Background:
India produces a large amount of rice straw; wheat straw and sugarcane wastes which are burnt abundantly to clear fields for the next crop. This burning adds huge number of pollutants to the atmosphere. Conversion of these waste biomasses to char is environment friendly and cost-effective solution because of its carbon neutrality or carbon negativity. A continuous pyrolysis system can deliver a higher capacity of production of bio-char. From extensive interaction with the farmers and visits to the villages it was found that they have an increased interest towards utilizing crop residues for fetching remunerations. Due to lack of proper technological support, they are unable to do so. The proposed technology is capable of converting crop residues to two valuable products, fuel and bio-char, both of which will bring good monetary return:
Technology Details:
The technology described here is a screw pyrolysis reactor that has been designed for continuous production of bio-char from crop residues. The unique feature of the unit is that it is heated by producer gas and no electricity is used for heating purpose. Its effective length is 1200 mm, inside diameter is 275 mm, wall thickness is 5 mm and made of stainless steel. A screw of 265 mm outer diameter and 100 mm flight has been used for material transport inside the reactor. Screw shaft diameter is 40 mm. The shaft is rotated by a 2 hp geared motor and speed is controlled by a VFD drive. Feeding is done by a rotary airlock valve controlled by a VFD. Size of biomass particle should be <1.5 mm for smooth running of the feeding unit. Product gas after being withdrawn from the reactor is passed through three cooling cylinders where volatiles are condensed using cold water spray. Six burners have been provided at the bottom of the reactor for heating. Producer gas is generated by using a downdraft gasifier attached with the unit. Maximum temperature reached inside the reactor is 450°C. Feeding rate can be varied from 10 kg /h to 20 kg/h. The average recovery was found to vary from 20% to 48%. It was seen that with increasing loading rate there was higher recovery but fixed carbon content reduced in the bio-char indicating lesser carbonization.