Oxygen Content In Flue Gas Research Articles

Predictive modelling and optimization of nitrogen oxides emission in coal power plant using Artificial Neural Network and Simulated Annealing

In this research paper, predictive modelling of NOx emission of a 210 MW capacity pulverized coal-fired boiler and combustion parameter optimization to reduce NOx emission in flue gas is proposed. The effects of oxygen concentration in flue gas, coal properties, coal flow, boiler load, air distribution scheme, flue gas outlet temperature and nozzle tilt are studied. The data collected from parametric field experiments are used to build a feed-forward back-propagation artificial neural net (ANN). The coal combustion parameters are used as inputs and NOx emission as outputs of the model. The ANN model is developed for full load condition and its predicted values are verified with the actual values. The algebraic equation containing weights and biases of the trained net is used as fitness function in simulated annealing (SA) to find the optimum level of input operating conditions for low NOx emission. The result proves that the proposed approach could be used for generating feasible operating conditions. DOI: http://dx.doi.org/10.11591/ij-ai.v1i1.286 Full Text: PDF

Soft-sensing of Oxygen Content of Flue Gas Based on Mixed Model

In order to increase the measuring accuracy of oxygen content of flue gas, a kind of new soft-sensing method of oxygen content in flue gas based on mixed model was presented. The main body of the model was set up with support vector regression (SVR), the input set was pretreated with principal component analysis (PCA) method to reduce input number of dimensions, the training output set was pretreated with empirical mode decomposition (EMD) method to eliminate the influences caused by high-frequency interference, and model calibration was carried with K-fold cross validation (K-CV) method. The simulation result shows that this mixed model method has better accuracy and the ability of generalization than those single-models with support vector machine or neural network.

Research on Energy-Saving Control Technology of Boiler

Focusing on energy-saving issues of boiler, this paper finds out the combustion conditions inside boiler furnace by monitoring and analysis on oxygen content of flue gas, carbon content of fly ash, CO and CO2 contents. The intelligent control of boiler combustion was achieved and combustion efficiency was rosen. Using neural network controlling model, automatic optimization of oxygen delivery volume,coal delivery volume, the total wind pressure of primary air, the secondary air-door opening degree and furnace negative pressure were achieved, and the boiler efficiency increasing by 5 ~ 7%.

Novel Fluidized Bed Reactor for Integrated NOx Adsorption−Reduction with Hydrocarbons

In order to avoid the negative impact of excessive oxygen in the combustion flue gases on the selectivity of most hydrocarbon selective catalytic reduction (HC-SCR) catalysts, an integrated NO(x) adsorption-reduction process has been proposed in this study for the treatment of flue gases under lean burn conditions by decoupling the adsorption and reduction into two different zones. The hypothesis has been validated in a novel internal circulating fluidized bed (ICFB) reactor using Fe/ZSM-5 as the catalyst and propylene as the reducing agent. Effects of propylene to the NO(x) molar ratio, flue gas oxygen concentration, and gas velocity on NO(x) conversion were studied using simulated flue gases. The results showed that increasing the ratio of HC:NO improved the reduction performance of Fe/ZSM-5 in the ICFB reactor. NO(x) conversion decreased with an increasing flue gas flow velocity in the annulus U(A) but increased with an increasing reductant gas flow velocity in the draft tube U(D). The NO(x) adsorption ratio decreased with increasing U(A). In most cases, NO(x) conversion was higher than the adsorption ratio due to the relatively poor adsorption performance of the catalyst. Fe/ZSM-5 showed a promising reduction performance and a strong inhibiting ability on the negative impact of excessive O2 in the ICFB reactor, proving that such an ICFB reactor possessed the ability to overcome the negative impact of excessive O2 in the flue gas using Fe/ZSM-5 as the deNO(x) catalyst.

Absorption of NO2 into Na2S solution in a stirred tank reactor

To understand the absorption mechanism of nitrogen dioxide into a sodium sulfide solution, a stirred tank reactor with a plane gas-liquid interface was used to measure the chemical absorption rate of diluted nitrogen dioxide into sodium sulfide solution. The absorption rates under various experimental conditions were measured and the effects of experimental conditions on nitrogen dioxide absorption rate were discussed. The results show that, in the range of this study, nitrogen dioxide absorption rate increases with increasing sodium sulfide concentration, nitrogen dioxide inlet concentration, and flue gas flow rate, but decreases with increasing reaction temperature and oxygen content in flue gas.

A compact optimization strategy for combustion in a 125 MW tangentially anthracite‐fired boiler by an artificial neural network

AbstractIn the past decade, artificial neural networks (ANNs) have been widely utilized to model, control, and optimize combustion processes in utility boilers. Since many highly correlated factors influence the combustion process in a furnace, it is necessary to select several important parameters to form a more simplified ANN model, which can be easily put into real‐time operation. In this paper, a parameter representing the secondary air assignment mode was quantified by the ratio of the damper opening values between the upper and lower secondary air. This parameter, together with the oxygen concentration in flue gas, the volatile matter and the heating value of coal, constitute the four input parameters of the ANN. Its output is the efficiency of the boiler. The ANN model was trained from 34 samples obtained from experiments on a 125 MW pulverized‐coal‐fired boiler, and the results predicted by the network model agreed well with the experimental results. A compact optimization strategy for combustion was proposed, by which the best combination of the oxygen concentration and the secondary air assignment mode can be determined directly according to the volatile matter and the heating value of coal. For two coals, the combustion in the furnace was obviously improved with the help of the optimization strategy, and its applicability was validated. Copyright © 2008 Curtin University of Technology and John Wiley & Sons, Ltd.

Effects of air excess control in a heat storage solid fuel-fired household furnace

Due to a significant increase in electricity prices during the last decade and insufficient production capacity of the electric power industry in Serbia, many households that are currently using electric heat storage furnaces for heating have been forced to find an alternative solution for heating. A possible solution is replacing electric heating appliances with similar solid fuel-fired ones. Existing solid fuel-fired furnaces are often unsatisfactory with respect to their efficiencies and flue gas emissions. A prototype of a new concept of heat storage, solid fuel-fired furnace has been developed to meet these growing needs, providing electricity saving together with considerable environmental benefits. In order to examine furnace performance, efficiency and environmental aspects, and to assess the influence of air excess control in the furnace on the efficiency and flue gas emissions, numerous experimental tests were conducted. The amount of combustion air, the flue gas flow rate and the fuel feeding regime have been adjusted in order to keep the flue gas oxygen content in a relatively narrow range, thus obtaining controlled combustion conditions and, correspondingly, lower carbon monoxide emission and higher furnace efficiency. In this way, the furnace was made able to respond to the changes in heating needs, fuel quality and other parameters, which is considered to be advantageous in comparison with similar solid-fuel fired furnaces.

Reduction of carbon monoxide emission from a solid-fuel thermo-accumulation furnace

Many households in Serbia, using electric thermo-accumulation furnaces for heating, have been forced to find an alternative solution, due to a significant increase in electricity prices during the last decade. A possible solution is replacing electric heating appliances with the solid fuel-fired ones. A prototype of a new concept of thermo-accumulation solid fuel-fired furnace has been developed to meet these growing needs, providing electricity saving together with considerable environmental benefits. Two strategies for reduction of carbon monoxide emission are examined in the paper: application of Pt/Al2O3 catalyst, in the form of 3 ? 0.3 mm spheres, providing further combustion of flue gases within the furnace, as well as an additional emission reduction by means of the air excess control. Experimental investigations of the catalyst influence on the conversion of carbon monoxide have been done for different operation regimes and positions of the catalyst. The paper presents selected results regarding carbon monoxide emission during wood and coal combustion. Investigations suggest a considerable effect of the catalyst and a strong influence of the catalyst position within the furnace to carbon monoxide emission reduction. In addition, experimental tests have been conducted to asses the effect of the air excess control in the furnace on carbon monoxide emission. The amount of combustion air, the flue gas flow rate, and the fuel feeding regime have been adjusted in order to keep the flue gas oxygen content in a relatively narrow range, thus obtaining controlled combustion conditions and lower carbon monoxide emission. In this way, the furnace has been made able to respond to the changes in heating needs, fuel quality and other parameters, which is advantageous in comparison with similar solid-fuel fired furnaces. .

Gas-Phase Mercury Reduction to Measure Total Mercury in the Flue Gas of a Coal-Fired Boiler

Gaseous elemental and total (elemental + oxidized) mercury (Hg) in the flue gas from a coal-fired boiler was measured by a modified ultraviolet (UV) spectrometer. Challenges to Hg measurement were the spectral interferences from other flue gas components and that UV measures only elemental Hg. To eliminate interference from flue gas components, a cartridge filled with gold-coated sand removed elemental Hg from a flue gas sample. The Hg-free flue gas was the reference gas, eliminating the spectral interferences. To measure total Hg by UV, oxidized Hg underwent a gas-phase, thermal-reduction in a quartz cell heated to 750°C. Simultaneously, hydrogen was added to flash react with the oxygen present forming water vapor and preventing Hg re-oxidation as it exits the cell. Hg concentration results are in parts per billion by volume Hg at the flue gas oxygen concentration. The modified Hg analyzer and the Ontario Hydro method concurrently measured Hg at a field test site. Measurements were made at a 700-MW steam turbine plant with scrubber units and selective catalytic reduction. The flue gas sampled downstream of the selective catalytic reduction contained 2100 ppm SO2 and 75 ppm NOx. Total Hg measured by the Hg analyzer was within 20% of the Ontario Hydro results.

Modelling of dynamics of combustion of biomass in fluidized beds

New process concepts in energy production and biofuel, which are much more reactive than coal, call for better controllability of the combustion in circulating fluidized bed boilers. Simplified analysis describing the dynamics of combustion in fluidized bed and circulating fluidized bed boilers is presented. Simple formulas for the estimation of the responses of the burning rate and fuel inventory to changes in fuel feeding are presented. Different changes in the fuel feed, such as an impulse, step change, linear increase and cyclic variation are considered. The dynamics of the burning with a change in the feed rate depends on the fuel reactivity and particle size. The response of a fuel mixture with a wide particle size distribution can be found by summing up the effect of different fuel components and size fractions. Methods to extract reaction parameters form dynamic tests in laboratory scale reactors are discussed. The residence time of fuel particles in the bed and the resulting char inventory in the bed decrease with increasing fuel reactivity and differences between coal and biomass is studied. The char inventory affects the stability of combustion. The effect of char inventory and oscillations in the fuel feed on the oscillation of the flue gas oxygen concentration is studied by model calculation. A trend found by earlier measurements is explained by the model.

NOX selective catalytic reduction control based on simple models

Abstract In the paper, a new approach to the control of the selective catalytic reduction process of NO X is presented. The reduction process can be efficiently controlled using a combination of feed-forward and feed-back control structures. However, this approach requires expensive measurement equipment. It is shown that measurement of nitric oxide concentration at the input of the catalytic converter and measurement of the flue gas flow rate can be successfully substituted by corresponding “software sensors”. The software sensors are based on simple mathematical models and on measurements of excess oxygen concentration in flue gas and the fuel flow rate which are usually parts of already available standard combustion control system equipment. In the paper the complete derivation of the required mathematical models is given, and the proposed new control structure is described. The structure is tested using simulation and implemented on an industrial pilot plant.

Coal combustion in O2/CO2 mixtures compared with air

AbstractAs part of CO2 abatement strategies for climate change, we are investigating coal combusion behaviour in various O2/CO2 mixtures and in air. The goal is to simulate conditions of coal combustion with flue gas recirculation in order to maximize the CO2 concentration in the flue gas prior to its recovery. A western Canadian sub‐bituminous coal and a U.S. eastern bituminous coal were investigated. Thermal input was set at 0.21 MW with a flue gas oxygen concentration of 5 vol%. Experiments were done using various O2/CO2 mixtures and air. The oxygen concentration ranged from 21% to 42%. Up to 95% CO2 concentrations were achieved in the flue gas. This paper describes experimental results in terms of flame temperatures and pollutant emissions (NOx', SO2 and CO).

Nonlinear process model based control and optimization of a model IV FCC unit

Nonlinear process model based control (PMBC) has been applied to the Amoco/Lehigh University Model IV FCC industrial challenge problem. A dynamic simulator which was originally written in ACSL (Advanced Continuous Simulation Language) was converted into FORTRAN and benchmarked against the open-loop responses provided in the problem statement. The riser model in the simulator was replaced by a plug flow reactor model and a simple yield model was added. This addition made it possible to apply a simplified optimization analysis as well. Nonlinear model based control was applied for the control of reactor temperature, regenerator temperature and the flue gas oxygen concentration. The temperature of the feed entering the reactor riser, the catalyst circulation rate and the regenerator air flowrate were used as manipulated variables. The dynamic macroscopic oxygen and energy balances in the regenerator and the steady state energy balance for the reactor were used as nonlinear models for control. The Generic Model Control (GMC) law was used for the nonlinear PMBC controller. The nonlinear PMBC and conventional proportional-integral (PI) controllers were tested first for the unconstrained control. The PI results are included as a point of reference. The nonlinear PMBC constraint controllers were developed for constraints on the feed preheater, the air flowrate to the regenerator and the catalyst circulation rate. The feed rate to the system was manipulated based upon maximizing the process throughput without violating any of the constraints. The constraint controllers were tested successfully for a set of disturbances. The same controller models were then used for optimization studies to analyze the operation at the economic optimum in the face of variations in feed characteristics and variations in operative constraints.

Nonlinear process model based control and optimization of a model IV FCC unit

Nonlinear process model based control (PMBC) has been applied to the Amoco/Lehigh University Model IV FCC industrial challenge problem. A dynamic simulator which was originally written in ACSL (Advanced Continuous Simulation Language) was converted into FORTRAN and benchmarked against the open-loop responses provided in the problem statement. The riser model in the simulator was replaced by a plug flow reactor model and a simple yield model was added. This addition made it possible to apply a simplified optimization analysis as well. Nonlinear model based control was applied for the control of reactor temperature, regenerator temperature and the flue gas oxygen concentration. The temperature of the feed entering the reactor riser, the catalyst circulation rate and the regenerator air flowrate were used as manipulated variables. The dynamic macroscopic oxygen and energy balances in the regenerator and the steady state energy balance for the reactor were used as nonlinear models for control. The Generic Model Control (GMC) law was used for the nonlinear PMBC controller. The nonlinear PMBC and conventional proportional-integral (PI) controllers were tested first for the unconstrained control. The PI results are included as a point of reference. The nonlinear PMBC constraint controllers were developed for constraints on the feed preheater, the air flowrate to the regenerator and the catalyst circulation rate. The feed rate to the system was manipulated based upon maximizing the process throughput without violating any of the constraints. The constraint controllers were tested successfully for a set of disturbances. The same controller models were then used for optimization studies to analyze the operation at the economic optimum in the face of variations in feed characteristics and variations in operative constraints.

泥炭の流動燃焼

The experimental investigations on fluidized bed peat combustion were performed in a 0.108m i. d. and 2.0m high fluidized bed to obtain the combustion charac-teristics of peat. The peat used contained 40-45‰ moisture and the particle size of it was less than 25mm. When the bed temperature was keeping more than 750°C and the residual oxygen concentration in flue gas was controlling invariable, 5‰, the combustion efficiency reached more than 95‰ and the NOx and SOx emission levels were lowered to less than 180ppm and 20ppm, respectively. It can be suggested that higher combustion efficiency will be achieved by the combustion of the elutriated ash because its heating value was ranged from 1000 to 2000kcal/kg. Moreover, the ash contained few heavy metals. The fluidized bed peat combustion is considered as one of the useful methods of local energy supply.

Inverse Nyquist array technique in the design of a multivariable controller for a solid-fuel boiler

Abstract This paper presents an application of the inverse Nyquist array (INA) technique to the design of a multivariable controller for a boiler subsystem. The boiler is a 1.6 MVV water boiler using solid fuel. The subsystem studied consists of the boiler underpressure and the flue-gas oxygen content. First a simple transfer function model based on step response measurements is constructed. The subsystem model is analysed and the interactions are decreased with a constant compensator using Rosenbroek's INA method. Finally, scalar PI controllers are tuned for the approximately decoupled system. A brief description of the microcomputer control system is given. The control system and the designed multivariable controller have worked well since their installation in February 1983.

Kalman Filter Based Fuel Quality Estimation In Power Plants

Variation in the quality of solid fuels cause difficulties in the control of power plants because the heat power of the fuel flow may vary remarkably. For example in a peat power plant the heat value of the fuel can vary from 1200 to U600 MJ/m3. If we want to stabilize the burning process and the heat power released through combustion we must know the heat value of the fuel to be able to control the fuel feed precisely. However there exists no on-line measurement for the heat value.The estimation of the heat value of the fuel can be carried out by measuring the oxygen content in the flue gases and calculating the oxygen amount used in the combustion process. The oxygen consumption correlates accurately with the heat power released in the combustion. The flue gas oxygen content should be measured with a fast ZrO2 in-situ oxygen sensor. To estimate the heat value a model for fuel feed, combustion and oxygen measurement is constructed. A Kalman type estimator has given excellent results when tested with measurement data from the biggest Finnish pent fuelled power plant. Also a new control strategy based on oxygen consumption is developed.