Cement Energy and Environment

production, respectively. The geometry and identification of inlets and outlets of the three studied calciner configuration are presented in Figure 2. 4. Simulation results Two simulations were carried for each calciner: one considered a base case; and one in which design and operational conditions modifications were made to the calciner to implement or to improve reburning as a NOx reduction techniques. 4.1 Calciner Cl In the Calciner C1 configuration (Figure 3), petcoke in injected by two burners (in this case a simple pipe) below the tertiary air inlet. The volatiles are then released in a substorichiometric region. The fuel-bound nitrogen is converted mainly in HCN, which in turn can react with 02, forming NO, or react with NO forming N2. In a fuel– rich environment, as in the riser duct, the formation of fuel NOx, is not favored and the hydrocarbon radicals (CH1) react with part of the kiln generated NOx by means of reburning reactions. However, part of the volatiles and HCN are transported to the oxidizing region, above the inlet tertiary air level. In the original design (C1 - 1), a high formation of fuel NOxwas observed above the inlet tertiary air due to the reaction between HCN and 0 2. The predicted and industry measured values for temperature, oxygen concentration and NOx concentration at the outlet gas stream of calciner configuration C 1-1 are presented in Table 1. Notice that the MI-CFD simulations provided results within 5 % difference concerning the industry measured values for the same calciner configuration , thus verifying the ability of the software to model and reasonably accurately describe such system. In order to reduce NOx emissions in this calciner, a relocation of the burners was proposed, from the back and front walls to 3 m lower at the side walls, and a reduction of the meal fed at the smoke chamber inlet, from 30 % to 15 % of the total meal fed at the calciner (configuration Cl-11) in Figure 3). With the proposed modifications, the volatiles are released in a different re– gion, altering the volatiles concentration profile in the calciner. In this case, the region with the highest volatiles concentration is observed close to the left wall. The localized 0 2 concentration is almost null as the volatiles are concentrated in a small region, creating fuel-rich conditions. The formation of fuel NOx is not favored above the tertiary air inlet in this case and some reburning is observed in this region . The redistribution of meal causes increases in temperatures of up to 200°C on the lower meal path, which increase the reaction rate between NO and HCN (from fuel-bound nitrogen and from re– burning reactions). Both the proposed modifications promoted a reduction of 33 % in NOx emissions at the outlet gas stream of the calciner. 4.2 Calcincr C2 Calciner configuration C2 (Figure 4) has combustion chamber with a single burner on its top through which 100% of the petcoke is introduced into the calciner. The formulation of the fuel NOx is favored in this case as the fuel is injected close to the tertiary air inlets in an oxidizing environment. In the original design there are appropriate conditions to allow for the reduction of the kiln formed NOx by reburning. Hence, the implementation of two additional burners at the riser duct is processed, each injecting 20% of the calciner fuel. The petcoke injected at the riser duct consumes part of the oxygen from the kiln gases, creating fuel-rich regions (Figure 4). The hydrocarbons released in this region then react with the kiln-generated NOx. With 40% of the fuel being injected at the riser duct, it is possible to achieve a 17% reduction in NOx emissions at the calciner exit. 4.3 Calciner C3 Calciner C3 configuration (Figure 5) has six burners, two of them placed in the cone and four of them placed in cylindrical body above the bottom tertiary air inlets. Two operation conditions are considered in this study. In the first one , 100% of the Calciner petcoke is injected into four upper burners (C3-I). In the second one, 25% of the Calciner petcoke is injected into the two burners at the cone and 75% is injected into the four upper burners (C3-11). 31