Method for the manufacture of calcareous bonding agents, particularly cement

A method and apparatus for the manufacture of calcareous bonding agents, particularly cement, through the burning of finely grained substances by means of hot gases. The finely grained materials in the form of a suspension pass through a preheating and calcining zone where ordinarily accumulations of alkali and chlorine leading to deposits and incrustations in the lines would occur. In order to minimize such deposit formation, a branch stream of suspended particles is removed from the main stream and the finely grained solid matter contained therein is burned to clinker in a separate reaction zone in suspension with a combustible gas. The airborne clinker thus produced may be eventually recombined with the clinker produced from the main line stream which passes through a rotary kiln.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention is in the field of treating calcareous bonding 
agents, particularly cement, involving the calcining of finely grained 
solids, the latter being conveyed by means of hot gases through a 
preheating and calcining zone, and subsequently into a rotary kiln where 
the solid matter separated from the hot gases is converted into clinker. 
The clinker is then cooled and ground to a cement product. The present 
invention involves separating off a branch stream of the suspended solid 
particles and treating them in parallel with the rotary kiln to produce an 
airborne clinker. 
2. Description of the Prior Art 
It is well known that cement calcining systems are susceptible to a 
build-up of alkali and chlorine compounds during the internal circulation 
of the suspended materials in the calcining system. In order to 
effectively counteract the known difficulties resulting therefrom, 
particularly due to the deposition of incrustations, it has previously 
been proposed to remove from the primary gas circulation stream between 
the rotary kiln and the heat exchanger system, a partial stream, to cool 
the stream for condensation of the harmful substances, to deposit and 
dispose of the harmful substances in the form of dust, and to exhaust the 
remaining gas in a bypass. 
This existing system leads to losses of heat energy in the discharged 
partial gas current, as well as losses of solids. An additional 
disadvantage is the fact that the elimination or the further utilization 
of the dust deposited in the bypass installation must be eliminated from 
the production process. The difficulties caused by such deposition are 
detailed in the publication "Zement-Kalk-Gips", Vol. 5, 1962, page 203. 
SUMMARY OF THE INVENTION 
The present invention seeks to reduce harmful substance accumulations to a 
tolerable degree for undisturbed continuous operation and to reduce, if 
not largely avoid, the losses of heat and material and thereby reduce the 
manufacturing costs of cement production. In addition, the outlay of 
capital expenditure costs is to be achieved through a further reduction of 
the dimensions of the rotary kiln as well as the clinker cooler and the 
grinding installation for grinding the clinker aggregate. 
Basically, the present invention involves separating a branch stream from 
the main stream of suspended cement meal being processed and conveyed 
through the preheating and calcining zone, the branch stream with the fine 
grained solid material contained therein is thereupon calcined to clinker 
in a separate reaction zone in suspension in a combustible gas. 
Through the use of the present invention, there is an advantage that the 
hot raw meal contained in the branch stream need not be driven off from 
the system. As a consequence, in accordance with one of the underlying 
objectives, losses of material energy and heat energy are avoided. Because 
a relatively high fraction of chlorine and alkali compounds is contained 
in the branch stream, the alkali and chlorine management is so 
advantageously controlled that a building up of the alkali and chlorine in 
the kiln system and, in particular, in the heat exchanger system is 
substantially prevented. The branching-off of the side stream according to 
the present invention proceeds at a location between the preheating zone 
and the clinker reactor. At this location, concentrations in the meal of 
chlorine compounds and alkali compounds are comparatively high for which 
reason a relatively low quantity of the branched stream is sufficient in 
order to maintain an undisturbed circulatory equilibrium. 
In a preferred embodiment, the branching off of the branch stream proceeds 
at a temperature between 450.degree. and 950.degree. C. and preferably in 
the range from 750.degree. and 950.degree. C. 
In another preferred form of the invention, the branch stream is burned in 
a suspension reactor with the addition of a gaseous fuel. It is further 
provided that the branch stream in the suspension reactor is burned by 
means of a combustible gas at temperatures in the range of alite 
formation, which exist at about 1,250.degree. to 1,400.degree. C. At these 
temperatures, chlorides are volatilized, and thus the most frequently 
harmful chlorine compounds in the material to be burned are reduced 
whereas the concentration of alkali sulphates may possibly increase due to 
the sulphur concentration of the supplied fuel. 
There is another advantage that the branch stream, after the clinker 
burning, is separated into solid matter and gas, with the solid matter 
being cooled in a dust cooler and subsequently at least partially mixed 
with mill cement. By this measure, several advantages are realized. For 
one, the load on the clinker cooler is reduced and, for another, a solid 
matter loss is very advantageously prevented. Finally, mill capacity and 
grinding energy are saved since the dust or pulverized clinker need not, 
for the most part, be ground to reduce its coarse grain. 
Another advantage resulting from the invention is that the combustible gas 
separated from the solid matter, with a low harmful substance 
concentration, can at least partially be returned to the preheating zone. 
A loss of heat energy is thus avoided. This is permissible in many cases 
because the predominating portion of the harmful substances is bound to 
the finely grained solid matter. In the case of a higher harmful substance 
concentration in the combustible gas, it is possible for the gas to be 
driven off at least partially in a bypass. This flexibility is one of the 
significant advantages of the method of the present invention. 
An additional recovery of heat is also possible in that hot exhaust air 
from the dust cooler may be conveyed in the form of tertiary air into the 
calcining zone. This procedure has a particularly favorable effect in the 
case of systems in which the air flow combustion for the calcinator is 
drawn by the rotary kiln, which systems accordingly do not possess any 
separate tertiary air line. 
A significant embodiment of the method of the present invention consists in 
suspending fine grained solid matter such as cement meal in hot gas, 
preheating the same, dehydrating the same, and at least partially 
calcining it. The stream is then divided into a primary and a branch 
stream. The solid matter is conveyed in a main stream after separation 
from the suspending gas in a rotary kiln, and is burned to a clinker. The 
solid matter carried along in the branch stream which is in suspension in 
a combustible gas is passed to a parallel burning operation in a 
suspension type reactor adjacent the rotary kiln where it is burned to 
form an airborne dust clinker. The rotary kiln clinker is cooled in a 
clinker cooler and the airborne dust clinker is cooled next to the clinker 
cooler in a dust cooler. The rotary kiln clinker is ground and is 
processed with the fine grained airborne dust clinker, with the possible 
addition of additional substances, to form the end product. Thus, a 
possibly excessive high free calcium concentration, particularly in the 
airborne dust clinker is at least partially reduced. 
An additional feature of the present invention provides for the addition of 
iron carriers such as iron oxide in the region between the branching-off 
of the branch stream and the rotary kiln. These iron carriers involve the 
addition of melt phase-forming iron oxide compounds and the like which up 
to the present time have customarily been added to the furnace inlet meal 
during the raw meal dressing. 
In the method of the present invention, it is advantageous that only a very 
low fraction of melt phase-forming compounds is contained in the branch 
stream in order to not endanger the operation of the suspension or 
airborne dust reactor as well as the separator connected thereafter. This 
can be achieved according to the present invention since the addition of 
iron carriers proceeds only in the region between the branching-off of the 
branch current and the rotary kiln. 
The apparatus for the manufacture of calcareous bonding agents according to 
the present invention includes a preheater, a calcinator, a rotary kiln 
which functions as the clinker burning installation, a clinker cooler and 
optionally a subsequent clinker grinding system. Between the preheater and 
the clinker burning installation there is provided a branch for a stream 
of suspended particles which empties into a suspension reactor or airborne 
dust reactor, respectively. With this arrangement, a compact system 
results whose capital expenditure costs are reduced by virtue of the fact 
that both the clinker reactor as well as the clinker cooler and the 
subsequent clinker grinding installation can be reduced by a proportion of 
capacity which corresponds to the throughput in the branch circuit. Since 
the airborne reactor is a stationary installation in comparison with the 
rotary kiln, this type of reactor uses smaller dimensions, and has lower 
radiation losses, higher thermal efficiencies, and relatively lower 
capital expenditures. The airborne dust reactor includes at least one 
inlet for the addition of fuel. The airborne dust collector is connected 
to a solid/gas separating installation which comprises a solid discharge 
means which advantageously discharges into a dust cooler. 
Further advantages are achieved in that the solid discharge of the dust 
cooler after possibly being temporarily stored in a storage bin, is 
subjected to transport to an apparatus for mixing and/or homogenizing. In 
this apparatus, the discharge of the clinker cooler and grinding system is 
combined with the solid discharge from the dust cooler to produce a final 
product. Accordingly, different cement products can be manufactured by 
blending various amounts of mill cement with airborne dust clinker and 
possibly additional additives. 
In accordance with the present invention, the dust cooler is equipped with 
an exhaust air line which is connected to the calcinator. Consequently, 
the heat energy contained in the airborne dust clinker is recuperated and 
introduced as hot tertiary air into the calcinator. This produces an 
efficient use of additional hot tertiary air for the reactions occurring 
in the calcinator and provides special advantages in the case of systems 
that have no separate tertiary air line and as a consequence must draw 
combustion air for the calcinator in the form of air passing through the 
furnace. 
In order to get rid of the harmful substances, at least a portion of the 
exhaust gas occurring in the separating installation can be discharged in 
the bypass. An additional bypass line can be connected to the exhaust gas 
line, and throttle members are provided in both lines.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The system shown in FIG. 1 includes a meal inlet 25 which delivers the raw 
meal to a heat exchanger system identified generally at reference numeral 
1. Following the heat exchanger 1 is a calciner 2, a rotary kiln 3, and a 
clinker cooler 4 through which cool air is admitted through an inlet 4'. 
The system also has a clinker grinding system 5 as well as a mixing and 
homogenizing installation 15 into which a cooled dust clinker is admitted 
through a line 42, mill cement through a line 43, and, optionally, an 
additive through a line 44. The result is a mixed product of calcareous 
bonding agents, consisting of cement which is discharged through a 
discharge line 18. 
In the region of the calcinator 2 there is a branch conduit 6 which leads 
to a suspension reactor or airborne dust reactor identified at reference 
numeral 7. It will be seen that the reactor 7 is in parallel relationship 
with the rotary kiln 3. Fuel is added to the calcinator 2 by means of a 
line 26 and to the airborne dust reactor 7 by means of a line 28. The 
branch stream in suspension in gas enters the airborne dust reactor 7 at 
temperatures between 450.degree. and 950.degree. C., preferably in the 
range from 750.degree. to 950.degree. C. where it is heated through 
combustion of the fuel entering through the inlet 28 to alite formation 
temperatures of between 1,250.degree. and 1,450.degree. C. The fine 
grained solid matter is thus burned to an airborne dust clinker. In the 
following separation installation 8, the separation of solid and gas takes 
place and the solids, by means of the line 45, are introduced into a dust 
cooler 9. The latter receives cooling air through a blower 10 and releases 
heated tertiary air by means of a line 11 into the calcinator 2. The 
cooled airborne dust clinker is discharged into an intermediate receptacle 
12 and temporarily stored therein. A conveyor member 13 supplies the 
cooled airborne dust clinker as required to a transport installation 14 
and subsequently to the inlet line 42 leading to the mixing and 
homogenization installation 15. 
In the separation installation 8, exhaust gas which has been separated from 
the solid matter is removed through an exhaust line 46 and, depending upon 
the concentration of harmful substances is either supplied by means of a 
line 21 to the heat exchanger system 1 or in the case of high harmful 
substance concentration, is conducted into the air by means of a bypass 
line 22, an exhaust gas cleaner 23 and then an exhauster 24. A gas branch 
line 29 may also be provided to deliver the gas to a heat utilization 
source 30. 
Fuel is supplied to the rotary kiln 3 through an inlet 27, and the fuel in 
the overall heat balance can be reduced by the fraction of the fuel 
supplied to the airborne dust reactor through the line 28. Since the 
airborne dust reactor 7 in comparison with the rotary kiln 3 possesses 
smaller exterior dimensions, and as a consequence of the high active 
surface properties of the airborne dust, it achieves a substantially 
better efficiency in the case of heat transfer than the rotary kiln 3. 
Therefore, there exists a higher utilization degree of the primary source 
of energy and to this extent an increased economy in operation results. 
From the clinker cooler 4 there is a tertiary air line 41 which leads to 
the calcinator 2. The latter also, in the case of the new system, can be 
kept smaller in its dimensions than customarily since with the additional 
tertiary air line 11, high temperature tertiary air is introduced from the 
dust cooler 9 into the calcinator 2. The system may also include inlets 17 
for the addition of plaster of paris and/or other additives to the clinker 
grinding system 5 or to the mixing and homogenizing system 15, 
respectively. The gas flow of the system which is conveyed in 
countercurrent relation to the furnace meal inlet 25 after delivery of its 
useable heat content by means of the exhauster 19 is removed from the 
system and customarily is passed through a gas cleaning apparatus 20. 
In FIG. 2, the same system is illustrated as in FIG. 1 in a more schematic 
representation. The individual functional areas such as the heat exchanger 
system 1, calcinator 2, rotary kiln 3, clinker cooler 4, separator 
grinding system 5, airborne reactor 7, and the cyclone cooler 9 are 
illustrated in fields bounded by dash-dot lines. The same functional 
elements as in FIG. 1 are identified with the same reference numerals. 
The heat exchanger system 1 includes a charging installation 25 for the 
furnace inlet meal and in addition has four cyclone stages 31 through 34. 
The calcinator 2 comprises a reaction column 35 as well as a depositor 35' 
and at least one charging point 26 for fuel. The rotary kiln 3 is 
connected with the clinker cooler 4 in the usual fashion through a common 
housing part in which a burner 27 is arranged. The cooler 4 comprises a 
cooling air blower 4' and in addition a transport installation 47 for 
charging cooled clinker into the grinding system 5. The latter, in turn, 
includes a mill 37 with a hot gas supply 39 as well as a sifter or 
separator 48. Coarse powder is discharged through a line 40, the finished 
product goes into a depositor 38 and then into a finished product 
discharge line 18. Indicated purely schematically is a transport 
installation 14 from the dust cooler 9 by means of an intermediate storage 
installation 12, 13 shown in FIG. 1. 
In the example of FIG. 2, a sifter 48 simultaneously serves as a mixing and 
homogenizing device and combines this function with the advantage that 
minor oversized powder components, possibly contained in the dust clinker, 
are separated from the fine product and by means of the coarse powder 
discharge line 40 are supplied to the mill 37 for crushing. The sample 
embodiment in FIG. 2 further shows a branch 6 of the branch circuit from 
the region of the calcinator 2 to the subsequent suspension reactor or 
airborne dust reactor 5, respectively. The latter includes a reaction zone 
36 having fuel charge inlets 28, 28' and 28". In addition, the airborne 
dust reactor 7 includes a separating installation 8 provided with a 
discharge line 45 which delivers hot airborne dust clinker into the 
cyclone cooler 9. The latter contains two cyclone cooling stages 49 and 50 
with fans or blowers 10 arranged between the two. A charging inlet for 
iron compounds is indicated in the region of the rotary kiln inlet by an 
arrow 56 in a purely schematic fashion. 
The operation of the device is apparent from the sample embodiments 
illustrated in FIGS. 1 and 2. A furnace inlet meal charged into the inlet 
line 25 is heated in the heat exchanger system 1 by passing through the 
heat exchanger cyclone stages 31 through 34 in countercurrent relationship 
with hot gas. The heated raw meal is delivered from the lowest cyclone 
stage 34 by means of a line 51 to a connection line 52 running from the 
rotary kiln head to the calcinator 2. It is there completely calcined 
pursuant to the supply of fuel entering through the line 26 together with 
tertiary air from a line 41 as well as hot furnace gases from the rotary 
kiln 3 in the reaction column 35 at temperatures of about 950.degree. C. 
The meal is then separated in the separator 35' from the gas and delivered 
by means of the line 53 into the furnace inlet head of the rotary kiln 3. 
There, the mealy calcined product in the product bed, possibly with the 
addition of iron carriers to the line 56, is burned to clinker 
temperatures up to about 1450.degree. C. The clinker is cooled in the 
clinker cooler 4 to such an extent that the cooled clinker can be charged 
into the mill 37. 
In accordance with the present invention, a suspension branch stream is 
branched off through the branch line 6 from the main suspension stream in 
the region of the calcinator 2 and, in the suspension reactor or airborne 
dust reactor 7, is delivered through the reaction zone 36. With the 
addition of fuel at the inlet points 28, 28' and 28", the branch stream is 
burned at clinker temperatures of between 1,250.degree. and 1,400.degree. 
C. In the separator 8, the airborne dust clinker is separated from the gas 
current and by means of a line 45 is charged to the cyclone cooler 9 
wherein it is delivered in the conventional manner through cyclone cooling 
stages 49 and 50 in direct contact with cooling air. After cooling, it is 
charged at temperatures of about 150.degree. C. through the transport 
installation 10 into the stream of the separator grinding system between 
the mill 37 and the separator 48. That portion of the airborne dust 
clinker which has a satisfactory fineness in accordance with 
specifications, is then discharged through the separator line 54 into the 
separator and subsequently into a discharge line 18. Oversized powder 
together with coarse powder or granules is supplied through coarse powder 
inlet line 40 to the charging side of the mill 37. In this manner, an 
absolutely homogeneous mixing of mill cement and airborne dust clinker to 
provide the end product is obtained. 
As is apparent from FIG. 1, inlet line 17 may be used to supply plaster of 
paris and/or other additives to the mill 37 or to the homogenizing and 
mixing installation 15. Entering into the airborne dust reactor 7 through 
the branch line 6 are components of mineral meal, enriched with alkali and 
chlorine compounds from the burning system. The removal of these harmful 
components in this fashion unburdens the interior circulation of the 
burning system and prevents building up harmful accumulations of these 
substances. As a consequence of the clinker burning stage up to 
temperatures of around 1,350.degree. C., chlorine compounds are thus 
volatilized and either conducted into the free air in the exhaust gas of 
the airborne dust reactor by means of line 21, through the cyclone 
preheater 1 and the exhauster 19, or at least partially driven off by 
means of the bypass line 22. In both lines 21 and 22 there are provided 
throttle members 55 which render possible an adjustment of the exhaust gas 
partial stream. 
By branching off the branch stream in the line 6 not only is the interior 
circulatory system of the burning system unburdened, but also the quantity 
of materials passing through the rotary kiln 3 is reduced by a factor of 
usually 10 to 15%. As a consequence, the rotary kiln 3 can be reduced in 
dimensions, thus providing savings in capital expenditures and operating 
costs. In addition, the system through the steps of product-mixing, 
possesses the advantage of a multiple variable adjustment of cement 
properties. Through the production of the airborne dust clinker, grinding 
energy and heat energy are saved. 
Also significant is the disposition of the rotary kiln unit and the dust 
clinker unit in parallel in a common production unit as well as the 
possibility of mixing mill cement with dust clinker during or after the 
cement grinding so as to obtain or modify different optimum cement 
properties. 
It should be evident that various modifications can be made to the 
described embodiments without departing from the scope of the present 
invention.