The Thermal Waste to Energy (TWtE) industry is well established and growing globally, with hundreds of plants operating all over the world utilising different forms of technology, diverting waste from landfill to create a clean energy source.
Some countries are so well established that they import waste to be converted into energy!
Modern TWtE technologies apply heat to waste to convert it into a gas, which is not incineration, as there is no oxygen present in the process. The process results in the production of few, or no, emissions (depending on the type of technology used).
TWtE technologies are a key component of the Waste Management hierarchy, with all recyclables and recoverable resources extracted before they can be converted into energy.
The basic process
All energy from waste plants will have the same basic steps
- A reception area to receive & sort the waste and get it ready for combustion or removal for recycling
- Thermal treatment – this essentially releases the energy from the waste
- Conversion to a transportable form of energy – e.g. electricity, heat, fuels
- Emissions clean-up – ensuring waste gases are safe
The overall environmental benefits will depend not only on the thermal treatment but the energy conversion technology to which it is coupled. The emissions clean-up step ensures that all the waste gases emitted from the plant meet the very tight limits placed on them by EPA legislation. As a result, energy from waste plants contribute only a small fraction of both local and national particulate and other emissions.
Thermal processing for waste offers a variety of Gasification technologies to choose from: plasma arc, pyrolysis, close coupled , moving grate and more.
Typically, but not always, the only treatment the waste needs is to give it a physical consistancy (same shape and size).
The Gasification of waste occurs typically at temperatures greater than 1000C, in the presence of limited oxygen resulting in partial combustion. This produces a synthesis gas (Syngas) containing mainly carbon monoxide, hydrogen and methane.
Plasma Arc uses much higher temperatures (>1000 C) in an oxygen starved environment to produce syngas.
For Pyrolysis, the waste is heated to between 300-850oC in the absence of oxygen. The waste is broken down to produce a gas containing carbon monoxide, hydrogen, methane and a broad range of other volatile organic compounds (VOCs). Parts of this gas mixture may be condensed to form a pyrolysis oil.
Most of the energy from Thermal Waste to Energy processes are produced in the form of Syngas, which is used to generate electricity. However, more and more plants are also looking to use the heat generated; this is known as combined heat and power (CHAP). More innovative technologies have the potential to also transform the waste into other energy products such as transport fuels or substitute natural gas.
Tyres are a specific waste type that can be processed to be converted into an oil using technology that EcoEnergy Ventures can provide. This technology is scalable and can provide a variety of grades of oil, depending on the refining process undertaken.
Waste products and emissions
Most forms of Gasification produce a vitreous ash that can be reused in construction, typically in road bases.
Modern forms of Gasification (for example plasma arc) produce minimal or no emissions. Older style Gasification plants produce some emissions that are actually cleaner than the ambient air.