Most particles of coal … Tel. Experimental investigation on ignition modes of pulverized coal clouds relating to the dust concentration is performed in a drop tube furnace. However, when using higher rank coal (coal C), the ignition was significantly prolonged with decreasing the temperature from 1300 K to 1100 K or with increasing the particle size to above 150 μm. Normally, the traditional coal process systems use ball mills to pulverize coal. 1990;79:569–78. At the same time, the flow rate of the air must be as small as possible to prevent reductions in boiler efficiency. An unsteady‐state model of a pulverized coal cloud including the submodels of radiation and convection was used to study the ignition characteristics of a Datong bituminous coal under the conditions of O 2 /N 2 and O 2 /CO 2 atmospheres. However, little oxygen is consumed during this initial visual event. 12. Pyrolysis of large particles was delayed, but accelerated after ignition by radiant heat transfer from coal flames. slightly increased the ignition temperature (30-40K). The direct ignition of pulverized coal in accordance with the present invention contemplates the delivery of a dense phase coal/air stream to an ignition zone where it receives ignition energy and the thus ignited mixture is thereafter contained in a recirculation region until the flame becomes self-sustaining. The raw coal is then fed into the pulverizer along with air heated to about 650 °F (340 °C) from the boiler. Ignition temperature was examined analytically by using a modified distributed activation energy model for pyrolysis. Fuel 2010 , 89 (3) , 743-751. : +86 -2787545526; fax: . We use cookies to help provide and enhance our service and tailor content and ads. It is found to be very close to the flame formation temperature. For example, a thermogravimetric technique ... Pulverized coals are ignited by the high temperature gas in the recirculation flow. Ignition temperatures increased with the enhancement of coal rank in either air or oxy-fuel combustion conditions. Auto Ignition Temperature table that shows the minimum temperature required to ignite a gas or vapor in air without a spark or flame being present. E-mail address:zliu@mail.hust.edu.cn. Switching from conventional pulverized-coal combustion to oxy-fuel combustion brings significant changes in flame properties among which the most important are ignition properties and … This phenomenon was noticed to be more evident at higher coal ranks (coals D and E), while the influence of particle size seemed to be stronger than the ambient temperature. This characteristic temperature decreases with an increase in the ambient oxygen concentration but appears to be independent of particle size. Many accidents and protection techniques have been reported by former investigations [1-3]. Laboratory measurements of the visual and combustion sequences during the ignition of pulverized coals, chars, and petroleum coke are reported. Three coal types of … Ignition behavior of pulverized coals in lower oxygen content ... devolatilization of bituminous and subbituminous coal at a gas temperature of 1700K over a range of 12~36% O2in both N2 and CO2diluent gases.Zhang(2010)employed the high speed camera to capture the particle imagesin the Corresponding author. The first flash temperature, commonly referred to as the minimum gas temperature for ignition, is shown to decrease with an increase in the volatile matter content of coal, particle size, and ambient oxygen concentration. Flue gases are used as drying and conveying medium in the pulverizing process. These two temperatures appear to be better indicators of the ignitability of pulverized coals in combustors than the first flash temperature. Coal particles were ignited by injecting high temperature gas flow. Minimum ignition temperature (dust layer) / °C 200 Minimum ignition temperature (dust cloud) / °C 560. Anthracite coal has also been widely used in hand-fired furnaces. Optical measurement of pulverized coal combustion in a laminar flow reactor: ignition, particle temperature, and alkali release April 2015 DOI: 10.13140/RG.2.1.1440.7209 Figure 19 shows gas temperature, gas composition, and coal burnout profiles along the center axis. Then, the effects of ambient temperature, oxygen mole fraction and coal rank on the characteristic ignition delay are examined. Abstract. The high temperature sufficed to promote NO x formation. Two coals of different rank (sub-bituminous and lignite), two particle size fractions (180-212 μm and 106-125 μm) at two furnace temperatures (1550 K and 1800 K), with oxygen concentration in the ambient gas varying from 10% to 50% by volume were used for the experiments. The physical process of ignition of pulverized coal is simplified and analyzed. Pulverized coal producing processes are widely used in thermal power stations, cement and iron-smelting industry. At a gas temperature, about 100°–200°C higher than the first flash temperature, the oxygen consumption is seen to increase rapidly and this is accompanied by the rapid generation of NOx. The ignition behavior of coal particles was studied through an enhanced numerical model, combined with experimental investigations in a visual drop tube furnace in the temperature range of 1100–1300 K. The devolatilization and the combustion of volatile and char during combustion of single coal particle were thoroughly studied. Pulverized coal combustion in mixture of oxygen and recycled flue gasses, known as oxy-fuel combustion, is considered as one of the several possible alternatives to conventional pulverized coal combustion. At a gas temperature, about 100°–200°C higher than the first flash temperature, the oxygen consumption is seen to increase rapidly and this is accompanied by the rapid generation of NOx. 5—Concept of In-flame NOx Reduction. The clouds are formed by premixing pulverized coal and air with different dust concentrations. The basic idea of a firing system using pulverised fuel is to use the whole volume of the furnace for the combustion of solid fuels. Fig 1 Pulverized coal combustion and gas composition in raceway. 5.3 Due to variation of ignition temperature with layer thickness, the test data at one thickness may not be applicable to all industrial situations (see Appendix X1). In the pulse experiments, when a pulse of coal containing 104-105 particles was injected, only a tiny flash of light with a low intensity was detected. For example, a dimensionless criterion named C 0 is obtained, one oil-free ignition technique studied. 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