DESC:TECHNICAL FIELD
[0001] The present disclosure relates to the technical field of process industries equipment. In particular, the present disclosure pertains to a plate type gas-gas heat exchanger for efficient heat transfer. More specifically, the present disclosure pertains to an air preheater for efficient heat transfer for a combustion system.

BACKGROUND
[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[0003] In process industries, heat exchangers such as air preheaters or furnaces are well-known in the art. The fired heaters or the furnaces are the key equipment in refineries and other similar industries. Since this equipment is the major consumer of energy, thus this is required to be designed for the best achievable fuel efficiency. One method of achieving the same is through the utilization of air preheaters by preheating the combustion air (referred by “F2” in Figures) using the energy available in the flue gases (referred by “F1” in Figures) which otherwise would have been lost to the atmosphere. The cast and glass-type air preheaters have been conventionally adopted in the fired heaters (also interchangeably referred as “furnaces” herein). However, these conventional air preheaters are bulky and require a significant plot area within the robust structure to support their heavy load.
[0004] Over time, another type of air preheater enters in the air preheater segment which is a Plate-type Air Preheater (PAPH). These types of preheaters are comparatively compact and lower-weight heat exchanger. Although it is widely adopted in hydrocarbon feed reformers, the utilization of outboard PAPHs in petroleum and petrochemical process fired heaters is a recent practice. In these air preheaters, several plates are configured in parallel with suitable gaps between them. Flue gas and cold combustion air pass through the alternate gaps/channels and exchange the heat through the plate surface area. PAPH designs typically follow the cross-current, counter-current or combination of cross and counter-current flow (hybrid) arrangements of the flue gas and combustion air. However, out of all these arrangements, the counter-current flow pattern of hot and cold streams requires the least heat transfer area for a certain heat duty. Therefore, designers prefer to adopt counter-current APH designs to optimize the heat transfer area of the equipment. As shown in FIG. 1, in the counter-current flow pattern in heat exchanger equipment’s, two fluids flow in opposite directions the heat exchanger for heat transfer, where THin is a hot stream inlet temperature, THout is a hot stream outlet temperature, TCin is a cold stream inlet temperature, and TCout is a cold stream outlet temperature.
[0005] Fired heaters are considered as the critical and most energy-demanding equipment. A significant quantity of fuel is required to be combusted for the operation of fired heaters to achieve the desired heat duty. Therefore, fired heaters contribute to the emission of various pollutants and greenhouse gases substantially. Hence, it is pertinent to optimize their operation by increasing fuel efficiency to reduce emissions and operating costs. For decades, the fuel efficiency of fired heaters may be enhanced by recovering the waste heat by utilizing Steam generation and superheating systems, and air preheaters (APH). Among these options, outboard APH systems in the fired heaters are most commonly utilized to reduce fuel consumption by supplying preheated air to burners. Traditionally a combination of Cast & Glass APHs is commonly utilized in the fired heaters for increasing fuel efficiency. One of the prime advantages of Cast and Glass APHs is their suitability to handle various quality of fuels. However, the requirement of heavy structure supports, and plot area are other downsides of this equipment and it becomes even more challenging while retrofitting the existing fired heaters with APH during the fired heater revamp.
[0006] In today's scenario when plot optimization is the most stringent challenge, a type of air preheater i.e. Plate type APH is introduced by designers for refinery fired heaters also. Plate-type air preheaters (PAPH) may be the smart fit due to their compact and lower weight design. Initially, PAPH was widely considered in reformers. Plate-type air preheaters (PAPH) are often designed and supplied for the specified heat duty requirements with pre-defined pressure drop limits and other mechanical design conditions. This equipment is composed of multiple heat transfer plates which are arranged with appropriate gaps between the plates. Several modules of heat transfer plates are placed inside the APH casing. The hot flue gases and cold combustion air travel in alternate gaps between the plates and exchange heat through the plate surface area. The flow direction of the hot flue gases and combustion air remains either in cross flow (at 90 degree angle) or counter flow pattern (at 180 degree angle) with respect to each other in any pass or section of the APH, as shown in FIGs. 2A-2D. As the counter-current direction flow of hot and cold streams has a larger temperature gradient, it is often prioritized by equipment designers to maintain this type of flow array to achieve optimum heat transfer area. However, due to the inherent design and construction features of conventional Plate-type APH designs, achieving counter-current pattern throughout PAPH is more challenging, especially at the entry and exit sections of the passes, as shown in FIGs. 2B and 2D.
[0007] Typically, flue gas cooling up to 150° C is achieved with these exchangers similar to conventional Cast and Glass APHs. However, further cooling of flue gases may be achieved in case of clean fuel is fired in the fired heaters. Additionally, glass/ suitable acid-resistant material enameled plates are utilized by designers to avoid flue gas dew point condensation issues in case of extended flue gas cooling. Typically, in PAPH, Plates are built of MOC like CS / Corten / Alloy steels or Stainless steel usually having thicknesses in the range of 1.0 to 2.0 mm. Further, similar to other heat transfer equipment, the surface area of the PAPH plates is also estimated by the fundamental heat transfer equation which may be noted here as below:
Q = U. A .LMTD. Ft …………… (1)
(Reference: Process heat transfer by D.Q.Kern)
where Q is heat duty, U is the overall heat transfer coefficient, A is heat transfer area, and LMTD is the Log mean temperature difference of hot and cold streams. LMTD for counter-current flow is calculated by the formula given below:
LMTD = where ???1=(???????? -??????????) & ???2 = (?????????? - ????????)
Ft = correction factor for LMTD, Ft =1 for true counter-current flow However, for cross-current pattern, Ft value typically ranges as 0.90 < Ft <1.0. Thus requiring more heat transfer area compared to the counter current flow patterns for a fixed heat duty (Q), heat transfer coefficient (U), and LMTD.
[0008] In the prior art, Plate-type air preheaters are already used with various configurations as shown in FIGs. 2A to 2D i.e. cross, counter-current, or a combination of cross and counter current patterns for flue gas and combustion air. It is evident that no model is truly following the counter-current pattern across the full length of the APH. Even in counter-current model of the conventional PAPH model, only a partial portion has a counter-current flow pattern and the remaining significant portion still has a crosscurrent flow pattern, especially at entry and exit sections of combustion air. Hence, the LMTD correction factor (FT) in the below-indicated models (as shown in FIGs. 2A-2D) is not realized to the value 1.0 as the flow pattern still is not converged to the complete counter-current pattern. Therefore, in the conventional counter-current PAPH model, a higher heat transfer area is required to achieve the duty compared to the area estimated by adopting truly counter-current pattern (FT ~1.0). Hence, there remains significant potential to modify the existing available designs of the plate type APH, to achieve complete counter current flow throughout the module, with an aim of improving the heat transfer area. There are key geometry details and parameters of the prior art counter current model, as below:
[0009] APH terminals orientation: As shown in FIG. 2B and 2D, at the entry and exit points of the APH, flue gas and combustion air streams are maintained at 90 degree apart (cross pattern) from each other. In these arrangements, flue gas enters vertically from the top and exits from the bottom. However, combustion air enters horizontally from the bottom and exits from the top end of the APH in a cross pattern.
[0010] Flow arrangement: As shown in FIGs. 2B and 2D, the counter-current heat transfer is targeted in the prior art designs. In these designs counter current pattern is not achieved across the full length of the APH. Specifically at entry and exit points, cross current pattern is observed.
[0011] In the PAPH, single pass cross current pattern is shown in FIG. 3A, where black strips show blocked channels on surface only. Two pass arrangement is shown in FIG. 3B, where first pass is cross current, and second pass is hybrid .i.e. cross and counter pattern. In these designs, counter current pattern is not achieved across the entire length of the APH.
[0012] The present disclosure is directed to overcome one or more limitations stated above or any other limitations associated with the prior art.
[0013] There is, therefore, a need to overcome the above-mentioned drawbacks, shortcomings, and limitations associated with the known air preheaters, by providing an improved design of a plate type gas-gas heat exchanger for efficient heat transfer.

OBJECTS OF THE INVENTION
[0014] An object of the present disclosure is to provide a plate type gas-gas heat exchanger that overcomes above-mentioned limitations of the existing pre heaters.
[0015] An object of the present disclosure is to provide a plate type gas-gas heat exchanger such as an air preheater designed to optimise heat transfer efficiency.
[0016] An object of the present disclosure is to provide an air preheater designed in a manner that ensures reduced heat transfer area in the air preheater compared to conventional available designs.
[0017] Another object of the present disclosure is to provide an air preheater that facilitate reduction in pressure drop across a flow path to improve efficiency of the preheater and reduce energy consumption.
[0018] Another object of the present disclosure is to provide an air preheater that eliminates the need for special provisions at the plate ends to absorb differential thermal stresses, thereby simplifying the design and improving the overall reliability and efficiency of the air preheater.
[0019] Another object of the present disclosure is to provide a compact, and space-efficient air preheater that require less plot area for installation.
[0020] Yet another object of the present disclosure is to provide an air preheater with improved operational flexibility and ease of maintenance by facilitating better access and control.
[0021] Still yet another object of the present disclosure is to provide an air preheater that seeks to lower both capital and operational costs by reducing overall size of the pre heater, minimizing heat transfer area, and enhancing energy efficiency, which in turn reduces fuel consumption and operational energy costs.

SUMMARY
[0022] Aspects of the present disclosure relate generally to the technical field of process industries equipment. In particular, the present disclosure pertains to a plate type gas-gas heat exchanger for efficient heat transfer. More specifically, the present disclosure pertains to an air preheater for efficient heat transfer for a combustion system.
[0023] According to an aspect, the present disclosure pertains to a plate type gas-gas heat exchanger (referred simply as “heat exchanger” hereinafter) comprises a casing having a first end and a second end, where each of the first and second ends includes a first portion and a second portion. Further, the heat exchanger comprises a first fluid inlet configured in the first portion of the first end. The first fluid inlet is adapted to receive a first fluid at a first temperature (T1) from a first apparatus. Furthermore, the heat exchanger comprises a second fluid inlet configured in the first portion of the second end. The second fluid inlet is adapted to receive a second fluid at a second temperature (T2) lower than the T1, within the heat exchanger. Furthermore, the heat exchanger comprises a first fluid outlet configured in the second portion of the second end. The first fluid outlet is configured to allow exit of the first fluid at a third temperature (T3) less than the T1. Moreover, the heat exchanger comprises a second fluid outlet configured in the second portion of the first end. The second fluid outlet is configured to exhaust the second fluid at a fourth temperature (T4) higher than the T2, from the heat exchanger.
[0024] In addition, positioning of the first fluid inlet and outlet, and the second fluid inlet and outlet are such that the first fluid flows in a direction opposite to a direction of flow of the second fluid, thereby creating a true counter-current flow pattern across an entire length of the heat exchanger for effective heat transfer between the first and second fluids.
[0025] In one or more embodiments, each of the first and second end may include a curved profile defining a dome-shaped structure of the first and second ends. The dome-shaped structure may facilitate uniform distribution of the first and second fluids within the casing, and minimize pressure drop through the casing.
[0026] In one or more embodiments, the first fluid inlet and outlet may be configured at diagonally opposite sides of the casing, and the second fluid inlet and outlet may be configured at another diagonally opposite sides of the casing.
[0027] In one or more embodiments, the heat exchanger may include a plurality of plates disposed within the casing extending towards the first fluid inlet, the second fluid inlet, the first fluid outlet, and the second fluid outlet, wherein the plurality of plates having a pre-determined gap between adjacent plates among the plurality of plates creating alternate channels, for flow of the first and second fluids.
[0028] In one or more embodiments, the alternate channels may include a first set of channels adapted for flow of the first fluid, and a second set of channels adapted for flow of the second fluid, in the true counter-current flow pattern, such that temperature gradient is created between adjacent plates for facilitating transfer of heat from a hot side to a cold side through direct conduction across the surfaces of the adjacent plates, and through convective heat transfer as the first and second fluids flow over the surface of the plates.
[0029] In one or more embodiments, each of the plurality of plate may include a corrugated surface configured to increase turbulence and heat transfer between the first fluid and the second fluid.
[0030] In one or more embodiments, the heat exchanger may include at least four collection chamber ducts (collectively referred as “collection chamber ducts” hereinafter) configured to direct flow of the first and second fluids towards respective set of channels. The collection chamber ducts may include a first collection chamber duct, a second collection chamber duct, a third collection chamber duct, and a fourth collection chamber duct. The first collection chamber duct may connect the first fluid inlet with the first portion at the first end of the casing. Further, the second collection chamber duct may connect the second fluid outlet with the second portion of the first end of the casing. Furthermore, the third collection chamber duct may connect the second fluid inlet with the first portion at the second end of the casing. Moreover, the fourth collection chamber duct may connect the first fluid outlet with the second portion of the second end of the casing. A central axis of each of the at least four collection chamber ducts may be at a pre-defined angle ? with a central axis of the casing. The pre-defined angle ? may be ranging from 0 to 90 degrees.
[0031] In one or more embodiments, the dome-shape structure of the first and second ends may have a pre-defined arc radius to optimize heat transfer and pressure drops through the casing.
[0032] In one or more embodiments, the first fluid may be flue gas, the second fluid may be air.
[0033] In one or more embodiments, the heat exchanger may include a plurality of guide vanes positioned over at least one of: the plurality of plates, or in a least one of the collection chamber ducts to direct flow the first and second fluids within the heat exchanger.
[0034] In one or more embodiments, each of the plurality of plates may include a plurality of studs (collectively referred as “studs” herein) configured over the surface of the plate in a staggered manner, where adjacent studs among the plurality of studs may be positioned spaced apart from each other to allow uniform distribution of the first fluid and the second fluid across the surface of the plate.
[0035] In one or more embodiments, a height of each of the studs may be equal to a width of the each channel of the first set and second set of channels.
[0036] In one or more embodiments, the plate may include a plurality of metal strips (collectively referred as “metal strips” herein) configured over the surface of the plate to allow uniform distribution of the first fluid and the second fluid across the surface of the plate.
[0037] In one or more embodiments, widths of the first and second set of channels may vary along the length of the casing.
[0038] In one or more embodiment, the heat exchanger may be an air preheater.
[0039] Various objects, features, aspects and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.

BRIEF DESCRIPTION OF THE DRAWINGS
[0040] The accompanying drawings are included to provide a further understanding of the present disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.
[0041] FIG. 1 illustrates a schematic view of a counter-current flow in heat exchanging equipment known in the prior art.
[0042] FIG. 2A-2D illustrate a schematic views of conventional plate-type air preheaters with single pass cross current flow, single pass cross & counter current (hybrid) flow, multi-pass cross current flow, and multi-pass cross & hybrid current flow known in the prior art.
[0043] FIGs. 3A-3B illustrate schematic views of conventional plate-type air preheater indicating single pass flow pattern, and two pass arrangement, known in the prior art.
[0044] FIG. 4A illustrates a schematic view of an air preheater as a heat exchanger, in accordance with one or more embodiment of the present disclosure.
[0045] FIG. 4B illustrates another schematic view of the air preheater, according to an embodiment of the present disclosure.
[0046] FIG. 4C illustrates another schematic view of the air preheater, according to an embodiment of the present disclosure.
[0047] FIG. 5A illustrates a representation of plates arranged in the air preheater with uniform longitudinal gap, according to an embodiment of the present disclosure.
[0048] FIG. 5B illustrates another representation of the plates arranged in the air preheater with variable longitudinal gap, according to another embodiment of the present disclosure.
[0049] FIG. 5C illustrates an isometric view of the plates arranged in the air preheater, according to an embodiment of the present disclosure.
[0050] FIG. 5D illustrates an internal detail of the plate of FIG. 5C showing studs arranged in staggered manner, according to an embodiment of the present disclosure.
[0051] Skilled artisans will appreciate that elements in the drawings are illustrated for simplicity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the drawings may be exaggerated relative to other elements to help to improve understanding of embodiments of the present disclosure.

DETAILED DESCRIPTION
[0052] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such details as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[0053] In the present disclosure, the term “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment or implementation of the present subject matter described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments.
[0054] The terms “comprises”, “comprising”, or any other variations thereof, are intended to cover a non-exclusive inclusions, such that a device/system that comprises a list of components does not include only those components but may include other components not expressly listed or inherent to such setup or device. In other words, one or more elements in a system or apparatus proceeded by “comprises… a” does not, without more constraints, preclude the existence of other elements or additional elements in the system or apparatus.
[0055] The terms like “at least one” and “one or more” may be used interchangeably or in combination throughout the description.
[0056] Reference will now be made to the exemplary embodiments of the disclosure, as illustrated in the accompanying drawings. Wherever possible, the same numerals will be used to refer to the same or like parts. Embodiments of the disclosure are described in the following paragraphs with reference to FIGs. 4A to 4C. In FIGs. 4A to 4C, the same elements or elements that have the same functions are indicated by the same reference signs.
[0057] Embodiments explained herein relate to the technical field of process industries equipment. In particular, the present disclosure pertains to a heat exchanger for efficient heat transfer. More specifically, the present disclosure pertains to an air preheater for efficient heat transfer in a combustion system.
[0058] The present disclosure presents a unique design of a counter-current plate-type air preheater for efficient heat recovery in reformers, crackers, and fired heaters in petroleum refineries, petrochemicals, and other industries. The present disclosure specifically focuses on combustion air preheater. This unique plate-type air preheater design can be adopted for industrial gas-to-gas heat exchangers as applicable. In the present disclosure, the plate-type air preheater (PAPH) is disclosed. The said preheater ensures that a steady counter-current flow pattern is achieved for the flue gases and combustion air across a full length of the air preheater (APH). Accordingly, the heat transfer area of the PAPH can be significantly optimized. This configuration of PAPH enhances the overall performance of the fired heater system. The present design envisaged for the PAPH helps to achieve a complete counter-current flow pattern across the full length of the APH. This design of the air preheater ensures a reduced and optimized heat transfer area, effective heat recovery, and lower pressure drops along with limited plot requirement for the APH. Further, in this proposed design of PAPH, the inlets and outlets of the PAPH can be designed to be in an arc-domed type structure at top and bottom ends of the APH.
[0059] Referring to FIGs. 4A to 4C, the disclosed plate type gas-gas heat exchanger 400 includes a casing 402 having a first end 402a and a second end 402b, where each of the first 402a and second ends 402b include a first portion 402a-1, 402b-1 and a second portion 402a-2, 402b-2. In a preferred embodiment, and for illustration purpose, the heat exchanger 400 used in the present disclosure can be selected as the air preheater. However, it should be understood that the invention is not limited to this specific type of heat exchanger. The principles of the invention can be applied to reformers, crackers, Industrial fired heater and combustion systems, and other types of heat exchangers such as exhaust gas heat exchanger, Waste Heat Recovery Unit (WHRU), Refrigeration and Air Conditioning Systems, and the like, without any limitations whatsoever, depending on the application areas in various industries and systems, in which it is to be implemented. In addition, in the accompanying figures, the reference numeral 400 is used to denote the proposed heat exchanger. For illustrative purposes, this reference numeral may also be interchangeably used to represent an air preheater, without limiting the scope of the invention to this specific type of heat exchanger.
[0060] In an embodiment, each of the first 402a and second ends 402b can include a curved profile defining a dome-shaped structure of the first 402a and second ends 402b, wherein the dome-shaped structure facilitates uniform distribution of the first and second fluids within the heat exchanger 400, and minimizes pressure drop through the casing 402. In an embodiment, the APH 400 can be configured in a vertical configuration as shown in FIGs. 4A to 4C. The first end 402a can be a top end, and the second end 402b can be a bottom end. In an alternate embodiment, the APH 400 can be configured in a horizontal configuration. In that case, the first end 402a can be a left end, and the second end 402b can be a right end. The dome-shape structure of the first 402a and second ends 402b can have a pre-defined arc radius to optimize heat transfer and pressure drops through the casing 402. The selection of the pre-defined arc radius can depend on factors such as but not limited to length of the casing, casing length to casing width ratio, dimensions of other internal components of the APH 400. The pre-defined arc radius can help in directing flow of the first and second fluids more efficiently through the APH 400, and reducing pressure drop across the APH 400.
[0061] In an embodiment, the casing 402 can be made of materials having properties such as heat-resistant, corrosion resistant, and can withstand high pressure. The materials that can be used for manufacturing the casing 402 can be selected from but not limited to carbon steel, stainless steel, aluminium, nickel-based alloys, titanium alloys, composite materials, and the like.
[0062] Further, the APH 400 includes a first fluid inlet 404 configured in the first portion 402a-1 of the first end 402a. The first fluid inlet 404 is adapted to receive a first fluid F1 at a first temperature T1 from a first apparatus. In an embodiment, the first fluid F1 can be flue gas, and the first apparatus can be any one of: a boiler, an economizer, a fired heater, a reformer, a cracker, and the like, without any limitations. The APH 400 further includes a second fluid inlet 406 configured in the first portion 402b-1 of the second end 402b. The second fluid inlet 406 is adapted to receive a second fluid F2 at a second temperature T2 within the heat exchanger 400. The second temperature T2 is less than the first temperature T1. In an embodiment, the second fluid F2 can be a cold air. Furthermore, the APH 400 includes a first fluid outlet 408 configured in the second portion of the second end 402b. The first fluid outlet 408 is configured to allow exit of the first fluid F1 at a third temperature T3, which T3 is less than T1. Moreover, the APH 400 includes a second fluid outlet 410 configured in the second portion 402a-2 of the first end 402a. The second fluid outlet 410 is configured to exhaust the second fluid F2 at a fourth temperature T4 from the heat exchanger 400. Here, the fourth temperature T4 is higher than the second temperature T2.
[0063] In an embodiment, positioning of the first fluid inlet 404 and outlet 408, and the second fluid inlet 406 and outlet 410 are such that the first fluid F1 flows in a direction opposite to a direction of flow of the second fluid F2, thereby creating a counter-current flow pattern across an entire length of the casing 402 or the heat exchanger 400 for effective heat transfer between the first and second fluids F1, F2. As can be appreciated that the counter-current flow pattern across the entire length of the casing 402 of the APH 400 shows significant advancement in efficiency of the APH 400. By positioning of the first fluid inlet 404 and outlet 408, and the second fluid inlet 406 and outlet 410 are such that the first fluid F1 flows in the direction opposite to the direction of flow of the second flow, maximizes temperature gradient across a plurality of plates 414 (collectively referred as “plates 414” hereinafter) disposed within the casing 402 including the first fluid inlet 404, the second fluid inlet 406, the first fluid outlet 408 and the second fluid outlet 410. The result is enhanced heat recovery, as the first and second fluids F1, F2 remain in contact with the plates 414 for longer duration, thereby facilitating continuous and efficient heat transfer.
[0064] In an embodiment, an outer surface of the casing 402 can include a heat insulation layer applied to prevent loss of heat from the hot flue gas F1 and to keep thermal energy within the preheater. The heat insulation layer can be ceramic fiber insulation layer, mineral wool insulation layer, aerogel insulation layer, polyurethane foam insulation layer, reflective insulation layer, and the like, without any limitations whatsoever.
[0065] In an embodiment, the first fluid inlet 404 and outlet 408 can be configured at diagonally opposite sides of the casing 402, and the second fluid inlet 406 and outlet 410 are configured at another diagonally opposite sides of the casing 402. A person skilled in the art would appreciate that the configuration of the first fluid inlet 404 and outlet 408 at diagonally opposite sides of the casing 402, combined with the second fluid inlet 406 and outlet 410 positioned at the other diagonally opposite sides, effectively facilitates the true counter-current flow pattern across the plates 414. This design ensures that the first and second fluids F1, F2 flow in opposite directions, promoting optimal heat transfer efficiency by maintaining a continuous temperature gradient across the entire length of the APH 400. The opposing flow paths allow for maximum contact between the fluids and the plates 414, thus enhancing the heat exchange process.
[0066] In an embodiment, the APH 400 can include the plurality of plates 414 disposed within the casing 402 having a pre-determined gap between adjacent plates among the plurality of plates 414 creating alternate channels 416, for flow of the first and second fluids F1, F2. The alternate channels 416 can include a first set of channels 416-1 adapted for flow of the first fluid F1, and a second set of channels 416-2 adapted for flow of the second fluid F2, in the true counter-current flow pattern, such that temperature gradient can be created between adjacent plates 414 for facilitating transfer of heat from a hot side to a cold side through direct conduction across the surfaces of the plates 414, and through convective heat transfer as the first and second fluids F1, F2 flow over the surface of the plates 414. In an embodiment, the plates 414 can be coated with glass, polymer, ceramic and like, without any limitations.
[0067] In addition, each of the plates 414 can include a corrugated surface configured to increase turbulence and heat transfer between the first fluid F1 and the second fluid F2. In alternate embodiment, the plate 414 can include a ribbed surface as an alternate to the corrugated surface. In an embodiment, the plates can be configured either in a horizontal orientation or in a vertical orientation. In an embodiment, the material for the plates 414 can withstand high temperature, corrosion, and mechanical stresses while providing good thermal conductivity for optimal heat exchange. The material for the plates 414 can be selected from but not limited to stainless steel, carbon steel, Corten steel, Alloy steels, aluminum, titanium, hastealloy, silicon carbide, and the like. In an embodiment, the plate 414 can have a thickness ranging from 0.5 mm to 2. 5mm, and is governed by the material used and its thermal and mechanical properties. In an embodiment, the APH 400 can include at least four collection chamber ducts such as 412-1, 412-2, 412-3, and 412-4 (collectively referred as “collection chamber ducts 412” hereinafter) configured to direct flow of the first and second fluids F1, F2 towards respective set of channels 416. The collection chamber ducts 412 can include a first collection chamber duct 412-1, a second collection chamber duct 412-2, a third collection chamber duct 412-3, and a fourth collection chamber duct 412-4. The first collection chamber duct 412-1 can connect the first fluid inlet 404 with the first portion 402a-1 of the first end 402a of the casing 402. Further, the second collection chamber duct 412-2 can connect the second fluid outlet 410 with the second portion 402a-2 of the first end 402a of the casing 402. Furthermore, the third collection chamber duct 412-3 can connect the second fluid inlet 406 with the first portion 402b-1 of the second end 402b of the casing 402. Moreover, the fourth collection chamber duct 412-4 can connect the first fluid outlet 408 with the second portion 402b-2 of the second end 402b of the casing 402. A central axis Y-Y of each of the at least four collection chamber ducts 412 can be at a pre-defined angle with a central axis X-X of the casing 402. The pre-defined angle ? may be ranging from 0 to 90 degrees. The pre-defined angle ? can be measured as a shortest angle between the central axis Y-Y of each of the collection chamber ducts 412 and the central axis X-X of the casing 402. For instance, in FIG. 4A, type-I of the APH 400 is disclosed, where the pre-defined angle ? may be preferably 45 degrees to allow the entry and exit of the first and second fluids F1, F2 to the APH 400 through the collection chamber ducts 412 at preferably 45 degrees. In this type of the APH 400, the plates 414 can be cut in nearly “V” shaped (inverted / straight V at opposite APH ends) as shown in FIG. 4A.For instance, in FIG. 4B, the pre-defined angle ? can be 90 degrees. In type -2 of the APH 400 as shown in FIG. 4B, the first and second fluids F1, F2 can entry or exit at 90 degree angles to the APH 400 through the collection chamber ducts 412. The collection chamber ducts 412 can have terminal flanges for connection to the outside of the fluid inlets 404, 406 and outlets 408, 410. In this model, the plates 414 can be cut in nearly “M” shape (inverted / straight M at opposite APH ends ) as shown in FIG. 4B. In another instance, as shown in FIGs. 4C, a type-3 of the APH 400 is disclosed, where the pre-defined angle ? can be preferably 45 degrees, as in type 1 of the APH 400. This type is similar to type-I except fact that the first and second set of channels 416-1, 416-2 can be extruded into the collection chamber ducts 412 exactly similar to the spacing between the plates 414 inside the APH 400. In an embodiment, the collection chamber ducts 412 can be welded to corner ends of the casing 402. One end of the collection chambers 412 can be connected to the inlets 404, 406 and outlets 408, 410 via bolted-connection.
[0068] Further, in FIGs. 4A to 4C, various section view are illustrated the configuration of the first and second set of channels 416-1, 416-2. For sections A-A, and D-D, the second set of channels 416-2 reserved for air can be blocked, and blocked channels can be shown by black strips. On the other hand, for sections B-B, and C-C, the first set of channels 416-1 reserved for flue gas can be blocked, and shown by the black strips in the FIGs. 4A to 4C. Another section view E-E, F-F, G-G, and H-H of the collection chamber ducts 412 in FIGs. 4A and 4C, show the placement of the plates 414 in the collection chamber ducts 412.
[0069] In an embodiment, the APH 400 can include a plurality of guide vanes (not shown) (collectively referred as “guide vanes” hereinafter) positioned within the casing 402, and configured to further direct flow the first and second fluids F1, F2 within the APH 400. In an embodiment, the guide vanes can be configured over the plates 414. The guide vanes can be radially arranged radiating outward from a centre of the casing 402. In some embodiments, the guide vanes can be arranged along flow direction of the fluids. The shape of the guide vanes can be flat rectangular vanes, curved guide vanes, tapered guide vanes, S-shaped guide vanes, V-shaped guide vanes, and the like, without any limitations. In some embodiments, the guide vanes can be configured in the collection chamber ducts 412 to direct the flow of the first and second fluids F1, F2.
[0070] In the counter current flow pattern utilized in the proposed APH 400, the flue gas F1 and combustion air F2 can be in a true counter-current pattern throughout the casing 402 including the inlets and outlets. Hence, this innovative solution results in achieving the higher LMTD (Correction factor Ft~1.0) and hence reduced surface area for the same heat duty requirement.
[0071] Additionally, various mechanical design components such as flue gas and combustion air inlets and outlets angles at entry-exit points, guide vanes, curves for smooth flow at terminals, domed head angle, devices for achieving efficient turbulence are also effectively utilized to optimize the heat transfer and pressure drops through the APH 400.
[0072] Referring to FIGs. 5A to 5B, arrangement of the plates 414 are illustrated in various embodiments. In an embodiment, the plates 414 can be arranged within the casing 402 such that the first set of channels 416-1 and the second set of channels 416-2 can have widths uniform along the length of the casing 402 or the APH 400 as shown in FIG. 5A. The arrangement shown in FIG. 5A can be considered as straight plate model with uniform longitudinal gap, where longitudinal gap refers to the width of each of the channel. For better illustration of the straight plate model with uniform longitudinal gap, isometric view of the arrangement of the plates 414 is shown in FIG. 5C. In another embodiment, the plates 414 can be arranged based on bent plate model with variable longitudinal gap as shown in FIG. 5B. In this arrangement, the first set of channels 416-1 and the second set of channels 416-2 can have widths varying along the length of the APH 400. The first set of channels 416-1 (also referred as “flue gas channel gap 416-1” herein) can have higher width for a first section S1 along the length of the casing 402, near the first end 402a of the casing 402, and can have reduced width for a second section S2, near the second end 402b of the casing 402. Similarly, the second set of channels 416-2 (also referred as “air channel gap 416-2” herein) can have higher width along the length of the casing 402 in the second section S2 at the second end of the casing 402 and can have reduced width near the first end of the casing 402 in the first section S1. Hence, in the section S1 where the flue gas channel gap 416-1 is on higher side, the air channel gap 416-2 is at lower side, and vice-versa so that the overall depth of the APH 400 is fixed throughout the APH 400.
[0073] For instance, the first section S1 can be 2/3rd section of the length of the casing 402, and the section can be 1/3rd of the length of the casing 402. Thus, the higher but uniform flue channel gap can be maintained in 2/3rd section of the length of the casing 402 (flue gas entry side), and lower but uniform gap in 1/3rd section of the length of the casing 402 (flue gas entry exit). Accordingly, lower but uniform air gap in 2/3rd section of the length of the casing 402 (air exit side) and higher but uniform gap in 1/3rd section of the length of the casing 402 (air entry side).
[0074] In optional embodiment, the variations of the first and second set of channels can be kept in more than two sections. In addition, the length of the sections for a uniform gap can change on the basis of requirement and design of the plates 414 and the APH 400.
[0075] Referring to FIG. 5D, in order to maintain the desired gaps (pre-defined gap) between the plates 414 uniformly along the length of the plates 414 in the longitudinal direction of the APH 400, a plurality of studs 500 (collectively referred as “studs 500” hereinafter) can be configured with each plate 414. The studs 500 can be designed as solid cylinders. In other embodiments, the studs 500 can be designed as solid circular plates, hollow or solid cylinders, hollow circular plates, circular plates with raised peripheral rim, and the like, without any limitations. The studs 500 can be made of material selected from but not limited to ceramics, glass, metals, polymeric materials, and the like. In a preferred embodiment, the studs 500 can be made of metals such as carbon steel, stainless steel, titanium, aluminium, brass, copper and the like, preferably carbon steel. The studs 500 can be made with metals coated with material such as but not limited to ceramics, glass, metals, polymeric material layers, and the like, to enhance its properties such as durability, and resistance to wear, corrosion, or heat. In a preferred embodiment, the plates 414 can be joined together by welding on the periphery. The studs 500 can be welded to the surfaces of the plates 414 and its height can be maintained equal to the width of each of the channel. In an embodiment, diameter of each of the studs 500 can be ranging from 4 mm to 10 mm. The studs 500 can be arranged in a staggered manner and can be placed at a pre-defined spacing ranging from 50 mm to 250 mm. The studs 500 can be included in the first set and second set of channels 416-1, 416-2. In some embodiments, the plates 414 can be detachably connected to each other via any detachable connection mechanism such as but not limited to snap-fit connection mechanism, bolted connection mechanism, clamping mechanism, interlocking groove and locking pins mechanism, slide and lock mechanism, and the like. For instance, one side of the stud 500 can be welded to the surface of the plate 414, and an upper surface of the stud 500 can have snaps, which can align and fit into slots provided on adjacent plate for connecting the plates. For another instance, the stud 500 can be configured in between the adjacent plates 414 via the bolted connection. Thus, the utilization of the detachable connection mechanism can help in easy cleaning of the plates 414, and replacement of the plates 414, in the event of any defect in the plates 414. Thus, this enables simplification of maintenance and repair of the plates 414 while reducing downtime during operational cycles. In an embodiment, the APH 400 can be placed either in vertical or horizontal orientations. Additionally, in some embodiments, when implementing two or more APHs 400, the two or more APHs 400 can be configured either in series or parallel configurations, and also in different orientations such as but not limited to vertical, horizontal, or combination thereof to suit the plot and layout design requirements associated with the APHs 400, ensuring the most optimized solution to achieve desired output.The desired fluid output here refers to temperature level of the second fluid F2 that exits the air preheater 400 after heat exchange. Further, the one or more APHs 400 can either have identical or different configurations, allowing each APH 400 to fulfill the desired output.
[0076] In an alternate embodiment, the surfaces of the plates 414 can include a plurality of metal strips 502 (collectively referred as “metal strips 502” hereinafter) configured to ensure uniform distribution of individual streams across the surfaces of the plates 414. The metal strips 502 can be made of material selected from but not limited to carbon steel, stainless steel, titanium, aluminium, brass, copper, Inconel, and the like. In a preferred embodiment, the metal stripes 502 can be made of carbon steel. However, the material selection can vary depending on operating conditions of the APH 400 and service conditions. These metal stripes 502 can be welded to the surfaces of the plates 414 and can be arranged in such a way that it can ensure uniform distribution of streams across the surfaces of the plates 414. In an embodiment, thickness of each metal strip 502 can vary between typically ranging from 0.5 mm to 2.5 mm. In an embodiment, the metal strips 502 can be arranged in any configurations such as in staggered manner, zig-zig manner, in step form manner, parallel configuration, circular pattern arrangement, helical arrangement, and the like, without any limitation to ensure uniform distribution of individual fluid streams across the surface of the plates 414. For instance, the metal strips 502 can be configured in the staggered manner, in which the metal strips 502 can be positioning in alternating pattern across the surface of the plate 414, where each metal strip 502 can be slightly offset from the adjacent metal strip 502. This staggered configuration/arrangement can facilitate more effective heat transfer, and ensure even distribution of the fluid streams across the surface of the plate 414. In another instance, the metal strips 502 can be configured in the zig-zag pattern, to direct flow of the first and second fluids F1, F2 in a controlled and in serpentine path, thereby ensuring that the fluid streams can be forced to interact with the plate 414 across a larger area. Yet in another instance, the metal strips 502 can be configured in the step-like patterns, in which each metal strip 502 can be placed at varying heights across the surface of the plate 414. This can create a dynamic flow path where the fluid is forced to travel over different elevations, creating turbulence and enhancing fluid contact with the surface of the plate 414, further improving the heat exchange efficiency. Nevertheless, the metal strips 502 can also be arranged in the spiral or helical patterns, where the metal strip 502 can configured in the spiral pattern around the plates 414 to provide gradual path for flow of the first and second fluids F1, F2.
[0077] Thus, the present disclosure overcomes the drawbacks, shortcomings, and limitations associated with existing air preheaters, by providing a novel counter current plate APH 400 designed to have various benefits. As the efficiency of the APH 400 will significantly improve due to achieving a complete counter-current flow arrangement, the required heat transfer area in the APH 400 may be reduced and optimized compared to conventional available designs. The proposed APH 400 can also lead to a reduced pressure drop due to smooth flow pattern in full length. This will also optimize the power consumption requirement of Forced Draft fans. In addition, the proposed APH 400 can help in saving plot area / space around the APH 400 by changing the entry and exit ducts of combustion air from cross (90 degrees) pattern to counter arrangement with flue gas. Also, the APH 400 eliminates need of return headers and associated steel Structural, thereby saving Steel usage and cost associated with it. Further, the proposed APH 400 helps in reducing overall Capital expenditures (CapEx) and Operating expenses (OpEx) resulting in lower payback period.
[0078] While the foregoing describes various embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims that follow. The invention is not limited to the described embodiments, versions, or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.

ADVANTAGES OF THE INVENTION
[0079] The present invention provides a plate type gas-gas heat exchanger that overcomes above-mentioned limitations of the conventional pre heaters.
[0080] The present invention provides a plate type gas-gas heat exchanger such as an air preheater designed to optimise heat transfer efficiency.
[0081] The present invention provides an air preheater designed in a manner that ensures reduced heat transfer area.
[0082] The present invention provides an air preheater that facilitate reduction in pressure drop across a flow path to improve efficiency of the preheater and reduce energy consumption.
[0083] The present invention provides a compact, and space-efficient air preheater that require less plot area for installation.
[0084] The present invention provides an air preheater with improved operational flexibility and ease of maintenance by facilitating better access and control.
[0085] The present invention provides an air preheater that seeks to lower both capital and operational costs by reducing overall size of the pre heater, minimizing heat transfer area, and enhancing energy efficiency, which in turn reduces fuel consumption and operational energy costs.
[0086] The present invention provides an air preheater that eliminates the need for special provisions at the plate ends to absorb differential thermal stresses, thereby simplifying the design and improving the overall reliability and efficiency of the air preheater.
,CLAIMS:1. A plate type gas-gas heat exchanger (400) comprising:
a casing (402) having a first end (402a) and a second end (402b); wherein each of the first (402a) and second ends (402b) include a first portion (402a-1, 402b-1) and a second portion (402a-2, 402b-2);
a first fluid inlet (404) configured in the first portion (402a-1) of the first end (402a), the first fluid inlet (404) is adapted to receive a first fluid (F1) at a first temperature (T1) from a first apparatus;
a second fluid inlet (406) configured in the first portion (402b-1) of the second end (402b), wherein the second fluid inlet (406) is adapted to receive a second fluid (F2) in at a second temperature (T2) less than the (T1), within the heat exchanger(400);
a first fluid outlet (408) configured in the second portion (402b-2) of the second end (402b), wherein the first fluid outlet (408) is configured to allow exit of the first fluid (F1) at a third temperature (T3), wherein the T3 is less than the T1;
a second fluid outlet (410) configured in the second portion (402a-2) of the first end (402a), wherein the second fluid outlet (410) is configured to exhaust the second fluid (F2) at a fourth temperature (T4) higher than the T2, from the heat exchanger (400),
wherein positioning of the first fluid inlet (404) and outlet (408), and the second fluid inlet (406) and outlet (410) are such that the first fluid (F1) flows in a direction opposite to a direction of flow of the second fluid (F2), thereby creating a true counter-current flow pattern across an entire length of the casing (402) for effective heat transfer between the first and second fluids (F1, F2).
2. The heat exchanger (400) as claimed in claim 1, wherein each of the first (402a) and second end (402b) includes a curved profile defining a dome-shaped structure of the first (402a) and second ends (402b), wherein the dome-shaped structure facilitates uniform distribution of the first and second fluids (F1, F2) within the heat exchanger (400), and minimizes pressure drop through the heat exchanger (400).
3. The heat exchanger (400) as claimed in claim 1, wherein the first fluid inlet (404) and outlet (408) are configured at diagonally opposite sides of the casing (402), and the second fluid inlet (406) and outlet (410) are configured at another diagonally opposite sides of the casing (402).
4. The heat exchanger (400) as claimed in claim 1, comprises a plurality of plates (414) disposed within the casing (402) extending towards the first fluid inlet (404), the second fluid inlet (406), the first fluid outlet (408), and the second fluid outlet (410), wherein a pre-determined gap between adjacent plates (414) among the plurality of plates (414) creates alternate channels (416), for flow of the first and second fluids (F1, F2).
5. The heat exchanger (400) as claimed in claim 3, wherein the alternate channels (416) comprise a first set of channels (416-1) adapted for flow of the first fluid (F1), and a second set of channels (416-2) adapted for flow of the second fluid (F2), in the true counter-current flow pattern, such that temperature gradient is created between adjacent plates (414) for facilitating transfer of heat from a hot side to a cold side through direct conduction across surfaces of the plates (414), and through convective heat transfer as the first and second fluids (F1, F2) flow over the surface of the plates (414).
6. The heat exchanger (400) as claimed in claim 1, wherein each of the plurality of plates (414) comprises a corrugated surface configured to increase turbulence and heat transfer between the first fluid (F1) and the second fluid (F2).
7. The heat exchanger (400) as claimed in claim 1, comprises at least four collection chamber ducts (412) configured to direct flow of the first and second fluids (F1, F2) towards respective channels (416), wherein the at least four collection chamber ducts (412) comprise:
a first collection chamber duct (412-1) connecting the first fluid inlet (404) with the first portion (402a-1) of the first end (402a) of the casing (402);
a second collection chamber duct (412-2) connecting the second fluid outlet (410) with the second portion (402a-2) of the first end (402a) of the casing (402);
a third collection chamber duct (412-3) connecting the second fluid inlet (406) with the first portion (402b-1) of the second end (402b) of the casing (402); and
a fourth collection chamber duct (412-4) connecting the first fluid outlet (408) with the second portion (402b-2) of the second end (402b) of the casing (402),
wherein a central axis (Y-Y) of each of the at least four collection chamber ducts (412) is at a pre-defined angle (?) with a central axis (X-X) of the casing (402), wherein the pre-defined angle (?) is ranging from 0 to 90 degrees.
8. The heat exchanger (400) as claimed in claim 1, wherein the dome-shape structure of the first (402a) and second ends (402b) have a pre-defined arc radius to optimize heat transfer and pressure drops through the casing (402).
9. The heat exchanger (400) as claimed in claim 1, wherein the first fluid (F1) is flue gases, the second fluid (F2) is air.
10. The heat exchanger (400) as claimed in claims 4 and 7 , wherein the heat exchanger (400) comprises a plurality of guide vanes positioned over at least one of: the plurality of plates (414), or in at least one of the at least four chambers (412) to direct flow the first and second fluids (F1, F2) within the heat exchanger (400).
11. The heat exchanger (400) as claimed in claim 4, wherein each of the plurality of plates (414) comprises a plurality of studs (500) configured over the surface of the plate (414) in a staggered manner, wherein adjacent studs among the plurality of studs (500) are positioned spaced apart from each other to allow uniform distribution of the first fluid (F1) and the second fluid (F2) across the surface of the plate (414).
12. The heat exchanger (400) as claimed in claim 11, wherein a height of each of the studs (500) is equal to a width of the each channel of the first set and second set of channels (416-1, 416-2).
13. The heat exchanger (400) as claimed in claim 4, wherein the plate (414) comprises a plurality of metal strips (502) configured over the surface of the plate (414) to allow uniform distribution of the first fluid (F1) and the second fluid (F2) across the surface of the plate (414).
14. The heat exchanger (400) as claimed in claim 5, wherein widths of the first and second set of channels (416-1, 416-2) vary along the length of the casing (402).
15. The heat exchanger (400) as claimed in claim 1, wherein the heat exchanger (400) is an air preheater.