Claims:1. A thermic fluid heater comprising:

a plurality of radiant membrane panels including closely spaced tubes connected together in substantially parallel flow by headers, at least one of said radiant membrane panels encompassing a combustor and at least one of said radiant membrane panels defining an internal reversal chamber for conveying flue gases from the combustor; and

a convective coil assembly positioned at least partly operatively above said radiant membrane panels, said convective coil assembly comprising at least one set of coils, said set of coils entwined with each other and being adapted to receive thermic fluid to be heated by said flue gases.

2. The thermic fluid heater as claimed in claim 1, wherein the combustor is selected from stationary grate, bubbling bed, chain grate, moving grate, reciprocating grate, underfeed stoker and fluidized bed.

3. The thermic fluid heater as claimed in claim 1, wherein said convective coil assembly comprises two sets of serpentine coils entwined with each other and affixed at ends to headers.

4. The thermic fluid heater as claimed in claim 1, wherein said thermic fluid heater comprises a smoke chamber.

5. The thermic fluid heater as claimed in claim 1, wherein said thermic fluid heater comprises one or more refractory baffle walls for allowing multiple passes to the flue gases.

6. The thermic fluid heater as claimed in claim 1, wherein access doors are provided on said convective coil assembly for cleaning and maintenance. , Description:FIELD OF DISCLOSURE
The present disclosure relates to packaged thermic fluid heaters.

BACKGROUND
Thermic fluid heaters have lately gained preference over classic steam boilers in process heating applications given their numerous advantages. Thermic fluid heaters are safe, user-friendly, give higher efficiency and provide very high temperature thermic fluids for use in a variety of processes.

Several configurations are known for thermic fluid heaters, which typically employ helical coil heat exchangers. The thermic fluid flows inside the tube of the helical coil while flue gases flow over and between the gaps of the helical coils. In a general arrangement, a pair of the radiant and the convective coils is used.

A known configuration of a thermic fluid heater is illustrated in the FIG. 1 of the accompanying drawing, the heater being generally referenced by the numeral 10. A helical coil heat exchanger forms the radiant section 14 defining the first pass. A coil in a jacket type heat exchanger defines the second and the third pass of a convective section 18. The helical coil heat exchanger is covered in a metal jacket. A refractory lined flue gas duct 16 connects the radiant section 14 and the convective section 18. The flue gases from the combustor 12 are conveyed through the radiant section 14, the flue gas duct 16 and then the convective section 18. A settling chamber 20 is located below the convective section 18.The jacket, outer coil and inner coil of the jacket type heat exchanger are indicated by reference numerals 22, 24 & 26, respectively. The two separate sections 14 & 18 of the heat exchanger assembly result in a large foot print. The flue gas duct 16 is exposed to very high temperatures of about 800 to 1000°C resulting in a relatively lower life of the duct 16.

Another known configuration of a thermic fluid heater is illustrated in the FIG. 2 of the accompanying drawing. The heater is generally referenced by numeral 30. The thermic fluid heater 30 is a coil-in-coil type of heat exchanger. The inner coil 40 serves as a radiant section 34 and the outer coil 38 and metal jacket define a convective section. The flue gases are conveyed in the heat exchanger as shown by the arrows 36. The heater 30 is tall as the combustor 32 is placed below the heat exchanger. These heat exchangers are less efficient and require a huge heat transfer area to achieve the desired thermal performance. This is due to the poor heat transfer coefficient of the coil-in-coil type of heat exchanger. The coil-in-coil type of heat exchanger also requires more space due to hollow helical coils and higher heat transfer requirement.
Therefore, there is felt a need for a thermic fluid heater that limits the aforementioned drawbacks.

OBJECTS
Some of the objects of the thermic fluid heater of the present disclosure, which at least one embodiment herein satisfies, are as follows:

It is an object of the present disclosure to provide a packaged thermic fluid heater.

It is another object of the present disclosure to provide a thermic fluid heater, which has a relatively long life, reliability in operation, low operating costs, and high efficiency.

It is yet another object of the present disclosure to provide a thermic fluid heater, which has a compact and simple construction that provides better accessibility for maintenance and service.

It is an additional object of the present disclosure to provide a thermic fluid heater, which gives longer thermic fluid life owing to optimal flow velocities, temperature profile and heat transfer coefficients.

Other objects and advantages of the present disclosure will be more apparent from the following description when read in conjunction with the accompanying figures, which are not intended to limit the scope of the present disclosure.

SUMMARY
The present disclosure envisages a packaged thermic fluid heater. The thermic fluid heater comprises a plurality of radiant membrane panels that comprises closely spaced tubes, which are connected with each other by headers. The thermic fluid heater further comprises a convective coil assembly, smoke chamber and refractory baffle walls. The convective coil assembly is at least partly positioned above the radiant membrane panels. In accordance with the present disclosure, the radiant membrane panel encompasses a combustor that includes an internal reversal chamber for conveying flue gases from the combustor. The combustor used in the radiant membrane panel is at least one of stationary grate, bubbling bed, chain grate, moving grate, reciprocating grate, underfeed stoker, and fluidized bed. The convective coil assembly includes a set of coils for receiving the thermic fluid to be heated by the flue gases. Further, access doors are provided on the convective coil assembly for cleaning and maintenance purpose.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The thermic fluid heater of the present disclosure will now be described with the help of the accompanying drawings, in which:

FIG. 1 illustrates a schematic of a typical configuration of a thermic fluid heater having a helical coil heat exchanger;

FIG. 2 illustrates a schematic of another typical configuration of a thermic fluid heater having a coil-in-coil type of heat exchanger;

FIG. 3 & FIG. 4 illustrate a schematic of a preferred embodiment of the thermic fluid heater in accordance to the present disclosure;
FIG. 5 illustrates a schematic of the convective coil assembly;

FIG. 6 illustrates a schematic of the thermic fluid heater assembly with a stationary grate combustor;

FIG. 7 illustrates a schematic of the complete heater assembly with a stationary grate combustor; and

FIG. 8 illustrates a schematic of the complete heater assembly with a horizontal reciprocating grate combustor.

DESCRIPTION
A system and a method of the present disclosure will now be described with reference to the embodiments which do not limit the scope and ambit of the disclosure.

The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.

The known configurations of thermic fluid heaters are illustrated in the FIGS. 1 & 2 of the accompanying drawings. FIG. 1 shows a thermic fluid heater with a helical coil heat exchanger consisting of a separate radiant section and a convective section. This arrangement is very bulky and less efficient. FIG. 2 shows a thermic fluid heater with a coil-in-coil type heat exchanger. This arrangement is tall, difficult to maintain and gives low efficiency.

To overcome the drawbacks pertinent to the known configurations of thermic fluid heaters, the present disclosure envisages an innovative assembly of radiant membrane panels and serpentine convective coil assembly, in which the serpentine convective coil assembly is positioned above the radiant membrane panels. FIGS. 3 & 4 show a preferred embodiment of the thermic fluid heater of the present disclosure, the thermic fluid heater being generally referenced by the numeral 100.

A helical coil has a lower heat transfer coefficient compared to a serpentine coil. In helical coil heat exchangers, the gap between the two coils is restricted by factors including accessibility for cleaning and the flue gas velocity required for achieving the heat transfer coefficient. If the gap is more, there is better accessibility, but a lower heat transfer coefficient, and vice versa. Also the arrangement of soot blowers on these coils is difficult from a manufacturing point of view. Thus, the thermal performance of these helical coil heat exchangers is not good resulting in higher flue gas temperatures (about 350 to 400 °C) at the outlet of the heater. A high velocity of the flue gas at the turning points can erode the heat exchanger coils.

Further, the thermic fluid velocities are relatively lower resulting in higher film temperature, early degradation of the thermal oil, and thus a shorter shelf life of the oil. Also, the combustor and the heat exchanger assembly must be built on-site for helical coil configurations.

Some of the aforementioned problems can be solved by using the serpentine coil configuration as envisaged in this disclosure. Normally the serpentine coils are placed after the radiant section. However, a multi-pass arrangement of the serpentine coils must be provided to achieve a desired result. Although this configuration can provide better heat transfer performance, it has a bulky structure.

Referring to Fig. 3 and 4, the radiant membrane panel consists of alternate arrangement of tubes and fins. The thermic fluid heater 100 comprises three sets of radiant membrane panels. The thermic fluid flows through a first radiant membrane panel 102 and absorbs the heat generated in a combustor by combustion of a fuel. The flue gases from the combustor are carried through an internal reversal chamber to the convective coil assembly 108. The internal reversal chamber is designed by a second radiant membrane panel 104. The second radiant membrane panel 104 is taller than the first radiant membrane panel 102. The first radiant membrane panel 102 encompasses the combustor. No external ducting is required for transporting the flue gases from the radiant membrane panels to the convective coil assembly 108. The convective coil assembly 108 comprises horizontal serpentine tubes, which tubes are welded to headers. FIG. 4 illustrates the front view 110 and the rear view 112 of the thermic fluid heater 100 showing the assembly of the first radiant membrane panel 102, the second radiant membrane panel 104, and the convective coil assembly 108. As the serpentine convective coil assembly 108 is positioned above the first radiant membrane panel, the foot print of the heater 100 is small. Also, the overall height of the heater 100 is low.

The convective coil assembly 108 is illustrated in FIG. 5. The thermic fluid to be heated enters in the convective coil assembly 108. The convective coil assembly has a split-type construction containing a first serpentine coil 120 and a second serpentine coil 122, both coils 120 & 122 are entwined with each other. The ends of the first serpentine coil 120 and the second serpentine coil 122 are fixed at vertical headers 116 provided along horizontal headers 118. The flow of the thermic oil is divided between the two sets of serpentine coils 120 & 122, preferably equally, at the entry, and combined at the exit of the coils 120 & 122. The heated thermic fluid from the convective coil assembly 108 is conveyed through the second radiant membrane panel 104 before finally passing through the first radiant membrane panel 102. The radiant membrane panels have a multiple-pass arrangement. The heated thermic fluid is discharged from the front of the heater.

FIG. 6 of the accompanying drawings shows the heater assembly with a stationary grate combustor and refractory baffle walls, the assembly being generally referenced by the numeral 200. The stationary grate combustor 202 including fire door 204 and settling chamber 206 is positioned below the thermic fluid heater. The refractory baffle walls of the stationary grate combustor 202 are indicated by numeral 210. A smoke chamber 208 is provided at the exit of the flue gases. The heater assembly 200 can be assembled in-house and does not require that the different parts be assembled on-site.

The first radiant membrane panel 102 is designed such as to allow the panel to encompass different kinds of combustors. The combustor may be a stationary grate, bubbling bed, chain grate, moving grate, reciprocating grate (inclined or horizontal), underfeed stoker and the fluidized bed. The refractory baffle walls 210 allow multiple passes of the flue gases in the radiant membrane panels. The baffle walls 210 facilitate higher residence time for complete combustion of the fuel. The turning of the flue gases also results in improved emissions. The configuration does not hold any constrain on the gaps between the coils. Thus, the velocity of the flue gases can be optimized to achieve higher thermal performance. The temperature of the flue gases at the outlet of the heater is in the range of 300 to 320°C using this configuration.

FIG. 7 of the accompanying drawings illustrates the complete heater assembly with stationary grate combustor, the assembly being referenced by the numeral 300. Different types of soot blowers like compressed air based, sonic soot blowers can be used. The thermic fluid enters at a thermic fluid inlet 304. The plenum chamber for the stationary grate combustor, the air duct and the ash door are shown by numerals 306, 308 & 310. The smoke chamber is shown by numeral 312. Access doors 314 are provided on the convective coil assembly for easy cleaning and maintenance. Sheet metal covering panels 302 are provided to improve the aesthetics of the heater unit. The thermic fluid velocities are comparatively higher resulting in lower difference between bulk and film temperature of the thermal oil. Thus, thermal oil life is increased by this configuration.

FIG. 8 of the accompanying drawings illustrates the complete heater assembly with horizontal reciprocating grate combustor, the assembly being referenced by the numeral 400. The thermic fluid enters at a thermic fluid inlet 404. The horizontal reciprocating grate combustor, the fuel chute and the smoke chamber are shown by numerals 406, 408 & 410. Access doors 412 are provided on the convective coil assembly for easy cleaning and maintenance. Sheet metal covering panels 402 are provided to improve the aesthetics of the heater unit.

TECHNICAL ADVANCEMENT
The present disclosure as described herein above, has several technical advantages including, but not limited to, the realization of a packaged thermic fluid heater that:
• gives flexibility for the type of fuel and combustors;
• has a longer life, reliable operation, low operating costs, and high efficiency;
• requires less heat transfer area due to the higher heat transfer coefficient of serpentine tubes;
• requires less space as the more heat transfer area of serpentine tubes can be packed in less volume;
• requires less volume due to horizontal transportation of the flue gases and the placement of convective tube pass over radiant pass;
• has a compact and simple construction that provides better accessibility for maintenance and service; and
• provides longer thermic fluid life owing to optimal flow velocities and heat transfer coefficients.

Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the invention to achieve one or more of the desired objects or results.

Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the invention as it existed anywhere before the priority date of this application.

The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the invention, unless there is a statement in the specification specific to the contrary.

The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.