Cement plant operation involves handling of large quantities of materials and in order to maintain the correct chemical composition, the present day instrumentation is providing solutions in a big way. Rajendra Mishra of PANalytical India explains the advantage of CNA analyser.
Bulk material analysis is a cost-effective way to optimize and stabilise limestone stockpile and cement raw meal. The PFTNA CNA (Controlled Neutron Activated) Online Analyser provides all the benefits of high-frequency bulk material analysis with the additional benefit and safety of controlled neutrons. High-frequency analysis delivered by the CNA provides guidance for quarry development, stockpile construction and raw mix proportioning. The cement plants will benefit from making the most efficient use of the quarry, optimised stockpile quality, and real time control of additives to the raw mix resultingin lower additive usage and improved quality of the raw mill output. In addition,cement plants can realise savings associated with lower laboratory testing and labourcosts, tailoring the raw feed for grindability to reduce electricity consumption and providing theoptimal chemistry to the kiln to reducefuel costs and extend refractory life.
The CNA analyser located upstream of the limestone pile is able to track the cumulative chemistry of the pile. Thus allowing the operator to direct and haul the trucks to different sections of the quarry in a way that will result in the final elemental composition of the pile closer to target.
The deployment of CNA also helps optimise consumption of expensive high-grade limestone or sweetener that results in handsome savings.
Similarly, the CNA analyser placed just upstream of the raw mill can monitor the chemistry of raw mix and automatically trigger an adjustment in the proportions of the reclaimed stockpile and the additives. By doing so, the plant is able to reduce variability in the raw mix and later on the kiln feed. Consistent kiln feed chemistry in turn leads to lower fuel consumption per ton of clinker produced.
The parameters used in the control of the Raw Meal are lime saturation factor (LSF), silica modulus (SM) and iron modulus (IM). These are actual proportions of the various chemical components / additives which are desired in the resultant clinker. Proportioning Raw Mix Components helps adjust weigh-feeders to maintain accurate feed of additives to limestone.
Stable Raw Mix results in:
Installation of a CNA system at the quarry makes it possibleto safely maximise the use of lower grade materials (and conserve high grade materials) by pre-blending before the stockpile. This cansignificantly increase the lifetime of the quarry.
CNA ahead of the stockpile ensures that pile quality targetsare met, the chemical variation is reduced and minimal correction is required upon reclaim.
Raw mix control
Using the CNA to monitor the raw mixchemistry at one minute intervals allows for the immediate correction of source proportioning ratios with no mill transport delay. This results in themaximum possible reduction in chemical variation of the kiln feed.
Using high energy neutrons to determine the chemistry of materials is very useful for the process control because the analysis is done instantaneously.
CNA Online Real Time Analysers based on the PFTNA technique generates neutrons electrically in a pulsed manner, allowing the detector(s) to differentiate between the 3 neutron-nucleus interactions. High frequency pulsing can only be achieved with an electric neutron source. The neutrons generated by the PFTNA generators bear high energy of 14 MeV as compared to that of mere 2.5 MeV in the PGNAA emanating from hazardous Cf252 which is ~ 5.6x weaker. High energy of neutron results in an overall enhancement in sensitivity and performance.
The maintenance needs for a PFTNA based analysers are minimal as compared to the PGNAA systems that need periodic recalibration once in 3 months to compensate for 5% drop in intensity owing to its 2.6 year half life. The PFTNA generator voltage is continuously adjusted as the tube ages providing constant neutron flux. The decaying Cf252 source provide a constantly decreasing neutron flux which reduces precision and necessitates recalibration. The Neutron Tube can be easily replaced by the user himself without any special´Radiation Protection´gears and training.
By Rajendra Mishra of PANalytical India, Spectris Technologies Pvt Ltd.