Combustion Of Coal In Boilers Research Articles

Pulverized Coal-Fired Boilers: Future Directions of Scientific Research

The paper provides an outlook on future directions of research and the possible applications for pulverized coal-fired boilers. One potential direction for future research is to focus on the ways to improve the efficiency of pulverized coal-fired boilers. This could involve developing new combustion technologies that are able to more thoroughly burn the coal and produce less waste or finding ways to capture and use the excess heat that is generated during the combustion process. The pulverized coal combustion process in power boilers is still being improved by the preliminary cleaning of coal and the use of various catalytic additives. Another area of research that could be valuable is the development of advanced control systems and monitoring technologies for pulverized coal-fired boilers. These systems could be used to optimize the performance of the boiler and ensure that it is operating at maximum efficiency while also providing real-time data on the condition of the boiler and any potential problems that may arise. The analysis of literature shows that several future paths of development and scientific research related to the technology of pulverized coal combustion in boilers can be distinguished.

Fouling and Slagging Investigation on Ash Derived from Sasol Coal Using ICP and XRF Analytical Techniques

During coal combustion in boilers, light fly ash particles are carried away along with the hot flue gases and the heavier bottom ash particles fall to the bottom of the boiler. The fly ash particles stick on the convective heat transfer surfaces and the furnace wall, causing fouling and slagging deposition problems during the boiler operation. The fouling and slagging effect reduces the boiler’s operational efficiency. This study was motivated by the decline in the operational efficiency of the installed boilers at Sasol synfuel operations in Secunda, Mpumalanga province in the Republic of South Africa. It was assumed that the drop in the boiler efficiency was caused by the coal ash deposition during the boiler operations. The rate of ash deposition and accumulation in the convective heat transfer tubes and furnace water walls during the boiler operation depends on the chemical composition of the coal ash produced during combustion. Coal fly and bottom ash samples were collected from the operational site for laboratory analysis to determine their chemical composition using induced coupled plasma optical emission spectroscopy, induced coupled plasma mass spectroscopy (ICP-OES, ICP-MS) and X-ray fluorescence (XRF) analytical methods. The major, minor and trace elements by mass (%) in the ash samples were obtained from the ICP-OES and ICP-MS, whereas the elemental composition in an oxidised atmosphere was obtained from the XRF analysis. The amount of unburnt coal particles within the ash samples was determined from the loss on ignition (LOI) test. The fouling and slagging prediction during Sasol boiler operation was evaluated using previously developed fouling and slagging indices as a guide using the analysed ash chemical composition results obtained in this study. It was concluded from the analysed results using the guided evaluated indices from the analysed coal ash chemistry that during the operations of Sasol boiler(s) there is a low to medium fouling prediction occurrence on the convective heat transfer tubes and a low slagging in the boiler furnace walls.

CFD modeling of sodium transformation during high-alkali coal combustion in a large-scale circulating fluidized bed boiler

The ash-related problems of fouling and slagging occur easily during high-alkali coal combustion in boilers. In this study, numerical calculations were performed to investigate the sodium migration mechanism and ash deposition on heating surfaces in a large-scale circulating fluidized bed (CFB) boiler during the burning of high-alkali coal. The calculation principle was based on a comprehensive three-dimensional CFB combustion model and a sodium migration model from our previous study. The computing object of this study was a 300 MW subcritical CFB boiler. By performing a simulation, the distributions of NaCl(g) and Na2SO4(g) along the furnace were displayed. The rates of sodium deposition via condensation, inertial impaction, and thermophoresis on the water walls and suspended panels were analyzed. Additionally, the net deposition rates of fly ash on the water walls and suspended panels were determined. Then, the tendency of fouling and slagging in different areas of the CFB furnace could be predicted and judged. Calculation results for the gas–solid flow, furnace temperature, and gaseous species agreed with the measured data.

Research Progress on Control and Removal Technology of SO3 of Coal-fired Power Plants

SO3 is one of pollutants in flue gas of coal power plants. It mainly derived from coal combustion in boiler and selective catalytic reduction denitrification system. The content of SO3 in flue gas were influenced by the combustion mode, sulfur content in fuel, composition of denitrification catalyst and fly ash. SO3 and water vapour generated H2SO4 droplets. Sulfate secondary particles in atmosphere could cause haze, acid rain and other disastrous weather. High concentration of SO3 could cause blockage and corrosion and affect the safe operation of the units. The generation mechanism of SO3 was discussed. The latest research progress on control and removal technology of SO3 was summarized. The study in this paper provides a reference for pollutant treatment in coal-fired power plants.

Results of testing the efficiency of dry flue gas desulphurization of coal-fired boilers of small capacity

Power plants, such as coal boilers, emit flue gases containing solid particles and gases resulting from the combustion of coal. One of the most dangerous pollutants emitted is certainly sulfur dioxide. Therefore, the reduction of emissions of sulfur dioxide has become a legal obligation. So far the most successful method of reducing the content of sulfur dioxide in the combustion products leaving the environment is injecting limestone or lime in combustion and to provide conditions for the reaction between the injected lime and sulfur dioxide from combustion products still in the combustion chamber. This method has been successfully used in thermal power plants to coal. This paper deals with the possibility of introducing the process of dry flue gas desulphurization created during coal combustion in boilers of smaller.

Winter Heating or Clean Air? Unintended Impacts of China's Huai River Policy

This paper assesses the role of heating entitlements in generating stark air quality differences across China. During the 1950-1980 central planning period, the Chinese government established free winter heating of homes and offices as a basic right via the provision of free coal fuel for boilers. The combustion of coal in boilers is associated with the release of air pollutants, especially total suspended particulates (TSP). Due to budgetary limitations, however, this heating entitlement was only extended to areas to the north of the line formed by the Huai River and Qinling Mountains in central China. We find this procrustean policy led to dramatically higher TSP levels in the north; the difference is roughly 5-8 times current TSP concentrations in the US. This result holds both in a cross-sectional regression discontinuity-style estimation approach and in a panel data setting that compares the marginal effect of winter temperature on TSP in northern and southern China. In contrast, we fail to find evidence that the heating policy has a meaningful impact on sulfur dioxide (SO2) and nitrogen oxide (NOx) concentrations.

Utilization of Fly Ash for the Production of Crockery and Novelty Wares

The feasibility of utilizing fly ash, a waste inorganic product obtained by the combustion of coal in boilers of thermal power plant, was studied for the development of value added glazed ceramic materials like crockery and novelty wares. Progressive incorporation of fly ash in replacement of silica and potash feldspar in the standard crockeryware body compositions resulted in an increase in unfired and fired strengths coupled with vitrification at 1250°C up to the addition of 30% fly ash. Further incorporation of fly ash, up to 50%, showed a decrease in fired strength and increase in water absorption at the same temperature. Improved stoneware crockery body utilizing 30% fly ash in the standard body composition was sucessfully produced.

97/04829 High-efficiency low-cost and coal-saving additives for coal combustion in boiler: Xia, J. Faming Zhuanli Shenqing Gongkai Shuomingshu CN 1,096,811 (Cl. C10L9/10), 28 Dec 1994, Appl. 93,106,593, 7 Jun 1993, 3 pp. (In Chinese)

97/04829 High-efficiency low-cost and coal-saving additives for coal combustion in boiler: Xia, J. Faming Zhuanli Shenqing Gongkai Shuomingshu CN 1,096,811 (Cl. C10L9/10), 28 Dec 1994, Appl. 93,106,593, 7 Jun 1993, 3 pp. (In Chinese)

The use of recycle for enhanced volatile metal capture

Metal compounds vaporize and condense during the combustion of coal in boilers and cement kilns, leading to interesting challenges in the design and operation of equipment to recover compounds from the flue gases prior to stack release. In cement kilns, the solids and combustion gases flow counter current to each other, with active exchange between gases and solids. The mixing is promoted by particle entrainment and deposition from and to the moving solid bed. This behavior leads to recycling of metal compounds between the hot and cold kiln ends with a concomitant enrichment of the ash in volatile metals. It is shown that the recycle amount can be varied by the removal of some of the combustion products through a by-pass duct. Flue gas removal through the by-pass provides a degree of freedom that can be utilized to control emissions. The technique used in the cement industry may lead to a possible approach for the use of carbon in the fly ash (through recycle) to regulate mercury emissions from pulverized-coal-fired boilers.

Coal combustion in boilers: A mature technology facing new constraints

Three techniques are being used currently for combustion of coal in boilers: stoker firing, pulverized-coal combustion, and cyclone furnaces. Combustion characteristics of these techniques are discussed from the viewpoint of the impact of modern-day demands on combustion of coal. Constraints imposed by three demands are singled out: adaptation of state-of-the-art techniques to major changes in coal quality; environmental protection requirements; and the need to develop modifications of existing techniques allowing rapid increased utilization of coal. Specifically, the discussion is about: (i) Implications of the requirement to hold the emissions of three major pollutants—SOx, NOx, and flyash—within prescribed U.S. standards. (ii) Effects of increased and decreased ash content, respectively, on combustion characteristics. (iii) Combustion of coal/oil dispersions, allowing coal to be burned in boilers designed for combustion of oil. An attempt is made at identifying gaps in the technical knowledge of the existing technologies, and some research needs are suggested. In addition, a brief mention is made of the ways in which two new (developing) technologies—fluidized-bed combustion and coal-fired magnetohydrodynamic generators—are expected to deal with modern-day constraints.