Modeling of NOX Reduction by Reburning

Abstract

rates for the nonspecific gas transport measured on the pure PMMA membrane decrease in the opposite order, namely, H 2 > n-C 4 H 10 > CH 4 > SF 6 (cf. Fig. 3).In order to increase the effect of the influence of a photochemical isomerization on mass transport membrane systems which have a larger ratio of specific to nonspecific mass transport should be selected. ConclusionsAmong the three types of polymer membranes tested, only the PMAZB membrane with AZB chemically bound to the side chain of the polymethacrylate showed a modified permeation behavior for different gases and methanol vapor when the AZB is photochemically switched into the trans or cis state. Due to the switching effect of the mass transport, this type of membrane acts like a microvalve. Possible applications of this membrane could be in microreactors for the controlled dosing of the educts or for the light controlled removal of products.Due to the high permeability of the polymethacrylate matrix, however, the trans/cis switching of the AZB has only a small modifying influence on the total permeability of the membrane. It is planned, therefore, to transfer the photochemical trans/cis switching to zeolite membranes which can accommodate adsorbed AZB in their well-defined pore system. For this AZB/zeolite composite membrane, we expect a higher influence of the trans/cis photoisomerization on the transport behavior of gases.This strong modification of the permeation pattern by the photochemical switching of the membrane should become evident by the comparison of bulky and nonbulky as well as of polar and nonpolar molecules. AcknowledgmentsWe thank the DFG (grants No 322/1-1 and Ma 1745/2-1) for financial support. References[1] Weh, K.; Noack, M.; Ruhmann, R.; Hoffmann, K.; Toussaint, P.; Chemie Ingenieur Technik, in press. [2] Okahata, Y.; Lim, H.; Hachiya, S.; J. Chem. Soc. Perkin Trans. II (1984) No. 6, pp. 989±994. [3] Balasubramanian, D.; Subramani, S.; Kumar, C.; Nature 254 (1975) pp. 252±254. [4] Tachibana, H.; Nakamura, T.; Matsumoto, M.; Komizu, H.; Manda, E.; Niino, H.; Yabe, A.; Kawabata, Y.; J. Am. Chem. Soc. 111 (1989) pp. 3080±3081. [5] Anzai, J.; Osa, T.; Tetrahedron 50 (1994) pp. 4039±4070. [6] Ruhmann, R.; Zschuppe, V.; Dittmer, M.; Wolff, D.; Makromol. Chem. 193 (1992) pp. 3073±3082.Reburning is a powerful and relatively inexpensive technique to reduce the NO x emission from industrial incinerators or coal fired power plants. NO x reduction is achieved by means of secondary fuel injection. The aim of the reported theoretical and experimental investigations has been to develop modeling tools for combustor design and layout. Detailed kinetic models from the literature have been tested and modified to describe species interconversion under practical reburning conditions. Furthermore, a hybrid model has been developed which allows calculation of the NO reduction in practical flows. It separates the computation of the turbulent flow from the computation of NO reduction. The latter is performed by a postprocessor using detailed kinetics. Bot...

Feasibility of the Constrained Free Energy Method for Modeling NO Formation in Combustion

“…In general, four different routes leading to NO X formation in combustion have been identified 2: (i) in the thermal process, atmospheric nitrogen is oxidized under high temperatures and thermal NO X is formed; (ii) prompt NO X is generated during combustion in a fuel‐rich environment when hydrocarbons are reacting with atmospheric nitrogen; (iii) N 2 O is either volatilized from fuel or formed when NO is reacting with radical derived from HCN and NH 3 ; (iv) nitrogen bound to the fuel becomes released during the devolatilization stage and is oxidized to fuel NO X . NO X emissions can be controlled by introducing additional fuel in the upper level of boilers, by staging air in combustion, or by flue gas recirculation 3, 4.…”

Switchgrass derived producer gas as a reburn fuel

“…Computational models of the rebuming process typically consist of hundreds of elementary reactions and greater than 60 different chemical species [19,20]. Because of this, global mechanisms are employed to model the rebum process.…”