Study on Combustion Characteristics and Ignition Performance of a Reverse Pulverized-Coal Flame Stabilizer

The effectiveness of a novel coal-igniting-fuel technology and application in a direct current burner

This study investigates the application of new-type centralized particle concentrating swirl combustor (NCPCSC) to enhance the flame stability of a 350 MW boiler at low-load conditions. Using numerical simulations investigates the combustion performance of a 350 MW boiler using NCPCSC under varying load conditions through numerical simulations. The results reveal a significant improvement in the uniformity of the temperature field and combustion stability, with NCPCSC enhancing the burnout effect and reducing pollutants. Under 100% load, the furnace forms a symmetrical high-temperature main combustion zone, with the average temperature across the cross-section reaching 1500°C. The flue gas temperature at the furnace outlet rises from 1040.52°C to 1106.4°C, while NO x emissions are reduced from 735.94 mg/m3 @6%O2 to 572.27 mg/m3 @6%O2, and the combustible matter in fly ash decreases from 4.79% to 3.17%. At 47% load, the furnace maintains a stable high-temperature combustion zone with a peak temperature of 1300°C and a significant decrease in NO x emissions from 832.19 mg/m3 @6%O2 to 517.81 mg/m3 @6%O2. Even under extreme low-load conditions of 30% and 20%, stable combustion is achieved, with an average peak temperature above 1300°C and the boiler operating without fuel oil assistance at 20% load. These findings demonstrate that NCPCSC offers strong adaptability to load variations, ensuring efficient, clean, and stable combustion, while significantly reducing unburned losses and NO x emissions, making it a promising solution for improving boiler performance across a wide load range.

Investigation on effect of mixing distance on mixing process and combustion characteristics of double-cone burner

The characteristics of self-ignition and self-sustained combustion of a solid fuel under supersonic cross flow have been investigated theoretically and numerically. A time dependent two-dimensional, axisymmetric compressible Navier-Stokes equations and species transport equations are solved numerically. Turbulence model is using the Shear Stress Transport k  model. The PMMA fuel and a global one step reaction mechanism are used in this study. The reaction rate is determined by finite-rate chemical kinetics with the turbulence-chemistry interaction modeled using eddy-dissipation model. The numerical model is validated by comparing the numerical results with experimental data. The flame spread and pressurization during self-ignition of PMMA in combustor have been studied. The behaviors of both sustained and un-sustained combustion in SFSCRJ combustor have been analyzed. The simulation results reveal that three stages of flame spread are identified during the self-ignition transient, which consists of heat accumulation, self-ignition in the secondary recirculation zone, and whole combustor self-ignition orderly. The pressure suddenly rises in combustor during the third stage. The difference of combustor shape affects the self-ignition. There have always been high temperature zone and high mass fraction of reaction products in combustor during sustained combustion. Once the recirculation zone area and residual time provided by cavity are unable to meet the time needed for chemical reaction of reactants and the ignition of fresh mixture, flame is blew out by supersonic cross flow.

Experimental study on control of flame inclination in a thermal flow reversal reactor with extra lean premixed methane/air intake

China's retrofitting measures in coal-fired power plants bring significant mercury-related health benefits

Occupational accidents in the world and in our country affect the energy sector as a serious problem. It has become important to take the necessary precautions for the uninterrupted continuation of energy. The effective prevention of occupational accidents and diseases by coal-fired power plants depends on their evaluation of OHS performance and continuing their improvement efforts. In the implementation phase of the OHS performance model in coal-fired thermal power plants, a total of 170 OHS performance measurement criteria, including 8 main criteria and 162 sub-criteria, were determined and 162 sub-criteria were evaluated with the PROMETHEE method. As a first step, the sub-criteria of the three riskiest sections in terms of OHS in coal-fired thermal power plants, which were previously selected with AHP, were evaluated by 10 occupational safety experts in the range of 0-100 for each coal-fired power plant alternative. Performance factor results were obtained by using the "Visual PROMETHEE" package program to obtain PROMETHEE results with criterion weights. The data obtained from alternative power plants were evaluated and prioritized with the PROMETHEE method based on the weights determined with the help of AHP according to the OHS performance measurement model we proposed, and coal-fired power plants were ranked. This study; An objective OHS performance measurement method based on measurable indicators, reflecting OHS performance in the most accurate way, practical to use, has been developed and applied in coal-fired thermal power plants.

The design and model simulation of a can combustor has been made for future syngas (mainly H2/CO mixtures) combustion application in a micro gas turbine. In previous modeling studies with methane as the fuel, the analysis indicated the design of the combustor is quite satisfactory for the 60-kW gas turbine; however, the cooling may be the primary concerns as several hot spots were found at the combustor exit. When the combustor is fueled with methane/syngas mixtures, the flames would be pushed to the sides of the combustor with the same fuel injection strategy. In order to sustain the power load, the exit temperature became too high for the turbine blades, which deteriorated the cooling issue of the compact combustor. Therefore, the designs of the fuel injection are modified, and film cooling is employed. Consequently, the simulation of the modified combustor is conducted by the commercial CFD software Fluent. The computational model consists of the three-dimensional, compressible k-ε model for turbulent flows and PPDF (Presumed Probability Density Function) model for combustion process between methane/syngas and air invoking a laminar flamelet assumption. The flamelet is generated by detailed chemical kinetics from GRI 3.0. Thermal and prompt NOx mechanisms are adopted to predict the NO formation. At the designed operation conditions, the modeling results show that the high temperature flames are stabilized in the center of the primary zone where a recirculation zone is generated for methane combustion. The average exit temperature of the modified can combustor is 1293 K, which is close to the target temperature of 1200 K. Besides, the exit temperatures exhibit a more uniform distribution by coupling film cooling, resulting in a low pattern factor of 0.22. The NO emission is also low with the increased number of the dilution holes. Comparing to the results for the previous combustor, where the chemical equilibrium was assumed for the combustion process, the flame temperatures are predicted lower with laminar flamelet model. The combination of laminar flamelet and detailed chemistry produced more reasonable simulation results. When methane/syngas fuels are applied, the high temperature flames could also be stabilized in the core region of the primary zone by radially injecting the fuel inward instead of outward through the multiple fuel injectors. The cooling issues are also resolved through altering the air holes and the film cooling. The combustion characteristics were then investigated and discussed for future application of methane/syngas fuels in the micro gas turbine. Although further experimental testing is still needed to employ the syngas fuels for the micro gas turbine, the model simulation paves an important step to understand the combustion performance and the satisfactory design of the combustor.

To achieve ultra low NOx emission as well as high efficiency for industrial burners, premixed or partial premixed combustion technology is becoming more attractive than flue gas recirculation approaches, which tend to cause low combustion stability and low energy use efficiency. A well designed premixed combustion system can achieve lower and more uniform combustion zone temperatures thus resulting in reduced thermal NOx generation. A multi-stage premixed industrial scale gas burner with oil backup capability has been developed by the authors, with the assistance from CFD simulation. By using staged combustion, combustion heat release is better distributed into a larger volume to avoid high peak flame temperature zone to occur. By using a primary stage combustion with a fuel rich flame and a hot high emissive metallic chamber wall, the burner combustion stability is ensured. The CFD tool was used to simulate and optimize the whole burner combustion and heat transfer process, with proper fluid dynamics and reaction models for this full size burner development. With the CFD efforts, the final burner design can achieve a very uniform temperature field, with peak flame temperatures below 1650°C, therefore thermal NOx generation is minimized. The numerical results show that this new gas-fired burner can achieve high efficiency with low NOx emission. Using the CFD simulation tool, the burner global parameters, such as its peak flame temperatures, its exhaust flue gas temperatures, and its NOx concentration distributions, have been studied under different burner operation conditions, e.g., different excess air levels, different burner firing rates, and different mixture inlet temperatures. The CFD simulation tool has been proved a good assistance for the burner design, as well as the burner performance optimization.

Life cycle assessment shows that retrofitting coal-fired power plants with fuel cells will substantially reduce greenhouse gas emissions

Experimental study and RANS calculation on velocity and temperature of a kerosene-fueled swirl laboratory combustor with and without centerbody air injection

Effect of swirler geometry on the outlet temperature profile performance of a model gas turbine combustor

In the following decades there will be a fundamental structural change in the European power supply system. This structural change is forced by several factors, e.g. the European Union Greenhouse Gas Emission Trading Scheme, the strategic goal for the European Union of a more sustainable development, energy policy targets to double the share of renewable ener-gies, the phase out or moratoria of the nuclear industry in some European Union member states, and the need of more than 200 GW of new power plant capacities in EU-15. The struc-tural change has to be embedded into an economic, social and ecological framework. Within this framework, there is a variety of possible options to create a future power supply which fulfils the multiple criteria. Generally, different technologies can be chosen which all have their own advantages and disadvantages. It is a challenging decision-making process because fossil-fired power plants tend to be economically advantageous and ecologically disadvanta-geous whereas renewable energy systems tend to be ecologically advantageous and economi-cally disadvantageous. This study gives a comparison of the estimated external costs (environmental aspects) and internal costs (economic aspects) of different power generation technologies in the year 2010 in order to support the decision-making process of future power plant investments in the framework of a sustainable development. A life cycle analysis gives considerable life cycle data for photovoltaic systems, wind turbines, fuel cells, bio-fuelled combined heat and power plants, biomass, water, solar thermal, geothermal, coal-fired, lignite-fired and natural gas-fired power plants as well as nuclear power plants. This database is used for the estimation of external costs which is based on updated factors of damage and avoidance costs for selected emissions. The damage factors are calculated with the software tool EcoSense following the impact pathway approach. Global warming and discounting are considered to be the hot spots in the external costs discussion. An avoidance costs approach is applied which is assumed to fulfil sustainability criteria. The comparison of the external costs of the technologies analysed shows that external costs of power generation technologies using renewable energies and nuclear power plants are in the range of 0.03-3.79 €-Cent/kWhel whereas the external costs of power generation technologies using organic fossil fuels are in the range of 3.37-27.98 €-Cent/kWhel. However, the comparison of the internal costs shows that fossil-fuelled power plants have the lowest internal costs compared to the other technologies analysed. This trade-off between external and internal costs requires a comparison of the social costs which are the sum of internal and external costs. The comparison of the social costs shows five social cost clusters for the ana-lysed technologies for the year 2010. Nuclear power plants have social costs of less than 10 €-Cent/kWhel. Wind turbines and river power plants have slightly higher social costs of 10-15 €-Cent/kWhel. Biomass power plants, bio-fuelled combined heat and power plants, solar ther-mal power plants, geothermal power plants and natural gas-fired power plants have social costs in the range of 15-20 €-Cent/kWhel. Photovoltaic systems in Spain, fuel cells, coal-fired power plants and lignite-fired power plants have social costs in the range of 20-35 €-Cent/kWhel. The highest social costs are caused by Photovoltaic systems in Germany with more than 35 €-Cent/kWhel.

Energy conversion systems have assumed a crucial role in current society. The threat of climate change, fossil fuel depletion and the growing world energy demand ask for a more sustainable way of electricity production, eg, by using renewable energy sources, by improving the conversion efficiency and/or by controlling power plant emissions. Despite the relationship between exergy and sustainability stated in literature, exergy losses are usually not considered when comparing systems and energy sources for power generation. The exergetic sustainability assessment method named Total Cumulative Exergy Loss (TCExL) has been used to assess several systems for electricity production, ie, a coal-fired power plant, a coal-fired power plant including carbon capture and storage, a biomass-fired power plant, an offshore wind farm and a photovoltaic park. The results of the TCExL method have been compared with an environmental sustainability indicator, ie, the overall ReCiPe endpoint indicator and the economic indicator named Present Worth Ratio. The offshore wind farm is the best system from the exergetic and environmental point of view. The photovoltaic park is the system with the second-best scores. However, from the economic viewpoint including subsidy by the Dutch government, the photovoltaic park performs better than the wind farm system and the system that performs best is the biomass-fired power plant. Without subsidy, only the coal-fired power plant without carbon capture and storage is profitable. The exergetic sustainability scores of the coal-fired and biomass-fired power plants are similar, but from the environmental sustainability viewpoint, the biomass-fired power plant performs better than both coal-fired power plants. As the results of environmental and economic sustainability assessments strongly depend on models, weighting factors, subsidy, market prices, etc, while the results of the exergetic sustainability assessment do not, it is recommended that the exergetic sustainability be taken into account when assessing the sustainability of power generation and other technological systems.

Underground Coal Gasification (UCG) is thought to be the most favourable clean coal technology option from geological-engineering-environmental viewpoint (less polluting and high efficiency) for extracting energy from coal without digging it out or burning it on the surface. UCG process requires only injecting oxidizing agent (O2 or air with steam) as raw material, into the buried coal seam, at an effective ratio which regulates the performance of gasification. This study aims to evaluate the influence of equivalent ratio (ER) on the flow and combustion characteristics in a typical half tear-drop shape of UCG cavity which is generally formed during the UCG process. A flow modeling software, Ansys FLUENT is used to construct a 3-D model and to solve problems in the cavity. The boundary conditions are- (i) a mass-flow-inlet passing oxidizer (in this case, air) into the cavity, (ii) a fuel-inlet where the coal volatiles are originated and (iii) a pressure-outlet for flowing the product Syngas out of the cavity. A steady-state simulation has been run using k-? turbulence model. The mass flow rate of air varied according to an equivalent ratio (ER) of 0.16, 0.33, 0.49 and 0.82, while the fuel flow rate was fixed. The optimal condition of ER has been identified through observing flow and combustion characteristics, which looked apparently stable at ER 0.33. In general, the flow circulation mainly takes place around the ash-rubble pile. A high temperature zone is found at the air-releasing point of the injection pipe into the ash-rubble pile. This study could practically be useful to identify one of the vital controlling factors of gasification performance (i.e., ER impact on product gas flow characteristics) which might become a cost-effective solution in advance of commencement of any physical operation.