Method and plant such as a kiln plant for treating granular or pulverous raw material

A method is disclosed for treating granular or pulverous raw material in a kiln plant including a preheater stage, a precalciner stage and a separator stage coupled to one another. Precalcined material is separated after the separator stage into a first and second material flow. The first material flow is suspended in spent cooling air and fed to a reaction zone zone for burning and melting the material therein. The melted material is fed to a cyclone for separating smoke gases therefrom and thereafter to a rotating nodulization drum. The second material flow is also fed to the rotating nudulization drum and mixed therein with the melted material so as to avoid any sticking and clogging of the melt. A kiln for practicing the method of the present invention is also disclosed. In preferred alternative embodiments, the reaction chamber can be either a shaft-like chamber or a cyclone burner.

TECHNICAL FIELD 
The invention relates to a method and an apparatus for burning granular or 
pulverous raw material for instance cement raw material. 
BACKGROUND ART 
For many years manufacture of cement and the like has preferentially taken 
place in kiln plant including a rotary kiln allowing for, compared with 
shaft kilns, a continuous treatment of raw materials fed to the plant. The 
development of such rotary kiln plant has through recent times undergone a 
change towards reducing the size of the mechanically rather complicated 
kiln construction by arranging some of the previous functions of the 
rotary kiln to take place in stationary parts of the plant such as 
separate preheating and precalcining installations. Such plants are known 
for example from British Patent Specifications Nos. 1,108,589, 1,434,091 
and 1,428,828 according to which the rotary kiln carries out two functions 
in addition to the transport function of treated materials, namely heating 
from about 900.degree. C. to the reaction temperature in the kiln of the 
material precalcined in the precalcination zone, and providing retention 
time in the kiln for the reacting material under treatment. 
The next logical step in this development is to move the heating function 
from the rotary kiln out into a separate, stationary installation thereby 
making it possible to further reduce the functions of the rotating plant 
installation. This reduction is desirable due to smaller overall 
construction costs and a better running or operating economy of the plant. 
A plant of this type is known from German OLS No. 2,846,584. However, the 
problem of moving the heating function to a stationary installation may be 
encumbered by the melting of as much as 20% of the material. Such melting 
may cause the charge to stick and clog and therefore render the charge 
difficult to handle during further treatment in the plant. 
I have invented a method and a kiln plant where the heating of the treated 
material to its reaction temperature takes place in a stationary burning 
installation and where the above mentioned problem concerning 
transportation of treated material in the plant has been solved. 
DISCLOSURE OF THE INVENTION 
According to the present invention, a method of treating granular or 
pulverous raw material, e.g., cement raw material, comprises preheating 
and precalcining the raw material in suspension; separating the 
precalcined material from smoke gases; providing two separate subsidiary 
flows of the precalcined material; feeding one of the subsidiary flows to 
a stationary burner chamber for burning in suspension and at least partial 
melting of the material; separating this material from smoke gases and 
feeding it to a nodulising zone; feeding the other subsidiary material 
flow to the nodulising zone for mixing with the material from the burning 
chamber for burning in suspension and at least partial melting of the 
material; separating this material from smoke gases and feeding it to a 
nodulising zone; feeding the other subsidiary material flow to the 
nodulising zone for mixing with the material from the burning chamber 
whereby the mixed material is subjected to a final reaction and 
nodulisation during its retention in the nodulising zone; and feeding the 
material from the nodulising zone to a cooler. 
In particular, the method comprises mixing the melted material flow and the 
second material flow in a rotating nodulisation drum in predetermined 
proportions such that the heat proper of the mixture is solely sufficient 
for the final reaction and nodulisation of the treated material. 
The present invention also relates to a plant for carrying out the 
above-mentioned method, the plant being characterised by means for 
preheating and precalcining the raw material, means for providing the two 
separate subsidiary material flows, means for leading the one subsidiary 
flow to a stationary burning chamber, means for separating this material 
from smoke gases and feeding it to a rotating nodulisation drum defining a 
nodulisation zone, means for leading the other subsidiary flow directly to 
the drum for mixing with the material from the burning chamber, and means 
for leading the nodulised product from the drum to a cooler. 
Preferably, the plant for treating pulverous raw materials comprises means 
for preheating the material in a preheating zone, means for precalcining 
the preheated material in a precalcination zone, means for separating the 
precalcined material from smoke gases in a separator zone, means for 
dividing the separated material into a first material flow and a second 
material flow, means for suspending the first material flow in cooling air 
from a cooler, means for burning and melting the suspended first material 
flow in a generally stationary reaction zone, means for separating the 
melted material flow from smoke gases, means for feeding the melted 
material flow to the nodulisation zone, means for feeding the second 
material flow to the nodulisation zone for mixing with the melted material 
flow so that the mixture is nodulised therein, and means for feeding the 
nodulised mixed material flows to a cooler. 
After the treatment in a preheating zone for preheating the material, and 
in a precalcination zone for removal of carbon dioxide from the material, 
the material is separated and part fed to a reaction zone in a stationary 
burning chamber where significant burning of the material in suspension 
and melting takes place. Thereafter the at least partly melted material is 
separated from the hot gases and fed to a nodulising zone, preferably a 
rotating nodulising chamber, where the material is mixed with other 
precalcined material. Powdery precalcined material fed directly to the 
nodulisating zone coats the melted material particles so that the problem 
of sticking or clogging is mitigated. The mixture then undergoes a final 
reaction during its retention in the nodulising zone, the overall 
temperature of the mixture ensuring that the finished reaction including 
the nodulisation can preferably take place without the supply of any other 
heat to the nodulising zone other than that already contained in the 
material supplied thereto. 
The first material flow is preferably suspended in spent cooling air when 
fed to the burning chamber. The stationary burning chamber may be a 
shaft-like chamber, or a cyclone burner. In the latter case, the cyclone 
burner will act both as the burning chamber and as the separator in which 
the burnt material is separated from the smoke gases before being fed to 
the nodulising zone. The hot gas from which the burnt material is 
separated, before being fed to the nodulizing zone, is preferably fed to 
the precalcination zone for use as combustion air. 
Pipes feeding spent cooling air from the cooler to the burning chamber 
and/or the precalciner, may be provided with movable dampers for 
regulating the gas streams. 
The preheated and precalcined material may be divided into the two 
subsidiary material flows by the use for example of a splitting gate. 
Alternatively, the two subsidiary flows may be provided by the use of a 
two string preheater and precalciner working in parallel.

BEST MODE FOR CARRYING OUT THE INVENTION 
In the FIGS., the same reference numerals are used for identical or like 
parts of the apparatus according to the present invention. 
Raw material is fed to a preheater installation 1 at an inlet 2 the 
preheater installation being of a known multistep cyclone type or shaft 
type. Preheated material leaves the preheater via a pipe 11 and is fed to 
a precalciner 3, directly through pipe 11b and/or via a pipe 11c and a 
riser pipe 16. Flow through pipes 11b and 11c is regulated by a valve 11a. 
Fuel is fed at 15 to the precalciner 3 and combustion air is supplied 
through the pipe 16 and a pipe 18. Precalcined material leaves the 
precalciner 3 in suspension via pipe 10 and is separated from the hot 
smoke gases in a separator 4. The hot smoke gases are fed to the preheater 
installation 1 via a pipe 9 and are drawn through the preheater by a fan 
24 in an exhaust pipe 23. 
Separated, precalcined material is, at a splitting gate 12 immediately 
after the separator 4, divided into two subsidiary flows. One of these 
flows, amounting to 25-75% of the total is, via a pipe 13, led to the pipe 
18 for suspension in spent cooling air from a cooler 8. The suspension is 
fed to a vertical, tubular or shaftlike burning or reaction chamber 6 as 
shown in FIG. 1 for burning and melting the material. The chamber has fuel 
inlets and burners 19. Melted material and smoke gases leave the reaction 
chamber 6 through a pipe 20 leading to a cyclone 5 in which the melt is 
separated from the smoke gases. The latter are fed as combustion air to 
the precalciner 3 via the pipe 16 as mentioned above, whereas the melt, 
via a pipe 17, is fed to a rotating nodulisation drum 7. The other 
subsidiary, precalcined, powdery material flow, amounting to 75-25% of the 
total is, via the splitting gate 12 and a pipe 14, fed directly to the 
inlet of the drum 7 to be mixed in the drum with the melt. This mixing 
prevents the risk of sticking and clogging of the melt during its 
treatment in the drum 7. Also, the heat proper contained in the melt and 
in the subsidiary second material flow respectively ensures that the final 
reaction in the form of nodulisation of the product in the drum 7 takes 
place. The product leaves the drum 7 through a pipe 21 and is fed to the 
cooler 8, from which it leaves as the final product at 22. 
In the embodiment shown in FIG. 2 the reaction zone for burning and melting 
the treated material is a cyclone burner 60 instead of the shaft-like 
chamber 6. The cyclone burner 60 has a fuel inlet and a burner 
installation 61, and precalcined material to be treated in the reaction 
zone is fed to an upper part 50 of the pipe 18 for suspension here in 
spent cooling air from the cooler 8 before being fed to the cyclone burner 
60. Also, in this case the spent cooling air acts as combustion air both 
in the cyclone burner 60 and in the precalciner 3. 
Movable dampers 25 and 26 are used for regulating the combustion air supply 
to the reaction zones 6, 60, and the precalciner 3.