Previous Questions

Question:
Sir,my question is on analysis of raw meal using XRF.LSF is a major quality control parameter used by me.In the absence of XRF, Total carbonate(TC) is also used as a control parameter. What is the relationship between LSF and Total carbonate, is there a relating formula or analytical equation relating this two parameters, such that knowing the %TC you can aswell determine the LSF? Thanks

Answer:
Daniel, total carbonate gives you a measure of the (CaO + MgO) content of the raw meal. This means it gives you an estimate of the denominator of the LSF equation. It tells you nothing about numerator, which is dependent on the SiO2, Al2O3 or Fe2O3 content. However, if you are using your normal raw materials and proportions of those raw materials then switching between XRF & total carbonate should not present any problems.

Question:
Dear Dr.Clark, It's been a long time since my last question. I'd like to supply a construction company with premixed cement for constructing a skyscraper that has 123 stories and is 555m height. The premixed cement is composed of OPC 13%, slag powder 61.5%, fly ash 25% and anhydrite 0.5%. But someone is apprehensive about the durability and chemical resistance etc of the concrete, and says the OPC content is too low. He insists that OPC content be above 30%. What do you think about the possible minimum OPC content? As the reference, the specification of concrete is 20(aggregate Size)-40MPa-650(slump flow). And they are planning to use limestone aggregates because of its better elasticity instead of the existing granite aggregate. What's your opinion about that? And if you have some references on the OPC content and the advantages of limestone aggregates, please let me read.... Thanks.

Answer:
Dear Kwon, It's good to hear from you again. I agree that the cement content of the premixed cement seems low, but I would not be concerned about durability and chemical resistance as the pozzolanic reaction of the slag and fly ash will ensure a very low porosity concrete. My concern would be the compressive strength. That will be determined by the concrete mix design and how much of the premixed cement is used per cubic metre of the concrete. That is the critical consideration. Regarding the aggregates, granite is generally considered to be a superior aggregate to limestone. Limestone can be excellent but there is significant variability between aggregates produced from different limestones, so it depends on the limestone. I see no advantage in using limestone instead of granite aggregate. The elastic modulus of the concrete will be determined by the properties of aggregate-paste interface.

Question:
Dear sir, Iwould like to know thay our kiln coating is unstable .

Answer:
Dear Shaikarif, There are many reasons why the coating might be unstable in your kiln. This might be caused by variable feed composition or erratic operation. You need to provide more details.

Question:
HELLO MR.CLARK I WOUDLD LIKE TO KNOW THAT OUR KILN IS FACING MUCH PROBLEM DUE TO REFRACTORY LINING FAILURE WHY IS IT SO AND ALSO SNOW MAN FORMATION IN COOLER IN STATIC GRATE IS ALSO VERY FREQUENT. WHAT IS THE REASON FOR THAT.

Answer:
There could be many reasons for frequent refractory failure ranging from poor technique in the installation of the kiln to unstable operation of the kiln. Much more information is required to make any diagnosis. Snowman formation in the cooler is caused by high residual liquid content in the clinker after it passes into the cooler.

Question:
Our kiln feed rate is 230 tons/hr, five stage RSP (Re Suspension preheater).we use coal at PC and main burner.We are also using TDF at 3rd stage preheater and TDF size 6" *12". From last few months our feed rate is reduced to 200 to 215 Tons/hr. We have changed, LSF, MS , MA, Residue only kiln opperation become stable and liter weights improved but kiln feed not increased. We started imported Indonesia coal again opperation was stable but Kiln feed was not increased.We are very much distrubed please give your expert comments on this?

Answer:
It is impossible to diagnose the problem of reduced feed rate to the kiln on the basis of this information. What criteria are you using to determine the required feed rate to the kiln? What is stopping you from increasing the feed rate to 230 t/h?

Question:
Sir I mean to ask the cause for jamming on preheater with reaction

Answer:
Preheater blockages are most often a result of the recirculation of volatile species from the rotary section of the kiln to the preheater known as the "alkali cycle". Volatile species evaporate in the burning zone of the kiln and recondense in the colder preheater. This can cause stickiness and lead to blockages.

Question:
Dear Dr Michael Clark, Thank you very much for your techical support. Im looking for an instrument for free lime analysis in clinker for our Quality control Lab.

Answer:
Most cement companies use the glycol extraction and acid titration for free lime analysis. If you are looking for an instrument then X-ray diffraction (XRD) is the technique to use. Phillips or ARL supply combined XRD and XRF spectrometers. With XRD you can also monitor the real mineralogy of your clinker, which opens many possibilities for enhanced quality control. Bear in mind that these spectrometers are expensive and require calibration.

Question:
cause for jam in cement plant

Answer:
You must be more specific Ravindra. What do you mean by a "jam".

Question:
what could possiby cause a crack of the refactories made of basic bricks in the uper transition zone of the kiln. if it is sulphur how

Answer:
No, sulphur would not normally be expected to cause a crack in upper transition zone refractories. Most likely this would be cause by some deficiency in the installation of the refractory lining.

Question:
Thanks Dr Clark, Plz fined the requested information: 1-Whether this will lead to an increased rate of production will depend on the capacity of induced draft fan. Ans: our Fan design is 460,000M3/hr at temp: 450 Deg C and total design pressure: 640mmWG. 2. Is the fan operating at full speed, or with its flow control damper fully open? Ans: At present operation PH fan is operating at about 80% speed and fan inlet damper opening is 90-100 %. 3. What is the installed motor capacity in kW and what kW does it draw at full production rate? Hoping to hear from soon.Dear Dr. Clark Best regards Ans: Installed PH fan motor power is 1250KW and Fan operating power at present @ 1460 tpd clinker production (drawn power) is 800 KW. 4. Secondary firing in the current situation is only likely to increase the preheater exit gas temperature and thermal energy losses from the kiln. Ans: Our actual measurement indicated the CO formation in kiln inlet: 8000 to+10,000 ppm and No oxygen is available. PH outlet CO traces is: 3000-4000 ppm and Oxygen is 3-4.5 %.

Answer:
OK Hussein, There seems to be spare capacity in the induced draft fan, but a problem drawing sufficient combustion air into the kiln. The problem with a counter-current shaft kiln is that increasing the draft is likely to result in greater recirculation/residence time of the feed in the preheater shaft. Water injection at the top of the preheater will create more draft in the shaft and kiln, but is likely to lead to the feed holding up in the shaft. For this reason I am doubtful that it will be effective. A also don't think secondary firing will be effective because of the lack of oxygen at the kiln inlet. Dependent on where you are in the world I suggest you consider oxygen enrichment or slag addition at the kiln inlet.

Question:
We are operating dry process rotary kiln, with double-strings preheater ( SKET /ZAB Shaft preheater technology, made up of 3 shaft stages , one technological cyclone one de-dusting cyclone- East Germany)of rated capacity 1600 TPD, dia.4.6 m x L69 m We are trying to push the kiln up to 1600 TPD, However, we were not successful, and the exhaust gas temperature goes up to 450 deg C. 1- Can water spray system, at the top cyclone reduce the gas temperature and increase the rate of production? 2-Can secondary firing improve the production rate, and what the technological consequences? Thanks

Answer:
Water sprays with appropriate atomisation nozzles can certainly reduce the gas temperature. It will also reduce the volume and increase the mass of exhaust gas. Whether this will lead to an increased rate of production will depend on the capacity of induced draft fan. Is the fan operating at full speed, or with its flow control damper fully open? What is the installed motor capacity in kW and what kW does it draw at full production rate? Secondary firing in the current situation is only likely to increase the preheater exit gas temperature and thermal energy losses from the kiln.

Question:
Dr.Clark,is there a relationship between LSF and rawmeal temperature?Our LSF range is 0.910-0.930.Whenever this is exceeded,more fuel is pumped in the system to attain the required rawmeal temperature of 815 degrees and burning in the kiln is harder leading to reduction in the kilnfeed to the kiln.

Answer:
Certainly there is a relationship between the LSF and the thermal energy consumption of the kiln. Higher LSF means more CaCO3 and more CO2 that must be calcined off the kiln feed. Calcination of CaCO3 is a highly endothermic (energy consuming) reaction. I presume you mean the precalciner temperature when you say raw meal temperature of 815 degrees? I am surprised that this is sensitive to the LSF.

Question:
Thanks,for your reply on the Rings question.But can you please tell me any procedure to quantify the cement in the crumbled ring sample? So, I can actually go back time to the process that lead to the crumbling of the ring. Abiola

Answer:
Well the only thing you can do is analyse the failed concrete chemically and thermally to see at whatb temperatures there is loss of weight. Interpreting the results will be tricky and you will need to also characterise the aggregates used.

Question:
A friend recently had a problem with his ring construction.Rings are usually used in the construction of well.He discovered that after 24 hours the ring was niether strong enough nor had attained good setting thereby leading to crumbling of the rings and the attendant loss.He brought the crumbled "ring" sample to me to help him find or deduced the cement quantity that mght have been used for its formation. I do you think I can go about this? and what do you think is the likely cause of this problem. Thanks Abiola

Answer:
Well, the problem is likely to be not enough cement used in the original mix, or too much water being added. Beyond that there might be some exotic reason such as some sugar getting into the concrete mix or other contaminant. Most likely not enough cement or too much water.

Question:
Respected Sir, Is nittrile rubber based insulation is used in cement Industry? Regards Arun Joshi

Answer:
Not that I am aware of Arun.

Question:
Sir, I am very much interested in the subject of XRD. We have been trying our best to see the best use of XRD in prediction of our Kilnfeed behaviour,our clinker propertises and even the reaction going on in the hotmeal.Maybe this will help us to optimized our Energy profile since we are always stock with frequent ring formation in the Kiln and Kiln inlet jamming.Kindly furnish us with the best practise to balance the above questions.

Answer:
XRD can certainly be used in all these investigations. The amount of quartz in raw materials will have a direct impact on the kiln feed reactivity. However, you must ensure that you are differentiating between quartz and silica in clay minerals. In hot meal you should be able to see different intermediate compounds being formed. If you find sulphate spurrite that is likely to be a cause of your kiln inlet ring and jamming problems. The hydraulic reactivity of the clinker will also be directly related to the real mineral composition. Remember that XRD is only one technique. You should combine that with other techniques to build an understanding of the behaviour of your raw materials and the performance of the kiln.

Question:
Sir, During my recent XRD Quantification of our Kilnfeed material below are the Phases result as determined using the Virtual Crystal Softwares, C3S -0 C/Graphite - 9.8 CaO/Lime -61.6 SiO2-/Quartz - 28.6 Sir,What can you really make out of this? and will this likely affect our operation. Regards, Saka Abiola A

Answer:
Well Abiola, I will be very surprised if there is 9.8% carbon as graphite in the kiln feed. This would cause CO and unburnt hydrocarbon emissions from the kiln. I think that must be an error in the software. The lime and silica are also much too high for kiln feed. It seems to me that there needs to be some calibration of the XRD.

Question:
We are looking to set up some KPI's about the reactivity of the clinker. We have some ideas, however, we would like to use some relevant indicators. Can you help us ? E.Lalancette Canada

Answer:
Ultimately this has to relate to the real mineralogy and the polymorphs of the clinker minerals that are present in the clinker. Do you have XRD? Or do you use microscopy on a regular basis? For many years Whitehopleman has been involved with Cementaren Povazska in Slovakia where they place great emphasis on real clinker mineralogy and clinker reactivity. They use XRD to monitor the real mineralogy of every clinker sample taken on shift and adjust the kiln operation to meet mineralogy targets. In the past they have used Dr Chromy's techniques to predict real clinker mineralogy from the oxide composition with the predictions being calibrated by microscopy performed on day shifts.

Question:
Sir, My question is regarding job.I have completed my B.E with ECE in 2009 and i want to make my career in cement industry.so i just want your suggestion regarding job..waiting for your reply

Answer:
Dear Peeyush, In which country are you located? The way to make your career in the cement industry would be to seek employment with one of the cement companies in your country. Best regards, Dr Michael Clark