Fluidized bed apparatus

A fluidized bed apparatus having an outer vessel provided at a lower region with a plenum chamber as well as a grid situated directly above the plenum chamber and carrying a plurality of nozzles through which gas flows from the plenum chamber into the space in the vessel above the grid. These nozzles provide a given pressure drop in the gas flowing therethrough while as the gas flows from the plenum chamber through each nozzle there is also provided by way of a suitable structure a preliminary pressure drop, so that a two-stage pressure drop is provided in the gas flowing through each nozzle from the plenum chamber into the vessel above the grid. In this way it is possible to achieve a flow of gas above the grid sufficient to maintain the particles suspended in the fluidized bed while attrition of the particles is maintained at a minimum so that very little if any fines flow out of the vessel with gas which is formed therein. According to this method, the particles are petroleum coke particles while the gas is a mixture of steam and air maintained in the plenum chamber at a pressure of only 1-5 psig above the pressure in the bed while at the region of the interior of the vessel above the grid the temperature is on the order of 1500.degree.-1800.degree. F. The grid supporting the nozzles is sloped 3.degree. to 5.degree. downwards towards a center well and supporting member to allow solid agglomerations such as lumps of coke and slag to move radially inward into the well for withdrawal.

BACKGROUND OF THE INVENTION 
The present invention relates to fluidized bed apparatus and methods for 
operating the same. 
Apparatus of this type is conventionally used for the purpose of gasifying 
particles such as petroleum coke particles into a fuel gas such as methane 
gas. When utilizing a fluidized bed apparatus for such purposes, one of 
the problems encountered is in connection with attrition of the particles. 
In other words, the movement of the particles about in the fluidized bed 
in which they are suspended is sufficiently violent to cause the particles 
to impact each other in a highly undesirable manner creating fines which 
undesirably flow out of the reactor vessel, together with the generated 
fuel gas. As pointed out above, in the case of petroleum coke particles, 
this gas will be essentially a methane type of low BTU fuel gas. Thus, 
because of the attrition occurring in conventional fluidized beds it is 
unavoidable that an undesirably large amount of fines will issue from the 
reactor vessel with the gas achieved from the particles such as petroleum 
coke particles. 
Moreover, in conventional fluidized bed apparatus there is a problem in 
connection with achieving a uniform distribution of the fluidizing gas 
over the grid as well as in connection with achieving proper support for 
the grid and maintenance of the grid at a temperature low enough to assure 
a long operating life. Furthermore, conventional nozzles tend undesirably 
to become clogged and replacement of the nozzles very often creates great 
difficulties. 
SUMMARY OF THE INVENTION 
It is accordingly a primary object of the present invention to provide a 
fluidized bed apparatus and method for operating the same which will avoid 
the above drawbacks. 
Thus, it is primarily an object of the present invention to provide a 
fluidized bed apparatus and operating method according to which it becomes 
possible to treat particles such as petroleum coke particles in such a way 
that attrition thereof in the fluidized bed is maintained at a minimum so 
that in this way the amount of fines which issue from the reactor vessel 
with the desired fuel gas or the like is maintained at minimum. 
Also, it is an object of the present invention to provide a construction 
which makes it possible to provide an effective support for the grid of 
the fluidized bed as well as to maintain the grid at a desirably low 
operating temperature. 
In addition it is an object of the present invention to provide a fluidized 
bed apparatus according to which it becomes possible to automatically and 
continuously eliminate from the upper surface of the grid agglomerations 
of particles which may form on the grid. 
In addition, it is an object of the present invention to provide a 
construction wherein the nozzles can readily be replaced when required and 
at the same time have a construction which will reduce clogging to a 
minimum. 
A still further object of the invention is to provide an improved nozzle 
design which, even in the presence of severe erosion or total fracture, 
will not create severe maldistribution of the air/steam flow through the 
bed. 
According to the invention, the fluidized bed apparatus includes an outer 
vessel having at a lower region a plenum chamber and a grid situated 
directly above the plenum chamber and carrying a plurality of nozzle means 
through which gas flows from the plenum chamber into the reactor vessel 
above the grid. The plurality of nozzle means provide a given pressure 
drop in the gas as it issues from the nozzle means into the space above 
the grid. According to the invention, a preliminary pressure-drop means is 
provided in the path of gas flow to each nozzle means at the region of the 
grid for providing a pressure drop preliminary to the pressure drop 
occurring as the gas issues out of each nozzle means into the space above 
the grid, so that by way of this two-stage pressure drop operation at each 
nozzle it is possible to achieve for the gas flowing into the vessel above 
the grid from the chamber a speed of flow which while sufficient to 
maintain the particles suspended in the fluidized bed nevertheless will 
maintain attrition of the particles to a minimum, even in the presence of 
nozzle failure. The splitting up of the total pressure drop between the 
plenum chamber and the bed into two pressure drop stages has a further 
significant advantage in the event of individual failure by corrosion or 
erosion of one or more nozzle assemblies. This is because the first stage 
orifice is integrally located in the base of the nozzle assembly in the 
plane of the grid so that even if the upper portion were to wear or break 
off the first stage orifice of the nozzle assembly would remain intact. 
Were this not the case, significant flow maldistribution across the bed 
would otherwise result. 
According to the method of the invention, the pressure of the gas in the 
plenum chamber is on the order of 1-5 psig above bed pressure and in 
connection with the treatment of petroleum coke particles the gas is 
preferably a mixture of steam and air while the temperature in the reactor 
vessel is maintained on the order of 1500.degree.-1800.degree. F.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to FIG. 1, there is illustrated therein a fluidized bed 
apparatus including an outer vessel 10 having at a lower region thereof a 
plenum chamber 12 to which gas is supplied through suitable gas inlets 14. 
Situated in the lower region of the vessel 10 just above the plenum 
chamber 12 is a grid 16 supported by a number of upright supporting 
assemblies 18. 
It will be noted from FIG. 1 that the grid 16 slopes downwardly from its 
outer periphery, which is supported at the inner surface of the vessel 10, 
toward the central region of the grid where the grid is again supported by 
a downwardly extending well 20. It will be seen that the well 20 along 
with the members 18 all contribute to the support of the grid. The center 
well 20 is connected to a lock hopper (not shown). The slope of the grid 
which is on the order of 3.degree.-5.degree. downwardly toward the center 
well allows large solids agglomerations such as lumps of coke, lumps of 
refractory or lumps of slag formed during gasification of coke particles, 
for example, to move slowly in a radial direction toward the grid center 
along the surface of the grid to the center well where these 
agglomerations can be withdrawn. 
Such withdrawal is important since accumulation on the grid of 
agglomerations would undesirably influence the distribution of the gas 
which in the case of gasification of petroleum coke particles is 
preferably an air-steam mixture. Thus, without this withdrawal of the 
agglomerations there would otherwise be unavoidably localized high 
temperatures and concentration of slag formations particularly from trace 
metals such as vanadium and sodium contained in the petroleum coke 
particles. 
The grid 16 includes a lower metal plate structure 22 which is covered by a 
thermal insulating refractory lining 24, and it will be noted that the 
metal plate structure 22 and lining 24 continues along the well 20. The 
center well supports the grid which is subjected to an upward differential 
pressure by the air-steam injected into the fluid bed above the grid for 
fluidation and gasification of coke particles above the grid. The 
illustrated central location of the well is ideal inasmuch as radial 
differential expansion between the grid plate and the center well shell is 
through the use of the thermal insulating refractory linings on the upper 
grid surface and on the internal surface of the center well. The underside 
of the grid plate and the external surface of the well is cooled by the 
air-steam mixture injected into the fluid bed through the plurality of 
nozzle injectors referred to below. The thermal insulation on the surfaces 
keeps the metal at an essentially uniform temperature so that relatively 
lowcost steel such as carbon steel, rather than alloy steel, can be used 
for the grid-well construction. It will also be seen that the reactor 
vessel 10 also includes an outer steel shell 11 suitably lined with 
refractory insulation material 13. 
FIG. 2 illustrates the arrangement of the supporting structures 18 along 
concentric circles as well as the relatively large number of closely 
spaced nozzle means 26 used for receiving the gas from the plenum chamber 
12 and distributing the gas into the space in the vessel 10 above the grid 
therein. A preferred embodiment of nozzle means in accordance with the 
invention is illustrated in FIGS. 3-5. Thus, it will be seen from FIG. 3 
in particular that the illustrated nozzle means includes an upright metal 
tubular portion 28 threaded into a nipple fitting 30 welded to the upper 
surface of the plate 22. Additional refractory or other insulation 40 may 
be packed about the nipple 30 after the nozzle 26 is installed to fill the 
space adjacent the refractory 24. The nipple 30 is coaxially aligned with 
an opening 42 passing through the plate 22 to provide communication 
between the plenum chamber and the interior of the upright tubular portion 
28 of the nozzle means 26 which is illustrated in FIG. 3. 
At the region of the upper end of nozzle means 26 is provided a plurality 
of tubular outlets 44 fixed to and projecting radially from the upright 
tubular portion 28 at the region of the upper end thereof, these nozzle 
outlets 44 being arranged as fully illustrated in FIG. 4 so that in the 
illustrated example they are spaced by 120.degree. apart from each other 
around the axis of the upright tubular portion 28. The three tubular 
outlets 44 extend horizontally from the upper end region of the upright 
tubular portion 28, and then curve downwardly so as to terminate in 
downwardly extending portions 46 having downwardly directed open ends 48. 
As a result of this feature, the gas received from the plenum chamber is 
directed downwardly toward the grid and at the same time clogging of the 
nozzle outlets 48 is avoided. 
The entire nozzle structure is covered by a refractory material 50 
providing thermal insulation for the nozzle structure. Suitable anchoring 
wires 52 are welded to the exterior surface of the nozzle and distributed 
as illustrated so as to serve to anchor the refractory thermal-insulating 
material 50. For integral reinforcing of the refractory, alloy fibers are 
added to the refractory to control shrinkage and to facilitate anchoring 
of the refractory to the nozzle components 28 and 44 by means of anchor 
52. 
It will be noted that the internal diameters of the nozzle outlets 44 are 
smaller than the internal diameter of the upright tubular portion 28, so 
that a given pressure drop is provided in the gas issuing from the nozzles 
into the space of the grid. The upper end region of the tubular portion 28 
is formed with relatively small orifices 54 through which the nozzle 
outlets communicate with the interior of the upright tubular portion 28, 
so that these orifices 54 contribute to the pressure drop in the gas 
flowing out of the nozzle means 26. With this placement of the second 
stage pressure drop orifice, even if one or more of the tubes 44 were to 
break off from the upright tube 28, the total nozzle pressure drop would 
remain essentially unchanged with little resultant maldistribution of gas 
flow in the bed. 
According to a particular feature of the invention, a preliminary 
pressure-drop means is provided for providing a first stage pressure drop 
in the gas flowing from the plenum chamber to each nozzle means, prior to 
the pressure drop in the gas issuing out of the nozzle means at the 
outlets 44 thereof. In the example of FIG. 3, this preliminary 
pressure-drop means takes the form of a plate 56 extending across the 
bottom end of the upright tubular nozzle portion 28 and formed with an 
orifice 58. As the gas from the plenum chamber flows upwardly through the 
opening 42, it must flow through the orifice 58 and experiences a first 
stage pressure drop when flowing through the orifice 58, and then the 
second stage pressure drop is provided when the fluid flows through the 
three orifices 54 into each of the outlet nozzles 44. 
This two-stage pressure drop is an important feature of the present 
invention inasmuch as in this way it is possible to achieve a uniform 
distribution of the gas over the grid and in the fluidized bed while at 
the same time maintaining attrition of the particles suspended in the 
fluidized bed to a minimum. Thus, the pattern of the injector nozzles is 
such as to promote a uniform distribution of gas across the grid surface. 
As previously brought out, the protected location of the first stage 
pressure drop orifice at the base of the tube 28 prevents severe flow 
maldistribution should tube 28 fail. Similarly, should either of the one 
or more outlet tubes 44 fail, the orifices 54 would remain unaffected. 
With the two-stage pressure drop of the invention it is possible to 
achieve a gas-exit velocity for each injection nozzle on the order of 150 
feet per second, although this speed may range between 80 and 200 feet per 
second, and such a gas velocity is sufficient to maintain adequate 
pressure for uniform distribution. 
It is desirable to provide a grid pressure drop of 0.4 times the static 
head of the fluid coke bed to achieve a good air-steam distribution. For 
this purpose there is maintained in the plenum chamber 12 a gas pressure 
on the order of 1-5 psig above bed pressure. For this particular pressure 
drop a velocity on the order of 225-350 feet per second would result in 
excessive attrition of petroleum coke particles in the fluidized bed as 
well as high loss of coke fines by entrainment in the effluent gas. Thus, 
referring to FIG. 1, in the case of treating petroleum coke particles in 
the fluidized bed, these particles will be gasified to extinction by the 
air-steam mixtures supplied to a low BTU fuel gas, primarily methane gas 
which flows out through the upper outlet 60 shown at the upper portion of 
FIG. 1. Petroleum coke particles are supplied to the fluidized bed 61 
through the inlet 62, and excessive coke particles will flow out through 
the outlet 64. The temperature in the interior of the vessel 10 above the 
fluidized bed is on the order of 1500.degree.- 1800.degree. F. Thus, the 
two-stage pressure drop provides less entrainment of coke particles 
through outlet 60 by reducing the velocity of the air/steam entering the 
bed through nozzles 44 and 80. 
Referring to FIG. 5, there is illustrated therein the circular 
configuration of the upright tubular portion 28 of the nozzle means 
together with the alloy fiber reinforced thermal insulation 50 and 
anchoring members 52. It is to be noted that the nozzle means can easily 
be replaced simply be being threaded out of the nipple fitting 30 and 
replaced by a new nozzle. 
Referring to FIG. 6, according to the embodiment illustrated therein 
instead as in FIG. 3 of providing the preliminary pressure drop by way of 
a plate 56 and an orifice 58 at the bottom end of the upright tubular 
portion 28, the preliminary pressure-drop means takes the form of a nipple 
66 threaded into the opening 42 in the manner illustrated. In this case 
the bottom end of the upright tubular portion 28 of the nozzle means does 
not have a plate with an orifice extending across the same. The nipple 66 
is formed with an elongated passage 68 coaxial with the upright tubular 
portion 28 of the nozzle and having a diameter smaller than the interior 
diameter of the upright tubular portion 28 so that through this nipple 66 
it is also possible to achieve the preliminary pressure drop referred to 
above. 
According to the embodiment of the invention which is illustrated in FIGS. 
7 and 8, the nozzle means 70 is identical with the nozzle means 26 except 
that at the upper end region of the tubular portion 72, which otherwise is 
identical with the tubular portion 28, the nozzle means 70 only has 
horizontal openings 74 passing radially through the wall of the upright 
tubular portion 72 and distributed in the manner apparent from FIG. 8, 
these openings continuing through the thermal insulating layer 76 which 
may be made of the same material as the layer 50 and which also is 
anchored to the nozzle by way of anchoring wires 78 which may be identical 
with wires 52. Thus, the outlets 74 for the nozzle means 70 communicate 
with bores 80 formed in the insulating material 76 so that the bores 80 
form extension of the bore 74, and while the several bores are arranged 
radially around the axis of the tubular portion 72 they may be vertically 
staggered, as is apparent from FIGS. 7 and 8. 
With this arrangement also it is possible to achieve the results of the 
invention. It is to be noted that at the bottom end of the tubular portion 
72 there is also an orifice plate 82 serving the same function as the 
orifice plate 56 in FIG. 3. 
Undesirable clogging by coke particles of the nozzle outlet 74,80 may be 
avoided by providing a predetermined length to diameter ratio of these 
outlets. Thus, if this ratio is maintained between 1.8 and 3.0, backflow 
of coke during bed slump will be reliably avoided. 
Thus, while the construction shown in FIG. 3 is preferred, it is also 
possible to use a construction as shown in FIGS. 7 and 8. The construction 
of FIG. 3 particularly avoids accumulation of slag on the nozzle tips. 
The nozzle may be made of carbon steel or alloy steel having the refractory 
covering for corrosion, erosion and thermal protection. The slag which 
contains sulfur, sodium and vanadium compounds has been found to attack 
essentially all common structed alloys. The metals most resistant to such 
attack are the high chromium (i.e., 25-27% chrome alloys), but even this 
alloy requires protection by refractory for extended exposure. The 
refractory layer is cast around the metal structure of each nozzle and 
secured to the structure by the submerged alloy wire anchor loops which 
are welded to the exterior surface of the injector structure. Metal fiber 
reinforcing of the refractory in the amount of 1% fine wire fiber 
reinforcement by volume of refractory is added to the refractory. This 
provides added strength to the refractory, keeps the refractory layer 
together after initial shrinkage (and cracking) of the refractory on 
dryout, and facilitates anchorage to the structure by means of the 
submerged alloy wire loops. Castable refractory with high alumina 
(Al.sub.2 O.sub.3) content (i.e., in excess of 55%) is required for 
corrosion attack resistance. 
While specific embodiments of the invention have been shown and described 
in detail to illustrate the application of the inventive principles, it 
will be understood that the invention may be embodied otherwise without 
departing from such principles. For instance, while applicant has chosen 
to illustrate his nozzle assembly as providing a two-stage pressure drop, 
those skilled in the art will readily appreciate that if conditions 
warrant the total pressure drop across each assembly could be divided up 
into three or more stages to give even greater protection against gas flow 
maldistribution in the event of nozzle failure.