Apparatus for continuous calcining in noxious gas

Materials to be calcined are introduced through an outer entrance into a front chamber while keeping an inner entrance closed. The outer entrance is then closed, the inner entrance is opened, and the materials are advanced into a calcining furnace through the inner entrance and are calcined therein. The calcined materials are then advanced into a rear chamber through an inner exit while an outer exit is kept closed. The inner exit then is closed, the outer exit is opened, and the calcined materials are carried out of the rear chamber through the outer exit. The calcining apparatus includes a tubular calcining furnace. A feed pipe and an exhaust pipe for reaction gases are attached to both ends of the furnace. The apparatus also includes a front chamber and a rear chamber, each having an inner entrance/exit and an outer entrance/exit. The front chamber and the rear chamber are also attached to the exhaust pipe. Finally, the calcining apparatus includes a carrier containing the materials to be calcined which is passed through the front chamber, the tubular calcining furnace, and the rear chamber, consecutively.

BACKGROUND OF THE INVENTION 
The present invention relates to a method and apparatus for calcining and 
more particularly to a method and apparatus for continuous calcining under 
a noxious gas atmosphere. 
Fluorescent calcium sulfide (CaS) is an excellent material for forming the 
fluorescent screen of a cathode-ray tube because it is inexpensive and it 
has favorable characteristics when compared with other fluorescent 
materials. However, calcium sulfide also deteriorates when in contact with 
water during the application of the fluorescent screen, rendering it 
inadequate for practical use. 
As a result, investigations have been performed concerning methods of 
treating fluorescent calcium sulfide to prevent its deterioration by water 
so that its excellent luminous efficiency can be utilized. Consequently, 
remarkable progress has been made concerning a number of red-colored 
calcium sulfide fluorescent materials. These materials are expected to be 
adopted for practical use in the near future. 
Fluorescent calcium sulfide can be obtained by calcining calcium carbonate 
under a hydrogen sulfide atmosphere. However, it is quite difficult to 
continuously calcine the fluorescent calcium sulfide because hydrogen 
sulfide is extremely flammable and noxious, having a lethal dose of 1,000 
to 1,500 ppm. 
The previous method of calcining fluorescent calcium sulfide material is 
based on a batch process wherein a fixed quantity of calcium carbonate is 
calcined under an isolated hydrogen sulfide atmosphere. After the material 
is completely calcined, drawn out of furnace, and replaced by fresh 
calcium carbonate, this process is repeated. This type of batch 
processing, however, is not adequate for mass production. 
In view of the prior art, there is a need for a method for continuous 
calcining under a noxious gas atmosphere as well as an apparatus to carry 
out such a method, enabling the mass production of fluorescent calcium 
sulfide. 
SUMMARY OF THE INVENTION 
According to the present invention, continuous calcining is achieved by 
first introducing the materials to be calcined into a front chamber. This 
transfer is made by way of an outer entrance while an inner entrance is 
kept closed. The outer entrance is then closed, the inner entrance opened, 
and the materials are advanced through the inner entrance into a calcining 
furnace where they are calcined. The calcined materials are then advanced 
into a rear chamber by way of an inner exit while keeping an outer exit 
closed. The inner exit is then closed, the outer exit opened, and the 
calcined materials are carried out of the rear chamber through the outer 
exit. 
Also, according to the present invention, the calcining apparatus suitable 
for carrying out the above-mentioned method includes a tubular calcining 
furnace. A feed pipe and an exhaust pipe for reaction gases are attached 
to both ends of the tubular calcining furnace. The apparatus also includes 
a front chamber and a rear chamber each having an inner entrance/exit and 
an outer entrance/exit. The front and rear chambers are also attached to 
the exhaust pipe. Finally, the calcining apparatus includes a carrier upon 
which the materials to be calcined are placed and passed through the front 
chamber, the tubular calcining furnace, and the rear chamber, 
sequentially. 
The interiors of the front and rear chambers are provided with a shuttle 
and a pusher. The shuttle receives the carrier and changes the course of 
the carrier, and the pusher thrusts the carrier out of the shuttle. The 
shuttle and pusher in the front chamber are operated to advance the 
carrier into the calcining furnace. Conversely, the shuttle and pusher in 
the rear chamber are operated to bring the carrier out of the calcining 
furnace.

DETAILED DESCRIPTION 
FIG. 1 illustrates the external appearance of a calcining apparatus 
according to the present invention. A front chamber 4 and a rear chamber 6 
are disposed at both ends of a tubular calcining furnace 2, respectively. 
Actuators 8, 10, 12, and 14, which operate shuttles and pushers, are 
installed around the front chamber 4 and the rear chamber 6. Other 
actuators 16, 18, 20, and 22, which open and shut the inner and outer 
entrances/exits, are installed above the front chamber 4 and the rear 
chamber 6. 
A feed pipe 24 is attached to one end of the furnace 2 to supply the 
reaction gas to the furnace 2, and an exhaust pipe 26 is attached to the 
other end of the furnace 2 in order to remove the reaction gas from the 
furnace 2. The exhaust pipe 26 is also attached to the front chamber 4 and 
the rear chamber 6 by conduit pipes 26a and 26b. 
A conveyer 28 which advances carriers to the front of the front chamber 4 
is installed parallel to the tubular calcining furnace 2. 
As seen in FIG. 2, an aluminum calcining tube 32 of circular cross-section 
and surrounded by an adiabatic layer 30 (e.g., firebricks) is installed 
inside the tubular calcining furnace 2. The calcining tube 32 has an 
electric heater 34 at its periphery. 
The front chamber 4 and rear chamber 6 each includes inner and outer 
entrances/exits 36, 40, 42 and 44. The inner entrance 36 and the inner 
exit 42 lead to the furnace 2, and the outer entrance 40 and outer exit 44 
lead to the outside. These entrances and exits are opened and closed using 
doors which are operated by means of the actuators 16, 18, 20, and 22. 
A pusher 46 moves back and forth coaxially with respect to the longitudinal 
axis of the furnace 2 by means of the actuator 8. A shuttle 48 moves back 
and forth perpendicularly with respect to the longitudinal axis of the 
furnace 2 by means of the actuator 10. Both the pusher 46 and the shuttle 
48 are disposed inside the front chamber 4. 
Similarly, a pusher 50 and a shuttle 52 are moved back and forth coaxially 
and perpendicularly, respectively, to the longitudinal axis of the furnace 
2 by means of actuators 12 and 14, respectively. Both the pusher 50 and 
the shuttle 52 are disposed inside the rear chamber 6. 
The pusher 46 is operated through the inner entrance 36 and the shuttle 48 
is operated through the outer entrance 40. The pusher 50 is operated 
through the outer exit 44 and the shuttle 52 is operated through the inner 
exit 42. 
Carriers 54 are forwarded to the front of the outer entrance 40 by means of 
a conveyer 28. 
FIG. 3 illustrates a carrier 54 which has just been advanced by the 
conveyer 28 and is about to be moved onto the shuttle 48. 
In order to fit the circular cross-section of the calcining tube 32 seen in 
FIG. 2, the bottom of a vessel 56 (which contains the materials to be 
calcined by advancing them through the calcining tube 32) is shaped with a 
semicircular cross-section. The carrier 54, which carries the vessel 56, 
as well as the groove on the shuttle 48, which receives the carrier 54 
thereon, are also of semicircular cross-section. 
The carrier 54 is transferred from the conveyer 28 to the shuttle 48 which 
extends to the position represented by the dashed line in FIG. 2. The 
carrier 54 and the shuttle 48 are advanced through the outer entrance 40 
by means of the actuator 10 in the front chamber 4. Because the inner 
entrance 36 is kept closed, no leakage of the noxious gas is detected at 
this step. 
As the shuttle 48 and the carrier 54 are withdrawn into the front chamber 
4, the outer entrance 40 is closed and the inner entrance 36 is 
subsequently opened. The carrier 54 is then thrust from the shuttle 48 
into the furnace 2 by means of the pusher 46 which is extended by the 
operation of the actuator 8. 
Referring to FIG. 2, after the carrier 54 is inserted into the calcining 
tube 32 of the furnace 2 through the inner entrance 36, the pusher 46 is 
retracted in situ and the inner entrance 36 is again closed. Although 
noxious gas from the furnace 2 enters the front chamber 4 while the inner 
entrance 36 is opened, no leakage of the noxious gas is detected on the 
outside because the outer entrance 40 is kept closed. 
After a while, the noxious gas inside the front chamber 4 is completely 
discharged through the conduit pipe 26a and the exhaust pipe 26. This 
discharge occurs while the inner and outer entrances 36 and 40 of the 
front chamber 4 are kept closed. 
Once inserted into the calcining tube 32 of the furnace 2, the carrier 54 
is pushed through the calcining tube 32 by subsequent carriers which are 
thrust into the calcining tube 32 of the furnace 2. 
FIG. 4 illustrates the carrier 54 passing through the calcining tube 32. 
The feed pipe 24 and the exhaust pipe 26 are attached to the entrance and 
exit ends of the calcining tube 32, respectively. The reaction gas 
(noxious gas) supplied by the feed pipe 24 passes through the calcining 
tube 32 in the direction shown by the arrow in FIG. 4 and is then 
discharged through the exhaust pipe 26. The calcining tube 32 is heated to 
1,200.degree. C. by the electric heater 34. 
The materials in the vessel 56 react with the reaction gas and are calcined 
inside the calcining tube 32 as the carrier 54, which carriers the vessel 
56, passes through. 
Referring to FIG. 2, once pushed to the exit of the calcining tube 2, the 
carrier 54 s transferred to the shuttle 52, which is extended to the 
position represented by the chained line in FIG. 2. Then, the actuator 14 
is operated to move the shuttle 52, conveying the carrier 54 through the 
inner exit 42 into the rear chamber 6. The outer exit 44, of course, is 
kept closed during this operation. 
As the carrier 54 is brought into the rear chamber 6, the inner exit is 
closed and, after allowing the noxious gas inside the rear chamber 6 to 
discharge through the exhaust pipe 26, the outer exit 44 is opened. The 
carrier 54 on the shuttle 52 is then thrust out of the rear chamber 6 by 
means of the pusher 50 which is operated by the actuator 12. 
Thus discharged, the carrier 54 is collected and sent to the next process. 
As detailed above, the calcining method according to the present invention 
can be carried out in a continuous cycle wherein the carrier which carries 
the vessel containing the material to be calcined is circulated in the 
direction represented by the arrow in FIG. 2. 
Although particularly suited to the calcining of calcium carbonate under a 
hydrogen sulfide gas atmosphere to obtain fluorescent calcium sulfide, the 
application of the present invention is not limited to this process. The 
method and the apparatus of the present invention can also be applied to 
other types of calcination where noxious reaction gases are concerned, 
resulting in shortened working hours and greatly-enhanced productivity. 
When compared with the batch processing previously employed, the 
continuous processing provides for safer operation with no leakage of 
noxious gas.