Green coal is charred in pre- and post- treatment carbonizers, then crushed, mixed with pitch, briquetted, tempered in a tempering oven, recirculated with succeeding green coal to char in a reducing atmosphere through only the latter part of the pre-treatment carbonizer and through the post-treatment carbonizer, cooled, and separated from the as yet unbriquetted char. The pre-treatment carbonization is characterized by having air updrafted through all the airbox zones under the travelling grate.

PRIOR ART 
Mansfield, U.S. Pat. No. 3,969,088; Scott, U.S. Pat. No. 4,156,595; Work, 
U.S. Pat. No. 3,140,241 and 3,140,242. 
BACKGROUND OF THE INVENTION 
This process is an improvement over that disclosed in Mansfield U.S. Pat. 
No. 3,969,088 wherein sized green coal starting material is devolatilized 
by successively passing it through a horizontal chain grate pre-carbonizer 
furnace having a zoned airbox, and a shaft furnace, i.e., a soaking pit, 
then crushed and mixed with pitch binder, formed into green briquettes, 
and then recirculated with the green coal starting material through the 
pre-carbonizer furnace. In that process the green briquettes were cured in 
the oxidizing atmosphere of the pre-carbonizer furnace simultaneously with 
the partial devolatilization of the green coal starting material. Also, in 
that process, the pitch binder was obtained by downdrafting the first few 
airbox zones so as to pull off the low temperature volatiles, and then 
condensing them. In the subject process, however, the green briquettes are 
tempered prior to recycling through the pre-carbonizer furnace with the 
incoming green coal and they are imposed as an overburden onto the green 
coal bed at a point downstream from where it is introduced onto the chain 
grate. A somewhat comparable formcoke process, without the tempering step, 
is disclosed in Scott et al. U.S. Pat. No. 4,156,595. 
OBJECTS OF THE INVENTION 
The object of the invention is to produce formcoke briquettes of improved 
strength and hardness, suitable for blast furnace and foundry use, in a 
substantially closed system by a method having improved running and 
maintenance conditions, with less likelihood of the occurrence of 
explosions. 
SUMMARY OF THE INVENTION 
As will be detailed hereinafter, several advantages are obtained including 
closer process control, full-hardening of the briquettes before 
re-introduction into the pre-carbonizer furnace, near complete 
devolatilization of the briquettes prior to recirculation through the 
pre-carbonizer furnace, and enhancement of the coking or charring of the 
green coal as a result of the overburdening of the cured briquettes onto 
it after it has been fully ignited and passed partway through the 
pre-carbonizer furnace. 
In the improved formcoke process of this invention, a tempering oven is 
used to harden the green briquettes and to remove the low temperature 
volatiles from them before recycling through the latter part of a 
pre-treatment carbonizer and through a shaft furnace. The briquettes are 
tempered in a tempering oven, which increases their strength before they 
enter the pre-treatment carbonizer and are deposited as an overburden on 
top of the green coal partway along the travelling grate. The low 
temperature volatiles emitted from the briquettes in the tempering oven 
enter the system at approximately the same point as the briquettes, and 
form a reducing atmosphere above the layer of tempered green briquettes 
which have been deposited on the already ignited green coal. The amount of 
air updrafted is controlled so that the green coal is controlledly charred 
in an oxidizing atmosphere but the layer of tempered green briquettes 
deposited on top of the green coal is carbonized in a reducing atmosphere 
present above the grate. If too much air is updrafted, the lower surfaces 
of the layer of briquettes will be oxidized. If insufficient air is 
updrafted, the green coal will be insufficiently charred or coked. The 
controlled process of this invention produces briquettes of increased 
strength and hardness. Furthermore, the presence of the briquettes 
overlaying the layer of green coal serves to increase the density, and 
thus increase the strength, of the green coal as it passes through the 
pre-treatment carbonizer. 
The green coal on the travelling grate must be fully ignited before the 
briquettes are added on top of the coal and this ignition occurs over the 
first few airbox zones in the oxidizing updraft before the briquettes are 
added. 
The process may be practiced using any type of coal including lignite, 
bituminous coal, anthracite, etc. Choice of coal may be determined by the 
end use of the briquettes, for example, steel industry specifications 
require use of coal having relatively low ash and low sulfur content.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows an apparatus 2 suitable for practicing the process of present 
invention. The pre-treatment carbonizer 4 has an input, for example a 
hopper 6, to which green coal preferably sized 2.times.0 inch, with a 
maximum of about 40% minus 1/4 inch, is charged, and then spread by gate 8 
to form bed 10 on the continuously moving chain grate 12. Beneath the 
chain grate is a zoned airbox 14 having, for example, eight zones a to h 
inclusive, all of which are supplied with updrafted air, preferably at 
ambient temperature, from an air supply 16 in amounts which are carefully 
controlled and limited by valves 18. About 1 to 3 lb. air per lb. of green 
coal is used. Tempered green briquettes which have been hardened in 
tempering oven 42 enter the furnace downstream of the entry of the green 
coal, for example oven airbox zones c or d. Appropriate methods of 
allowing the briquettes to enter the furnace are such that only a minimal 
amount of air enters the furnace atmosphere with the tempered briquettes. 
For example, in a suitable method, the roof of furnace 4 has a series of 
window openings or portholes 7 approximately 4-8 ins. in diameter at 2-4 
ft. intervals across its width through which the briquettes fall. The 
tempered briquettes fed from tempering oven 42 to hopper 80 fall through 
openings 7 to form an overburden of average depth 6-8 ins. on the bed 10 
of ignited coal travelling on the grate. The tempered briquettes should be 
distributed evenly to the openings 7. Exhaust gases from the system at a 
temperature of 1800.degree.-2000.degree. F. are taken off through stack 
20. Stack 20 may supply gases to a boiler 21, or heat exchanger, whereby 
the temperature of the exhaust gases is reduced to 400.degree.-500.degree. 
F. for use in devolatilizing the briquettes in the tempering oven. From 
the output end of the chain grate 12, the material being treated falls 
into post-treatment carbonizer 22 which, in this instance, is a vertical 
shaft furnace having a reducing atmosphere, essentially a soaking pit, and 
from which, after a suitable residence time, the material exits to cooler 
26 which may be a water quencher such as that disclosed in U.S. Pat. No. 
4,409,067. At start-up, the exiting material consists of char, but as will 
be apparent hereinafter, the exiting material, after start-up, consists of 
char and post-treated briquettes which together pass from the 
post-treatment carbonizer 22 to cooler 26, where the material is cooled to 
400.degree. F. or less. From cooler 26 the char and briquettes move to a 
separator 27, for example, a screen from which the then cooled and fully 
coked briquettes which constitute the end product are taken. The char from 
which the fully coked briquettes have been separated moves from the size 
separator 27 to crusher 28 where it is sized to minus 1/4 inch, and then 
to mixer 30 into which pitch from pitch supply 32 is fed. Steam from a 
suitable source 38 is also fed into mixer 30 and the fully mixed hot pitch 
and crushed char, then at from about 170.degree. F. to 250.degree. F., are 
fed to briquetter 40. The steam mixed in with the pitch and char 
strengthens the briquettes, both as to green strength and as to carbonized 
strength. The briquetter is preferably of the double roll type. Green 
briquettes are fed from briquetter 40 into tempering oven 42. 
Referring now to FIG. 2, the tempering oven 42 has running through it from 
to rear a perforate conveyor or chain grate 44. Between the upper and 
lower grate runs is a zoned gas box 46 having valve controlled input lines 
48. Above the grate input is briquette hopper 50 from which the green 
briquettes 58 are deposited to form a bed 52. The gas which is used for 
tempering the briquettes is forced through the travelling briquette bed by 
the gas fan 54 by way of gas line 56, input lines 48 and zoned gas box 46. 
In typical operation, briquettes 58, sized, for example, 
2.times.2.times.11/8 inch, are loaded into briquette hopper 50 from which 
a uniform briquette bed 52 is formed by the adjustable feed gate 60 with 
bed depth from 4 inches to 8 inches. The grate speed is regulated to allow 
for a briquette retention time of one to two hours. A flapper gate 62 is 
located at the discharge end of the oven to prevent an excessive amount of 
air from being pulled into the oven. Flapper gate 62 is hinged at 63 at 
the top and allowed to drag on the briquettes to maintain a good seal even 
if the bed depth is changed. Tempered briquettes are discharged from the 
tempering oven onto conveyor 64 and thence to hopper 80 (see FIG. 1) for 
input to the pre-treatment carbonizer 4 above airbox zones c or d. 
The tempering gas after being forced through the briquette bed 52 is drawn 
from the oven by way of flue 66 and recirculated through line 67 and fan 
54 through the system, as described above. Additionally, the hot gas is 
supplied to the tempering gas circuit by way of line 68. The gas used for 
tempering may be flue gas from the carbonizers. The gas in the tempering 
oven 42 is maintained at 400.degree..+-.20.degree. F. by temperature 
controller 70 which modulates damper 72 which controls the flow of hot gas 
into the tempering oven. The oven draft is controlled by pressure 
controller 74 which modulates damper 76 which controls the discharge of 
gas from the circuit. The discharged gas is combustible and may be used 
for steam generation, etc., or it may be recycled through the tempering 
oven by means of line 67. 
It is important in the general operation of the tempering process to heat 
the green formcoke briquettes gradually and uniformly to a temperature 
that will drive off the low boiling volatile oils from the pitch binder. 
The temperature of the briquettes must be raised gradually to a 
temperature that is barely high enough to remove the volatile oils, in 
order to prevent the briquettes from disintegrating due to the rapid 
expulsion of the volatile oil vapors. It must also be accomplished at a 
uniform temperature to prevent the oil vapors from condensing on the 
cooler briquettes and dissolving them. 
Several advantages over the prior art processes accrue from use of this 
improved process. Insertion of the tempering oven step as a pre-treatment 
of the briquettes allows the tempered briquettes to be added downstream of 
the entry point of the green coal in the pre-treatment carbonizer, for 
example, over airbox zones c or d in FIG. 1, and thus all the airbox zones 
can be updrafted. Furthermore, the briquettes are physically strengthened 
by the pre-tempering treatment. Other advantages accrue from this 
arrangement. When the green coal first reaches the travelling grate in the 
pre-treatment carbonizer the updrafted air allows the bed of green coal to 
ignite fully and carbonize in an oxidizing atmosphere. The tempered 
briquettes are added on top of the green coal when the bed of green coal 
is fully ignited, above under-grate airbox zones c or d, and at the same 
time, the low temperature volatiles from the tempering oven also enter the 
atmosphere above the travelling grate. The oxygen in the updraft air is 
limited so that it is fully consumed by the green coal, allowing the 
tempered briquettes on top of the coal to carbonize in a reducing 
atmosphere, further increasing their strength. Furthermore, the updrafted 
air is preferably at ambient temperature, needing no preheating, and this 
advantageously reduces the maintenance required to keep the travelling 
grate in running condition. 
Another important advantage of this improved process using updrafted air 
through all the airbox zones is that the system is readily stabilized, 
creating a safer process environment by enabling greater control of the 
temperature and pressure in the essentially closed system. 
Variations and modifications can be effected within the scope of the 
invention as described above, and as defined in the appended claims.