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The following process control elements should be considered in selecting the most suitable configuration for an online slurry analysis system:

- Elements to be analyzed. For example, analyzers utilizing the Prompt Gamma Neutron Activation Analysis (PGNAA) technique have a distinct advantage over analyzers using X-ray fluorescence by being able to measure light elements (those lower than calcium on the periodic table)
- Frequency of analysis (assay update time) as dictated by the process control strategy
- Residence time of upstream process
- Importance of stream in overall control strategy
- Confidence required in assay-based control decisions

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The elements to be analyzed are determined by the objectives of the process control strategy and the particular metallurgical problems which are anticipated from prior metallurgical test work. The frequency of analysis required, often referred to as the assay update time, depends on the following criteria:

- The fluctuation in assays in a given process stream considering the residence times of the processes immediately upstream
- The stability of the circuit
- At a minimum, the assay update times of the analyzers for the critical streams should be less than half of the retention time of the preceding process stage

Therefore, in the tailings stream from a scavenger bank of cells with a retention time of 5 mins, the grade can be expected to vary considerably in 2 mins during upset conditions or reactions to process control actions so on-line analysis should be made at an interval less than this to provide the best visibility of real-time plant performance. To obtain these sorts of assay update times, one requires dedicated analyzers or a centralized analyzer with just a few streams located nearby the process sample points.

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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 be sent 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.

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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.

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Online analyzers for sinter are situated directly on the conveyor belt and penetrate the entire raw material cross-section, providing minute-by-minute, uniform measurement of the entire material stream, not just a sub-sample. The location chosen for an online elemental analyzer should be after the agglomeration drum, taking into account safe access for installation and maintenance as well as environmental protection for service personnel.

Other critical factors to be considered in placement of sinter feed analysis equipment include:

- Belt width and troughing angle
- Maximum and minimum feed rates
- Belt speed
- Range of belt loading
- Maximum burden height of material
- Location of existing sampling infrastructure
- Iron ore mineralogy
- Intended process control strategy

Read more about products used in the sintering process and iron and steel manufacturing on our Iron Ore Sintering Process in Steel Manufacturing web page (https://www.thermofisher.com/us/en/home/industrial/cement-coal-minerals/iron-ore-sintering-process-steel-manufacturing.html).

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Yes, and it could be significant. First, let's assume that all streams are analyzed as intended. Cycling around each stream takes time and the frequency of measurement is therefore lower than with a dedicated analyzer. Each additional stream means a longer time between measurements. For some applications, this isn't a problem, a measurement every 15 mins may be sufficient. However, for greater process control and benefit from real-time continuous measurement, the Thermo Scientific AnStat-330 Sampling and Analysis Station combines representative sampling and elemental analysis into one product. However, the second challenge comes from routing several streams to a single location. In a sizeable plant, this often involves large pumps, pumping slurry through long sections of pipes, creating risks such as pipe blockage or pump failure. Analyzers measuring 20 streams could be reduced to 4 or 5 streams only after a few months of operation because of the reduced availability of each lines from blockages. Slurry density and viscosity often makes it difficult to transport and sample representatively. Using dedicated analyzers on critical streams and then strategically placing multi-stream analyzers to measure between 3 and 12 streams typically provides a good balance between cost, analysis intervals, and uptime.

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If the critical streams are monitored frequently as per the recommended criteria, the operators should be able to control the plant to give overall stability and best metallurgical results at minimum cost. The less critical intermediate streams can then be monitored at a lower frequency for the fine tuning of the circuit.

The degree of confidence required in the assay-based control decisions must be known. Streams that are more critical for control of the plant need to be monitored more frequently. Trends in plant performance will then be shown in more detail, showing effect of control actions on grade in real-time and giving greater confidence in control decisions. For example, in a base metal concentrator, the main objective might be to minimize metal losses in primary floatation while producing a particular concentrate grade in the cleaners. In addition, test work may show that recirculating loads tend to build up in the cleaning stages which is a result of recovery of excessive gangue in the rougher concentrate. Continuous analysis of tailings grades provides a critical tool in the operation of rougher flotation. On-line analysis of concentrates provides a tool to manage grade-recovery in the cleaners and better control impurities to meet the smelter requirements.

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If the process environment has water hose down, CIP, dust, high temperature, corrosive or explosive chemicals, the Antaris FT-NIR analyzer needs to be placed in a safe area or enclosed in an environmentally stabilized enclosure. Fiber optics run from the NIR analyzer to probes or flow cells installed in production process pipes, tanks, hoppers, conveyors, reactors, etc. The fiber optics carry the NIR source light to the probe sampling window and then carry the light after it has interacted with the sample back to the NIR analyzer detector. The end of the probe will have a window or an air gap for reflection or transmission analysis. The product being analyzed must be self-cleaning or the probe engineered to automatically clean itself by high pressure air. The computer that controls the NIR analyzer is also located in the safe area with Thermo Scientific RESULT Software exporting NIR results to text or Microsoft Excel files, LIMS, OPC or by 4-20 mA.

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Before selecting an online slurry analysis system, consider if light elements will need to be measured and if the measurement technique is amenable, given the expected variation in mineralogical and particle size for the process. In addition, look at the streams to be measured and ask these questions:

- What is critical for control of process (usually includes Feed, Final Tail, and Concentrate)?
- Is there a need for understanding trends within the process (usually includes Rougher Concentrate and Cleaner Tails)?
- What are the elements to be measured in each stream?

Based on this information, the various trade-offs taking into account all factors between centralized and dedicated analyzers, Prompt Gamma Neutron Activation Analysis (PGNAA) and X-ray fluorescence (XRF), capital and maintenance cost etc., can be worked out and a recommendation made for the optimum system configuration for the particular plant

For example, in a nickel concentrator, it is essential to control the concentration of talc (or MgO) in the concentrate stream. To be able to control the concentration of talc in the concentrate, one requires measurement of Ni and talc in each of the feeds, rougher concentrate, and final concentrate streams so that the appropriate concentration gradients between these can be optimized and the ratio of Ni/talc can be maximized at each stage for minimum reagent usage. It may also be useful to measure Fe and S in the feed stream because this may give an indication of the nickel mineralogy entering the plant. In all other streams, it is only necessary to measure Ni because the information from these streams is used only for monitoring the recovery of Ni. Thus, PGNAAA would be required with multiplexing for the three main streams, and possibly a multi-stream analyzer (using XRF technology) for the other streams).

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The Niton XL5 Plus Handheld XRF Analyzer is used in the following industries:

Oil and gas - for positive material identification (PMI) of piping material, which is critical where flow accelerated corrosion or sulfidic corrosion is a concern
Metal fabricating - for non-destructive elemental analysis to ensure that no incorrect or out-of-specification metals or alloys enter the manufacturing process
Automotive & aerospace - for incoming inspection and quality control of metallic and coated parts
Scrap metal recycling - for fast and accurate sorting of scrap metals, which is essential to enhance both workflow efficiency and profitability
Precious metal recycling - for accurately determining grade of precious metals and to prevent deleterious metals from entering the recycling process
Mining & exploration - for quickly identifying and recovering the most economically viable resources
Construction & environmental engineering - for screening risk assessment, hazardous site modeling, and remediation quality control

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Each cement 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 that 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.

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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 individual oxides can also be used if desired. An online analyzer coupled with automated high frequency control can help reduce process variability.

In a case study of 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 on a real-time basis using Prompt Gamma Neutron Activation Analysis (PGNAA) technology. This eliminated errors that could occur from the time delay for sampling and sample preparation, which was almost 90 mins. 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.

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When selecting the right online slurry analysis system, there are several capital constraints that should be considered, including

- Capital investment,
- Economic benefits expected
- Cost of on-going maintenance
- Flexibility of system modules
- Incremental benefits of less essential assays.

The economic benefits of having an on-line slurry analysis system coupled to a control system, be it manual or fully automatic, comes from one or more of the following: increase in metal recovery, improvement in concentrate grade and control of impurities, reduction in reagent consumption, decrease in operating costs, and improvement in stability of the operation.

These benefits have to be weighed against the capital investment of the analysis system and the cost of on-going maintenance including mechanical repairs, sample pump servicing or replacement, sample transport system troubleshooting, electronic repairs, analyzer downtime and calibration. The flexibility of hybrid systems of dedicated analyzers for the critical streams and multi-stream analyzers for the less critical streams enables the most cost effective analysis system to be selected for each particular plant. In working out what streams are to be measured, a cost benefit analysis should be carried out to guide the decision making process.

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Sinter feed composition control is important because the various sinter feed materials are not perfectly characterized and their chemical make-up varies within a batch and between batches. Therefore, the raw feed material chemistry changes and the additives feed rates should be adjusted to smooth out these variations in the sinter strand feed chemistry.

In a typical sintering operation, the control of the sinter feed chemistry is based on composite samples of the final sinter product. In addition to errors normally associated with sampling and analytical lab errors, there is a lag of many hours between receipt of composite sample assays and current sinter feed chemistry. The sinter operation may also lack sampling equipment on the sinter feed conveyor. Sinter product composite samples are typically obtained by incremental sampling. If the sampling frequency is too long, short term variability in sinter composition will be missed. Composite samples tend to smooth out and hide true process variability so are not on a short enough time scale to achieve optimum sinter feed chemistry control. Consequently, process upsets and missed chemistry targets in the sinter product will unknowingly be passed along to the blast furnace.

Through the use of real-time chemical analysis data from an online analyzer, the sinter feed basicity can be controlled to provide a more consistent feed to the sinter strand.

Control is made possible by using the analysis of CaO, SiO2, as well as other elements that affect basicity within a per-determined additives control strategy.

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