Following years of development work on energy plants around the world - which included gasification, gas burner technology, and the Bubbling Fluidised Bed (BFB) technique - DGA engineered a superior method for combustion of refuse derived fuel (RDF).
The Vibrating Grate System (VGS™), commonly referred to as the Vee Grate, features a combination of high pressure air and vibrations and is more cost effective and more powerful than the BFB method.
The system uses a closed air box with adaptive pin hole technology. High pressure air passes under the grates which lifts the flames from the combustion bed. Spreader stokers spread the fuel (i.e RDF or biomass) through the flames in transit to the grate which means the fuel is ignited and doesn't have to wait until it comes into contact with the grate. This means that 'all' the fuel on the grate is ignited. Alternative systems require twice the bed area to ignite the fuel. The size of grate has an immediate effect in the size and therefore cost of the boiler. The highly intense flame and combustion is caused by fluidisation during vibration and the high press PA nozzles.
Our experience with large gas burners led to the development of a unique secondary air delivery system which injects up to 50% of total combustion air into the furnace via layered jets.
Frequent short bursts of vibration shake the grate and ensure that there are no blockages in the PA nozzles.
Water cooling allows the grate structure to remain as design with the grate bars reaching 400 degrees Celsius which is hot enough to ignite any melted plastics in the RDF waste.
The Vee Grate has been successfully tested on a variety of biomass fuels including wet palm waste, old wet Eucalyptus bark, rice husk, corn cob and corn straw. It is designed to work with prepared fuel, i.e. Dried and sized. Burning prepared waste results in higher combustion temperatures and it allows for the firing system to be built into the boiler – a critical design factor for small plants up to 12 MWe.
From a technical perspective, the Vee Grate has been designed for no-fuss service and maintenance. There is only one moving component: the grate. It is suspended on springs which can be replaced with the boiler and grate still firing ie not shut down.. The grate can be unclamped and removed from the furnace in just half a day and, in the likelihood of a major fault, the grate can be accessed without having to wait for the boiler to cool down. The hoses which supply the water to the grate are mounted externally in plain view of the operators and can be replaced immediately there is any sign of any leakage whilst the plant is online.
VGS Outperforms BFB
In comparison, DGA's VGS™ is more cost effective, uses less power to operate and is easier to maintain.
The Bubbling Fluidised Bed system evolved for burning volatile fuels such as wood, biomass sludges and plastics. Most combustion takes place in the furnace freeboard. It has two inherent weaknesses: it uses too much power (Parasitic load) and it does not like large non-combustible items in the hot fluid bed. A lot of care is required to ensure the suspension burning, which behaves like a gas burner, has a well designed secondary air system otherwise the flames can lift off and stablise elsewhere in the boiler causing flame instability and pulsation.