CA1062460A - Apparatus for calcining raw material - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
An apparatus for calcining raw material such as the raw material used for making Portland cement. The apparatus is used in conjunction with a preheater and a calciner, such as a rotary kiln, and a cooler. The calciner includes a vessel with means for supplying combustion gas to the bottom of the vessel, an outlet at the top of the vessel, for spent combustion gas and calcined material, a burner for producing a combustion zone intermediate the combustion air supply and the calcined material outlet. Raw material can be supplied to the vessel either from above the combustion zone and below the outlet or from below the combustion zone. The combustion air may be supplied from the cooler or a combination of the cooler and the exhaust gases from the clinkerer. The apparatus is primarily designed for using coal as a fuel.

Description

~C~62460 ' I
B~C~GRQ~ OF_THE_INVENTION
The present invention relates to apparatus for calcining fine solid particulate material and in particular apparatus for flash calcining raw material such as that used to manufacture Portland cement. The invention may also be employed in othex ~' processes where fine solid particulate material must be calcined.
Prior to the present invention, it was generally known in the manufacture of Portland cement that the raw material must first be heated to a calcining temperature and then further heated to a clinkering temperature. After clinkering, the material is cooled by any of several well known techniques such as air quenching. The general practice today is to employ a rotary kiln for calcining a~d clinkering. More recent innovations include the use of some form of preheater employing the waste gases from the rotary kiln to preheat the raw material supplied to the xotary kiln.
Prior to the present invention it was known to employ a separate fired vessel for calcining the material thereby using the rotary kiln solely for clinkering. In this arrangement, there may be a separate preheater with the material discharged from the preheater being supplied to the calciner. The calcined material is then supplied to the rotary kiln for final clinkeringO Fuel ~ is supplied to the calciner for acheiving calcining temperatures ~`

r ~ and additional fuel is supplied to the kiln for achieving the clinkering temperatures. Early systems employing this se~uence are shown in U.S. Patents Nos. 1,468,168 and 1,557,873. More recent systems employing this flow pattern are shown in U.S.
~, Patent No. 3,452,968 and Japanese Patent No. 47-30405 issued August: ` ;
8, 1972 to Onoda Cement Company Ltd. With the more recent develop-ments, a '!flash calciner" is employed wherein combustion of fuel takes place in a vessel to produce high temperatures in the vessel, ~i and raw material is passed through the vessel. The high tempera- `
tures in the vessel result in rapid calcination of the ine solid -~particulate material.

~ `'',"~

~ '`''', i ~
,~ 624~
The more recent systems are beginning to make an impact , -on the Portland cement making industry in view of their ability J' ' '", .
to increase production capacity while employing a smaller kiln ,~
and achieving a more efficient production with a given amount of fuel. The more recent systems are primarily designed to operate with either oil or gas as a fuel. In order to have an apparatus -;
which is useful for all types of fuel and in particular coal, modifications to the known designs have become necessary. This is because it is necessary to increase the retention time of the fuel in the calciner vessel when coal is employed as a fuel as opposed to the retention time for oil or gas. Increasing the fuel retention time insures complete combustion of the fuel and . .
thereby provides an efficient system. `
SUMMARY
-~ It is therefore the principal object of this invention to provide an improved apparatus for calcining raw material which is capable of being operated with all types of fuel.
~ It is another object of this invention to provide an :~ apparatus for manufacturing Portland cement which employs a ~ 20 flash calciner which can be operated with all types of fuel.
!'' ~ ` It is a further object of this invention to provide a i~i calciner for raw material wherein the retention time of the fuel c;
;, in the calcining vessel is increased so that the calciner can be operated with coal.
In general, the foregoing and other ob~ects of this invention will be carried out by providing apparatus for calcining a raw material comprising a vessel having an inlet for combustion ~;~
air and an outlet for spent combustion air: an inlet for raw material to be calcined downstream of the inlet for combustion l 30 air in the direction of combustion air flow and burner means for ~ producing a co~bustion zone intermediate the inlet for raw ?'~
'~ material; said outlet for spent combustion air being an outlet -..
~ - 2 -, :

6Z46(~
~or calcined material and being downstream of said inlet for raw mAterial in the direction of combustion air flow, The objects will also be carried out by providing apparatus for calcining raw material comprising; a vessel having an inlet for raw material to be calcined, an inlet for fuel for .
combustion herein, means for producing a combustion zone m said ,?,~
vecsel and an outlet for spent combustion air and calcined material;`;~
said combustion zone and said outlet for spent combustion air in the direction of combustion air flow.
. 10 PREFERRED DESCRIPTION OF THE DR~WINGS
. , , . ~
~`~ The invention will be described in connection with the ;................... . .
annexed drawlngs wherein:

Figure 1 is a diagrammatic view of a clinkering system ~; -., .,~
i~/ employing the present invention;
Figure 2 is a view on an enlarged scale of the calciner of the present invention; i~
¢ .
Figure 3 is a view similar to Figure 2 showing a modification of the present invention;
Figure 4 is a view similar to Figure 1 showing a further ~; 20 modification of the present invention; and Figure 5 is a view similar to Figures 2 and 3 showing a still further modification of the present invention.
~`ji DESCRIPTION OF THE PREFERRED EMBODIMENTS
f,i;, - - - . ~ . . . .
Referring to the drawings, there is shown in Figure 1 a diagrammatic view of a system according to the present invention which may be used for manufacturing Portland cement. In general, ,j`
the apparatus includes in the direction of material flow a 'i;, preheater generally indicated at 1 which is in the form of a suspension preheater generally well known in the art. The pre-heater 1 is followed by a flash calciner generally indicated at -3, a clinkerer 5 in the form of a rOtary kiln and a cooler 6.

~æ`: - 3 - ' .. ;;~ " ,. . .
,~.. ~ . ;. . .
s,' .. i .. ...

106;~:46~
The preheater 1 includes a plurality of seriall~
connected gas sOlias separators in the form of cyclones 7, 8 and 9. The cyclone 7 includes an inlet 10 for gas and entrained solids, an outlet 11 for separated gases and an outlet 12 for separated solids. The cylone 8 includes an inlet 13 for gas and entrained solids, an outlet 14 for separated gases and an outlet 15 for separated solids. Similarly, the cyclone 9 includes an inlet 16 for gas and entrained solids, an outlet 17 for separated - gases and an outlet 18 for separated solids.
An .inlet 20 for raw materîal is provided in the out~et ' 14 of the cyclone 8. A high-efficiency dust collector 21 is flow connected to the outlet ll of the cyclone 7 and includes an outlet 22 suitably connected to a stack.
The flash calciner of the present invention is generally indicated at 3 and is flow connected in series to the preheater 1.
The calciner may be in the form shown in any of Figures 2, 3 or i 5, but for the present, that shown in Figure ? will be described.
Referring to Figure 2 there is shown a generally upright vessel ~ :
30 which includes a first portion 31 having a first diameter 20 and a second, upper portion having a second diameter larger than i~
the first diameter. A transition section33 may be provided. The vessel includes an inlet 34 for raw material to be calained flow ~ -connected to the outlet 18 o~ cyclone 9 of the preheater 1. In Figure 2, this inlet 34 is shown as located at the transition section 33, but may be located in the second portion 32. The vessel 30:also incluaes an inlet 35 for fuel which is suitably connected to a source 36 of fuel such as pulverized coal. A
burner 37 may be provided in the vessel 30 in the first portion 31.
- The burner may be centered in the vessel 30 or outside the vessel with the flame directed into the center of the vessel. The coal may be conveyed to the burner and the inlet 35 by compressed air as at 48 from a suita~le source. Depending upon the burner used, -,~

.' ''.

.- ~', ', ~ lOG2460 c igniter flame of oil such as that indicated at 49 my be required.' The burner produces a Combustion zone in the first portion 31 of the vessel. The inlet 34 for raw material to be calained is designed to direct material to~ard this combustion zone.
A source of combustion air is supplied from a conduit 3~ `~
to an inlet 39 of a vessel below the inlet 35 for fuel. If desired, a gas diffuslon or distributor plate 40 ma~ be provided ~-' above the combustion air inlet 39 and below the fuel inlet 35.
An outlet ~1 for calcined material and spent combustion air i5 `, provided in the top of the vessel 30. Thus, in the direction '~
of combustio'n gas flow, the combustion zone is ~ownstream of the `~
combustion gas inlet and upstream of the inlet for material to ,' be calcined and the spent combustion gas outlet. ''', A gas solids separator 43 in' the form of a cyclone is ,' flow connected to the vessel 30 by means o~ a conduit 44 connected , ;, to the outlet 41 of the vessel 30. The cyclone 43 includes a ',, ;
tangential'inlet 45 for the gas and entrained solids, a separated gas outlet 46, and a sepa'rated solids outlet 47. ,i ~ The clinkerer 5 in the form of a conventional rotary _, , kiln 50 is flow connected to the calciner 3 and in particular ~"
' is supplied raw material through conduit 47 from the cyclone 43. ,~
The discharge end 51 of the kiln 50 includes means 52 for supplying '' fuel to the kiln and means 53 for supplying combustion air to the ',~
, ~.
kiln. The fuel supplied to the kiln is used ~or clinkering the ~
~, .
raw'material. ' ''~
The cooler generally indicated at 6 in Figure 1 includes , means 61 for supplying cooling air for passage through a bed of hot material in the cooler 6. As the cool air passes through the hot material it serves to cool the hot clinker and the air is heated by such hot clinker. At least some of the thus heated air ;~
is supplied to the kiln 50 to serve as preheated combustion air. ~' This is supplied to the kiln through conduit 510 Additional .' '.'; '':
- 5 ~

"; :.'. .:.::

~6246~ 1 .. ` :
heated air is supplied through conduit 54 to the calciner 3 to serve as combustion air in the calciner 3. The remaining spent .....
cooled air is discharged into conduit 63 to a high-efficiency dust collector 64 for discharge to atmosphere.
In the embodiment shown in Figure 1, the calciner may include a mixlng chamber 70 and exhallst gases from the kiln 50 is supplied to this mixing chamber 70 through a suitable conduit .~:
.; , . ..
71 and the heated cooling air from conduit 54 is supplied to the mixing chamber 70. The combustion air conduit 38 of the calciner vessel 30 is connected to the mixing chamber 70. . .
In operation, raw material is supplied to the preheater l'A'; ~ '' ';
1 at 20 and in particular to the conduit connecting the outlet 14 ;~
of cyclone 8 and the inlet 10 of cyclone 7. Hot gases discharged ?~ .
. from cyclone 8 entrain the raw material and convey the same to `j~
inlet 10 of cyclone 7 thereby preheating the raw material a . ~, . .
certain amount. `~
In the cyclone 7 the particulate material is separated ~;
from the gas and discharged through the outlet 12 to the conduit ~. connecting the gas outlet 17 of cyclone 9 and the gas-solids in- .~
:; 20 let 13 of the cyclone 8. The gases are discharged from cyclone 7 ~.
through outlet ll to dust collector 21~ The solids from outlet 12 are entrained in the gases discharged from cyclone 9 and ~.
conveyed to the cyclone 8. Thesc gases further preheat the raw material. In the cyclone 8, the gases are separated to the out~ . ,.
let 14 and.the solids are discharged through conduit 15 into the ~:
gas outlet 46 of the cyclone 43 of the calciner 3. These hot .
gases entrain the solids and convey them to inlet 16 of the cyclone .
,;,.. ..
9. In the cyclone 9, the solids are separated from the gases and .:
discharged through conduit 18 to the inlet 34 of the calciner 3. . ~ :
In the calciner 3, the combustion takes place in the r- ,, first portion 31 and the preheated raw material is directed . .
downwardly into the combustion zone generally countercurrent to : .
. ~ . . .
., : . .
- 6 - .. : :
.
.; .

~` ~O~Z~60 ~ e upward flow of combustion gases. When coal is used as a fuel, complete combustion of the fuel takes longer than gas or oil.
It is important to keep the coal particles in the calciner until complete combustion takes place. Because the combustion air inlet is below the fuel supply inlet 35 and the combustion zone, the upwardly flowing air keeps the fuel and raw material in suspension and insures that all of the fuel is burne~ and will not drop out of the combustion zone~ With the raw material directed toward the combustion zone, the material passes through the combustion zone to achieve rapid or "flash" calcination of the raw material. The larger diameter portion 3~ serves to reauce i~
~, the velocity of gas ~lowing through the calciner 3 so that re-tention time in the vessel 30 will be increased and insure com- ;
plete calcination of the raw material. -~
With the addition to the calciner of preheated com-bustion air from the cooler and hot exhaust gases from the kiln, less fuel need be added directly to the calciner to achieve the `~
., . j'~'"
desired calcination temperature.
The spent combustion gas and calcined raw material are discharged from the vessel 30 at 41 and conveyed by conduit 44 to cyclone 43.- The separated gases are discharged at 46 and the separated solids are discharged at 47 and supplied to the clinkerer S for further processing. i;
In the modi~ication shown in Figure 3, the mixing chamber 70 has been eliminated and the exhaust gases from the clinker 5 are conveyed directly to the vessel 30 by conduit 71 and the hot gases from the cooler 6 are supplied to the vessel 30 ~ :
by conduit 54. The bottom of the vessel 30 serves as a mixing `
chamber. In the embodiment shown in Figure 3 the conduit 71 and 54 are spread around the vessel 30 to insure proper mixing of the spent cooler gases and the hot kiln exhaust gases. A1SQ in the embodiment of Figure 3 the distributor plate 40 has been removed. i`
*,'.'.',. ';.
- 7 - i ;

~ 106;~ 60 In the modification shown in Figure 4, the exhaust gases from the clinker 5 are not used in the calciner 3, but are ..`
supplied directly to the preheater l, bypa5sing the calciner 3.
All of the combustion air used by the calciner 3 is supplied ~;:
from the condiuit 54 from the cooler ~
In the modification shown in Figure 5, the raw material .
is supplied to the calciner 3 ~elow the fuel source 35 and com~
bustion zone rather than above the fuel inlet 35 as shown in .
Figures 2 and 3. It is beli.eved that by supplying the raw material with the combustion air below the combustion zone, proper mixing of the fuel and raw material and combustion air will take place. As in the embodiments of Figures 2 and 3 the calcined -.
material outlet is located at the top of the vessel.30. :
From the foregoing it should be apparent that the objects of the present invention have been carried out. The calcining vessel serves to rapidly calcine the solid particulate material. .~ :.
The combustion air and.raw material inlets, the combustion zone and the calcined material and spent combustion gas outlet are -~
positioned to insure complete combustion.of the fuel and compleke . calcination of the raw. material. This arrangement is particularly ~; .
~ advantageous for using coal as a fuel. ~ ~:
:~ - It is intended that the foregoing be merely a des ;;~
cription of a preferred embodiment and that the inv~ntion be ..
limited solely by that which is within the scope of the appended ,`A ' cl aims . . . , ' i'~
"~
'',~' "...
',-' .' '1, "
'I'i ~,, .

- 8 ~ ~;
., '' ' " .

Claims (2)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. Apparatus for calcining raw material comprising:
a vessel having an inlet for raw material to be calcined, means for producing a combustion zone in said vessel, including an inlet for fuel, an inlet for combustion air and an outlet for spent combustion air and calcined material;
said inlet for raw material and combustion air being located upstream of said inlet for fuel and said outlet for spent combustion air in the direction of combustion air flow.

2. Apparatus according to claim 1 further comprising means for supplying fuel to said means for producing a combustion zone and said fuel is coal.