The Comparison Between IISc Open Top Gasification System And Others
All the existing designs are closed top designs using MS as outer wall and the reactor also acting as a storage bin. They are all based on World War II class designs.
The IISc design is the only open top twin air entry system in the world for woody class of biomass.
It is a multi-solid biofuel system. It can accept biomass of varying sizes, ash content and reactivity. All light and pulverisable biomass would be dried, pulverized and briquetted at sizes appropriate for the power level. All solid biomass will need to be sized appropriately.
It can accept coconut shells broken to size with no problems of tar; On the other hand, one gets high quality activated char through the use of coconut shells.
Closed top designs are seriously prone to tar problems with biomass like coconut shells.
The IISc design is shown to accept rice husk briquettes, and urban solid waste briquettes with good performance.
The reactors for rice husk from China and adopted by other manufacturers noted above are also open top designs. But they are not twin air entry. The twin air entry system is crucial to good quality gas.
The choice of the twin air entry is done so as to have high enough temperatures for tar cracking and low enough to prevent ash fusion that will be caused by high potassium filled residues (like sugarcane wastes, for instance).
The advantages of open top twin air entry system are (a) low tar fraction in the gas at a wide variety of loads demanded of the gasification system, (b) gas quality which permits diesel replacement in diesel engines up to 85 % in non-turbo-supercharged engines, whereas even according to the best claims of closed top WW II class designs in our country the maximum diesel replacement is 70 %.
The peak output on producer gas engine –alternator system is 15 to 20 % more from IISc design than closed top designs because of better gas quality.
The IISc design has a ceramic shell in the most critical zone and thus promises much higher life compared to other systems. Even in other chemically or thermally affected zones specific coatings are provided to prevent corrosion.
The IISc system has been tested by an international team of experts at IISc and in Switzerland. The test reports have been published and examined by a large number of experts in India and overseas.
This testing of the system has taken place at 100 kWe and 500 kWe levels. At power levels of 500 kWe, no gasifier in the world has been tested and this is unique to IISc system.
Performance of the systems in field locations are documented and made available to users, scientists, senior administrators so that better appreciation of the problems, solutions and status of systems is possible. This is particularly needed with new Technologies of the kind discussed here.
An additional advantage of the adoption of this technology is that IISc will provide technical back up on all difficult-to-resolve issues that may crop up from time to time.