FIELD OF INVENTION
The present invention generally relates to a device capable of efficiently
collecting the particles of finer size in fluidized bed system. More particularly, the
invention relates to a truncated vortex finder for hot refractory or water or steam
lined/cooled, circular/rectangular/any regular shape at cross sectional cyclone of
a Fluidized Bed Combustion (FBC) Boiler.
BACKGROUND OF THE INVENTION
In Circulating Fluidized Bed boilers (CFB), the inert bed material remaining in a
fast fluidization regime causing the solids to move vertically upwards, and then
separated by cyclones and returned to the bottom of the furnace. As the name
implies in a circulating fluidized bed boiler, the fluid particles remain in the
furnace until they burn up, or until they reach the size at which the cyclones
cannot separate them from the combustion particles.

Combustion takes place at a temperature between 800 to 900°C; inert material
in the furnace is a mixture of sand, ash, limestone and anhydrate. The
fluidization velocity of the combustion particles is higher than the transport
velocity of the inert particles. The inert particles are in fast fluidization regime
and are, together with the fine unburned fuel particles, removed from the
combustion chamber. In cyclone, the solid material is separated from the
gaseous combustion products and reintroduced into the furnace. Thus,
recirculation of the solid particles (inert material and fuel particles) is realized in
a closed circuit. Regulation of solids recirculation rate is achieved at the cyclone
outlet by controlling the solid particle mass flow rate in the stand-pipe or through
a special device called a pneumatic valve.
A vortex finder is a component which determines efficiency of a cyclone. It is
used for separation of solid/liquid/gas phases. Cyclone has an inlet through
which the flue gas with solids like fly ash enters tangentially creating a rotational
flow. Centrifugal force separates the phases within the cyclone, which then
allows gas to exit from the top through a gas orifice or vortex finder, and the

solids from the bottom openings. A vortex finder with a truncated version has
flexibility in adjusting efficiency of the cyclone. The vortex finder experiencing
the first gust of solid inventory of high temperature, carried by the flue gas is
readily prone for erosion. High efficiency truncated vortex finder can be adjusted
to match this erosive forces and it provides a possibility for natural vortex in a
cyclone.
US Patent No. 2,044,614 discloses that there is a pressure gradient, i.e. the
pressure decreasing toward the centre of vortex, in any vortex of swirl in a fluid
stream which completely fills vortex chamber.
US Patent No. 7,001,448 B1 describes an improved vortex tube for use in
separating an immiscible liquid component from a gas stream and more
particularly for a system and a method of operating a system for separating
liquid components from a gas stream.

US Patent No. 5,362,149 teaches a mud mixer using vortex finder principle for
thoroughly mixing of mud.
US Patent No. 5,658,359 provides a method of operating a fluidized bed reactor
system, and a system for cleaning gas cooler.
US Patent No. 7,318,849 B2 provides a cyclonic fluid separator for separating
one or more condensable components from a mixture that has a tubular housing
having a fluid inlet section in which the fluid mixture is accelerated to a
supersonic velocity and thereby expanded and cooled such that condensable
components condense.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a high efficiency truncated
vortex finder for a cyclone in fluidized bed combustion boilers, which is enabled
to control the solid particles entraining with gas at exit of the cyclone.
Another object of the invention is to propose a high efficiency truncated vortex
finder for a cyclone in fluidized bed combustion boilers, which is designed such a
way that the ratio of fly ash and bottom ash can be adjusted to improve boiler
efficiency when operated with high ash fuels.
A still another object of the invention is to propose a high efficiency truncated
vortex finder for a cyclone in fluidized bed combustion boilers, which is enabled
to reduce the erosion across various solid suspension rates across the cyclone.
SUMMARY OF THE INVENTION
According to the invention, a truncated vortex finder with an innovative
configuration for customized particle capture is provided which reduces material
content.
The truncated vortex finder is enabled to provide an efficient particle separation
in the cyclones. The particles entering tangentially in the cyclone is allowed to
hit the cylindrical wall, loose its energy and fall back. The gas, which
enters tangentially makes a turn and swirl along the cylindrical portion. A natural
vortex is created inside the cyclone by the swirling gas which is made to travel
up the cyclone by the vortex finder. The flue gas entering in the cyclone
tangentially, including the gust further affects the vortex finder collection
performance.
The invention adopts a combination of interconnected data obtained from
analytical and numerical analysis carried out in a typical circulating fluidized bed
boiler. The truncated vortex finder serves the purposes of adjusting the vortex
inside the cyclone, including adjustment in cyclone performance for various fuels.
The truncated vortex finder is utilized for regulating the particles flow in the
outlet of the cyclone. The truncated vortex finder has the profile and
configuration to regulate the particles escaping in flue gas out of the cyclone.
The truncated vortex finder allows reduction in the erosion pattern for various
gas solid suspension across the cyclone of the primary loop.
In a fluidized bed boiler, the bed particles in the form of inventory coming to the
recyclable part like cyclone, the external fluidized bed heat exchanger, and the
seal pot return which constitute the solids flowing back to the grate grid along
the walls. The mean site fraction of the inventory after attrition reduces
substantially so as to have a high particle loading in the recyclable part.
The truncated vortex finder in the cyclone captures the particles, and ensures a
good solid circulation rate inside the combustor.
The optimum efficiency truncated vortex finder employed in the cyclone of a
circulating fluidized bed boiler maintains a good solid inventory having a uniform
temperature over the combustion height. It is held at a position to have an
optimum particle capture and pressure drop across the cyclone.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - shows a typical arrangement of a cyclone with a vortex finder.
Figure 2 - shows a truncated vortex finder in a FBC boiler according to the
invention.
DETAILED DESCRIPTION OF THE INVENTION
A conventional arrangement of typical vortex finder for cyclone in circulating
fluidized bed boilers is shown in Figure 1, which comprises a circular /
rectangular / regular shape at cross section (1) with supporting structures along
the length (2), arranged with provision of eccentricity, axial and rotational
adjustment in the roof of a cyclone (3) with a duct connecting at an outlet (4).
The high efficiency truncated vortex finder (5) as shown in Figure 2, comprises a
circular / rectangular / regular shape at cross section (1) with supporting
structures along the length (2), arranged in centre/eccentrically hanging in the
roof of the cyclone (3), with a duct connecting at the outlet (4), is incorporated
in a FBC boiler (6).
The invention proposes a high efficiency truncated vortex finder (5) to utilize the
vortex created by the centrifugal force generated due to the cyclonic action.
This novel system ensures an optimized way of adjusting the vortex created due
to the centrifugal action of the cyclone. Flue gas with entrained solids carried off
from the combustor is separated in a mechanical separator cyclone. High velocity
and high temperature of the two phase flow containing solids and gas create the
erosion of materials in the flow stream. The truncated vortex finder arrangement
enables an efficient and optimized collection of solids to achieve efficient boiler
performance.
The advantage of the invention lies in the system to adjust the vortex finder to
match the velocity profile which allows separation of the solids and reduction in
the erosion in cyclone. The operational time of the boiler gets increased with the
truncated vortex finder. Shutdown time due to the replacement of the vortex
finder gets reduced. The boiler efficiency is improved by systematic operation
when using high ash fuels like lignite.
WE CLAIM:
1. A high efficiency truncated vortex finder in a cyclone for fluidized bed
boilers, comprising a member (5) having a circular/rectangular/regular shape at
the cross section (1) with supporting structures disposed along the length (2),
and arranged with a provision of eccentricity, axial and rotational adjustment in
the roof of a cyclone (3); a duct connecting a plurality of cyclones (3) at an
outlet (4), the member (5) being incorporated in a FBC boiler (6), wherein the
truncated vortex finder is configured such that a profile of the vortex generated
due to the centrifugal action of the cyclone allows a translational and/or a
rotational movement to generate a variation in the ari-flow resistance through
the exit of the cyclone.
2. A high efficiency truncated vortex finder in a cyclone for fluidized bed
combustion boilers as substantially described and illustrated herein with
reference to the accompanying drawings.

A high efficiency truncated vortex finder in a cyclone for fluidized bed boilers,
comprising a member (5) having a circular/rectangular/regular shape at the
cross section (1) with supporting structures disposed along the length (2), and
arranged with a provision of eccentricity, axial and rotational adjustment in the
roof of a cyclone (3); a duct connecting a plurality of cyclones (3) at an outlet
(4), the member (5) being incorporated in a FBC boiler (6), wherein the
truncated vortex finder is configured such that a profile of the vortex generated
due to the centrifugal action of the cyclone allows a translational and/or a
rotational movement to generate a variation in the air-flow resistance through
the exit of the cyclone.