The paper presents the results of the mechanical, electrical, CCSEM and XRD measurements of hard coal, conducted in simulated conditions of sintering in atmospheres of O2/CO2,. The changes of the coal ash resistivity are correlated with the content of the oxides and with the sintering temperature determined by the mechanical test and Leitz method. The SEM-EDS analysis was conducted for deposits on the probe. The changes of the measured ash samples, observed during sintering process in O2/CO2 atmosphere, were discussed in the ash microstructure point of view.
The paper presents results of coal behaviour during combustion in oxy-fuel atmosphere. The experiment was performed using 3 meter long Entrained Flow Reactor and 1 meter long Drop Tube Reactor. Three hard coals and two lignites were analysed in order to investigate NOx, SO2 emission and fly ash burnout. The measurements were performed along and at the outlet of a combustion chamber for one- and two - stage combustion. In the second stage of the experiment, kinetic parameters for nitrogen evolution during combustion in oxy - fuel and air were calculated and the division of nitrogen into the volatile matter and the char was measured. The conducted experiment showed that emissions in oxy - fuel are lower than those in air.
The paper presents current reports on kinetics and mechanisms of reactions with mercury which take place in the exhaust gases, discharged from the processes of combustion of solid fuels (coals). The three main stages were considered. The first one, when thermal decomposition of Hg components takes place together with formation of elemental mercury (Hg0). The second one with homogeneous oxidation of Hg0 to Hg2+ by other active components of exhaust gases (e.g. HCl). The third one with heterogeneous reactions of gaseous mercury (the both - elemental and oxidised Hg) and solid particles of fl y ash, leading to generation of particulate-bound mercury (Hgp). Influence of exhaust components and their concentrations, temperature and retention time on the efficiency of mercury oxidation was determined. The issues concerning physical (gas-solid) and chemical speciation of mercury (fractionation Hg0-Hg2+) as well as factors which have influence on the mercury speciation in exhaust gases are discussed in detail.
The paper describes the results of various actions and industrial tests conducted in order to decrease the content of unburned carbon in the fly ash of a circulating fluidised bed combustor (CFBC). Several attempts to improve the situation were made and the effects of several parameters on the unburned carbon content in the fly ash were investigated (e.g. bed temperature, cyclone separation efficiency, fuel particle size distribution, boiler hydrodynamics, grid design, and fuel data). Unfortunately, no satisfactory solution to these problems was found. Probably, apart from attrition and char fragmentation, additional factors also contributed to the formation of unburned carbon in the CFBC fly ash.
In the processes of coal mining, preparation and combustion, the rejects and by-products are generated. These are, among others, the rejects from the coal washing and dry deshaling processes as well as the coal combustion by-products (fly ash and slag). Current legal and industry regulations recommend determining the content of mercury in them. The regulations also define the acceptable content of mercury. The aim of the paper was to determine the mercury content in the rejects derived from the coal cleaning processes as well as in the combustion by-products in respect of their utilization. The mercury content in the representative samples of the rejects derived from the coal washing and dry deshaling processes as well as in the coal combustion by products derived from 8 coal-fired boilers was determined. The mercury content in the rejects from the coal washing process varied from 54 to 245 μg/kg, (the average of 98 μg/kg) and in the rejects from the dry deshaling process it varied from 76 to 310 μg/kg (the average of 148 μg/kg). The mercury content in the fly ash varied from 70 to 1420 μg/kg, (the average of 567 μg/kg) and in the slag it varied from 8 to 58 μg/kg (the average of 21 μg/kg). At the moment, in light of the regulations from the point of view of mercury content in the rejects from the coal preparation processes and in the coal combustion by-products, there are no significant barriers determining the way of their utilization. Nevertheless, in the future, regulations limiting the maximum content of mercury as well as the acceptable amount of leachable mercury may be introduced. Therefore, preparing for this situation by developing other alternative methods of using the rejects and by-products is recommended.
Power boilers should be characterized by high flexibility in terms of loads, which results from the demand for electricity. In addition to the flexibility of the boiler, it is also important for the boiler to operate under technical minimum conditions while maintaining harmful emissions standards. A boiler operating with a technical minimum should also exhibit a stable combustion process. The paper presents the results of numerical combustion research for the minimum load of the two-pass ultrasupercritical boiler with front wall swirl burners system. The combustion stability for the minimum boiler load of 40% for the three mill system configurations has been demonstrated. Based on the numerical tests carried out in terms of obtaining the most favourable combustion conditions and the emission of harmful substances, the most favourable of them cases was indicated.
Balanced distribution of air in coal-fired boiler is one of the most important factors in the combustion process and is strongly connected to the overall system efficiency. Reliable and continuous information about combustion airflow and fuel rate is essential for achieving optimal stoichiometric ratio as well as efficient and safe operation of a boiler. Imbalances in air distribution result in reduced boiler efficiency, increased gas pollutant emission and operating problems, such as corrosion, slagging or fouling. Monitoring of air flow trends in boiler is an effective method for further analysis and can help to appoint important dependences and start optimization actions. Accurate real-time monitoring of the air distribution in boiler can bring economical, environmental and operational benefits. The paper presents a novel concept for online monitoring system of air distribution in coal-fired boiler based on real-time numerical calculations. The proposed mathematical model allows for identification of mass flow rates of secondary air to individual burners and to overfire air (OFA) nozzles. Numerical models of air and flue gas system were developed using software for power plant simulation. The correctness of the developed model was verified and validated with the reference measurement values. The presented numerical model for real-time monitoring of air distribution is capable of giving continuous determination of the complete air flows based on available digital communication system (DCS) data.
Trace elements contained in coal escape with flue gas from energy sources into the air or move
towards other components of the environment with by-products captured in electrofilters (EF) and flue gas
desulphurisation (FGD) plants. The existing knowledge about the distribution of frequently dangerous trace
elements contained in these products is insufficient. Studies were therefore undertaken in selected power plants
to investigate the distribution of trace elements in coal, slag, as well as dust containment and flue gas desulphurisation products, such as fly ash captured in dust collectors, desulphurisation gypsum and semi-dry scrubbing
FGD products. Using the technique of flame atomic absorption spectrometry (F-AAS) and mercury analyser,
the following were determined in the research material samples: Cr, Cu, Hg, Mn, Ni, Pb and Zn. The studies
have a reconnaissance character. The authors have presented the results of determinations for selected trace
elements in samples taken at Jaworzno III and Siersza Power Plants, which burn hard coal, and in Bełchatów
Power Plant, burning brown coal. A balance of the examined trace elements in a stream of coal fed into the
boiler and in streams of waste and products carried away from the plant was prepared. The balance based on
the results of analyses from Bełchatów Power Plant was considered encouraging enough to undertake further
investigations. The research confirmed that due to the distribution in the process of coal combustion and flue
gas treatment, a dominant part of particular trace elements’ stream moves with solid waste and products, while
air emission is marginal. Attention was paid to the importance of research preparation, the manner of sample
taking and selection of analytical methods.
Trace metal composition of snowpack, snow-melt filter residues and top-soils were determined along transects through industrial towns in the Usa River Basin: Inta, Usinsk and Vorkuta. Elevated concentrations of deposition elements and pH in snow and soils associated with alkaline coal ash within 25-40 km of Vorkuta and Inta were found. Atmospheric deposition in the vicinity of Vorkuta and Inta, added significantly to the soil contaminant loading as a result of ash fallout. The element concentrations in soils within 20-30 km of Vorkuta do not reflect current deposition rates, but instead, reflect an historical pollution legacy, when coal mining activity peaked in the 1960s. There is little evidence of anthropogenic metal deposition around the gas and oil town of Usinsk.