Item
Background

Descriptions

Vertical roller mill for raw
materials

Application process
Raw material process

Grinding raw materials needs lots of energy. Tube mills had been used for grinding,but the energy efficiency level was lower. Therefore, the introduction of highly efficient
grinding equipment was anticipated.
The vertical roller mill has high energy efficiency and the installation space is smaller
compared with tube mills. These days, the vertical roller mills have been widelyadopted.
A）Structure(1) The rollers are hydraulically pressedagainst a disc table and the feed is groundbetween the rollers and the disc table.
(2) The classifier is housed above the rollers.
B）Feature(1) The power consumption level for grinding
is lower than that of tube (ball) mill.
(2) The remaining time of raw materials in thistype of mill is much shorter than that in
tube (ball) mill; therefore, the crushingprocess and mixing process became more
harmonized and this contributes to quality
control.
(3) The installation space is smaller and thisleads to lower noise level.
(4) This type of mill can crush materials which
Fig.1 Vertical roller mill
are too large to be fed into the tube (ball)mill.
(5) Ground materials are dried by the flue gas
from the kiln.

Fig.2
Schematic process flow of vertical roller mill for grinding of raw
materials
Vertical roller mills are adopted in 20 cement plants (44 mills) in Japan.
Table

Results

Production
Specific power
consumption
The reduction ofpower
consumption(*)

Cost
estimation
Relatedmatters
References

Energy saving effect of the vertical roller mill
Ball millVertical roller
mill

Effect(%)％

１００

160〜180

60〜80(increase)

kWh/t-RM

20〜26

14〜18

kWh/y

About 30
(Reduction)

2,240,000

About 14million US$ [Newly-built] and about 230 million US$ [retrofitted], including
the cost of supplemental facilities [200t-RM/h][1US$=¥110]

-167

Item

Background

Descriptions

External circulating system tovertical roller mill

Application process
Raw material
process

In the vertical roller mill which is widely used in the raw material grinding process, rawmaterials input grinding table are crushed and pulverized on it and transported toseparator by kiln exit gas introduced into the mill as drying, transporting and separating
purpose. In case that the proposed external circulating system is not installed, which iscalled conventional system, uncrushed and/or half crushed large size materials
undergone rotating and grinding works on the table and jump out from it have to be kept
above the table or transported to separator by the gas blown around the table to holdthem in the mill inside until desired particle size by clinkering process is gotten. This
internal material holding and separating works by the gas requires huge energy. Itamounts about 60% of this raw material grinding process. Around 1980, it is proposed
the external material circulating system that uncrushed large size raw materials jumped
out from the table is re-transported by mechanical system in order to reduce gas blow
and transportation energy.
In case that the proposed external circulating system is provided to the vertical mill,the uncrushed materials jumped out from the table fall through gas inlet box to andcollected by the mechanical transportation equipment installed below the mill suchas chain conveyor and bucket elevator etc. And then they are re-transported to freshmaterial feed equipment to re-send the mill. Since the uncrushed raw materials are
not blown-up by the gas, transportation energy of the gas, which is generated by millfan, extremely decreases.
Raw matarials

Mill fanExternal circulating
systemKiln IDF(Kiln gas exhaust fan)Fig. Flow chart of roller mill adopting the external circulating system.
As compared with conventional internal circulating system, power consumed for fan is
reduced until half and it’s possible to reduce power of grinding system by about 30%
Table

Results

The comparison of external circulating system

CapacityGas pressure loss
(draft)Gas flow ratet/hConventional
system490

External
circulating system
496

mmAq

1,110

770

m3/min15,40012,000

19.4

13.5

8.9

7.7

10.5

5.7

Total electricalkWh/tpower consumption
Mill and Separator
Mill Fan

Costestimation

Effect30%(Reduction)
22%(Reduction)
30%(Reduction)
50%(Reduction)

It depends on scale of facilities. For example, about 820,000 US$ per unit.
[1US$=¥110]

Relatedmatters
Reference

-268

Item

Background

Direct dust collection system tovertical mill grinding process

Application process
Raw material
process

At the beginning stage when vertical roller mill was adopted to cement
manufacturing, mill gas circulation fan and dust collection fan are required and theirpower consumption was larger.
The conventional process gas flow of the mill grinding system generally consists ofvertical roller mill with separator, cyclone, mill circulation fan, and electrostatic
precipitator (EP) and EP fan as shown in Fig.1. Pulverized final products, which iscalled kiln feed raw meal, are collected at the cyclone and EP. Because of largepressure loss at the cyclone and in order to control mill gas flow, mill circulation fan
and EP fan are provided after the cyclone and EP respectively. Power consumptionof these two fans reaches about 10kwh/t-raw-material.
In the direct dust collection system shown in Fig.2, process flow is simple. The raw
materials are dried and ground by the mill simultaneously in one-pass kiln exit gas
and then fine product after separation is sent to EP directly. Since the cyclone is notinstalled, system pressure loss reduces. And as the mill fan treats de-dusted gas
only, its power consumption largely decreases.
As of 2002, this system is used at four plants in Japan.
Raw materials

VerticalMill

Descriptions

Fine
product

Raw
Mill EP
Raw Mill
EP fanMillcirculation fan

Chimney

Kiln IDF(Kiln gas exhaust fan)Fig.1 Flow of Conventional Vertical Mill Grinding System

Raw materials
Raw
Mill EP
Raw Mill
EP fanVerticalMill

Chimney

Fine
product
Kiln IDF(Kiln gas exhaust fan)Fig.2 Flow of direct dust collection system

Results
Costestimation

Power consumption of fan(s) reduces about 3 to4 kWh/t.
When a mill with a production capacity of 420 t/h was newly constructed, the total cost
was about 25 million US$. [1US$=¥110]

Relatedmatters
Reference

-369

Item

Background

Descriptions

Pre-grinding equipment for raw
material grinding process

Application process
Raw material
process

Recently, the vertical roller mill having great grinding performance is widely applied to theraw material grinding process. However, tube mill, which has about 30% poor grinding
performance as power consumption, has been still used many existing cement plant. The
improvement of this tube mill grinding system is highly expected.
The tube mill comminutes raw materials by impact and friction between grinding balls,
which hit raw materials as well as between grinding ball and mill lining. Many of thistype mills have two grinding chambers for coarse and fine grinding. Grinding ball size
and their distribution are designed and adjusted considering raw material conditions
and mill dimensions etc. However, the energy efficiency in the coarse grinding
chamber is extremely poor and there is limitation to improve both performances forcoarse and fine grinding on the same mill by ball size selection etc.
Therefore, a new system was proposed and developed by installing a pre-grinder,
which is roller mill or roller press, as coarse grinding before the existing tube mill,which is exclusively used for fine grinding. This system greatly reduced the specificpower consumption and improved the production capacity. This system is now
installed at three plants in Japan and improvement of production of 50 to 100% has
been achieved when roll mill type pre-grinder is used.
As the pre-grinder, vertical roller mill is often used considering its great grinding
efficiency.

Separ
ator

Mixed raw materials
Pre-grinder

Product

Coarse powder
Raw material tube
mill

Coarse powder

Fig. Raw material grinding system
Table Effect of implementing raw material pre-grinder

Production Rate

Results

Beforeimplementation

After
implementation

Effect97% upt-RM/h180354

Fineness: 88µm (residue)

%

17

22

(Tube mill power)

kW

2550

2650

(Pre-grinder power)

kW

―

1120

Total power consumption
Specific power consumptionof tube mill only

kW

2550

3770

kWh/t-RM

14.2

10.6

25% down

kWh/t-RM

34.3

26.6

22% down

Departmental power
consumption rate

By this production increasing, it is expected that operation in the daytime can beshortened and then power cost can be reduced.

Cost
estimation
Relatedmatters

About 7.3 million US$ (depending on the scale) [1US$=¥110]

Reference
-470

Item

Background

Classification of powder returned
from raw material separator

Application process
Raw material process

When raw materials are ground in a closed circuit by a double-rotator mill, grids remain
underground in the second chamber for fine grinding, lowering the grinding efficiency.
The cause of this phenomenon is that grids contained in the separator returned power
directly enters the second chamber. To separate grids from the returned powder andreturn them to the first chamber for coarse grinding, a simple grid screen (classifier)
was installed at the return chute of the separator. The grids and coarse powder wereground with large balls. The ball diameter of the second chamber can be made small
because only fine powder is returned to the room.

Grid screen
To EP

CoarsepowderFine
powderDescriptions

Refined powder
Raw materialsFirstchamber

Secondchamber

Double-rotator millFig. Classification of returned powder by double-rotator mill

Results
Costestimation

The work for removing grids from the second chamber can be mitigated. The decreaseof power consumption rate is not remarkable but below 1 kWh per ton of raw materials.
18,000 to 36,000 US$ per system [1US$=¥110]

Relatedmatters
Reference

-571

Item

Background

Automation of raw material
mixing control

Application process
Raw material process

To keep the components of continuously produced raw materials at the targets is themost basic requirement for stable operation (energy conservation) and maintaining
quality of production out of the burning process.
Since the raw material mixing ratio must always be adjusted to keep the components of
raw materials at the targets, an automatic control system was developed andimplemented.
The basic management of the components of cement raw materials is to set the mixing
ratio target based on the chemical composition of various raw materials and feed backthe results of analyzing the components of raw materials and adjust precisely themixing ratio.
Therefore, an online automatic control system was developed and implemented by
combining such systems as continuous measuring equipment, an automatic sampler,an X-ray fluorescence spectrometer of the glass bead method, and a computer
program for mixing control.

Mixingtank

EP dustDescriptions

Limestone

CFW

Clay

CFW
Reservoir

SilicaCFW

Iron rawmaterial

CFW

Industrialwaste,

CFW

etc.

Raw
material millAuto sampler

CPU

X-ray
fluorescence
spectroscopy

CFW

To kiln

Results

1) The hydraulic modulus and other coefficients for component management become
stable and the heat consumption rate creases according to the degree of
improvement.
2) The clinker quality becomes stable.

Costestimation

X-ray fluorescence spectrometer of the glass bead method: 0.9 to 1.8 million
US$ [1US$=¥110]

Relatedmatters
Reference

-672

Item

Background

Optimization of raw material
fineness

Application process
Raw material
process

Raw materials used to be ground to a rather finer level because the fineness of themaffects the clinker burning efficiency. Since the power consumption rate is high for thefine grinding of raw materials, great efforts were made to save energy by making raw
materials coarse.
The fineness of raw materials used to be controlled at the level of several percents of
90 micron residue in the old wet process or others. As the burning method changed to
SP and NSP, efforts were made to reduce the power consumption rate at the raw
material process by increasing coarseness. These efforts resulted in great
achievements.
Since the fineness of raw materials affects the formation of hydraulic minerals atburning, increasing coarseness is naturally limited. If raw materials are made toocoarse, however, free limes are likely to increase in clinkers and more heat is required
to maintain the conventional level. To optimize the fineness of raw materials, therefore,
it is important to find out the limit of making raw materials coarse under specificconditions.

Descriptions

Means of making raw materials coarse
1) Adjusting the separator2) Converting multiple separators into single one3) Reducing the ball filling factor of tube mill

Achievement and estimated effect: The table below gives the results of calculation by
Bond's formula with the new feed size fixed.
Year of Survey

Results

Costestimation

1975
1981
1987
1996

90-micron Residue(%) Estimated Power Saving Effect(%)

8.0
11.7
15.4
21.2

Basically, the above adjustment only

Relatedmatters
Reference

-773

Base
11
17
22

Item

Background

Intermittent charging of electric
dust collector

Application process
Raw material process

The conventional electric dust collectors use the continuous charging method.
However, the intermittent charging method was developed to save energy and is now
being implemented.
To meet the following demand for more efficient electric dust collectors, the pulse
charging method was developed and is now being implemented.
The intermittent charging method uses a waveform (semi-pulses) thinned out from theoutput of the continuous charging method periodically. Thinning out the output saves
power. In addition, the dust collection efficiency is said to be a bit superior to that of thecontinuous charging method and the alteration cost is not high because only the control
device of the continuous charging method should be altered.
The reduction of dust collection efficiency of electric dust collector became unsatisfying
as coal ashes and other wastes having great electric resistance and fine particles ofsubmicron-level diameters were used in greater amount. Under these circumstances,the pulse charging method was implemented to save power and improve the dust
collection efficiency.
The pulse charging method uses a voltage waveform where pulses are superposed ona DC voltage. The DC voltage, pulse voltage, and period are controlled.
This method costs higher than the others.

Descriptions

As of 1996, 120 systems use continuous charging, 21 systems use intermittent
charging, and 16 systems use pulse charging in Japan.
Pulse charging

Intermittent charging
Voltage

Voltage

Time

Time

Current

Current

Time

Results

Costestimation

Power Saving
EffectDust Collection
Capacity

Ratio by Power
Consumption(%)
Ratio by Dust Collection
Efficiency(%)

Time

Continuous
Charging

Intermittent
Charging

Pulse Charging

100

65

45

100

110

150

1) Conversion to the intermittent charging method: 0.8 to 1.6 million US$ (electricalequipment only) [1US$=¥110]2) Conversion to the pulse charging method: 2.3 to 4.5 million US$ [1US$=¥110]

Relatedmatters
Reference

-874

Item

Background

Transportation of raw materials
for input into kiln

Application process
Raw material process

For a kiln with preheater, such as SP or NSP, mixed raw materials are transported to the
top of the preheater and then fed into the system. When the SP kiln was developed, aircompression transpotation by a Quinion pump was initially adopted. Because of greatpressure loss, high power consumption rate, and frequent compressor faults, however, amore reliable and efficient method was expected.
Compressed air transportation was replaced with mechanical transportation such as a
combination of bucket elevator (BE) and air slider (AS).
Two or three Bes are installed up to the top of the preheater. Raw materials are lifted tothe top by changing the Bes and fed into the preheater through the AS.
BE has small no-load power because of its structure and AS is a means of transportation
using the self weight of powder. Therefore, this method can reduce power consumption
greatly compared with air compression delivery.
Air compression transportation used to cause great fan power loss because of large
volume of compressed air flowing into the system with raw materials. Mechanicaltransportation can minimize the air inflow.
The initial BE used a short-link chain that caused many problems of abrasion or
elongation. A plate-type chain reduced these problems greatly and achieved the current
high reliability.
As of 1996, 72 systems use mechanical transportation and two systems use aircompression transportation in Japan.

Descriptions

Guided-discharge
bucket elevator

Combination of BE and AS

Preheater

Dust
collector

Air slider
BlowerPowder

To kiln

Results
Costestimation

Mechanical transportation reduced power consumption by even 80%, although dependingon the distance of transportation.
Bucket elevator (2 units): About 1.4 million US$(For a kiln having a capacity of 3000 t/d)

Relatedmatters
Reference-975[1US$=¥110]

Item

BackgroundThe new suspension preheaters burning system

Application
Burning process

Clinker burning system for has switched from wet-process kilns to more efficientsuspension pre-heater (SP) type since 1965. But in an SP burning furnace, allmaterials were fully combusted at once and this gave damage to the refractory inside.
Besides with the increasing cost for maintenance, adhesion troubles in the pre-heater
arouse, and it hindered from long time operation or capacity expansion.
To solve those problems, a separate pre-calciner was installed within suspension preheater, which enabled reduction of specific energy consumption per unit clinker by 5060%. This technology was developed and applied in Japan.
With SP type burning furnace, the raw materials were only 20-30% calcined at the kiln
gate. While with the NSP type, it reaches over 90%. This reduces heat energy
consumption in the rotary kiln for clinker production to approximately 40-50%,
enhance production level, and mitigate damage to the refractory materials in the kiln.
NOx emission levels are also reduced.
These days, up to 320 days operation a year became possible thanks to thistechnology.
Exhaust gas
Raw meal

Descriptions

Raw meal

Suspension preheater

Precalciner
Coal

Coal
Rotary kiln

Clinker

Rotary kiln

Fig.1 Suspension Preheater

Results

Costestimation
Relatedmatters

Fig.2 New Suspension Preheater

1. Max. output increment
SP type burning furnace 4,000t/d; NSP type 10,000t/d
2. Reduction in average unit consumption of energy (in calorific value)
SP type burning furnace 3,470~3,600kJ/kg; NSP type 2,930〜3,350kJ/kg
3. Reduction in NOx emissions compared with SP type burning furnace, due to lower
combustion temperature and two-staged combustions prevailing in a precalciner
4. Reduction of specific consumption of refractory
SP type burning furnace 800〜900g/t-cl; NSP type 500〜600g/t-cl
About 273 million US$ for new facility from “Raw material process” to “Burning
process” [4000t-clinker/d] [1US$=¥110]

Reference- 10 76

Item

Background

Fluidized bed cement kiln system

Application
Burning process
In cement manufacturing, global environmental preservation such as the reduction ofgreenhouse effect gas (CO2) emission is required in addition to the reduction of NOx andSOx emission these days. Furthermore, the cement market needs to produce special
cements such as high compressive strength cement and early hardening cement.
In response to these needs, the fluidized bed cement kiln system has been researchedand developed to comply with the global environment preservation since 1989.
The fluidized bed cement kiln system consists of the following equipment:
1) Suspension Preheater (SP) with Calciner (SC):consisting of 4-stage cyclones for preheating and calcining
raw materials, which applies the conventional technology.

SP2) Granulating kiln (SBK):
for granulating raw materials into granules of 1 to 2mm
average diameter without feeding seed-core clinkers at
high temperature (1300°C)
level. This is the key technology of the system.
3) Sintering Kiln (FBK):
for efficiently completing the sintering of the granules
produced in SBK at high temperature (1400°C) level.
Descriptions4) Fluidized Bed Quenching cooler (FBQ):
for quickly cooling down the burnt clinker from 1400°C
level to 1000°C in order to get good quality.

SB
Fuel
ＦＢＱ
ＦＢＫ

Blow
Ｂ

Blow

5) Packed Bed Cooler (PBC):Ｂ
for efficiently recovering the sensible heat of clinker
and cooling down the clinker to the specified temperature.

ＰＢＣ

Stoc

1)Economic advantages(1) Due to improvement of the burning and heat transfer characteristics, it is able touse low grade coal such as low volatile coal and low calorific coal.
(2) The heat recovery efficiency of the system can be improved by 20 % as comparedwith the conventional cooler due to increase of waste heat recovery.
(3) Both of construction and maintenance costs can be decreased because there are
no movable apparatuses.

Results

2) Lower environmental pollution(1) The emission of thermal NOx emission can be greatly decreased because
combustion takes place in the fluidized bed without generating flame.
(2) The emission of CO2 can be decreased by approximately 10% due to reduction offuel consumption and so on.
(3) The system is able to control temperature more tightly and keep a longer reaction
time, and it enables the quality improvement and the production of special cementwith higher grade.

Costestimation
Relatedmatters
Reference- 11 77

Item

Background5-stage system ofsuspension preheater

Application
Burning process

The suspension pre-heater is multistage heating system, using exhaust gas. In caseof 4-stage, the temperature of gas at the outlet of the pre-heater is around 400℃．
This exhaust gas is used for drying raw materials. The unexploited heat is let out
after himidiffication. For achieving energy saving, remodeling of pre-heater from 4stage to 5-stage is carried out.
There are two cases for 5-stage preheater. One is remodeling and the other is the
adoption of 5-stage preheater in the case of new construction of kiln. By addition of
one cyclone, the temperature of gas at the outlet of the preheater is decreased about
30〜50℃． By adopting the 5-stage system, heat exchanging ability increases andthe heat efficiency of the total system increases. As results, the specific heatconsumption decreases.
This technology usually applies to small capacity kilns that power station by the waste
heat is not economically applicable.
The example of remodelingraw meal
raw meal

5th stage cyclone(Newly installed)

4th stage cyclone

Descriptions
3rd stage cyclone
2nd stage cyclone
1st stage cyclone

4th stage cyclone
3rd stage cyclone
2nd stage cyclone
1st stage cyclone

kiln

Compared with 4-stage preheater, the specific thermal energy consumption
decreases about 125〜170kJ/kg-clinker (plant average) in case of 5-stage preheater.
Ratio of 5-stage preheater is 23 percentage in 1996 [Japan].

Results

The specific heat consumption compared with 4-stage system
5-stage system
NSP type
96％
SP type95％

Costestimation
Relatedmatters

1.4 ~2.7 million US$ for additional 1-stage cyclone [2500t-clinker/d]
Low-pressure-loss-cyclone

Reference- 12 78[1US$=¥110]

Improvement of the calciner

Item

Background

Application
Burning process

A calciner installed at a suspension preheater consumes about 50 to 60% of necessaryheat to promote the thermal decomposition of limestone in raw materials.
When NSP was popular, the main fuel was heavy oil and the calciner was also designed
according to the combustion characteristics of heavy oil but has been optimized
according to the change of fossil fuel after the Oil Shock in 1970s.
1) The initial calciner that used to burn heavy oil of good combustibility did not have an
enough volume to complete the combusion of pulverized coal slow to burn. (A)2) To make pulverized coal stay long, the volume of the calciner was increased. In
addition, positions of burners and a way of connecting tertiary air duct from the cooler
were improved. (B)3) Since highly volatile coal of comparatively good combustibility was mainly used in theburning, the volume of the calciner was increased only a little by making its ceilinghigher. To burn less volatile coal, however, the duct was extended from the calciner tothe bottom cyclone for securing enough pulverized coal combustion time. (C)For cost reduction, the use of oil coak and other fuels of low combustibility are increasingthese days. To improve their combustibility, high temperature to some extent isnecessary. To improve temperature distribution in the calciner, some measures aretaken: 1Making the tertiary air from the cooler hot (raising the cooler efficiency),
2Reducing the grain size of pulverized coal, and 2Raising the burner efficiency andoptimizing the setting position.
(C)

(B)

(A)
Raw meal

Descriptions
BottomcycloneCalciner

BottomcycloneCalciner Raw
meal

BurnerBurnerMixture oftertiary air
from cooler
and kiln
exhaust gas

Bottomcyclone

Tertiary air
from cooler

Calciner

Tertiary air
from cooler

Burner

Raw meal

Effective volume of the calciner
V = 169 m3

Raw meal

V = 230 m3

Raw meal

V = 460 m3

Example of improvement

Results
Costestimation
Relatedmatters(1) Solid fuels of the average volatile matter content from 15 to 20% can be used.
(2) The heat consumption goes down to 80 to 125 kJ/kg (20 to 30 kcal/kg) from the systemof (B).
3 to 4 million US$ (Burning capacity: 3,000 t/d) [1US$=¥110]
Improvement of burning in calciner

Reference- 13 79

Item

Background

Improvement of burning in calciner

Application
Burning process

For a calciner, coal of comparatively high volatility used to be used. To meet the demand
for less expensive fuels, the combustion technology has been improved to use coal of
low volatility.
When a fuel of low volatility is used under the conditions for a fuel of high volatility, theburning temperature of the calciner falls and the outlet gas temperature of the bottom
cyclone rises as the burning time becomes long. Since the production output and theheat consumption rate deteriorate, technological development was promoted to utilize afuel of low volatility.
To improve burning in a calciner, the following technologies are adopted:

Descriptions

1) Reducing the air ratio (solid-gas ratio) for transporting pulverized coal (Reducing thecold air blow-in rate)2) Rising temperature of tertiary air for calciner(1) Insulation lining of the tertiary air duct for calciner(2) Improving the heat recovery efficiency of the cooler
3) Increasing the fuel fineness(1) Improving the fuel grinding mill and separator (improving the fine grinding
performance and classification efficiency)
4) Changing the burner set position (for quick contact and mixing with the tertiary air)
5) Adopting a swirl vane structure for the burner (promoting fuel dispersion andignition)
6) Securing a high-temperature combustion area in the calciner (adjusting the timing ofcontact with raw meal)

Diverting Damper

Mixing Chamber
BurnerCombustion Chamber
Tertiary Air
Rotary Kiln

Example of split raw meal feeding

Results
Costestimation
Relatedmatters

1)
2)

A fuel of low combustibility does not deteriorate the heat consumption.
Pulverized coal of the average volatile matter content from 15 to 20% can be used.
(The fuel cost goes down.)

1)

Burner alteration: 10 to 50 thousand US$ [1US$=¥110]

Improvement of the calciner

Reference- 14 80

Item

Background

Automatic control of bottom cyclone
outlet temperature

Application
Burning process

For a stable kiln operation, it is necessary to keep almost constant the decomposition(decarbonization) rate of raw materials input into the kiln. The outlet temperature of thebottom cyclone is used as an operation index on behalf of the decomposition rate andthe kiln is operated to keep its transition stable.
Since the outlet temperature varies with various factors, such as the fluctuation of heatvalue of the fuel, it is difficult to deal with all fluctuations manually. This is why technology
such a automatic control was put to practical use.
1) In general, the outlet temperature of the bottom cyclone is detected and the fuel supply
to the calciner is automatically controlled to make the outlet temperature match thesetting.
2) The outlet gas temperature of the cyclone or the outlet temperature of raw meal is usedas the outlet temperature detection end.
3) The temperature is also adjusted by controlling the supply of raw materials or both the
supplies of fuel and raw meal.
Raw meal

Descriptions

Automatic controller

Coal 1

Coal 2

Coal 3

Pulverized coalweigher
Fixed-rate coal supplier

Coal dryer

Coal ﾐﾙ
Coal millOutlet gas temperature control flow of bottom cyclone

Results

The heat consumption for burning clinkers goes down by 0.8%.

Costestimation
Relatedmatters
Reference- 15 81

Item

Background

Chlorine bypass system

Application
Burning process
Chlorine contained in cement raw materials is evaporated by a high-temperature sectionin the kiln and condensed at the lower part of the preheater where the temperature iscomparatively low. This is repeated for condensation up to about 200 times. By reaction
with raw materials, chlorine or sulfur generates various compounds of low melting points
and forms scales (coating) on the internal wall of the preheater, causing such processproblems as an increase of ventilation resistance and clogging in the cyclone.
Drastic measures were necessary to prevent these problems from causing great energy
losses.
The cause of scales deposited in the preheater corresponds to the melting point ofcompound and the temperature distribution of the preheater. Scales in the rising duct ismainly attributed to sulfide and those in the cyclone to chloride. Their excessive
resistance causes a serious problem synergetically.
Chlorine bypass is a technology to efficiently recover chlorine from the lower part of thepreheater where chlorine is condensed most. Raw materials are partially extracted or
gas is extracted to recover fine dust. Chlorine recovery reduces the chlorine
condensation in raw materials and solves or mitigates the formation of scales
attributable to chlorine condensation.
As of 2000, the implementation rate was 54% and the gas bypass method accounted for
80% of them. The bypass rate was 1 to 3% for 74% of the gas bypass systems and 1%
or less for all of the raw material bypass systems.

Descriptions

C2

Bag filter
Kiln
exhaust gas

Fan

C1
Dust tankFeederBlowerProbe

cycloneKiln

AQC

SP feed raw material

Gas
Cooling fan

Gas bypass system

Results

1) Scales causing great chlorine condensation can be reduced greatly to prevent anenergy or production loss. (The bottom cyclone clogging ratio is down 60% or more in
most of the installed kilns.)2) Wastes of great chlorine contents can be used more efficiently.

Costestimation

Chlorine bypass system for a daily output of 5,000 tons (clinker basis): About 3.2 to 4.5
million US$ [1US$=¥110]

Relatedmatters

Cyclone descaler

Reference- 16 82

Item

Background

Cyclone descaler

Application
Burning process

Chlorine, alkali, or sulfur contained in cement raw materials and fuels evaporates in ahigh-temperature section of the kiln and condenses at the lower part of the preheater.
This phenomenon is repeated such elements and gradually concentrate. Reaction ofthese with raw meal generates various compounds of low melting points and forms
scales (coating) on the internal wall of the preheater, causing such process problems as
an increase of ventilation resistance and clogging in the cyclone.
Various measures were taken to prevent these problems from causing great energy
losses.
A descaler was adopted to prevent the growth of scales deposited on the internal wall of
the preheater.
1) Blowing compressed air periodically against the internal wall of the preheater (Airblaster)2) Blowing high-pressure water or steam periodically against the internal wall of thepreheater (Soot blower)
The descalers are installed at many locations where manual cleaning is difficult or the
scale is deposited severely and activated periodically to prevent the growth of scale.

Steam out

Descriptions

Refractories

Soot blower

Steam inIn this example, the internal cylinder thrusts and withdraws. After thrusting, the cylinder
tip rotates and blows steam out.

Results
Costestimation
Relatedmatters

1) This is effective for preventing the growth of scale, but the effect differs individually.
2) The work load of preheater cleaning can be reduced.
1) Soot blower (set): About 50 thousand US$ [1US$=¥110]2) Air blaster (set): About 8 thousand US$ [1US$=¥110]
Chlorine bypass system

Reference- 17 83

Item

Background

Combustion management

Application
Burning process

The clinker burning process consumes great thermal energy to make clinker. Fuels
combustion management is the most fundamental energy-saving activity to be
conducted everyday at cement plants.
Combustion management approaches are made from various aspects relating to
combustion.
1) Fuel management
The main fuel used in Japan is coal and its supply sources are selected, taken into
consideration the price, fuel ratio (fixed carbon to volatile matter), and Hard Grobe
Index (HGI).
Technically speaking, the capacities of grinding mills, performance of burners, burnerperformance, volume of calciner, and other items relating to fuel combustion should
be considered enough at the time of selection.
2) Fuel grinding management
According to the combustion characteristics of fuels, fuel grinding should be managed
to achieve fineness appropriately set. In particular, the separator should have highclassification performance because the mixing of coarse particles increases noncombusted part of coal.

Descriptions

3) Air ratio management
For complete fuel combustion, air beyond the theoretical volume is required when
actual operation is made. If too much air is supplied, however, thermal energy
necessary for its heating becomes a loss. To maintain an appropriate air ratio, theoxygen concentration in the combustion exhaust gas requires strict management.
Oxygen densitometers are installed at the kiln inlet, exhaust gas outlet of thepreheater, etc. For gaining values, they should be checked periodically andmaintained properly.
4) Exhaust gas management
In addition to the above oxygen management, CO and NOx are measured and theirmeasurement data are used for combustion management. NOx is generally said toreflect the temperature of a burner flame but requires appropriate management
because its emission concentration is regulated.
5) Kiln burner management
According to the combustion characteristics of fuels, the basic designs such as thefuel discharge angle of the burner, the primary air ratio, etc., should be reviewed tomaintain the optimum combustion conditions. Even during operation, it is necessary
to optimize the frame shape by changing the burner set position, adjusting the
primary air ratio, etc. according to a fuel change.
6) Cooler operation management
Heat recovery at the cooler greatly affects the combustion management of the kilnburner. Therefore, scheduled maintenance and adjustment and management ineveryday operation are important.

Results

The thermal energy utilization efficiency is improved. (The heat consumption goes down.)

Costestimation
Relatedmatters
Reference- 18 84

Item

Background

Stabilization of coating in kiln

Application
Burning process

Coating formed on the brick working surface in the kiln burning zone lowers the shelltemperature to reduce radiant heat and protects the brick. Unstable coating easily leads
to a brick problem and generates an energy loss by disturbing stable run.

Various measures are taken to form and maintain stable coating in the kiln burning zone.
1) Preventing fluctuation of components in raw meal
One of the causes of unstable coating is the fluctuation of components in supplied
raw meal. For a kiln of unstable coating in the burning zone, the fluctuation ofcomponents in raw meal should be checked and corrective measures should betaken if the fluctuation is great.
2) Preventing the fluctuation of fuel combustion status
If the fuel is changed unreadily to a brand of greatly different combustion
characteristics, the frame pattern will change greatly and the coating may break. It isalso important to prevent the blow-in rate from fluctuating.
3) Preventing kiln hunching
Where the burning conditions change periodically, breakage of coating easily occurs.
Since hunching is often attributable to the fluctuation of the clinker cooler, it isnecessary to stabilize the cooler operationj

Descriptions4) Improving the kiln burner
If the combustion performance of the kiln burner is low, coating generally does notadhere and easily breaks from a slight heat shock. If coating comes off frequently, theburner performance should also be noted.
5) Selecting quality of bricks
The deposition of coating also differs depending on the brick quality. The lining
position should be determined by considering that spinel bricks are less adhesive
than magnesia-chrome bricks.
6) Cooling the kiln shell
Coating is considered to form when liquid-phase mineral of high temperature contacts
with and cooled by the brick working surface and becomes solid. It is thought thatcoating deposition can be strengthened by cooling the shell temperature forcibly to
reduce the temperature of the brick working surface. Both air cooling and watercooling are in practical use.

Results
Costestimation

1) Radiation heat is reduced.
2) Brick abrasion is mitigated (to prevent brick problems).
Kiln shell air-cooling equipment: about 91 thousand US$ [1US$=¥110]

Relatedmatters
Reference- 19 85

Item

Background

Strengthened air sealingat kiln outlet

Application
Burning process

The kiln outlet shell is structurally a free end under very severe thermal conditions, being
exposed to high-temperature clinker and radiant heat from the refractories in the cooler
hood. If the outlet shell has cracks, opens a bell shape and causes a great losses like akiln stoppage by bricks drop.
To protect the kiln outlet shell, the lining refractory of appropriate quality, fixing tip
casting, and forced air cooling is adopted in general. If air sealing at the outlet is notadequate, cool air leaks into the cooler, lowers the secondary air temperature, anddeteriorates the heat consumption.
The kiln outlet has a dual-shell structure where forced cooling is made by air from an
exclusive fan or branched fan from a cooling fan of the clinker cooler.
To prevent part of the air after heat exchange from leaking into the cooler and lowering
the secondary air temperature, a spring-type seal or brush type air seal is adopted.
Air leakage at the kiln outlet produces a much greater influence than that at any othersection because it not only lowers the combustion efficiency of the burner but also
increases the fuel consumption to heat the leaked air.
Air leakage at the outlet must be minimized.
Exhaust air from cooler

Tertiary air
for calciner

To coal dryer

Clinker

Kiln

Cooling fan ofeach chamber

Descriptions
Fig.1 Schematic of the kiln mouth
Tip casting

Outlet refractory
Kiln shell
Cooling air
Air sealing

Fig.2 Air seal at the kiln outlet (Brush type air seal)
As kiln outlet refractories, refractory castables and fired spinel bricks are popular.
SCH13 occupies the greatest percentage used for the tip casting.

Results
Costestimations
Relatedmatters
Reference

As the leaked air was reduced by 160Nm3/min, the heat consumption became about 42
kJ/kg-cl (10 kcal/kg-cl ) less.
50 thousand US$ (5,000t/d) [1US$=¥110]- 20 86

Item

Background

Strengthened air sealing at kiln inlet

Application
Burning process

Air leakage into the cement manufacturing process deteriorates the heat and power
consumption. Since the air leakage at the inlet of the kiln cools high-temperature
combustion exhaust gas and lowers the heat value greatly, it is important to prevent air
from leaking in.
Air sealing at the inlet of the kiln has a structure to mechanically prevent kiln shellrotation and thermal expansion from causing a gap. The figure shows an example of air
sealing structure.
1) Air is sealed by the slide plates installed on the preheater side and the kiln side.
2) The slide plates are always pressed against each other by the air pressure of the air
cylinder.
3) The slide plates have greasing holes to strengthen the airtightness and prevent theirabrasion.
4) The slide plates on the kiln side have raw meal lifting device (boxes or plates) toprevent the leakage of raw meal.
Raw meal guide plates
Brick retainer

Preheater

Brick

Descriptions

Raw meal lifter

Brick retainer
Packing

Slide plates

Kiln shell
Air cylinder

Structure of air sealing at the kiln bottom

Results
Costestimations

The deterioration of heat and power consumption is prevented.
0.2 million US$ (kiln diameter: 6 m) [1US$=¥110]

Relatedmatters
Reference- 21 87

Item

Background

Application

Vertical coal millBurning process

Tube mill had been used for coal grinding. Steel balls were used as the grinding
media, and tube mill should have enough room to allow attrition between the balls
and coal. This result in higher initial costs, higher electricity consumptions and limits
the downsizing of the tube mill.
In a vertical coal mill, drying, grinding, and separating/classifying of coal can bedone simultaneously. Hence, production and energy efficiency is higher. This
technology became popular after oil shock time, when the fuel switched from oil tocoil.
1. Wet coal is feed from the upper part or side of the mill onto the rotating table.
2. It was then crushed and ground by the pressing of the steel roller.
3. Fine coal particles are dried and swept away into the separator by a high velocity
of hot air flow from the bottom of the mill.
4. Separated fine coal particles are captured by a bag filter and used as fuel.
Pulverized coal exit [air sliders]
Coal

Classifier

Descriptions

RollerAir entrance for dryness
Table

Motor reducer

Results

Capable of reducing electricity consumptions for coal grinding by 20-25%.

Cost
estimation
Relatedmatters

About 9 million US$ including cost of supplemental facilities [20t-coal/h][1US$=¥110]

Reference- 22 88

Item

Background

Pulverized coal constant feeder

Application
Burning process

The accuracy of constantly feeding pulverized coal to a cement rotary kiln affects thestability of the burning process and the cement quality.
The selection and daily maintenance of feeding and measuring devices are extremely
important.
The constant feeders for pulverized coal now used in Japan can be classified into thefollowing types. Both types feature high feeding accuracy within ±1% and highmomentary accuracy as well.

Descriptions

Results

1) Table typeThis is a combination of a volumetric table feeder and a weighing hopper that
calculates the table feeder discharged amount from the weight reduction speed of
the table feeder for constant feed.
There is a horizontal rotation table under the hopper. Pulverized coal on the table isscraped off by the scraper board while being rotated with the table. The feedamount is adjusted by the press-in depth of the scraper board.
2) Screw + impact line typeThe impact flowmeter is based on theprinciple that the horizontal component
with impaction force of naturally falling
pulverized coal on the detection plate is
proportional to the momentary weightflow rate.
An impact flowmeter is combined with a
Hopperscrew feeder which enables constantfeeding by controlling the screw feeder
rotation speed.
3) Table + impact line type
FeederAn impact flowmeter is combined with a
Impact line
table feeder which enables constantfeeding by controlling the table feeder
rotation speed.
4) Loop conveyor scale type
A loop-shaped conveyor itself has a
Microcomputerbalance structure. This conveyor has aline
powder inlet on one side and a powder
outlet on the other side with both ends ofthe centerline as fulcrums. Since themechanical structure of either sides ofthe fulcrum is uniform, the tare iscanceled.
Figure: Constant feeder (impact flowmeter)

Stable constant feed free of flushing or pulsation is realized.

Costestimation
Relatedmatters
Reference- 23 89

Item

Background

Adoption of lifter brick

Application
Burning process

To improve thermal efficiency in the calcinating zone of a kiln and to prevent thedeposition of coating to the preheater by a temperature decrease of the kiln bottomgas, four or more bricks are projected per circle to stir raw materials.
Four or more lifter bricks per circle are projecting 100 to 200 mm out of the base bricks
in the calcinating zone to stir raw materials and promote their heat exchange. In
addition, the full conduction of thermal energy to raw materials is expected to lower thekiln bottom temperature and reduce coating deposition to the preheater. As shown in
Fig.1, the lifter brick have an arc shape when the base bricks have an arc shape or asector shape when the base bricks have a sector shape.
Since the lifter bricks are projecting out of the base bricks, their projections easily
crack or spall due to abrasion, thermal stress, or mechanical stress. Therefore, theservice lives of lifter bricks have been extended by improving the material.
Regarding the number of lifter bricks per circle, there must always be lifter bricks in the
raw material beds as shown in Fig.2 because they must stir raw materials without
letting them slip on the bricks in the kiln. If the filling factor of raw materials in the kiln isassumed to be 10%, the central angle of the raw materials is about 90°. Then at least
four or more lifter bricks are necessary per circle. (As the kiln diameter is greater, more
lifter bricks are necessary.)
The lifter brick installation is mainly 2 to 10 m. The locations are not fixed but usuallyalmost from 0.1 to 0.4 if the kiln bottom is 0 and the kiln mouth is 1.

Descriptions
Arch type

Sector
Fig.1 Lifter brick shapes

Lifter brickBase brickRaw materials

Fig.2 General view of lifter brick and the number of bricks installed

Results
Costestimation
Relatedmatters

Deposition to the preheater decreased because the kiln end temperature was lowered
50 to 100°C.
Usually high-alumina brick = 640 to 820 US$ [1US$=¥110]
Lifter brick = 1,800 to 2,700 US$ [1US$=¥110]

Reference- 24 90

Item

Background

Heat insulation of refractories

Application
Burning process

For high-temperature burning in the burning process, reftractories are used for theinternal walls of various facilities. Various heat insulation measures are taken to prevent
heat radiation losses from walls.

The heat dissipation loss at the burning process corresponds to about 4% to 6% of thethermal energy. To reduce this loss, heat insulation measures are taken according toeach section.
1) Kiln burning zone
In this zone, burnt products are the hottest and coating is deposited on the surfacesof refractories (bricks) to protect the bricks and insulate heat. Therefore, the heatinsulation measures in this zone is to form and maintain stable coating.

Descriptions

2) Kiln deposit/defoliation zone
In this zone where coating is frequently deposited and defoliated, spinel bricks ofgreat thermal conductivity advantageous for long-life bricks are often used and theshell temperature is high. Therefore, the following measures were aggressively
attempted to insulate spinel bricks thermally.
1. High porosity: Raising the brick porosity to lower the thermal conductivity
2. Double-layer structure: Double-layer brick made of different materials on the highand low temperature sides
3. Attachment: Attaching a heat insulator partially to the back of the low temperatureside
All of the above measures, however, have a problem in life and almost none ofthem is now in use.
3) Kiln calcining zone
For the calcinating zone of comparatively low temperature, refractory heatinsulating bricks of low thermal conductivity are used, as well as the conventional
refractory bricks made of high alumina or clay. The refractory heat-insulating bricks
are also burnt or not burnt according to the purpose of use.
4) Preheater
Excluding the lower part of the preheater where the temperature is comparatively
high, the two-layer structure is used with heat-insulating castables on the back. A
wet spraying process for castables was recently developed and the construction
efficiency is being improved.
5) Cooler and extraction air duct
Two-layer heat insulation is applied with a heat insulator of calcium silicate on theback.

Results

Heat dissipation decreased with a decrease of the kiln surface temperature.

Costestimation
Relatedmatters

Stabilization of coating in kiln

Reference- 25 91

Cooler width control

Item

Background

Application
Burning process

With a production capacity increase by the implementation of the SP and NSP methods,
the grate-type clinker cooler also became large. Since the effective width of the cooler
was too large for the clinker drop width, the problems of cooling air blowing through andheat spot occurred simultaneously.
The blow-through problem lowers the secondary air temperature and the heat spot
damages the grates. To prevent these problems from disabling stable run, the cooler
was altered.
As a solution to these problems, width control was attempted to adjust the substantiallyeffective width of the cooler appropriately. Through a lot of experiences, individualcompanies have established their unique technologies.
1) The effective width of the cooler should be set appropriately by comprehensively
considering the clinker load, the cooler length, the cooling blow rate in each air room,and the ability of each cooling fan. Experience in actual operation is also an
important factor for this judgment.
2) General width control is for the clinker layer thickness of 500 to 800 mm at a grate
driving speed not mechanically difficult.
3) It is also necessary to determine a width control position. By considering theunevenness of grain size caused by a drop from the kiln, width control on the finestream side should be stronger.
Width control is a basic technology to optimize a grate cooler of the air chamber type.
However, the same concept applies to the air-beam cooler recently becoming prevalent.

Descriptions

Fixed (no-hole) grate installation position
Rotary kiln

Holed grate
Figure: Width control (arrangement of holed grates and fixed grates with no holes)

Results
Costestimation
Relatedmatters

1) Heat recovery efficiency was improved by preventing the blow-through of cooling air(heat consumption rate down).
2) Grate burn is prevented.
64,000 US$ [1US$=¥110]
Automatic AQC speed control
Air-beam cooler

Reference- 26 92

Automatic control of
AQC grating speed

Item

Background

Application
Burning process

Recovering the hot secondary air and transporting clinkers are the two importantfunctions of a clinker cooler. For the balanced execution of these two functions, it isnecessary to always maintain the clinker layer of appropriate thickness on grates.

1) With the wind pressure in Chamber 1 of the cooler as a substitute characteristic forthe clinker layer thickness on grates, the driving speed of Level 1 grates is
automatically controlled to keep the wind pressure always at the setting.
2) Under this control, if the clinker properties change, the response may become
sensitive. Therefore, step control with insensitive zones may be combined and thecontrol method may be switched according to the cooler status.
3) The volume of clinker transportation changes with the driving speed of Level 1
grates. To keep the clinker layer thickness constant, the proportional control of grate
driving speed with a time delay in mind is applied to the grates of Levels 2 and 3.

Calciner secondary air

Coal mill cooler
exhaust fan

Rotary kiln

Descriptions
Secondary air for burning

Level 1 grates

UP

Level 2 grates
Level 3 grates

Chamber 1 Chamber 2 Chamber 3 Chamber 4 Chamber 5 Chamber 6

Chamber 7

Figure: Outline of automatic AQC speed control

Results
Costestimation
Relatedmatters

The thermal recovery efficiency was improved by maintaining appropriate layer thickness(heat consumption rate down).

Cooler width control

Reference- 27 93

Item

Background

Installation of partition plates

Application
Burning process

A clinker cooler is divided into an area where cooling air equivalent of the necessary air
volume is blown in (hereinafter, the secondary air recovery zone) and the succeedingarea (hereinafter, the exhaust heat recovery zone). To recover the secondary air of hightemperature in the clinker cooler, the efficiency of heat recovery from the former area
should be maximized.
Since the hot clinkers on grates are cooled from the lower layer, the top of the clinker
layer remains hot in the secondary air recovery zone and dissipates heat much byradiation.
1) To gather this radiant heat in the secondary air recovery zone and use it for heating
the secondary air, a partition plate is installed at the border between the secondary
air recovery zone and the exhaust heat recovery zone.
2) A partition plate is installed each behind the air extraction port for calciner and above
the rear end of Level 1 grates. Partition plates are generally fixed but may also be
movable or hanged.

Secondary air recovery zone

Exhaust heatrecovery zone

Coal mill cooler
exhaust fan

Calciner secondary air

Rotary kiln

Secondary air
for burning

Partition plate

Descriptions
Level 1 grates

UP

Level 2 grates

Chamber 1 Chamber 2 Chamber 3 Chamber 4 Chamber 5

Level 3 grates

Chamber 6

Chamber 7

Figure: Installation of AQC partition plates

Results
Costestimation
Relatedmatters

The thermal recovery efficiency was improved by maintaining appropriate layer thickness(heat consumption rate down).
45,000 US$ [1US$=¥110]
Cooler width control

Reference- 28 94

Item

Background

Application

Air beam type clinker cooler

Burning process

Improvement of heat recovery rate for secondary or tertiary air from the heat inclinker is one of the most important technologies in the burning process. As
heat recovery rate in conventional grate coolers are approximately 50 to 60 %,more improvement has been desired.
When high temperature clinker is dropped on the grate of cooler from the outlet of kiln,
it is not in flat or balanced. With the conventional cooler, cooling air is supplied to each
air chambers, therefore, improvement of heat recovery rate is limited by imbalance ofcooling air.
This problem is solved by installing air beam type cooler which has unique point
as follows;
1) Cooling air is supplied directly to each block that is constructed by 4 to 8 piecesof grate plate.
2) The grate plate is structured, as more air tight and fined clinker is not able tospill down through grate.
3) This type of grate can be installed to the part of kiln outlet or main heatrecovery area.
As cooling air is controlled for each block, air distribution can be optimized.
Therefore, heat recovery rate is improved and the life of grate plate is extended.

Descriptions

By 2000, these types of coolers have been installed into approx. 30% ofJapanese cement plants. Most of them (71%) have been installed at kiln outlet
part of existing cooler. For 57% of these cases, improved heat recovery rate is
not more than 5 %. In case only installed at kiln outlet part, improvement ratecannot be adequate.
Fixed

MovableFixedClinker layer

MovableClinker layer
For
Movable beam
Fixed beam
Air chamber

Air chamber typeAir beam typeComparison of cooling air supply

Results
Costestimation
Relatedmatters

1) Heat consumption: Approx. 42 – 167 kJ/kg decrease2) Power consumption: Approx. 0.5 – 1.5 kWh/t decrease3) Maintenance cost of grate plate: decrease (Extension of life)
About 2.7 ~4.5 million US$ for 1-stage cooler retrofitting

Reference- 29 95[1US$=¥110]

Item

Background

Automatic measuring device
for free lime in clinker

Application
Burning process

As well as the bulk density (liter-weight) of clinker, free lime (herein after, f-CaO) content
in clinkers is an important factor to know clinker quality and clinkering conditions.
f-CaO measurement used to be performed a few times a day by chemical analysis
method. However, implementing an automatic measuring device remarkably increases
the measuring frequency to 24 times a day or more.
The volume of information about the clinker quality and clinker condition increases. By
reflecting this information, stabilization of clinker quality can be gotten and then heatconsumption of the kiln process can be reduced.
For the automatic online measurement of f-CaO in clinkers, the following two methods
are known:
1) X-ray diffraction method
This method is based on a technology developed in Japan. Prepared
representative clinker sample are ground into fine particles and molded by press.
Then the diffraction strength of CaO is measured by using an X-ray diffraction device
to determine the f-CaO concentration (content). In this method, clinker chemicalcomponents can be analyzed from same molded sample on X-ray fluorescence
spectrometer. Unlike the chemical analysis method or electrical conductivity method,
no chemical agents (solvents) are necessary for treatment.

Descriptions2) Electrical conductivity method(1) Principle of measurement
f-CaO in clinkers is dissolved into the ethylene glycol solvent by the following
reaction:
CaO + (CH2OH)2 → Ca2+ + (CH2O)22- + H2O
2+
Ca and (CH2O)22- give conductivity to the solution.
Since these ions indicate conductivity proportional to the concentration, the amountof f-CaO in clinkers can be estimated by measuring the conductivity.
(2) Outline of system
Prepared representative clinker sample is transported to a f-CaO measuring device
and ground by a disk mill. Fixed amounts of the clinker powder and the ethylene
glycol solvent are put into beaker and the electrical conductivity is measured.

Results

By reflecting the tendency of f-CaO data transition in running operation, the clinker
quality can be stabilized and the kiln heat consumption rate can be reduced.
As of Year 2000, the implementation rate is 35% (electrical conductivity method: 57%,
X-ray diffraction method: 43%).

Cost
estimation(1) X-ray diffraction method: About 460 thousand US$ (Kiln capacity: 5,000 t/d)
[1US$=¥110](2) Electrical conductivity method: About 410 thousand US$ (Kiln capacity: 5,000 t/d)
[1US$=¥110]

Relatedmatters

Automatic measurement of clinker bulk density (liter-weight)

Reference- 30 96

Item

Background

Automatic measuring device forclinker bulk density (liter-weight)

Application
Burning process

Keeping the clinker quality constant is important factor for getting better and stablecement product. Because the value of clinker bulk density (liter-weight) shows orreflects kiln burning conditions and clinkering conditions of materials, it is widelyused as an important indicating factor for kiln operation.
However, there are problems such as accuracy of measured value and/or longer
sampling interval since the works were done manually. Automatic sampling system
and measurement are expected.
A sampler is installed at the appropriate point of clinker transportation line. The
clinker of 5 to 10mm diameter is selectively sampled with it and then pre-decided
quantity of sampled clinker is automatically send to weighing vessel in order tomeasure the clinker bulk density. Using this measured value, kiln operator adjusts
kiln operating conditions, if necessary, to keep optimum conditions.
This device is usually installed and used with automatic f-CaO measurement devices
and automatic clinker chemical component measurement devices.
As of 2000, implementation rate is about 20% and most of the above devices are usedon the on-line system.

Sampling damper
Sieving

Bucket elevator

Descriptions

Over 40 mm

Sieving

Less than 5 mm

Over
FeederScreenClinkerOver 10mm
and lessthan 5mm(5 to 10mm)
Measurement of clinker
bulk density(Return line)
To f-CaO measuring devices

Automatic measuring system for volume weight

Results
Costestimation
Relatedmatters

The reliability and continuity, which is gotten by shortened sample interval, of thedata of clinker bulk density are improved. And more appropriate kiln operating
conditions can be gotten.
Main unit only: About 91 thousand US$ (excluding the sampler and sample transportation
system) [1US$=¥110]
Automatic measuring device for free lime

Reference- 31 97

Closed-circuit grinding system

Item

Background

Application
Finishing process

In the initial grinding system using a tube mill, ground materials are fed into and groundin the mill and all the output from the mill is used for products.
This open-circuit grinding system required improvement both in quality and operating
efficiency to solve the problem of wide grain size distribution caused by inadequate
grinding and excessive grinding.
The closed-circuit grinding system is the open-circuit system with a large classifier. All
ground materials are led into a separator and classified into refined powder (products)
and coarse powder (return powder). The coarse powder is returned to the mill andground again with newly-fed raw materials.
One of the important indexes to indicate the run status of the closed-circuit grinding
system is the circulation ratio that is the ratio of the amount of powder returned from theseparator and the newly-fed amount. The optimum value depends on the mill conditions(ball size, liner shape, and slit size), the separator’s classification performance, and theraw material characteristics (clinker grain size and crushability). Therefore, it is importantto check the optimum value for each mill.
Groundmaterials

Tube mill

Refined powder (Product)

Descriptions

Classifier

Coarse powder(Returned powder)
Refined powder(Product)

Groundmaterials

Tube millPower consumption rate of groundmaterials (kWh/t)

Fig.1 Open-circuit grinding system

Specific surface area of cement (cm 2 /g)

Fig.2 Closed-circuit grinding system

Results

Costestimation
Relatedmatters

1)
2)
3)
4)
5)
6)

Fig.3 Power consumption rates foropen-circuit and close-circuit grinding(cement grinding)

The grinding capacity increases.
The grain size distribution of refined powder becomes sharp.
The refined powder temperature becomes low.
The power consumption rate decreases.
The abrasion of liners and balls is suppressed.
The grain size distribution of products can be adjusted by changing the circulation ratio and theclassifier’s run status.

455 million US$ (3000 kW mill) [1US$=¥110]

Reference- 32 98

Item

Background

Use of grinding aid

Application
Finishing process

In general, the grinding energy efficiency of a grinder is very low. To raise the grinding
efficiency, therefore, a small amount of third substance other than the grinding media andground materials is added as a grinding aid.
1) A grinding aid works as follows:
A tube mill generally loses its grinding efficiency remarkably at fine grinding. This isbecause fine particles from ground materials agglomerate and adhere to the millliners or grinding media as coating, reducing the impulsive force of the mill. In
addition, the agglomerated particles are mixed into the coarse powder in theseparator and recirculated throughout the mill. There are various theories about thecause of agglomeration. The most convincing theory is that destruction in a crystal
grain by alite biases the polarity of the fractured surface. A grinding aid prevents thisagglomeration to improve the grinding efficiency.

Descriptions

Results

Costestimation

2) There are many substances that improve the grinding efficiency. For actual use,
however, the following conditions must be satisfied:(1) The price is reasonable for the grinding costs.
(2) The substance is not detrimental to the product quality but improves it instead.
(3) Diethylene glycol is used most widely as a grinding aid satisfying the above
conditions.
(4) A grinding aid is generally added to the clinkers at a fixed rate from 0.01 to 0.03%
before supply to a finishing mill.

1) The grinding amount is up 4% to 6% per addition of 0.01%.
2) The aid also improved the dispersibility and fluidability of cement (powder) and delayed
weathering.
Diethylene glycol: 1,360 to 1,820 US$/kl [1US$=¥110]

Relatedmatters
Reference- 33 99

Item

Background

Classification liner for the second
chamber of tube mill

Application
Finishing process

The second chamber of a finishing mill is mainly for fine grinding. Therefore, using smallballs was known to be more efficient because its increases the surface area of media andstrengthen the grinding effect.
For the conventional mill using a liner with lifter, however, it was difficult to reduce the balldiameter drastically because the grinding efficiency is extremely lowered by reverse
classification where small balls gather at the inlet of the second chamber and mediumsized balls gather at the outlet.
To solve this reverse classification status, a classification liner was developed.
The classification liner is inclined toward the inlet of the mill to make scraped balls roll inthe direction. Under the influence of the rotational force (centrifugal force) of the mill,larger balls roll toward the inlet of the mill more easily (larger balls gather at the inlet ofthe second chamber).
The development of this classification liner allowed small balls from 20 to 17 mm indiameter to be used for the second chamber and enabled efficient grinding without
excessive grinding.
Since this liner also improved the coarse grinding capacity at the inlet of the second
chamber, the grinding performance of the entire mill may improve of the first chamber ismade short and the second chamber long.

Classification liner (example)

Liner with lifter (example)

Rotating
direction

Descriptions
Liner with lifter

Inlet

First
chamberClassification liner

SecondchamberA-A view

Fig.1 Classification liner and liner with lifter
Example 1
Example 4

Example 2
Scraping classification liner
Example 3

Fig.2 Types of classification liner

Results
Costestimation
Relatedmatters

1) The power consumption rate is down 1 to 2 kWh/t.
2) The optimum circulation ratio becomes smaller than ever and reduces load on theseparator and conveyor.
682,000 US$ (3000 kW mill) [1US$=¥110]
Introduction of pre-grinder

Reference- 34 100

Item

Background

Clinker flow rate regulator
for tube mill

Application
Finishing process

For efficient grinding by a tube mill, it is important to secure an appropriate amount ofground materials for the balls, or to maintain the powder level.
The powder level of clinkers ground coarsely in the first chamber is affected by theaperture rate of the partition butt strap at the outlet and the slit size. In general, however,the powder level is set higher than the optimum value to prevent clogging in the mill.
Under these conditions, large balls idle and waste energy because the powder level inthe first chamber is low. Since clinkers move to the second chamber before full grinding,the fine grinding efficiency in the second chamber becomes low.
The powder level can be kept optimum in the first chamber by adjusting the slit size andquantity of the partition. Since fine adjustment (clinker size) is not possible because
welding takes time and the crushability (coarse grinding) changes with the conditions, aclinker flow rate regulator was implemented or developed for adjustment according to theconditions.
For clinker flow rate adjustment, the angle of scooping ground materials that flowed into
the partition is adjusted or an on-off valve attached to the ground material discharge port
is operated from outside the mill.
The sound pressure level in the first chamber is the substitute characteristic for the
powder level. A loss of crushing energy can be prevented by judging the sound pressurelevel and adjusting the flow rate regulator for full coarse grinding in the first chamber.
Scoop

Descriptions

Fig.1 Clinker flow rate regulator(example)

Results
Costestimation

Fig.2 Clinker flow rate regulator(example)1) The power consumption rate is down 2 to 3 kWh/t.
2) The lives of liners and partition butt straps are extended.
3) The deterioration of coarse grinding efficiency by ball cracks is prevented.
About 320,000US$ (1000 kW and ∅ 3 m class mill) [1US$=¥110]

Relatedmatters
Reference- 35 101

Item

Background

Optimization of grinding media

Application
Finishing process

To minimize the power consumption rate of a finishing tube mill, the ball size and themixing and filling factors have been optimized. These years, however, the ball diameter isdecreasing as a classification liner and a pre-grinder are adopted.
In addition, the lives of such grinding media as balls and back plates are being extended
by improving the material (abrasion resistance).
1) Optimum ball size and mixing ratio
For the optimum ball size and ball mixing, Starke, Bond, Paulsen, Bombled, andothers have been proposing various calculation formulas from a long time ago.
Based on these formulas and empirical rules, mixing has been determined.
In recent years, the ball size is decreasing by the adoption of a classification liner anda pre-grinder. (The rate of tube mills using the smallest ball of 17 mm was about 10%
in the 1979 survey by Japan Cement Association but increased to 80% in the 1991
survey.)Descriptions

2) Filling factor of grinding media
The filling factor of grinding media greatly affects the grinding capacity and power
consumption of a mill. For cement grinding, the optimum value is in the range from
20% to 40% around 30%.
To keep the filling factor of grinding media appropriate for high grinding efficiency,
appropriate replenishment is necessary for compensating the abrasion of grinding media.
Methods of determining media replenishment timing can be classified into five types
below. Actually, however, they are used independently or in combination.
(1) Load power(2) Blank height measurement(3) Run time(4) Ground tonnage(5) Other (mainly grinding efficiency)
The amount of replenishment is determined by the following three elements:(1) Blank height measurement (Ball center measurement)(2) Load(3) Other
These elements are used independently or in combination for determination.
3) Improving the material (abrasion resistance) of grinding media
Many back plates used to be made of high-magnesium cast steel and many balls
used to be made of carbon steel. The recent advance of manufacturing technology isincreasing both back plates and balls made of high-chromium cast iron.

Results

A finishing tube mill can be operated in the optimum status.

Costestimation
Relatedmatters
Reference- 36 102

Item

Background

Improvement of separator

Application
Finishing process

With the conventional separator, which has built-in fan, such as “sturtevantseparator”, it is difficult to expand the grinding capacity by the scale-up because oflower classification efficiency. Therefore, a new high efficiency separator has beendeveloped.
The separators are divided into three types according to their structures. The first
generation is the built-in fan type, the second is the cyclone air type, and the third is
the rotor type.
１）Mechanism(1) The cyclone air separator comprises the separation section and the cyclones tocollect the fine particles. The air circulates by the outside (located) fan. The
separation section consists of air vanes and turning blades.
(2) The rotor type separator is the vortex flow type air separator comprised of guidevanes and rotating rotor. The fine particles are collected by a bag filter andcyclones equipped outside the separator housing.
２）Characteristics(1) The second and third types have lower circulation of the fine particles andhigher classification efficiency with more grinding capacity and less specific power
consumption. The third type boasts higher classification efficiency with morecompact structure.
(2) The second and third types can adjust easily the fineness of products undervarious operating conditions. The third type can control classifying points in amore wide range just by varying the revolutions per minute.
(3) The products temperature has been decreased as a result of the second andthird types introducing much cooler air into the separator. The false set of
cement is hard to occur.

Descriptions

Fig. 1. Cyclone air separator①separation chamber② tailings cone
③ air vanes④ distributor plate⑤ counterblades⑥ feed spout⑦ gearbox⑧ motor⑨ fines outlet⑩ tailings outlet⑪ cyclones⑫ air duct to fan⑬ fan⑭ dust collecting
pipe to filter⑮ return air duct

① guide vanes② rotor blades③ distributor plate④ rotor shaft⑤ feed spouts⑥ sealing⑦ air + fines outlet⑧ tailings outlet⑨ air inlet⑩ gear box⑪ motor① separator part②optional duct ext. to fit layout③ desagglamerator④ grit separator⑯ spreader plate⑤ fines outlet⑰ feed from press⑥ bearling housing ⑱ air by-pass⑦ shaft rotor joint ⑲desagglomerator rotor⑧ guide vane
⑳ guide vane sections⑨ rotor blade
6 outlet to press⑩ reject cone
7 air inlet⑪ support
8 rotor blades⑫ reject outlet valve⑬ feed inlet⑭ densit wearcast 2000
⑮ air lockFig. 3. Rotating type separator

Fig. 2. Rotating type

- 37 103Results
Costestimation

1)Grinding capacity2)Specific power consumption

15% to 25% (Increase)
10% to 20% (Reduction)

About 4.5 million US$ for 3,000kW-mill

Relatedmatters
Reference- 38 104[1US$=¥110]

Item

BackgroundPre-grinding of roll press system

Application
Finishing process

To decrease the specific power consumption in finishing process or to increase the output
of finish mill, pre-grinding roll crasher, which is installed in the upstream of tube mill, hasbeen introduced since the middle of 1980s.
1) System & StructureThis system increases the output of finish tube mill by installing the pre-grinding rollcrusher in upstream of the tube mill.
By passing through the opening between two rolls (a fixed roll and a movable one),materials are crushed by high-pressure(as shown in Fig.1). High-pressure to
crush the materials are generated by oil-hydraulics. Abrasion-resistant material is
attached on the surface of rolls.
Various kinds of system are available, and the typical one is shown in Fig.2.
2) Operation & Maintenance(1) Exerting pressures are 50 to 100bars on the basis of the projected area of theroll, onto the layer of clinkers passing between the two rolls.
(2) Abrasion-resistant parts are classified in one unit type or segment type. In any
type, abrasion-resistant parts should be replaced to new one or hard facing, if
they are worn out.
Bucket elevator
Motor,
Gear
reducerMovable roll

Clinker
Pre-grindingroll crusher

Fixed
roll

Descriptions

Frame

Separator

Product

ClinkerTube millFig. 2 Flow sheet

Fig.1 Structure

Results
Costestimation

1) Grinding capacity of finish mill increases about 30%.
2) Specific power consumption in finishing process decreases about 10%.
The installation cost is about 2.7 million US$ including auxiliary and construction cost,in case of 100t/h output. [1US$=¥110]

Relatedmatters
Reference- 39 105

Item

Background

Application

Pre-grinding of roller mill system

Finishing process

For the purpose of decreasing the specific electrical power consumption in thefinishing process, this installs a vertical roller mill for pre-grinding of clinker in the
upstream of the tube mill. The roll press system preceded as pre-grinding system,
but there are many machinery troubles (flake and crack of roll surface, damage of roll
shaft and bearing) for high pressure. This system was developed on the verticalroller mill which has achieve satisfactory results. It was introduced from the latter halfof the 1990s, and the introduction rate in 2000 is 13%.
This system installs a vertical roller mill (of high grinding efficiency) for a pre-grinding
in the upstream of the tube mill. Clinkers are milled the turn table and 2〜4 rollers.
The basic structure is the same as vertical roller mills for raw materials or cement.
But the roller mill for pre-grinding have no classifier and air sweep. Pre-groundclinkers were discharged outside mill. Fine particles are separated from pre-groundclinkers with vibrating screen, and they are fed to finishing tube mill.
The structure (Fig.1) and the flow (Fig.2) are shown below.

material feeding

ＢＥ（gypsum）
clinker

Descriptions

ＢＥ

separatorrollerproducttablerollermill
pre-grainding
Fig.1 Structure

Results
Costestimation
Relatedmaterials

tube mill

Fig.2 Flow1) rinding capacity of finish mill increases about 30~60%.
2) Specific power consumption in finishing process decreases 10~20%.
6.4~9.1 million US$ including cost of ancillary facilities and construction [100t/h][1US$=¥110]1) Raw material pre-grinding roll crusher

Reference- 40 106

Item

Background

Automatic run control of tube mill

Application
Finishing process

Only several percent of the power consumption for a tube mill is used effectively andmost of the energy is dissipated as heat or sound. Therefore, raising the grinding
efficiency of the mill is very important for reducing the power consumption rate. To raise
the efficiency, the filling factor of grinding media and materials to be crushed in the millshould be kept optimum. For this control, the power of the bucket elevator at the milloutlet used to be kept constant. This control method, however, has a disadvantage ofreverse operation in case that the mill should be clogged. To compensate for thisdisadvantage, mill acoustic control and mill vibration control have been adopted. In
addition, fuzzy control was also developed and implemented.
The filling factor in a mill is kept constant by the following automatic control:
1) Power (current) control of the bucket elevator at the outlet of the mill
The power of the elevator at the outlet of the mill is detected and the mill supply rate
is adjusted to achieve the target power value. This method became popular at theearliest. This control has a disadvantage of reverse operation that the elevator power
decreases and the supply amount increases when the slit clogging of the butt strap
in the mill progresses. In this case, slit clogging must be monitored by the air flowrate through the mill. As of Year 2000, this control is adopted by about 70% of thefinishing tube mills in Japan.

Descriptions

2) Mill acoustic control
This control uses the fact that the grinding sound in a mill changes with the filling
factor of ground materials in the mill. The grinding sound in the first chamber ispicked up by a microphone and the supply amount is controlled by the pitch of thesound. When several mills are running adjacently at the same time, it is difficult to
detect the grinding sound. This control is adopted by about 10% of the mills inJapan.
3) Mill vibration control
This control uses the fact that the vibration of the large metal of a mill changes withthe filling factor of ground materials in the mill. It is comparatively difficult to receive
the influence of adjacent mills simultaneously running. As of Year 2000, the adoption
ratio in Japan is less than 10%. According to the result of a survey by theCommittee, the operators are very satisfied with the control performance.
Fuzzy control automatically optimizes the filling factor in a mill.
4) Fuzzy control
Based on the mill acoustic level, elevator power, mill differential pressure, and somemore process data, fuzzy inference from present rules is conducted on changes ofmill grinding conditions by a computer. Then the target value of filling factor in themill is optimized to improve the grinding efficiency. Experiences and techniques areneeded to set the rules. Once the rules have been set appropriately, efficient run ispossible. As of Year 2000, this control is adopted by less than 10% of the mills inJapan.

Results

1) The power consumption rate is down about 2 to 10%.
2) The labor for running operation can be reduced.
3) The quality becomes stable because of stable run.

Costestimation
Relatedmatters
Reference- 41 107

Item

Background

Vertical roller mill for
cement grinding

Application
Finishing process

In the cement grinding process, grinding system using the tube mill is widely applied forlong year. Recently, especially from 1980s, grinding system using the vertical roller mill,which has effective grinding performance, is developed and applied in the cement
grinding process.
Basic equipment structure of the vertical roller mill for cement grinding is the same as
the vertical roller mill of raw material and coal grindings.
The materials such as clinker and gypsum fed into the mill are ground by compression
and shearing forces between the grinding table and two or four rollers, which are
hydraulically loaded and controlled. Ground cement materials are sent to separator
installed in mill upper position by air and classified to coarse particles and fine product.
Coarse particles are returned on the grinding table to re-ground and the fine product issent to dust collectors such as cyclone and/or bag filter.

Descriptions

The advantage of the vertical roller mill for cement (comparison with the tube mill)
1) Highly efficient grinding is possible with considerably low electrical power
consumption.
2) The residence time of cement grinding in the vertical roller mill is much shorter
than that of tube mill. Since system operational control response is superior,quality management on the cement product is easy.
3) Therefore the vertical roller mill for cement produces little heat for grinding, andquality trouble due to the excessive rise of temperature of cement is less likely tooccur.
4) The installation area of the vertical roller mill is about half of tube mill grinding
system.
But the introduction of a pre-grinding grinder has become mainstream in Japan, and theabove-mentioned technology is spreading mainly overseas.

Results

Electrical power consumption can be reduced by 30 % (compared with the tube mills).

Costestimation
Relatedmatters

External circulating system to vertical roller mill for cement.

Reference- 42 108

Item

Background

External materials circulating system
to cement grinding vertical mill

Application
Finishing process

In the cement grinding process, the vertical roller mill having high grinding
performance is applied especially cement grinding instead of the conventional tube
mill. For further power saving, external material circulating system is adopted assame as raw material grinding process.
As described in Page 2 of External Circulating System to Vertical Roller Mill, theexternal circulating system is adopted to vertical roller mill grinding process in order toreduce power consumption of mill fan. As explained in it, uncrushed large size
materials jumped out from table of the mill fall through gas inlet box and collected by
the external circulating system installed below the mill. And then they are retransported to fresh material feed equipment to re-send the mill. Since the uncrushed
raw materials are not blown-up by the gas, transportation energy of the gas, which is
generated by mill fan, extremely decreases.
In the conventional roller mill system, in which the proposed external material
circulation system is not installed, the power consumption by the mill fan occupies
60% of the system because high speed gas flow is blown at the around of the table toprevent falling of uncrushed larger material jumped out from the table.
To the contrary, vertical roller mill having external circulating system does not require
the high and large gas flow because the uncrushed materials can fall from the table toit and be re-sent to mill.
As the result, gas flow rate is reduced about 30%, pressure loss is also reduced about
30% and power consumption of the mill fan reduces about 50%.
The external circulation ratio (=external circulation material flow / new feed material flow)
is about 50 to 100%[Conventional process]Descriptions
Mill fan
New feedmaterials

Gas

Dust collector(cyclone, EP etc.)

Vertical mill

Product (cement)
Stone discharge amount: To zero

[New process](External circulation)

Mill fan

New feedmaterials

Gas

Dust collector(cyclone, EP etc.)

Vertical mill

Product (cement )External circulation system

Results
Costestimation
Relatedmatters

Specific power consumption is down about 10%.
System with a grinding capacity of about 100 t/h (including the incidental facilities andconstruction expenses): About 730 thousand US$ [1US$=¥110]
External circulating system to vertical roller mill / Raw material process

Reference- 43 109

Item

Background

Automatic control
of cement grain size

Application
Finishing process

The grain size management of cement as the final product is important for maintaining
stable quality and efficient run. When an finishing mill is in actual operation, however, thecement grain size changes with the passage of time under the influence of many factors.
Therefore, a technology was developed and implemented to adjust the separator
automatically.
In finish grinding, the grain size of refined powder (product) changes with the passage oftime under the influence of various factors even when the running conditions are fixed.
These factors are as follows:(1) Crushability of clinker(2) Grain size and temperature of clinker(3) Type and addition rate of plaster and mixture
Of these factors, a change of the clinker properties cannot be avoided to some extent asa main factor if the conditions of ground materials and facilities are considered. A means
was expected to stabilize the grain size by absorbing the influence.
For finish grinding, the mill run is often intermittent. The early stabilization of refined
powder grain size after mill activation is another subject to solve for maintaining thestable quality and making the run efficient.
Refined powder is automatically sampled and measured by a grain size distribution
measuring device of the laser diffraction type. Then the separator blade or rotor rotation
speed is automatically adjusted so that the measured value will match the target.

Descriptions

Results
Costestimation

1) The cement quality (grain size) is stable.
2) The power consumption rate is down 3 to 5%.
About 364,000US$ [1US$=¥110]

Relatedmatters
Reference- 44 110

Item

Background

High efficiency grinding of
blast furnace slag

Application
Finishing process

In the past, slag grinding is performed in a tube mill with dryer. This requires
relatively higher power consumptions, and efficiency improvement in this process
has become a great concern.
Improvements in slag grinding efficiency wasdeveloped and implemented with existing cement manufacturing technology.
Improvements in the grinding process to produce fine granulated blast furnace slag
suitable for use in the production of blast furnace cement was achieved with pregrinding and vertical mill technologies used in cement manufacturing.
1. The installation of vertical mill
In a vertical coal mill, drying, grinding, and separating/classifying of groundmaterial are done simultaneously. The hot air used for drying is supplied with a
hot wind generator. Slag contains iron grain, which could damage the rotatingtable and aggravate grinding efficiency. Hence, the removal of these irongrains before commencing the grinding process, using an external circulation
system with a magnetic-separator device, is crucial.
2. The installation of pre-grinding equipment
There are cases where a vertical mill is installed to the existing tube mill toenhance grinding efficiency while reducing power consumption. With the use ofvertical mill, pre-grinding and cement grinding processes are performed
separately. Reduction in the size of grinding media used in the tube mill is
expected to improve grinding efficiency. However this would partially ruin
overall efficiency improvement level.

Descriptions
Bag
Filter

Separater

Separater

External Circulation

Vertical M ill
Heat Generator

Tube M ill

Fig. The example of the combination of tube mills andvertical mill

Results

Reduction in unit electricity consumption (Blended value 4,000cm 2/g)
* Tube mill 70kWh/t (approx., excluding drying)* Vertical mill
<40kWh/t (including separator, wind-chamber/fan, conveyor
systems, and etc)

Cost
estimation

About 7.3 million US$ including cost of supplemental facilities and construction fees
[40t/h] [1US$=¥110]

Relatedmatters
Reference

Introduction of vertical raw material mill, vertical cement mill, vertical coal mill.

- 45 111

Automatic input facilities
for waste tires

Item

Background

Application
Use of Alternative Fuels
and Raw materials <AFR>

Waste tires used to cause illegal disposal and other social problems because theirrecycling by tire manufacturers or effective use as a fuel could not catch up with thegrowth.
The cement industries in Japan tackled this problem early and has been using waste tires
as a substitute fuel since about 1980.
1)

After used tires from passenger cars, trucks, and buses are cut or kept them on ashelf as they are, they are put into a kiln inlet (kiln bottom) to use them as a heatsource for burning clinkers.
2) The tire input facilities generally consist of an aligner to automatically align tires and aconveyor to transport the aligned tires to the kiln inlet. A specified number of tires are
input at fixed intervals.
3) In addition, waste tires may be processed with a fluidized bed furnace in the middle ofan air bleed duct to heat the secondary air (air recovered from the clinker cooler) for
calcinery.
Fig. shows a waste tire processing flow by the kiln inlet input system and the fluidized bed
furnace system.
Fluidized bed furnace system

Preheater

Waste tire

Descriptions

Aligner
DumperConveyor
Fluidized bed
furnacecalciner
Fuel
Waste tire
Aligner
DumperKiln

Conveyor

Clinker coolerkiln inlet input system

Fig. Waste tire processing flow

Results
Costestimation
Relatedmatters

The effective heat from waste tires is about 25 to 29 MJ/kg (6,000 to 7,000 kcal/kg). Fossil
fuels for the same amount of heat can be saved.
System for 10,000 t/year: About 2.7 million US$ [1US$=¥110]
Waste tire gasification facilities

Reference- 46 112

Item

Background

Waste tire gasification facilities

Application
Use of AFR

Waste tires used to cause illegal disposal and other social problems because theirrecycling by tire manufacturers or effective use as a fuel could not catch up with thegrowth.
The cement industry tackled this problem early and has been using waste tires as a
substitute fuel since about 1980s.
The conventional method of putting waste tires into a kiln as they are, however, has aquantitative limit depending on the kiln size. The gasification technology was developed toincrease the capacity and improve the heat energy efficiency.
1) Used tires from passenger cars, trucks, and buses are put into a gasification furnace
as they are or after cutting. The tires are heated in a reducing atmosphere and gas
produced by their thermal decomposition is led into a calciner for effective use as a
substitute fuel.
2) Steel and other incombustibles are discharged from the gasification furnace andeliminated from the system. This solves such problems as non-uniform components
attributable to the mixing of much steel.
3) There are several types of gasification furnaces, such as the fluidized bed type and thekiln type.
Fig. shows a flow of waste tire gasification flow by a fluidized bed furnace.

Preheater

Descriptions

Fluidized bed
furnace

Waste tire
AlignerConveyor
Incombustibles
calciner
Fuel

Kiln
Clinker cooler

Fig. Waste tire gasification flow

Results
Costestimation
Relatedmatters

The heat energy from waste tires is about 25 to 29 MJ/kg (6,000 to 7,000 kcal/kg). Fossil
fuels for the same amount of heat energy can be saved.
System for 7,000 t/year: About 1.8 million US$ [1US$=¥110]
Automatic waste tire input facilities

Reference- 47 113

Waste oil and oil sludge
input facilities

Item

Background

Application
Use of AFR

Waste oil and oil sludge used to be left oil drums or incinerated. As the future shortage offossil fuels is anticipated, waste oil and oil sludge utilization technologies have beendeveloped and implemented since about 1985 in Japan, as part of energy conservation
activities.
1) After waste oil and oil sludge brought in by oil drums or tank trucks are stored in atank, they are put into a kiln or calciner by a pump for effective use as a heat energy
for burning clinkers.
2) Flowmeters are installed on oil & oil sludge transportation pipes for the remoteadjustment of flow to a set rate by controlling the pump rotation speed.
Fig. shows a flow on a waste oil & oil sludge processing flow by calciner or kiln.

Tank truck
Agitator

Descriptions

Preheater

Pump

Pump
Ｐ

FlowmeterＰ
Waste oil & oilsludge tank

Flowmeter

calciner
Fuel

Kiln
Clinker cooler

Fig. Waste oil and oil sludge processing flow

Results

Waste oil and oil sludge vary greatly in quantity but can produce heat energy of about 10
MJ/kg (several 1,000 kcal/kg). Fossil fuels for the same amount of heat energy can besaved.

Cost
estimation

Storage and processing facilities for about 10,000 kl/year: About 727 thousand
US$ [1US$=¥110]

Relatedmatters
Reference- 48 114

Item

Background

Waste plastic processing facilities

Application
Use of AFR

Waste plastics generally used to be reclaimed on final disposal sites. Since it is difficult tosecure final disposal sites and the shortage of fossil fuels is anticipated, waste plastic
utilization technologies are being developed as part of resources and energy
conservation activities.
The waste plastic processing technologies recently developed and now in use are mainly
to shred waste plastics until almost the same combustion characteristics as the main
fuels can be obtained.
1) After foreign matter is removed, waste plastics are shred into pieces of 10 to 20 mm.
Then the shreded plastics are fed to a kiln or calciner quantitatively rate for effective
use as an alternative fuel.
2) A constant weigh feeder allows the remote adjustment of weighing or rotation speed.
For transportation, a roots blower is used as the pneumatic conveyor.
Fig. shows a waste plastic processing flow.

Waste plastics

Pneumatic conveyor
Preheater

Descriptions

Constant weight feeder

Blowercalciner
Fuel

Kiln

Clinker cooler

Fig. Waste plastic processing flow

Results
Costestimation
Relatedmatters

There are various kinds of waste plastics. The effective heat from waste plastics is about
17 to 42 MJ/kg (4,000 to 10,000 kcal/kg). Fossil fuels for the same amount of heat can besaved.
System for about 10,000 t/year (including shredding facilities): About 3.6 million
US$ [1US$=¥110]

Reference- 49 115

Item

Background

RDF processing facilities

Application
Use of AFR

Waste used to be incinerated or reduced in volume and then reclaimed on final disposalsites. Since the emission of dioxins from incinerators and the securing of final landfill
sites are posing problems, however, it is expected to reduce and recycle waste.
As a method of recycling, general garbage and industrial wastes are being solidified as
RDF for use as a fuel (RDF: Refuse Derived Fuel). RDF processing is effective at cement
plants where incinerated ashes are available as raw materials.
1) Burnable waste sorted and collected by local governments is crushed, sorted, dried,
and molded into RDF of 10 to 30 mm in diameter and 20 to 50 mm in length for easystorage and transportability.
2) RDF carried to a cement plant is put into a kiln bottom or mouth by pneumatictransportation facilities to use effectively as a heat energy for burning clinkers.
3) This saves fossil fuels of the amount for heat energy. Incinerated ashes require no
separate processing because they are used as part of the raw materials.
4) In addition, no dioxins are generated because of long stay at a high temperature in a
cement kiln.

HopperDescriptions
BlowerRDF

HopperCalcination
raw meal
BlowerRDF
Rotary kiln
Pulverized
coal

Results

RDF produces heat of 15,000 to 20,000 kJ/kg (3,500 to 4,500kcal/kg). RDF use of 10 t/d
reduces coal consumption by about 5 t/d.

Costestimation

Facilities for accepting and processing 10 t/d (excluding chlorine bypass facilities): 646
thousand US$ [1US$=¥110]

Relatedmatters

Cyclone clogging prevention technology

Reference- 50 116

Item

Background

Application
Use of AFR

Recycling of “pachinko machine”

In Japan, it is estimated that pachinko machines (Japanese pinball machine) areproduced about 2.2 million units every year and are disposed as the same.
The establishment of technologies for optimum processing and recycling has been
expected because illegal disposal and large field heaping posed social problems.
“Pachinko,” a machine for entertainment, consists of electronic parts and also metallic,plastic, and wooden sections and is difficult to handle at a later process if merely crushed
for recycling. Therefore, a comprehensive processing system is constructed for complete
recycling.
This system consists of the following processes:
1) Recovery of LCD and other recyclable electronic parts and their return tomanufacturers2) Sorting and recovery of iron parts by magnetic force and their sale as scraps3) Manufacture of solid fuels mainly from plastic and wooden materials
4) Fixed-quantity feed to and processing in cement kiln
For solid fuel production, a volume reducer by compressive extrusion is used. Plastics
molten by friction heat work as adhesives for molding and solidification.
The solid fuel size is about 100 mm in diameter and 150 mm in length (about 2 kg/piece).

Flowchart

DescriptionsMagnetic
selectorPrimary
crusher

Secondarycrusher
Volume reducer
Chip silo

Solid storage
Scrap
Hopper scale

Rawmaterials
Rotary kiln

Results
Costestimation

Clinker

1) Slid fuel: 15 kg/unit
Heat: 27 MJ/kg (6,500 kcal/kg)
2) Substitute of coal fuel1) System for processing 400,000 units/year: About 8.2 million US$ [1US$=¥110]

Relatedmatters
Reference- 51 117

Item

Background

Substitute raw material processing
technology (Coal ashes)

Application
Use of AFR

Coal ashes recovered by dust collectors at pulverized coal combustion boilers aredischarged a lot mainly from thermal power plants throughout the nation and predicted tofurther increase in future. Although various processing methods are now underaggressive study, further utilization at cement plans is expected because it is difficult toprocess large quantities and to secure disposal sites.
1) Coal ashes are mainly made of silica (SiO2) and alumina (Al2O3) and used as a
substitute for natural raw materials of cement.
2) According to the properties, coal ashes are put into a system at the stage of mixing
non-processed raw materials or after the stage of grinding raw materials as part of
mixed raw materials.
3) Coal ashes containing carbons not burnt help saving fossil fuels because their
combustion heat is available as a heat source for burning clinkers. If coal ashes areused in large quantities, however, the heat balance may be lost.
4) Coal ashes are already used at many cement plants and the unit consumption is about
10 to 100 kg/t-cl.

Fan
Limestone

Descriptions

Electrostatic
Precipitator
ExhaustClay

SilicaIron sourceRawmaterial mill

Coal ashes
(wet)

Coal
ashes
(dry)

Raw meal silo

BlowerResults
Costestimation

1) Natural raw materials (mainly clay) can be saved.
2) Fossil fuels can be saved by carbons not burnt (hundreds to thousands kJ/kg).
2000 ton-silo and input facillities: 2.7 to 3.2 million US$ [1US$=¥110]

Relatedmatters
Reference- 52 118

Item

Background

Substitute raw material
processing technology (Slag)

Application
Use of AFR

At the process of manufacturing iron & steel or nonferrous metals, a product of reaction
between impurties in raw materials and limestone added as an agent to eliminate sulfur
and impurities is discharged as a molten oxide. The oxide is cooled and crushed. This iscalled slag and discharged a lot throughout the nation. From a long time ago, slag has
been used as cement raw materials and also road construction materials.
As a representative slag having a hydraulic property, blast furnace slag is ground to fineparticles, mixed with cement, and used widely as blast furnace cement.
On the other hand, various kinds of slag lower in quality are used as raw materials for
cement.
1) Blast furnace slag and convertor slag from iron & steel manufacturing and slag fromnon-ferrous metal manufacturing are used as substitutes for cement raw materials.
2) As one of raw materials, slag is used at the stage of mixing non-processed raw
materials. The maximum consumption is about 250 kg/t-cl.
3) Slag contains CaO about 40 to 45%. Unlike limestone, however, decompositionheat is
not necessary because decarboxylation reaction is already completed. The heatconsumption rate is reduced corresponding to the amount of use.

Descriptions

Fan

Limestone

Electrostatic
precipitator
ExhaustClay

SilicaRaw material
mill

Iron source

Raw meal silo
Slag

Results

1) When slag of 10kg/t-cl is used, the heat consumption rate is reduced by about 17
kJ/kg-cl (4kcal/kg-cl).
2) As the generated carbon dioxide decreases, the fan power consumption is also
reduced slightly.

Costestimation
Relatedmatters
Reference- 53 119

Item

Background

Substitute raw material processing
technology (Sludge)

Application
Use of AFR

A large amount of construction sludge generated throughout the nation used to bereclaimed for final disposal.
With the decrease of land for reclamation, illegal disposal increased. Since it is alsodifficult to secure disposal sites, an effective utilization technolgy is expected.
1) Construction sludge containing a certain amount of water or more is used at the stageof mixing non-processed raw materials. Construction sludge not containing so muchwater is supplied before the grinding of raw materials as a substitute for cement raw
materials.
2) Construction sludge has various properties and components. The sludge ispreprocessed when difficult to use as it is.
3) Construction sludge containing much water is used after handling is improved by filter
press or mixing with other dry raw materials.

FanElectrostatic
Precipitator
ExhaustLimestone

Descriptions

Clay
Mixing adjustment

SilicaIron source

Raw material
mill

Raw
meal
silo
Feedback

Construction
sludgeCalciner
Rotary kiln

Results

Costestimation
Relatedmatters

1) The use of natural raw materials is reduced.
2) The service life of final disposal site is extended.
The use of existing facilities cuts costs.
Unchoking measures : hundreds of thousands to million of US$
Automation of raw material mixing control

Reference- 54 120

Clinkeranalysis

Item

Background

Substitute raw material processing
technology (Sewage sludge)

Application
Use of AFR

Sewage sludge from local governments throughout the nation used to be disposed ofmainly by reclamation or sea dumping.
The sea dumping of industrial wastes is becoming a social problem and their effective
utilization is expected.
Sludge from sewage plants is brought to cement plants in the form of dehydrated cake(water content: about 80%) or incinerated ashes.
1) Incinerated ashes are mixed as a substitute for raw materials at the stage of mixing
raw materials.
2) Because of the smell and difficult handling, dehydrated cake is directly put from thepressure feed pump into the furnace (rotary kiln or calciner).
3) The cake contains burnable organic substances. Because of high water content,
however, the cake is thermally offset and used as a substitute for raw materials.
Electrostatic

Fan Precipitator

Mixed rawmaterials
SewagesludgeExhaustRawmaterialdryer
Rawmaterial
mill

Descriptions

Rawmaterialsilo

SewagesludgeCalciner
SewagesludgeResults
Costestimation
Relatedmatters

Rotary kiln

1) The consumption of natural resources is reduced.
2) The service life of final disposal site is extended.
Pressure feed pump into the furnace : 1.8 to 3.6 million US$ [1US$=¥110]

Automation of raw material mixing control

Reference- 55 121

Item

Background

Waste acid and alkali
processing facilities

Application
Use of AFR

The general method of disposing of waste acids and alkalis in large quantities used to besea dumping after neutralization. Since sea dumping is now prohibited by the London
Dumping Convention, a safe and effective processing method is expected.
1) Combustion exhaust gas discharged from a preheater is used effectively for drying
and then its dust is collected by an electrostatic preciputator. To optimize theconditions of dust collection, industrial water is sprayed to adjust the temperature andhumidity of exhaust gas.
2) Instead of this industrial water, waste acid and alkali solutions are used to evaporate
the water content occupying a great percentage of waste liquid.
3) There is a comprehensive recovery system for treating waste liquid from liquor
brewery and photographic development easy to collect and transport.

Waste acidreservoir tank

P

Electrostatic
Precipitator

Waste alkali
reservoir tankDescriptions

Outlet gas
temperatureP

Industrial water
Preheater exhaust gas
Non-processed raw materials
Dried rawmaterials

Results
Costestimation
Relatedmatters

Rotary dryer

The consumption of water resources and the energy for waste water treatment can be
reduced.
Receiving and spray facilities : several hundreds of thousand US$
Chlorine bypass system

Reference- 56 122

Power generation utilizing
waste heat

Item

Background

Application

Waste heatrecovery

The temperature of the exhaust from the suspension preheater (SP) or the newsuspension preheater (NSP) is about 400℃. The exhaust has the surplus heat even
if it is used to dry the raw materials. Also the surplus heat comes from the clinker
cooler.
It was desired to utilize the surplus heat (= waste heat) for energy saving.
The power generator by the waste heat has been installed with the progress oftechnologies on the waste heat generation and after the appearance of large-scalekilns.
The popular system is as follows.
The boilers are installed at the outlet of suspension preheater or clinker cooler.
The low pressure steam is made in boiler by waste heat recovery. And, theelectrical power is generated with the steam turbine.
The amount of generated electrical power per 1 ton of clinker is 35-40kW on anaverage. In the case of kiln of 5000 ton per 1 day, the 8000kW of electrical power
are generated.
In the typical NSP kiln equipped with power station by waste heat, the energy
utilization efficiency on the burning process reaches about 80% and thetemperature of the exhaust after using of drying raw materials is about 100℃.

Descriptions

SP

SP
boiler

AQC

Precalciner

K−IDF

boilerRotary kiln
AQC

Results

The power station by waste heat can generate electrical power of about 35 to 40
kW per 1 ton of clinker.

Costestimation

About 27.3 million US$ including cost of supplemental facilities

Relatedmaterials

The recycled utilization of the exhaust gas of the clinker cooler

Reference- 57 123[1US$=¥110]

Item

Background

Recirculation of exhaust air
from cooler

Application
Waste heat recovery

A clinker cooler exhausts air of about 200 to 300°C. This exhaust air used to be released
into the atmosphere as it is. Installing a waste heat boiler is an effective means of using
potential heat from the exhaust air. However, means of thorough energy conservation
are expected.
Regarding a cooler, it is most important to improve the recovery of heat to the secondary
air for combustion. From the viewpoint of an whole kiln, it is also important to thoroughly
make an effective use of residual heat not having a very great value as heat.
From air discharged out of a cooler, dust is removed by an electrostatic precipitator or
bag filter. Then the low-temperature air is circulated again to cool clinkers. This cooler
exhaust recirculation technology minimizes heat discharge out of the system by using
potential heat effectively.
(a) If a waste heat boiler is installed on a cooler, exhaust air of about 100°C at theboiler outlet is led again to the fan for the rear stage of the cooler to increase heatrecovery at the boiler. The cooler exhaust of a great heat value increases therecovery efficiency at the boiler.
(b) In a grate-type cooler, low-temperature exhaust air is led again to the fan for thefront stage of the cooler to get the high-tempetrature secondary air for burning.

Descriptions

Example : With waste heat boilerＥＰＴ ｅｒｔｉａ ｒｙ ａ ｉｒ
Ｂｏｉ ｌｅｒ

Ｓ ｅｃｏｎ ｄ ａｒ ｙ ａｉ ｒ
Ｃ ｌｉｎ ｋｅ ｒ

Ｃ ｌｉｎ ｋｅ ｒ

Ｃ ｏｏｌ ａ ｉｒ
Ｒｅｃｉ ｒｃｕ ｌａｔ ｉｏｎ： Fan

Results

1) (a): Waste heat recovery rate up about 10% (50% of exhaust air circulated)
2) (b): Heat consumption rate down about 25 kJ/kg-cl (6 kcal/kg)

Costestimation

0.9 to 1.4 million US$ [1US$=¥110]

Relatedmatters

Power generation from waste heat

Reference- 58 124

Item

Background

Reduction of cyclonepressure loss

Application
CommonThe power consumption rate of an exhaust fan at a preheater is affected by cyclonepressure loss. If the negative pressure is great, leakage air increases. Therefore, acyclone of low pressure loss was expected.
A cyclone pressure loss is reduced by the following technologies:
1) Adopting a cyclone of a special shape
The inlet shape of an ordinary cyclone is devised to reduce the inlet wind velocity.
This exhibits the gravity sedimentation effect and reduces the pressure loss while
maintaining the dust collection efficiency. Such special types as axial and horizontal
are also available.
2) Installing a guide vane
A vane is installed where the inlet gas flow collides against the swirling gas flow.
This prevents the inlet gas flow from diminishing and assists the formation of adownward flow in the cyclone to reduce the pressure loss while maintaining the dust
collection efficiency.
3) Devising the cylinder in the cyclone
By considering the applicable cyclone position, the internal cylinder and the lengthof the rectifier plate in the cylinder are adjusted. According to a report, the pressure
loss at inversion can also be reduced greatly by installing a special device at thelower part of the internal cylinder.

Descriptions
Ｇａｓ ｏｕｔｌｅｔ

ｄｕｓｔ

Ｇｕｉｄｅ
Vａｎｅ

Ｇａｓ ｉｎｌｅｔ

Ｍａｉｎ ｄｕｓｔ ｏｕｔｌｅｔ

特殊形状サイクロン
Special cyclone

Guide
vane
ガイドベーン

Results

1) Guide vane type: Pressure loss down 5 to 10% (equivalent dust collection efficiency)
2) Special cyclone: Pressure loss down 30 to 40% (equivalent dust collection efficiency)

Costestimation

1) About 9,000 to 14,000US$ [1US$=¥110]2) About 55,000US$ [1US$=¥110] (straight body of 4,000 mm in diameter × 2 + duct
alteration)

Relatedmatters

Five-stage preheater

Reference- 59 125

Reduction of bag filter
pressure loss

Item

Background

Application
CommonThe conventional bag filter has disadvantages that the pressure loss and power
consumption rate increase with the passage of time as the filter cloth deteriorates andthat the filter cloth is damaged in a short period.
Therefore, a filter cloth of a low pressure loss was expected to support stable run for along period.
The conventional bag filter uses a felt cloth for filtration.
This cloth is for three-dimensional filtration where the primary dust layer formed on thesurface of the cloth filters later dust.
Therefore, dust penetrates into the material and increases the pressure loss with thepassage of time.
To solve this disadvantage, a new filter cloth was developed by laminating a finemultipore film on the surface of a felt substrate. Since this is surface filtration by
micropores, dust comes off easily from the filter cloth. By shaking off dust appropriately,
the pressure loss of the filter cloth can be kept almost constant.
Compared with the felt filter cloth, the filter cloth has a slightly great pressure cloth at the
beginning of use but is almost free of influence by residual dust. Therefore, the new filter
cloth can be used stably for a long time with a low pressure loss.

Pressure loss offilter cloth

濾布の圧力損失

Descriptions

3D３次元濾過タイプ
filtration type

破損
DamageSurfacefiltration type
面濾過タイプLifeof filter cloth
濾布の寿命

Life of filter cloth and pressure loss

Results

Costestimation

1) The pressure loss is down about 30%. (Electric power down or processing wind rateup)2) The maintenance frequency is reduced.
3) The bag filter can be used for a long period at a stable wind rate.
4) The filter cloth has a twice or longer life.
150 mm dia. × 3,500 mm long: About 450US$ [1US$=¥110]

Relatedmatters
Reference- 60 126

Fan rotation control

Item

Background

Descriptions

Application
CommonAt the cement manufacturing process, many large fans are used. Power consumption by
these fans is regulated by throttle control and rotation speed control. Rotation speed
control is superior to throttle control in energy saving performance. Rotation speed
control can be classified into mechanical control, like fluid joint and secondary resistancecontrol, and into electric control, like Scherbius control and inverter control.
Depending on the motor types, there are several methods of controlling the fan rotation
speed by varying the rotation speed of the motor that drives the fan. The representative
static Scherbius control is explained here.
A wound-rotor induction motor for a large fan, like a preheater ventilation fan, used to becontrolled by secondary resistance control that changes a rotation speed with a variable
resistor on the secondary side. The typical variable resistor is liquid resistor. This control
method is more economical than any other method because the structure is simple.
However, the method also has disadvantages that the rotation speed changes by steps
and that the efficiency is low, compared with other methods, because the secondary
resistance loss becomes greater at a low speed.
Low efficiency attributable to the secondary resistance loss did not matter in the past
production for maximum output but began to appear a problem during the long-term
suppressed production. Replacing this, the static Scherbius control was aggressively
adopted as a control method of high efficiency.
The static Scherbius control changes the rotation speed by applying a voltage to thesecondary circuit. Of the secondary power, the secondary slip power is converted into
AC by an inverter for the primary power (power supply).
Therefore, this control method features higher efficiency than secondary resistancecontrol and a smaller loss attributable to a decrease of power factor at a low speed.
However, the cost is higher.

Pi

Pi

.
.

I.M.

Po

PＭ
Po

.
..

(Power)Pb（電力）

IM

Rectifier DC

P（熱損失）L (Thermal loss)

Transformer

Inverter

ACR
二次抵抗制御Secondaryresistance control

Results

Costestimation
Relatedmatters

静止ｾﾙﾋﾞｳｽ方式
Static Scherbius
control

Control Method

Output(kW)

General Efficiency
(%)

Input
(kW)

Power Saving(kW)

Scherbius control

1,487

93.0

1,599

220

Secondary resistancecontrol

1,487

81.7

1,819

--

270 thousand US$ (Motor ratings: 2,350 kW, 6 P, 3,300 V, and 60 Hz) [1US$=¥110]

Reference- 61 127

Fan impeller cutting

Item

Background

Application
CommonAt the cement manufacturing process, many fans are used to process combustion gas
and air. These fans have necessary capacities for their positions. However, some fans
may have excess margins which may increase as process changes.
Since these margins waste power, fan impeller cutting is executed.

Fan impeller (runner) cutting is generally executed as shown below.

Φ2380

Φ2620

Cut

Descriptions
When the rotation speed is the same, the wind rate is proportional to the ratio of impeller
diameter. The pressure is proportional to the second power of the ratio and the electric
power is proportional to the third power of the ratio. Therefore, the energy saving effectis great.
The limit of impeller cutting is generally said to be about 20% of the original diameter.
Excess cutting may
1) lower the fan efficiency to an non-ignorable level,2) reduce the mechanical strength of fan greatly,3) increase mechanical instability at a high speed, causing vibration, or4) cause problems easily due to insufficient margin.
When reducing the wind rate more 20% or more, the impeller should be replaced.

Effect on 1700 kW kiln IDF (same wind rate)

Results

Costestimation

Impeller Diameter(mm)

Rotation
Speed-1(min )

Power
Consumption(kW)

Power Saving(kW)

Before cutting

2,620

1,200

1,475

--

After cutting

2,380

1,300

1,313

162

Fan impeller replacement: 0.5 million US$ [1US$=¥110](Impeller cutting, including the main and side plates)
Vane cutting only: 27 thousand US$ [1US$=¥110]

Relatedmatters
Reference- 62 128

Material sealing

Item

Background

Application
CommonUndesired air leakage, which is made by huge pressure difference, especially occurredat material feed area of vertical mill, makes many operational troubles such as un
desired increasing of gas flow, reduction of mill grinding capacity by poor drying
performance caused by decreasing of gas temperature with cold leak air and undesired
increasing of power consumption of mill fan caused by increasing of gas flow by leak air.
Air leakage can be reduced by using flap dampers of multiple stage or screw feeders
having multiple screw shafts.
The figures below show the 3-stage FD method.
The 3-stage FD consists of three flaps. Flaps sequentially open from top, middle andlower stage. When one stage is open, the remaining other stages are fully closed andtheir spaces are fully filled by materials. This makes strong seal for leakages.
Raw material

FLAP OPERATIONUNDER OPENING OPERATIONUNDER CLOSING OPERATION

1−1

2−1

1−2

2−2

1−3

2−3

CLOSE

1−1 FLAP
1−2 FLAP OPEN
1−3 FLAP
2−1 FLAP
2−2 FLAP
2−3 FLAP

Descriptions
In the double screw method, Raw materials are fed and discharged to vertical mill by
the filled up conditions made by double parallel shaft screw rotating inward. Thismechanism makes effective seal conditions.
Raw materials

M

Results

Costestimation

The 3-stage FD method reduced 30,000 m3 N/h or 30% of 100,000 m3 N/h leakage from
330,000 m3N/h gas flow at the outlet of a vertical raw material mill. This corresponds to a
reduction of 150 kW or 4% in IDF power.

3-stage FD system: 180 thousand US$ [1US$=¥110]

Relatedmatters
Reference- 63 129