Syngas preparation by NiO–CaSO4-based oxygen carrier from chemical looping gasification technology

Abstract

Phosphogypsum (PG) is a by-product in the phosphate fertilizer industry with high production. It is necessary to alleviate the problem of the storage pressing of PG. Nowadays, PG is applied as an oxygen carrier in lignite chemical looping gasification (CLG) in order to prepare syngas. In this process, the reaction temperature is usually above 1173 K, requiring much energy to reach this temperature. Here, the Ellingham diagram has used as a guide to finding the active phase of NiO combining with PG to prepare the NiO–CaSO4 composite oxygen carrier. Using a variety of characterization techniques, it was found that in the oxygen carrier NiO–CaSO4 with the waste-PG has a good dispersion of Ni specie. After analyzing the activity of the as-obtained oxygen carrier, it was demonstrated that the NiO–CaSO4 could reduce the reaction temperature, resulting in reduced energy consumption. Notably, the oxygen carrier is essential for lignite conversion and CO and CO2 production, especially for H2 production. To promote the preparation of CO, the recommendable molar ratio of Ni element to PG is ≈ 1:1. As the number of cycles increases, agglomeration and cracks are occurring on the surface of the material. Based on these results, this work provides an oxygen carrier with the waste to reduce the reaction temperature for chemical looping and offer recommendations for future research.