Evaluation of Ultrasonic Cavitation Treatment Effects on the Beneficiation of Bituminous Coal

Open Access
Author:
Barry, Branden Lane
Graduate Program:
Energy and Mineral Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
June 09, 2014
Committee Members:
  • Mark Stephen Klima, Thesis Advisor
Keywords:
  • Ultrasonic
  • Cavitation
  • Bituminous Coal
  • Energy and Mineral Engineering
  • Hydrocyclone
  • Filter Press
  • Pressure Filtration
Abstract:
Laboratory testing was conducted to evaluate the effects of hydroacoustic cavitation (HAC) treatment on two bituminous coal slurries and the performance of various subsequent separation processes. Separation process units studied were the hydrocyclone, spiral concentrator, froth flotation, and plate filter press. The pilot-scale HAC circuit consisted of a stainless-steel ultrasonic resonator chamber and in-line flow reduction cavitation orifice. The two materials processed were nominal -1-mm and -0.15-mm Illinois Basin bituminous coal slurries. The -1-mm material (Sample A) was the feed stream to a coal preparation plant classifying hydrocyclone while the -0.15-mm material (Sample B) was the overflow stream from the same hydrocyclone. Laboratory analyses showed that Sample A had an value of 34.44±2.28% and was 4.16% total sulfur while Sample B had an ash value of 53.39±1.16% and was 2.3% total sulfur. Over 70% of the total sulfur was pyritic sulfur for both samples. Heating values were 8,656 Btu/lb and 6,423 Btu/lb for Sample A and Sample B, respectively. HAC treatment of Sample A demonstrated that 100% power sonication (Son) and 100% power sonication with all slurry flow through the cavitation orifice (SonCav) reduced feed particle size and ash values of coarser size intervals (+150 μm). After only 5 s of treatment, the 50% cumulative passing size was reduced by about 50 μm with ash values for certain size fractions decreasing over 5% between untreated and SonCav tests. Extending treatment time led to greater degradation of the +1180-μm material with increases in the -25-μm material and reductions in ash values of central size fractions (-850+150 μm). Utilizing the hydrocyclone at an inlet pressure of 20 psi, solids splits to the underflow stream of about 90% and 40% were achieved for Sample A and Sample B, respectively. HAC treatment concentrated sulfur in the underflow stream while reducing underflow ash values and increasing heating values as compared to the feed material. From untreated to SonCav treatment, ash was reduced by about 16% for Sample A and 25% for Sample B while heating value increased 7% and 33% for Sample A and B, respectively. Hydrocyclone desliming of Sample A followed by spiral concentration of the underflow stream was effective at reducing ash and total sulfur values of the feed material. SonCav treatment prior to hydrocyclone desliming and spiral concentration produced a yield of nearly 70% with reductions in ash value of almost 60% and total sulfur by 6%. The spiral negated the effect of hydrocyclone concentration of sulfur in the product stream. Desliming Sample B by hydrocyclone followed by froth flotation reduced yields about 33% despite HAC treatment, but reduced ash values by almost 40% in some instances. Decreasing flotation time led to more dramatic reductions in product ash values (>70%) but yields were poor (~10%). The effects of desliming were more prominent than treatment in reducing ash and sulfur values for the froth product. Pressure filtration of Sample B by plate filter press was minimally affected by HAC treatment in terms of cake moisture content as treatment caused high levels of feed stream dispersion and surface fine liberation. Reduction of filter press feed slurry pH to 4 and flocculation by a high molecular weight polymer had more noticeable effects, decreasing final cake moisture. Test runs for an untreated and 5-min SonCav treated feed stream which was flocculated and pH reduced exhibited the best performance, reaching a final cake moisture of about 36%.