Cement Energy and Environment

the main technology employed for such tasks is the selective Non-Catalytic Reduction (SNCR), in which nitrogenous compounds, such as urea and ammonia, are injected in order to react with the NOx formed in the process. Due to 1he need of continuous injection of high amounts of ammonia or urea, the use of reducing agents incurhigh operational costs, related to the costs of the reactant itself, of handling and respective of storage. Further, if the position of the injection pipes is not well established and optimized, it may cause NH3 emission or even increase NOx em1ss1ons. For these reasons, secondary measures should only be implemented after the primary measures have been optimized to their highest efficiency level and still the NOx, emission limits were not attained . 3. "Reburning" Among the primary measurements, reburning presents good potentials in systems with mine inline calciners. In order to be implemented, the calciner fuel must be injected in a substequiometric region , so that the hydrocarbons radicals generated by the fuel devolatilization react with the NOx formed in the kiln. To reduce kiln-formed NOx with reburning it is mandatory to have high volatiles concentration and low oxygen concentration in a specific region. The higher temperatures and the longer gas residence times, high is the NOx, reduction efficiency. In order to implement the reburnin~J technique successfully, the gas flow patterns, the temperature profile and the gas concentration profile (e.g . volatiles, 0 2, and NOx) within the calciner ought to be well known. - • , r~., .... -- a Cl ... ,_ ........ 0 ..... '"""' - 2 Inlets oUICil 0t1llets i~tiflcation on cakin~ ers C1, 0 dnd 0 . Burners ~re identified by red circk"S In the present study, MI-CFD (Mineral Interactive Computational Fluid Dynamics) modelling, developed by Cinar Ltd., was used to study NOx formation and reduction in three distinct industrial calciner configurations. The MI-CFD combines basic fluid dynamics modelling with advanced models for turbulence radiation , calcination reaction and solid combustion including devolatization, and volatiles and char combustion. The NOx reactions are calculated in a post– processor after a converged solution for the main components is obtained . This is possible because NOx, concentration is in ppm order, very low compared to the main species, so it does not influence the flow. - - ~ "" o• , ,, ......._!'-* ,. Voktiln and NO, ~~Won pu;~flle-, Pt!CO~t tJ&t«~orln onC1k:tNr CJ c.Oftstck-Mc::0-1· 100%of tttl-lud lnfK!td ln lilt tour upperbumen.:0 ·11 - 75' of the- lutlln~tttd In Uw lour "W"f' ~ ..t 15% m tJM:o (WQ "-' b..irMf\ 81U'f!fl) arr ioclt'f'l~ by red drdn PROCESS C1-l C1·11 O,<~~trtt.""""'"' •O"'tcoio~lr~ C1-f C1-U "''ICOI'IICHrt!M~f\1•)'""' .r. Oxygen cu1d NO, conc~ntn.tlon profiles. petcoke traJectories on CaldMrC2 consider· tng: 0 ·1- 100% of the fueJ injede<f In the burner ~t the: combustion chambtr: Q .u - 60% of the fuel injeded In the burnerat the combustion cN.mber 01nd 40% or the futol lnJetled In two additional bu1nersat the riser ducl8umet! are Identified by red drdes The mechanism involved in NOx, formation/ reduction are depicted in Figure 1. In order to demonstrate the effectiveness of the reburning technique to reduce NOx emissions, three different inline calciners were selected (C1, C2 and C3). All of them with petroleum coke (petcoke) as main fuel and are designed to operate at 3000, 3000 and 4000 t/day of clinker 30 ,