CLAIM OF PRIORITY

This application is a U.S. national stage application of International Patent Application No. PCT/FI2018/050603, filed Aug. 24, 2018, now published as International Publication No. WO 2020/039117 A1 on Feb. 27, 2020.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an arrangement for and a method of controlling flow of solid particles. More particularly, the invention relates to leading controlled first and second sub flows, formed in a flow controlling arrangement from an initial flow of solid particles flowing downwards in a vertical inlet pipe, to first and second outlet chutes. The invention also relates to a fluidized bed reactor with an arrangement for forming controlled sub flows from an initial flow of solid particles

Description of Related Art

When operating fluidized bed reactors, such as circulating fluidized bed boilers, there is often a need into control flow of solid particles, especially, the division of an initial flow of solid particles to two or more sub flows. Especially, when returning solid particles separated from exhaust gas emanating from the fluidized bed reactor, there is often a need to lead a controlled portion of the separated particles via a heat exchanger, as cooled particles, back to the reactor, whereas another portion of the separated particles is returned uncooled directly to the reactor. U.S. Pat. Nos. 4,312,301, 4,552,203, 4,672,918, 4,473,032, 5,570,645, 5,642,676, 6,264,465 B1, 5,442,919, European patent EP 2 179 218 B1, Korean patent document KR 2017-0031407, and U.S. Pat. No. 7,543,553 B2 show prior art solutions in which a mechanical flow control device, such as a plug valve, throttle valve, or a rotary lock is used to control the ratio of two sub flows formed from an initial flow of solid particles. However, such mechanical flow control devices are often quite complicated structures and may have a tendency to get stuck caused by solid particles entering between moving parts of the device.

Another conventional way to control solid particle flows in a fluidized bed reactor is to utilize a particle chamber with separately fluidized areas to enable or to prevent flow of particles to certain paths, as needed. European Patent EP 0 682 761 B1 teaches using separately fluidized areas in a chamber to direct solid particles to different paths towards outlet openings in a heat exchange chamber. This structure, however, does not allow definite independent control of the formed sub flows. U.S. Pat. No. 5,140,950 discloses independently fluidized areas in a heat exchanger divided by division walls. Such a construction improves independent control of the sub flows, but makes the structure more complicated and may cause stagnation of particles to corner areas of the chamber. Moreover, the structures of EP 0 682 761 B1 and U.S. Pat. No. 5,140,950 do not allow independent control of the particle flows and heat exchange efficiency in the heat transfer surfaces.

U.S. Pat. No. 4,457,289 shows, inFIG. 6, a fluidized bed reactor comprising a particle separator for separating solid particles from exhaust gas emanating from the reactor and a return duct system for returning separated particles from the particle separator back to the reactor. The return duct system comprises a gas seal with a non-mechanical flow controlling arrangement comprising a fluidized bed with outlets at two opposite ends thereof so as to divide the initial flow of particles to two sub flows. The first sub flow is returned over a weir directly back to the reactor and the second sub flow is returned over another weir to a heat exchange chamber, from where the second flow can be returned back to the reactor. A problem in the dividing gas seal shown in U.S. Pat. No. 4,457,289 is that the controllability of the ratio of the two sub flows is relatively weak. Patent document KR 2002-0031687 appears to show a downwards slanted outlet chute directly connected to a side wall of the lower portion of a vertical inlet duct of a seal pot.

U.S. Pat. No. 4,733,621 relates to a different problem, a need to enable even distribution of particles returned from a particle separator to the reactor. U.S. Pat. No. 4,733,621 teaches arranging a horizontal distribution pipe symmetrically at the lower end of a vertical inlet pipe. The horizontal distribution pipe comprises multiple separately fluidized sections, vertical riser pipes at the ends of the horizontal intermediate pipe, and inclined outlet chutes to the reactor at the upper end of the riser pipes. In this construction, a relatively long horizontal pipe is needed to enable independent control of the sub flows through the vertical riser pipes.

Chinese Patent No. 102901093A teaches arranging a division wall at the central portion of a vertical inlet pipe to improve independent controllability of the ratio of two sub flows to two outlet chutes via riser pipes at the ends of a relatively short the horizontal intermediate pipe. A problem with this structure is that a non-even distribution of the initial flow of particles in the vertical inlet pipe may prevent obtaining desired distribution of the sub flows in the outlet chutes.

An object of the present invention is to provide an advantageous arrangement for and a method of controlling flow of solid particles in which the problems of the prior art are avoided or minimized.

SUMMARY OF THE INVENTION

According to one aspect, the present invention provides an arrangement for controlling a flow of solid particles, the arrangement comprising a vertical inlet pipe for directing the flow of solid particles downwards therein and having a bottom at a level L0, a first outlet chute and a second outlet chute in particle flow connection with the vertical inlet pipe and a fluidizing device for directing controlled first and second sub flows formed from the flow of solid particles to the first and second outlet chutes, respectively, wherein the arrangement comprises a branch in particle flow connection with an opening on a side wall of the vertical inlet pipe for directing the first sub flow of solid particles to the first outlet chute, wherein the opening has a lower edge at a level L1that is higher than L0, and a horizontally extending intermediate pipe for directing the second sub flow of solid particles to the second outlet chute, the horizontally extending intermediate pipe comprising at least one nozzle for feeding fluidizing gas to the horizontally extending intermediate pipe and having a first end in particle flow connection with the bottom of the vertical inlet pipe at the level L0.

The arrangement also advantageously comprises a vertically extending riser pipe with a bottom end in particle flow connection with a second end of the horizontally extending intermediate pipe. An upper end of the vertically extending riser pipe is then in particle flow connection with the second outlet chute at a level L2that is higher than L1.

According to another aspect, the present invention provides a method of controlling a flow of solid particles, comprising directing the initial flow of solid particles downwards in a vertical inlet pipe having a bottom at a level L0, forming controlled first and second sub flows of solid particles from the initial flow of solid particles and leading the first and second sub flows to first and second outlet chutes, respectively, wherein the method comprises forming a fluidized bed of solid particles from the initial flow of solid particles to a horizontally extending intermediate pipe extending from the bottom of the vertical inlet pipe at the level L0to a bottom end of a vertically extending riser pipe, leading the first controlled sub flow to the first outlet chute via a branch from an opening on a side wall of the vertical inlet pipe at a level L1that is higher than L0, and leading the second controlled sub flow from an upper end of the vertical riser pipe to the second outlet chute at a level L2that is higher than L1.

According to the present invention, the downwardly directed first and second outlet chutes are non-symmetrically connected to the vertical inlet pipe so that the second outlet chute advantageously begins at a higher level than does the first outlet chute. By the beginning of an outlet chute is herein meant the level at which the corresponding flow path of the solid particles is finally turned downwards, for example, from a vertically extending riser pipe. According to a main feature of the present invention, the particle flow path to first outlet chute branches from the vertical inlet pipe at a level L1that is clearly higher than the level of the bottom L0of the vertical inlet pipe, whereas the particle flow path to the second outlet chute passes via the bottom of the vertical inlet pipe.

The first outlet chute is advantageously connected to the vertical inlet pipe via a branch arranged at the level L1to an opening on a side wall of the vertical inlet pipe. More precisely, the opening has a lower edge at the level L1and an upper edge at a level L4. According to a preferred embodiment of the present invention, the branch comprises a horizontally extending portion with fluidizing nozzles leading to a weir over which solid particles must flow to enter to the first outlet chute. The weir advantageously extends to a level L3that is higher than the level L4of the upper edge of the opening, so as to collect a gas lock forming fluidized bed of particles in the branch. The branch may advantageously comprise a horizontally extending shift pipe from the opening to an intermediate riser pipe, wherein a portion of a side wall of the intermediate riser pipe forms the weir.

According to another embodiment of the present invention, the first outlet chute is directly connected to an opening, having a lower edge at the level L1, on a side wall of the vertical inlet pipe. Thereby, particles can fall or drop from the vertical inlet pipe directly to the first outlet chute. During normal operation a bed of particles extending up to the level L1is formed to the bottom of the vertical inlet pipe, and additional solid particles flow freely from the vertical inlet pipe to the first outlet chute. Thus, when solid particles are entering through the vertical inlet pipe to the flow controlling arrangement, the particles primarily flow to the first outlet chute. In this embodiment, the particle flow path to the first outlet chute does not form a gas lock. The embodiment is, therefore, only usable in applications in which a gas lock is not needed or a gas lock is provided in another part of the particle flow path, for example, in a heat exchange chamber downstream of the flow controlling arrangement.

Even when the first outlet chute is directly connected to the vertical inlet pipe, the flow path towards the second outlet chute advantageously comprises a horizontally extending intermediate pipe having a first end attached in particle flow connection with the bottom of the vertical inlet pipe at the level L0and a second end attached in particle flow connection with a bottom end of a vertically extending riser pipe. During the operation of the system, a gas lock forming bed of particles is collected to the horizontally extending intermediate pipe and to the vertically extending riser pipe. The gas lock then prevents gas from flowing backwards to the vertical inlet pipe.

The horizontally extending intermediate pipe advantageously comprises at least one nozzle for feeding fluidizing gas. According to advantageous embodiments of the present invention, one or more fluidizing nozzles are arranged at one or more of the second end of the horizontally extending intermediate pipe, between the first end and the second end of the horizontally extending intermediate pipe, and the first end of the horizontally extending intermediate pipe. According to a preferred embodiment of the present invention, also, the vertically extending riser pipe comprises at least one nozzle for feeding fluidizing gas at a level between levels L0and L2. When it is desired that a portion of the initial flow of solid particles flows through the second outlet chute, fluidizing gas is advantageously fed at a suitable velocity to the horizontal intermediate pipe and/or to the vertical riser pipe. Thereby, when a high enough fluidizing velocity is used, an upper level of the fluidized bed in the vertical riser pipe reaches the level L2of the second outlet chute and a second sub flow of particles flows through the second outlet chute.

On the other hand, when it is desired that the whole particle flow is directed to the first outlet chute, the particle flow through the second outlet chute can be prevented by keeping the fluidization of the horizontal intermediate pipe and the gas flow to the vertical riser pipe at a low enough level. Then, all solid particles flowing downwards in the vertical inlet pipe continue to the first outlet chute and, for example, via the first outlet chute, to a heat exchanger. Because the branch leading to the first outlet chute is connected to the vertical inlet pipe at a level higher than the bottom of the vertical inlet pipe, and the horizontally extending intermediate pipe, directing the particle flow through the first outlet chute does not require using any such fluidization in the system, which would otherwise cause an unwanted flow of particles through the second outlet chute.

The invention is specifically directed to applications in which, from the initial flow of particles is formed a first sub flow, which can be called main sub flow, and a second sub flow, which second sub flow is in normal operating conditions less than the first sub flow. The ratio of the first and second sub flows is, however, advantageously controllable to any value, from 1:0 to 0:1. Thus, according to the present invention, it is advantageously possible to direct the initial flow of particles through any of the first and second outlet chutes, or to split the initial flow between the first and second sub flows in any desired ratio.

In order to achieve desired controllability of the flow ratio of the first and second sub flows to the first and second outlet chutes, the level L1is preferably at least 0.3 meters higher, even more preferably at least 0.5 meters higher than the level L0. Correspondingly, the level L2that is preferably at least 0.2 meters higher, even more preferably at least 0.4 meters higher than the level L1. Thus, the arrangement for controlling flow of solid particles according to the present invention enables versatile control, by a non-mechanical control device, of the ratio of first and second sub flows formed from the initial flow of solid particles. In embodiments comprising a branch with a weir extending to a level L3in the flow path to the first outlet chute, the level L2is advantageously at least 0.1 meters higher than the level L3.

According to a preferred embodiment of the present invention, the second outlet chute is directed vertically downwards at the side of the vertically extending riser pipe at the upper end thereof, at the level L2. Alternatively, the upper portion of the second outlet chute may be slanted so as to form an angle from ten to sixty degrees with the vertical direction, or the direction of the vertically extending riser pipe. Correspondingly, the upper portion of the first outlet chute may be directed vertically downwards or it may be slanted from the vertical direction so as to form an angle from ten to sixty degrees with the vertical direction.

Above are described embodiments in which a first sub flow and a second sub flow are formed from the initial flow of solid particles. According to a variant of the present invention, the second sub flow may be divided into further sub flows, for example, by forming two, or even more than two, branches of a particle flow path comprising a horizontally extending intermediate pipe, a vertically extending riser pipe and an outlet chute, corresponding to distributing solid particles as shown in U.S. Pat. No. 4,733,621. According to a still further variant of the present invention, the first sub flow may be divided into further sub flows, for example, by forming two, or even more than two, horizontally extending shift pipes from an opening on a side wall of the vertical inlet pipe to an intermediate riser pipe, as described above.

The present invention also provides a fluidized bed reactor comprising a particle separator for separating solid particles from exhaust gas emanating from the reactor and a return duct system for returning separated particles from the particle separator back to the reactor, the return duct system comprising an inlet duct, a first return path for returning separated solid particles back to the reactor, the first return path comprising a heat exchange chamber for recovering heat from the separated solid particles, and a second return path for returning separated solid particles directly to the reactor, wherein the return duct system comprises an arrangement for controlling flow of solid particles as defined in any of the embodiments described above, wherein the inlet duct forms the vertical inlet pipe, the first return path comprises the first outlet chute, and the second return path comprises the second outlet chute.

The above brief description, as well as further objects, features, and advantages of the present invention will be more fully appreciated by reference to the following detailed description of the currently preferred, but, nonetheless illustrative, embodiments in accordance with the present invention, when taken in conjunction with the accompanying drawings.

