Studies on Microwave-Assisted Pyrolysis of Rice Straw Using Solar Photovoltaic Power

Pyrolysis of one of the most underutilized lignocellulosic biomasses, namely rice straw (RS) has been carried out through solar photovoltaic (PV)-powered microwave heating with biochar as an additive for the microwave absorption. Through the preliminary studies, microwave power of 700 W and reaction times of 20 min have been chosen optimum for maximizing the yield of bio-oil, a desired product for the study along with biochar ignoring gas, due to their easy collection, storability and transportation and higher commercial value. The results of the study revealed the highest yield of bio-oil as 25% and 23% with and without additive respectively. The net energy recovery percentage was calculated to be around 71 and 56 in using solar PV and grid electricity respectively. The exergy efficiency of pyrolysis system under this study was estimated to be about 55%. The payback period of the set-up is 6.5 and 3.12 years if solar PV system and grid electricity are respectively used. The monthly income of $ 33 may be earned from the pyrolytic products such as biochar, wood vinegar and tar by pyrolysing 675 kg of RS annually (2.25 kg per day at 450 g per batch with 5 batches per day and 300 days per year). The potential of mitigating CO(2)emission during the total life time of 30 years from the existing set-up is 55 tons and the earning of carbon credit is $ 1600 considering the current price of carbon credit as $ 30/ton.

Automated summary

The pyrolysis of rice straw using solar PV-powered microwave heating with biochar as an additive is effective in maximizing the yield of bio-oil and biochar. The study showed higher commercial value and energy recovery percentage with the use of solar PV compared to grid electricity, with an estimated exergy efficiency of 55%.