A Combustion Process Optimization and Numerical Analysis for the Low Emission Operation of Pulverized Coal-Fired Boiler

The paper presents experimental and numerical investigation of pulverized coal combustion process analysis and optimization. The research was conducted on the front-fired pulverized coal boiler with dedicated low-NOx furnace installation. In order to find optimal boiler operating conditions the acoustic gas temperature measurement system and mass flow rate of pulverized coal measurement system was applied. The uniform temperature distribution as a result of uniform coal and air flow provides the optimal combustion process with low level of NOx emission and total organic carbon content in ash. Experimental results confirm that the monitoring and control of fuel and air flow distribution allows to optimize combustion process by increasing thermal efficiency of the boiler. In the numerical part of investigation, the complex CFD model of pulverized coal boiler was made. The calculations of turbulent, reactive, and thermal flow processes were performed at different boiler operating conditions retrieved from power plant on-line monitoring system. The results of numerical simulations enable to identify the optimal boiler operating conditions

OxyCAP UK: Oxyfuel Combustion - academic Programme for the UK

The OxyCAP-UK (Oxyfuel Combustion - Academic Programme for the UK) programme was a £2 M collaboration involving researchers from seven UK universities, supported by E.On and the Engineering and Physical Sciences Research Council. The programme, which ran from November 2009 to July 2014, has successfully completed a broad range of activities related to development of oxyfuel power plants. This paper provides an overview of key findings arising from the programme. It covers development of UK research pilot test facilities for oxyfuel applications; 2-D and 3-D flame imaging systems for monitoring, analysis and diagnostics; fuel characterisation of biomass and coal for oxyfuel combustion applications; ash transformation/deposition in oxyfuel combustion systems; materials and corrosion in oxyfuel combustion systems; and development of advanced simulation based on CFD modelling

Low NOx coal burner temperature profile evaluation

A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Engineering. Johannesburg 2016Stringent worldwide emissions legislation, the drive to lower carbon emissions, together with the ever increasing demand to preserve the environment has led to a considerable demand for cleaner and more efficient coal combustion technologies. A primary technology for the reduction of emissions of oxides of nitrogen (NOx) is the installation of low NOx coal combustion burners. Extensive research into various burner characteristics and, in particular, the aerodynamic characteristics required to improve combustion performance of low NOx coal burners has been extensively undertaken and is ongoing. In this work the aerodynamic behaviour of a full-scale, aerodynamically staged, single low-NOx coal burner was numerically investigated. The objective of the study was to develop a single low NOx burner CFD model in Ansys Fluent, to better characterize and understand the flame shape in terms of the temperature profile achieved. CFD serve as an additional tool to assist with plant optimization, design proposals and occurrence investigations. To have confidence in the single burner coal combustion CFD model, the results of the model were compared to data obtained from an existing operational low NOx burner on site during a pre-defined load condition. To further improve on the theoretical CFD combustion model, drop tube furnace (DTF) experiments have been done to calculate the single rate Arrhenius kinetic parameters (pre-exponential factor and activation energy) for coal devolatilization and char combustion of the specific South African coal used. The combustion CFD simulations showed with a lower than design air flow through the burner, a reduced amount of swirl was achieved. This reduced amount of swirl produces a jet like flame and influences the way in which the combustion species are brought together. Under these operating conditions the flame distance from the burner mouth was predicted to be 1.2 (m). A very promising result was obtained through CFD and compared well with the in-flame temperature measurement obtained through the burner centre-line of approximately 1.4 (m). In an attempt to improve the aerodynamic profile of the burner under the same operating conditions the swirl angle on the tertiary air (TA) inlet was increased. The increased swirl on the TA inlet of the burner showed an improvement on the aerodynamic profile and had a significant impact on the temperature distribution within the flame. The increased swirl resulted in an improved flame distance of approximately 0.5 (m) from the burner mouth. The effect of increased swirl on the temperature profile of the flame displayed the aerodynamic dependence of the low NOx burner on combustion performance.MT201

Influence of different cover ratios on Gas-particle flow characteristics of a centrally-fuel-rich primary air burner: experiment and simulation

AbstractThe flow field for different cover ratios within a three-level conical ring concentrator of a centrally-fuel-rich swirl coal combustion burner has been studied both experimentally and numerically. A particle dynamics anemometer measurement system was employed in the study to measure velocity and particle volume flux after the outlet of third-level ring. And the numerical simulations were used to calculate the flow field in the conical ring region. In each cross-section, after the outlet of third-level ring, concentration ratio for each cover ratio is always larger than 2. With conical ring concentrator in the primary air tube, the coal concentration can be concentrated to a suitable range. In the cross-sections 0.5<x/D<4.0, as cover ratio increases, concentration ratio decreases and resistance coefficient increases

A Study on Co-firing Empty Fruit Bunch (EFB) with Coal as Potential Fuel

The aim of the project was to understand the effects of both coal firing and co-firing coal with Empty Fruit Bunch (EFB) in terms of carbon dioxide concentration emission and temperature in the furnace. This dissertation looks into the utilization of Empty Fruit Bunch (EFB) as a source of renewable and sustainable energy source for co-firing in coal power plants in Malaysia through the feasibility of the EFB as a fuel, the combustion technology options for co-firing, and the fuel blend suitable for co-firing in local coal fired power plants

A thermofluid network-based methodology for integrated simulation of heat transfer and combustion in a pulverized coal-fired furnace

Coal-fired power plant boilers consist of several complex subsystems that all need to work together to ensure plant availability, efficiency and safety, while limiting emissions. Analysing this multi-objective problem requires a thermofluid process model that can simulate the water/steam cycle and the coal/air/flue gas cycle for steady-state and dynamic operational scenarios, in an integrated manner. The furnace flue gas side can be modelled using a suitable zero-dimensional model in a quasi-steady manner, but this will only provide an overall heat transfer rate and a single gas temperature. When more detail is required, CFD is the tool of choice. However, the solution times can be prohibitive. A need therefore exists for a computationally efficient model that captures the three-dimensional radiation effects, flue gas exit temperature profile, carbon burnout and O2 and CO2 concentrations, while integrated with the steam side process model for dynamic simulations. A thermofluid network-based methodology is proposed that combines the zonal method to model the radiation heat transfer in three dimensions with a one-dimensional burnout model for the heat generation, together with characteristic flow maps for the mass transfer. Direct exchange areas are calculated using a discrete numerical integration approximation together with a suitable smoothing technique. Models of Leckner and Yin are applied to determine the gas and particle radiation properties, respectively. For the heat sources the burnout model developed by the British Coal Utilisation Research Association is employed and the advection terms of the mass flow are accounted for by superimposing a mass flow map that is generated via an isothermal CFD solution. The model was first validated by comparing it with empirical data and other numerical models applied to the IFRF single-burner furnace. The full scale furnace model was then calibrated and validated via detailed CFD results for a wall-fired furnace operating at full load. The model was shown to scale well to other load conditions and real plant measurements. Consistent results were obtained for sensitivity studies involving coal quality, particle size distribution, furnace fouling and burner operating modes. The ability to do co-simulation with a steam-side process model in Flownex® was successfully demonstrated for steady-state and dynamic simulations

Analysis of Oscillating Combustion for NOx-Reduction in Pulverized Fuel Boilers

Thermal power plants in different fields are regularly adapted to the state-of-the-art emissions standards, applying “The Best Available Techniques Reference”. Since 2016 in the power plant area new, more stringent limits for power plant units with a thermal output of more than 300 MW operated with black coal are valid. Usually, in order to reach the new limits e.g., for NOX emissions, downstream reduction processes (Selective Non-Catalytic Reduction, SNCR or Selective Catalytic eduction) are applied, which use of operating resources (essentially ammonia water) thereby increase. By the means of an xperimentally validated process, by which pulverized fuel is fed by oscillation through a swirl burner into a pilot ombustion chamber with a thermal output of 2.5 MW, nitrogen oxides can be reduced without further activities, for nstance from 450 mg/mN3 in non-oscillation operation mode (0 Hz) to 280 mg/mN3 in oscillation operation mode (3.5 Hz), normalized to an O2–content of 6% each. These findings were patented in EP3084300. Particularly promising are the experiments which utilize oscillation of a large portion of the burn out air instead of the fuel in order to minimize the fatigue of the pulverized fuel oscillator, amongst others. Thereby, the nitrogen conversion rate, which describes the ratio of NOX to fuel nitrogen, including thermal NOX can be reduced from 26% for non-oscillation operation mode down to 6%. The present findings show that fuel oscillation alone is not sufficient to achieve nitrogen oxides concentrations below the legislative values. Therefore, a combination of different primary (and secondary) measures is required. This paper presents the experimental results for oscillating coal-dust firing. Furthermore, an expert model based on a multivariate regression is developed to evaluate the experimental results

Application of mass and energy balances to determine coal, air required and flue gas flow rates in a power plant

Thesis (MEng (Mechanical Engineering))--Cape Peninsula University of Technology, 2019The primary objective of this study was to determine the heat rate of the power plant using the measurements of critical parameters and MEB calculations. An additional goal of the project was to determine the flue gas and air mass flow rates which influence the efficiency of the coal power plant. The consumption of coal is a critical parameter affecting the efficiency of coal-fired steam boilers. From an operational perspective, the mass flow rate of pulverised coal is a major indicator of the rate of combustion and plant heat rate. However, the cost of electricity production in thermal coal power plants operated by ESKOM, is predominantly influenced by pulverized coal which represents between 60-70% of the total cost. Monitoring the consumption of coal can determine corrective actions which will ultimately improve the power plant’s efficiency, reliability and associated economic benefits. Initially, the fundamental concepts of a boiler and its auxiliaries were studied, which led to the required coal, air and flue gas systems required in a coal-fired boiler plant. From the literature review, it was established that coal consumption is a critical indicator of a plant’s performance in terms of cost and efficiency. The different methods used for the flow measurements of coal, air and flue gas in a coal-fired boiler plant, such as MEB and CFD were reviewed. The MEB method was used to determine the pulverised coal, air, and flue gas mass flow rates and the plant’s heat rate. The MEB method was used to establish a coherent set of input and output data for the boiler, as well as to troubleshoot existing measurements from ESKOM’s coal-fired power plant. The plant’s coal consumption and heat rate results were calculated by means of a Mathcad model that was developed using BMEB methodology. Mathcad was chosen because it allows to visually check calculations. Furthermore ANSYS Fluent was used for the CFD simulation in the secondary air system