Observation of Behavior of Dioxins and Some Relating Elements in Iron Ore Sintering Bed by Quenching Pot Test

Abstract

Understanding of the formation mechanism of dioxins in the sintering bed is of importance in developing countermeasures to reduce the emission of dioxins from sintering plants. This research has clarified the behavior and the possible mechanism of dioxin formation and the relation to Cl and Cu components in the sintering bed by conducting a series of quenching tests utilizing sintering pots.The progress of flame front was quenched by terminating the air supply, then introducing N 2 gas in the reverse direction when the sintering process progressed halfway through the test pots, specifically to the position of the thermocouples. The primary specimens were obtained from the raw mixture zone situated beneath the combustion interface for chemical analysis.Concentrations of dioxins, Cl and Cu were found at the depth of 10-20 mm beneath the combustion interface in raw mixture zone. This was considered to be the site of dioxin synthesis. Slight increase of dioxins in the wet zone was related to dioxin vaporizing from the site of the synthesis, then to be trapped in this zone. Significant amounts of dioxins escaping into the outlet gas at and after burn through point could be explained by both the releasing of trapped dioxins and the acceleration of the synthesizing process attributable to the increased concentration of Cl and Cu.KEY WORDS: agglomeration; copper; chlorine; dioxins; iron ore sintering; sintering bed.series of experiment, which was conducted to examine the influence of the use of Ore C containing a higher Cu content. The type and quantity of additives were varied according to the purpose of experiment. As the base condition of the experiment, 200 mg/kg NaCl was added to a raw mixture, so as to accelerate the dioxin formation during sintering to a detective extent. The chemical composition of the sintered product aimed for 5.1 mass% as SiO 2 , 9.5 mass% as CaO, and 1.9 mass% as Al 2 O 3 .The sintering pot was 300 mm in diameter and 600 mm in height. To quench the sintering at a specified position, a thermocouple was inserted into the bed at 400 mm from the top of the bed. Upward N 2 gas flow was applied to stop the combustion of coke and cool the bed when quenching (Fig. 1). Procedure of Sintering and QuenchingThe raw mixture was mixed for 60 s and granulated with adding water for 180 s in a drum-type mixer of 1 m in diameter. The moisture content was set at 6.5 mass%. The granulated mixture was charged into a pot to form a bed with 560 mm in thickness. The average mass of charges weighed 66 kg. After ignition at 1 100°C for 90 s, the sintering process was conducted under a constant suction pressure of 12 kPa.The quench technique applied in the present study was basically follows after Soma et al. 14) Quenching proceeded as follows: when the thermocouple gave the maximum bedtemperature, the main blower was stopped and simultaneously N 2 gas was introduced from the bottom of the pot. For experimental series 1 and 2, the flow rate of the N 2 gas was set at 0.3 Nm/s. It required 2 h to cool the bed. For se...

Identification the Content of the Windbox Dust Related to the Formation of PCDD/Fs during the Iron Ore Sintering Process

“…It might be because the involved raw materials for the iron ore sintering process, such as iron ore and return fines, were abundant in both K + , and Na + (Cieplik et al, 2003;Nakano et al, 2005). The above results were also comparable to that conducted by Tsai et al (2007).…”

“…Several laboratory studies have used alkali chlorides as raw material additives (act as catalysts and chlorine sources) to investigate the formation of PCDD/Fs during iron ore sintering process. They found that the alkali chlorides, such as NaCl and KCl, might catalyze the de novo synthesis (Kasai et al, 2001b;Cieplik et al, 2003;Kuzuhara et al, 2003;Nakano et al, 2005). Table 2 show the comparison between the amounts of alkali chlorides added in the above reference studies and the contents of K + , Na + and Cl -found in the present study.…”

“…The above result was quite comparable to that conducted by Tsai et al (2007), although their dust samples were collected from the stack rather than from the windbox. In principle, the high Cl -contents were quite expectable since the iron ore and coke used in this sintering process contains ~200 and 100 mg/kg of water-soluble chlorides (Nakano et al, 2005). But for SO 4 2-, its high content might be contributed mostly by the sulfur content containing in the fuels (such as coke oven gas (COG) and coke breeze for igniting the burner).…”

“…The above result is quite comparable to the results conducted by Tsubouchi et al (2006) and Tsai et al (2007). In principle, high Al, Fe, K, Pb and Ca concentrations found in the WB dust samples might be because: 1. fluxes, iron ore fines and coke breeze used in the iron ore sintering process could contain a variety of impurities, including Al 2 O 3 , and K 2 O (Cieplik et al, 2003;Nakano et al, 2005;Sammut et al, 2010); 2. the use of limestone (CaCO 3 ) and dolomite (CaMg(CO 3 )) as fluxes in the sintering process (Cieplik et al, 2003); and 3. the return fine used in the sintering process usually contains Pb compounds (Sammut et al, 2010). Among these five metal contents, several studies have shown that the existence of Fe and K might lead to the increase in PCDD/Fs formation (Hinton and Lane, 1991;Nganai et al, 2009;Fujimori et al, 2009).…”

An Overview of PCDD/F Inventories and Emission Factors from Stationary and Mobile Sources: What We Know and What is Missing

“…De novo synthesis is proposed as the dominant PCDD/F formation mechanism due to PCDF mean concentrations in the stack flue gas are generally higher than those of PCDD representing over 80% of the total concentration (Wang et al, 2003b;Aries et al, 2006;Sun et al, 2016). Nakano et al (2005), concluded that the dry zone layer was the primary area of PCDD/F formation in the sinter plant. The temperature range within this layer is between 100 to 1000°C (Arion et al, 2002), with presence of carbonaceous material from the coke and/or soot from the ESP when recycled.…”