Diagnosis method of rotary kiln interior

A method for diagnosing the interior of a rotary kiln, which method permits one to make a correct determination as to the state of deposit of ash on the inner wall of the rotary kiln. According to the method, a detector is inserted into a gas stream from the rotary kiln and kept there for a certain period of time so as to allow ash to deposit thereon. Then, the weight, density and composition of the thus-formed deposit of ash are determined. The weight is corrected in view of the ash present in pulverized coal which was used as a fuel for burners, thereby obtaining corrected ash deposit weight (Wa). The weight is also corrected in accordance with the percentage of fine iron ores present in prefired pellets and the percentage of fine iron ores present in the deposit of ash and determined by the composition of the deposit and that of the fine iron ores, thereby obtaining corrected weight (Wd) of the deposited fine iron ores. The weight of ash deposited at an elevated temperature zone in the kiln is also determined as "Ri" from Wd and the density of the deposit of ash. The extent of deposit of ash on the inner wall of the kiln is determined by comparing either one of the weight of the deposit of ash, Wa and Wd with its corresponding reference value while taking its density and optionally Ri into consideration. The above method permits one to enlarge the range of usable coal sources.

BACKGROUND OF THE INVENTION 
(1) Field of the Invention 
This invention relates to a method for diagnosing the interior of a rotary 
kiln employed for firing pellets of iron ore, calcining lime, sintering 
chromium ore or the like, and especially to a method for diagnosing the 
interior of such a kiln as mentioned above which method permits to make a 
correct determination as to the state of deposit of ash which occurs as a 
problem when pulverized coal is used as a indurating heat source. 
The present invention will be described with the induration work of pellets 
of iron ore as its principal application field, but the present invention 
can be equally utilized in a variety of other field such as lime-calcining 
kilns. 
(2) Description of the Prior Art 
As indurating methods of iron ore pellets, there have been known, roughly 
breaking down, three different types of systems which are the shaft kiln 
system, the travelling grate system and the grate-kiln system. Among these 
systems, it is the grate-kiln system or its improved model that the 
present invention pertains to. According to the grate-kiln system, the 
drying and preheating (hereinafter called merely "preheating") of green 
pellets is carried out on a travelling grate and, after indurating the 
thus-preheated pellets completely in a rotary kiln, the resultant 
indurated pellets are then cooled in a cooling apparatus which is 
generally called an annular cooled. These three processing steps are 
allotted to different facilities respectively but these facilities are 
closely connected and operated practically as a single unit. For example, 
the heating of the travelling grate is effected in its entirety by means 
of burners only, which burners are provided at the discharge end of the 
rotary kiln. Thus, the travelling grate unit (i.e., the travelling grate) 
is not provided with any rows of burners and its heating is dependent on a 
high-temperature gas supplied from the rotary kiln. This system enjoys 
such merits that pellets are subjected to little disintegration thereby 
assuring a high production yield and a uniform firing operation, because 
green pellets are kept in a stationary state on pallets during their 
preheating periods, in which the strength of green pelllets becomes 
lowest, and are indurated in the rotary kiln while caused to undergo 
cascading therein. Besides, the heat of off gas from the rotary kiln is 
used as a heat source for the preheating as is and the low heat 
efficiency, which is considered to be a common defect of general rotary 
kiln systems, does not become a problem from the practical viewpoint of 
the grate-kiln system. 
Although the grate-kiln system enjoys such merits as mentioned above, it 
still involves as an unsolved problem the problem common to the rotary 
kiln system, namely, the occurrence of rings. Therefore, rings must be 
removed at every scheduled shut-down which is carried out rather often. 
Such rings tend to develop intensively, especially, at two locations of a 
rotary kiln, i.e., at the feed end and an high temperature zone of the 
rotary kiln. As causes for the development of such rings, matter 
pertaining heat, heat properties of charged raw materials, the quality and 
quantity of iron ore dust resulting from the raw materials and the like 
are considered to interact, although their method of interaction has not 
yet been elucidated completely. On the other hand, it has become an 
important subject in the present field of art to regard coal as a fuel in 
the light of various changes surrounding oil, resulting in an change in 
the fuel injected from burners provided at the discharge end of each 
rotary kiln, or other words, leading to the conversion to pulverized coal. 
However, pulverized coal fuel contains a great deal of ash derived from 
coal and tends to promote the development of the above-mentioned rings. 
Thus, some coal-fired rotary kilns become unable to continue operations 
before their next scheduled shut-down. 
It is also known that occurrence of such rings takes place in various ways 
or fashions depending on the type of coal and as fuel materials (place of 
mine and kind of coal). According to a report on "A Study of Coal Firing 
in the Grate-Kiln System" (addressed at the 50th AIME Annual Meeting held 
in January, 1977), it is mentioned that use of coal having a DP 
(Deposition Parameter) value over 300, which DP value is given in 
accordance with the following empirical equation: 
##EQU1## 
where A means the percentage of ash and H.sub.v stands for the net heat 
value (unit: British Thermal Unit/lbs.) and indicates the susceptibility 
of deposition of ash and its analogous substances at the feed-end of a 
rotary kiln, is not recommendable because deposition of ash becomes severe 
at the feed-end of the rotary kiln. 
Furthermore, the susceptibility of ash deposition at a high temperature 
zone of a rotary kiln is represented by RP (Ringing Parameter). Any coals 
having RP values exceeding 150, which RP values are given by the following 
experimental equation: 
##EQU2## 
where F.multidot.T means the fluid temperature of the ash in an oxidizing 
atmosphere, expressed in terms of .degree.F., are said to be 
unrecommendable as they lead to considerable deposition of ash at the 
aforementioned high temperature zone. When using pulverized coal as a 
fuel, it is recommendable to determine DP and RP whenever the coal is 
changed from one supply source to another and to conduct the operation by 
principally using coals which satisfy DP.ltoreq.300 and RP.ltoreq.150. 
However, this operation method permits to use only coals which practically 
meet the above reference values. Accordingly, the above operation method 
is not only unable to contribute to the reduction of production cost but 
is also extremely poor in adaptability to situations as it cannot provide 
any countermeasure even if a change in the state of deposition of ash is 
observed following a change in operational conditions. 
SUMMARY OF THE INVENTION 
With the foregoing in view, a method which is capable of being successfully 
applied to a variety of coals to be supplied (more specifically, 
applicable to coals having high DP or RP values), permitting to 
satisfactorily use coals which have heretofore been considered as poor 
coals in view of their DP and RP values, and controlling the deposition of 
ash by precisely knowing the actual state of ash deposition and 
controlling the operational conditions in accordance with the actual state 
of ash deposition has been eagerly awaited. 
The present invention has been completed taking the above-mentioned state 
of the art into consideration. The present inventors thought that it would 
be necessary to give the priority for the establishment of means for 
precisely determining the state of deposition of ash in a rotary kiln in 
order to meet the above requirements, leading to completion of this 
invention. 
In one aspect of this invention, there is thus provided a method for 
diagnosing the interior of a rotary kiln operated using flames from 
pulverized coal burners as its heat source by determining the extent of 
deposition of ash and its analogous substances on the inner wall of the 
rotary kiln upon, after charging green pellets containing fine ore or the 
like as its principal raw material in a travelling grate and subjecting 
the green pellets to preheating, feeding the thus-preheated pellets in the 
rotary kiln to heat and indurate the pellets, which method comprises: 
inserting detector means for the total weight of ash and its analogous 
substances, at a position adjacent to the discharge end of travelling 
grate, into the gas stream from the rotary kiln; 
taking out the detector means after an elapsed time of a predetermined 
period; 
determining the measured deposit weight (Wi) on the detector means, the 
deposit density (.rho.m) and the composition of the deposit, respectively; 
calculating (a) a corrected ash deposit weight (Wa) by correcting the 
measured deposit weight (Wi) in view of the ash weight percentage (CA) 
present in pulverized coal used as fuel for the burners prior to 
operation, (b) a corrected weight of deposited iron ore dust (Wd) by 
correcting the measured deposit weight (Wi) in accordance with the iron 
ore dust percentage (F) present in the preheated pellets in the vicinity 
of the discharge end of the travelling grate and the percentage of iron 
ore dust (C) present in the deposit and determined on the basis of the 
composition of the deposit and that of the iron ore dust, and (c) the ash 
deposit weight (Ri) at an elevated temperature region in the rotary kiln, 
said ash deposit weight (Ri) being determined from the corrected weight of 
the deposited iron ore dust (Wd) and the deposit density (.rho.m), 
respectively; and 
determining the extent of deposition of ash and its analogous substances on 
the inner wall of the rotary kiln by comparing either one of Wi, Wa and Wd 
with its corresponding preset reference value and judging the value 
(.rho.m) while taking the state of the indurating operation into 
consideration, or optionally further taking Ri into consideration. 
The deposition of ash and its analogous substances has heretofore been 
controlled by such a passive measure that use of low-grade coals have been 
avoided. Contrary to such a conventional method, the method of this 
invention has made it clear that a variety of countermeasures can be taken 
in accordance with operational conditions and the type of coal because the 
present invention permits to determine the extents of ash depositions at 
various locations while taking the operational conditions and the type of 
the coal into parallel consideration. This encourages use of such 
low-grade coals that have conventionally been excluded from actual use. 
Thus, the present invention has brought about an extremely great 
economical effect, together with effects in the maintenance of facilities, 
stabilized operation, etc. 
The above and other objects, features and advantages of the present 
invention will become apparent from the following description and the 
appended claims, taken in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS 
From results of observation at the above-mentioned schedule shut-down, it 
has become clear that the deposition of ash in a rotary kiln takes place 
significantly at the feed-end region and central region thereof. It is 
however impossible to insert measurement instruments into such regions or 
to obtain samples from such regions while the rotary kiln is in operation, 
because the rotary kiln itself is of an extremely large diameter and is 
kept rotating. Accordingly, it was first of all necessary to find out a 
region where measurements of ash are feasible. As a location as near as 
possible to the rotary kiln, has been chosen a region adjacent to the 
discharging end portion of the travelling grate. 
Next, the measurement instrument disposed in the above measurement region 
will be described. Since it is impossible to reproduce the state of 
deposition of ash in the rotary kiln as is, the present inventors 
contemplated to assume the state of deposition of ash in the rotary kiln 
by catching ash present in the gas stream fed from the rotary kiln to the 
travelling grate. It appeared that there are both readily-depositing ash 
particles and hardly-depositing ash particles in the ash which has reached 
the measurement region while floating in the gas stream. Mere capture of 
such ash particles was expected to give deleterious effects to the 
accuracy of subsequent analyses. Accordingly, the present inventors 
contemplated to insert a foreign object in the above-mentioned gas stream, 
to take out only the ash deposit on the foreign object as a sample of 
deposit and then to determine the state of deposition of ash in the rotary 
kiln on the basis of the quantity, properties and the like of the sample. 
Namely, the foreign object is used as detector means for determination of 
the deposit ash weight. The detector means may take any shape such as a 
rod-like or plate-like shape provided that it permits ash and its 
analogous substances to deposit as uniformly as possible on its surface. 
It is thus unnecessary for the detector means to have any complex 
structure. 
Reference is now made to FIGS. 1 and 2, which are respectively a schematic, 
fragmentary, vertical cross-section of pellet indurating facilities 
according to the grate-kiln system and a fragmentary, transverse, 
cross-section of the pellet indurating facilities taken at a position 
where the detection rod is inserted for the determination of the weight of 
deposit. Namely, in the grate-kiln system, a grate 1, rotary kiln 2 and 
annular cooler 3 are connected together as shown in FIG. 1 and fans 10 are 
also arranged as illustrated in the same drawing. Since flames are blown 
out through burners indicated at the numeral 4, a gas stream flowing in 
the direction indicated by arrows is formed through the rotary kiln 2. On 
the other hand, pellets are successively indurated as they travel from the 
left to the right in FIG. 1 and finally cooled. Since the susceptibility 
of deposition to the region indicated by D and that to the region shown by 
R have been represented by a DP and RP values respectively, deposits at 
these regions will hereinafter be called the deposit D and deposit R 
respectively. It is the point P indicated by the .circle.X mark that 
detector 5 (see, FIG. 2) for the weight of deposit is inserted, where ash 
and its analogous substances present in the gas stream which has passed 
through the rotary kiln 2 are allowed to deposit on a detection rod 6 of 
the detector 5. Namely, the detector 5 is made of the detection rod 6 and 
a holder 11 as shown in FIG. 2 and is inserted into the furnace through a 
sealing unit 8. The holder 11 is continuously cooled with cooling water 
which is supplied and recycled through cooling water hoses 7,7'. The 
detection rod 6 is formed of a heat-resistant metallic material. Where the 
detection rod 6 is formed of a circular rod 6' for instance, ash and its 
analogous substances 12 are caused to deposit in such a state as shown in 
FIG. 3. Incidentally, the numeral 9 in FIG. 2 indicates pellets while the 
arrows in FIG. 3 indicate the direction of the gas stream. 
The insertion of the deposit weight detector 5 may be effected at will 
whenever desired to carry out measurement. For example, the detector 5 may 
be inserted during a steadystate operation, when the pulverized coal has 
been changed from one source to another, when the composition of raw 
material pellets (e.g., the proportion of a binder such as bentonite) has 
been changed, or a change has been made to the operational conditions. It 
is most recommendable from the view point of improving the accuracy of 
detection to insert the detector 5 when the state of the kiln appears to 
have been substantially stabilized subsequent to a change thereto. It is 
necessary, as the insertion time of the detector 5, to give a time period 
enough to permit ash and its analogous substances to deposit thoroughly on 
the detector rod 6 and to grow there sufficiently. The insertion time 
period of the detector 5 may be suitably determined empirically in 
accordance with the size of the kiln or the state of the kiln. However, it 
is impossible to make correct judgements if the measurement conditions 
should be changed from time to time. Thus, consistent judgements may be 
made if time periods of insertion of the detector 5 are set at the same 
length, for example, if the detector 5 is kept inserted for a time period 
required to burn up a preset constant amount of pulverized coal (for 
example, 5 tons or 10 tons). Needless to say, it is recommended to 
maintain the consumption of pulverized coal per unit hour and the grain 
size distribution of pulverized coal as possible as constant whenever a 
measurement is effected. 
The detector 5 is drawn out of the kiln when the predetermined amount of 
pulverized coal has been burnt. Since ash and its analogous substances 
deposited on the surface of the detection rod can be easily peeled off 
after cooling the detection rod, the weight (Wi) of the deposit is first 
of all measured. Then, the volume of the deposit is determined to 
calculate the density of the deposit. Alternatively, the density of the 
deposit may also be determined in accordance with the mercury methd or the 
like. Then, the deposit is subjected to a chemical analysis to determine 
its chemical components (Fe.sub.2 O.sub.3, SiO.sub.2, CaO, Al.sub.2 
O.sub.3, MgO, etc.). These chemical components are mixtures of those 
derived from the pulverized coal, i.e., the fuel and those originated from 
the starting iron ore. Thus, analysis data of chemical components provide 
very important information in knowing how much ash particles originated 
from the starting iron ore are contained in the ash deposit (in other 
words, how much the deposit is while taking the influence of iron ore dust 
released from pellets into consideration). Since there is no other 
possible sources for the ash deposit other than the two sources, i.e., the 
pulverized coal and iron ore dust, it is possible to make a correct 
judgement as to the degree of contribution of the iron ore dust by 
analyzing only two components whose original proportions are different and 
obtaining a solution of simultaneous binary equations. It is therefore 
unnecessary to make a complete analysis on each component. 
Wi,.rho.m and the degree of contribution of iron ore dust (the percentage C 
of iron ore dust present in the deposit of ash) have been determined 
above. Where the quality of starting materials and fuel and the 
operational conditions (inclusive of production scale) are extremely 
stabilized, it is possible to determine with a relatively high degree of 
accuracy the states of deposition of the deposit D and deposit R on the 
basis of these measurement and calculation values. Namely, if Wi is 
greater compared with its reference value (which may be set at a suitable 
level in view of the interval of scheduled repairs. The reference value is 
set at a low value when the interval is long but at a high value when the 
interval is short. This applies also to Wa and Wd.), it is judged that the 
weight of the deposit D is also high in view of the fact that the position 
of the detector 5 is close to the feed end of the rotary kiln. If Wi is 
low compared with its reference value on the other hand, it is also judged 
in accordance with the same way of thinking as followed in the above that 
the weight of the deposit D is also small. However, it is impossible to 
judge as a reason for the little deposit D whether the properties of the 
ash and its analogous substances render them difficult to become a deposit 
or ash and its analogous substances have already stuck and been 
accumulated at a position before reaching the position where the detector 
is inserted (more specifically, in the elevated temperature region at the 
center of the kiln) after they have passed through the interior of the 
rotary kiln and the available total quantity of ash and its analogous 
substances for their deposition on the detection rod has been rendered 
smaller. Next, the density of the deposit of ash is taken into 
consideration. When the density is higher than a reference value for usual 
ash deposits, the state of deposition of the ash on the detection rod 
seems to be close to a fushion-bonded state rather than a mere build-up 
state. Since the fusion-bonded state should be considered to be similar to 
the properties of the deposit R formed at the elevated temperature region, 
it becomes possible to come to a conclusion that the formation of the 
deposit R has been promoted further than that of the deposit D. When the 
deposit has a low density on the other hand, it is not reasonable to 
follow the above idea. Namely, it seems to be correct to make such a 
judgement that both deposit R and deposit D are little. The percentages of 
coal-originated ash and fine iron ores in a deposit of ash may be 
determined in the following manner for example. 
Paying attention for example to SiO.sub.2 and CaO among various components 
of a deposit of ash and supposing that the proportions of SiO.sub.2 and 
CaO in each of pulverized coal as a fuel and fine iron ores have been 
known (see, Table 1), T1 TABLE 1 SiO.sub.2? CaO? Proportion in pulverized 
coal as fuel 50.9% 2.1% Proportion in fine iron ores 3.1% 4.3% Proportion 
in the deposit of ash 27.5% 3.1% 
and representing the proportion of ash present in the deposit of ash and 
derived from the pulverized coal and the proportion of ash also present in 
the deposit of ash and derived from the fine iron ores by x% and y% 
respectively, the following simultaneous binary equations are established. 
EQU 50.9x+3.1y=27.5 
EQU 2.1x+4.3y=3.1 
Thus, the solutions of these equations are determined as follows: 
EQU x=51.2% 
EQU y=48.8%. 
In the above example, the ratio of the ash derived from the pulverized coal 
to that originated from the fine iron ores is approximately 1:1. 
Therefore, when the amount of the deposit D or deposit R has been judged 
to be too much from the determination of Wi and .rho.m and either one of x 
and y is biasedly greater than the other, it is recommended to effect a 
change to the operation in such a direction as to reduce the formation of 
the deposit D or R and to contemplate a major change to the raw material 
having a greater degree of contribution. 
When the type of coal in pulverized coal as the fuel has been changed on 
the other hand, it is necessary to correct the above-mentioned Wi in view 
of the influence of the amount of ash present in coal (%, symbol: CA) 
because no correct judgement can be made so long as the above-mentioned Wi 
is solely relied upon. The corrective equation may be established suitably 
whenever necessary. Although nothing will be placed outside the technical 
scope of this invention even if any corrective equation is used, the 
present inventors propose to use the following corrective equation: 
##EQU3## 
where k is a constant. Assuming that the content of ash in the pulverized 
coal as the fuel has become, for example, smaller after the pulverized 
coal was changed, compared with the content of ash in the pulverized coal 
before the change, the measured weight of the deposit of ash and its 
analogous substances (Wi) is believed to become smaller. However, it is 
difficult to say that actual operational conditions are always so. 
Supposing that, for example, Wi has not been changed substantially, it is 
indicated that the weight of the deposit has not been improved in spite of 
the reduction in the proportion of ash in the pulverized coal. This means 
development of new conditions which facilitate the deposition of ash more 
than the previous conditions, resulting in a large corrected value Wa. 
Thus, it is to be judged whether the conditions have been changed to ones 
facilitating deposition of ash or to those making deposition of ash 
difficult by analyzing whether the CA has been changed in the favorable 
direction (i.e., to a smaller one) or in the disfavorable direction (i.e., 
to a larger one) in combination with the phenomenon whether the Wi has 
been increased or decreased (in other words, by obtaining Wa in accordance 
with the above corrective equation). Namely, there was such tendency, 
according to the conventional general concept, to judge the extent of 
deposited ash directly on the basis of the proportion of ash in the 
pulverized coal used as fuel. Contrary to the conventional method, this 
invention has made it possible to determine the extent of deposited ash on 
the basis of the measured weight of deposited ash. A judgement is made 
whether the operation can be continued as is or not, by comparing Wa with 
a reference value which was chosen in accordance with the interval of 
scheduled shut-down. However, judgements relying upon Wa are in many 
instances carried out when the pulverized coal has been changed from one 
source to another, thereby mainly dealing with a re-change of the source 
for pulverized coal. Therefore, it becomes necessary to make various 
countermeasures which will be described below. 
When there is a change in the composition of raw materials in pellets or in 
the production scale although the source of the pulverized coal has not 
been changed, it becomes necessary to take the influence of the fine iron 
ores into consideration. Here, a correction must be made in view of the 
fine iron ore, similar to the case of ash. Although no specific limitation 
is vested to its corrective equation in the present invention, the present 
inventors propose to use the following corrective equation: 
##EQU4## 
where k.sub.2 and .alpha. are both constants, F means the proportion(%) of 
the fine iron ores contained in pellets at the discharging end of the 
travelling rate, and C denotes the proportion(%) of the fine iron ores 
present in the deposite of ash. The proportion of the fine iron ores, 
represented by F in the above equation, is normally expressed in terms of 
the proportion of fine iron ores and particles having diameters of 1 mm or 
smaller. Since the proportion of such fine iron ores and particles can be 
ignored to a certain extent, more specifically, to an amount up to 
.alpha.(%) in the corrective equation, (F-.alpha.) is considered to be a 
single corrective parameter. Here, the constant .alpha. may be suitable 
selected from 0.1-1%. In addition, C(%) is the proportion of the ash 
resulting from the fine iron ores which proportion is obtained from the 
above-described simultaneous binary equations. Namely, (F-.alpha.) relates 
to the fine iron ores which is to be charged into a rotary kiln and is to 
cause deposition of ash there. On the other hand, C means the proportion 
of the fine iron ores in actually deposited ash. Although the 
aforementioned Wa is a corrected value which is changed depending on the 
quality of coal to be used as a fuel, Wd may be considered to be a 
corrected value which varies depending on the influence of the fine iron 
ores, in other words, the influence of pellets used as a raw material as 
well as the level of operation control. Thus, the latter (Wd) is expected 
to exhibit its effectiveness particularly in the operation control when a 
change has been made in the conditions of raw materials or in the 
operational conditions. 
As to differences between the deposit D and the deposit R, it is said that 
the former shows the so-called physical adhesion--in which ash derived 
from e.g., fine iron ores is deposit while maintaining its powdery state 
in many instances--but the latter looks like a fused lump. This difference 
is believed to have arisen due to the fact that the deposit region of the 
former is generally at about 1100.degree. C. while the deposit region of 
the latter is generally at 1300.degree. C. or so, i.e., at extremely high 
temperatures. When comparing the properties of the former deposit with 
those of the latter deposit in terms of density, the deposit R has a high 
density whereas the deposit D has a low density. This difference in 
density has already been referred to in the above. Here, this difference 
in density will be discussed further by introducing the concept of Ri 
(ring index) so as to describe a method for making a still better 
judgement as to the state of formation of the deposit R on the basis of 
measured values obtained by the above-mentioned detector. Namely, Wi and 
Wa are values not taking the influence of fine iron ores into 
consideration too much, while Wd is a corrected value obtained by 
significantly taking the influence of fine iron ores into consideration as 
mentioned above. Deposition of rings at high-temperature zone in a rotary 
kiln has become a problem before pulverized coal was burned, i.e., since 
heavy oil was exclusively used. Accordingly, the proportion of deposit R 
derived from the fine iron ores is expected to be far more than the 
proportion of deposit R derived from coal ash, when both proportions are 
compared with each other. As a matter of fact, previous operational 
experiences teach that, when comparing operations in which pulverized coal 
containing a great deal of coal ash was used frequently as fuel with those 
carried out using more fine iron ores due to circumstances at producers' 
ends, the former resulted in relatively great deposit D and the latter 
gave apparently abundant deposit R. Therefore, these previous operational 
experiences justify the above-mentioned method in which the extent of 
deposited ash is judged by Wa when the coal has been changed from one 
source to another but Wd is relied upon for the same purpose when the 
operational conditions have been modified. Here, the present inventors had 
an idea that the susceptibility of deposition R would be predicted or 
estimated with still higher accuracy if Wd would be corrected further to 
Ri by taking the density parameter into consideration. Although the 
present invention is not limited to any particular calculation equation 
regarding the determination of Ri from Wd and .rho.m, the present 
inventors have found that there is an exponential correlation 
therebetween. The following equation has thus been proposed: 
EQU Ri=Wd.sup.k.sbsp.3.sup..multidot..rho.m 
where k.sub.3 is a constant. It has also been found that the constant 
k.sub.3 in the above equation can generally be given by 1/.rho.c, in which 
.rho.c is a preset reference value for the density of deposited ash and is 
set at a greater value where the interval of scheduled shut-down is short 
but at a smaller value where the same interval is long. Since it is 
necessary to apply a severe control to the increase of Ri where the 
interval of scheduled shut-down is long, it is required to set .rho.c at a 
low level (i.e., to set k.sub.3 .multidot..rho.m at a high level) so as to 
reflect a slight increase in Wd to the Ri value sensitively. Where the 
interval of scheduled shut-down is short on the contrary, .rho.c is set at 
a higher level because a higher increment of Ri is acceptable. 
As has been described, the present invention permits to estimate the state 
of development of the deposits D and R by taking, needless to say, not 
only the quality of coal but also operational conditions into parallel 
consideration. Thus, the present invention has made it possible to carry 
out the control of operation in such a way that the development of these 
deposits are minimized by readjusting all the operational conditions for a 
rotary kiln inversely based on the thus-obtained estimation results. 
Different from the prior art method in which the cause for the deposition 
of ash was attributed in its entirely to the coal and the range of usable 
coals was thus narrowed down, the present invention permits to make 
continuous use of the same coal as has been used by changing one or more 
parameters other than coal and, in some instances, provides room for 
studying a possible change even to coal of a lower grade, thereby 
considerably enlarging the range of usable coals. 
Next, certain countermeasures will be described to actually control the 
formation of the deposits D and R. 
Table 2 shows various analysis results obtained on coal samples which the 
present inventors used. In Table 3, there are summarized the states of 
operations and various analysis results for deposited ashes when the coal 
samples were used respectively. Whichever coal sample was used, it was 
possible to continue the operation successfully until the next scheduled 
shut-down owing to the prevention of operational trouble due to growth of 
deposit by controlling the operational conditions and the like. 
TABLE 2 
__________________________________________________________________________ 
Coal sample No. 
1 2 3 4 5 6 7 8 9 10 11 12 13 
__________________________________________________________________________ 
Industrial analysis 
data 
Ash (%) 6.19 
7.21 
6.09 
10.99 
10.04 
10.96 
8.82 
7.73 
7.67 
7.57 
8.62 
9.46 
7.42 
Volatiles (%) 
17.11 
30.04 
31.02 
38.15 
41.86 
39.62 
19.33 
29.29 
26.11 
28.37 
27.06 
36.20 
33.83 
H.G.I. 102 
71 69 48 54 50 100 
64 93 70 71 50 47 
Heat value (Cal/g) 
7978 
8006 
7957 
7002 
7030 
6820 
7889 
7731 
7977 
7762 
7779 
7456 
7200 
composition of 
ash (%) 
SiO.sub.2 50.96 
49.40 
51.61 
58.73 
63.94 
59.09 
58.31 
53.15 
51.48 
55.15 
48.08 
58.19 
40.99 
Al.sub.2 O.sub.3 
30.81 
28.58 
27.91 
18.25 
17.65 
14.84 
29.94 
27.29 
36.38 
30.75 
24.21 
25.46 
33.52 
Fe.sub.2 O.sub.3 
7.62 
9.69 
8.90 
3.45 
3.51 
4.86 
4.90 
9.00 
4.23 
5.09 
15.42 
6.84 
3.69 
TiO.sub.2 1.40 
1.42 
1.26 
0.42 
0.69 
0.59 
1.71 
1.30 
1.74 
1.03 
0.92 
0.93 
1.63 
MgO 1.01 
1.13 
0.85 
1.53 
0.98 
1.62 
0.52 
0.85 
0.45 
0.45 
1.30 
0.99 
0.82 
CaO 2.09 
3.81 
2.40 
7.42 
5.23 
10.51 
1.84 
1.85 
1.48 
1.88 
2.96 
2.29 
7.86 
Na.sub.2 O 
0.61 
0.64 
0.78 
0.63 
0.86 
1.70 
0.49 
0.30 
0.48 
0.15 
0.42 
0.60 
0.27 
K.sub.2 O 2.36 
2.40 
2.80 
0.72 
1.20 
0.72 
1.19 
3.50 
0.50 
0.87 
2.00 
1.10 
0.60 
P.sub.2 O.sub.5 
-- 0.27 
0.21 
0.39 
0.46 
0.24 
-- 0.88 
0.89 
1.36 
1.49 
0.87 
2.12 
SO.sub.3 -- 1.95 
0.27 
2.20 
0.82 
2.23 
-- 0.12 
0.07 
0.03 
0.21 
0.15 
1.45 
Others -- -- -- 6.26 
-- -- -- -- -- -- -- -- -- 
Melting point (.degree.C.) 
1403 
1353 
1376 
1275 
1300 
1200 
1390 
1382 
1410 
1387 
1330 
1377 
1403 
Elementary analysis 
(%) 
C 82.55 
80.70 
80.88 
70.36 
70.26 
68.18 
79.59 
77.18 
80.75 
77.14 
76.58 
73.70 
76.21 
H 4.16 
4.82 
4.89 
4.72 
4.92 
4.50 
4.28 
4.74 
4.67 
4.66 
4.64 
4.87 
4.62 
N 1.12 
1.29 
1.27 
1.08 
1.21 
0.95 
1.62 
1.45 
1.55 
1.73 
1.61 
1.61 
1.68 
S 0.72 
0.69 
0.77 
0.53 
0.70 
0.54 
0.56 
0.47 
0.56 
0.44 
0.51 
0.58 
0.63 
__________________________________________________________________________ 
##STR1## 
TABLE 3 
__________________________________________________________________________ 
Coal Sample No. 
1 2 3 4 5 6 7 8 9 10 11 12 13 
__________________________________________________________________________ 
Susceptibility of deposition 
DP 341 
531 
383 
1629 
928 
1827 
350 
534 
200 
299 
884 
589 
402 
RP 37 104 
93 89 76 199 
39 92 27 45 238 
78 27 
Deposited ash 
Wi (g/cm.sup.2) 
1.33 
3.12 
1.87 
4.45 
4.26 
3.17 
0.27 
2.00 
0.63 
1.47 
1.13 
2.32 
1.47 
Wa (g/cm.sup.2) 
2.11 
4.52 
3.17 
4.28 
6.36 
2.94 
0.29 
2.35 
0.82 
2.04 
1.36 
2.58 
1.99 
C (%) 51 59 57 89 82 86 67 76 76 73 70 69 69 
Composition of 
deposited ash (%) 
SiO.sub.2 27.45 
30.15 
31.19 
52.69 
52.71 
50.25 
40.08 
41.57 
40.66 
41.78 
34.84 
42.31 
29.59 
Al.sub.2 O.sub.3 
17.34 
17.95 
18.76 
14.85 
14.90 
12.81 
21.25 
22.09 
30.19 
23.12 
18.20 
20.07 
24.17 
Fe.sub.2 O.sub.3 
46.15 
41.99 
38.70 
17.96 
18.99 
22.06 
28.49 
25.45 
19.32 
26.03 
34.67 
25.78 
31.30 
TiO.sub.2 0.81 
0.89 
1.07 
0.60 
0.79 
0.71 
1.31 
1.22 
1.79 
1.09 
0.91 
1.14 
1.28 
MgO 1.52 
1.40 
1.47 
1.92 
1.37 
1.97 
0.96 
1.33 
0.97 
0.79 
1.43 
1.48 
1.34 
CaO 3.06 
3.60 
3.95 
6.92 
4.40 
8.29 
2.84 
2.70 
2.86 
3.13 
3.24 
4.47 
6.65 
Na.sub.2 O 0.60 
0.47 
0.66 
0.57 
0.66 
1.07 
0.71 
0.67 
0.57 
0.37 
0.49 
0.74 
0.39 
K.sub.2 O 2.51 
2.07 
2.99 
1.47 
1.84 
1.43 
2.92 
4.01 
1.91 
2.03 
2.63 
2.28 
1.74 
P.sub.2 O.sub.5 
0.21 
0.16 
0.19 
0.26 
0.30 
0.17 
0.58 
0.67 
0.86 
1.05 
0.92 
1.06 
1.38 
SO.sub.3 0.02 
-- 0.04 
-- -- -- 0.01 
0.08 
0.01 
-- -- 0.03 
-- 
FeO 0.29 
0.51 
0.16 
0.60 
0.43 
0.50 
0.51 
0.18 
0.25 
0.25 
0.57 
0.23 
0.50 
Ig. loss 0.26 
0.27 
0.37 
0.29 
0.14 
0.29 
0.20 
0.20 
0.23 
0.01 
0.23 
0.29 
0.44 
Particle size (%) 
of grained coal 
+177.mu. 7.1 
2.9 
3.2 
6.1 
6.9 
5.1 
4.6 
3.4 
0.8 
3.1 
3.0 
5.5 
4.3 
-88.mu. 71.7 
88.4 
87.0 
78.0 
73.5 
78.6 
79.7 
78.6 
86.9 
84.8 
87.2 
76.7 
82.9 
-44.mu. 42.6 
54.0 
64.8 
47.5 
42.3 
50.3 
53.4 
42.9 
55.3 
57.3 
61.3 
45.5 
54.6 
- 11.mu. 8.0 
30.5 
27.0 
16.2 
12.8 
17.3 
15.6 
11.5 
20.0 
20.9 
30.2 
13.9 
22.3 
Operational conditions 
Production (t/hr.) 
421 
252 
303 
279 
271 
278 
432 
300 
303 
299 
279 
292 
255 
Coal consumption (t/hr.) 
4.0 
5.8 
6.1 
7.0 
7.1 
7.0 
4.0 
6.4 
6.2 
6.3 
6.2 
6.1 
5.8 
Coal ratio (%) 
42.1 
77.9 
75.5 
80.6 
80.9 
75.6 
41.6 
76.7 
74.6 
79.1 
81.3 
72.0 
74.8 
__________________________________________________________________________ 
Note: 
(1) DP, RP, Wi, Wa and C are as defined 
(2) The coal ratio means the mixing ratio of coal to coke oven gas, i.e., 
the percentage of coal. 
As shown in Table 3, it is only the coal sample No. 9 and No. 10 that 
satisfied both of the above-mentioned conditions which are generally 
recommendable (DP.ltoreq.300; RP.ltoreq.150). Especially, the coal sample 
No. 6 and No. 11 did not satisfy the above conditions at all and were 
totally unacceptable fuels if the conventional standard was applied. 
However, these coal samples allowed to continue the operations without 
encountering any inconvenience owing to adjustment of various operational 
conditions including changes to sources of coals. As also appreciated from 
the same table, DP or RP which has been conventionally adopted as 
reference values did not always correspond to Wi and, even if only DP is 
taken into consideration, it did not correspond well to Wa. Therefore, it 
may be concluded that DP or RP cannot be relied upon too much when 
controlling the deposition of ash in accordance with this invention. 
However, DP and RP may be used as reference when a change is made only to 
the type of coal. Where the deposit D has been built up to a considerable 
extent and it is desired to change the coal to another type, it is 
necessary to choose a coal having a small DP. Where the deposit R has 
occurred to a considerable extent and use of another type of coal is 
desired, it is recommendable to choose a coal having a small RP. Even in 
these cases, it should be judged whether the above selections of new coals 
were correct or not, by measuring Wi again after the state of each kiln 
has been stabilized subsequent to the change of coal, and especially by 
correcting Wi into Wa. When changing the type of coal, it is certainly 
possible to use only a single type of coal. Unique tendency was observed 
as to the development of ash deposit when two different types of coal were 
combined. This unique tendency will thus be described below. 
FIG. 4 shows a deposition index for each mixing ratio when two types of 
coal, i.e., coal A and coal B of different types were mixed in various 
proportions (The amount of ash deposited when coal A was used alone was 
supposed to be 1. The deposition index is a measure of the amount of ash 
deposited.) According to the diagram, the deposit of ash increases as the 
ratio B/A becomes larger when the ash-abundant coal B is progressively 
incorporated in the ash-scarce coal A. However, the maximum appears around 
B/A=1/3 or so and the deposited ash decreases thereafter, reaching the 
minimum approximately at B/A=1/1. Then, the deposit of ash increases as 
the B/A ratio increases and, after reaching the maximum again near 
B/A=3/1, gradually decreases until B reaches 100%. This sort of quaternary 
curve is also seen in other coal compositions. The present inventors have 
reached to a conclusion that it is most effective to mix the coals A and B 
at the ratio of 1/1 or so when the economical view point is taken into 
consideration while achieving the principal object of reducing the amount 
of ash to be deposited. If the amount of deposited ash is still increased 
even after changing the coal to high-grade coal, it is necessary to 
increase the ratio of coke oven gas or the like. 
Next, FIG. 5 is a diagram showing the relation between the particle size of 
pulverized coal (more specifically, the ratio of particles passed through 
a sieve having the mesh diameter of 88.mu..) and deposition index (the 
highest possibility of continuous operation under scheduled shut-down work 
with a short interval being set at 1.0). The coal sample No. 8 given in 
Table 2 was ground in such a manner that pulverized coal samples of 
different grain size distributions were obtained. Study was made as to the 
weights of ash deposits (Wi) when thus ground coal samples were charged as 
fuels of pulverized coal. According to FIG. 5, Wi decreases apparently as 
the proportion of smaller particles of 88 .mu.m or less becomes higher. 
Accordingly, it becomes one of effective countermeasures to increase the 
degree of comminution of the pulverized coal fuel so that the proportion 
of fine particles (particularly, those having diameters of 88 .mu.m or 
smaller) is made higher when the value Wi, Wa or Wd (especially Wi or Wa) 
has been found to have increased through its determination by the 
aforementioned means. If Wi or the like value is sufficiently small, it is 
estimated that the degree of communition of the coal has reached an 
unnecessarily high level (in other words, the power cost for communition 
has become too high). Thus, it is possible to take such counter-measures 
as lowering the degree of communition slightly or somewhat lowering the 
grade of the coal. 
As other means to inhibit the increasing tendency of the deposit of ash, it 
is contemplated to adjust the production conditions, it is recommended 
first of all to employ such means as to change the temperatures in the 
kiln, thereby removing the deposit positively. Namely, separation of the 
deposits D and R is accelerated, for example, by lowering the temperature 
at the feed end of the rotary kiln when the deposit D is abundant or the 
temperature at the central region of the rotary kiln when the deposit R is 
present at a high level so as to make use of the differences in thermal 
expansion between the rotary kiln and the deposits D and R. The 
productivity will be lowered if the charging rate of pulverized coal is 
reduced as one method for lowering the temperature. Accordingly, it is 
prefrable to charge the exterior air positively to the feed end of the 
rotary kiln so that the temperature is lowered significantly only at the 
feed end of the rotary kiln or to changing the lengths of burner flames or 
the like so that the temperature is lowered only at the central region of 
the rotary kiln. As a second method, it is possible to lower the amount of 
iron ore dust to be carried into the rotary kiln from the grate. This 
method is particularly desirous as a countermeasure when the deposit R has 
been formed to a considerable extent. This method can be practiced, for 
example, by (1) increasing the proportion of the binder upon pelletizing 
so as to enhance the strength of resulting pellets; (2) increasing the gas 
quantity in the grate and drying pellets sufficiently on the grate in 
order to prevent occurrence of fine iron ores on the grate (the drying 
temperature may be somewhat lowered); or (3) allowing the sintering of 
pellets to proceed to a certain extent on the grate so as to protect 
pellets from being impacted and cracked due to the hand through which the 
pellets fall when feeding the rotary kiln from the grate. 
Various countermeasures have been described above. However, it should be 
borne in mind that methods for adjusting the amount of ash to be deposited 
are not limited to those mentioned above but a number of other methods may 
be employed for the same purpose. Such methods may be practiced 
independently or may be combined together for still better results from 
the practical viewpoint. 
Having now fully described the invention, it will be apparent to one of 
ordinary skill in the art that many changes and modifications can be made 
thereto without departing from the spirit or scope of the invention as set 
forth herein.