Ask Dr Clark - Cement Milling _ Whitehopleman

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Dr Clark - Cement milling | Whitehopleman

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Q: Ball mill filling level

s asked by someone regarding cement grinding ball mill filling level calculation through mill

main motor power gain, please kindly explained.

The power drawn by the main motor of a ball mill proportional to the weight of the

grinding media in the mill amongst other factors.

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Q: cement ball mill crush stoppage

Is there any standard procedure for cement ball mill crush stoppage & it's meter by meter

material sample sieve analysis with standard, if yes please communicate

You must stop the mill on full feed and immediately stop the ventiliation fan to prevent

the fines being pulled out the mill. This means it will take the mill a long time to cool down

before you can enter to take the samples. Alternatively the fan can be kept running to cool

the mill but you will then have to dig down into the charge to take the samples, which is

very hard work.

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Q: how to calculate ball mill balls filling percentage

There are various methods: (i) by measuring the free height above the media in the

chambers of the mill, (ii) from the kW drawn by the mill main motor, etc.

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Q: Mill Reject from Clinker VRM

We have Loesche mill for clinker grinding and we produce mainly fly ash PPC cement, we have

removed the damring fitted on the top of mill table, it has observed that there is zero mill

reject at mill reject conveyor. Is it normal or do we have any further cushion to optimize mill

performance in terms of energy consumption, production rate. if yes please let us know how?

It sounds as if all the material pasing over the table is sufficiently fine to be lifted the

separator. The only remaining opportunity would be to reduce the grinding pressure.

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Q: EPS dust emission problem

Hi sir. how we can omit or reduce EPS dust emission without water injection system in ball mill

unit? our water injection disable 15 years ego and we cant able it now. Regards Hamedi

An electrostatic precipitator relies on the condition (temperature and humidity) of the

gas passing through for it's collection efficiency. If you cannot properly condition the gases

then the only option is to reduce the foow of the gas and the throughput of the mill.

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Q: Dr. More blaine means more weight?

If my blaine is 2800 and packing bag is 50 kg, if my blaine 4400 and same packing bag will

use?

Maybe not. The higher the Blaine the more air is likely to be entrained with the cement

powder, so you might need a bigger bag to get 50kg into it.

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Q: Water spray on cement ball mill shell

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Is water spray is advisable on cement grinding ball mill with the aim to reduce cement

temperature? 1- If advisable how much quantity is required to be sprayed? & will reducer the

temperature how much?

It is not advisable. Much better is to ensure sufficient air flow through the mill and if

necessary to inject water into the mill for evaporative cooling.

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Q: High blaine impact short term & long term strength

What the rule of high blaine & low blaine on short term & long term cement strength

High Blaine will boost the short-term strength of cement. Longer-term strength will be

less affected. The Blaine has an impact on the rate of strength growth of the cement.

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Q: Sir,How to Calculate the Velocity of VRM in Nozzle area.. ?Pls explain

You would need to measure the total gas flow into the mill and the total cross sectional

area of the ports in the nozzle ring. One divided by the other will give you the gas velocity.

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Q: Elaboration Blaine to kwh

Will you please elaborate Blaine to kWh relationship that you mentioned earlier that is 1.5.??

The energy consumption is related to the surface area to which the material is ground

raised to the power 1.5. Please send an email to [email protected] is you need

further explanation.

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Q: OPC density and Sp. gravityOPC density is in the range of 1.3 to 1.45 kg/m3 and specific gravity is 3.15. If specific gravity

is a ratio of the density of a particular material with that of a reference/standard material, in

this case OPC density and specific gravity should be more or less the same.

But it is not a ratio. The bulk density is the dnesity of a powder including the air

entrained in the powder. The specific gravity will be higher as there is no air involved.

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Q: Blaine to Kwh relationship

Is there is any relationship between Blaine, residue with kWh for a ball mill

Certainly. The energy consumption in kWh/t of cement produced is reckoned to be

proportional to the surface area of the cement raised to the power 1.5.

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Q: la finesse du cimentquelle doit être la finesse idéal du ciment portland artificiel CPJ.

There is not an "ideal" fineness. This depends on the recipe of the cement and the

desired strength grade.

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Q: How do i calculate circulation factor in roller press.

How do i calculate circulation factor in roller press. We are having closed circuit cement mill,

roller press as a pregrinding system and single chamber ball mill. clinker is being added in

roller press while gypsum and fly ash is being added in ball mill directly.

You are going to have to take samples around the roll press and measure sieve residues.

You should then be able to estimate using the principles of a mass balance. Often the

recirculation around a roll press is simply etermi d by recirculating the outer edge product

from the press, in which caset you should be able to estiimate by inspection andcalculation.

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Q: 325 improvement by adding water

We have an open circuit ball mill, we notice that when we take off the cooling water that the

325 increase by 2.5-3%. What would be the scientific explanation for this

You need to explain what the "325" refers to.

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Q: GRINDING MEDIA PATTERN

We want to use ordinary portland cement grinding mill as portland slag grinding mill. What

changes we are required to make for this requirement interms of grinding media pattern. Slag

usedis blast furnace slag and granulometry is 2-4 mms. Slag % used in cement is 40 %.

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Anant(India)

As the slag is finer than the clinker you do not need the crushing effect of the larger

balls in the first chamber of the mill. However, as you are going to grind the clinker and

slag together you must still be sure to sufficiently crush the clinker. Much better would be

to separately grind the slag and clinker in different mills configured for each material and

then to blend the fine products in the required proportions.

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Q: What is difference of cement PSD at same blain of different grinding machines - VRM

,RP+BALL MILL & BALL MILL.

A vertical rooler mill will have the narrowest particle size distribution, a rool press & ball

mill combination a wider psd and a ball mill thye widest psd.

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Q: What's the ideal clinker size both for clinker production & cement grinding?

What would be impact of oversized Clinker in cement grinding & what the normal range of

Clinker size? (2)If two independent cement grinding units (a) ball mill (b) roller press. Does

hard grinding would same effect on these two grinding units efficiency?

Over size clinker requires more grinding work to reach a target fineness. Therefore the

effect will be raise the energy consumption in grinding or reduce the production rate from

the mill. The effect is likely to be more pronounced on the ball mill. With the roll press there

might be the need to adjust the recirculation around the roll press.

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Q: OPC Grades

What are the Apple to Apple difference in OPC grade 32.5,42.5 & 52.5?

The 32.5, 42.5 and 52.5 grades relate to the 28-day compressive strength attained by a

standard mortar mix made with the cement. If they are OPC cements then they are

composed of at least 95% clinker and gypsum with a maximum of 5% of other additions in

the cement (flyash, limestone, etc.) As the composition is fixed the question is how are

these different strength grades achieved from a fixed composition?There are 2 ways: (i) by

the fineness of grinding of the cement, and (ii) by the hydraulic reactivity of clinker in the

cement.

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Q: cement ball mill grindability

How we can measure the grindingbility of cement ball mill? & from chemical composition?

A ball mill does not have a "grindability". It is the material, i.e. clinker, that has a

grindability. That is normally measured in a laboratory mill and is the electrical energy

required to produce a given fineness of grinding. Grindability of clinker can be directly

related to the C2S content of the clinker. That can be calculated by the Bogue methodology

from the chemical composition. However, Bogue minera;logy is not the same as actual

mineralogy. Better to measure c;linker grindability in a laboratory ball mill.A ball mill has a

"grinding capability". Bond's 3rd law nof comminution can be used to assess that grinding

capability. This relies on a Bond "Work Index" of 13 kWh/ton for clinker. This equates to the

clinker grindability.

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Q: what type/model of osepa required for mill size(dia-3.8*13 meter)

need a osepa becoz of wear rate is so high, now we r using osepa N-1500

You need to calculate the specific loading on the separator in terms of the tonnes per

hour per m2 of the separator and also the specific air load in terms of the kgs of feed to

the separator per m3 of air. You will then be able to assess whether the separator is

overloaded and whether you need a larger separator.

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Q: High residue

What could be the possible reason behind high cement residue (greater then 5% on 90

microns) even our rest of the noms are with in range ( feed rate, blaine & kWh)

I presume there is no problem with the 90 micron sieve? If that is OK then there must be

a change in the grindability of the feed to the mill.

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Q: Ball mill piece weight

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What is meant by piece weight of grinding media, why calculating for ball mill and how to

calculate piece weight of grinding media.

It is common to calculate the average ball, or piece, weight of the media in the different

chambers of a ball mill. Also the total surface area of the charge in chambers. Higher piece

weights are required in the first chamber for crushing the clinker. In the second chamber a

high charge surface area is required to achieve the fine grinding of cement. How high

depends on the required fineness of the cement.

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Q: I want to ask about the reasons of oil leakage?

Dear Dr. clark There is Chronically oil leakage at gearbox and vibration I want to ask about the

reasons of oil leakage?

Well, it sounds as if the seals of the gearbox are broken.

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Q: IDEAL BLAINE & RESIDUE

What should be ideal blaine & residue (@ 90 microns) for a ball mill with multicyclone)

There is no "ideal". It depends on the fineness that you need in the mill product.

However, the fineness that can be achieved will be dependent on the cut size of the

separator. You need to construct a Tromp Curve for the separator.

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Q: What is difference between circulating factor and circulating load?

What is difference between circulating factor and circulating load?if circulating factor is higher

side what is effect on separator efficiency and what is ideal circulating factor?

Circulation factor and circulating load are the same thing. The load is expressed in total

tonnes while the factor is the load relative to the fresh feed rate to the mill. Ideal circulating

load or factor depends on the separator to some extent. A factor around 2 is typical. If too

high the separator can become overloaded and cease to cut the feed as requured.

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Q: Is possible to produce microcement in a closed circuit ball mill?

Finesses < 20 microns

A ball mill can grind very finely. More important will be the separator and cut size of that

separator. Do you have a Tromp curve for the separator?

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Q: HOW TO MAINTAIN SURFACE IN OPEN CIRCUIT CEMENT GRINDING IN A TWO CHAMBER MILL.

WE HAVE HI CH-ROME BALLS

Our clinker is having 45 % C3S, 30% liquid content. We are grinding cement in open circuit

miils & two chamber. We maintain 3200 cm2/gm fineness. We are maintaining full grinding

media as per recommendations. Of late we are not able to maintain fineness of cement.Mill

vent volume is maintained constant. Dr Clarke pl suggest for improvement of the fineness of

cement and reasons for the same . Anant(India)

Two chambers is short for an open circuit mill. Perhaps the grinding path length is

insufficient to achieve the required cement fineness. You must ensure that the lining of the

second chamber of the mill is classifying the grinding media. if that is the case then the

only possibility to control the fineness of the product is to vary the feed rate to the mill.

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Q: 1-Effect of high clinker temperture & its control through excess water injection. 2- Flushing

of clinker from pregrinding roller ?

Q1-To get maximum benefit of WHR our clinker temperature inter cement ball mill at 150C,

but we are reduce the same by multi water spray before ball mill. What it's disadvantages. Q2-

Our has a bin of 30tons above roller whom one discharge is for ball mill through belt conveyor

while the other line recalculate Clinker back to roller bin when we consume mix clinker ( silo &

yard) we face flushing of Clinker from roller resulting sudden drop in it bin might be due to

difference in bulk densities or fine clinker recirculation, this flushing normally chock our feed

belt to mill. How can this flushing can be minimized or eliminate.Advice, please.

It seems the cooler efficiency is being sacrificed to improve the electricity generation

from the waste heat recovery system. The hot clinker potentially results in safety issues.

There should be no problems with water injection rates up to 5% of the total mill

thorughput in tonnes per hour. However, you must ensure that the temperature of the mill

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exposed to the weather.

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Q: Diffrent type of Cement grinding in one Mill ?

Dear Dr., Please give procedure to grind SRC & OPC in same mill, mainly plz describe about the

switch-over process and timings to avoid mixing of cements in the mill & circuit ! We have

separate silos for both.

The SRC complies with OPC specifications therefore all changeover cement should be

ground into the OPC silo. Only when the cement is at the SRC specification should the

cement be switched into the SRC silo.

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Q: Ball Mill Media Crack

Sir we took 2nd chamber media of ball mill for sorting. After 2 days heavy rain came over

media and after rain observed that some media got cracked from center and split media into 2

pieces. What could be the possible reason?

The problem must be the quality of the grinding media. I suggest you contact your

supplier.

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Q: How many hour are needed to wait to grind the clinker after the cooler if the temperature of

the clinker is less than 60 'C

I want to know is it possible to grind the clinker with gypsum immediately after the cooler and

use the cement immediately after the cement mill as we want to produce cement asap.

There is no requirement to wait before producing cement and then using the cement.

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Q: We are not getting strength in our white cement. clinker analysis SiO2: 22.80, Al2O3 4.70,

Fe2O3 0.26, CaO 67.00, MgO 0.70, K2O 0.40, Na2O 0.17, SO3 1.80, we grind this clinker with

4.20% gypsum to maintain SO3 in cement 3.30%. we maintain Blaine 4000.

There is nothing in the chemical composition or fineness to suggest why your white

cement is not developing strength. You need to investigate the actual mineral composition

of the clinker.

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Q: Our ball mill effeciency became lower while consuming open yard clinker

We have pregrinder before ball mill, but while consuming yard clinker we face frequent mill

chocking tendency (material spillage from mill in let, lowering mill amps, high residue but with

higher blaine), low feed rate bcuz of mill chocking tendency, for this your expert opinion isrequested, please.

The clinker stored jn the open yard will have been prehydrated to some extent. So this

produced "false" surface as the calcium hydroxide is easily ground. Residues are higher

because the surface is false and the unhydrated cloinker remains in the coarse fraction. I

am surprised that this is having any effect on the pregrinder. You need to carefully add the

outside stored clinker at a controlled addition rate which avoids these problems. You should

control product fineness to the residues, not the Blaine.

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Q: What is the ideal power consumption of Portland composite cement where mixing Flyash,

GBFS, limestone in mill inlet and product fineness Blaine 4000 cm2/gm, Tahmid. BD

There is no such thing as "ideal" power consumption. It will be dependent on the milling

system and the recipe for the composite cement. There could be a wide range of specific

power consumption.

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Q: What is the benifit to use Rosin Rammler equitation ? Tahmid, BD

The benfit is that you can characterise the fineness of any powder. You can also predict

the residue at any grain size.

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Q: Which cement is better Portland composite cement or Portland Cement ? Please explain .

Tahmid

That depends on which concrete applications the cement will be used within. There are

many applications where composite cement is better. But there are also applications where

pure Portland cement is better.

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Q: What is the basis to calculate yearly production capacity of a cement mill having capacity

100 MT/hr

100 x 24 x 330 = 792,000 assuming that the mill will operate for 330 days per year.

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Q: our ball mill type unidan fls 5.0x13 is taking feed 150t/h.while its designed feed is 190t/h

sir our ball mill FLS type unidan 5.0x13 is operating in a closed circuit with Sepax separator

42.5.while ball mill is taking 150t/h feed opc.Designed feed of ball mill is 190t/h.We have a

roller press before ball mill with 830kw.Roller press no load gap is 12mm.our roller press

diameter is 1000mm.hydraulic pressure of roller press is 230bar,roller press is taking 500kw during operation.why our ball mill feed is low.Our first chamber length is 3meter.Our ball mill

centre diaphragm is made by estanda.Previously we were using FLS made diaphragm.This

diaphragm was having a screen(slot size 8-10mm) and ducrodan plates on it.Now we have

changed the FLS made diaphragm by Estanda diaphragm.Estanda diaphragm has screen 6mm

and ducrodan plates having slots 6mm.These ducrodan plates are often choked with clinker.plz

advise us what to do?

If the mill was achieving 190t/h with the FLS diaphramn why did you change? Maybe you

should go back to the FLS diaphramn?

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Q: How we can reduce the R-45 in PPC

We are having 2nd Generation ZUB separtor with Two chamber close circuit Ball Mill.On 3200

cm2/gms blaine we are getting 18-20% residue.We have calculated the separator efficiency it

coming 58-60% on R-45.

That separator efficiency seems normal for a 2nd generation separator. In order to

reduce the 45 micron residue you will need to increase the speed of the separator. You

should also evaluate the Tromp Curve of the separator. Perhaps it is incapable of cutting

the material fine enough to control 45 micron residue.

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Q: sir our ball mill type unidan 5.0x13 reject is 225t/h,while its taking only 175t/h feed

sir our ball mill type unidan 5.0x13 is operating in a closed circuit with Sepax separator

42.5.Ball Mill reject from separator is above 225t/h,while ball mill is taking 175t/h

feed.Designed feed of ball mill is 190t/h.We have a roller press before ball mill with

830kw.Roller press no load gap is 12mm.Why our reject from separaot is more 225t/h.Plz

advise

To make an analysis of the problem it would be necessary to understand the fineness of

the feed to thee mill and separator. Also the rejects and fines from the separator and target

fineness. What was the fineness corresponding to the guaranteed production rate of

190t/h?

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Q: sir,our FLS vertical roller cement mill type OK 36-4 is not producing cement as per

designed which is 175t/h

sir,our FLS vertical roller cement mill type OK 36-4 is not producing cement as per designed

which is 175t/h.Our current feed is 160t/h.our clinker feed temp is 200degree centigrade.our

mill dp is 32-34mbar.our dam ring height is 150mm.plz advise us

The temperature of the clinker is very high. This is a potential cause of your problem.

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Q: Why irregullar cement flow in airslides

what causes irregular cement flow in air slide of a closed circuit ball mill

Which airslides? This can only be caused by irregular discharge of the material from the

equipment delivering the material to the airslide.

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Q: dear sir,Our Vertical roller cement mill OK 36-4 FLS made is not taking feed.I mean feed is

below than the designed.

our VRM cement mill OK 36-4 is not taking feed as designed.Our mill DP goes on the higher

side as 32,34mbar.and mill is accumulated with material.Material accumulates at the inlet

ducts to mill.These ducts are from a fan.Plz reply

It sounds that there is some accumulation of material in the mill. I suggest you

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recirculate a greater volume of air around the milling circuit.

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Q: Sir,advantage and disadvantage of chemical gypsum and anhydrite gypsum on cement

quality and process. Thanks

The advantage is normally based on cost. The disadvantage can be handling problems

with chemical gypsum.

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Q: media size

our clinker feed size is normally 70% below 5mm. What is the ideal media charge in chamber 1

& chamber 2. mill is 4.2 x 11m.To give some guidance on that I would need to know the length of the first and second

chamber of the mill.

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Q: Cement mill residence time

How can we calculate residence time of cement in ball mill

This would not normally be calculated. You can measure it be adding some tracer to the

feed and taking reggular samples at the exit to see when the tracer appears in the product.

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Q: Hi Dr Clark, incase of Masonry Cement, do we add limestone fines instead of Pozzolana at

the Mill grinding or how do we go about it?

Yes, limestone fines with an air entraining agent. If the limestone is fine enough then

you can just blend with OPC. Otherwise grind the limestone together with the clinker andgypsum.

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Q: Sir, effect of gypsum dihydrate,hemihydrate and anhydrite on cement Quality ( setting time,

strength).Thanks

There must be sufficient soluble sulpahe available to retard the setting of the C3A

mineral when the cement is mixed with water in concrete. This is why we must optimise the

sulphate addition. The sulphate form, i.e. gypsum, hemihydrate or anhydrite is important

because each of these forms of calcium sulphate has a different solubility in water. You

need to ensure: (i) consistent calcium sulphate mineralogy in the cement, and (ii) that the

right amount of sulphate is present to match the amount and reactivity of the C3A. In

practice the way to that is by optimum sulphate trials where you vary the sulphate content

and test the physical properties of the cement with different levels to find the optimum. The

most common problem when the sulphate is not optimum is that the workability of moratr

and concrete made with the cement is impaired.

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Q: Sir, can we use gypsum anhydrite (CaSO4) instead of gypsum (CaSO4.2H2O)

Yes. However, the solubility of the anhydrite will be different to the gypsum therefore

you will need to optimise the sulphate content of the cement you produce.

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Q: Coarse 250 m2/kg blaine fly ash adding into the cement

Coarse 250 m2/kg blaine fly ash adding into the cement mill which cause reduce the mill

output from 160 t/h to 130 t/h. Is there any solution to grind such coarse fly ash into the mill

to maintain the output as 160 t/h?

I suppose the fly ash is being added to the separator but the coarse particles rejected bythe separator are very difficult to grind. The solution would be to pre-grind the fly ash

separately before adding to the cement mill.

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Q: FILLING RATE OF BALL MILL

DEAR Mr. DR CLARK I WANT TO KNOW EQUATION FOR CALCULATE GRINDING MEDIA OF MILL,

CLOSE CIRCUIT AND OPEN CIRCUIT. THANK YOU

There are no absolute equations. The appropriate media grading depends on the size of

the feed to the mill and the grindability of the material being ground.

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Q: What are the advantage and dis-advantage of insttalation of cyclone after O sepa ?

Tahmid.BD

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The advantage would be to collect the product from the O-Sepa before the dedusting

filter. The disadvantage would be increasing the pressure drop across the system and

therefore the required fan capacity.

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Q: Is it possible to co-grinding Slag and Clinker + Gypsum in VRM? If yes, what could be the

best scheme for the same.

Yes, it is possible. You may need to apply a hot air generator to dry the slag and

dehydrate the gypsum.

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Q: Cement mill configuration for OPC and SRC cement.Dear Sir, For a new 5000t/d plant we will install 2 cement mils 135t/h each. We will grind OPC

and SRC at about 60% to 40%. The question is shall we use same mill configuration or adapt

the one to SRC grinding ie plates, diafragm, grinding media, so that we have better efficiency

and less wear and cost. What will be grinding media consumption in gr/ton for each case?

(average values)Thank you in advance.

I would not expect the grindability of the OPC and SRC to be significantly different so

would use the same mill configurations. That will allow you the flexibility to grind the OPC

or SRC on either mill when one or other is stopped for maintenance.

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Q: Cement Blaine

How can we increase the cement blaine without lowering our feed tph when milling Portland

Cement using a compound mill

I need more information on a "compound mill". However, the way to do that would be to

increase the separator speed and the recirculating load of rejects from the separator back to

the mill. There will be a limit on how much you can do that. You may need to increase the

weight of media in the mill. There will also be a limit as to how much you can do that.

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Q: Cement Color

Dear Sir, We have a complaint from market that our grey cement color is changing to white

color after setting. what could be the reason?

This could be a problem of effluorescence. The leaching of salts from the hydrated

cement.

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Q: How to caliclulate the dust load when the 65% of fines are below 3mm for clinker stockpiling

Sir please let me know to caliculate the dust load when the Loading rate is 500 tph and falling

height 60ft

I am not aware of any formulae to calculate the dust generation in such a situation. I

expect there will be lots of dust!

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Q: HWO TO DO FOR CALCULATE MINERALOGICAL COMPOSITION OF CEM II

This depends on the constituents of the CEM II cement and what are the other

supplementary cementitious materials other than clinker and gypsum. The methods will be

different for a limestone CEM II cement than for fly ash CEM II cementt, etc.

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Q: Blaine and residueswhy is blaine used for portland cement where we add more cliner and residues are used for

masonry cement where we add less clinker

Because with Portland cement the surface area presented to the mixing water when

cement is used to make concrete is what is important. With Masonry cement we have more

components in the cement with different grindabilities. We need to control the reidue to

ensure that the clinker particles are sufficiently finely ground.

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Q: anhydrite (CaSO4)

What do you think about using anhyrite-CaSO4 in stead of Gypsum. What is the advantage or

disadvantage

The solubility of anhydrite is different to gypsum. Also there is no water oof

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crystallisation that can be lost during the cement grinding process, or in subsequent

storage causing lump formation in silos. So anhydrite can be good but you need to do some

optimum sulphate trials with the anhydrite.

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Q: Cement Mill ( Ball Mill) Puffing

Dear Mr. Clark, I wanted to know the possible reasons for the puffing of cement mill( ball

mill)at its inlet very frequently.

That is because there is insufficient negative pressure in the mill. Either the mill fan is

not running sufficiently fast or there is a restriction preventing the fan from adequately

drafting the mill. It might be that the intermediate diaphram is restricted.

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Q: kiln dust used in cement mill as additive?

Dear Sir, can we use kiln dust as additive in cememt mill?? and what will be the effect on

cement quality??

Yes, this is frequently done. The effect on cement quality depends on the amount of

dust added to cement. Up to 5% should have no major effect. The dust will be around 20%

insoluble therefore you can expect the insoluble residue of the cement to rise.

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Q: How I can measure Grindibility factor ?

How I can calculate Grindiblity factor? What is the Difference between on Shaft or meter basis ?

Tahmid MCF,BD

Normally this would be done in a laboratory mill determining the kWh/t to produce a

given residue on a sieve size, so 5.9 kWh/t grinding to a fineness of 10% +0.09mm, Alpine.

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Q: what are thmb Rules to select a bags for cement Industry to select bag hourses or bag filter

Dear Sir, I want to know how cement industry is selecting the bags for different application for

dust collector or bag houses, like for kiln bag house process filter. Temperature chemical

composition Blaine size & is their any thing else. I am using Ryton bags for cliner cooler but

within 20 days bags got damage. what to do.

The trend is to use baghouses for all major exhausts except clinker coolers.

Unfortunately it seems you have a baghouse on the cooler exhaust. The reason baghouses

are not normally selected for cliner coolers is the danger of temperature excursions (rises) if

the kiln flushes and the abrasiveness of clinker. What to do? Very difficult. Convert to an

ESP (probably too expensive)? Insert a de-dusting cyclone between the cooler and the

baghouse (will increase the pressure drop)?

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Q: What is the ideal power consumption for grinding portand cement

What is the ideal power consumption for grinding portland cement ? is it 30 Kw/mt 0r 32 Kw/t

which is correct ? Tahmid MCF, BD

That depends how finely you are grinding the cement, what the recipe is (clinker,

gypsum, limestone, fly ash, etc.) and the type of milling system you are grinding the

cement on. Either 30 or 32 kWh/t could be required, or maybe much more.

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Q: question about cement separator system

Hello dear Dr We have a 92 tph KHD cement ball mill , it is about 5 years from when we have

started and using this new ball mill. After 2 years working one of KHD process engineers was

invited to our plant and suggested us to open a window ( fresh air ) in the air ducting way

from main fan to separator which sucks air . ( the separator kind is high efficiency ) Now we do

not definitely know what was the reason or the logic of such suggestion , how much it should

be closed or opened ? What is the effection of more or less openness of the widow on our

process ? you will do us a big favor if you can help us and tell us about this . ( the picture

attached to the email shows the duct and the window which lately suggested to be opened )

yours Vahid peyravi , Fars Cement Company

Thank you for the pictures. The cut point, efficiency and bypass of a separator is

determined by the air flow through the separator in addition to the operating principle and

the rotational speed of the cage of the separator. In this case opening of the fresh air vent

will change the amount of air that is drawn through the separator and in that way adjust the

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cut point, efficiency and bypass. Determining by how much the vent should be opened will

be reliant on measuring the Tromp curve of the separator with the vent in different

positions to determine the optimum opening position.

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Q: Formula to calculate cement mill individual chamber length

Dear Sir, How to calculate close circute cement mill individual chamber length. is there any

formula to calculate?

There is a formula to calculate the electrical energy that will be drawn by the main motor

of the mill:Mill Motor kW = 0.225 x D x Actual speed x Media Weight Normally the length of

the first chamber of the mill is determined to draw between 8 and 12 kWh/t of production

by this formula. 10 kWh/t would be a typical value.

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Q: lower the residue

Dear sir We have a 80 tph cement ball mill and a dynamic separator of the first generation (

heyd or sturtevant separators ). The residue of the final cement send to silo has not been lower

than 7-9 % on 90µ sieve . I read somewhere that increasing the diameter of the distribution

plate inside the separator can help more separation and lower the residue. Is this idea correct ?

does it work ? You will do me a great favor if you help me and suggest me a way we can lower

the residue and get more finer particles out of our separator.

Unfortunaltey there is a limit to the efficiency of a first generation separator. I do not

think that you can modify the separator to achieve your requirements. I suggest reducing

the feed rate to the mill such that the mill outlet material contains less +90u material

therefore less will pass through the separator.

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Q: Blaine Vs Residue

In our closed circuit Ball Mill for cement grinding while using old clinker, the blaines are

coming on higher side and as well as residue. To control the residue we are increasing the

separator speed which further leads to higher blaines. So, how to control residue without

affecting the blaines and why this is happening while using old clinker which is exposed to

atmosphere as we stored outside.

This is happening because the old clinker is partially prehydrated. The calcium hydroxide

in the clinker causes the generation of high, "false", surface. The best strategy is to control

to a residue target and ignore the high surface area. In that way the good clinker will

continue to be ground sufficiently finely.

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Q:

Dear Sir, Is there any formula for calculation of 28 days strength of blended cement? I want to

know that if there is any laboratory test method to determine the 28 days strength before

actual test results of lab test results of 28 days block.

A formula could be developed for a particular cement factory based on the clinker

content of cement, the fineness of grinding and the type of supplementary material used

with the clinker in the blended cement. Such a formula would need to be calibrated against

actual strength tests on the blended cement produced on the factory.

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Q: Blaine Vs Residue to control cement quality (OPC & PPC)

Dear Sir, Kindly quide to us blaine vs residue on 45 mic which is better paramter to control

cement quality of OPC & PPC

Really the particle size distribution should be controlled. That implies controlling at least

two residues and calculating the Rosin Rammler grain size distribution. This will certainly

give better quality control for blended cement production such as PPC.

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Q: why shrinage cracks in Porland slag cement

we are producing PSC and we are getting complaints of shrinkage cracks on concrete. what are

teh reasons and how to avoid it

Shrinkage is a normal phenomena associated with the hydration of concrete produced

with Portland cement. It can be reduced or eliminated by shrinkage compensating agents.

The formation of ettringite during the hydration of the cement makes an important

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contribution.

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Q: Cement Fineness

Dear Sir Would you please say me the following accepted values for OPC cement ?And which

standards cover it? 1)sieve 45 micron 2)sieve 90 micron 3)blain

Blaine is the surface area of cement in cm2/g. Typical values would be 3000-4000.

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Q: What is falsh setting & flash setting ?

False setting is caused by too much soluble sulphate being present when cement is

mixed with water and the excess soluble sulphate precipitating as gypsum. Flash setting iscaused by insufficient soluble sulphate being present to retard the hydration of the C3A

when cement is mixed with water. The amount of soluble sulphate present in the cement

has to be matched with the amount and reactivity of the C3A in the cement.

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Q: mill

Vertical roller mill and vertical raw mill. Are they both same ? If not then what is the difference

?

Yes they are the same thing.

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Q: Cement Manufactring Plant

I want to establish a cement manufacturing plant. so how would your company is helpful me

or what type of service will you provide me. contact me as soon as possible Whitehopleman regularly advises investors on setting up cement plants. We can provide

feasibility studies through to tender issuing, evaluation, contract placing, project

implementation monitoring and operational staff training.

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Q: cement cooling temp

if cement out-let gas temp in consideration for mill internal water spray, pls specify at what

temp. (max in 0C)water spray to start ? Thanks n regards

Normally 110 or 115 degrees C.

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Q: cement temp

which temp of cement shall be consider for mill water injection, mill discharge cement temp Or

product temp (sep fine) ? This is for closed circuit cement ball mill with 0-Sepa.Normally the mill exit air temperature.

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Q: Is there any effect on milling cement with temperatures beyond 100

Certainly. The higher the cement milling temperature the greater the degree of

dehydration of the gypsum in the cement. Normally the milling temperature is controlled to

a maximum of 120 degrees C (more typically 110 degrees C).

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Q: ball mill grinding media calculation

sir please give the complete procedure for calculating grinding media for a three chamber ball

mill

With a 3 chamber ball I presume there is no classifier and recirculation of rejects from

that classifier to the mill inlet? The first chamber must have large enough balls to initiallycrush the material and ensure a maximum size of 1mm at the outlet diaphram of that

chamber. The media grading in the other chambers must then achieve a progressive

reduction in fineness until the required fineness at the outlet diaphram of the mill.

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Q: Clinker mineralogy

Hello Sir. What is more hydraulically reactive cliker?

One which makes cement with faster setting and higher strength growth. This is

determined by the chemical and mineral composition of the clinker.

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Q: particle size distribution

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Dr. I want to know that which grinding mill would give good particle size distribution, ball mill

or VRM ?

They will both give a particle size distribution. A VRM will generally give a narrower

particle size distribution than a ball mill. Narrower, but not necessarily better.

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Q: cement mill open circuit

we don not have static air seperator in an open circuit two compartment mill. how to control

residue? it is 7~9 on 90 micron and 25~27 on 45 micron at 3000 blaine. second chaber

grinding path is sylpebs.

I think you have a roll press in front of the ball mill? In that case you do not need a 2-

chamber mill. The mill should be single chamber with all small media.

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Q: cement mill open circuit

By increasing the velocity of the mill upto 1.5 m/s the course particles passed into finished

product, if reduced to 1.0m/s the temperature of the cement increased to 120 0C. What would

be best setting value to control both parameters?Can we coontro the residue on 15% on 45

micron with out effecting the designed out putput? or shall we go for VRM?

Do you have a static separator in the mill exit air duct? if so adjust the blades in that to

collect more coarse particles. Alternatively you could introduce water injection to control the

cement temperature independently of the air flow through the mill.

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Q: High Residue and high temperature in an open circuit maill

We have open circuit mill with roller press, we are facing high residue of about 7~9% on 90

micron and 22~25% on 45 micron at blaine value of 3000 cm2/gm. We are keeping filling

degree of 33%. How could we reduce the the residue and temperature?

Your Blaine is relatively coarse therefore high residues are not a surprise. You can try

changing the recirculation around the roll press. Alternatively the media grading in the ball

mill should be made finer.

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Q: cement setting time

Cement residue - 45 mic.< 5.0%, Blaine=3600 cm2/kg., So3=2.2, Initial setting time=195

mins. Please let me know how to reduce the initial setting time to 140 mins. as reducing the

SO3 is of no use.

Yes reducing the SO3 wil have no effect. You need to change the clinker mineralogy to

produce a more hydraulically reactive clinker.

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Q: sir why in cement grinding in 45 microns residues high

It is impossible to say. Perhaps the feed rate to the mill too high? Perhaps the separator

speed is too low? Much more information is needed.

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Q: cement grinding residue is alsways 7.0 in 212microns. How to reduce the residue less than

3.0 in 212 microns in 2 chamber ball mill with Close circuit classifier with Circulating fan

milling system

No email provided......

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Q: what are the factor affecting on the process bag filter fan efficiency?sir , regarding the fan efficiency, what i under stood that by changing stack height , ,changing

impeller size or modified impeller , replacing motor with drive(VFD) but not by removing fan

damper pressure loss ( if there is a damper ) is it write or wrong?

Fan efficiency itself will be affected by the impellor design. Fan performance will be

affected by the other factors.

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Q: What is the role of V seperator in closed circuit cement mill

We are having both V seperator and dynamic seperator in our closed circuited cement mill. we

are thinking to remove V sep from circuit . Please let me kow the effect on though put and

power consumption.

The V-separator will be making coarse, static, separation of the material. I would need

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to see the layout before I could understand the importance of the V-separator.

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Q: cement strength development

dear sir , our cement 3&7 day comp.strength usually are high (280&350kg/cm2) but 28d is

low(440kg/cm2)What could be the reason and what can we do. clinker so3-1.4 , na2o-0.6

,k2o-0.42,mgo-2,c3s-62,c2s-15,c3a-6.9,c4af-11

The alkalis and aprticularly the Na2O in your cement are high. It is a well known

phenomena that high alkali sulphates in cement leads to higher early strengths but lower

28-day strength. Is it possible to reduce the alkalis by selective quarrying of raw materials

or changes in raw mix design?

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Q: Effect of Sulpher Alkali ratio

Hello Dr. Clark, Ideally the value of Alkali Sulpher ratio of clinker should be as close to 1 as

possible - My asking is if this value decreases (say -4) or or increases (say +4) then what's the

effect of produced cement because of this abnormal value?

The immediate problem is usually on the coating formed in the preheater, which can

become very hard if the alkali:sulphur ratio is low. There will be more subtle effects on the

cement quality as the amount of soluble alkalis in clinker will be changed and some alkali

will be present in the clinker minerals if the alkali:sulphur ratio is high. It might become

difficult to fully combine the clinker if the K2O content is high.

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Q: Setting time and water demand

We have one open circuit mill that we have been using for some time and the water demand

and setting time has been o.k. We recently installed a new roller press (close circuit). With the

same clinker and gypsum the water demand has been higher and the setting time longer.Sales

dept are complaining. What can we do to shorten the setting time and water demand to what

we have on the open circuit mill?

This is a common problem when switching from open circuit grinding. There is not much

that can be done as the particle size distribution of the cement willl be different. You can

try adjusting the SO3 content of cement.

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Q: Effect of SM and A/F ratio in raw meal on clinker grinding

I would like to know the consequences of increasing/decreasing SM and A/F ratio on the raw

meal in the later cement grinding. Is it possible that a high SM (around 3) increases the clinker

hardness by adding silica to the clinker composition? Does a low A/F ratio (around 0,7)

contributes to form dusty clinker due to the lack of cohesion/low melt viscosity, thus being

unable to form big particles?. Thanks in advance

Higher silica content of clinker might lead to harder to grind to clinker due to higher C2S

content in clinker. It also depends on the lime saturation and combination degree. Low

alumina modulus would not be expected to cause dustry clinker. That is more likely caused

by high SO3 content due to SO3 volatilisation. That could be caused by poor combustion

conditions in the kiln.

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Q: with the increasing of seperator RPM why blaine not increasing

Perhaps the separator is overloaded? Perhaps the airflow through the separator is

inadequate? There could be many reasons.

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Q: Cement Mill,s operation

As a CCR operator, What are those important parameters to monitor before and after taking

the feed (starting operation) in cement grinding?

The power drawn by the mill main motor. The power drawn by the elevator. The rejects

return weigher. The microphone on the first chamber of the mill. The temperature and

pressure profile through the milling system.

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Q: Why First chamber length is smaller than second chamber in ball mill

Because the first chamber is for crushing the material and the second chamber is for fine

grinding.

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Q: Setting time & Strength

We produce CEM II 32.5N.The setting time average 140mins while 2-day strength is 14MPa.

Our competitor has initial setting time of about 190-220mins but 2-day strength of above

20MPa. The customers (especially blockmakers) always complain that our cement do not set as

fast as that of the competitor but I think they are confusing the early strength with setting

time. All attempts to convince the sales team team about this is abortive. What do you think is

the problem? Is setting time not more of theory than reality?

Setting time is different to early strength development and not necessarily related to

early strength development. Block makers need early strength development rather than

quick setting. It is not surprising that they prefer your competitor's cement as it has higher

early strength.

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Q: Slag Cement Vs Portland cement

Dear sir, Please explaine me that, Why there is higher limit(Aprox 10%) of MgO in Slag Cement,

while in Ordinary Portland Cement MgO limit is 6% only.

I have never heard of that difference in the MgO specifications for OPC and slag cement.

I presume it is because the slag contains more MgO and that MgO is combined in a mineral

with silicate rather than being present as free MgO (periclase).

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Q: Cement is not setting

Hi, Dr. Clark, we always 'the cement is not setting' comment from our clients. In our lab

process the setting time shows 100 minutes initial setting time by the addition of 3% gypsum.

Let me know how to control the cement setting time and what are the factors involved in the

setting time other than gypsum.

Hmmm. That is a difficult one. You have an initial setting time of 100 minutes using the

Vicat needle penetration test? In that case there should be no problem unless the

temperature is very low. Which country are you in?

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Q: what is the throughput in a ball mill if i feeding say 170tph

what is the throughput in a ball mill if i feeding say 170tph

The output of a ball mill equals the feeding rate. We cannot create mass in a ball mill (or

any other process). So conservation mass means that what goes in must come out.

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Q: cement temprature is high 135 maximum what effect in cement. gie me reason

At this temperature the gypsum in the cement will be fully dehydrated to anhydraite and

there is likely to be coating of the grinding media and loss of grinding efficiency in the mill.

The reason is inadequate cooling in the mill. That cooling should be provided by ambient

air sweeping the mill but is also likely to require water injection dependent on the

dimension of the mill.

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Q: What is Residue and blaines?

what is the difference between them?

They are both used as a measurement of the fineness of powders. Blaine is the surface

area of the grains of the powder in cm2/g. The higher the Blaine the finer is the powder.

Residue is the amount of the powder retained on a sieve of a particular mesh size. The

higher the residue the coarser is the powder.

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Q: sir, how to reduce opc cement temperature ?

There are lots of ways: (i) ventilation of the mill by ambient air and control of that, (ii)

water injection into the mill, (iii) clinker stock control to not feed the mill with hot clinker,

(iv) ventilation of the separator with ambient air and control of that, (iv) installation of a

cement cooler on the fines from the separator, (v) installation of a cooler on the rejects

from the separator.

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Q: Stone adding at finish grinding

Sir, Presently we are adding 15% of Silicious stone (CaO 25-30%) in Cement Mill along with

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Clinker. We found strength (3d,7d &28d) is very satisfactory and setting time of cement is

maintained as require. Is there any possibility to increase it further as present comp. strength

is much above than minimum requirement. Presently Stone is crushed and screened before

adding. Regards

That sounds as if it is working very well.

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Q: what are techniques used for removing heat in cement grinding?

how to prevent cement setting in grinding process of cement?

The temperature of cement grinding mills is controlled by a combination of ventilation of

the mill by ambient air and water injection into the mill to achieve evaporative cooling. The

requirement for water injection depends on the dimensions of the mill and the temperature

of the clinker ground in the mill, among other factors. There should be no tendency for the

cement to set in the grinding process of cement.

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Q: how to calculate gypsum requirement / feed rate n cement mill?

how to calculate gypsum requirement / feed rate n cement mill?

This cannot be caalculated. It is dependent on the C3A content of the clinker and the

hydraulic reactivity of that C3A. You need to conduct optimum sulphate trials to determine

the optimum gypsum addition rate to cement.

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Q: Cement mill seperator

Hi sir We have a closed circuit cement mill and documentary of the seperator is SKS-Z-

3500/290/4*3200 . The seperator included of dynamic and static separator The static

seperator have 100 blades (50blades in up and50blade in down). The rotation of the seperator

is between 43 to 170 and it work always in 115-120 RPM and the blaine is 2900-3100 in opc.

The efficiency of the seperator is between 65-70% .(over screen 90mic) AT first: 1.The

efficiency of this seperator is good or Bad? 2.How I can improve the efficiency By the change of

the distance between the blades in statitcs seperator?(in now The distance is 8-16 cm) Best

regard M.Bahrampour

65-70% separator efficiency is mid-range, neither good not bad. How are you assessing

separator efficiency? You will have to conduct trials with different setting of the separator

blades and remeasuring the separator efficiency.

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Q: Dr. What is concrete workability and what is the best way to measure workability in

laboratory beside slump test?

Workability is a combination of the ease of placing concrete in a mould and the

consistency of the concrete, i.e. the tendency of the concrete to segregate into its

constituent fractions. It is related with the quantity and the reactivity of the C3A component

of the clinker and the amount and mineral form of the calcium sulphate in the cement.

Besides slump you can get some indication of workability from the flow of standard mortar

measured on a flow table and the water demand of the mortar to achieve a certain flow.

This is one of the most difficult quality parameters to control requiring that the gypsum

addition to cement be matched to the amount and reactivity of the C3A in clinker and the

temperature regime in the cement be closely controlled.

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Q: What is the difference between fineness in blaine and in residue? Can we correlate both

together?

You can expect there to be an inverse relationship between Blaine and residue. As Blaine

rises so residue at a particular sieve size should fall. The relationship will not be perfect as

other factors such as the cement mill configuration and clinker grindability will affect both

Blaine and residue. That is why both should ideally be monitored and controlled.

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Q: Dr. If we substitute natural gypsum with synthetic gypsum and the only difference is the pH

of the synthetic gypsum is very low (between 1 - 3), will it affect the quality of cement

produced? Purity content is almost similar for both.

Yes, I would expect this synthetic gypsum to affect the quality of the cement produced.

The hydration of cement produces calcium hydroxide as one of the reaction products. The

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acidity of the gypsum will react with that calcium hydroxide.

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Q: If we stored clinker at open stockpile where it was vulnerable to prehydration due to rain

and humidity,can we still used the clinker for cement grinding?If can, what is the best control

parameter to monitor its addition so that cement quality is maintain

You can still use the clinker with a controlled addition rate to the cement mill. Perhaps

10 or 15% maximum. You should control the fineness of grinding to a residue target rather

than a surface area target.

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Q: Relationship between Fineness (Blaines) and TPHSir, I want to ask precisely if there is any formula to Calculate the relationship between fineness

and Ton per hour of Cement production. All I assumed is the Higher the Blaine's or Fineness

the likelihood of the drop in production ( Is this theory correct?). What techniques can be

applied to Increase the fineness without corresponding reduction in Production Output?. I will

appreciate your prompt response to these questions. Thank you .

Yes, there is an inverse relationship between increasing Blaine and the mill throughput in

tonnes per hour. To achieve greater fineness you need to complete more grinding work per

unit of product so the output of the mill goes down. The best way to increase fineness with

no loss of output would be use grinding aids. If these are already being used then some

precrushing of the feed to the mill in a hammer mill or roll press. The amount of grinding

work and the throughput rate of the mill are related to the change in fineness that must be

achieved. If you have a finer feed to the mill then less grinding work is required.

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Q: What is the difference in particle size distribution and strength between product from open

circuit grinding (product coming out from mill will straight away drive into silo without go

through separator for material separation) and closed circuit grinding

The particle size distribution will be wider with open circuit grinding than with closed

circuit grinding at equivalent Blaine. The separator has the effect of sending coarse grains

back to the mill for regrinding. This means there will also be less super-fines at the

equivalent Blaine. Whether the strength will be higher or lower depends on the Blaine. At

low Blaine (3000 cm2/g) I expect that the strength from an open circuit mill would be as

high or even higher as a closed circuit mill. At higher Blaine (4000 cm2/g) I expect that the

strength from a closed circuit mill would be higher.

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Q: why the cement stick on the silo wall and the bulk trucks wall

why the cement stick on the silo wall and the bulk trucks wall.. our cement analysis is SiO2

Al2O3 Fe2O3 CaO MgO SO3 K2O Na2O 20.49 5.04 3.67 64.34 2.05 2.48 0.13 0.23 LSF SM AM

C3S C2S C3A C4AF 97.95 2.35 1.38 55.01 11.92 7.17 11.14 Sieve Blain F.l 9 2950 1

The analysis of your cement is probably irrelevant. The alkalis are not high. The problem

is most likely delayed hydration of the gypsum in the cement. I will post my article

"Hornblower's first command". Read that for further explanation.

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Q: effect of high L.O.I cement of concrete

Sir, We got one customer in need of cement of class 42.5N, the customer also wants the L.O.I

of the cement to be less than 5%, our limestone cement (Class 42.5N) have L.O.I of 7.5%. what

do you think is the effect of the high L.O.I value to concrete strength.

There will be no effect if your cement complies with class 42.5N. The EN197 standard

makes the composition of the cement irrelevant. It is performance based, i.e. you are

guaranteeing that it will meet 42.5N.

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Q: Info: cement is getting lump in bags within two months; what is the remedy to be adopted

in the manufacturing plant

Many cement companies use cement sacks including a plastic membrane b

Ask Dr Clark - Cement Milling _ Whitehopleman

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