Tar Cracker cum Effluent Evaporator:
Tar has remained a major problem and concern for gasification technology. In all previous/old gasifier, tar is condensed and collected and physically removed and used either as coal tar in road making or in boiler or spray drier furnaces. During this process physical tar handling and burning a tremendous amount of VOC’s i.e. volatile organic compounds which are dangerous are emitted and create tremendous health hazards. Further, the combustion of tar in spray drier, boiler or furnace is also not advisable unless a residence time of 2 seconds at 12000C is provided to eliminate furans and dioxin from the product gas which is most dangerous pollutants.
In the present technology, first there is no physical movement or supply of tar and second no subsequent combustion in spray drier or any other boiler or furnace. Here a novel tar cracker is designed where in tar is cracked and reformed in presence of steam by indirect heating in a rotary tar kiln. The tar is collected in a tar storage tank which is water seal controlled so that VOC emission does not exist. The tar from tar tank is pumped to rotary tar cracker kiln inner pipe from where it is sprayed to a hot rotating catalytic metal shell of kiln which is maintained at temperatures of 550C to 650C and hence the tar is vaporized. The effluent from effluent storage tank which is also water seal controlled so no chances of VOC or gas leakage, is fed through high pressure pump in outer pipes in rotary kiln which is sprayed through spray nozzles on the inner hot rotary shell of the kiln and gets converted into steam. This steam and vaporized tar reacts with each other and tar gets reformed to a mixture of combustible and non-combustible gases. This mixture is taken to heat recovery unit from where it is refired back to oxidation zone of gasifier by a high pressure blower. The temperature levels in this zone being of the order of 1200° C to 1300° C; even thermal cracking of tar is achieved.
Thus, the energy of tar is 100% reutilized in the system which offers much better gasification efficiency. Also all the contaminated effluent is evaporated and refired back in the oxidation zone of gasifier. Hence there is no discharge of effluents.
Thus, this rotary tar-cracker kiln cum effluent evaporator is a unique feature of the present design which offers zero tar and effluent discharge, with zero gas and VOC leakage along with much better conversion efficiency.
Further, the complete operation of this tar cracker cum effluent evaporator is temperature controlled through SCADA and a mechanical safety valve as well as flame sensor is also provided which offers utmost safety to the entire system.