A Role of Mineral Oxides on Trace Elements Behavior during Pulverized Coal Combustion

Abstract

The issues of trace element emissions during coal combustion has been a concern in recent years due to their environmental pollutant. To study the trace element transformation, the thermodynamic calculation (FactSage 7.2) was used. Five kinds of pure mineral oxides (Al2O3, CaO, Fe2O3, K2O, and MgO) and As, B, Cr, F, and Se in fly ash were considered for trace elements. The results confirm that all mineral oxides have a good correlation with arsenic to form Ca3(AsO4)2, FeAsO4, K3AsO4, and Mg3(AsO4)2. Boron has a good relationship with Al, Ca, and Mg to form (Al2O3)9(B2O3)2, Ca3B2O6, and Mg3B2O6. Chromium has a good correlation with K and Ca to form K2CrO4, CaCr2O4. Furthermore, FeF3(s) KF(s), and AlF3(s) are predicted from the interaction of fluorine with Fe2O3, K2O, and Al2O3. The effect of mineral oxides on selenium partitioning are not observed. The inhibition order of trace elements by mineral oxides is as follow: As (Al2O3 > MgO > CaO > Fe2O3 > K2O), B (Al2O3, CaO, Fe2O3, K2O, > MgO), Cr (CaO > K2O > Al2O3, MgO, Fe2O3), F (CaO > MgO > Al2O3 > Fe2O3 > K2O). The results will be useful to control the trace element emissions.

Thermodynamic research on the effect of CaO on the transformation of arsenic and sulfur in coal in different pyrolysis atmospheres

“…Even though there are numerous pieces of literature about the effect of Ca on arsenic 2,4,23,28 or sulfur [34][35][36][37][38] separately, there are not too many papers about the effect of Ca on arsenic and sulfur together. The current related literature includes experimental work, 6,11,21,39 thermodynamic equilibrium calculation, 40 and kinetic behavior.…”

“…Duan 22 studied arsenic transformation in oxy‐fuel combustion, it was found that Arsenic, As 2 , and AsN are three dominant species from 900°C to 1400°C. The role of mineral oxides on arsenic behavior in coal combustion was studied by Kambara, 23 the result shows that arsenic has a good correlation with most of the mineral oxides, forming Ca 3 (AsO 4 ) 2 , FeAsO 4 , K 3 AsO 4 , and Mg 3 (AsO 4 ) 2 . Meng 27 examined arsenic between condensed and gaseous phases in coal combustion, the calculated results have a good match with experimental data.…”

“…The thermodynamic simulation is a useful tool to study the conversion process of sulfur in solid particles, with the influence of feed, reactor temperature, and other operational parameters. A few modeling software packages have been developed, such as Aspen Plus, 18 Fact, [19][20][21][22][23] Alex, 24 HSC Chemistry, 25,26 and so forth. Each chemical equilibrium is achieved when entropy is maximized and Gibbs free energy is minimized.…”

Functional Predictor Variables for the Leaching Potential of Arsenic and Selenium from Coal Fly Ash

“…In general, all major elements showed a negative correlation with leachable arsenic and selenium, for which these trends were consistent with adsorption by and co-precipitation with particles comprising the major elements. 23,55 In other words, solid phases that comprise Fe, Al, and Si can host As and Se species in coal and encapsulate As and Se in the combustion process, leading to less As and Se in fly ash leachate. Moreover, the specific role of the host mineral phases in reducing the leachability of As and Se is difficult to determine in light of the complex interactions between host mineral dissolution, re-precipitation, and desorption/re-adsorption of trace elements during the fly ash leaching process.…”

“…22 Moreover, thermodynamic calculations based on minimization of the Gibbs free energy at coal combustion temperatures demonstrate the possibility of distinct arsenic phases, including AlAsO 4 , Ca 3 (AsO 4 ) 2 , and FeAsO 4 . 23 Selenium in fly ash occurs in a variety of oxidation states, including elemental selenium (Se 0 ), Se IV (e.g., selenite SeO 3 2− ), and Se VI (selenate SeO 4 2− ). 24,25 Even though thermodynamic models of Se speciation under combustion conditions suggest that SeO 2 is the most stable form, previous research has found that Se 0 (g) , SeO (g) , and SeO 2(g) tend to chemically or physically adsorb onto Fe-or Ca oxide surfaces.…”