Cement plants strive for consistent raw material quality with minimal chemistry deviation to ensure stable process operations, minimize production costs and meet product specification.  Continual monitoring and control of mining operations, stockpile blending and raw material proportioning helps cement producers optimize quarry lifetime, reduce waste, ensure quality product and minimize energy usage. Online, real time chemical analysis of cement raw materials can make a dramatic difference in the way the above strategies can be implemented and helps the cement producer achieve world class process control easier and more efficiently. 

Here are some frequently asked questions and answers about the implementation of an online cement chemical analysis instrument for your raw material control needs.

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A:  Each plant is different and each has unique challenges and requirements. In general, it is good to start by reviewing the use of an online analyzer to control the raw material quality within a pre-blending stockpile. In this application the online analyzer is located after the primary crusher but before the pre-blending stockpile. Here the analyzer will monitor material in process from mining operations. If there are adverse materials found within the quarry deposit such as magnesium, alkalis, high sulfur, etc. an online analyzer can provide the immediate feedback needed to identify and avoid those materials.

As well, using an online analyzer to keep a pre-blend stockpile at target chemistry, while at the same time minimizing chemistry variations throughout the pile, ensures an optimized pre-blend reaches the raw mix proportioning station. Using this strategy, a reduction in the use of higher cost additives later in the process may be realized as well as a reduction in material variability at the raw mill. However, many times the most benefit can be achieved through the application of the instrument at the raw mix proportioning stage within the process. Here the analyzer monitors the process by providing high frequency analysis and automatically adjusts raw material feed proportions.

When considering where to place an online analyzer, discuss key application parameters and process goals including stockpile blending, sorting, raw mix proportioning or any additional installation locations with the manufacturer’s representative or application specialist.

A:  Online analyzers continuously measure the elemental composition of the entire raw material stream, in real time, being carried on a conveyor belt. The system provides an elemental analysis of the raw materials each minute, without touching the materials, and without errors and costs associated with material sampling for off-line laboratory analysis. The one minute analysis frequency can be adjusted if desired; however, from much experience it has been found that an analysis every minute is more than adequate to provide significant enhancement to existing process control methodology.

A: With increased and timely awareness of the quarried material chemical composition, a cement producer can significantly reduce the amount of quarried materials that may have been previously wasted and instead use them in the process. This can have a direct impact on lengthening the life of the quarry and minimizing costs associated with the purchase of outside raw materials.

A: Yes. A key tenet to minimal energy consumption in a cement manufacturing process is kiln feed with proper chemistry having low variability. High frequency process control using an online analyzer helps ensure this goal becomes a reality.

The control-loop cycle using offline X-ray analysis (laboratory instruments) can be relatively long and many times can miss high frequency variations in the raw material quality in process.  With control using an off line X-ray instrument, analysis measurements are made using a very small sample taken from the process.  A typical time period between sample collection and laboratory measurement is generally 1 to 2 times per hour. A lot can change and happen in an hour. Any changes implemented based on those results are an hour or two old and the process will likely be different. At times, material proportioning changes based on offline x-ray analysis could be incorrect for current conditions and drive the chemistry further off specification rather than closer to specification.

While laboratory X-ray analysis and process control have been an industry standard for many years, this strategy can be significantly enhanced through the addition of an online analyzer and automated high frequency proportioning control. Online analyzers have the unique ability to measure all the variations in the raw material and with control software can react to those changes every minute. Adjustments to material feed rates are made to smooth out those fluctuations.   

The same concept is applied with a pre-blending stockpile control application of an online analyzer but here, the control cycle is a little slower and different because feedback is to mining operations and loaders.

Kiln feed material with high chemistry variations requires more fuel in the kiln to properly react and more energy at the finish mill to grind over-reacted clinker. By using an online analyzer to minimize chemistry variation, fuel and energy consumption can be reduced and process upset conditions avoided.

Another contributor to potential errors when using a material sampling and offline laboratory analysis strategy is that representative samples needed to send to a laboratory are quite difficult to obtain. It is in this area where an online analyzer is extremely helpful in reducing energy consumption; it doesn’t need a sample, measures all the material and quickly tells mining operations they are sending the wrong material to the plant.

A:  Yes.  Reducing raw material chemistry variation is one of the primary tenets for installing an online analyzer. Other control parameters such as C3S, C2S, C3A, C4AF, etc. can also be used as control parameters and as well, individual oxides can be also used if desired. Within the answer to the question above, “Can an online analyzer help reduce energy consumption of a cement plant” some foundational information can be found that describes how an online analyzer coupled with automated high frequency control can help reduce process variability. Also, for additional information, it may be interesting to read a case study of such an online analyzer project that was undertaken with the goal to decrease the standard deviation of the modulus in the production of raw meal. It was found that the online analyzer eliminated the errors that occurred from sampling, since all the material that passed through the belt was analyzed by PGNAA technology.

The analysis was performed on a real-time basis with the use of PGNAA technology. This eliminated errors that could occur from the time delay for sampling and sample preparation, which was almost 90 minutes.

With the use of real-time analysis results from the online analyzer and the optimization parameters in the software, the standard deviation of modulus in raw meal production was decreased by 70% for LSF, 50% for SM, and 33% for AM.

With the production of more homogeneous and stable raw meal, the clinker quality was also increased.  Standard deviation of the free lime content in clinker production was decreased from .72 to 0.37, which was equal to almost 50% improvement. Also, kiln operation became more stable, which is believed to have decreased kiln thermal consumption and increased the life of kiln brick lining.

A:  One of the most popular uses of cross-belt online analysis systems is controlling stockpile chemistry to meet quality targets, thus ensuring smooth kiln operation and providing flexibility in quarry operations. Whether the stockpile is longitudinal or circular, online analysis systems allow consistent stockpiles, with minimal variations within and between piles. The analyzer can track the chemistry of the stockpile compared to the target chemistry and determine the preferred proportions of the source raw materials.

As an example, if you are trying to blend limestone and clay, here are some considerations for control in the pile. If you have only two distinct materials available, without much chemistry variation within those two material types, then in general terms, a single quality control parameter, such as Lime Saturation Factor (LSF) or an estimate of Alite (tricalcium silicate) using the Bogue equation for Ca3SiO2 (C3S), could be used to control the quality of the pile.  If however, the two raw materials you have available actually have chemistry variations such that the limestone and clay can be considered multiple different types of limestone and multiple different types of clay, then in reality there would be more than two materials available for control (e.g. High Grade Limestone, Low Grade Limestone, Low Silica/High Alumina Clay, High Silica/Low Alumina Clay, High Iron Clay, etc.).

This is usually the case within a quarry as typically there are fairly significant chemistry variations across an entire quarry with multiple differing grades of material on different mine benches.

Read additional details on this topic in the blog article: Question About Limestone and Clay Blending in Cement Production.

A:  Yes, the above answer about stockpile chemistry applies to both stockpile control and raw mix proportioning. See RAMOS Raw Mix Optimization Software for additional details about automatically adjusting multiple raw material source feeds to optimize blend proportioning, reduce chemistry variability, and minimize cost.

A:  The number of controlled moduli is one less than the number of different, controllable material types (i.e. control parameters = n-1 where N is the number of distinctly different materials. 4 different materials will allow the control of 3 quality control parameters, etc.

A: Prompt Gamma Neutron Activation Analysis (PGNAA) and pulsed fast thermal neutron activation (PFTNA) are non-contact, non-destructive analytical techniques used in online analysis systems to determine the elemental composition of bulk raw materials. Both of these techniques are known collectively as neutron activation analysis and function by bombarding materials with neutrons.

The neutrons interact with elements in the materials, which then emit secondary, prompt gamma rays that can be measured. Similar to X-ray fluorescence (XRF), each element emits a characteristic energy signature as it returns to a stable state.  

Learn more about PGNAA and PFTNA technology here.

A:  PFTNA is a form of PGNAA but it uses a Neutron Generator as its source of neutrons as opposed to an isotope. 

Learn more about PGNAA and PFTNA technology here.

A:  A neutron is a sub-atomic particle that is a component of the nucleus of all elements (except for simple hydrogen).

A: Essentially two types of neutron sources exist to enable PGNAA 1) A fissionable radioisotope (or combination of radioisotopes) or 2) created electronically by a specialized compact linear accelerator called a Neutron Generator. 

Radioisotopes that fission neutrons which can be used for PGNAA are: either 252Cf or the combination AmBe. By far, the most common radioisotope utilized is 252Cf for various reasons one of which is safety.

A: Yes, while online analyzers utilize neutrons in order to perform their measurements, the systems are designed to be completely safe. Leading manufacturers go to great lengths to ensure personnel are able to work around the analyzer without the need for access restrictions or radiation monitoring.

Note: Thermo Scientific online cement analysis systems are designed so that radiation levels around the sides of the system are significantly below regulation limits and are comparable to what is termed “background radiation” which is essentially the same radiation from day-to-day activities. Shielding materials used in the system allow access around the instrument and ensures personnel safety. The unit is inherently safe and does not require isolation and fencing to keep plant personnel away from the system.  As well, should a neutron generator system be selected as the source for neutrons, the generator can be turned off at any time.

A:  An advanced interface and spectral analysis tool processes, displays and archives data while at the same time tracks and monitors the health of the instrument. The data can be accessed by multiple users all at the same time from any remote workstation throughout a plant that is connected to the same network as the main operator console.

Learn more about OmniView online elemental analyzer interface software here.

A:  There are no moving parts so maintenance is minimal. On isotope based systems, the isotope will need to be periodically “refreshed”. Our recommendation is to add ½ the original amount each half-life of the isotope. As well, if a neutron generator is used, the tube inside the accelerator head will periodically need to be replaced. 

Software is available that provides continuous comparisons with the lab and timely, automatic calibrations. The software compares the results of your online crossbelt analyzer with the site laboratory and provides both a statistical and graphical data analysis. By having your online analyzer operating at peak accuracy, the kiln feed will be more consistent, which can lead to greater throughput, fewer BTUs of coal burned per ton of clinker, less electrical cost per ton of clinker and longer brick life.

Learn more about AccuLINK software here.

Note:  For many of the answers above, Thermo Scientific online analysis systems were referenced.  Check with your own manufacturer for specific details.  For more information about cement analysis and production technology, products, and applications, visit our Cement Analysis and Production pages for the latest application notes, videos, brochures, and other resource materials.

See where elemental online analyzers, x-ray analyzers, belt scales, weigh belt feeders, level sensors and indicators, flow detectors, impact weighers, stack emission gas detectors, material storage tracking software, and other instruments are used in the cement process.