Natural Gas Reburning Research Articles

98/03199 Mathematical modelling of circulating fluidized-bed combustion plants of industrial scale

This article presents a detailed experimental characterization of the reburning process in a large-scale laboratory furnace. Natural gas, pine sawdust and pulverized coal were used as reburn fuels. Initially, the study involved the collection of in-flame combustion data, without reburning, in order to define appropriate locations for the injection of the reburn fuels. Next, flue-gas data were obtained for a wide range of experimental conditions using the three reburn fuels and, subsequently, detailed measurements of local mean O2, CO, CO2, HC and NOx concentrations, and gas temperatures have been obtained in the reburn zone for three representative furnace operating conditions, one for each reburn fuel studied. The flue-gas data revealed that the sawdust reburning leads to NOx reductions comparable or even higher than those attained with natural gas reburning, while coal reburning yields much lower NOx reductions. The detailed data obtained in the reburn zone indicates that the reburning process remains active throughout all the reburn zone in the cases of natural gas and sawdust reburning, while in the case of coal reburning its relatively low volatile matter content is insufficient to establish an effective reburn zone. In the cases of the sawdust and coal reburning the burnout levels remain approximately constant, regardless of the NOx emissions reduction, with the sawdust reburning leading to higher particle burnout performance than the coal reburning.

Byproducts Emissions in Reburning and Advanced ReburningTechnologies

Natural gas reburning is a mature, commercial NOx control technology involving combustion of a fuel in two stages that has been successfully demonstrated at full scale. In a specific range of process conditions NOx concentrations can typically be reduced by 60%. The Advanced Reburning (AR) process, a combination of basic reburning and Selective Non-Catalytic Reduction (SNCR), can provide up to 85% NO reduction. Recent reburning research has focused on developing improved AR techniques to obtain up to 95% NOx control. Novel AR methods incorporate injection of N-agent promoters (sodium salts), N-agent injection into the reburning zone, and two stages of N-agent injection for deeper NOx, control. An important consideration with these innovative reburning technologies is whether they generate toxic byproducts. An experimental program to evaluate byproduct emissions from different reburning technologies was conducted in a 250kW Boiler Simulator Facility. Species evaluated included CO, CO2, NOx, N2O, SO2, SO3, total hydrocarbons, NH3, HCN, and fly ash. The goal of the program was to compare byproducts emissions from AR methods to those from existing commercial NOx control technologies. Experimental data are presented on byproduct emissions for different innovative AR technologies. The results show that AR technologies can be applied without significant adverse environmental impacts. In most cases, emissions from AR are lower than those from commercial technologies.

Removal of NOx from Flue Gas by Reburning with Plasma Activated Natural Gas: Review and Economics

By initiating chain reactions that consume NOx, CHi radicals play an important role in natural gas reburning. In conventional reburning, most of the methane is consumed in reactions with oxygen to form CO, and does not produce CHi- radicals as intermediate products, which limits NO reduction efficiency. Activating natural gas externally to the boiler may generate a mixture of CHi radicals by passing CH4 through a discharge before injection into the reburning zone. Five activation technologies are reviewed: microwave heating and discharge plasmas, electron beam irradiation-induced plasmas, corona discharge induced plasmas, and thermal plasmas. Wall, cyclone and tangentially fired boilers were considered in the economic assessment. From preliminary capital and operating cost estimates, pulse corona and electron beam techniques appear to be the most promising activation techniques

Optimization of combustion by fuel testing in a NO x reduction test facility

Combustion data for a wide range of coals were obtained in a 160 kW th NO x reduction test facility (NRTF). Parametric testing was undertaken under conditions of single-stage combustion, furnace air staging and natural gas reburning. From these tests, detailed information directly applicable to large utility furnaces on the effects of coal characteristics, excess air, stoichiometry and residence time on NO x , CO and unburnt loss is now available. The data show that there are considerable differences between coal types, but even coals of similar properties can display large variations in combustion performance. The differences between coals are reduced under advanced low-NO x combustion conditions. Confidence in the NRTF results is enhanced by comparison with large plant data; for NO x the NRTF gave good agreement with a large utility boiler in both absolute emission and coal effects.

96/05241 Experimental study and modeling of the influence of the inlet NO concentration in the natural gas reburning process

96/05241 Experimental study and modeling of the influence of the inlet NO concentration in the natural gas reburning process

96/01838 Experimental study and modeling of the burnout zone in the natural gas reburning process

The applicability of the laminar flamelet concept for the formation and destruction of nitric oxides in laminar and turbulent diffusion flames has been studied. In a first step, temperatures and species concentrations in an axisymmetric laminar diffusion flame have been calculated (i) by solving the detailed conservation equations and (ii) by applying the laminar flamelet concept. The main purpose of this step was the identification of differences between results from both approaches. It turned out that for highly temperature sensitive or relatively slow chemical processes, the inclusion of the full range of the prevailing scalar dissipation rates plays a major role for the calculated species concentrations. This behavior is obvious from the concept of the laminar flamelet model, where the scalar dissipation rate can be discussed in terms of the reciprocal of a residence time for attaining chemical equilibrium. In a second step, flamelet modeling of NOx formation was extended to a turbulent hydrogen diffusion flame. In both the steps, the flow fields of the flames were calculated by solving the Navier–Stokes equations in axisymmetric formulation using the SIMPLER algorithm. For the turbulent flow, Favre-averaged equations have been used and turbulence was modeled with the standard k–ϵ model including a correction term for axisymmetric systems. The averaging of the species concentrations was accomplished with presumed shape probability density functions (pdfs). The pdf of the mixture fraction was described with a β-function whereas that of the scalar dissipation rate was assumed to be log-normal. Buoyancy effects have been taken into account. The calculated temperatures and concentrations were compared with data from different experiments.

Experimental Study of the Influence of the Operating Variables on Natural Gas Reburning Efficiency

The process of reburning with natural gas has been demonstrated to be an attractive technique that can be applied to reduce the NO{sub x} emissions in coal combustion systems. The influence of the main operating conditions in the reburning zone using natural gas on the NO, HCN, and NH{sub 3} concentrations obtained at the exit of this zone has been analyzed. Experiments with a wider range of variable values than those presented in the literature have been performed. The variables analyzed have been the temperature (1,200--1,500 C), the natural gas concentration (1--4.5%) or reburning fuel fraction (0.08--0.50), the oxygen concentration at the inlet of the reburning zone (0--5%), the stoichiometric ratio in the reburning zone (0.75--1.05), the primary NO concentration (100--1,200 ppm), and the gas residence time (94--280 ms).

Experimental study and modelling of the burnout zone in the natural gas reburning process

The reburning process with natural gas is an effective technique which can be applied in existing coal combustors in order to reduce the NO x emissions. The importance of the burnout zone in this process is great, because significant amounts of CO, unburned fuel and reactive nitrogen can reach this zone. The influence of the temperature and the air excess introduced in the burnout zone on the concentration of the nitrogenous species has been studied. Experimental results have been determined of the concentrations of NO, HCN and NH 3 in the exit gas for temperatures ranging between 900 and 1100°C and air excesses between 5 and 15%. An empirical correlation which fits the output NO concentration has been obtained. A simplified model has been developed to predict the output concentrations of the most interesting nitrogenous species.

Influence of the Temperature and Oxygen Concentration on NOx Reduction In The Natural Gas Reburning Process

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTInfluence of the Temperature and Oxygen Concentration on NOx Reduction In The Natural Gas Reburning ProcessRafael Bilbao, Angela Millera, and Maria U. AlzuetaCite this: Ind. Eng. Chem. Res. 1994, 33, 11, 2846–2852Publication Date (Print):November 1, 1994Publication History Published online1 May 2002Published inissue 1 November 1994https://doi.org/10.1021/ie00035a039RIGHTS & PERMISSIONSArticle Views316Altmetric-Citations57LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (718 KB) Get e-Alerts Get e-Alerts

Application of Staged Combustion and Reburning to the Co-Firing of Nitrogen-Containing Wastes

The paper gives results of an evaluation of a 0.6 MW precombustion chamber burner, designed for in-furnace NOx control, high combustion efficiency, and retrofit applications, for use with high nitrogen content fuel/waste mixtures. The 250- to 750-ms residence time precombustion chamber burner mounted on a prototype watertube package boiler simulator used air staging and in-furnace natural gas reburning to control NOx emissions. The paper reports results of research in which the low NOx precombustor was used to examine the co-firing characteristics of a nitrogenated pesticide, containing dinoseb (2-sec-butyl-4,6 dinitrophenol) in a fuel-oil/xylene solvent. The dinoseb formulation as fired contained 6.4% nitrogen. NO emissions without in-furnace NOx control exceeded 4400 ppm (at 0% O2). When NOx controls in the form of air staging and natural gas reburning were used, these emissions were reduced to 99.99%. Mutagenicity studies of the dinoseb emissions showed that reburning (used for NOx control) reduced the mutagenic emission factor about 60-70% from that with air staging alone.

Reburning thermal and chemical processes in a two-dimensional pilot-scale system

An experimental investigation of the thermal and chemical processes influencing NO reduction by natural gas reburning, or fuel staging, in a two-dimensional pilot-scale combustion system is described. Reburning effectiveness for initial NO levels ranging from 50 to 500 ppm and reburn stoichiometric ratios ranging from 0.75 to 1.0 was evaluated in the low temperature environment (less than 1500 K) and simple aerodynamics of a firetube package boiler. Both exhaust and in-flame measurements are reported to provide insight into the controlling kinetic mechanisms. An overall reaction order with respect to initial NO between 1.5 and 1.6 was observed. N 2 formation was observed to occur in both the fuel-rich reburning and fuel-lean burnout zones. NO destruction in the reburning zone is attributed to the reaction CH+ NO→HCN+O, with less than 1 ppm CH radical required to produce the observed trends in nitrogenous species. Burnout zone N 2 formation is influenced by total fixed nitrogen speciation, with low fractional conversion of HCN and NH 3 observed. Under low primary NO conditions, N 2 destruction by hydrocarbon reaction becomes significant, resulting in reduced reburning effectiveness.

Fuel Oil Reburning Application for NOx Control to Firetube Package Boilers

Two pilot-scale (0.73 MW or 2.5 × 106 Btu/hr) firetube package boilers were retrofitted for fuel oil reburning application for NOx emission control. When firing distillate fuel oil (0.01 percent nitrogen content), an overall NOx reduction of 46 percent from an uncontrolled emission of 125 ppm (dry, at zero percent O2) was realized by diverting 20 percent of the total boiler load to a second stage burner; a 51 percent NOx reduction from 265 ppm was achieved in a distillate/residual fuel oil mixture (0.14 percent nitrogen content) reburning application. Nitrogen-free fuel oil reburning was found to be slightly more effective at reducing NOx than was natural gas reburning, although longer fuel-rich zone residence times were required to allow for evaporation and mixing of the fuel oil droplets. Key parameters investigated which impact the reburning process were: primary flame NOx, reburn zone stoichiometry, and reburn zone residence time. Reburning applied to firetube package boilers requires minimal facility modification. Reburning can be coupled with other NOx control techniques (e.g., distributed air low NOx burners) to achieve NOx emissions of less than 100 ppm. However, for very low primary flame NOx conditions (i.e., less than 200 ppm), reburning fuel nitrogen content is a limiting factor, and reburning with a low-nitrogen-content fuel, such as natural gas or nitrogen-free distillate oil, may be necessary to achieve 50 percent NOx reduction.