A CIRCULATING FLUIDIZED BED BOILER SYSTEM

FIELD

The present disclosure relates to the field of mechanical engineering and particularly relates to the field of circulating fluidized bed combustion boilers.

BACKGROUND Conventionally, in a circulating fluidized bed combustion boiler, fuel and inert material are circulating at a high velocity in a combustion chamber. The mixture of fuel and inert material is then passed to a cyclone. The cyclone receives the fuel and inert material and then supplies the fuel and inert material back to the combustion chamber using a loop seal device that is connected to the delivery end of a dip leg that connects the bottom of the cyclone and the loop seal. The same fuel enters the boiler several times, thereby providing sufficient residence time to the fuel for combustion. This improves the efficiency and reduces the emission of the boiler.

Further, flue gases leaving the cyclone have a vortex motion with a very large tangential velocity. Stabilization of the flue gases takes significant time as a result of this high tangential velocity. As soon as the flue gases enter the vertical column that includes a set of heat exchangers like a superheater and/or a convective tube bank, the circular motion of the flue gases causes non-uniform distribution thereof over the heat exchangers. The circular motion of the flue gases causes reduction in the utilization of the heat transfer area of the heat exchanger as they cause a non-uniform distribution of the flue gas contact with the exchanging surfaces, thereby leading to poor heat transfer performance. Erosion of an inner portion of the heat exchangers may also occur due to impinging of the abrasive particles present in the flue gases at high velocity.

Hence, there is felt a need for a circulating fluidized bed combustion boiler system that alleviates the abovementioned drawbacks. 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 to ameliorate one or more problems of the prior art or to at least provide an useful alternative.

An object of the present disclosure is to provide a circulating fluidized bed combustion boiler system that partially obstructs the flow of flue gases coming out of the cyclone and minimizes/eliminates the vortex phenomenon in the flue gas flow.

Another object of the present disclosure is to provide a circulating fluidized bed combustion boiler system that streamlines the flow of flue gases coming out of the cyclone as they enter the vertical column.

Yet another object of the present disclosure is to provide a circulating fluidized bed combustion boiler system that increases the heat transfer performance at the heat exchangers positioned in the vertical column like the super-heater, the economizer and the air heater.

Still another object of the present disclosure is to provide a circulating fluidized bed combustion boiler system that improves the velocity profile of flue gases.

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 circulating fluidized bed boiler system. The circulating fluidized bed boiler system comprises a combustion chamber for fluidizing and combusting fuel particles to generate flue gases.The combustion chamber has a flue gas outlet. The flue gas outlet is configured at an operative top end of the combustion chamber. A cyclone separator is in fluid communication with the flue gas outlet. The cyclone separator is configured to receive the flue gases and partly burnt fuel particles and is further configured to separate the partly burnt fuel from the flue gases. A flue gas conduit is in fluid communication with the cyclone separator, and is configured to receive the flue gases from the cyclone separator and transport the flue gases to a heat exchange column. A flue gas vortex breaker section is disposed within the flue gas conduit and includes a water wall membrane that is configured to streamline and resist the flow of the flue gases. In an embodiment, the water wall membrane includes a plurality of vertical tubes disposed therewithin and a plurality of fins is alternately disposed between the plurality of vertical tubes.

The water wall membrane is constituted by a near-end wall, a plurality of side walls and a far end wall that together define an interior space within the water wall membrane. The far end wall is opposite to the near-end wall. The near-end wall of the waterwall membrane is in fluid communication with a first outlet of the cyclone separator. The walls of the water wall membrane comprises a plurality of vertical tubes and a plurality of fins placed between them. The plurality of fins is arranged alternately such that water wall membrane has a mesh like structure.

In a preferred embodiment, the plurality of vertical tubes includes at least one bent tube. The plurality of vertical tubes has a cross-sectional shape selected from the group consisting of a circle, a rectangle, a square, a triangle, and any geometrical or non-geometrical shape thereof.

The heat exchange column includes at least one of a superheater, an economizer, an air pre- heater.

BRIEF DESCRIPTION OF ACCOMPANYING DRAWING

A circulating fluidized bed combustion boiler system of the present disclosure will now be described with the help of the accompanying drawing, in which: Figure 1 illustrates a schematic view of a conventional circulating fluidized bed combustion boiler system;

Figure2 illustrates a schematic view of a circulating fluidized bed combustion boiler system in accordance with an embodiment of the present disclosure;

Figure 3 illustrates an isometric view of a flue gas vortex breaker section of the circulating fluidized bed combustion boiler system of Figure 2; and

Figure 4 illustrates a schematic view of a portion of the flue gas vortex breaker section of Figure 3.

LIST OF REFERENCE NUMERALS 100 - Conventional system

101 - Combustion chamber

102 - Cyclone

103 - Vertical column

200 - Circulating fluidized bed boiler system

201 - Combustion chamber

201a - Flue gas outlet

202 - Cyclone separator

202a - First outlet

202b - Second outlet

202i - Inlet

203 - heat exchange column

204 - Water wall membrane

205 - At least one bent tube

206 - Plurality of vertical tubes

207 - Plurality of fins

208 - Flue gas conduit

209 - Flue gas vortex breaker section

210 - First end of the water wall membrane

211 - Second end of the water wall membrane

212 - Near-end wall of the water wall membrane

213 - Far end wall of the water wall membrane

214 - Plurality of sidewalls of the water wall membrane 215 - Mesh- like structure formed by the water wall membrane

220 - Superheater

221 - Economizer

222 - Air pre -heater DETAILED DESCRIPTION

Figurel illustrates a schematic view of a conventional circulating fluidized bed combustion boiler system 100 (hereinafter referred to as conventional system 100). The conventional system 100 comprises a combustion chamber 101, a cyclone 102 and a vertical column 103.

The combustion chamber 101 of the conventional system 100 comprises a bed of inert material (not shown in the figure) at an operative lower end of the combustion chamber 101. Coal is spread over the bed where the combustion of the coal takes place. Air is supplied to the combustion chamber 101 from under the bed at high pressure. The high pressure air lifts the coal and inert material, thereby keeping the coal and inert material in suspension. Further, the fine particles of partly burned coal, ash and inert material are carried along with the flue gases to an operative top end of the combustion chamber 101. The operative top end of the combustion chamber 101 is in fluid communication with the cyclone 102. In the cyclone 102, due to the centrifugal phenomenon, the coal particles separate from the flue gases and fall into a loop seal device placed at the bottom of the cyclone 102, thereby returning the coal particles back into the combustion chamber 101 for recirculation. The same coal particles enter the boiler several times, thereby providing sufficient residence time to the coal for combustion. This improves the efficiency and reduces the emission of the conventional system 100. The flue gases from the cyclone 102 is then passed to the vertical column 103.

In the conventional circulating fluidized bed boiler system 100, the flue gases entering the vertical column 103 from the cyclone 102 has a vortex motion of a very large tangential velocity. The high tangential velocity of the flue gases causes the flue gases to stabilize after a considerable amount of time. As soon as the flue gases enter the vertical column 103, the circular motion of the flue gases causes non-uniform distribution of the flue gases over the heat exchangers (not explicitly labelled in the figure), thereby leading to a poor heat transfer performance. A preferred embodiment of the circulating fluidized bed boiler system, of the present disclosure will now be described in detail with reference to the accompanying drawing. The preferred embodiment does not limit the scope and ambit of the disclosure. The description provided is purely by way of example and illustration. Figure 2 illustrates a schematic view of a circulating fluidized bed boiler system 200 in accordance with an embodiment of the present disclosure. Figure 3 illustrates an isometric view of a flue gas vortex breaker section 209 of the circulating fluidized bed boiler system 200 of the Figure 2. Figure 4 illustrates a schematic view of a portion of the flue gas vortex breaker section 209 of the Figure 3.

The present disclosure envisages a circulating fluidized bed boiler system 200. The circulating fluidized bed boiler system 200 (hereinafter referred to as the "system 200") includes a combustion chamber 201, a cyclone separator 202, and the flue gas vortex breaker section 209. The combustion chamber 201 has a flue gas outlet 201a at an operative top end. The combustion chamber 201 is configured to fluidize and combust fuel particles to generate flue gases. The flue gas outlet 201a is in fluid communication with an inlet 202i of the cyclone separator 202. The cyclone separator 202 is configured to receive the fluidized and combusted fuel particles from the combustion chamber 201 and is further configured to separate partly burnt fuel from the flue gases. A flue gas conduit 208 is in fluid communication with the cyclone separator 202, and is configured to receive the flue gases from the cyclone separator 202 and transport flue gases to a heat exchange column 203. The flue gas vortex breaker section 209 is disposed within the flue gas conduit 208. The flue gas vortex breaker section 209 includes a water wall membrane 204. The water wall membrane 204 is configured to streamline and resist the flow of the flue gases.

The combustion chamber 201 of the system 200 comprises a bed of inert material (not shown in the figure) disposed at an operative lower end of the combustion chamber 201. Fuel is spread over the bed where the combustion of the fuel takes place. In an embodiment, the fuel is coal. Air is supplied to the combustion chamber 201 from under the bed placed at the operative lower end of the combustion chamber 201 at high pressure. The high pressure air lifts the fuel and inert materials, thereby keeping the fuel and the inert material in suspension. Further, the fine particles of the partly burned fuel, ash and inert materials are carried along with the flue gases to the cyclone separator 202from the inlet 202i, via the flue gas outlet 201a of the combustion chamber 201. In the cyclone separator 202, due to the centrifugal phenomenon the partly burned fuel separates from the flue gases and falls into a loop seal device (not shown in the figures) via the second outlet 202b placed at the bottom of the cyclone separator 202, thereby returning the partly burned fuel back into the combustion chamber 201 for recirculation. The same fuel enters the combustion chamber 201 several times, thereby providing sufficient residence time to the fuel for combustion and improving the efficiency and reducing the emission of the system 200.

In accordance with the present disclosure, the heat exchange column 203 is in fluid communication with the cyclone separator 202 via the flue gas conduit 208. The flue gases travelling towards the heat exchange column 203 from a first outlet 202a of the cyclone separator 202 travels via, the flue gas vortex breaker section 209 that is disposed within the flue gas conduit 208. The water wall membrane 204 is placed within the flue gas vortex breaker section 209.

The water wall membrane 204 is defined by a near-end wall 212, a plurality of side walls 214 and a far end wall 213. The far end wall 213 is opposite to the near-end wall 212. The near- end wall 212, the plurality of sidewalls 214, and the far end wall 213 define an interior space within the water wall membrane 204. The near-end wall 212 is positioned in the path of the flow of the flue gases from the first outlet 202a of the cyclone separator 202 to the far end wall 213 of the water wall membrane 204, such that it is upstream of the far end wall 213 with respect to the flow of the flue gases.

A first end 210 of the water wall is defined by the near-end wall 212 of the water wall membrane 204 and is in fluid communication with the first outlet 202a of the cyclone separator 202, via the flue gas conduit 208. The first end 210 of the water wall membrane 204 is the side comprising the at least one bent tube 205. A second end 211 of the water wall membrane 204 is in fluid communication with the operative top end of the heat exchange column 203. The second end 211 of the water wall membrane 204 comprises the portion of the plurality of vertical tubes 206 leading to the heat exchange column 203. In an embodiment, the water wall membrane 204 resembles a mesh like structure 215.

The water wall membrane 204 includes a plurality of vertical tubes 206 disposed therewithin and a plurality of fins 207 that is alternately disposed between the plurality of vertical tubes 206. In an embodiment, the plurality of vertical tubes 206 includes at least one bent tube 205. In another embodiment, the plurality of vertical tubes 206 includes a bent section defined by at least one bent tube 205 placed in proximity of the near-end wall 212. In yet another embodiment, the plurality of vertical tubes 206 have a cross-sectional shape selected from the group consisting of a circle, a rectangle, a square, a triangle, and any geometrical or non- geometrical shape thereof.

The plurality of fins 207 of the water wall membrane 204 provides a resistance to the flow of the flue gases exiting the cyclone separator 202, thereby reducing the velocity vector and breaking the vortex of the flue gases. The plurality of fins 207 also partially obstructs and streamline the flow of the flue gases. In an embodiment, the streamlined flue gases with reduced velocity vector, enter the heat exchange column 203 and flow through a superheater 220, an economizer 221 and an air preheater 222 that are placed in the heat exchange column 203, thereby maximizing the heat transfer area for the effective heat transfer and significantly increasing the heat transfer performance of the system 200. The flue gases from the heat exchange column 203 exits to the atmosphere.

The circulating fluidized bed boiler system 200 of the present disclosure therefore, provides substantially increased heat transfer performance of the heat exchangers in the vertical column and also reduces the risk of erosion of the heat exchangers as compared to the existing systems.

TECHNICAL ADVANCES AND ECONOMICAL SIGNIFICANCE

The present disclosure described herein above has several technical advantages including, but not limited to, the realization of a circulating fluidized bed boiler system that: partially obstructs the flow of flue gases for elimination of vortex in the flue gas flow;

streamlines the flow of flue gases as they go into the vertical column comprising the various heat exchangers;

increases the heat transfer performance of the heat exchangers contained in the vertical column; and

improves the velocity profile of flue gases.

The disclosure has been described with reference to the accompanying embodiments which do not limit the scope and ambit of the disclosure. The description provided is purely by way of example and illustration.

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 foregoing description of the specific embodiments so fully revealed 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. 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 disclosure 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 disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.

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.