FIELD OF THE INVENTION:
The present invention relates to multiple sector rotor used in
Airpreheater. The invention particularly relates to Quad Sector Rotor of
Regenerative Airpreheater adaptable to CFBC (Circulating Fluidised Bed
Combustion) Boilers.
BACKGROUND OF THE INVENTION:
The present invention relates to Rotary Regenerative heat exchangers
generally used as Airpreheaters and more particularly to an improved
variable sector quad sector Regenerative Airpreheater for use in CFBC
boiler where the flue gas, primary air and secondary air are in high
pressure differential between them. Because of high pressure differential
between them more leakage of air to gas will take place during operation.
The Airpreheater is divided in to a flue gas side or sector and one or more
combustion air sides or sectors by sector plates. Flexible radial seals on
the rotor, usually mounted on the top and bottom edges of the
diaphragms, are in close proximity to these sector plates and minimize
leakage of gas and air between sectors to separate the air and flue gas
streams from each other. Likewise, a rotor shell is mounted to the
outboard ends of the diaphragms forming the periphery of the rotor, to
prevent the air and gas streams from flowing through the peripheral ends
of the sectors and bypassing the heat transfer surface. Circumferential
seals seal the gap between the rotor and the rotor housing to prevent
bypass flow through the annulus formed between the rotor and the rotor
housing.

A Rotary Regenerative Airpreheater transfers sensible heat from the flue
gas leaving a boiler to the entering combustion air through regenerative
heat transfer surface in a rotor which turns continuously through air
and gas streams. The cylindrical rotor is disposed on a horizontal or
vertical central rotor post divided into a plurality of sector shaped
compartments by a plurality of radial partitions, referred to as
diaphragms, extending from the rotor post to the outer peripheral shell of
the rotor. These sector shaped compartments are loaded with heat
exchange baskets which contain the mass of heat absorbent material
commonly formed of stacked plate-like heat transfer elements.
In a typical Rotary Regenerative heat exchanger, the hot flue gas and the
combustion air enter the rotor shell from opposite ends and pass in
opposite directions over the heat exchange material housed with in the
rotor. Consequently, the cold air inlet and the cooled gas outlet are at
one end of the heat exchanger, referred to as the cold end, and the hot
gas inlet and the heated air outlet are at the opposite end of the heat
exchanger referred to as the hot end.
Rotary regenerative Airpreheaters are comprised of slowly rotating rotor,
containing formed plate heat transfer surfaces that absorb heat from the
exhaust boiler flue gas and release it to the incoming cold air. The hot air
from the Airpreheater is used for drying the coal and carry the coal
powder to the combustor and also used as a secondary air for complete
combustion in a pulverised fuel fired boilers. It also provides 2 in 1
advantage, i.e. heating requirement of the primary air as well as
secondary air (which are at different pressure levels) in the same

equipment when the system is Cold PA system. Cold PA system (with Tri
sector Airpreheater) is more compact, economical and consumes less
auxiliary power consumption as compared to Hot PA system (with
Bisector Airpreheaters) or Cold PA system with Tubular primary and
Tubular secondary Airpreheaters in a pulverised fuel fired boilers.
In a pulverized fuel fired boilers, the pressure difference between air and
gas is low because of system requirement i.e. the primary air will dry the
coal and carry the coal powder to the furnace and the secondary air will
directly go to combustor to assist the complete combustion. Whereas in
CFBC boiler, the pressure difference between air and gas is very high
because the primary air function is to make the bed particles in fluidized
condition while the coal is fed from top for combustion.
In a pulverized fuel fired boiler, there is a loss of primary air to the gas
and the secondary air; on account of differential pressure and the
consequent leakage across the seals. In due course of operation of the
Airpreheaters, the primary air leakage to the gas side and the secondary
air side further increases due to the seal erosion, caused by the pressure
difference between primary air to secondary air, primary air to gas an
secondary air to gas. If we use the same Tri sector Airpreheater for CFBC
boiler, where the pressure difference between primary air and gas is very
much on the higher side thus the leakage of primary air to gas will be
enormous.
OBJECTS OF THE NVENTION:
1) An object of the present invention to propose a quadriple sector of
rotor for Regenerative Airpreheater adaptable to CFBC which
eliminates the disadvantage of existing state of Art.

2) Another object of the present invention is to minimize the leakage
from primary air side to gas side by using quadriple sector in place
of Tri Sector Airpreheater.
3) A still another object of the present invention is to economise the
performance of the Electrostatic precipitator sizing and auxiliary
(Induced Draught Fan) power consumption.
4) A further object of the present invention is to prevent abnormal
deterioration in electrostatic precipitator performance with
operation time.
5) A still further object of the present invention is to lower the
absolute leakage rate compared to tri sector Airpreheater.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Fig. 1 shows a Trisector Air Preheater of Gas Sector, Primary Air Sector
and Secondary Air Sector.
Fig. 2 shows a quadriple sector Air Preheater as per invention of a gas
sector and a primary air sector sandwiched between two secondary air
sector.
Fig. 3 shows the elevation view of a Quad Sector Regenerative
Airpreheater.
Fig. 4 shows the plan view of a Quad Sector Regenerative Air Preheater.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION:
The inventive concept in the Quad Sector Airpreheater design is that the
primary air sector is sandwiched on either side by secondary air sectors
(i.e. one gas sector, first secondary sector, one primary sector and second
secondary sector in that order) which helps in minimizing the air leakage
to the gas side.
The reduction in air leakage to the gas side will result in further
economises in the form of Electrostatic Precipitator sizing and auxiliary
(ID Fan) power consumption. This will also prevent abnormal
deterioration in Electrostatic Precipitator performance with operation
time (a absolute leakage rate is likely to be lower as compared to Tri
Sector Airpreheater) or with the use of poor grade coal (zero tempering,
high primary air side pressure drop and high pressure differential across
seals). Quad sector regenerative Airpreheater may also be useful in case
of CFBC boilers having high pressure differential across seals between
air and gas sides.
Thus the present invention provides a Quad sector Airpreheater design
for use in CFBC Boilers comprising four sectors i.e. one gas sector, first
secondary sector, one primary sector and second secondary sector in
that order which helps minimizing the air leakage to the gas side.
The Airpreheater is divided into a flue gas side or sector and three more
combustion air sides or sectors by sector plates. Flexible radial seals on
the rotor, usually mounted on the top and bottom edges of the
diaphragms, are in close proximity to these sector plates and minimize

leakage of gas and air between sectors to separate the air and flue gas
steams from each other. Likewise, a rotor shell is mounted to the
outboard ends of the diaphragms, forming the periphery of the rotor, to
prevent the air and gas streams from flowing through the peripheral ends
of the sectors and bypassing the heat transfer surface. Circumferential
seals seal the gap between the rotor and the rotor housing to prevent
bypass flow through the annulus formed between the rotor and the rotor
housing.
Quad sector Airpreheater referred in figure-3 and 4 consists of one gas
sector (01), first secondary sector (02), one primary sector (03) and
second secondary sector (04) compartmented by sector plates and the
rotor (05) is driven by the rotor drive (06) and is surrounded by the rotor
housing (07) and constructed between the cold end connecting plate (08)
at one end and hot end connecting plate (09) at other end. The rotor- is
supported by the support bearing (10) at the bottom and guide bearing
(11) at the top.
The cylindrical rotor (05) revolves at a very low speed and the plates are
alternatively, exposed to the gas and air flows. In the Quad sector
Airpreheater design, the primary air sector (03) is sandwiched on either
side by secondary air sectors (02 and 04) (i.e. one gas sector, first
secondary sector, one primary sector and second secondary sector in
that order) which helps minimizing the air leakage to the gas side.

WE CLAIM:
1. A quad sector regenerative Airpreheater for circulating fluidised
bed combustion boiler comprises
one gas sector (01), first secondary Air sector (02), one primary
air sector (03) and second sec©ndary air sector (04)
compartmented by sector plates;
a cylindrical rotor (05) driven by the rotor drive (06) and
surrounded by the rotor housing (07) and constructed between
the cold end connecting plate (08) at one end and hot end
connecting plate (09) at the other end;
a support bearing (10) at the bottom and a guide bearing (11) at
the top supports the rotor (05);
characterized in that the primary air sector (03) is sandwiched
on either side by the 'secondary air sectors (02) and (04)
minimizing air leakage to the gas side.
2. A quad sector regenerative Airpreheater for CFBC boiler as
claimed in claim 1, wherein it minimizes air leakage for boilers
having high pressure differential across seals between air and
gas sides.
3. A quad sector regenerative Airpreheater for CFBC boiler as
claimed in claim 1, wherein it prevents abnormal deterioration
in electrostatic precipitator performance with operation time.
4. A quad sector generative Airpreheater for CFBC boiler as
claimed in claim 1, wherein it economizes electrostatic
precipitator sizing and auxiliary (Induced Draught Fan) power
consumption.

5. A Quad sector regenerative Airpreheater for CFBC boiler as
substantially described and illustrated herein with reference to
the accompanying drawings.

A quad sector regenerative Airpreheater for circulating fluidised
bed combustion boiler comprises
one gas sector (01), first secondary Air sector (02), one primary
air sector (03) and second sec©ndary air sector (04)
compartmented by sector plates;
a cylindrical rotor (05) driven by the rotor drive (06) and
surrounded by the rotor housing (07) and constructed between
the cold end connecting plate (08) at one end and hot end
connecting plate (09) at the other end;
a support bearing (10) at the bottom and a guide bearing (11) at
the top supports the rotor (05);
characterized in that the primary air sector (03) is sandwiched
on either side by the 'secondary air sectors (02) and (04)
minimizing air leakage to the gas side.