Predicting the vanadium speciation during petroleum coke combustion by thermodynamic equilibrium calculation

Abstract

Petroleum coke (petcoke), as a substitute for natural gas and fuel oil, has been burning in boilers for heat and power production. The high content of vanadium (V) in petcoke is responsible for ash-related problems including fouling, corrosion and deposition. Thus, the behavior of V during petcoke combustion has become a subject of concern both in science and engineering. In this paper, thermodynamic equilibrium calculations were performed to investigate the V speciation with the presence of main associated mineral elements (Si, Ca, Al, Fe, Ni and Na) during petcoke combustion. The results demonstrate that V participates in the reactions with Ca, Fe and Na, yielding V-containing chemical compounds (CaO)V2O5(s), (CaO)2V2O5(s), Fe(VO3)2(s) and (Na2O)V2O5(s), respectively. The formation of liquid species NaVO3 also takes place. Moreover, no interactions of V with Si, Al and Ni occur because no other V-containing species is formed over the whole range of temperatures. However, the associated mineral elements may co-influence the V species equilibrium compositions dramatically. The formation of CaSiO3(s) and CaAl12O19(s) occurred at 1600 °C restrains the (CaO)2V2O5(s) production. Ca reacts with Si and Al to form CaAl2Si2O8(s), impeding the formation of (CaO)2V2O5(s). Na can also combine with Si and Al to generate NaAlSi3O8(s), inhibiting the (Na2O)V2O5(s) and NaVO3(l) production. It should be noted that VO2(g) exhibits high volatility (more than 90% (mol mol−1)) at high temperatures (1600 °C), whereas the presence of Ca results in a reduction in volatility of VO2(g) due to the formation of (CaO)2V2O5(s).