Dynamic NOx emission prediction based on composite models adapt to different operating conditions of coal-fired utility boilers

Aiming at the problem of the narrow combustion stability boundary, a conical swirler was designed and constructed based on the concept of fuel distribution. The blowout performance was studied at specified low operating conditions by a combination of experimental testing and numerical simulations. Research results indicate that the technique of the fuel distribution can enhance the combustion stability and widen the boundary of flameout within the range of testing conditions. The increase of the fuel distribution ratio improves the combustion stability but leads to an increase in NOx emission simultaneously. The simulation results show the increase of the fuel distribution ratio causes contact ratio increase in the area of lower reference velocity and gas temperature increase. The increased contact ratio and temperature contribute to the blowout performance enhancement, which is identical to the analysis result of the Damkohler number. The reported work in this paper has potential application value for the development of an industrial burner and combustor with high stability and low NOx emission, especially when the combustion system is required to be stable and efficient at low working conditions.

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A Nitrogen Oxides Emission Prediction Model for Gas Turbines Based on Interpretable Multilayer Perceptron Neural Networks

Volume 9: Oil and Gas Applications; Organic Rankine Cycle Power Systems; Steam Turbine ◽

10.1115/gt2020-15478 ◽

2020 ◽

Author(s):

Dawen Huang ◽

Shanhua Tang ◽

Dengji Zhou

Keyword(s):

Neural Networks ◽

Nitrogen Oxides ◽

Prediction Model ◽

Working Conditions ◽

Gas Turbines ◽

Middle Layer ◽

Operating Conditions ◽

Nox Emission ◽

Outlet Temperature ◽

Output Layer

Abstract Gas turbines, an important energy conversion equipment, produce Nitrogen Oxides (NOx) emissions, endangering human health and forming air pollution. With the increasingly stringent NOx emission standards, it is more significant to ascertain NOx emission characteristics to reduce pollutant emissions. Establishing an emission prediction model is an effective way for real-time and accurate monitoring of the NOx discharge amount. Based on the multi-layer perceptron neural networks, an interpretable emission prediction model with a monitorable middle layer is designed to monitor NOx emission by taking the ambient parameters and boundary parameters as the network inputs. The outlet temperature of the compressor is selected as the monitorable measuring parameters of the middle layer. The emission prediction model is trained by historical operation data under different working conditions. According to the errors between the predicted values and measured values of the middle layer and output layer, the weights of the emission prediction model are optimized by the back-propagation algorithm, and the optimal NOx emission prediction model is established for gas turbines under the various working conditions. Furthermore, the mechanism of predicting NOx emission value is explained based on known parameter influence laws between the input layer, middle layer and output layer, which helps to reveal the main measurement parameters affecting NOx emission value, adjust the model parameters and obtain more accurate prediction results. Compared with the traditional emission monitoring methods, the emission prediction model has higher accuracy and faster calculation efficiency and can obtain believable NOx emission prediction results for various operating conditions of gas turbines.

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Impact of Urea Direct Injection on NOx Emission Formation of Diesel Engines Fueled by Biodiesel

Volume 2: Emissions Control Systems; Instrumentation, Controls, and Hybrids; Numerical Simulation; Engine Design and Mechanical Development ◽

10.1115/icef2015-1059 ◽

2015 ◽

Author(s):

Wenming Yang ◽

Hui An ◽

Jing Li ◽

Dezhi Zhou ◽

Markus Kraft

Keyword(s):

Catalytic Reduction ◽

Injection Rate ◽

Simulation Software ◽

Operating Conditions ◽

Nox Emission ◽

Urea Solution ◽

Injection Timing ◽

Post Injection ◽

Nox Removal ◽

Aqueous Urea

There are many NOx removal technologies: exhaust gas recirculation (EGR), selective catalytic reduction (SCR), selective non-catalytic reduction (SNCR), miller cycle, emulsion technology and engine performance optimization. In this work, a numerical simulation investigation was conducted to explore the possibility of an alternative approach: direct aqueous urea solution injection on the reduction of NOx emissions of a biodiesel fueled diesel engine. Simulation was performed using the 3D CFD simulation software KIVA4 coupled with CHEMKIN II code for pure biodiesel combustion under realistic engine operating conditions of 2400 rpm and 100% load. To improve the overall prediction accuracy, the Kelvin-Helmholtz and Rayleigh-Taylor (KH-RT) spray break up model was implemented in the KIVA code to replace the original Taylor Analogy Breakup (TAB) model for the primary and secondary fuel breakup processes modeling. The KIVA4 code was further modified to accommodate multiple injections, different fuel types and different injection orientations. A skeletal reaction mechanism for biodiesel + urea was developed which consists of 95 species and 498 elementary reactions. The chemical behaviors of the NOx formation and Urea/NOx interaction processes were modeled by a modified extended Zeldovich mechanism and Urea/NOx interaction sub-mechanism. Developed mechanism was first validated against the experimental results conducted on a light duty 2KD FTV Toyota car engine fueled by pure biodiesel in terms of in-cylinder pressure, heat release rate. To ensure an efficient NOx reduction process, various aqueous urea injection strategies in terms of post injection timing and injection rate were carefully examined. The simulation results revealed that among all the four post injection timings (10 °ATDC, 15 °ATDC, 20 °ATDC and 25 °ATDC) that were evaluated, 15 °ATDC post injection timing consistently demonstrated a lower NO emission level. In addition, both the urea/water ratio and aqueous urea injection rate demonstrated important roles which affected the thermal decomposition of urea into ammonia and the subsequent NOx removal process, and it was suggested that 50% urea mass fraction and 40% injection rate presented the lowest NOx emission levels.

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Use of CFD Modeling for Design of NOx Reduction Systems in Utility Boilers

2002 International Joint Power Generation Conference ◽

10.1115/ijpgc2002-26081 ◽

2002 ◽

Cited By ~ 8

Author(s):

Bradley Adams ◽

Marc Cremer ◽

James Valentine ◽

Venkata Bhamidipati ◽

David O’Connor ◽

...

Keyword(s):

Nox Reduction ◽

Field Testing ◽

Nox Emission ◽

Injection System ◽

Cfd Modeling ◽

Unburned Carbon ◽

Port Placement ◽

Utility Boilers ◽

Ammonia Slip ◽

Combustion Optimization

CFD modeling has found increasing use in the design and evaluation of utility boiler retrofits, combustion optimization and NOx reduction technologies. This paper reviews two recent examples of CFD modeling used in the design and evaluation of NOx reduction technologies. The first example involves the staging of furnace combustion through use of overfire air (OFA) to reduce NOx emission in a B&W opposed-wall fired pc furnace. Furnace simulations identified locations of highest flue gas mass flows and highest CO concentrations and were used to identify OFA port placement for maximum NOx reduction with lowest increases in unburned carbon in fly ash and CO emission. Simulations predicted a 34% reduction in NOx emission with OFA. The second example summarizes the design and application of RRI with OFA and SNCR in a 138 MW cyclone-fired boiler. Simulations were used to design an aminebased injection system for the staged lower furnace and to evaluate NOx reduction and ammonia slip of the RRI system. Field-testing confirmed modeling predictions and demonstrated that the RRI system alone could achieve 25–30% NOx reduction beyond OFA levels with less than 1 ppm ammonia slip and that RRI in combination with SNCR could achieve 50–55% NOx reduction with less than 5 ppm slip.

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Set-Point Adaptation Strategy of Air Systems of Light-Duty Diesel Engines for NOx Emission Reduction Under Acceleration Conditions

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4038543 ◽

2018 ◽

Vol 140 (7) ◽

Author(s):

Kyunghan Min ◽

Haksu Kim ◽

Manbae Han ◽

Myoungho Sunwoo

Keyword(s):

Diesel Engines ◽

Performance Optimization ◽

Control Structure ◽

Engine Performance ◽

Optimization Method ◽

Driving Cycle ◽

Operating Conditions ◽

Nox Emission ◽

Exhaust Gas ◽

Set Point

Modern diesel engines equip the exhaust gas recirculation (EGR) system because it can suppress NOx emissions effectively. However, since a large amount of exhaust gas might cause the degradation of drivability, the control strategy of EGR system is crucial. The conventional control structure of the EGR system uses the mass air flow (MAF) as a control indicator, and its set-point is determined from the well-calibrated look-up table (LUT). However, this control structure cannot guarantee the optimal engine performance during acceleration operating conditions because the MAF set-point is calibrated at steady operating conditions. In order to optimize the engine performance with regard to NOx emission and drivability, an optimization algorithm in a function of the intake oxygen fraction (IOF) is proposed because the IOF directly affects the combustion and engine emissions. Using the NOx and drivability models, the cost function for the performance optimization is designed and the optimal value of the IOF is determined. Then, the MAF set-point is adjusted to trace the optimal IOF under engine acceleration conditions. The proposed algorithm is validated through scheduled engine speeds and loads to simulate the extra-urban driving cycle of the European driving cycle. As validation results, the MAF is controlled to trace the optimal IOF from the optimization method. Consequently, the NOx emission is substantially reduced during acceleration operating conditions without the degradation of drivability.

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Uncertainty Quantification of NOx Emission Due to Operating Conditions and Chemical Kinetic Parameters in a Premixed Burner

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4040897 ◽

2018 ◽

Vol 140 (12) ◽

Cited By ~ 1

Author(s):

Sajjad Yousefian ◽

Gilles Bourque ◽

Rory F. D. Monaghan

Keyword(s):

Sensitivity Analysis ◽

Uncertainty Quantification ◽

Gas Turbine ◽

Flow Reactor ◽

Epistemic Uncertainty ◽

Plug Flow ◽

Chemical Kinetic ◽

Operating Conditions ◽

Nox Emission ◽

Gas Turbine Combustion

Many sources of uncertainty exist when emissions are modeled for a gas turbine combustion system. They originate from uncertain inputs, boundary conditions, calibration, or lack of sufficient fidelity in a model. In this paper, a nonintrusive polynomial chaos expansion (NIPCE) method is coupled with a chemical reactor network (CRN) model using Python to quantify uncertainties of NOx emission in a premixed burner. The first objective of uncertainty quantification (UQ) in this study is development of a global sensitivity analysis method based on the NIPCE method to capture aleatory uncertainty on NOx emission due to variation of operating conditions. The second objective is uncertainty analysis (UA) of NOx emission due to uncertain Arrhenius parameters in a chemical kinetic mechanism to study epistemic uncertainty in emission modeling. A two-reactor CRN consisting of a perfectly stirred reactor (PSR) and a plug flow reactor (PFR) is constructed in this study using Cantera to model NOx emission in a benchmark premixed burner under gas turbine operating conditions. The results of uncertainty and sensitivity analysis (SA) using NIPCE based on point collocation method (PCM) are then compared with the results of advanced Monte Carlo simulation (MCS). A set of surrogate models is also developed based on the NIPCE approach and compared with the forward model in Cantera to predict NOx emissions. The results show the capability of NIPCE approach for UQ using a limited number of evaluations to develop a UQ-enabled emission prediction tool for gas turbine combustion systems.

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Modeling of pulverized coal combustion for in-furnace NOx reduction and flame control

Thermal Science ◽

10.2298/tsci160604186b ◽

2017 ◽

Vol 21 (suppl. 3) ◽

pp. 597-615 ◽

Cited By ~ 2

Author(s):

Srdjan Belosevic ◽

Ivan Tomanovic ◽

Nenad Crnomarkovic ◽

Aleksandar Milicevic

Keyword(s):

Coal Combustion ◽

Numerical Study ◽

Nox Reduction ◽

Combustion Process ◽

Pulverized Coal ◽

Operating Conditions ◽

Nox Emission ◽

Differential Model ◽

No Formation ◽

Turbulent Reactive Flows

A cost-effective reduction of NOx emission from utility boilers firing pulverized coal can be achieved by means of combustion modifications in the furnace. It is also essential to provide the pulverized coal diffusion flame control. Mathematical modeling is regularly used for analysis and optimization of complex turbulent reactive flows and mutually dependent processes in coal combustion furnaces. In the numerical study, predictions were performed by an in-house developed comprehensive three-dimensional differential model of flow, combustion and heat/mass transfer with submodel of the fuel- and thermal-NO formation/ destruction reactions. Influence of various operating conditions in the case-study utility boiler tangentially fired furnace, such as distribution of both the fuel and the combustion air over the burners and tiers, fuel-bound nitrogen content and grinding fineness of coal were investigated individually and in combination. Mechanisms of NO formation and depletion were found to be strongly affected by flow, temperature and gas mixture components concentration fields. Proper modifications of combustion process can provide more than 30% of the NOx emission abatement, approaching the corresponding emission limits, with simultaneous control of the flame geometry and position within the furnace. This kind of complex numerical experiments provides conditions for improvements of the power plant furnaces exploitation, with respect to high efficiency, operation flexibility and low emission.

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Determining the NOx emission from an auxiliary marine engine based on its operating conditions

E3S Web of Conferences ◽

10.1051/e3sconf/20184400155 ◽

2018 ◽

Vol 44 ◽

pp. 00155

Author(s):

Lukasz Rymaniak ◽

Jacek Pielecha ◽

Lukasz Brzeziński

Keyword(s):

Ecological Indicators ◽

Operating Conditions ◽

Nox Emission ◽

Pollutant Emissions ◽

Nox Emissions ◽

Marine Engine ◽

Marine Engines ◽

Engine Construction ◽

Emissions Intensity ◽

Theoretical Considerations

The article presents considerations regarding determining the NOx emissions from auxiliary compression-ignition marine engines. In order to determine the real impact of a given object on air pollution, it is necessary to first carry out research aimed at determining its emission characteristics. Thus, it is necessary to conduct tests in real operating conditions or to calculate the ecological indicators based on the operating conditions. The paper presents the NOx emissions intensity of an auxiliary Tier III standard marine engine, which is used in the drive system of various heavy, off-road vehicles and water vessels. Due to the structure characteristics of the considered engine group, the presented relations and results refer to only one cylinder. This data was used to calculate the NOx emission of a marine auxiliary engine, which used the operating conditions obtained from dynamometer tests and the engine construction (the number of cylinders). The presented methodology of activities can be used to assess the ecological indicators of ships in actual navigation, including primarily the maneuvers performed in the port. The article is supplemented with theoretical considerations regarding the problem of pollutant emissions from auxiliary marine engines.

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A Study on Biodiesel NOx Emission Control With the Reduced Chemical Kinetics Model

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4027358 ◽

2014 ◽

Vol 136 (10) ◽

Cited By ~ 1

Author(s):

Juncheng Li ◽

Zhiyu Han ◽

Cai Shen ◽

Chia-fon Lee

Keyword(s):

Chemical Kinetics ◽

Combustion Process ◽

Operating Conditions ◽

Nox Emission ◽

Kinetics Model ◽

Combustion Model ◽

Nox Emissions ◽

Soot Emission ◽

Start Of Injection ◽

Combustion Processes

In this paper, the effects of the start of injection (SOI) timing and exhaust gas recirculation (EGR) rate on the nitrogen oxides (NOx) emissions of a biodiesel-powered diesel engine are studied with computational fluid dynamics (CFD) coupling with a chemical kinetics model. The KIVA code coupling with a CHEMKIN-II chemistry solver is applied to the simulation of the in-cylinder combustion process. A surrogate biodiesel mechanism consisting of two fuel components is employed as the combustion model of soybean biodiesel. The in-cylinder combustion processes of the cases with four injection timings and three EGR rates are simulated. The simulation results show that the calculated NOx emissions of the cases with default EGR rate are reduced by 20.3% and 32.9% when the injection timings are delayed by 2- and 4-deg crank angle, respectively. The calculated NOx emissions of the cases with 24.0% and 28.0% EGR are reduced by 38.4% and 62.8%, respectively, compared to that of the case with default SOI and 19.2% EGR. But higher EGR rate deteriorates the soot emission. When EGR rate is 28.0% and SOI is advanced by 2 deg, the NOx emission is reduced by 55.1% and soot emission is controlled as that of the case with 24% EGR and default SOI. The NOx emissions of biodiesel combustion can be effectively improved by SOI retardation or increasing EGR rate. Under the studied engine operating conditions, introducing more 4.8% EGR into the intake air with unchanged SOI is more effective for NOx emission controlling than that of 4-deg SOI retardation with default EGR rate.

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