Nozzle

An exchangeable or removable nozzle arrangement for use in a fluidized bed furnace is movable and in sealing contact with a surrounding sleeve at one end of the nozzle and may be withdrawn from the sleeve through a valve at the other end of the sleeve. An inlet to the space between the sleeve and the nozzle is connected to a source of pressurized fluidizing gas. Upon removal of a nozzle, while the furnace is under load, the bed is maintained in its fluidized state.

The present invention relates to nozzles and distributor plates containing 
such nozzles for fluidised bed furnaces. 
A fluidised bed furnace is operated by blowing a combustible mixture of air 
and a fuel through a bed of inert particulate material to maintain the bed 
in a fluidised state. The fuel, which may be solid, liquid or gaseous, or 
a mixture, burns within the bed which is thereby maintained at an elevated 
temperature, e.g. in the range 700.degree.-1000.degree. C. 
Fluidised bed furnaces are capable of very high heat outputs and good heat 
transfer characteristics. 
In large scale fluidised bed furnaces particularly using oil as fuel, it is 
necessary to periodically check the state of the fuel injection nozzles, 
for example, for maintenance purposes so as to enable prolonged bed 
operation under optimum conditions. 
The present invention is directed towards this problem and envisages the 
use of injection nozzles which are exchangeable during fluidised bed 
operation. 
Thus according to the invention there is provided a nozzle arrangement 
suitable for use in a fluidised bed, said arrangement comprising a nozzle 
having a surrounding sleeve, the nozzle being movable and in sealing 
contact with its surrounding sleeve at one end of the sleeve, an inlet for 
a pressurised gas to the space between the sleeve and the nozzle, and a 
valve at the other end of the sleeve through which the nozzle may be 
withdrawn from the sleeve. 
By the term "in sealing contact" is meant close enough to substantially 
prevent bed particles from falling into the surrounding sleeve. 
In use of the removable nozzle with a fluidised bed, withdrawal of the 
nozzle from the sleeve enables the pressurised gas to pass into the bed 
whereupon the bed material is prevented from falling into the sleeve by an 
air cushioning effect. 
One or more of the nozzles are preferably incorporated into a distributor 
plate. Thus in an oil fired fluidised bed, a distributor plate may have 
one or more removable nozzles being supplied with fuel oil and air and a 
number of non-removable nozzles for supply of air to the fluidised bed. If 
and when the oil nozzles block or require servicing they may be removed 
preferably one at a time from the bed while still maintaining fluidisation 
and increasing oil flow to the remaining nozzles so as to substantially 
maintain the bed temperature. The nozzles are preferably moved by sliding 
through the surrounding sleeve. 
For an oil fired fluidised bed furnace, the distributor plate preferably 
has an air plenum chamber, most preferably also having a fuel gas chamber 
for use during start up of the fluidised bed. There may also be a liquid 
fuel chamber incorporated in the distributor plate. 
In one embodiment of the invention, the surrounding sleeve for the nozzle 
is connected to the air plenum chamber and the main fluidising air supply 
provides the source of pressurised gas also for the space between the 
sleeve and the removable nozzle. This embodiment of the invention is 
relatively straightforward in design and does not require any major 
structural changes from an existing fixed nozzle bed. However in the case 
of failure of the pressurised gas supply, the bed material will slump into 
the air chamber, and the second embodiment of the invention is an attempt 
to overcome this drawback, whilst offering the facility of removal of bed 
material for analysis of bed material, reducing bed height for load 
control, etc., under slumped or fluidised conditions. 
In a second embodiment of the invention, the surrounding sleeve for the 
nozzle may be a partition spaced from the main air supply tube and the 
nozzle and isolating the space between the nozzle and the tube from the 
air chamber of the fluidised bed distributor plate. The space between the 
sleeve and the nozzle then has a separate inlet for pressurised gas. The 
pressurised gas for the space between the sleeve and the nozzle may be the 
same as or independent of the pressurised gas for the fluidisation of the 
bed. 
The valve through which the nozzle may be withdrawn to separate it from its 
sleeve is preferably a ball valve. During nozzle removal as the nozzle 
passes out of the valve, some compressed air may escape but this loss does 
not usually present a problem. However to avoid this loss of compressed 
air, it is desirable to have a nozzle tube seal below the ball valve which 
maintains the seal against escape of compressed air whilst the ball valve 
is being closed. A similar purpose is served by this nozzle tube seal 
during replacement of the nozzle whilst the bed is under load. The nozzle 
tube seal preferably comprises an annular polymeric seal in a surrounding 
seat through which the nozzle is drawn.

In FIG. 1, the distributor plate assembly for a fluidised bed furnace 
comprises a plenum chamber 1, a fuel oil supply entry 2 and a vertical 
assembly of three co-axial tubes (3. 4. 10). The inner tube 3 of the 
co-axial tubes extends downwardly to a ball valve 6 (Worcester Type 44 
11/2 inch diameter) passing through the air plenum chamber 1 and a fuel 
gas chamber 5. The shorter outer tube 4 connects directly with the air 
plenum chamber 1 and the fuel gas chamber 5 and terminates in a head 7 
adapted to supply fluidising combustion air to the fluidised bed 8. 
(During start-up of the fluidised bed, the head 7 supplies a mixture of 
combustion air and fuel gas to the fluidised bed 8. The apertures 9 allow 
the fuel gas from the fuel gas chamber 5 to be entrained into the air tube 
4). The inner and outer tubes 3, 4 are spaced apart from each other, the 
inner tube 3 being surrounded by a guide tube 10. At a point between the 
valve 6 and the air plenum chamber 1, a source of compressed air 11 is 
supplied to the space between the guide tube 10 and inner tube 3. Separate 
air nozzles 12 are used to distribute air (and gas during start-up) 
through holes 9 so as to maintain the bed in a state of fluidisation. 
Fuel oil is supplied to the interior walls of the inner tube 3 through 
inlet 2 at a point below the ball valve 6 and air is also supplied to the 
tube 3 at its mouth. The oil thus introduced to the interior of the tube 3 
passes up the tube 3 in a stream of air to form a climbing film which 
eventually passes through the outlet head 13 of the tube 3 and into the 
fluidised bed 8. 
The oil tube 3 in its operating position is thus surrounded by a guide tube 
or sleeve 10 which tapers at the top 14 to give a loose fit between the 
oil tube 3 and guide tube 10. 
When it is desired to remove a nozzle 3 from the distributor plate during 
operation of the bed, the following procedure is adopted. A source of 
compressed air 11 is connected to the guide tube 10. The nozzle is then 
gradually withdrawn and as the nozzle head 13 passes the top 14 of the 
annular sleeve, the compressed air source 11 provides support for the 
fluidised bed and prevents bed material entering the guide tube 10. Nozzle 
withdrawal is continued until the head 13 is in position between the ball 
valve 6 and a nozzle tube seal 15. The nozzle 3 can be completely removed 
after closing the ball valve 6 thus permitting replacement or inspection 
as desired. The replacement procedure is a reversal of the removal 
procedure. 
The guide tube 10 acts to isolate the nozzle 3 from the plenum chamber 1 
and allows removal of fluid bed material at a controlled rate dependent on 
the air flow through supply tube 11 and the degree of opening of ball 
valve 6. The amount of fluidising air being supplied to the bed is not 
affected during nozzle removal and should any collapse of bed material 
occur into the guide tube 10, the material may be dealt with relatively 
easily. The fuel injection nozzles may be removed with the bed in a 
slumped or fluidised state, and in the latter case the bed is maintained 
in its fluidised state subsequent to nozzle removal. 
FIG. 2 shows a more basic version of FIG. 1 in which only two co-axial 
tubes are used. 
To remove the fuel injection nozzle from the distributor plate during 
operation of the fluidised bed, the following procedure is adopted. The 
nozzle 3 is gradually withdrawn until the nozzle head 13 passes the top of 
concentric tube 4. Upon further withdrawal, compressed air from the plenum 
chamber 1 rushes through the gap now created between the top of tube 4 and 
the nozzle head 13. This compressed air from the plenum chamber 1 passes 
into the bed 8 and helps to maintain fluidisation. Nozzle withdrawal is 
then continued through the ball valve 6 in the same manner as described 
under FIG. 1. The replacement procedure is substantially a reversal of the 
removal procedure. 
In this simplified version, no auxiliary compressed air supply is required, 
the device relying upon the supply of compressed air from the plenum 
chamber during nozzle removal. Although this arrangement offers no 
safeguards to bed material falling into the plenum chamber in the event of 
compressed air failure, it is simple to manufacture and relatively 
efficient in operation.