Cement, Energy and Environment July-Sep 2002

Previous ly. traditional limestone extraction in the quarry and its preparation for the cement plant. was ofte n based on insuffici ent knowledge or no knowledge ofthe rock chemistry on a day-by-day basis. Sampling efforts eventually resulted in the installation of costl y, sop hi sticated and compl ex mechanica l sampling stati ons, more or less automated, equipped with sample preparati on machi nery such as crushers. grinders and dryers. With the advent of so call ed PGNA online analysers 17 yrs ago. prospects fo r effect ive qua rry materials management decidedly took a turn tor the better. The first generation of PGNA analysers had a verti cal chute th at somewhat restricted material flow, but for the first time it was poss ible to analyse the elemental composition of raw materials in real time, without the need to sample in most cases. The next generation of PGNA analysers elim inated th e enclosed chu te restriction and, for the first ti me, allowed the online analysis of the entire material stream carried on a conveyor belt without touching the material. There rema ined one constraint in that the material bed height on the be lt had to be more or less constant. This fin al obstacle to freedom fro m material flow constraints was overcome in late 2000, by ASYS, who introduced the automatic belt load compensation, making it possible for the fi rst time to install the analyser directl y at the mouth of a crusher regardless ofthe material profi le. Thus, realtime, on! ine ana lysis of en tire bu lk mat e ria l streams, without tlow constrai nts wi th respect to variabi lity or maximum fl ow rate. became a rea li ty. Today, more than 60 PGNA analysers are in operation, controlli ng or moni tori ng the chem ical compos iti on of preblending piles in cement plants around the world. Whi le satis fying the demand of high kiln feed qual ity is an ove rr id ing concern th at IS successfu ll y be ing add ressed by PGNA analyscrs installed between raw mi x prOiJOrti oning bins and raw mill s. the analysers install ed at crusher out le ts a lso bring cons iderab le benefits to qu arry operations. Quarry managers now have real time visibil ity; a truckload can be analysed typic~lly in 3-4 min. Ma ny of these bene fit s, taken indi vid ua lly. arc large enough to provide economic justifi cation for PGNAA. Taken in conce rt, they make for powerful arguments and compe lling economi cs that are expected to dri ve the use of this techno logy in quarry operations at an accelerated pace. Raw material sorting So rt ing limestone or ot her rock material enables the operator to stoc kp il e various grades of materials of precise composition within a selectable range. Raw material monitoring The benefits include real time kn owledge of composition of all materi als for processing downstream and knowledge of the corresponding quarry sections by tracki ng dump truck movements. In many cases, this optimises quarry utiIisation by reduci ng the use of scarce and maximising the use of abundant materials. thus extending quarry life. Raw material blending .into stockpiles Benefits incl ude optimal use of qua rry mate ri als a nd imported addi ti ves, by avoiding compsitional overshoot and material was te for corrections: a more complete knowledge of quarry chem istry; more consistent kiln feed, as small chemical variations on the stacker be lt are eliminated by the pil e's homogenising action and a reduced usc of corrective mate rials. Ra11· material monitoringl hlending in remote quarries .A PGNAA dev ice in th e quarry enables the operator to shi p a prodm:t of consistent quality if he has correcti ve materials available. If he does not. he can at least ship a product of accurate ly know composition. enabling the plant to plan and optimise the requi rements of fi nal raw mi x. Benefits include a reduction in th e uti lisat ion of corrective materials at the plant. The avJilability of real time quarry mate rial compos1 t1 on info rm ation ha s cons ide rab ly improved the uti li sa ti on or raw materia l resources Jnd the quality of the prod ucts blended from them. Whereas dri II core sample analysers provide a global pictu re of quarry composition. PGNAA is supplyi ng min ll te-by-m inut e chcm istry infoi·mati on. as ma terials are extracted from the quar ry and processed into material blends of ti ghtly cont ro ll ed chemi cal specifications. Accu rate and time ly informa tion on quarry mate ri al chemi stry enab les th e operator to extend quarry Iife by optimising its use, and to provide the cement plant with controlled raw mate ri al quality of kno-,vn composition. The results arc better raw materials and reduced costs to produce them. Cour/esy : World Cemcnl .June 2002. Pp s--59 l~nqu ii)I IIO: I IJ, Fax: + ..f-1(0) 125rl8991 Email: mail rzi} li'Orldcemen/.com Web: 11'11'11'. li'Orldcement.cmn ..... . - ' ..