KR101897873B1 - Method of introducing primary fluidizing gas into a furnace of a fluidized bed boiler - Google Patents

Abstract

The present invention relates to a method for introducing a primary flow gas into a furnace 12 of a fluidized bed boiler 10 through a bottom grid system 22 arranged at the bottom of the furnace wherein the bottom grid system comprises a lower bottom grid portion 32, And a top bottom grid portion (34) located at a higher elevation than the bottom bottom grid portion, wherein a) the primary flow gas exclusively flows through the bottom bottom grid portion (32) at a first combustion condition, B) the primary flow gas is introduced into the furnace through both the lower bottom grid portion 32 and the upper bottom grid portion 34, in the second combustion condition, particularly at higher load conditions , The introduction of the primary flow gas into the furnace is controlled.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a method of introducing primary flow gas into a furnace of a fluidized bed boiler,

The present invention relates to a method for introducing a primary flow gas into a furnace of a fluidized bed boiler according to the preamble of claim 1. More specifically, the present invention relates to a method of introducing a primary flow gas into a furnace of a fluidized bed boiler, the furnace being defined primarily by vertical sidewalls, a loop, and a bottom, Wherein the bottom grid system includes a lower bottom grid portion and an upper bottom grid portion positioned at a higher elevation than the bottom bottom grid portion.

The requirement for a multipurpose fluidized bed boiler, such as a circulating fluidized bed boiler, is the ability to operate the boiler with a wide range of loads. In particular, at low loads, when the fuel feed rate is low, the bed temperature tends to be very low, which may increase CO and SO ₂ emissions. On the other hand, in order to maintain a sufficient and uniform flow of the layer, the flow rate of the flowing gas may not generally be very low. Conventionally, sufficient flow can be provided by increasing the supply of air required to burn fuel at the lowest load conditions, increasing the need for auxiliary power and high NOx emissions, or by increasing the manufacturing and operating costs by using a relatively high rate of flue gas recirculation .

Different arrangements and methods have been proposed to introduce the flow gas into the furnace of the fluidized bed boiler under various operating conditions. Patent document AT 385 109 discloses a fluidized bed furnace by reducing the flow rate in specific bed sections so that an essentially uniform average temperature distribution is maintained in the bed and by gradually changing the positions of the beds with reduced flow in the bed section, And a method of improving partial load behavior of the device.

Patent document WO 00/43713 A1 discloses a method for controlling a pipe grate of a fluidized bed boiler and a pipe grate at a partial load, for example. In this method, the region where the flowing air flows to the combustion chamber of the fluidized bed boiler is regulated by the specific-pipe control means. The control systems of the above-described arrangements are relatively complex, and such control systems may also increase emissions due to insufficient bed temperatures, particularly at incompletely fluidized boundary areas between the fluidizing and non-fluidizing zones.

US Pat. No. 3,387,590 discloses a method and apparatus for controlling the heat output of a fluidized bed that is divided so that the fluidized bed separates the compartments by partition walls having a series of ports, and the heat output is controlled by sequentially activating the separate compartments . In such a device, the boundary zones are removed, but the configuration becomes relatively complicated, and it may be difficult to maintain low exhaust and uniform combustion conditions due to fouling of the ports in the bulkheads, especially when burning different fuels.

CN 102913900 A has two side wind boxes below the two side grids that may be tilted by 0 to 800 mm above the level of the central grid and by 5 to 30 degrees towards the center, A fluidized-bed boiler having a central windbox is disclosed. In order to provide the possibility of arranging the heat exchange tubes in the rich fluidized bed circulating inside and the slowly fluidized side portions of the fluidized bed, the fluidization rate at the central portion is 4 to 5 m / s and the fluidization rate at the side portions is 1.5 to 2 m / s.

It is an object of the present invention to provide a method of controlling the introduction of a primary flow gas into a furnace of a fluidized bed boiler under different combustion conditions, in order to minimize at least some of the above-mentioned disadvantages.

According to one aspect, the present invention provides a method of introducing a primary flow gas into a furnace of a fluidized bed boiler, the furnace being defined primarily by vertical sidewalls, loops, and bottoms, Wherein the bottom grid system comprises a lower bottom grid portion and an upper bottom grid portion located at a higher elevation than the lower bottom grid portion, and wherein a) the primary flow gas is introduced into the furnace through a first combustion condition B) the primary flow gas is introduced through both the lower bottom grid portion and the upper bottom grid portion in the second combustion condition, the method further comprising introducing the primary flow gas into the furnace And the like.

According to the first preferred embodiment of the present invention, the first combustion condition is a lower load condition than the second combustion condition. This means that the primary flow gas, typically air, is introduced into the furnace only at low load conditions, i. E. Only in the first combustion condition, through the bottom bottom grid portion. Thus, the primary flow gas is introduced into the furnace at higher load conditions, i. E. In the second combustion condition, through both the lower bottom grid portion and the upper bottom grid portion.

According to another preferred embodiment of the present invention, the first combustion condition and the second combustion condition are related to the start-up condition of the fluidized bed boiler and the normal continuous operating condition, respectively.

According to a preferred embodiment of the present invention, the bottom grid system comprises only a single, upper, bottom grid portion arranged adjacent to the sidewalls of the furnace. According to another preferred embodiment of the present invention, the upper bottom grid portion comprises two distinct sections arranged adjacent to two opposite side walls of the furnace.

Thereby, the lower bottom grid portion is advantageously arranged in the horizontal direction between two sections of the upper bottom grid portion. The lower bottom grid portion may also include two or more sections that may be arranged adjacent to a portion or all of the side walls and / or even a central portion of the furnace.

It is preferred that the upper bottom grid portion is about 0.3 m to about 2 m, and most preferably about 1 m above the level of the lower bottom grid portion. The upper bottom grid portion is generally at a lower level than the ports for introducing the secondary air into the furnace. The upper and lower bottom grid portions include conventional nozzles such as flow gas supply nozzles, advantageously bubble caps or directional nozzles. According to a preferred embodiment of the present invention, the upper bottom grid portion includes directional nozzles that are oriented to deliver the flowing gas and layer particles toward the lower bottom grid portion.

An advantage provided by the above-described preferred embodiments of the present invention is that the flow region of the bottom of the furnace is in a lower load condition that is significantly smaller than the higher load conditions. The area of the lower bottom grid portion is preferably 20-80%, and even more preferably 25-50% of the total area of the lower bottom grid portion and the upper bottom grid portion. Due to the smaller flow area at low loads, the minimum pressure drop required at the grid nozzles can be achieved without increased excess air or high flue gas recirculation. Because the upper bottom grid portion is at a higher elevation than the bottom bottom grid portion, no septum or partition between the bottom grid portions is required. It also does not have any increased emissions that cause an incompletely fluidized boundary between the fluidized bottom grid portion and the non-fluidized bottom grid portion under any operating conditions.

The sections of the upper bottom grid portion can be horizontal and these sections can also be inclined toward the lower bottom grid portion. The inclination angle of the sections of the upper bottom grid portion is preferably at most 45 degrees. Adjacent edges of the upper bottom grid portion and the lower bottom grid portion are connected together by inner side wall portions and the inner side wall portions may be substantially vertical or slightly inclined to form a downward tapered bottom portion of the furnace .

It will be appreciated that some of the foregoing embodiments of the invention relate to a bottom grid structure with features similar to those described in patent application CN 102913900 A. However, the patent publication CN 102913900 A discloses a grid system for an entirely different purpose than that of the present invention, and thus the method disclosed in the above publication for using a grid system is entirely different from the present invention. Therefore, the method of introducing the primary flow gas into the furnace of the fluidized bed boiler according to the present invention is novel in view of the patent publication.

An advantage of the method of the present invention is that it can expand the available load range of the boiler from that of a conventional CFB boiler. More specifically, the present invention lowers the minimum load of the boiler, i.e. the minimum speed at which the fuel can be burned in the boiler without discharging the pest. In addition, the method of the present invention can avoid too low a layer temperature at low loads. The minimum load of the CFB boiler is typically about 30-40% of the total load. With the present invention, the minimum load can be reduced to less than 25%, preferably less than 20%, more preferably less than 15% of the total load.

In the following, an operating mode that includes introducing the primary flow gas into the furnace solely through the lower bottom grid portion, i.e., the operating mode used in the first combustion condition, is referred to as the first primary flow gas introduction mode. Thus, an operating mode that includes introducing the primary flow gas into the furnace through both the bottom and top grid grid portions, i.e., the operating mode used in the second combustion condition, is referred to as the second primary flow gas introduction mode.

The boundary line between the first combustion condition and the second combustion condition can be set so that, for example, the manner of introducing the flowing gas is switched from the first primary flow gas introduction mode to the second primary flow gas introduction mode according to the present invention The limited load may vary depending on the design of the burned fuel and furnace. The first primary flow gas introduction mode is preferably used up to 50%, more preferably up to 40%, and most preferably up to 30% of the total load condition from the minimum load.

According to a preferred embodiment of the present invention, the primary flow gas is introduced into the furnace through the upper bottom grid portion through the upper windbox in the second primary flow gas introduction mode. Thus, the primary flow gas is introduced into the furnace through the lower bottom grid portion through the lower windbox in all primary flow gas introduction modes, and the lower windbox is positioned primarily or entirely at a lower level than the upper windbox.

According to the present invention, the primary air is introduced into the furnace only through the lower bottom grid portion in the first primary flow gas introduction mode. Then, preferably, the primary gas flow rate through the lower bottom grid portion is such that the nominal flow rate in the lower portion of the furnace is at least 1.5 m / s. The primary flow gas flow rate through the upper bottom grid portion is zero or only very low gas flow rates prevent the pudding drop of the layer material to the upper windbox without actually causing combustion of the fuel or flowing the layer Is used.

The method of the present invention advantageously provides a primary flow through the lower bottom grid portion and the upper bottom grid portion in a second primary flow gas introduction mode such that a nominal flow rate of 3 m / s to 10 m / And introducing gas. Preferably, in the second combustion condition, the nominal flow rate is substantially uniform in the furnace. Typically, the average nominal flow rate directly above the upper bottom grid portion is 70% to 130% of the average nominal flow rate directly above the lower bottom grid portion in the second combustion condition.

The present invention provides a method for introducing a primary flow gas into a furnace of a fluidized bed boiler having a significantly improved performance. Embodiments of the present invention allow for an increase in the available load range of the boiler by providing a higher bed temperature and reduced excess air under low load conditions. In addition to reduced emissions, the method enables low load operation with reduced auxiliary power consumption. Other embodiments of the present invention enable faster start-up of the boiler, thereby requiring lower start-up burner power.

In the following, the present invention will be described with reference to the accompanying schematic and exemplary drawings.

1 shows a sectional view of a fluidized-bed boiler according to a first embodiment of the present invention.
2 shows a cross-sectional view of a fluidized-bed boiler according to a second embodiment of the present invention.

Figure 1 shows a cross-sectional view of a circulating fluidized bed boiler 10 comprising a furnace 12 defined by mainly vertical side walls 18, bottom 16 and loops 14 formed from evaporative water-tube panels. Fig. Generally, the furnace has a rectangular horizontal cross-section that is clearly longer than two sidewalls, so-called long sidewalls, two horizontally different sidewalls, so-called short sidewalls or end walls. Generally, the lower portions of the long side walls are inclined inward to form a downwardly tapering lower portion of the furnace with the end walls. The sidewalls include a means for supplying fuel, and possibly an inert layer material, and a sulfur reducing agent, such as limestone, into the furnace.

In the bottom of the furnace, a bottom grid system 22 is arranged for supplying a primary flow gas, generally primary air, to the furnace in order to flow the bed and also to combust the fuel introduced into the furnace through the fuel supply means 20 . In addition, the sidewalls 18 generally include means for supplying the furnace secondary air 24 to complete the combustion of the fuel. An outlet channel (26) is connected to the upper portion of the furnace for exhausting exhaust gas from the furnace. The outlet channel 26 leads to a conventional particle separator 28 having a return channel 30 for returning the particles separated from the exhaust gas to the lower portion of the furnace. The return channel 30 is generally provided with a gas airtight portion and a heat exchanger, but for simplicity, the gas airtight portion and the heat exchanger are not shown in FIG. Although a large circulating fluidized bed boiler is provided with several particle separators connected in parallel, for simplicity reasons, Figure 1 shows only one particle separator 28.

The bottom grid system 22 includes a lower bottom grid portion 32 and an upper bottom grid portion 34. The upper bottom grid portion 34 is located at a higher elevation than the bottom bottom grid portion 32. Fig. 1 shows the height difference between the upper and lower bottom grid portions as the vertical distance L. Fig. The vertical distance L is advantageously from about 0.3 m to about 2 m, and typically the vertical distance L is about 1 m. In Fig. 1, the upper bottom grid portion 34 is horizontal, but the upper bottom grid portion is alternatively arranged in the upper bottom grid portion 32 to align the lower bottom grid portion 32 Lt; / RTI > The upper bottom grid portion may advantageously be inclined at an angle of up to 45 [deg.], Preferably between 5 [deg.] And 40 [deg.] Toward the bottom bottom grid portion.

The primary flow gas is supplied from the gas supply, for example, the bottom (not shown in FIG. 1) through the two branches 36, 38 of the primary flow gas channel 40, Is introduced into each of the upper windboxes 44 arranged below the windbox 42 and the upper bottom grid portion 34. The two branches 36, 38 of the primary flow gas channel advantageously include means, e.g., valves 46, 48, for controlling the primary flow gas flow to the lower and upper windboxes, respectively. The bottom bottom grid portion and the top bottom grid portion 32, 34 include conventional nozzles 50, 52, such as bubble caps or arrow head nozzles, for introducing the primary flow gas into the furnace. In accordance with an advantageous embodiment of the present invention, the nozzles 52 of the upper bottom grid portion 34 are directional nozzles oriented toward the lower bottom grid portion 32.

In operation of the circulating fluidized-bed boiler 10, the oxide-containing combustion gases, such as air, are typically supplied as primary flow gas through the nozzles 50, 52 to burn the fuel at a temperature of about 850 ° C to 900 ° C, Is generally introduced into furnace 12 at a sufficient flow rate as a secondary combustion gas through line 24. The total gas introduction rate is generally controlled such that the nominal gas velocity in the furnace is 3 m / s to 10 m / s.

According to the present invention, the primary flow gas is introduced into the furnace by using one of the two primary flow gas introduction modes depending on the operating mode of the boiler. In the first primary flow gas introduction mode, the primary flow gas is introduced into the furnace only through the lower bottom grid portion 32, and in the second primary flow gas introduction mode, the primary flow gas is introduced into the lower bottom grid portion 32, And the upper bottom grid portion 34, respectively.

The first primary flow gas introduction mode is advantageously used at the lowest load condition of the boiler and the second primary flow gas introduction mode is advantageously used at the higher load conditions of the boiler. By using the circulating fluidized bed boiler described above in accordance with the primary flow gas introduction modes described above, excess air and harmful NOx emissions are reduced at low combustion loads. Moreover, higher temperature levels are obtained at low combustion loads, leading to reduced CO emissions and improved sulfur retention in the furnace.

2 shows another embodiment of the invention in which the features directly corresponding to the features already shown in Fig. 1 are represented by the same reference numerals as in Fig. The embodiment of Fig. 2 mainly consists of two sections 54, 54 (Fig. 2) in which the upper bottom grid portion 34 is positioned adjacent to the downward tapered portions of the two long side walls 18 of the furnace at substantially the same height as each other. '), Which is different from the embodiment of FIG. The lower bottom grid portion 32 is then arranged horizontally between the two sections 54, 54 'of the upper bottom grid portion 34. In the embodiment shown in Figure 2, the sections 54, 54 'of the upper bottom grid portion 34 have a lower bottom grid portion for directing the layer material descending to the upper bottom grid portion toward the lower bottom grid portion Lt; / RTI > Orienting the layer material toward the bottom bottom grid portion may be important in some applications, especially in the first primary flow gas introduction mode where the primary flow gas is only introduced into the furnace through the bottom bottom grid portion. However, in other embodiments of the present invention, sections 54 and 54 'may alternatively be horizontal as in FIG.

1, an upper wind box 44 is arranged below each of the first section and the second section 54, 54 'of the upper bottom grid section 34, and a lower bottom grid section 32, And a lower wind box 42 is arranged below. The primary flow gas channel 40 has three branches 36, 38, 38 'leading to two sections 54, 54' of the upper bottom grid section 34 and a bottom bottom grid section 32, . In FIG. 2, each of the branches 36, 38, 38 'includes a respective valve 46, 48, 48' to control the flow of primary flow gas to the respective windboxes. Alternatively, the two branches 38, 38 'leading to the two sections 54, 54' of the upper bottom grid portion 34 may be divided into a common channel portion and both sections 54, 54 ' It is possible to have only one valve for simultaneously controlling the flow of the flowing gas of the gas.

Figure 2 shows the sections 54, 54 'of the upper bottom grid portion 34 adjacent the lower portions that are inclined to the inside of the two long side walls 18 of the furnace. The area of the lower bottom grid portion is preferably 20 to 60%, even more preferably 25 to 40% of the total area of the bottom bottom grid portion and the top bottom grid portion. According to a preferred embodiment of the invention, the sections of the upper bottom grid portion extend the entire length of the horizontally long sidewalls, i. E. From one end wall to the other end wall. However, not limited to this type of arrangement of the present invention, the sections of the upper bottom grid portion or the upper bottom grid portion may alternatively be provided on one long side wall as in FIG. 1, or on one of the end walls of the furnace It can be adjacent to all. Also, the upper bottom grid portions may be arranged continuously or discontinuously adjacent the entire or any number of sidewalls of the furnace. It is even possible, in some applications, to arrange the sections of the upper bottom grid portion or the upper bottom grid portion in the middle portion of the furnace.

While the present invention has been described by way of example with reference to what are presently considered to be the most preferred embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments, but is intended to fall within the scope of the invention as defined in the appended claims. It is to be understood that the invention is intended to cover various combinations or alterations to the described features and various other applications. Details referred to in connection with any of the above-described embodiments may also be used in connection with other embodiments when such a combination is technically feasible.

Claims (18)

A method of introducing a primary flow gas into a furnace (12) of a fluidized bed boiler (10)
The furnace is defined by side walls (18), a roof (14), and a bottom (16) that are vertical or lower inwardly inclined, and the primary flow gas is defined by a bottom grid System 22 and the bottom grid system includes a lower bottom grid portion 32 and an upper bottom grid portion 34 positioned at a higher elevation than the bottom bottom grid portion and,
a) the primary flow gas is introduced into the furnace only through the lower bottom grid portion 32 at a first combustion condition, and
b) the primary flow gas is introduced into the furnace through both the lower bottom grid portion (32) and the upper bottom grid portion (34) in a second combustion condition,
Introducing a primary flow gas into a furnace (12) of a fluidized bed boiler (10) in which introduction of said primary flow gas into said furnace is controlled,
Wherein the first combustion condition is a lower load condition than the second combustion condition. The method according to claim 1,
Wherein the first combustion condition is a start-up condition of the fluidized bed boiler and the second combustion condition is a continuous operating condition of the fluidized bed boiler. A method for introducing a flow gas. 3. The method of claim 2,
Wherein the first combustion condition extends from a minimum load of the fluidized bed boiler to at most 50% of the total load of the fluidized bed boiler. The method of claim 3,
Wherein the first combustion condition extends from a minimum load of the fluidized bed boiler to a maximum of 40% of the total load of the fluidized bed boiler. 5. The method of claim 4,
Wherein the first combustion condition extends from a minimum load of the fluidized bed boiler to at most 30% of the total load of the fluidized bed boiler. 6. The method according to any one of claims 3 to 5,
Wherein the minimum load of the fluidized bed boiler is at most 25% of the total load of the fluidized bed boiler. 6. The method according to any one of claims 3 to 5,
Wherein the minimum load of the fluidized bed boiler is at most 20% of the total load of the fluidized bed boiler. 6. The method according to any one of claims 3 to 5,
Wherein the minimum load of the fluidized bed boiler is at most 15% of the total load of the fluidized bed boiler. The method according to claim 1,
The primary flow gas is introduced into the furnace through the upper bottom grid portion 34 through the upper windbox 44 and through the lower bottom grid portion 32 through the lower windbox 42, A method of introducing a primary flow gas into a furnace (12) of a fluidized bed boiler (10), characterized in that the windbox is located at a higher level than the lower windbox. delete The method according to claim 1,
Wherein the upper bottom grid portion is adjacent a side wall (18) of the furnace. The method according to claim 1,
Wherein the upper bottom grid portion includes two distinct sections (54, 54 ') arranged adjacent to two spaced side walls (18) of the furnace, the lower bottom grid portion (32) Is arranged horizontally between the two said sections of the bottom grid section. ≪ Desc / Clms Page number 13 > 14. A method of introducing a primary flow gas into a furnace (12) of a fluidized bed boiler (10). The method according to claim 1,
The primary flow gas is supplied to the lower bottom grid portion (32) and the upper bottom grid portion (34) such that a nominal flow rate of 3 m / s to 10 m / s is maintained in the furnace (12) of the fluidized-bed boiler (10), characterized in that the primary flow gas is introduced into the furnace (12) of the fluidized bed boiler (10). 14. The method of claim 13,
Wherein the nominal flow rate is uniform in the furnace at the second combustion condition. ≪ RTI ID = 0.0 > 11. < / RTI > 14. The method of claim 13,
Characterized in that the average nominal flow rate directly above the upper bottom grid portion (34) is between 70% and 130% of the average nominal flow velocity directly above the bottom bottom grid portion (32) in the second combustion condition 10) into the furnace (12). The method according to claim 1,
Characterized in that the upper bottom grid portion (34) is horizontal with respect to the lower bottom grid portion (32) or the upper bottom grid portion is inclined at an angle of at most 45 degrees toward the bottom bottom grid portion Introducing the primary flow gas into the furnace (12) of the furnace (10). The method according to claim 1,
Wherein the upper bottom grid portion comprises directional nozzles. ≪ Desc / Clms Page number 12 > delete

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