The principle behind gasification is that energy matter cannot be created or destroyed, but can be transformed. The waste-to-energy facility includes three major sections: (1) gasification, (2) syngas cleaning, and (3) power generation. The plasma gasifier uses plasma torches with an external energy source (electricity) to heat the waste to very high temperatures in an oxygen-starved atmosphere (less oxygen than is needed for complete combustion).
The chemical bonds in the waste material are broken down into very simple molecules, hydrogen (H2) and carbon monoxide (CO), as at those temperatures these are the main things that can exist.
This mixture of primarily carbon monoxide and hydrogen gases is often called synthesis gas, or "syngas" which can be directly used to generate electric power; produce transportation fuels, such as ethanol, green hydrogen, and diesel; and can also be used to generate process steam or offset the use of natural gas in industrial facilities. The amount of syngas generated depends upon the type of feedstock placed into the process; high carbon content feed stocks create more syngas.
The inorganic materials in the waste flow out of the bottom of the gasifier at about 3000 degrees Fahrenheit. This eliminates potential pollutants, destroys hazardous compounds, and locks up minerals and trace metals in a non-toxic inert solid that is much like obsidian (volcanic glass). Metals in the glassy slag flow in layers, and scientists can separate, capture, and recycle metals including gold, aluminum, and copper.
The syngas cleaning section of the facility is focused on cleaning the syngas so that it has a purity like that of natural gas or better. The syngas is cleaned up to eliminate environmentally toxic elements to protect human health and the environment. The syngas cleaning process consists of multiple steps utilizing:
- Venturi Scrubber
- Spray Tower
- Wet Electrostatic Precipitator
- Activated carbon beds, and Sulfur removal system
At this point, the syngas has been thoroughly cleaned and is ready for use as a fuel in the power generation section of the facility, or as a feedstock for producing transportation fuels, such as ethanol or hydrogen.
When the focus is on producing electricity, the syngas will be used as a fuel in a high-efficiency combined-cycle power plant (with a gas turbine and a steam turbine). The power plant would produce electricity both for internal use (about 20%) and for sale on the public grid (about 80%). Emissions from the combined-cycle power plant would be typical for facilities of that nature; they're some of the cleanest power plants in existence.
The most detailed public description of the process is provided in an independent report by Juniper Consultancy Services, Ltd. provides a candid, in-depth examination of the technology provided by Alter NRG and Westinghouse Plasma Corporation, including emissions data from existing facilities. It is important to note, however, that the system design we have proposed makes significant improvements compared to the design of the existing facilities operating today.