Nitrogen oxide abatement by distributed fuel addition

The research reported here is concerned with the application of secondary fuel addition, otherwise known as reburning, as a means of NO{sub x} destruction downstream of the primary flame zone in boilers. This paper consists of two parts: First, results from a statistically correct design of parametric experiments on a laboratory coal combustor are presented. These allow the effects of the most important variables to be isolated and identified. Second, mechanisms governing the inter-conversion and destruction of nitrogenous species in the fuel rich reburning zone of a laboratory coal combustor were explored, using fundamental kinetic arguments. The objective here was to extract models, which can be used to estimate reburning effectiveness in other, more practical combustion configurations. Emphasis is on the use of natural gas as the reburning fuel for a pulverized coal primary flame. Then, reburning mechanisms occur in two regimes; one in which fast reactions between NO and hydrocarbons are usually limited by mixing; the other in which reactions have slowed and in which known gas phase chemistry controls. For the latter regime, a simplified model based on detailed gas phase chemical kinetic mechanisms and known rate coefficients was able to predict temporal profiles of NO, NH{sub 3} and HCN. Reactions with hydrocarbons played important roles in both regimes and the Fenimore N{sub 2} fixation reactions limited reburning effectiveness at low primary NO values

Nitrogen oxide abatement by distributed fuel addition

A combustor has been designed in order to retard the formation of nitrogen oxides by injection of reburning fuel. The design and the rebuilding of the new combustor was completed. Several new features were incorporated in the new design so that it would last longer. The design and construction of the furnace are discussed in this report. (VC

Detection of Streptococcus mutans Genomic DNA in Human DNA Samples Extracted from Saliva and Blood

Caries is a multifactorial disease, and studies aiming to unravel the factors modulating its etiology must consider all known predisposing factors. One major factor is bacterial colonization, and Streptococcus mutans is the main microorganism associated with the initiation of the disease. In our studies, we have access to DNA samples extracted from human saliva and blood. In this report, we tested a real-time PCR assay developed to detect copies of genomic DNA from Streptococcus mutans in 1,424 DNA samples from humans. Our results suggest that we can determine the presence of genomic DNA copies of Streptococcus mutans in both DNA samples from caries-free and caries-affected individuals. However, we were not able to detect the presence of genomic DNA copies of Streptococcus mutans in any DNA samples extracted from peripheral blood, which suggests the assay may not be sensitive enough for this goal. Values of the threshold cycle of the real-time PCR reaction correlate with higher levels of caries experience in children, but this correlation could not be detected for adults

Detection of Streptococcus mutans Genomic DNA in Human DNA Samples Extracted from Saliva and Blood

Caries is a multifactorial disease, and studies aiming to unravel the factors modulating its etiology must consider all known predisposing factors. One major factor is bacterial colonization, and Streptococcus mutans is the main microorganism associated with the initiation of the disease. In our studies, we have access to DNA samples extracted from human saliva and blood. In this report, we tested a real-time PCR assay developed to detect copies of genomic DNA from Streptococcus mutans in 1,424 DNA samples from humans. Our results suggest that we can determine the presence of genomic DNA copies of Streptococcus mutans in both DNA samples from caries-free and caries-affected individuals. However, we were not able to detect the presence of genomic DNA copies of Streptococcus mutans in any DNA samples extracted from peripheral blood, which suggests the assay may not be sensitive enough for this goal. Values of the threshold cycle of the real-time PCR reaction correlate with higher levels of caries experience in children, but this correlation could not be detected for adults

Genetic mapping of high caries experience on human chromosome 13

Background: Our previous genome-wide linkage scan mapped five loci for caries experience. The purpose of this study was to fine map one of these loci, the locus 13q31.1, in order to identify genetic contributors to caries.Methods: Seventy-two pedigrees from the Philippines were studied. Caries experience was recorded and DNA was extracted from blood samples obtained from all subjects. Sixty-one single nucleotide polymorphisms (SNPs) in 13q31.1 were genotyped. Association between caries experience and alleles was tested. We also studied 1,481 DNA samples obtained from saliva of subjects from the USA, 918 children from Brazil, and 275 children from Turkey, in order to follow up the results found in the Filipino families. We used the AliBaba2.1 software to determine if the nucleotide changes of the associated SNPs changed the prediction of the presence of transcription-binding site sequences and we also analyzed the gene expression of the genes selected based on binding predictions. Mutation analysis was also performed in 33 Filipino individuals of a segment of 13q31.1 that is highly conserved in mammals.Results: Statistically significant association with high caries experience was found for 11 markers in 13q31.1 in the Filipino families. Haplotype analysis also confirmed these results. In the populations used for follow-up purposes, associations were found between high caries experience and a subset of these markers. Regarding the prediction of the transcription-binding site, the base change of the SNP rs17074565 was found to change the predicted-binding of genes that could be involved in the pathogenesis of caries. When the sequence has the allele C of rs17074565, the potential transcription factors binding the sequence are GR and GATA1. When the subject carries the G allele of rs17074565, the potential transcription factor predicted to bind to the sequence is GATA3. The expression of GR in whole saliva was higher in individuals with low caries experience when compared to individuals with high caries experience (p = 0.046). No mutations were found in the highly conserved sequence.Conclusions: Genetic factors contributing to caries experience may exist in 13q31.1. The rs17074565 is located in an intergenic region and is predicted to disrupt the binding sites of two different transcription factors that might be involved with caries experience. GR expression in saliva may be a biomarker for caries risk and should be further explored. © 2013 Küchler et al.; licensee BioMed Central Ltd

Nitrogen oxide abatement by distributed fuel addition. Final report

Reburning is examined as a means of NO{sub x} destruction in a 17 kW down-fired pulverized coal combustor. In reburning, a secondary fuel is introduced downstream of the primary flame to produce a reducing zone, favorable to NO destruction, and air is introduced further downstream to complete the combustion. Emphasis is on natural gas reburning and a bituminous coal primary flame. A parametric examination of reburning employing a statistical experimental design, is conducted, complemented by detailed experiments. Mechanisms governing the inter-conversion of nitrogenous species in the fuel rich reburn zone is explored. The effect of reburning on N{sub 2}O emissions, the effect of primary flame mode (premixed and diffusion) and the effect of distributing the reburning fuel, are also investigated

Nitrogen oxide abatement by distributed fuel addition. [Reburning, mixing, effect of concentration of nitrogen]

Reburning experiments are presented in which the effect of the primary flame mode is examined. The application of reburning downstream of an axial diffusion primary flame without swirl is compared to reburning results in which the primary flame is premixed. The comparison is qualitative and is intended to examine reburning under more realistic conditions of utility boilers, where premixed flames are not common. Experimental results of reburning tests using nitrogen containing reburning fuels (ammonia doped natural gas and coal) are presented. The effect of reburning fuel type and nitrogen content on nitrogenous species profiles in the reburn zone are discussed. The last section is concerned with the applications of the kinetic model to predict overall reburning effectiveness from the primary NO level and to identify configuration for low total fixed nitrogen concentration. The effects of mixing in the early stage of reburning are examined and appropriate corrections are incorporated with the kinetic model to allow the prediction of nitrogenous species concentrations in the region where mixing effects are important. An empirical correlation is used to estimate the conversion of the total fixed nitrogen in the reburn zone to NO in the final stage of reburning. The kinetic model is also applied to the testing of hypothetical fuel-rich configurations to identify kinetic limits that would prevent further reductions in nitrogenous species

CONTINUED DEVELOPMENT OF THE ROTARY COMBUSTOR FOR REFIRING PULVERIZED COAL BOILERS

The Rotary Combustor is a novel concept for burning coal with low SO{sub 2} and NO{sub x} emissions. It burns crushed coal in a fluid bed where the bed is maintained in a rotating drum by centripetal force. Since this force may be varied, the combustor may be very compact, and thus be a direct replacement for a p.c. burner on existing boilers. The primary objective of this project is to demonstrate that a typical industrial boiler can be refired with the modified prototype Rotary Combustor to burn Ohio high-sulfur coal with low emissions of SO{sub 2} and NO{sub x}. The primary problem that must be resolved to demonstrate sustained operations with coal is temperature control in the rotating fluid bed. The prototype Rotary Combustor was assembled and installed on the T-850P CNB boiler at the CONSOL Energy site in South Park, Pennsylvania. Several design improvements were investigated and implemented during the assembly to improve the prototype Rotary Combustor operations compared to prior tests at Detroit Stoker in Monroe, Michigan. An Operating Manual and Safety Review were completed. The shakedown test phase was initiated. Two major problems were initially encountered: binding of the rotating drum at operating temperatures, and reduced fluid-bed pressure drop after short periods of operation. Plating the brush seal rotary land ring with a chrome carbide plasma spray and lubricating the seal prior to each test sufficiently resolved these problems to permit a limited number of operations tests. Unlike previous tests at Detroit Stoker, sustained operation of the prototype Rotary Combustor was accomplished burning a high-Btu fuel, metallurgical coke. The prototype Rotary Combustor was operated with coke in gasifier mode on two occasions. Fluid-bed temperature spiking was minimized with manual control of the feeds (coke, air and steam), and no clinker formation problems were encountered in either test. Emission levels of NO{sub x} were measured at about 270 ppmv which were higher those targeted for the device which were 100 ppmv. This was assumed to be because of the aforementioned temperature spiking. The primary operating problem remains control of the fluid-bed temperature. Although improvements were made, steam flow control was manual, and very coarse. To accomplish this will require finer control of the steam flow to the rotary drum air plenum, and development of an algorithm for automatic control using the Moore APACS{trademark}. This is the recommended succeeding step in the development of the Rotary Combustor for industrial or utility use