Optimization of process parameters for conversion of pine needles to bio-oil, biochar and product gas through batch and continuous pyrolysis
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Date
2018-04
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G.B. Pant University of Agriculture and Technology, Pantnagar - 263145 (Uttarakhand)
Abstract
Experiments were conducted to convert pine needles into bio-oil, biochar and product gas through pyrolysis as an alternate way to use pine needles to reduce forest fire. Batch pyrolysis of pine needles was carried out in a stainless steel tubular reactor using CO2 as sweep gas. Process parameters such as pyrolysis temperature, gas flow rate, vapour cooling temperature, heating rate, holding time were optimized by employing central composite design (CCD) in Response Surface Methodology (RSM) for the batch process. Continuous pyrolysis experiments were conducted in a screw reactor using N2 as sweep gas. Process parameters were optimized by Taguchi’s L9 Orthogonal Array. A batch type biochar production unit was also designed and developed to convert pine needles to biochar in bulk. Chemical characterization of bio-oil was conducted using Fourier Transform Infrared (FTIR) spectroscopy and gas chromatographic/mass spectroscopy (GC/MS). Fuel properties of bio-oil and biochar were determined using ASTM standard methods. Product gas composition was determined using gas chromatography. Bio-oil was produced from pine needles with a recovery rate of 26.7 wt.% in batch pyrolysis experiment and 28.98% in screw pyrolysis. The adaptation of response surface methodology indicated the optimum conditions for maximum bio-oil yield at pyrolysis temperature of 547C, 1.85 l min−1 gas flow rate, 15C vapour cooling temperature and 50C min−1 heating rate. The optimum conditions in screw pyrolysis experiments were pyrolysis temperature of 500C, particle size of 1.25 – 2.0 mm, residence time of 15 min and N2 gas flow rate of 30 l h–1. Bio-oil produced at optimum condition had a high heating value of 28.52 MJ kg−1 and had less oxygen content than parent material. The GC/MS analysis showed presence of about 50% phenolic compounds and many other valuable compounds. Conversion efficiency of the biochar production unit with pine needle as substrate was found to be 28.88% at 80% loading, 12% moisture and air flow rate of 40 m3 h1. Bio-char had a higher pH value and high heating value with suitability for both acid soil ameliorant and solid bio-fuel. The average composition of product gas was 6.8% H2, 65.7% N2, 3.9% CH4, 10.46% CO, 12.1% CO2 and 1.06% C2H4 with a high heating value of 4.16 MJ Nm3. The quantitative results of energy analysis indicated that the all three processes could be used to produce bio-oil, biochar and product gases to recover energy from pine needles. Among three processes, screw pyrolysis process was most energy efficient.
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