Method for heat treatment of fines with atmosphere control

A method to operate a flash calcination unit with both atmosphere and temperature control is described for mineral processing requirements and other atmosphere controlled processes. The method can be used to process phosphate, gold ore or activated carbon. The critical steps of the method involve an initial mixing of fine material combined with stoichiometric burning using at least one staged combustion furnace in a vertically oriented suspension calcination furnace. This effects control of oxygen or atmosphere in the combustion furnace with attendant control of temperature in that furnace.

FIELD OF THE INVENTION 
The invention relates to a method utilizing a flash calcination unit and 
gas reaction system. Typical uses include phosphate calcination and 
processing of ore or of activated carbon. 
BACKGROUND OF THE INVENTION 
This invention relates to a method for heat treatment of fine material 
using a flash calciner. The method specifically relates to phosphate 
calcination, as well as calcination of various ores. The present method 
can also be utilized to process fines generated from activated carbon 
rotary kiln systems. 
Pyrometallurgical operations when applied to ores generally alter the 
chemical and physical properties of the materials processed. These known 
processes are characterized by chemistry which mainly involves gas-solid 
reactions such as calcination. 
A basic pyrometallurgical operation is the decomposition of hydrates and 
carbonates. A typical reaction is the decomposition of pure limestone 
(CaCO.sub.3) to calcium oxide and carbon dioxide: 
EQU CaCO.sub.3 (s).fwdarw.CaO(s)+CO.sub.2 (g) 
where the symbols (s) and (g) represent the solid and gaseous state, 
respectively. This reaction is strongly endothermic, and in a conventional 
processing system requires high heat input and long retention times. 
Lime is an important raw material for the metallurgical industry. It is 
used primarily as a flux in smelting and converting, but it is also a 
neutralizing agent for hydrometallurgical processes. The calcination of 
magnesite (MgCO.sub.3) yields magnesia (MgO) which is an essential raw 
material for furnace refractories. The calcination of dolomite (CaCO.sub.3 
.multidot.MgCO.sub.3) also yields a calcine used as a feed for the 
preparation of magnesium metal, as well as other uses. 
Other examples of similar process are phosphate calcination and gold ore 
processing. 
The unique characteristics of flash calcination are particularly suited to 
processing phosphate. Phosphate is a complicated mineral, that varies from 
deposit to deposit with each ore requiring its own special processing 
considerations. When phosphate rock is processed to produce 
super-phosphates and phosphoric acid, thermal processing is required to 
remove carbon, sulfides and certain trace elements. In addition, there can 
also be some upgrading of the P.sub.2 O.sub.5 content by the elimination 
of certain components such as lime. In processing, it's important not to 
destroy the delicate crystal structure of the phosphate by overheating. 
This is important because the porosity of the phosphate is very important 
in the digestion steps that follow calcination. Flash calcination offers 
the unique advantages of very short retention times, high heat transfer 
rates, very good oxygen contact and rapid cooling. All of these 
characteristics are very important in the production of high quality 
calcined phosphate. 
Many gold ores contain sulfides and carbon, which result in high cyanide 
consumption in the recovery process. Heat treating the ore prior to the 
cyanide leach will reduce cyanide consumption, which is vital to the 
economics of processing. Processing in an oxidizing atmosphere where there 
is above average mixing of the ore with the gas is very important to the 
oxidizing roast. For the present invention, a properly sized ore when 
processed in the flash calciner is subjected to excellent dispersion and 
mixing in the gas stream. Oxygen and temperature can be controlled over 
the whole length of the calcining zone. 
Applicants method achieves energy conservation by control of temperature 
and gas atmosphere of a flash calcination unit during a protracted 
residence time of the material being calcined. 
The system of the present invention offers several advantages compared to 
the prior art. The system permits maximum gas to solid contact for 
reaction to take place. Excellent control is permitted. The present system 
also has high fuel efficiency as a result of heat recovery from solids and 
gases. Excellent temperature control is achieved for heat sensitive 
products and flame contact can be eliminated if desired. The present 
system can also eliminate reduction gas components internally ahead of the 
preheat system immediately after the reaction furnace using bleed air 
which eliminates the use of an external afterburner. With these advantages 
in mind, applicants will begin to describe in greater detail their 
discovery and achievements. 
SUMMARY OF THE INVENTION 
The invention relates to a method for heat treatment of fine material using 
a vertically oriented suspension calciner comprising: 
a) preheating fine material; 
b) injecting preheated material into a swirling gas flow in a suspension 
furnace; 
c) controlling a mixture of fine material and gas in the suspension furnace 
to limit availability of oxygen in contact with the material while 
maintaining a desired gas temperature in the suspension furnace; and 
d) collecting a product. 
This invention further relates to a method for heat treatment of fine 
material using an essentially vertical suspension calciner comprising: 
a) preheating fine material; 
b) injecting preheated material into a swirling gas flow effected by a 
stationary impeller in a suspension furnace; the suspension furnace 
containing at least one combustion furnace along the length of the 
suspension furnace to inject controlled quantities of fuel and oxygen to 
maintain a neutral or reducing atmosphere in the suspension furnace; 
c) controlling a mixture of fine material and gas in the suspension furnace 
to limit availability of oxygen in contact with the material while 
maintaining a desired gas temperature in the suspension furnace by 
maintaining substantially stoichiometric burning in the combustion 
furnace; and 
d) collecting a product. 
This invention also relates to a method to separate heavy metals and 
gaseous components during heat treatment of fine material using an 
essentially vertical suspension calciner comprising: 
a) preheating fine material; 
b) injecting preheated material into a swirling gas flow effected by a 
stationary impeller in a suspension furnace; the suspension furnace 
containing at least one combustion furnace along the length of the 
suspension furnace to inject controlled quantities of fuel and oxygen to 
maintain a neutral or reducing atmosphere in the suspension furnace; 
c) controlling a mixture of fine material and gas in the suspension furnace 
to limit availability of oxygen in contact with the material while 
maintaining a desired gas temperature in the suspension furnace by 
maintaining substantially stoichiometric burning in the combustion 
furnace; 
d) separating or vaporizing heavy metals or gaseous components; and 
e) collecting a product.

DETAILED DESCRIPTION OF THE INVENTION 
The method of the present invention operates by controlling both atmosphere 
and temperature for mineral processing requirements and other atmosphere 
control processes. Some examples follow in which such control can be 
effected. 
One example is phosphate calcination which involves reduction of sulfides 
and cadmium. Here, swirling combustion gas inlet would be controlled to 
remove carbonacious materials and some forms of sulfides by effecting an 
oxidizing atmosphere. Cadmium removal has been found to require reducing 
conditions as will some forms of sulfur minerals. Another example is gold 
ore processing. There, carbonacious material and sulfide contaminant which 
reacts with cyanide leach process requires roasting in a high oxygen 
atmosphere. This converts sulfide and reduces its interference with the 
cyanide leach process. Another example is activated carbon processing. 
This involves fines generated from activated carbon rotary kiln systems. 
The fines can be processed in this invention under reducing conditions to 
produce a usable product. The present method is adaptable to all other 
systems which require temperature and atmosphere control to separate or 
vaporize forms of heavy metals and gaseous components, such as sulfur. 
An object of the present invention is to improve the economics of such 
processing while avoiding undesirable side reactions such as collapsing of 
phosphate crystals during phosphate calcination. This is achieved by 
controlling both temperature and atmosphere in an essentially vertical 
suspension furnace. The purpose of the control of the suspension furnace 
is to reduce the amount of oxygen available to either oxidize material or 
reduce material in the process. Ultimately, this results in lengthening 
the zone of the reaction so that a more uniform temperature in the 
reaction zone is achieved. This is done by the manner of injecting the 
fuel to have staged combustion along the length of the suspension furnace. 
While fuel is injected at the bottom of the suspension furnace in a 
conventional manner, that is, using primary (feed) and secondary 
(supplemental) air to burn that fuel, upper portions or stages in the 
suspension furnace are maintained so that temperature and atmosphere 
promote combustion on a stoichiometric basis. This neutral or reducing 
atmosphere produced by stoichiometric combustion is critical to the 
invention. Thus, the air that is required to burn the fuel is injected 
along with the fuel so that the upper portions or stages maximize the 
temperature without disturbing control of the atmosphere. This 
sophisticated technique prolongs the reaction and residence time in the 
suspension furnace so that desired temperature and atmosphere control can 
be achieved. 
Atmosphere means that oxygen availability is controlled. This is achieved 
by a critical feature of the present invention which is the stoichiometric 
burning of fuel in combustion chambers. This is done by controlling oxygen 
or fuel to the combustion furnace. The method operates by essentially 
eliminating excess oxygen in the combustion process. Then a neutral 
atmosphere can be obtained in the suspension calcination furnace. Of 
course, a reducing atmosphere can be provided by providing insufficient 
oxygen so that excess fuel enters the suspension calcination furnace. This 
fuel depleats oxygen from the gas use to transport fine material. 
Manipulation of the reaction is used to control temperature. Thus, 
temperature and atmosphere can be controlled to effect superior 
particulate products economically. Optionally, oxygen can be injected 
during the processing of fine material. Fuel can be injected 
conventionally at the bottom of the suspension calcination furnace. 
More particularly, atmosphere is controlled by using multiple burners and 
by using direct fired combustion chambers. Thus, in a vertical suspension 
furnace it is possible to overfuel with the lowest direct injection 
burner. The whole heat load does not have to be handled by this one burner 
because there are additional burners. Through use of combustion chamber 
burners above the initial burner, applicants achieve the advantage of 
adding additional heat and a controlled atmosphere. With the combustion 
chambers, total control over the fuel and air is achieved which permits 
control of the atmosphere. Heat is injected using the combustion chamber 
and therefore, the hot zone of the suspension furnace is lengthened. By 
stoichiometric burning or by adding some excess air for reducing 
atmosphere in the suspension furnace, the combustibles in the vessel can 
be burned or trimmed while even increasing temperature. 
For an optional oxidizing atmosphere in the suspension furnace, heat can be 
added with the combustion chamber, excess air can be added or burning can 
occur with the deficiency of air to trim the oxygen in the suspension 
furnace. Bleed air can be added at the exhaust gas outlet to ensure 
complete combustion of the fuel. 
To better understand the invention, it will now be described regarding to 
the apparatus shown in the drawing. 
In conduit 6 and flash dryer 10, moist material is dried to a powder. The 
cyclone 10 includes an inlet 18 for gas and entrained solid material and 
an outlet for gas connected to the conduit 13 and an outlet 19 for dried 
material flow connected by conduit 21 to cyclone 32. Thus, the dryer 10 
serves to carry out the process step of drying solid material while it is 
in suspension in hot spent preheater gases. Exhaust gas from the flash 
dryer 10 is supplied through conduit 13 and fan 14 to a high efficiency 
dust collector 15 such as a scrubber or fabric filter bag house with the 
cleaned air being supplied to a stack 16 for exhaust. 
The dried material discharged from drier 10 through conduit 21 is entrained 
in hot gas flowing through conduit 23. Feed material is supplied to a 
conduit 30 where it is supplied to a cyclone 10 having an inlet 23 for gas 
and entrained material, an outlet 13 for gas and an outlet 21 for 
preheated material. 
The cyclone 10 and 55 and the associated duct work 30, 23 and 52 constitute 
a preheater 36 for preheating the dried material while suspended in a 
stream of hot gas. It should be understood that the preheater may be a 
single stage cyclone or more than two stages may be used. Actually 1 to 4 
stages of suspension preheat can be used depending on the operating 
temperature of the calciner. The higher the temperature, the greater the 
number of stages used to recover off-gas heat for fuel efficiency. The 
flow of material in the preheater is generally counter-current to the flow 
of hot gas. Thus, the preheater 36 includes an inlet (conduit 21) for 
dried material to be processed, an outlet 23 for spent preheating gas and 
an outlet 60 for preheated material. 
The apparatus of the present invention includes a vertically oriented 
elongated suspension or calcining furnace generally indicated at 42 and 
defined by a vessel 43 having a lower end 44 and an upper end 45. The 
lower end 44 has a tangential inlet 47 for fuel, and an inlet 49 for air 
for combustion in the vessel 42 whereby combustion takes place. The lower 
end of the vessel also includes means or inlet 60 for supplying preheated 
material to be processed to the lower end of the vessel via an optional 
recycle conduit 25. This inlet is flow connected to the outlet 35 of the 
collection cyclone 32. 
The upper end 45 of the vessel 43 has an outlet 51 (preferably tangential) 
for spent combustion gases and processed material so that the flow of 
combustion gases and entrained material is co-current from the lower end 
44 of the vessel 43 to the upper end 45. While the preheated fine material 
is suspended in the hot combustion gases, it is calcined. 
A gas-solids separator or collecting cyclone 32 has an inlet 33 for gas and 
entrained processed material, an outlet 34 for separated gas and an outlet 
35 for processed solid material. The cyclone 32 is flow connected to 
cyclone 55 by conduit 52. The outlet 34 for gas is flow connected to the 
preheater 36 by duct 52 and this duct 52 defines the inlet for spent 
combustion gas of the preheater flow connected to the outlet 34 for spent 
combustion gas of the gas-solids separator 32. 
A material cooler is generally indicated at 65 and is a device for cooling 
the material by suspending it in ambient air and is shown as a pair of 
serially connected cyclones 66 and 67 each having an inlet for gas and 
entrained material, an outlet for separated solids and an outlet for 
separated gas. Ambient air is supplied from atmosphere by means of a fan 
68 through a conduit 69 to cyclone 66. A duct 71 interconnects the outlet 
for separated gas of cyclone 66 with the inlet for gas and entrained 
solids of cyclone 67. The solids outlet of cyclone 67 is connected to duct 
74 to conduit 69. The cyclone 67 separated the product from the cooling 
gas and supplied it through an outlet 74 to conduit 69 where it is again 
entrained in the cooling gas further cooled and conveyed to cyclone 66. 
The cyclone 66 discharged product or processed material through outlet 76 
and preheated cooling gas through conduit 71. The cyclone 67 discharges 
preheated air for combustion through an outlet 77 to the inlet 49 for air 
for combustion of the calciner furnace 42. 
A mechanical spinner of any suitable type is provided at 80 for inducing 
and maintaining a helical or swirling motion to the air for combustion. 
This mixing step is critical to the invention. Those skilled in the art 
will know how to design such an apparatus for imparting a helical motion 
to the preheated air for combustion, but such a device may take the form 
of stationary helical vanes (not shown) on the inside of the duct, an 
impeller which is rotated by an external motor, or other suitable means 
such as a tangential inlet. 
The process of the present invention also includes recirculating a portion 
of at least partially calcined material back to the calcining furnace 42. 
This process is carried out by providing a splitter valve 59 at the outlet 
35 of cyclone 32 and a conduit 25 connecting cyclone 32 to the lower end 
44 of the vessel 43. The splitter 59 controls the flow of material to 
either conduit 25 or conduit 62 with the usual practice being to supply 
part of the material to conduit 25 for recirculation to the calciner for 
further calcining and the balance of the material is discharged to cooler 
65 through conduit 62. See generally U.S. Pat. No. 4,381,916, hereby 
incorporated by reference, for the recirculation of material in a flash 
calciner. Prior to the present invention, it is not believed that 
recirculation was even attempted with the fine materials, because such 
recirculation could result in overburning. 
With the present invention, the preferred form of supplying thermal energy 
to the calcining furnace is in the form of direct injection of fuel to the 
lower part of the calcining furnace with material supplied through conduit 
60 to the calciner above the fuel inlet 47. The preheated material will 
drop down near the flame generated by the fuel injection in lower cone 47a 
and is initially contacted by the high temperature associated with direct 
combustion within the calciner. While the inlet for preheated material is 
above the inlet for fuel, because of gravity flow, the preheated material 
may tend to drop through the flame generated by the injection of fuel 
within the calciner. This contact with the flame is believed to cause a 
prompt calcination of at least the surface of the material. The inner core 
of the material is processed by maintaining the calciner at the desired 
temperature so that the residence time of the material in the high 
temperature vessel completes the process. The inlet for the fuel and 
material may be tangential. 
Additionally, thermal energy is supplied in the form of direct injection of 
small amounts of fuel to the vessel 43 at points intermediate the lower 
fuel inlet and the upper outlet 51. The injection may be tangential. It is 
desirable not to provide additional high temperature flame contact for the 
material to avoid overburning the surface of the material. Fuel is not 
directly injected into the vessel at the upper levels. External combustion 
chambers 90 are provided to supply additional thermal energy between the 
lower end 44 and upper end 45 of the calcining vessel. Both fuel as 
indicated by the solid line arrows 91 and air for combustion as indicated 
by the dotted lines 92 are supplied to each of the combustion chamber 90. 
Element 93 is an air bleed. The close coupled combustion chambers are 
mounted so that hot gases of combustion are injected into the calcining 
vessel 43 at vertically spaced apart points above the fuel inlet 47 and 
the material inlet 60 and 48 of the vessel 43. It has been found that it 
is important to maintain the helical flow of material through the vessel 
43 which was initially established by the spinner 80. This is maintained 
by having the hot combustion air supplied to the calciner by substantially 
tangential inlets as illustrated. Preferably, these inlets may be at 
slight angles such as 20.degree. to 30.degree. to the tangential. The 
burner 47 should also be positioned tangentially or nearly so at 
20.degree. to 30.degree. from tangential. This helical flow of hot gases 
prevents the material from sticking to the sides of the calcining furnace. 
Further, it has been found that with the helical flow and injection of hot 
combustion gases rather than the use of flame, that a product loss on 
ignition or LOI of between 1% and 2% can be maintained. 
The use of external combustion chambers allows greater control over the 
quantity of thermal energy that can be supplied to the upper levels of the 
vessel compared to the direct injection of fuel into the vessel and makes 
it easier to maintain a uniform temperature throughout the vessel 42 
thereby achieving more uniform calcining of the material as a whole. Thus, 
with separate combustion chambers, maximum thermal energy can be supplied 
by fuel inlet 47 and supplemental thermal energy supplied at the upper 
levels, but in some use it may be desirable to add the majority of the 
thermal energy at the upper levels. This configuration permits the 
necessary flexibility to achieve optimum operations. 
With the present invention, it has been found desirable to maintain the 
temperature within the calciner approximately between 1600.degree. F. and 
1800.degree. F. This also includes maintaining exit gas temperature at 
outlet 51 in the range of approximately 1650.degree. to 1750.degree. F. 
Product discharged from cyclone 55 will have a temperature between 
1500.degree. to 1700.degree. F. and ideally approximately 1600.degree. F. 
The temperature at gas outlet 34 will be on the order of 1100.degree. to 
1500.degree. F. with a preferred range of 1300.degree. to 1470.degree. F. 
These temperatures are accomplished by maintaining combustion temperatures 
in the auxiliary combustion chambers 90 between 2000.degree. F. to 
2500.degree. F. Thermalcouples (not shown) may be provided in each of the 
combustion chambers to provide for proper control of the temperature 
within the calcining furnace 42. It is to be understood that for thermal 
processing of ores, some other temperature may be appropriate and those 
skilled in the art will be able to achieve the desired temperature through 
routine experimentation. For example, processing temperature in the 
calciner for phosphate is between about 800.degree. C. to about 
1100.degree. C. For gold ore, it is between 400.degree. C. to about 
600.degree. C. For activated carbon, it is between about 1000.degree. C. 
and about 1300.degree. C. 
Also, with the calcining of fine materials, it has been found that the 
oxygen content within the calcining furnace should be maintained 
approximately in the range of about 0.5 to 2% while the oxygen content in 
the duct 52 should be maintained between approximately 0.5 and 
approximately 1%. 
The product temperature may be in the range of 200.degree. to 450.degree. 
F. and ideally between 250.degree. to 350.degree. F. 
Feed material is generally -20 mesh of finer. Cold feed material enters 
into an off-gas stream via conduit 30 from preheater 55. Thus, the feed 
material is preheated while being conveyed to preheater 10 via conduit 23. 
With the temperature of the material increased, it drops down in preheater 
10. The material is injected into heated gas and is separated from it. The 
gas becomes spent gas and exits to bag collector 15. The separated 
preheated material now drops into another duct 52 in second stage 
preheater 55 where it is preheated by the gas of preheater 55 to higher 
temperature. It is separated from that gas which goes on to preheat the 
first material as mentioned above. The material drops down from outlet 58 
via conduit 60 to the flash calciner 43 into the processing zone. This 
zone contains temperature controls known in the art which facilitates 
maintaining the temperature at a desired processing temperature for the 
particular material being processed. 
For example, a reducing atmosphere is required to process phosphate from 
which cadium is removed. Phosphate is injected into the zone which 
advantageously shortens retention time, thereby precluding overheating the 
phosphate and causing the crystal structure to collapse. However, a 
sufficiently high enough temperature is required to vaporize the cadmium 
while maintaining the proper atmosphere. 
Fuel is injected at four different points in the flash calciner 43. The 
fuel is injected in a quantity to create a reducing atmosphere. As the 
material comes up the flash calciner from the lower end 44 to upper end 
45, fuel is injected in the combustion chamber 90 to maintain temperature 
in the established reducing atmosphere. When the process material reaches 
the top 45 of the flash calciner, the cadmium has been separated from the 
phosphate. At this point, bleed air is added along with some excess 
reduction components. Bleed air is injected to eliminate components so 
that hydrocarbons are not emitted from the system. At this stage, a fully 
processed material is obtained. 
The collector 32 separates the vaporized cadmium from the remainder of the 
material. Cadmium goes off with the off-gases. The processed phosphate 
drops down to a location such as at valve 59 where a portion can be 
recycled by passing it through conduit 25 to the bottom 44 of the flash 
calciner 43. The recirculation on the collection cyclone 32 discharged can 
be adjusted to obtain up to a 10 to 1 recycle rate to the furnace if 
additional retention time is required. Of course, the remainder of the 
product is passed via conduit 62 to cooling cooler 65 which cools the 
phosphate. The final product is recovered from conduit 76. The phosphate 
is cooled using air blown in through conduit 69. 
Off gas from the cooler 66 are passed via conduit 71 to upper cooler 67. 
This heated off-gas enters beneath the swirling means or impeller 80. The 
impeller spins the gases immediately below the fuel injection point 47. 
For low temperature processing, fuel injection is not used and material is 
contacted with preheated cooler gases only with controlled atmosphere as 
required at the lower section of furnace 44. The material and swirling 
gases mix at the lower end 44 of the calciner 43. Above this point, 
multiple tangential gas fired combustion chambers 90 are spaced to supply 
hot gases with controlled atmosphere (reducing or highly oxidizing). They 
are placed to maintain the tangential flow started by the impeller 
EXAMPLES 
The invention will now be described by experimentation which is considered 
to be illustrative, but not limiting. 
EXAMPLE 1 
Five experiments were conducted in the treatment of phosphate as explained 
above. The operation followed the procedure set forth above. Operating 
conditions and results are described in the following table. 
TABLE 
__________________________________________________________________________ 
PHOSPHATE/CALCINER RUN 
PRIMARY OPERATING CONDITIONS AND RESULTS 
Phase 
1 2 3 4 5 
__________________________________________________________________________ 
Time (Hrs.) 1600-1655 
0935-1130 
1200-1330 
1400-1625 
1625-1700 
Phase Duration 52 115 90 145 35 
Product 0 0 0 0 3:2 
Recirculation 
Ratio 
Feed Rate 1197 1233 517 125 219 
(lbs/hr.) 
Loss-Free 1133 1168 489 119 208 
Feed Rate 
(lbs/hr.) 
Product Rate 1124 1110 467 93 182 
(lbs/hr.) 
Baghouse Rate 32 25.5 25.5 25.5 25.5 
(lbs/hr.) 
Chemical Analysis (Cadmium) 
PPM in Product 44 32 18.5 15 12.2 
PPM in Baghouse 
169 340 485 425 -- 
PPM in Feed 57 57 57 57 57 
Gas Analysis 
Collection Cyclone 
0.25 0.56 0.20 0.20 1.2 
Inlet O.sub.2 (%) 
Collection Cyclone 
1.9 0.7 0.7 0.8 0.1 
Inlet Combustibles (%) 
Temperatures 
Combustion Chamber 
700 710 703 725 730 
Exit Temp. (.degree.C.) 
Avg. Burning 873 1002 1096 1199 1180 
Zone Temp. (.degree.C.) 
Collection Cyclone 
900 980 1100 1163 1160 
Inlet Temp. (.degree.C.) 
Collection Cyclone 
850 918 1010 1053 1065 
Exit Temp. (.degree.C.) 
Collection Cyclone 
890 955 1023 1045 1060 
Discharge Temp. (.degree.C.) 
Preheat Cyclone 
385 445 470 550 540 
Inlet Temp. (.degree.C.) 
Preheat Cyclone 
305 355 383 458 450 
Inlet Temp (.degree.C.) 
Fuel 
Combustion Chamber 
4.99 5.42 5.11 5.32 5.35 
#2 Fuel Oil (GPH) 
Lower Duct Burner 
7.5 9.3 9.9 6.5 8.6 
#2 Fuel Oil (GPH) 
Middle Duct Burner 
2.42 2.67 1.74 3.63 3.18 
#2 Fuel Oil (GPH) 
Upper Duct Burner 
1.31 4.51 5.17 3.28 2.33 
#2 Fuel Oil (GPH) 
Airflow 
Total Airflow to 
384 384 384 384 384 
Flash Calciner (SCFM) 
lb/Material/ 0.65 0.64 0.27 0.05 0.11 
lb. Air 
BTU/lb. Product 
1876 3565 6102 26182 12163 
__________________________________________________________________________ 
Although the invention has been described in conjunction with specific 
embodiments, it is evident that many alternatives and variations will be 
apparent to those skilled in the art in light of the foregoing 
description. Accordingly, the invention is intended to embrace all of the 
alternatives and variations that fall within the spirit and scope of the 
appended claims.