WO2022074633A1

WO2022074633A1 - A boiler with an economizer

Info

Publication number: WO2022074633A1
Application number: PCT/IB2021/059283
Authority: WO
Inventors: Lokesh CHAUDHARY; Vijay GORANE
Original assignee: Forbes Marshall Private Limited
Priority date: 2020-10-10
Filing date: 2021-10-11
Publication date: 2022-04-14

Abstract

The present disclosure relates to the field of boilers with economizers, and envisages a boiler (100) with an economizer. The boiler (100) comprises a boiler compartment (5), a smoke tube economizer (14) and a flue gas transfer conduit section between the boiler compartment (5) and the economizer (14). The smoke tube economizer (14) has a smoke tube section (14a) and a shell section (14b). The flue gas transfer conduit section receives flue gases from the boiler compartment (5) and transfers the received flue gases to the smoke tube section (14a) of the smoke tube economizer (14). The smoke tube economizer (14) is supported on the boiler compartment (5) through the flue gas transfer conduit section. Thus, no additional floor space is required for the smoke tube economizer (14).

Description

A BOILER WITH AN ECONOMIZER

FIELD

The present disclosure relates to the field of boilers with an economizer.

DEFINITION

As used in the present disclosure, the following term is generally intended to have the meaning as set forth below, except to the extent that the context in which they are used indicate otherwise.

Boiler: The term “boiler” refers to a closed vessel in which fluid (generally water) is heated. The fluid is not necessarily heated to a boiling temperature of the fluid. The heated or vaporized fluid exits the boiler for use in various processes or heating applications, including water heating, central heating, boiler-based power generation, cooking, and sanitation.

Economizer: The term “economizer” refers to a mechanical device (heat exchanger) intended to reduce energy consumption, or to perform useful function such as preheating a fluid. Economizers recycle energy produced within a system or leverage environmental temperature differences to achieve efficiency improvements.

Smoke tube economizer: The term “smoke tube economizer” refers to a shell-and-tube type economizer having a shell and smoke tubes within the shell, wherein flue gases are passed through the smoke tubes and the fluid to be heated, such as water, is made to flow through the shell and over the smoke tubes.

BACKGROUND

The background information herein below relates to the present disclosure but is not necessarily prior art.

Conventional economizers have water tube type construction. They are either external or integral type. However, the integral type of economizer has no provision to bypass economizer either from water or flue gas side. The integral type of economizer can be either outside the boiler but connected to the boiler via flue gas duct or it can be coupled with the boiler without any need for separate duct. In both the types, most of the economizers have water tube construction. Specifically, when the economizers are coupled with boiler, the economizers are invariably of water tube type construction.

Having an economizer outside the boiler increases the floor space requirement at the operation site.

Further, water tube economizers require elaborate soot cleaning arrangement such as using soot blower, if operated on dirty gases. Not all tubes of the economizer are accessible for inspection, maintenance or repair. Dust accumulation gets more aggravated if the water tubes are fitted with extended surfaces.

Furthermore, water tube economizers are often subject to damage due to oxygen pitting. These are also susceptible to tube vibration especially if steaming occurs. Due to lower water holdup in the water tubes, water tube economizer is more likely to vibrate.

Therefore, there is felt a need to develop an assembly of a boiler with an economizer, that overcomes the above mentioned limitations.

OBJECTS

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

It is an object of the present disclosure is to ameliorate one or more problems of the prior art or to at least provide a useful alternative.

An object of the present disclosure is to provide an assembly of a boiler with an economizer.

Another object of the present disclosure is to provide an assembly of a boiler with an economizer which is economical, user-friendly, and compact.

Still an object of the present disclosure is to provide an assembly of an economizer integrated into the boiler itself so that no separate floor space is required.

Yet an object of the present disclosure is to provide an assembly of a boiler with an economizer which is easy to clean, maintain and repair.

Still another object of the present disclosure is to provide an assembly of a boiler with an economizer which has a sturdy construction. Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.

SUMMARY

The present disclosure envisages a boiler. The boiler comprises a boiler compartment, a smoke tube economizer and a flue gas transfer conduit section in fluid communication with the boiler compartment and the smoke tube economizer. The boiler compartment is configured to emit flue gases. The smoke tube economizer is configured to receive the flue gases emitted by the boiler compartment. The smoke tube economizer is defined by a smoke tube section and a shell section. The smoke tube section comprises smoke tubes. The smoke tube section is configured to facilitate flow of flue gases therethrough. The shell section surrounds the smoke tube section. The shell section has a fluid inlet and a fluid outlet. The shell section is configured to facilitate flow of a fluid between the fluid inlet and the fluid outlet to enable exchange of heat between the fluid and the flue gases. The flue gas transfer conduit section is configured to receive flue gases from the boiler compartment and to transfer the received flue gases to the smoke tube section of the smoke tube economizer. The smoke tube economizer is supported on the boiler compartment through the flue gas transfer conduit section.

In a preferred embodiment, a vertical plane passing through the longitudinal axis of the smoke tube economizer is perpendicular to a vertical plane passing through the longitudinal axis of the boiler compartment.

In an embodiment, the boiler compartment has a rear end plate. Preferably, the vertical plane passing through the longitudinal axis of the smoke tube economizer is offset from the rear end plate.

In an embodiment, the rear end plate has a flue gas aperture. In a preferred embodiment, the flue gas transfer conduit section includes an intermediate channel and an economizer inlet chamber. The intermediate channel is configured to receive flue gases from the boiler compartment through the flue gas aperture. The economizer inlet chamber is in fluid communication with the intermediate channel and the smoke tube economizer and is coaxial with the smoke tube economizer. In a preferred embodiment, the flue gas transfer conduit section includes a diverter-cum- support plate placed in the intermediate channel for guiding flue gases towards the economizer inlet chamber. The smoke tube economizer is supported on the boiler compartment through the flue gas transfer conduit section through the diverter-cum-support plate.

Preferably, the smoke tubes are arranged along the longitudinal axis of the smoke tube economizer.

Preferably, wherein the smoke tube economizer is placed inside an insulating enclosure.

In a preferred embodiment, the smoke tube economizer has an economizer door on each longitudinal end for providing access to the longitudinal end.

In an embodiment, the smoke tube economizer is supported on a rear side of the boiler compartment. Specifically, the smoke tube economizer is positioned adjacent to the top and rear corner edge of the boiler compartment.

In an embodiment, the flue gas transfer conduit section includes an economizer outlet chamber in fluid communication with the smoke tube economizer. The economizer outlet chamber is located at the downstream end of the smoke tube economizer. The economizer outlet chamber has a flue gas external outlet.

Preferably, the fluid inlet is provided on an operative bottom surface of the shell section of the smoke tube economizer and the fluid outlet is provided on an operative top surface of the shell section of the smoke tube economizer.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING

The boiler with an economizer, of the present disclosure, will now be described with the help of the accompanying drawing, in which:

Figure 1 illustrates a rear view of boiler without an economizer, as a prior art;

Figure 2 illustrates a side view of boiler of figure 1 ;

Figure 3 illustrates a rear view of boiler with an economizer, in accordance with the present disclosure; Figure 4 illustrates a side view of the boiler of figure 3;

Figure 5a illustrates a schematic isometric view showing the interface between a rear end plate of a boiler compartment of the boiler and an intermediate channel, in accordance with an embodiment of the present disclosure; and Figure 5b illustrates a diverter-cum-supporting plate, in accordance with an embodiment of the present disclosure.

LIST OF REFERENCE NUMERALS USED IN DETAILED DESCRIPTION AND DRAWING

DETAILED DESCRIPTION

Embodiments, of the present disclosure, will now be described with reference to the accompanying drawing.

Embodiments are provided so as to thoroughly and fully convey the scope of the present disclosure to the person skilled in the art. Numerous details are set forth, relating to specific components, and methods, to provide a complete understanding of embodiments of the present disclosure. It will be apparent to the person skilled in the art that the details provided in the embodiments should not be construed to limit the scope of the present disclosure. In some embodiments, well-known processes, well-known apparatus structures, and well-known techniques are not described in detail.

The terminology used, in the present disclosure, is only for the purpose of explaining a particular embodiment and such terminology shall not be considered to limit the scope of the present disclosure. As used in the present disclosure, the forms “a”, “an” and “the” may be intended to include the plural forms as well, unless the context clearly suggests otherwise. The terms “comprises”, “comprising”, “including” and “having” are open ended transitional phrases and therefore specify the presence of stated features, elements, modules, units and/or components, but do not forbid the presence or addition of one or more other features, elements, components, and/or groups thereof.

A typical smoke tube-type boiler of prior art with a boiler compartment 5’ is illustrated in Figures 1-2. The boiler compartment 5’ has a furnace for combustion of fuel and a plurality of smoke tubes through which flue gas flows. Heat is received by the water surrounding the smoke tubes that boils the water and generates steam. The boiler compartment 5’ has a rear casing 3’ with rear doors 4’, and a flue gas outlet box 1’ with a flue gas outlet 2’.

Incorporation of an economizer with such a boiler would require generally additional floor space. When the economizers are coupled with boiler, the economizers are typically of water tube type construction. Further, water tube economizers require elaborate soot cleaning arrangement such as using soot blower, if operated on dirty gases. Not all tubes of the economizer are accessible for maintenance or repair. Dust accumulation gets more aggravated if the water tubes are fitted with extended surfaces. Furthermore, water tube economizers are often subject to damage due to oxygen pitting. These are also susceptible to tube vibration especially if steaming occurs. Due to lower water holdup in the water tubes, water tube economizer is more likely to vibrate.

To solve the aforementioned problems, the present disclosure envisages a boiler 100 with an economizer 14. Figures 3-4 illustrate a boiler 100 with the economizer 14 in accordance with an embodiment of the present disclosure. The boiler 100 comprises a boiler compartment 5, a smoke tube economizer 14 and a flue gas transfer conduit section disposed between the boiler compartment 5 and the smoke tube economizer 14. The boiler compartment 5 boils a fluid such as water to generate steam using heat generated by combusting a fuel. The boiler compartment emits flue gases generated due to the combustion. The smoke tube economizer 14 receives the flue gases emitted by the boiler compartment 5. The smoke tube economizer 14 is defined by a smoke tube section 14a and a shell section 14b. The smoke tube section 14a comprises smoke tubes. The smoke tube section 14a facilitates flow of flue gases therethrough. The shell section 14b surrounds the smoke tube section 14a. The shell section 14b has a fluid inlet 15a and a fluid outlet 15b. The shell section 14b facilitates flow of a fluid between the fluid inlet 15a and the fluid outlet 15b to enable exchange of heat between the fluid and the flue gases. The flue gas transfer conduit section is in fluid communication with the boiler compartment 5 and the smoke tube economizer 14. The flue gas transfer conduit section receives flue gases from the boiler compartment 5 and transfers the received flue gases to the smoke tube section 14a of the smoke tube economizer 14. The smoke tube economizer 14 is supported on the boiler compartment 5 through the flue gas transfer conduit section.

Thus, heat from the flue gases flowing in the smoke tubes of the smoke tube section 14a of the economizer 14 is efficiently transferred to the fluid that is passed through the shell section 14b of the economizer 14. Further, since the smoke tube economizer 14 is supported on the boiler compartment 5, no additional floor space is required for the smoke tube economizer 14. Preferably, the smoke tubes are arranged along the longitudinal axis of the smoke tube economizer 14.

According to an aspect of the present disclosure, a vertical plane passing through the longitudinal axis of the smoke tube economizer 14 is perpendicular to a vertical plane passing through the longitudinal axis of the boiler compartment 5, as illustrated in Figures 3-4. In other words, the smoke tube economizer 14 is horizontal and is transverse to the longitudinal axis of the boiler compartment 5. Any vibrations along the longitudinal axis of the smoke tube economizer 14 are not transmitted to the boiler compartment 5.

Preferably, the boiler compartment 5 has a rear end plate 5a. According to another aspect of the present disclosure, the vertical plane passing through the longitudinal axis of the smoke tube economizer 14 is offset from the rear end plate 5a, as illustrated in Figure 4. Such an offset positioning of the smoke tube economizer 14 with respect to the vertical extent of the boiler compartment 5 provides ease of fitment and maintenance by improving the accessibility to the various components of the smoke tube economizer 14. The accessibility through the rear doors 4 of the boiler compartment 5 is not compromised, as will be evident by comparing Figure 3 with Figure 1. The arrangement having the offset positioning of the smoke tube economizer 14 with respect to the vertical extent of the boiler compartment 5 further creates a possibility of retrofitting smoke tube economizers onto existing boilers. Besides, the offset arrangement makes it easy for bypassing the economizer from the flue gas side. The overall cost of installation and maintenance is lowered.

In a preferred embodiment, the smoke tube economizer 14 is placed inside an insulating enclosure 16. The insulation 17 of the enclosure is illustrated in Figure 4.

According to another aspect of the present disclosure, the smoke tube economizer 14 has economizer doors 18a, 18b on each longitudinal ends for providing access to the longitudinal end, as illustrated in Figure 4. The doors 18a and 18b can be opened with the help of handles 18c and 18d. Hence, direct access to the longitudinal ends of the smoke tube section 14a, and thus to every smoke tube, for inspection, maintenance and cleaning purposes, is facilitated through the economizer doors 18. Preferably, each economizer door has a door lock and has a sealing. Further, each economizer door is also insulated to prevent dissipation of heat there through. Thus, ease in handling, inspection, maintenance and cleaning of the smoke tube economizer 14 makes the boiler 100 user-friendly. An elaborate soot cleaning arrangement is not required.

According to another aspect of the present disclosure, the smoke tube economizer 14 is supported on a rear side of the boiler compartment 5, as illustrated in Figure 3. More specifically, the smoke tube economizer 14 is positioned adjacent to the top and rear corner edge of the boiler compartment 5. Hence, the smoke tube economizer 14 does not create an additional floor-space requirement. The boiler 100 becomes compact overall. In an embodiment, the boiler 100 includes an economizer outlet chamber 13 in fluid communication with the smoke tube economizer 14, as illustrated in Figure 3. The economizer outlet chamber 13 is located at the downstream end of the smoke tube economizer 14. The economizer outlet chamber 13 has a flue gas external outlet 20. The flue gas external outlet 20 is provided at an operative top surface of the enclosure 16. The flue gas external outlet 20 may be adapted for connection with a conduit such as a chimney, which would vent out the flue gases at a stipulated height.

In an embodiment, the rear end plate 5a has a flue gas aperture 5c, as shown in Figures 3, 4 and 5 A. The flue gas transfer conduit section includes an intermediate channel 10 and an economizer inlet chamber 12. The intermediate channel 10 receives flue gases from the boiler compartment 5 through the flue gas aperture 5c. The economizer inlet chamber 12 is in fluid communication with the intermediate channel 10 and the smoke tube economizer 14 and is coaxial with the smoke tube economizer 14. As illustrated in Figure 4, the intermediate channel 10 has a triangular cross-section having an oblique rear surface. The oblique rear surface of the intermediate channel 10 facilitates smooth upward flow of the flue gases into the flue gas inlet channel 12.

In a preferred embodiment, the flue gas transfer conduit section includes a diverter-cum- support plate 11 placed in the intermediate channel 10 for guiding flue gases towards the economizer inlet chamber 12. The smoke tube economizer 14 is supported on the boiler compartment 5 through the flue gas transfer conduit section through the diverter-cum-support plate 11. In an embodiment, the circular aperture in the diverter-cum-support plate 11, as shown in Figure 5B, supports the cylindrical smoke tube economizer 14. Moreover, the portion of the diverter-cum-support plate 11 surrounding the cylindrical smoke tube economizer 14 also acts as a partition between the economizer inlet chamber 12 and the economizer outlet chamber 13, thus sealing any path external to the economizer between the economizer inlet chamber 12 and the economizer outlet chamber 13 and preventing any leakage of flue gases directly to the economizer outlet chamber 13.

In a preferred embodiment, the fluid inlet 15a is provided on an operative bottom surface of the shell section 14b of the smoke tube economizer 14 and the fluid outlet 15b is provided on an operative top surface of the shell section 14b of the smoke tube economizer 14, as illustrated in Figure 3. Specifically, the fluid inlet 15a is in the vicinity of the downstream end of the smoke tube section 14a and the fluid outlet 15b is in the vicinity of the upstream end of the smoke tube section 14a of the smoke tube economizer. As a result, water, which is the most commonly used fluid for extracting flue gas heat, flows between the fluid inlet 15a and the fluid outlet 15b in a direction opposite to the flow of the flue gases through the smoke tube economizer, thus, enhancing heat exchange rate.

The thick arrows shown in Figure 4 represent the flow of flue gases through the boiler 100.

In a preferred embodiment, pressurized water is supplied to the smoke tube economizer 14 for preheating. Feed water pumps (not shown) provides the pressurized water to the smoke tube economizer 14. The feed water pumps suck water from a tank. Typically, the tank receives water from either a water treatment plant or from condensate returning from a process, typically from where the steam generated by the boiler 100 is utilized, or any other process in a plant. At of around 20°C is gained by the pressurized water between the fluid inlet 15a and the fluid inlet 15b of the smoke tube economizer 14. Water is pumped into the smoke tube economiser 14 from where it enters into the boiler compartment 5. Since this water needs to enter into an operating boiler compartment 5 which is pressurised, water needs to be at slightly more pressure than the boiler compartment 5. Due to this, the entire assembly of the smoke tube economiser 14 is pressurised, or in other words, the smoke tube economizer 14 is a pressure vessel. The pressurized preheated water is passed in the boiler compartment 5, which is also of smoke tube type. The pressurized preheated water boils in the boiler compartment 5 to produce superheated steam, which is supplied for use in industrial processes. At the same time, hot gases generated due to combustion of fuel in a furnace (not shown) of the boiler 100 are passed through the smoke tubes in the boiler compartment 5 for generating steam. The smoke tubes in the boiler compartment 5 may be distributed into two sets or passes. After losing most of the heat during steam generation, the flue gases are made to flow through the smoke tubes of the smoke tube economizer 14 to discharge the remaining useful heat contained in the flue gases to the pressurized water that is supplied to the smoke tube economizer 14. In this manner, the smoke tube economizer 4 provides an economic utilization of heat in the apparatus.

In a non-limiting illustrative example, The flue gases exit the boiler compartment and enter the flue gas transfer conduit section at a temperature in the range of 230-260°C. At the flue gas external outlet 20, finally, the flue gases at a temperature of around 140°C exit the smoke tube economizer 14. Thus, the typical flue gas temperature drop in the smoke tube economizer 14 would be about 80°C. The flue gases leave the smoke tube economizer 14 at a temperature in the range of 150-180 °C. Pressurized water at a pressure of about 10 bar and temperature in the range of 50-70°C is fed at the fluid inlet 15a of the smoke tube economizer 14. The pressurized water undergoes a temperature rise of about 20-25 °C between the fluid inlet 15a and the fluid outlet 15b of the smoke tube economizer 14. After gaining heat in the smoke tube economizer 14, the pressurized water flows out of the fluid outlet 15b and is fed to the boiler compartment 5, at a temperature of around 70-90°C for boiling and generating steam.

The presently envisaged boiler with a smoke tube economizer eliminates the shortcomings of the more widely used water tube economizers, i.e., of dirtying of tubes due to external flow of flue gases over the tubes, dust accumulation in case extended surfaces are fitted on the water tubes, vibration in water tubes if steaming occurs and /or due to lower water holdup in water tubes.

The foregoing description of the embodiments has been provided for purposes of illustration and not intended to limit the scope of the present disclosure. Individual components of a particular embodiment are generally not limited to that particular embodiment, but, are interchangeable. Such variations are not to be regarded as a departure from the present disclosure, and all such modifications are considered to be within the scope of the present disclosure.

TECHNICAL ADVANCES AND ECONOMICAL SIGNIFICANCE

The present disclosure described herein above has several technical advantages including, but not limited to, the realization of a boiler with an economizer, that:

• reduces floor space required if a separate economizer was to be given;

• eliminates elaborate soot cleaning arrangement;

• provides direct access to every tube for ease of maintenance, inspection and repair;

• reduces the possibility of oxygen pitting on tubes;

• provides a sturdy construction so that there are no tube vibrations;

• eliminates any site work to make it site ready in the factory itself;

• makes the installation easy and compact;

• makes the boiler operations more user friendly; and

• reduces the overall cost for the customer and the manufacturer. 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 foregoing description of the specific embodiments 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.

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 disclosure to achieve one or more of the desired objects or results.

While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiment as well as other embodiments of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation

Claims

CLAIMS:

1. A boiler (100) comprising: a. a boiler compartment (5) configured to emit flue gases; b. a smoke tube economizer (14) configured to receive the flue gases emitted by the boiler compartment (5), the smoke tube economizer (14) defined by: i) a smoke tube section (14a) comprising smoke tubes, the smoke tube section (14a) configured to facilitate flow of flue gases therethrough, and ii) a shell section (14b) surrounding the smoke tube section (14a), the shell section (14b) having a fluid inlet (15a) and a fluid outlet (15b), the shell section (14b) configured to facilitate flow of a fluid between the fluid inlet (15a) and the fluid outlet (15b) to enable exchange of heat between the fluid and the flue gases; and c. a flue gas transfer conduit section in fluid communication with the boiler compartment (5) and the smoke tube economizer (14), the flue gas transfer conduit section configured to receive flue gases from the boiler compartment (5) and to transfer the received flue gases to the smoke tube section (14a) of the smoke tube economizer (14), wherein the smoke tube economizer (14) is supported on the boiler compartment (5) through the flue gas transfer conduit section.

2. The boiler (100) as claimed in claim 1, wherein a vertical plane passing through the longitudinal axis of the smoke tube economizer (14) is perpendicular to a vertical plane passing through the longitudinal axis of the boiler compartment (5).

3. The boiler (100) as claimed in claim 2, wherein the boiler compartment (5) has a rear end plate (5a), and the vertical plane passing through the longitudinal axis of the smoke tube economizer (14) is offset from the rear end plate (5a).

4. The boiler (100) as claimed in claim 3, wherein the rear end plate (5a) has a flue gas aperture (5b), the flue gas transfer conduit section includes an intermediate channel (10) and an economizer inlet chamber (12), wherein the intermediate channel (10) is configured to receive flue gases from the boiler compartment (5) through the flue gas aperture (5b), and the economizer inlet chamber (12) is in fluid communication with the intermediate channel (10) and the smoke tube economizer (14) and is coaxial with the smoke tube economizer (14). The boiler (100) as claimed in claim 4, wherein the flue gas transfer conduit section includes a diverter-cum-support plate (11) placed in the intermediate channel (10) for guiding flue gases towards the economizer inlet chamber (12), and the smoke tube economizer (14) supported on the boiler compartment (5) through the flue gas transfer conduit section through the diverter-cum-support plate (11). The boiler (100) as claimed in claim 1, wherein the smoke tubes are arranged along the longitudinal axis of the smoke tube economizer (14). The boiler (100) as claimed in claim 1, wherein the smoke tube economizer (14) is placed inside an insulating enclosure (16). The boiler (100) as claimed in claim 1, wherein the smoke tube economizer (14) has an economizer door (18a, 18b) on each longitudinal end for providing access to the longitudinal end. The boiler (100) as claimed in claim 1, wherein the smoke tube economizer (14) is supported on a rear side of the boiler compartment (5). The boiler (100) as claimed in claim 9, wherein the smoke tube economizer (14) is positioned adjacent to the top and rear corner edge of the boiler compartment (5). The boiler (100) as claimed in claim 1, the flue gas transfer conduit section includes an economizer outlet chamber (13) in fluid communication with the smoke tube economizer (14), the economizer outlet chamber (13) located at the downstream end of the smoke tube economizer (14), the economizer outlet chamber (13) having a flue gas external outlet (20). The boiler (100) as claimed in claim 1, wherein the fluid inlet (15a) is provided on an operative bottom surface of the shell section (14b) of the smoke tube economizer (14) and the fluid outlet (15b) is provided on an operative top surface of the shell section (14b) of the smoke tube economizer (14).