Note: Descriptions are shown in the official language in which they were submitted.
075S~98
lhis invention relates to a nozzle injection unit suitable
for supplyilng liquid fuel to a fluidised bed combustor.
A fluidised bed combustor is operated by flowing air through
a bed of inert particulate material to maintain the bed in a
fluidised state and injecting fuel into the bed so that combustion
occurs. The fuel,which may be solid, liquid or gaseous,or a mixture,
burns within the bed which is maintained at a temperature which may
typically be in the range 700 - 1800C and from which a controlled
extraction of heat may be made.
Fluidised bed combustors are capable of very high heat outputs
per unit volume capacity and high rates of heat transfer can be
transmitted to cooling surfaces immersed in the bed. The use of the
term "fluidised bed combustor or furnace" is intended to cover the
use of a fluidised bed as both a combustor and as a gasifier whereby
partial reaction of a fuel and an oxygen containing gas produces a
combustible gas which may be stored or burned at a point remote from
the fluidised bed.
Difficulties, however, have sometimes been encountered in
supplying liquid fuels, suchias fuel oil to fluidised bed furnaces,
since there is a tendency for supply nozzles to becom blocke~ and the
combustion characteristics can be very sensitive to fuel distribu~
tion.
Our British Patent No 1368352 describes a distributor
plate comprising a chamber having a fuel inlet and an air tube
passing through the chamber, the interior of the air tube being
in communication with the chamber, one end of the air tube
terminating in a head having outlets adapted to supply a combustible
mixture including f~el and air to a fluidised bed furnace, there
being a surrounding tube around the air tube, which surrounding
tube has an air inlet and air outlet, the air outlet being adapted
to supply air to a region of the fluidised bed beneath the head
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supplying the combustible mixture to the fluidised bed.
The present invention uses a direct oil inJection technique
into the air tubes in contrast to the climbing oil fi]mtechnique
used in the aforementioned patent.
In certain applications, the climbing oil film technique
is not entirely suitable as an air supply at a significantly
higher pressure is required to carry a liquid such as oil along
the air tubes than is required for mere fluidisation of the bed
alone. Thus separate air supplies may be needed for each purpose.
The present invention is di~ected towards a means of supply of
fuel oil to the bed which uses the same air supply as for bed
fluidisation thereby potentially simplifying the equipment.
According to the invention there is provided a nozzle
injection unit suitable for use in a fluidised bed combustor, the
nozzle injection unit comprising first and second co-axial tubes,
the first co-axial tube being partly surrounded by the second
co-axial tube, each having an inlet for an air supply and an
outlet which comprises a lateral passageway through the tube wall
the first co-axial tube projecting beyond and having its outlet
beyond the outlet of the second co-axial tube, characterised in
that there is a third tube capable of supplying fuel oil which
has its outlet within the first co-axial tube and near to the
outlet of the first co-axial tube.
The air supply is pressurised so as to fluidise the furnace
bed.
The second co-axial tube is also preferably connected to a
supply of fuel gas, e.g. propane, so that prior to the fluidised
bed furnace being used for, say,oil burning, it is started up
; by pre-heating the bed by cumbustion of the fuel gas and air.
The oil supply or third tube preferably comprises a vertical
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tube connected to an oil chamber (integral with a distributor
plate or externally supplied) and co-axial with the other tubes,
the open upper end of the vertical tube beingsituated near to
the outlet of the internal co-axial tube. The term "near" is
intended to mean that the outlet of the third tube is situated
not more than a distance of one diameter of the first co-axial
tube above the outlet of the first co-axial tube and not more
than a distance of twice the diameter of the first co-axial tube
below the outlet of the first co-axial tube.
The invention also comprises a distributor plate for a
fluid bed which distributor plate preferably comprises a
plurality of nozzle injection units.
The density of the nozzle injection units may be varied
to suit each particular requirement and preferably a density
of nozzle injection units of 0.25 to 1 per square foot is used.
(Additional air for fluidising and combustion purposes may be
supplied by open ended tubes passing through the distributor
plate).
The lateral outlets of the co-axial tubes form passageways
through the tube walls, the direction of the passageways being
preferably substantially perpendicular to the tube wall. Preferably
the cross-sectional area of the outlets of the first co-axial tube
is less than 1% of the total area of the plate.
In one embodiment of the invention, an oil chamber is
formed beneath the nozzle injection units by means of a pair of
substantially horizontal plates. Preferably the oil chamber
has air tubes, most preferably vertical, passing through it.
These air tubes preferably have a cross-sectional area of about
1 to 5% of the total area of the plate.
The air supply to the first and second co-axial tubes may
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be common or separate, but preferably the former.
The proportion of air entering the first co-axial
tube depends on the bed material being fluidized but it is
typically 10 to 50% of the total.
The inner air tube and oil tube may be designed so
that they are removable, e.g. for cleaning and inspection,
while the fluidized bed combustor is in operation by a method
similar to that described in our Canadian Patent Application
No. 286,087.
The bed itself comprises mineral particles of a size
range and bulk density appropriate to the velocity of the
fluidizing gas.
~ The invention will now be described with reference
i to the accompanying drawing.
The drawing shows a partial vertical cross-section
through a distributor plate according to the invention, the
section shown a single oil injector unit for oil, air (and
fuel gas) distribution to a fluidized bed.
The fluidized bed furnace may comprise a plenum
chamber, a distributor plate and a fluidized bed of sand.
, The bed is contained by a refractory-lined or water cooled
vessel.
The distributor plate comprises a fuel gas chamber 1,
; and oil chamber 2 and a vertical assembly of two concentric
tubes 3, 4. The inner tube 3 of the two tubes terminates in a
head 5 adapted to supply a combustible mixture of oil and air
to the fluidized bed through outlets 7. The shorter outer
tube 4 has outlets 6 adapted to supply combustion air to the
fluidized bed. The air is supplied to the tubes 3, 4 through
the oil chamber 2 and air chamber 9.
The passage of air through outlets 6 fluidizes the bed
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below the oil injection point to discourage stagnation of the
bed, i.e. to obtain as effective a fluidisation of the bed as
possible.
During use of the furnace, the fluidised bed is pre-heated
by means of propane supplied from the fuel gas chamber 1 through
holes 10 and along tube 4. After suitable bed operating condi-tions
have been reached, the propane supply is gradua]ly reduced and the
oil feed supply switched in.
The central tube 8 supplies oil under pressure fro~
chamber 2 to the fluidised bed. The oil is sheared from the
outlet of tube 8 by air passing along the inner tube 3 and the
combustible mixture of oil and air passes via head S and outlets 7
into the fluidised bed. The fuel oil is supplied to the central
tube 8 by means of a pump (not shown). The distribution of oil
to each tube 8 is equalised by arranging for the pressure drops
along each tube to be in the range 5 to 10 p.s.i.
A fluidised bed of 6 inches diameter was filled with about
30 lbs. of sand of -10+16 BSS mesh size and bulk density of
80-100 lbs. per cubic foot. The distributor plate had a single
nozzle injection unit, the central oil tube 8 being about 1/8 inch
; bore, and the internal diameter of tube 3 being 11/32 inches and
having four outlet holes of 7/32 inches diameter. The outer tube 4
had eight outlet holes of 3/16 inch diameter. The oil was pre-heated
to about 65 C and at a freeboard gas oxygen content of less than 5%
the oil flow was about 0.4 gallons/hour. The air flows through the
tubes were of the order 200 to 500 cubic feet per hour.
