Upgrading of 6–0 mm low rank high sulfur lignite by a compound dry cascade separation bed

Abstract

In this paper, the effect of vibration intensity on the spatial distribution of sulfur content in bed particles was studied. The effects of vibration and airflow on the mechanical characteristics of particles were studied, the collision behavior mode of particles was determined, the spatial saltation law of particles was investigated, the spatial functional axis of beds was determined, and the saltation separation period of particles was determined. The test results show that: When separation bed provides inlet airflow velocity (Uin) is 2.55 m/s, the airflow distribution interval of I, II and III areas were UI=2.55–2.57 m/s, UII=1.33–1.35 m/s, UIII=0.35–0.38 m/s, respectively; when separation bed vibration amplitude (A) A=2.4–2.5 mm, separation bed vibration frequency (f) f=23–24 Hz, the desulfurization effect is the best. When vibration intensity (C) C=1.22, Uin=1.05 m/s, the particles have disordered contact and collision behavior. When C=14.89, Uin=3.18 m/s, the particles have a transition cataclastic collision. When C=5.80, Uin=2.55 m/s, the particles have directional collision behavior. It is determined that the OX axis is the transverse stable diffusion axis of the material, the OY axis is the longitudinal gradient transport axis of the material, and the OZ axis is the vertical density cascade distribution axis of the material. When separation time (T) T=0–10 s was the period of disorderly diffusion and mixing of particles, T=10–20 s was the period of directional migration and stratification of particles, and T=20–30 s was the period of cascade distribution and separation of particles. Finally, separation experiments conducted under optimal operating parameters demonstrated that the clean coal yield was 72.02% with a sulfur content of 0.98%.

1. Introduction

Energy serves as a critical material foundation for the economic and social development of humanity [1]. In China, the predominance of coal as the primary energy source is a fundamental national condition, making coal the ''ballast stone'' of energy security. Following the end of the COVID-19 pandemic, global coal production capacity and utilization efficiency have shown an upward trend in the post-pandemic era [2,3]. According to the World Energy Statistical Yearbook 2024, global coal production in 2023 reached 9.096 billion tons, with China''s coal production accounting for 4.71 billion tons, representing 51.8% of the global total. This underscores China''s position as the leading producer and consumer of coal worldwide [4,5].

Lignite, characterized by its low degree of coalification, exhibits high moisture content, low calorific value, and strong chemical reactivity [6]. As high-quality coal resources are progressively depleted, energy security faces significant challenges. Against this backdrop, the development and efficient utilization of low-grade lignite resources have become pivotal for mitigating energy shortages and ensuring energy security [7]. Globally, lignite resources are abundant, with total reserves of approximately 2622.9 billion tons, accounting for about 40% of total coal resources. China''s lignite reserves total 211.8 billion tons, approximately 13% of the national coal resource base, with over three-quarters concentrated in northern China, particularly Inner Mongolia, which alone holds 166.7 billion tons or about 70% of the total lignite resources [8,9]. Fig. 1 illustrates the distribution of lignite resources globally and in China.

The primary applications of lignite include power generation as fuel, chemical raw materials, catalyst carriers, carbon adsorbents, wastewater purification, and metal recovery. However, lignite''s low degree of coalification results in an unstable structure, making it prone to spontaneous combustion and fragmentation, thus unsuitable for direct combustion or transportation. Additionally, its high content of inorganic mineral impurities poses environmental risks, as [truncated]