Impact of reacting pressure on Na thermal transformation in two full‐scale devices using Zhundong coal at similar temperature

Abstract

Gasification and combustion are two common methods for Zhundong (ZD) coal utilization. In the present study, it was intended to investigate the thermal transformation of Na in ZD coal at the Lurgi fixed bed gasifier (Lurgi) and circulating fluidized bed boiler (CFBB). To this end, raw coal samples before gasification and gasified slags were gathered from Lurgi, and the raw coal before combustion, burned slag, and fly ash were collected from CFBB. The occurrence form of Na was analyzed by extraction experiments, and the samples were analyzed by inductively coupled plasma-optical emission spectrometry (ICP-OES), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The obtained results revealed that insoluble Na in Lurgi slag exceeded 90% under the high-pressure gasification process. It was found that the high temperatures and high in Lurgi intensify the conversion of sodium to Na 2 Ca 3 Si 2 O 8 and NaAlSiO 4 . The performed analyses revealed that the insoluble Na content in CFBB slag and fly ash was above 92%, and Na 2 SiO 3 and NaAlSi 3 O 8 were the main sodium minerals in CFBB solid residue. It was found that 76.64% of the initial Na content of raw coal in Lurgi migrated into slag after the gasification process, which was 7.05% higher than the sum of slag and fly ash in CFBB after combustion. During the sodium thermal transformation in Lurgi and CFBB, high pressures significantly reduce the release of gaseous Na from coal ash so more Na was retained in slag.