Lignin as Both Fuel and Fusing Binder in Briquetted Anthracite Fines for Foundry Coke Substitute

Open Access
Author:
Lumadue, Matthew Robert
Graduate Program:
Environmental Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
January 11, 2012
Committee Members:
  • Fred Scott Cannon, Thesis Advisor/Co-Advisor
Keywords:
  • Lignin
  • Coke
  • Pyrolysis
  • Binder
  • Strength
  • Cupola
Abstract:
Lignin that had been extracted from Kraft black liquor was investigated as a fusing binder in briquetted anthracite fines for a foundry coke substitute. Cupola “heat zone” pyrolytic temperatures of 300-1550°C were appraised, with the focus on 900°C. Briquettes with favorable strength were made with 86-92% anthracite fines, 2.3-8.6% lignin, 4.5% silicon metal powder, and 0.9% hydrolyzed collagen (gelatin) by mass. Briquettes were pyrolyzed under a nitrogen atmosphere or a starved air condition to simulate a cupola pyrolytic heat zone, and then crushed after this pyrolysis so as to discern their unconfined compressive (UC) strength. These tests mimicked key features of the crushing load that coke endures in a cupola. After 30 minutes of 900°C pyrolysis, UC strength reached 2,200-3,000 kPa (320 to 440 psi), when these briquettes contained 4.5% softwood lignin or 2.3% hardwood lignin. With ≥ 6.5% hardwood lignin, the UC strength after 900°C pyrolysis reached 6,000-6,500 kPa. When no lignin was incorporated to the briquette, the UC strength after 900°C pyrolysis was 200 kPa. Gelatin quantity affected lignin heat zone strength, despite by itself losing strength around 300°C: 1.8% gelatin doubled the strength of 0.45% gelatin briquettes. Lignin provided strength up to 1400°C. Moreover above 1100°C, silicon carbide nanowires greatly enhanced UC strength relative to lignin alone. Briquettes gained strength from lignin fusing reactions that increased in rate with increasing temperature. For example, at 900°C, maximum UC strength occurred within 2-3 minutes of pyrolysis. From the UC strength vs. pyrolysis temperature/time, an Arrhenius plot was constructed, which exhibited activation energies of 26-28 kJ/mol. Both the softwood and hardwood lignin briquettes exhibited the same activation energy, with the hardwood Arrhenius plot higher but parallel to that for softwood. A manufacturing rationale for using bindered anthracite fines rather than large chunks of anthracite is to obtain a fast burning rate. The results herein showed that the bindered briquettes burned at an equal rate as did coke when these were burned at 1100°C in air. The briquettes also contained an energy density that was 38% higher by volume than that of coke. FTIR characterizations of pyrolyzed lignin showed that as temperature increased, oxygen-containing functionality decreased. Further, Raman spectra of 900°C lignin and ambient coke (commercially pyrolyzed bituminous coal) showed almost identical responses to one another, with each exhibiting both the graphitic, G, and first disorder, D, bands. Harnessing these high temperature pyrolytic lignin fusing reactions creates a valuable foundry coke substitute for the future, as well as large scale applications for otherwise underutilized industrial streams of lignin.