NOx control in coal combustion by combining biomass co-firing, oxygen enrichment and SNCR

There has been renewed interest in evaluating NOx emission control by selective non-catalytic reduction (SNCR) combined with biomass co-firing to meet impending enforcement of NOx emission limits for power generation plant. Oxygen enrichment for the concentration of CO 2 in the flue gas has been observed in this work to have benefits for NOx emission control. This paper presents new information on the effect of combining biomass co-firing with SNCR under various oxygen enriched and air-staging conditions performed in the 20 kW combustion facility. Biomass has a higher tendency to generate CO and produced better reductions in NO x emission with and without using SNCR. NO reduction of around 80% were attained using SNCR for 15% and 50% blending ratios of biomasses at 21% overall O2 concentration for unstaged combustion. Whereas, a range of 40-80% NO reductions were attained for coal (Russian Coal) and 15% co-fired biomasses with 3.1-5.5% overall O2 concentration at 22-31% levels of flame staging. Moreover, it was found that better NOx removal efficiency was attained for higher NOx emission baselines under both oxygen enriched and normal firing conditions. However, SNCR NOx control for both coal or coal-biomass blends was observed to produce higher NOx reductions during O2 enrichment, believed to be due to the self-sustained NOx reduction reactions. Hence, NOx control by SNCR, oxygen enriched co-firing in power station boilers would result in lower NOx emissions and higher CO2 concentration for efficient scrubbing with better carbon burnouts. © 2012 Elsevier Ltd. All rights reserved

Calcium magnesium acetate and urea advanced reburning for NO control with simultaneous SO2 reduction

Calcium magnesium acetate (CMA) shows potential as a reductant for simultaneous NOx and SOx removal from coal-fired combustion plant. The performance of urea co-injection with CMA on NO reduction in an ‘advanced reburn’ (AR) configuration has been investigated with a view to optimization of the process in a pulverized coal fired furnace operating at 80kW. The impact on SO2 reduction has also been investigated. Urea/CMA solution was sprayed into the reburn zone of the furnace using twin-fluid atomisers over a range of reductant/NO stoichiometric ratios (NSR). The influence on NO reductions of primary zone stoichiometry (1) was investigated for a range of CMA reburn feed rates (Rff) and reburn zone stoichiometry (2). In addition the effect of temperature on the SNCR performance of urea was investigated. Optimum process conditions were categorized either by maximizing NO and SO2 reductions (Modes A and B respectively) or maximizing reductant utilisation efficiencies (Modes C and D). NO control was best performed at 1=1.05 but SO2 reductions were greatest at more fuel lean primary zone conditions (1=1.15). Highest NO reductions of 85% under AR-rich conditions were achieved under Mode A, but were only slightly higher compared with reductions of 79% under Mode B where SO2 reductions were optimized at 85%. N-utilization was also at an acceptable level of 25% compared to the maximum utilization efficiency which was obtained at NSR = 1.5 of 30% for the same conditions of stoichiometry operating in Mode C. Operation at this lower level of reburn (9.6%) could significantly reduce the consumption of CMA with some impact on NO reduction (73%). SO2 removal performance would be compromised severely with reductions lowered from 75% at Mode A to 35% at Mode C. Optimizing Ca utilisation (Mode D) resulted in poor NO and SO2 reductions, at 61% and 22% respectively and can be discounted as a viable option. The technique offers flexibility of operation depending on the emission control requirements

Characterization of Two-Dimensional Chiral Self-Assemblies L- and D-Methionine on Au(111).

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Characterization of Two-Dimensional Chiral Self-Assemblies l- and d‑Methionine on Au(111)

A combination of XPS, in situ RAIRS, LEED, and STM experiments together with ab initio DFT calculations were used to elucidate the self-assembly properties at the atomic level, and enabled the interpretation of the expression of surface chirality upon adsorption of both enantiomers of methionine on a clean Au(111) surface under UHV conditions. The combination of experimental results, in particular, LEED and STM data with quantum chemical calculations is shown to be a successful setup strategy for addressing this challenge. It was found that the methionine molecular self-assembly consists of the first molecule lying parallel to the gold surface and the second interacting with the first methionine through a 2D H-bond network. The interaction with the gold surface is weak. The stability of the assembly is mainly due to the presence of intermolecular H bonds, resulting in the formation of ziplike dimer rows on the Au(111) surface. The methionine molecules interact with each other via their amino acid functional groups. The assembly shows an asymmetric pattern due to a slightly different orientation of the methionine molecules with respect to the surface. Simulations of the STM image of methionine assemblies were consistent with the experimental STM image. The present study shows another example of Au(111) stabilizing a self-assembled biological layer, which is not chemically perturbed by the surface