Deposit Formation in a Grate-Kiln Plant for Iron-Ore Pellet Production. Part 1: Characterization of Process Gas Particles

Abstract

Slag formation in the grate-kiln process is a major problem for iron-ore pellet producers. It is therefore important to understand the slag formation mechanism in the grate-kiln production plant. This study initiated the investigation by in situ sampling and identifying particles in the flue gas from a full-scale 40 MW grate-kiln production plant for iron-ore pelletizing. Particles were sampled from two cases of combustion with pulverized coal and heavy fuel oil. The sampling location was at the transfer chute that was situated between the traveling grate and the rotary kiln. The particle-sampling system was set up with a water-cooled particle probe equipped with nitrogen gas dilution, cyclone, and low-pressure impactor. Sub-micrometer and fine particles were size-segregated in the impactor, while coarse particles (>6 μm) were separated with a cyclone before the impactor. Characterization of these particles was carried out with environmental scanning electron microscopy (ESEM), and the morphology of sub-micrometer particles was studied with transmission electron microscopy (TEM). The results showed that particles in the flue gas consisted principally of fragments from iron-ore pellets and secondarily of ashes from pulverized coal and heavy fuel oil combustions. Three categories of particle modes were identified: (1) sub-micrometer mode, (2) first fragmentation mode, and (3) second fragmentation mode. The sub-micrometer mode consisted of vaporized and condensed species; relatively high concentrations of Na and K were observed for both combustion cases, with higher concentrations of Cl and S from heavy fuel oil combustion but higher concentrations of Si and Fe and minor P, Ca, and Al from coal combustion. The first fragmentation mode consisted of both iron-ore pellet fines and fly ash particles; a significant increment of Fe (>65 wt %) was observed, with higher concentrations of Ca and Si during heavy fuel oil combustion but higher concentrations of Si and Al during coal combustion. The second fragmentation mode consisted almost entirely of coarse iron-ore pellet fines, predominantly of Fe (∼90 wt %). The particles in the flue gas were dominantly iron-ore fines because the second fragmentation mode contributed >96 wt % of the total mass of collected particles.

Scaling of Pulverized-Fuel Jet Flames That Apply Large Amounts of Excess Air—Implications for NOx Formation

“…This section contains brief descriptions of the full-scale iron ore rotary kiln and the pilot-scale kiln that this work is based on, as well as descriptions of the used fuels and the detailed reaction model. For more detailed descriptions regarding kiln design and dimensions, the reader is directed to previous studies [14,15,23]. The scaling ratio, R i , describes the ratio of parameter i in the full-scale to that in the pilot-scale.…”

“…No secondary measures for NO x emissions reduction are implemented at the plant. More details about this plant can be found in the paper of Jonsson et al [23].…”

On the use of alternative fuels in rotary kiln burners — An experimental and modelling study of the effect on the radiative heat transfer conditions

“…A particle size distribution was then obtained consisting of the large cyclone particles and the 13 stages in the DLPI corresponding to particle diameters from 30 nm to 10 μm. Details on a similar probe and analysis system can be found in the work by Jonsson et al [1]. The extracted particle mass in the low-pressure impactor and the cyclone was recalculated following the methodology presented in Ref.…”

“…This process combines a travelling grate and a rotary kiln in which the pellets are dried, oxidized and sintered. A description of a typical grate-kiln pelletization plant can be found in the work by Jonsson et al [1]. The fuel used in these plants is often coal, and the emissions of CO 2 from combustion of fossil fuels, such as coal and oil, in the industrial sector have been recognized as necessary to address to comply with future climate targets [2].…”

Iron Ore Pellet Dustiness Part II: Effects of Firing Route and Abrasion Resistance on Fines and Dust Generation

“…For example, inside of induration furnaces, dust particles from pellets and coal combustion deposit on furnace walls and degrade refractory liners (Jonsson et al 2013). Furnace gases must then be extensively scrubbed using wet scrubbers, cyclones, baghouses, or electrostatic precipitators (Bolen 2014) before they are emitted to the atmosphere.…”