces comprising a lower part and an upper part. The lower part comprises the struts 160, 161, 162, the sections of the bars 144, 146, 150, 152 forming the frameworks 140, 142 which are located in the lower region as well as the bars 145, 151 and 148, 154 in their entirety. The upper part comprises the struts 164, 165, 166, the bars 147, 153 (in their entirety) arranged in the upper region of the mounting 136 as well as the bars 144, 146, 150, 152 (the sections located in the upper region).
It is preferred that the lower part of the mounting 136 be equipped with the second heat storage medium 138 first, and that the first heat storage medium (not shown) be placed on the second heat storage medium thereafter. Following thereon, the upper part of the mounting 136 can then be connected to the lower part as shown exemplarily in
With this approach, the heat storage media can be inserted into the lower part of the mounting 136 both manually and in automated manner. It is particularly expedient hereby, that the mounting is subdivided into an upper and a lower part, since the entire axial height of the struts 150, 151, 144 and 146 does not then have to be overcome during the insertion process. Alternatively, the upper and the lower part of the mounting 136 can be connected to one another before being fitted with heat storage media, whereby the insertion and placement of the second and the first heat storage medium can then no longer occur from above, but must take place from the side.
The strips 137 are then mounted on the mounting 136 only after the heat store component 120 has been fully equipped with the heat storage media.
In
Here too in the case of the mounting 172, there are frame parts 174, 176 which are each in the form of four bars that are provided on the radially inwardly and radially outwardly located sides of the heat store component 170 and 200. These frameworks 174, 176 are connected and held spaced by struts 178, 180 and 182, 184 so as to form a basket-like seating. The struts 180, 178 and 182, 184 are each arranged such as to be spaced from one another.
In the exemplary embodiment of a heat store component 170 of
The gas stream through the heat store component 170 flows from the upper side through the first heat storage medium 192 and the flow channels formed by the corrugated shape of the profiled steel sheets to the second heat storage medium 190 wherein, as a continuation of the flow channels of the first heat storage medium 192, there are provided flow channels in the honeycomb block structure which lead to the bottom side of the heat store component 170 (as will be described in more detail in connection with
In
This heat store component 200 is provided for reason that the flue gas is fed up from the bottom side through the first heat storage medium 102 and from there, it is then fed up to the upper side and, in the last third of the height of the heat store component 200, it flows through the flow channels of the honeycomb block structure of the second heat storage medium 204 and emerges at the upper side through the flow channels which end there.
By virtue of these different arrangements of the first and second heat storage media 190, 192 or 202, 204, account can be made for the different direction of flow in the rotors in the case of different plants or applications so that the second heat storage media formed in accordance with the invention from honeycomb blocks are always arranged in the so-called cold end position in which the flue gas reaches the dew point TD or a temperature below it.
Due to the design of the heat store component in accordance with the invention which is described in more detail in connection with
Even if it is not shown in detail in
In the same way, the heat store components 170 and 200 could also be provided with a two-piece structure of the mounting 172 in a manner similar to that shown in
Supporting strips 103 (c.f.
Due to the construction of the heat store components 120, 170 and 200, it becomes a simple matter to equip the respective mountings with the first and second heat storage media, as too is the process of securing them in the respective mounting.
Overall, the heat store components 120, 170 and 200 can be easily handled as a whole and inserted into a rotor and/or into a chamber provided in the rotors or be extracted therefrom again.
In particular, the heat storage media can also be secured in the mounting of the heat store components in such a way that they can be handled mechanically and in an automated manner during the processes of inserting and dismantling them. This means both considerably lower downtimes of the flue gas cleaning systems as well as greater industrial safety.
The pre-assembly and the fitment of the heat store components 120, 170, 200 with the heat storage media can be effected independently of the processes of inserting and dismantling the rotor of the heat exchanger.
Due to the possibility of mechanically handling them, the heat store components can be of greater dimensions so that the insertion and the dismantling processes become additionally more efficient.
The overall economic efficiency of a power plant can also be improved by the use of heat store components in accordance with the invention and heat exchangers equipped therewith.
The cross-sectional area of the flow channels 252 is hexagonal. In the case of a flow channel wall thickness of 1.2 mm wherein the spacing of the mutually opposite flow channel walls is 14.3 mm (the extent of the channel walls being in each case ca. 7.2 mm), there is a free cross section for the passage of the gases flowing through the honeycomb block 250 of ca. 83% taken with reference to the basal area of the honeycomb block 250. The resultant specific surface area is ca. 150 m2/m3.
If the dimensions of a honeycomb block amount to a basal area of 450 mm×440 mm and a height of 150 mm, this results in the weight of the honeycomb block being ca. 13 kg (for example, consisting of a virgin agglomerate of Inoflon 230 PTFE; primary particle size D50=25 μm; particle size of the agglomerate D50=350 μm; Manufacturer Gujarat Fluorochemicals Ltd., India).
Another embodiment having a basal area of 525 mm×510 mm with a height of 250 mm has a weight of ca. 34 kg (virgin agglomerate of Inoflon 230 PTFE).
Alternatively, non-agglomerated virgin PTFE (e.g., Inoflon 640; particle size D50=25 μm; Manufacturer Gujarat Fluorochemicals Ltd., India) can be used, to which a filler in the form of a homogeneously distributed heat conductive pigment based on graphite or soot can also be added if so required in the course of a compounding process. The particles that are produced and subsequently agglomerated during the compounding process have a smaller bulk density than the agglomerated virgin PTFE. Due to this, the honeycomb blocks of the sizes specified above will then have weights of ca. 11 kg and ca. 28 kg.
For production reasons, the heat storage media are frequently not made as a whole in one-piece manner but, depending upon the required size, a plurality of parallelepipedal honeycomb blocks, two or four for example, are connected to one another, and in particular, welded to one another and then produced by cutting them into the requisite wedge-shaped or trapezoidal shape of the heat storage media.
The heat store components or their heat storage media must be regularly cleaned—even in their prepared, dust-freed form—due to the input of corrosive gases and ash particles from the flue gas so that the simple and safe handling thereof on the one hand, but in addition, a simple process for cleaning the honeycomb structure on the other hand are of great importance. Hereby, the tear resistance and the elongation at break (measured according to ISO 12086-2) of the honeycomb block walls as well as their surface finish, in particular the chemical resistance and the roughness, measured as roughness depth and average roughness value (measured according to DIN EN ISO 1302), play a significant role.
The heat resistance of the PTFE material is also important in light of the temperatures of the flue gases of e.g., ca. 250° C. occurring in the heat exchangers.
The parameters for the thermal capacity and the thermal conductivity of the heat storage and the heat transmission media being used are of crucial importance to the effectiveness of the rotor containing the heat storage media during the heat transfer process from the one gas flow to the respective other gas flow that is being fed in the opposite direction.
The present invention also takes into consideration these criteria by virtue of the selection of the plastics materials and possibly too of the fillers utilised for the production of the heat storage media.
The attainable advantageous attributes of the honeycomb blocks or of the heat exchanger elements produced therefrom that are used for the second heat storage medium in accordance with the invention will be explained in more detail hereinafter with the aid of Examples and Comparative Examples.
EXAMPLES AND COMPARATIVE EXAMPLESThe tools which were used for the production of honeycomb blocks in the Examples in accordance with the invention and in the Comparative Examples are comparable with those that are recommended in DE 195 12 351 C1 for the second variant of the process for the production of the honeycomb blocks.
Suitable requirements for the processing of the conventional plastics materials that are used in accordance with the invention for forming honeycomb blocks together with the dimensions mentioned in connection with the description of
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- compressing the plastics materials filled into a honeycomb block shape at ambient temperature with a pressure of 250 bar (Examples 1 and 2 as well as the Comparative Examples V1 and V2) or 120 bar (Examples 3 to 6 and Comparative Examples V3 and V4) to form a blank;
- sintering the blanks in the circulating air furnace at ca. 380° C. for 500 min (all Examples and Comparative Examples);
- controlled cooling of the sintered honeycomb blocks from ca. 380° C. to ca. 300° C. at a cooling rate of ca. 0.35° C./min (Examples 2 and 4 to 6 as well as Comparative Examples V2 and V4); thereafter, they can be cooled down more quickly at ca. 0.5° C./min for example;
- controlled cooling of the sintered honeycomb blocks from ca. 380° C. to ca. 320° C. at a cooling rate of ca. 0.35° C./min (Examples 1 and 3 as well as Comparative Examples V1 and V3); thereafter, they can be cooled down more quickly at ca. 10° C./min.
Although in principle, as the test results show, more rapid cooling commencing from a starting temperature of 320° C. is possible, this is less recommendable because recrystallization of the then gel-like PTFE has not yet occurred at a temperature of 320° C. This only happens commencing from a temperature of about 312° C. If one begins the more rapid cooling process commencing from 320° C., this can lead to unwanted, uncontrollable shrinking of the volume so that the prescribed geometry of the component frequently cannot be obtained.
For the purposes of determining the tear resistance and the elongation at break, samples with the dimensions 1 mm×5 mm in cross section and a length of 60 mm were taken from the honeycomb blocks and subjected to the testing process according to ISO 12086-2. The freely suspended length during the test amounted to 23 mm.
The surface roughness values Ra and Rz were determined in the longitudinal direction of the flow channels in accordance with DIN EN ISO 1302 on the wall surfaces of the honeycomb blocks obtained.
When using a virgin agglomerated PTFE material (e.g., Inoflon 230) and a pressure of 120 bar, this results in a specific weight of 360 kg/m3 for the honeycomb blocks 150 described in connection with
If, on the other hand, one uses a non-agglomerated virgin PTFE (e.g., Inoflon 640) together with a filler (3% by weight) of a heat conductive pigment based on graphite or soot (e.g., Timrex C-therm TM002, particle size D50=38 μm; Manufacturer TIMCAL Ltd., Switzerland), then a compound (granular granulates) consisting of the non-agglomerated virgin PTFE and the filler must first be made in order to ensure a homogeneous distribution of the filler in the plastics material. Subsequently, the non-free-flowing compound is subjected to a granulation process for producing agglomerated particles. The particle size D50 of the agglomerates obtained thereby can, for example, lie in a range of ca. 1 to ca. 3 mm. Due to the agglomerate formed in such a way, which has a lower bulk density than the agglomerated virgin PTFE, there then results a smaller filling weight for the mould and consequently a smaller specific weight of the honeycomb blocks of ca. 300 kg/m3, although the agglomerate particles disintegrate when compressed (pressure of ca. 120 bar for example). This sintered material is also referred to by the designation PTFE (black) hereinafter.
Despite the smaller specific weight for the PTFE materials modified by the filler as opposed to the unfilled denser PTFE materials, this surprisingly results in a somewhat better thermal capacity which, moreover, is significantly higher than the thermal capacity of polypropylene or even steel and is comparable with the thermal capacity of enameled steel (see Table 1). Moreover, the considerably lower weight of the honeycomb blocks also facilitates the handling thereof.
The aforesaid materials result in different heat transferal values per revolution of a rotor having a diameter of 21 m, which are likewise listed in Table 1. Typical rotor speeds are ca. 40 revolutions/h up to ca. 90 revolutions/h.
For the Examples 1 to 5 that are described hereinafter, an agglomerated virgin PTFE (Inoflon 230) is employed as the plastics material.
For the Comparative Examples, a pre-sintered PTFE (Inoflon 510; particle size D50=400 μm; Manufacturer Gujarat Fluorochemicals Ltd., India) having processing properties which are comparable with those of a recycled PTFE or a regenerated PTFE is used instead of the regenerated PTFE that is recommended in the state of the art (DE 195 12 351 C1) for reasons of further processability.
The test results in respect of different parameters for the Examples and Comparative Examples are listed hereinafter in Table 2:
From the values for the mechanical properties, there result significantly better tear-resistances for the honeycomb blocks in accordance with the invention compared with those manufactured in accordance with DE 195 12 351 C1, namely, even when using a pressure which is less than half of that recommended in the state of the art and this to a large extent, independently of the selected cooling temperature profile.
Moreover, in the case of the honeycomb blocks used as the second heat storage medium in accordance with the invention, one obtains substantially smoother surfaces which make the cleansing of the deposits from the flue gases much simpler.
Consequently, not only is the handling of the heat storage media improved due to the substantially improved mechanical robustness, but the cleaning process can also be effected more efficiently and more economically.
Thus, in summary, this results in substantially more economical operation of the heat storage media in accordance with the invention compared with the one proposed in DE 195 12 351 C1, even when taking into consideration the higher costs for the raw materials used for the production thereof.
In both cases, a hollow cylindrical test piece having an outer diameter of 75 mm and an internal diameter of 40 mm was compressed at a pressure of ca. 120 bar and thereafter sintered at a temperature of ca. 380° C. for a duration of 240 min. The cooling process from ca. 380° C. down to ambient temperature was effected at a cooling rate of ca. 1° C./min in accord with the specifications laid down for test standard ASTM D 4894.
Disks having a thickness of 1 mm were separated from the cylindrical test pieces and examined under the measuring microscope (see the images in
Whereas in the case of the sample of the cylindrical test piece composed in accordance with the invention a foil having a thickness of 1 mm could be peeled off, the mechanical strength and consistency of the comparison sample were so low that a foil could not be peeled off.
It is apparent from the comparison of the two samples as illustrated in
On the other hand, the mechanical properties of the sample based on regenerated PTFE are so inadequate that heat storage media which are employable over the long term in an operational rotor are not producible. This is of particular importance since the PTFE materials as such would permit very long operational lifetimes for the heat storage media due to their chemical inertness. These extremely long operational lifetimes, of 15 years or more for example, can, however, be ensured by usage of the heat storage media manufactured in accordance with the invention.
Claims
1. A heat store component for the passage of a flow of gas therethrough, in particular in heat exchangers of flue gas cleaning systems, comprising a mounting, a first heat storage medium and a second heat storage medium, wherein the mounting forms an inlet side and an outlet side of the heat store component for the flow of gas that is to be fed therethrough, wherein the first and second heat storage media are arranged one behind the other in the direction of flow of the gas between the inlet side and the outlet side of the mounting and each comprises a plurality of substantially parallel flow channels, wherein the second heat storage medium is formed of one or more honeycomb blocks, wherein the honeycomb block or the honeycomb blocks comprise a body that is produced in one-piece manner from a plastics material and incorporate a plurality of flow channels which are arranged in parallel with one another and are separated from each other by channel walls, wherein the plastics material comprises a plastics which contains virgin polytetrafluoroethylene (PTFE) as a fraction of ca. 80% by weight or more and optionally a high performance polymer differing from the PTFE as a fraction of ca. 20% by weight or less.
2. The heat store component in accordance with claim 1, wherein the second heat storage medium extends over ca. 10% to ca. 60% of the flow path from the inlet side to the outlet side of the heat store component.
3. The heat store component in accordance with claim 1, wherein the first heat storage medium is of identical construction to the second heat storage medium, wherein the first and the second heat storage medium are optionally connected to form a unit.
4. The heat store component in accordance with claim 1, wherein the first heat storage medium is formed of steel, stainless steel, Cortén, enamel coated steel, steel coated with an epoxy resin corrosion protector or highly corrosion resistant nickel-chromium-molybdenum alloys.
5. The heat store component in accordance with claim 1, wherein the mounting is built up of two parts, wherein a first part of the mounting comprises the inlet side and a second part comprises the outlet side of the heat store component and wherein the first part is connectable to the second part, preferably directly, for forming the mounting.
6. The heat store component in accordance with claim 1, wherein the mounting is in the form of a basket structure, wherein a bottom side and an upper side preferably comprise mutually spaced struts and preferably form the inlet and outlet sides of the heat store component at the same time.
7. The heat store component in accordance with claim 6, wherein each of the struts extends substantially entirely over the surface of the bottom side and the upper side of the heat store component at which the flow channels of the heat storage media end.
8. The heat store component in accordance with claim 1, wherein the mounting comprises four side walls, of which two or more side walls and in particular mutually oppositely located side walls are in the form of closed surfaces.
9. The heat store component in accordance with claim 1, wherein all of the side walls are open and bounded only by bars.
10. The heat store component in accordance with claim 8, wherein the heat store component has a substantially block-like shape, optionally with a trapezoidal bottom side and upper side.
11. The heat store component in accordance with claim 8, wherein two of the side walls have bars connected to form a framework, wherein the frameworks are connected to two or more struts in the region of the bottom side and the upper side, wherein the mounting optionally consists of the two frameworks and the struts connecting them.
12. The heat store component in accordance with claim 1, wherein the mounting is produced from structural steel, stainless steel, Cortén, enameled steel, steel covered with epoxy resin corrosion protector or special materials made from highly corrosion resistant nickel-chromium-molybdenum alloys.
13. The heat store component in accordance with claim 1, wherein the virgin PTFE comprises a co-monomer fraction of ca. 1% or less by weight, preferably ca. 0.1% by weight or less, wherein optionally, the virgin PTFE and optionally the high performance polymer differing from the PTFE have a mean primary particle size D50 of ca. 10 μm to ca. 200 μm, preferably of ca. 10 μm to ca. 100 μm.
14. The heat store component in accordance with claim 1, wherein the plastics material that has been processed into the form of a honeycomb block exhibits a tear resistance, which, measured in accord with ISO 12086-2 on the basis of a strip-like test piece having a cross section of 1×5 mm2, amounts to ca. 10 N/mm2 or more, in particular ca. 15 N/mm2 or more, preferably ca. 20 N/mm2 or more and even more preferably ca. 25 N/mm2 or more, but preferably however ca. 35 N/mm2 or less, and/or that the elongation at break of the plastics material of the honeycomb block, measured in accord with ISO 12086-2 on the basis of a strip-like test piece having a cross section of 1×5 mm2, amounts to ca. 80% or more and in particular to ca. 100% or more, preferably to ca. 150% or more, and more preferably to ca. 200% or more.
15. The heat store component in accordance with claim 1, wherein the average roughness value Ra of the surfaces of the honeycomb block as measured in the longitudinal direction of the honeycomb block channels amounts to ca. 10 μm or less, and in particular ca. 5 μm or less, and/or in that the surface roughness Rz of the surfaces of the honeycomb block as measured in the longitudinal direction of the flow channels of the honeycomb block amounts to ca. 50 μm or less, in particular ca. 40 μm or less, preferably ca. 30 μm or less, and more preferably ca. 20 μm or less.
16. The heat store component in accordance with claim 1, wherein the plastics material of the honeycomb block comprises a non-metallic filler and/or a metallic filler, wherein the particle size D50 of the respective filler amounts to preferably ca. 100 μm or less.
17. The heat store component in accordance with claim 16, wherein the non-metallic filler is contained in the plastics material as a fraction of ca. 80% or less by weight, preferably ca. 40% or less by weight and more preferably ca. 35% or less by weight, and/or in that the metallic filler is contained in the plastics material as a fraction of ca. 90% or less by weight, preferably ca. 60% or less by weight.
18. The heat store component in accordance with claim 16, wherein the entire volumetric fraction of the non-metallic and metallic fillers in the plastics material amounts to ca. 90% or less by volume, preferably ca. 50% or less by volume and more preferably ca. 40% or less by volume.
19. The heat store component in accordance with claim 1, wherein the plastics material of the honeycomb block has a thermal conductivity of ca. 0.3 W/(m·K) or more and/or honeycomb block has a thermal capacity of ca. 0.9 J/(g·K) or more.
20. The heat store component in accordance with claim 1, wherein the channel walls of the flow channels of the honeycomb block have a thickness of ca. 0.8 mm to ca. 2 mm, preferably of ca. 0.8 mm to ca. 1.6 mm.
21. A heat exchanger manufactured using a plurality of heat store components in accordance with claim 1.
22. The heat exchanger in accordance with claim 21, wherein the heat store components are placed in the heat exchanger such as to be exchangeable.
23. The heat exchanger in accordance with claim 21, wherein the heat exchanger is in the form of a rotor and optionally comprises chambers for accommodating the heat store components.
Type: Application
Filed: Mar 24, 2017
Publication Date: Jul 13, 2017
Inventors: Michael Schlipf (Burgkirchen), Katja Widmann (Aalen)
Application Number: 15/468,679
