Aimed at offering technologies to produce clean energy for small scale projects, Nimbkar Agriculture Research Institute (NARI) has developed an eco-friendly commercial-scale gasifier for thermal applications.
Equipped to utilise low density and leafy biomass materials like sugarcane leaves, bajra stalks & sweet sorghum, the technology also produces char which can be briquetted to form an excellent fuel for wood stoves or can be used as a soil conditioner.
A specifically designed high temperature resisting induced-draft fan ensures that the entire system is under negative pressure so that in the event of leaks, outside air gets sucked into the system, but the combustible gas does not leak out making it very environment-friendly.
Innovator Dr Anil K Rajvanshi, Director, NARI informs, “Initially developed in the year 1997, the technology has been tested for more than 700 hours under laboratory conditions at 288-1080 MJ h-1 output levels.” Sharing his experience on the efficiency of the model, he further elaborates, “After successful laboratory testing, it was found that the gasifier can be successfully retrofitted to existing oil-fired furnace/boilers in metallurgical and other industries. The product quality is on par with, if not better than, that obtained during oil fired production.”
The major attribute of the model is that it has a gas conditioning system which is a dry dust collection system eliminating the problem of wastewater. “A specifically designed high temperature resisting induced-draft fan ensures that the entire system is under negative pressure so that in the event of leaks, outside air gets sucked into the system, but the combustible gas does not leak out making it very environment-friendly,” Dr Rajvanshi explains.
User Friendly and Economical
Extremely simple to operate, two operators on per shift of eight hours are required to operate the system, including the fuel and ash handling operations.
“Economics of the system is also very attractive if the landed cost of biomass, including drying and sizing, is less than `1350 T-1 for capacity of 1080 MJ h-1. At higher capacities, the economics will be even more favourable for the gasification systems,” Dr Rajvanshi concludes.
Gasification System Design
While designing the gasifier, certain critical engineering design norms of the gasification system were first developed on a laboratory-scale model and were then validated on a bench-scale model. These norms were then used to design a full-fledged commercial scale system with a thermal output of 1080 MJ h-1.
The Bio Mass Gasifier comprises of a reactor, a gas conditioning system, a biomass feeding system and the instrumentation and controls. The salient features of these components are given below.
a. Reactor: This is a downdraft, throatless and open-top reactor with an internal diameter of 75cm and an active bed height of 1.25m. It is designed for a heavy-duty cycle of 7500 hour per year operation. High temperature resisting firebricks conforming to IS 8 grade are used for the hot face followed by a cold face insulation.
b. Gas conditioning system: A completely dry dust collection system eliminates altogether the problem of wastewater. This consists of a high temperature char/ash coarse settler and a high efficiency cyclone separator. The char-ash from the coarse settler and the cyclone is collected in barrels and emptied in an ash pit once every 45 minutes. This char-ash which typically has a gross calorific value of 18.9 MJ kg-1 can be briquetted to form an excellent fuel, or can be used as a soil conditioner.
c. Biomass feeding system: This consists of a scraper drag-out conveyor and a hopper to convey the biomass fuel from the storage pile to the reactor. The conveyor is completely enclosed.
d. Instrumentation and Control System: A Programmable Logic Controller (PLC)-based control system is designed to take automatic corrective actions under certain critical conditions. Thus, the biomass feeding and ash removal rates are fully controlled by this system.
Besides, it also helps the operator in trouble-shooting by monitoring temperatures at various critical points in the gasification system. Automatic burner sequence controllers are provided for ignition of the producer gas.
The gasification system is extremely simple to operate. A cold start takes about 10-15 minutes whereas a hot start gets effected in less than five minutes.
