Natural Gas Reburning Research Articles

Cold-state Experimental Study on Flow Characteristics of Multi-nozzle in Natural Gas Reburning Burner

Based on the prototypes of a 130 t/h boiler, constant proportional cold-state test bench is established, flow characteristics of multi-nozzle in natural gas reburning burner and its influence on the covering effect for the upflow in the furnace are researched. Numerical simulations of this process are also made with standard turbulence model. The results show that air flow fullness in furnace is better in the case of the reburning zone with 8 nozzles compared to 4 nozzles and also coverage effect of the reburning flow for the updraft gas in the furnace is better. In the condition each nozzle airflow velocity is constant, the effect of reburning flow on coverage of up-secondary air is best when the incident angle for four corners is 14.17?, while Center of the furnace wall is 84.57. And while the best incident angle is invariable, the effect of reburning flow on coverage of up-secondary air is best when the speed of reburning gas in the corners of furnace is 51 m/s, the same to the center of the furnace wall’s.

Detailed measurements in a laboratory furnace with reburning

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.

Efficient and cost effective reburning using common wastes as fuel and additives

Potential substitutes of natural gas and lignite fly ash as NO and HCN reducing agents, respectively, for heterogeneous reburning were examined in a bench-scale apparatus equipped with a simulated reburning and a burnout furnace. Selection of NO reducing agent is based on fuel volatility and nitrogen functionality. HCN reducing agent selection is based on literature data. A wide range of waste materials and industrial by-products show overall NO reduction efficiency up to 88% at reburning stoichiometric ratio 0.90 or 0.95. Mixed fuel containing scrap tire and Fe 2O 3 is particularly effective. Though its cost is constrained by the energy-intensive operation of grinding the tire, the estimated raw-material cost is better than that of natural gas reburning and highly competitive against SCR. A first-level approximation study of the selectivities of nitrogen species to form NO in burnout zone reveals the importance of HCN and char nitrogen reaction mechanisms.

Experimental evaluation and detailed characterisation of biomass reburning

Previous works demonstrate that biomass is a valid reburn fuel, displaying NOx reductions close to those obtained in natural gas reburning. However, available information on biomass reburning basically refers to parametric studies based on exhaust emissions, lacking a thorough description of the process. The present work is an attempt to provide a detailed experimental characterisation of biomass reburning, including parametric studies in propane and pulverised coal flames, as well as in-furnace spatial distributions of the relevant variables. The tests were performed in a semi-industrial-scale furnace. Both natural gas and sawdust were used as reburn fuels for a range of residence times (0.41–1.44 s) and stoichiometries (0.85–1.05) in the reburn zone. NOx and unburnt (CO and UHC) emissions were measured in all the tests. A detailed characterisation of the local temperatures and concentrations of CO, UHC, NOx, HCN and NH3 inside the reducing zone was accomplished for some selected cases.

Evaluation of the use of coal volatiles as reburning fuel for NO x reduction

In this study, computational fluid dynamic (CFD) and kinetic models were used to investigate the relative performances of coal volatiles and natural gas reburning. This modeling approach considers fluid dynamic and non-isothermal effects, which were not considered in past laboratory flow reactor studies. The commercial CFD code FLUENT 6.1 was used to predict the residence times and temperatures for reburning tests in the down-fired combustor (DFC), a 0.5 MMBTU/h research combustor at The Pennsylvania State University. To predict NO x concentrations within the combustor, this data was then applied to an advanced reburning kinetic model used in past studies. For equal firing rates and stoichiometric ratios, reburning using methane yielded lower concentrations of NO x (and, therefore, better NO x reduction performance) than reburning using coal volatiles. The coal volatiles give increased flame temperature over natural gas, which apparently offsets the increased reburn zone hydrocarbon radical yield of coal volatiles over natural gas.

Study of the particulate matter emitted from residual oil combustion and natural gas reburning

In this work, a study of the particulate matter emitted from standard residual oil combustion and from natural gas reburning during oil combustion in a pilot scale furnace was carried out. The sizes, morphologies and chemical element distribution of particles were analyzed through scanning electron microscopy coupled to an X-ray energy dispersive spectrometer (EDS). The microscopy results show three sorts of particles: spherical, very compact and smooth cenospheres with sizes of 0.6-1.5 mm; cenospheres with a few pores with sizes of 10-20 mm and larger porous cenospheres with sizes of 20-50 mm. The particulate emitted from standard oil combustion shows predominantly spherical and very compact small cenospheres, with a smooth surface, while those emitted from the reburning process present a majority of larger porous cenospheres. The EDS microanalysis showed mainly Al and Si in the smaller cenospheres and mostly S and V in the cenospheres with a few pores and in the larger porous cenospheres.

Kinetic model for natural gas reburning

Kinetics of natural gas reburning is modeled on the basis of GRI3.0 and the method of Gear. The calculation results indicate that the model agrees with experiments. HCN, NH i and HCCO play an important role in the reburning system. Injecting NH 3 and increasing the fraction of HCCO in the reburning system will promote NO reduction. Injecting natural gas at the places wherein the fraction of NO is highest is a benefit to de-NOx. There exists an optimal value of ratio of natural gas: NO for reburning system. The influences of temperature, excess oxygen ratio and pressure are also discussed in the reburning system.

Reburning and burnout simulations of natural gas for heavy oil combustion

Reburning and burnout simulations were carried out through PLUG code of CHEMKIN-III using a reduced mechanism, in order to determine preliminary experimental parameters for achieving maximum NO x reduction to implement the reburning technology for heavy oil combustion in pilot scale equipments in Brazil. Gas compositions at the entrance of the reburning zone were estimated by the AComb program. Simulations were performed for eight conditions in the usual range of operational parameters for natural gas reburning. The maximum NO reduction (ca. 50%) was reached with 10 and 17.5% of power via natural gas and 1.5 and 3.0% O 2 excess, respectively, at 1273 K. The model predicts 250 ppm of NO, 50 ppm of CO and air mass flows in the range of about 50–130 kg/h for burnout.

Prediction of furnace and boiler performance: coal quality factor : Chudnovsky, B. et al. Proceedings of the International Technical Conference on Coal Utilization & Fuel Systems, 2002, 2, (27), 979–989

Previous works demonstrate that biomass is a valid reburn fuel, displaying NOx reductions close to those obtained in natural gas reburning. However, available information on biomass reburning basically refers to parametric studies based on exhaust emissions, lacking a thorough description of the process. The present work is an attempt to provide a detailed experimental characterisation of biomass reburning, including parametric studies in propane and pulverised coal flames, as well as in-furnace spatial distributions of the relevant variables. The tests were performed in a semi-industrial-scale furnace. Both natural gas and sawdust were used as reburn fuels for a range of residence times (0.41–1.44 s) and stoichiometries (0.85–1.05) in the reburn zone. NOx and unburnt (CO and UHC) emissions were measured in all the tests. A detailed characterisation of the local temperatures and concentrations of CO, UHC, NOx, HCN and NH3 inside the reducing zone was accomplished for some selected cases.

Prediction of Nitric Oxide Destruction by Advanced Reburning

Advanced reburning refers to a process wherein injection of a hydrocarbon fuel such as natural gas aft of the combustion zone is followed by injection of a nitrogen-containing species such as ammonia. In recent work, the authors used a systematic reduction method to develop a four-step, eight-species reduced mechanism from a 312-step, 50-species full mechanism for advanced reburning processes. The four-step model has been integrated into a comprehensive computational fluid dynamics combustion code, PCGC-3. In this work, the integrated model for advanced reburning has been evaluated through comparisons with experimental data for species and temperature profiles as well as effluent NO concentrations. Comparisons are shown herein for a base case, with reburning only (natural gas addition) and with advanced natural gas reburning (natural gas addition followed by NH3 addition). Profile comparisons show that the predicted flow-average axial NO concentration with advanced reburning followed the trends of experimental data, though the predicted initial NO level was lower than experimental data by 20−30%, partly due to both inaccurate prediction of flame structure and experimental error. Comparisons of effluent molar flux of NO with variation in swirl number, (NH3/NO)in and location of NH3 injection show that predicted trends and magnitudes of change were consistent with measured trends, though the predicted NO reduction was typically much higher than measured. Measurements and predictions both showed that NO reduction increased with increasing swirl number, (NH3/NO)in and reburning zone residence time. Most of the NO reduction is caused by chemical reaction, and only a small part of the NO reduction is due to dilution. Study results provide directions for further research.

00/02438 Detailed measurements in a pulverized coal flame with natural gas reburning

00/02438 Detailed measurements in a pulverized coal flame with natural gas reburning

00/02044 Detailed measurements in a pulverized coal flame with natural gas reburning

Flash Vacuum Thermolysis of 1,5-bis-(1-chloroethenyl)anthracene (6) gives cyclopent[hi]-aceanthrylene (2) which at T≥9000 °C rearranges to cyclopent[hi]acephenanthrylene (1). This conversion occurs more readily than that of the monocyclopenta-fused aceanthrylene to acephenanthrylene.

Modeling finite-rate mixing effects in reburning using a simple mixing model

Natural gas reburning is a NO x to N 2 conversion technology in which turbulent jets are used to mix reburning fuel into furnace gases. Modeling of the reburning process requires a description of the detailed chemical kinetics and the turbulent mixing between the reburn fuel (natural gas) and oxidizer (the furnace gases). The simple mixing models developed for the reburning application by Alzueta et al. [1], Cha et al. [2], and Han et al. [3] are able to incorporate the necessarily large chemistry sets with little computational overhead. These simple mixing approaches, e.g., the One-Reactor Model (1RM), yield good predictive capabilities over the parametric range in reburn zone stoichiometries [2]. This study investigates the role of finite-rate mixing on reburn performance over the parametric range in temperature. This is done through the application of the 1RM to the reburn pilot-scale data sets of Mereb and Wendt [4, 5]. Results show weaknesses in the simple mixing model at relatively low temperatures. Possible causes for this breakdown of the 1RM and similar simple mixing model approaches at low temperatures include uncertainties in the chemistry and/or the influence of the “homogeneity assumption” in the mixing model.

99/03868 Detailed measurements in a pulverized coal flame with natural gas reburning: Nazeer, W. A. et al. Fuel, 1999, 78, (6), 689–699

99/03868 Detailed measurements in a pulverized coal flame with natural gas reburning: Nazeer, W. A. et al. Fuel, 1999, 78, (6), 689–699

99/03848 Illinois power's online dynamic optimization of cyclone boilers for efficiency and emissions improvement: McVay, M. and Patterson, P. D. FACT (Am. Soc. Mech. Eng.), 1998, 22, (1), 715–723

Kinetics of natural gas reburning is modeled on the basis of GRI3.0 and the method of Gear. The calculation results indicate that the model agrees with experiments. HCN, NHi and HCCO play an important role in the reburning system. Injecting NH3 and increasing the fraction of HCCO in the reburning system will promote NO reduction. Injecting natural gas at the places wherein the fraction of NO is highest is a benefit to de-NOx. There exists an optimal value of ratio of natural gas: NO for reburning system. The influences of temperature, excess oxygen ratio and pressure are also discussed in the reburning system.

99/03839 Combustion of Kansk-Achinski coals in steam boilers of Ryazanskaya hydropower plant 300 MW energy blocks: Dvoinishnikov, V. A. and Shumilov, T. I. Teploenergetika, 1998, (6), 2–7. (In Russian)

Kinetics of natural gas reburning is modeled on the basis of GRI3.0 and the method of Gear. The calculation results indicate that the model agrees with experiments. HCN, NHi and HCCO play an important role in the reburning system. Injecting NH3 and increasing the fraction of HCCO in the reburning system will promote NO reduction. Injecting natural gas at the places wherein the fraction of NO is highest is a benefit to de-NOx. There exists an optimal value of ratio of natural gas: NO for reburning system. The influences of temperature, excess oxygen ratio and pressure are also discussed in the reburning system.

Detailed measurements in a pulverized coal flame with natural gas reburning

Gas composition and temperature profiles were measured inside a 200 kW, entrained flow, pulverized coal Controlled Profile Reactor, using reburning for NO reduction. NO, CO, CO 2, NO x , O 2, and NH 3 samples were collected with a water-cooled and water-quenched stainless steel probe and analyzed on a dry basis with on-line gas analyzers and an ion-sensitive electrode (NH 3) over a grid of 36 locations within the reactor. Temperature data were obtained with a suction pyrometer using an S-type shielded thermocouple. NO reduction with reburning was investigated over a range of residence times and reburning zone stoichiometric ratios to optimize for maximum NO reduction in the flue gases. A decrease in stoichiometric ratio of the reburning zone resulted in an increase in NO reduction up to a maximum of 70% at a stoichiometric ratio of 0.78. The residence time in the reburning zone was varied by moving the tertiary air injector up and down axially. Increasing residence time in the reburning zone was initially beneficial but became unimportant when residence time became longer than 700 ms. The location of the reburning zone was found to be optimal when reburning fuel was directed at the location of highest NO concentration (i.e., immediately following NO formation). In comparison to a baseline case without reburning, the rate of carbon burnout was found to be higher with 20 cm of primary fuel injection, but proceeded very slowly through the reburning zone. At the end of the reactor, burnout was more complete in the baseline case. The species, temperature, and solid sample elemental concentrations appeared to be self-consistent and should provide accurate data for comparison with modeling results.

Alternative fuel reburning

Advanced reburning is a NO x control technology that couples basic reburning with the injection of nitrogen agents and promoter compounds. Pilot scale experiments were conducted in which efficiency of basic and advanced reburning processes were characterized with a wide range of reburn fuels. Test fuels included natural gas, pulverized coal, coal pond fines, biomass, refuse derived fuel, and Orimulsion. Process variables that were studied included reburn fuel type, reburn fuel heat input, reburn zone residence time, initial NO x concentration, nitrogen agent injection temperature, and promoter type and amount. Reburn fuel properties found to affect the performance most significantly include fuel nitrogen content, volatiles, and ash constituents. Basic reburning performance for the tested solid fuels was found to approach that of natural gas reburning, with over 70% NO x reduction achievable at reburn heat inputs above 20%. Advanced reburn tests were conducted in which reburning was coupled with injection of nitrogen agents and promoters. The most effective promoter compounds were found to be alkalis, most notably sodium compounds. At reburn heat input of 10%, NO x reductions in the range of 85%–95% were achieved with natural gas and biomass advanced reburning.

Effect of Mixing on Natural Gas Reburning

AbstractThe purpose of this work is to understand the influence of the mixing process on reburning performance. Modeling is done in a one‐dimensional approximation by utilizing a detailed chemical mechanism, staged addition of reactants, and mixture stratification. Natural gas is used as both the main fuel and the reburning fuel. The most important parameters that affect the efficiency of the reburning process are: the amount of the reburning fuel, the initial NO level, the initial temperatures of the injected reburning fuel and overfire air (OFA), temperature of flue gas at the points where reburning fuel and OFA are injected, and intensity of mixing of the reburning fuel and OFA with the stream of flue gases. It is shown that fuel stratification in the mixing zone improves reburning efficiency for small heat inputs of the reburning fuel and degrades reburning efficiency for large heat inputs. Initial temperatures of the reburning fuel and OFA affect NO reduction and can be optimized for deeper NO control. Reactions of N‐containing species in the burnout zone play an important role in NO reduction for large heat inputs of the reburning fuel.

98/03984 NO x reduction capabilities of the internally fuel staged burner with coal of different rank

The reburning performances of thirteen world coals of different rank and natural gas were investigated in an isothermal drop-tube reactor. The NO reduction by coal reburning was strongly related to the burnout of the reburning fuel. It was possible to reduce NO even in lean burned gases. Decreasing the primary flame NO concentration for coal reburning resulted in a significant deterioration of system performance in comparison to natural gas reburning, where the NO reduction efficiency was almost unaffected. The optimum reburn zone stoichiometry and peak NO reduction efficiency of natural gas reburning was found to depend on the method of varying the primary combustion zone equvalence ratio.