Technical, financial and environmental assessment of bio-oil production from pyrolysis of pigeon pea [cajanus cajan (L.) millsp.] wood

Abstract

Pigeon pea (Cajanus cajan (L.) Millsp. wood was pyrolyzed using a semi-continuous gram-scale reactor at optimized conditions of temperature (469°C), nitrogen flow rate (14.2 mL min-1), and particle size (1.3 mm), yielding bio-oil (54%), biochar (26%), and syngas (16%). The cost of bio-oil production for 1 t yr-1 was estimated to be US$ 681.00. Financial analysis revealed a net present value (NPV)of US$ 24,322.00 at 12% discount rate, an IRR of 343.85 %, with breakeven quantity of 199 L. Sensitivity analysis showed that an increased price of raw materials up to 30 %, and a decreased price of products down to 25 %, resulted to an increased NPV and IRR. Decreasing the bio-oil yield below 40 % gave a negative NPV with an IRR of 9%. If bio-oil and biochar were tapped as alternative bioenergy, 360,000 L of fuel oil and 259 t of coal could be saved. A total greenhouse gas emission of 749 t of CO2 equivalent can be avoided. Thus, pigeon pea pyrolysis for bio-oil production provided a net positive energy output and was proven to be profitable investment, and environment-friendly as potential bioenergy resource to replace petroleum-based fuels.