Utilising thermal processes to break down waste into a fraction of its original size, these plants use a series of filters, scrubbers, and catalyst reactors to reduce the output gases well below European Environmental standards.
Additionally when comparing landfills to E.F.W, the plants produce 0.95kg of CO2 /kg of waste, where if a landfill produced the same amount of electrical and thermal output it would produce 1.71kg of CO2 /kg of waste.
history
Thermal treatment of waste has existed since humans first discovered fire and has been used throughout history, with the first large scale thermal plant being built in Nottingham, England in 1874. From there plants were built throughout Europe and America helping solve the chronic waste issue faced during the Industrial Age, bringing in the Age of Sanitation. Though these plants helped reduce the amount of waste filling landfills, they were inefficient, and their outputs not used to generate renewable energy.
In the 1920's Josef Martin (of Martin GmbH) invented the 'reverse-acting grate' that is based on the premise that fuel ignites more easily when an already existing glowing mass is pushed back underneath it.
The concept was developed over time and the grate proved to be the solution to creating efficient combustion of MSW. This system has been in commercial operation since 1959.
A Martin GmbH plant located in Brescia, Italy. Click to enlarge.
The Danish Energy Statistics report published in 2005 shows that Energy from Waste plants in Denmark now produces over 4.8% of the electricity and 13.7% of domestic heat requirements.
Today there are over 500 Energy from Waste plants in operation around the globe, of these over 390 plants have been designed by Martin GmbH making them the world leader in this field designing and creating plants that supply a cleaner and renewable source of electricity, heat, and useable commodities.
how it works
Waste crane loading up the grate with MSW.
Click to enlarge.
In a typical plant MSW (Municipal Solid Waste) is brought in by waste collection vehicles and handed over to a holding bin containing the 'waste crane'. This crane will pick up waste and place it into the grate designed by Joseph Martin ensuring a constant flow of fuel into the grate. Within the firing chamber though the manner in which the MSW is managed and brought to combustion is critical to the performance and effectiveness of the plant and to its emissions. By its very nature MSW is not an entirely predictable fuel in its consistency or its constitution. It is therefore this component of the process which is required to be unique to MSW creating an optimised, efficient and complete combustion.
Process diagram of a Martin GmbH Plant. Click to enlarge.
Air is supplied via vents below the grate, which ensures the grate is kept at a constant temperature, and also via nozzles directly into the boiler to generate a greater oxygen mix to break down flue gases.
To breakdown organic toxins, during certain parts of the process the temperate is raised to at least 850 °C. After which it's then cooled in the superheaters, transferring the excess heat to steam turbines to generate electricity. Finally the remaining gasses are passed through a series of filters, scrubbers and catalyst reactors to remove any hazardous material.
Plasma Convertors can also be used in conjunction with EFW plants to further break down any remaining waste, and outputs. To find out more about Plasma Convertors click here.