Tangentially-fired Boiler Research Articles

Numerical Simulation Analysis of the Optimized and Transformed 200MW Pulverized Coal Fired Boiler Burner

With the use of computational fluid mechanics software – FLUENT, the numerical simulation computation of combustion process inside a certain 200MW corner tangential firing boiler whose combustor is transformed by the multi-grade efficient low-nitrogen combustion technology was conducted, thus the furnace temperature, velocity, mixture and NOx concentration field at rated conditions before and after the transformation were obtained. The calculation results were highly identical with the industrial test results. The results show that after using the multi-grade efficient low-nitrogen combustion technology, the NOx emissions significantly lowered down with the drop of about 40% compared with the emissions before transformation, while the furnace coking and high temperature corrosion were effectively controlled, achieving good economic and social benefits and providing a reference to the design and transformation of the same types of boilers.

Computational Modelling of a Tangentially Fired Boiler With Deposit Formation Phenomena

Abstract Any complete CFD model of pulverised coal-fired boiler needs to consider ash deposition phenomena. Wall boundary conditions (temperature and emissivity) should be temporally corrected to account for the effects of deposit growth on the combustion conditions. At present voluminous publications concerning ash related problems are available. The current paper presents development of an engineering tool integrating deposit formation models with the CFD code. It was then applied to two tangentially-fired boilers. The developed numerical tool was validated by comparing it with boiler evaporator power variation based on the on-line diagnostic system with the results from the full CFD simulation.

300 MW Coal Tangential Boiler Furnace Numerical Simulation

By using the computational fluid dynamics software Fluent and the choice of the reasonable mathematical model, the flow, heat transfer and combustion are simulated in a 300 MW tangential firing boiler furnace. In the process of numerical simulation in the furnace, the gas phase turbulent flow usesRealizable model for both sides and solves the governing equations using SIMPLEC algorithm. Calculation results show that the highest temperature in the furnace is in the burner area,the whole furnace space rotates flow field, residual rotation still exists in the exit of the furnace, and the smoke temperature deviation causes in the residual rotation of furnace exit.

Computational Fluid Dynamic Modelling of a 550 MW Tangentially-Fired Furnace under Different Operating Conditions

In the present paper, a computational fluid dynamics (CFD) modelling study was performed for the combustion of the brown coal in a large-scale tangentially-fired furnace (550 MW) under different operating conditions. The AVL Fire CFD code has been used to model the furnace. The mathematical models of coal combustion with the appropriate kinetic parameters were written and added to the code as user defined functions. It consists of pulverised coal (PC) devolatilization, char burnout, heat and mass transfer, and nitric oxide formation. The simulation of the PC combustion was carried out using multi-step reaction chemistry schemes. The level of confidence of this numerical model was based on the previous validations of the lignite combustion in a lab-scale furnace, as well as the validation parameters of the present furnace at the standard existing conditions in terms of temperature values and species concentrations. Performance of the boiler under different operating conditions was investigated, from which the effects of air and coal mass flow rates were considered at full load with different operating schemes of coal mills (out-of-service operations). The validated model was used to perform the following investigation parameters: furnace gas temperatures, species concentrations (CO and CO2), and velocity distributions. This study provides good information to optimize the operations of the utility tangentially-fired boiler with less emissions production.

CFD modelling of air-fired and oxy-fuel combustion in a large-scale furnace at Loy Yang A brown coal power station

Oxy-fuel combustion technique is a viable option to reduce several types of greenhouse gases (GHGs) emissions from the pulverized coal (PC) combustion systems. In this paper, a computational fluid dynamics (CFD) modelling study has been developed in order to investigate the Victorian brown coal combustion in a 550MW utility boiler under the air-fired (reference case) and three oxy-fuel-fired scenarios. The reference firing case was modelled based on the operating conditions of Loy Yang A power plant located in the state of Victoria, Australia. While Chalmers’ oxy-fuel combustion approach was selected for the present oxy-fuel combustion simulations, which referred to as OF25 (25vol.% O2), OF27 (27vol.% O2), and OF29 (29vol.% O2). User-defined functions (UDFs) were written and incorporated into the CFD code to calculate the following mathematical models: the PC devolatilization, char burnout, multi-step chemical reactions, mass and heat transfer, carbon in fly-ash, and NOx formation/destruction. A level of confidence of the CFD model was achieved validating four different parameters of the conventional combustion case, as well as the previous preliminary CFD studies that conducted on a 100kW unit firing propane and lignite under oxy-fuel combustion environments. The numerical results of OF29 combustion condition were considerably similar to the reference firing results in terms of gas temperature levels and radiative heat transfer relative to the OF25 and OF27 combustion cases. This similarity was due to increasing the residence time of PC in the combustion zone and O2-enriched in feed oxidizer gases. A significant increase in the CO2 concentrations and a noticeable decrease in the NOx formation were observed under all oxy-fuel combustion scenarios. The combustion chemistry was adopted in these investigations in order to capture the effects of O2 concentrations and gas temperatures on the CO/CO2 production rate and equilibrium between H2 and H2O in the combustion zone. Also, the use of O2-enriched atmospheres during oxy-fuel-fired cases was slightly enhanced the carbon burnout rate. These predicted results were reasonably consistent with the experimental investigations and numerical modelling found in the literature. This study of Victorian brown coal oxy-fuel combustion in a large-scale tangentially-fired boiler is important prior to its implementation in real-life.

Research of Cold Test in 170t/h Tangentially Fired Boiler

The characteristics of the WGZ170/9.8-3 pulverized coal boiler were obtained based on cold test，Including the air velocity distribution in tangential firing boiler and the relation between air distribution with opening of each secondary air dampe，The test results had determined that the baffle of blower at around 40% and two parallel draft fan about 45% were relatively appropriate. and the air distribution and opening of each secondary air dampe and balancing the distribution of primary air and second air along the width direction of the boiler hearth were confirmed through test，and the aerodynamic field inside the boiler was investigated based on the tie-floating test．and good aerodynamic field can be obtained after distributing the primary air and second air reasonably，which guarantee the ignition and stable operation of the boiler．

Prediction of Performance From PRB Coal Fired in Utility Boilers With Various Furnace and Firing System Arrangements

The present regulatory requirements enforce the modification of the firing modes of existing coal-fired utility boilers and the use of coals different from those originally designed for these boilers. The reduction in SO2 and NOx emissions was the primary motivation for these changes. Powder river basin (PRB) coals, classified as subbituminous ranked coals, can lower NOx and SOx emissions from power plants due to their high volatile content and low sulfur content, respectively. On the other hand, PRB coals have also high moisture content, low heating value, and low fusion temperature. Therefore when a power plant switches from the designed coal to a PRB coal, operational challenges were encountered. A major problem that can occur when using these coals is the severe slagging and excess fouling on the heat exchanger surfaces. Not only is there an insulating effect from deposit, but there is also a change in reflectivity of the surface. Excess furnace fouling and high reflectivity ash may cause reduction in heat transfer in the furnace, which results in higher furnace exit gas temperatures (FEGTs), especially with opposite wall burners and with a single backpass. Higher FEGTs usually result in higher stack gas temperature, increasing the reheater spray flow and therefore decreasing the boiler efficiency with a higher heat rate of the unit. A successful modification of an existing unit for firing of PRB coals requires the evaluation of the following parameters: (1) capacities or limitations of the furnace size, (2) the type and arrangement of the firing system, (3) heat transfer surface, (4) pulverizers, (5) sootblowers, (6) fans, and (7) airheaters. In the present study we used a comprehensive methodology to make this evaluation for three PRB coals to be potentially fired in a 575 MW tangential-fired boiler.

PDA research on a novel pulverized coal combustion technology for a large utility boiler

In this paper, a new technology for a tangential firing pulverized coal boiler, high efficiency and low NOx combustion technology with multiple air-staged and a large-angle counter flow fuel-rich jet (ACCT for short) is proposed. To verify the characteristics of this technology, experiments of two combustion technologies, ACCT and CFS-1 (Concentric Firing System-1), are carried out under a cold model of a 1025 t/h tangential firing boiler with a PDA (particle dynamics anemometer). The distributions of velocity, particle concentration, particle diameters and the particle volume flux of primary air and secondary air are obtained. The results show that the fuel-rich primary air of ACCT can go deeper into the furnace and mix with the main flow better, which means that the counter flow of fuel-rich jets in ACCT can realize stable combustion, low NOx emission and slagging prevention.

Experimental flow field characteristics of OFA for large-angle counter flow of fuel-rich jet combustion technology

In this paper, the flow field characteristics of over fired air (OFA) for novel low NOx pulverized coal combustion technology are studied. The research was conducted with a 300 MWe tangential firing boiler that was adapted for this technology, and a three-dimensional particle-dynamics anemometer (PDA) was employed on the model to measure the characteristics of gas flow in the burnout area and gas/particle flows under the front panel superheater. The impact of a positive offset at 15°, counter offset at 15° and design case without an offset the OFA relative to the direction of the secondary air jet in the main combustion were considered. With different OFA offsets, the deflection characteristics, the velocity and root mean square (RMS) fluctuation velocity of OFA jet are obtained, as well as the gas/particle flows characteristics under the front panel superheater. The results show that, with a positive offset, an over-large tangential circle is formed, which produces slagging and temp-bias under the panel superheater. However, with a counter offset, the OFA is sent into the center of the chamber, and the particle is forced to the water wall. Compared with the other two conditions and combined with the counterflow of primary air, OFA without an offset for the jet contains a proper tangential circle, strong inflexibility and turbulence, which prevents slagging and burn out.

Coupled fluid dynamics and whole plant simulation of coal combustion in a tangentially-fired boiler

This paper describes the development and validation of an advanced boiler simulation tool for Units 1 and 2 at the Youngheung Power Plant in South Korea. By combining 3-D computational fluid dynamics (CFD) analysis of the furnace with a 1-D steam-water side model it is possible, for example, to simulate the effects of burner and SOFA settings, firing patterns and coal blending on the boiler efficiency and pollutant formation, as well as the combustion efficiency. The models are coupled by exchanging temperature and heat flux values on furnace walls and heat exchangers at each iteration of the calculation to ensure that the final converged solution is a self-consistent solution for the combined furnace, boiler and turbine system. The ANSYS CFX software was used to develop the CFD model, while the 1-D boiler model was created in the PROATES Off-Line software of E.ON Engineering. The model has been validated for a typical operating condition by comparing the simulated results with the plant data. Good agreement is obtained, confirming that the coupled model has the capability to contribute significantly to the comprehensive optimisation of the boiler operation as well as acting as a problem solving tool. It is expected that the same coupling strategy can be adapted for any type of pulverised coal-fired boiler.

Control of ash related problems in a large scale tangentially fired boiler using CFD modelling

The objective of this study is to develop a three-dimensional combustor model for predicting the performance of full-scale tangential fired (TF) boiler and to determine the flow patterns of the gas and coal particles, with an emphasis on formation mechanism of gas flow deviations and uneven temperature on the super-heaters, re-heaters and divisional super-heater sections of the furnace. The importance of these simulations is to identify the locations of optimum additive injection ports to achieve maximum impact of additives in the combustion process to minimize the temperature deviation and reduce ash-related issues. This study is a classic example of numerical investigation into the problem of turbulent reacting flows in large scale furnaces employed in thermal power plants for the remediation of ash deposition problems. Present work also provides an investigation of the influence of number of tripped burners on the characteristics of the flow and thermal fields. Excellent agreement between the simulation results and key boiler design values and available site operation records following full-scale trials indicate that the calculations are reliable. The results obtained from the present work are directly relevant to coal-fired utilities for not only demonstrating the effectiveness of computational fluid dynamics (CFD) based tools in combating operational issues but also provides an alternative to conventional remediation strategies.

Research of Low NOx Combustion with Large-Angle Counter Flow of a Fuel-Rich Jet and Its Particle-Dynamics Anemometer (PDA) Experiment

On the basis of counter flow of primary air with fuel rich in company with overall air-staged technology, this paper introduces a new pulverized coal combustion technology that can realize low NO x emission, high combustion efficiency, slagging, and high-temperature corrosion prevention by employing overall air-staged combustion, large-angle counter flow of primary air with a fuel-rich jet and forming a partial area of high-temperature and high pulverized coal concentration in the furnace. To verify technical data, research has been conducted on a 1025 t/h tangential firing boiler adopting this technology and a three-dimensional particle-dynamics anemometer (PDA) is employed on this prototype for measurement of the characteristics of two-phase gas/particle flows in the burner area. The distribution of the particle concentration and size distribution of the primary air, as well as the gas/particle velocity field were obtained. The experiments also measure the flowing characteristics of over-fired air (OFA) and secondary air. The results show that, with counter flow of fuel-rich jet technology, more particles can be injected into the high-temperature side in the furnace, the concentration of the particle is higher at the high-temperature side than that near the water wall, and the particle concentration of large particles is also lower near the water wall. The research shows that the counter-flow technology combined with overall air-staged technology of the tangential firing boiler can realize low NOx emission and high efficiency combustion and can prevent slagging on the surface of the water wall and high-temperature corrosion.

Aerodynamics of an isolated slot-burner from a tangentially-fired boiler

The aerodynamic development of fully turbulent isothermal jets issuing from rectangular slot-burners was modelled by obtaining a solution to the Reynolds averaged Navier–Stokes equations. A finite-volume method was used with the standard k–ε, RNG k–ε and Reynolds stress turbulence models. The slot-burners were based on physical models, which were designed to be representative of typical burner geometries found in tangentially-fired coal boilers. Two cases were investigated, in which jets from three vertically stacked rectangular nozzles discharged at 90° and then 60° to the wall containing the burner. The nozzle angle had little effect on jet centreline velocity decay, with the 60° nozzle showing a marginally higher rate of decay. The jets from the 60° nozzles were found to deviate slightly from their geometric axis slightly due to internal pressure redistribution in the flow at the nozzles. The simulations were validated against the physical models and were found to reproduce the flow field of the jets accurately with the Reynolds stress model producing the best results.

E304 FLOW FIELD IN A MODEL OF A 2950 T/H TANGENTIAL-FIRED BOILER UNDER DIFFERENT CONDITIONS OF SEPARTED OVER-FIRE-AIR INJECTIONS(Boiler-1)

1000MWe capacity supercritical utility units employ 2950 t/h tangential-fired boiler, which uses the low NOx concentric firing system (LNCFS) and the deep air staged technology for reduce the NOx emission. The large capacity boiler uses eight burners at the same level, located at corner and the middle of the wall, which form the double fire balls in the furnace. In this work, the flow fields in the furnace were obtained by measuring the air velocity in the model furnace with over fire air and concentric firing system, the diameter of the air circle is also measured.

A comprehensive slagging and fouling prediction tool for coal-fired boilers and its validation/application

RMT, Inc., a subsidiary company of Alliant Energy Corporation, and the University of North Dakota Energy and Environmental Research Center (EERC) have developed an ash behavior prediction tool, called AshProSM, to assess slagging and fouling in coal-fired boilers. This tool integrates boiler computational fluid dynamic (CFD) simulations with ash behavior models including ash formation, transport and deposition, as well as deposit growth and strength development. AshProSM was applied to a 512-MW tangentially-fired boiler at Wisconsin Power & Light's Columbia Energy Center to evaluate the localized slagging on furnace walls and fouling in convective pass. The predicted boiler ash deposition pattern is reasonably consistent with that observed on the furnace walls and super heater division panels. The prediction of slag state transition (solid/liquid) through deposit viscosity was verified by the observation in the plant.

NUMERICAL SIMULATION ON PULVERIZED COAL COMBUSTION PROCESS IN A TANGENTIAL FIRING FURNACE

The computational fluid dynamics (CFD) code, PHOENICS 3.5, is employed to evaluate horizontal pulverized coal bias combustion process in a 200 MW tangential firing boiler. Multi-fluid two-phase model and coal comprehensive combustion model are integrated in the code. Gas temperature, particle distribution, gas species concentration and radiation heat flux at different sections of furnace are obtained from the numerical simulation at different secondary air (SA) vertical distribution. The calculation results show that a high particle concentration and high gas temperature zone exist, together with the separation of particle and gas downstream primary air (PA) nozzles, which ensure suitable ignition time, high temperature level of PA mixture and resistance to slag on the water-cooled walls. The calculated burnout of coal particles, O_2 concentration at furnace exit and gas averaged temperature in furnace are compared with in situ measurement data, resulting in good agreement. The simulation results of staged SA distribution case show that gas temperature of down part of furnace increase and the final burnout of char is decreased for the postponing mixing between fuel and oxygen. Simulation results are also compared with in situ measurement data, resulting in good agreement with each other. Thus the comprehensive coal combustion model has reasonably simulated PF combustion process in large boiler furnace, which is benefit for optimizing unit operation conditions and reducing pollutants emission.

98/00052 Coal pond fines cleaning with classifying cyclones, spirals, and column flotation

Large reserves of coal pond fines arc found in the Illinois Basin--over 40 million tons in Western Kentucky, over 65 million tons in Southern Illinois, and over 35 million tons in Southern Indiana. If these fines are used to produce coal-water slurry (CWS), fuel costs, NO{sub x} emissions, and pond closure costs can be reduced. Coal fines from this region that are used to produce CWS for co-fire or re-burn may require processing, however, to attain proper particle size distribution and fuel quality. To evaluate the effectiveness of using coal cleaning technologies to control these CWS quality parameters, a simple flowsheet for recovering and processing coal pond fines was designed and tested. Coal fines processing consisted of using classifying cyclones to size at nominal minus 200 mesh, cleaning the classifying cyclone underflow using spirals, and cleaning the overflow using column froth flotation. Ash content of the dean coal from the spiral was reduced to about 10 percent, winch is satisfactory to use for CWS co-firing in a cyclone-fired boiler. The clean coal from column flotation may be used for re-burn in a cydone-fired boiler or as co-fire fuel in a wall-fired or tangentially-fired boiler Heating value recovery during laboratory scale,more » pilot-scale, and commercial-scale coal cleaning testing was about 80 percent.« less