Biomass electricity: New boiler technology enables use of all agricultural residue

Context

A vibrating grate boiler launched recently in Denmark can be a solution for firing any kind of biomass. 

• These boilers have a capacity of 75 tonnes per hour. 

About New boiler technology 

• A new technology introduced this year that accommodates all kinds of agricultural residues to be used as fuel can be cost-effective, greener and help reduce the burden of stubble.
• Use of biomass to fire steam boilers at electricity generation units is also increasing to produce cleaner power. 
• These boilers are designed only for specific types of agro residue such as paddy husk, paddy straw, mustard, among others to be fired for its lifetime. 
• This combustion technology is advantageous because of the vibrating grate. 
• The grate of a steam boiler supports the solid fuel in the furnace. 
• It is so designed that it can also allow air to admit air in the solid fuel for combustion. 
• Vibrating grate is different from the more common stationary, travelling and reciprocating grates since it accommodates biomass of every density. 
• The moisture content of the fuel, however, has to be 15-20 per cent. 
• The vibrating grate supports firing agro residue of any size, it saves energy consumed for processing biomass for energy generation. 

Process of combustion 

• Instead of converting biomass into pellets or briquettes, the agro residue is converted into bales right after procurement from the farmers. 
• Before it is conveyed to the combustion system, it is subjected to a bale string cutter and dosing screw to cut the string tying the bales and mixing the bales to reduce its size respectively. 
• The size of the bale is reduced for achieving complete combustion of the biomass fed into the boiler.
• Then, the bales are sent to a vibrating grate for combustion. Here, the combustion happens as a series of events. 
• For the first 250 seconds, a set of fuel is fired, and then it is moved to the next combustion stage by vibration.
• After the first set of biomass is moved to the next grate, fresh biomass enters the firing system for combustion. 
• After complete combustion, the burnt biomass in the form of ash is let out for disposal. 
• The biomass-based boiler is as efficient as a coal-based boiler. 
• The average steam to fuel ratio of this biomass-fired boiler is 4-4.5 and the efficiency is also achieved upto 85 per cent, which is equivalent to coal-based thermal power generation. 

Significance

• This system costs around Rs 35-40 crore for complete installation and doesn’t require any major structural change to accommodate any kind of agro-residue, making it a better choice for reducing the burden of stubble. 
• The flexibility of using any form of biomass also reduces the cost of transporting the fuel from a longer distance. 
• This in turn saves energy and emissions due to transportation as well.
• The move was aimed at enhancing biomass combustion in a controlled environment for energy production.
• The new Denmark-based technology allows the plant to fire a wide range of fuels with less fuel preparation and handling, and mainly avoid the energy-intensive process of briquetting and pelletisation.