In today's world of fixed resources, using a new alternative energy source, such as municipal waste to produce clean energy, can be the real change needed to sustain future life for people and nature alike. U.S. Science & Technology has identified an innovative waste disposal and treatment system to do exactly that. The process is a true waste-to-energy (WTE) system that is far more environmentally friendly and commercially beneficial than traditional waste treatment processes. One component of USST's waste treatment system is an innovative technology called plasma gasification.
Plasma gasification is proven technology that is advancing commercially. It is rapidly emerging as the best response to many of the earth’s increasing waste disposal and energy problems of the 21st century.
Current technologies using plasma gasification can cleanly convert almost any waste material into usable resources such as electricity, synthetic fuels, and valuable commercial products. The high gasification temperatures create the plasma state sometimes referred to as the "fourth state of matter," following gas, liquid, and solid. In nature, well-known examples of plasma are lightning and the sun.
The centerpieces of the plasma gasification technology system are the plasma torches which create intensely high temperatures, to create an ionized gas stream or plasma. Plasma torches and heating technology were first used by NASA in the early 1960's to test the durability of its space vehicle's heat shields for re-entry into our atmosphere. Their successful commercial application has led them to be considered for use in various industries.
Although plasma gasification is not a new technology, waste-to-energy is a recent innovative application that has emerged within the past decade because of the technology’s superior ability to:
- Achieve sustainability goals, specifically 100% conversion of municipal solid waste (MSW) into usable/saleable by-products, e.g., energy, alternative fuels, metal recovery, glass, and construction materials.
- Minimize air emissions compared to other WTE technologies and manage the release of greenhouse gases.
- Eliminate the need for landfill disposal of municipal solid waste and its related environmental concerns.
|Technology||Temperature||Conversion to Energy|
|Plasma Gasification||7,200 – 12,600° F||816 kWh/ton of MSW|
|Conventional Gasification||1,400 – 2,800° F||685 kWh/ton of MSW|
|Pyrolysis Gasification||1,400 – 2,800° F||685 kWh/ton of MSW|
|Pyrolysis||1,200 – 2,200° F||571 kWh/ton of MSW|
|Mass Burn (Incineration)||1,000 – 2, 200° F||544 kWh/ton of MSW|
Source: Dr. Young, Chemical Engineer, Gyco Inc.
With the exception of plasma gasification, all of the technologies mentioned above have environmental issues and consequences for disposing of byproducts such as ash or sludge. USST's system incorporating plasma gasification technology eliminates this problem, and produces valuable products in the process.
Plasma gasification technology uses electricity and high pressure air to reach temperatures of 7,200 to 12,600 degrees Fahrenheit or higher and creates an ionized gas capable of conducting electrical current. The technology operates at temperatures nearly five times greater than conventional gasification and pyrolysis technologies, and nearly seven times greater than incineration. At such intense temperatures, the enclosed oxygen-starved plasma gasification process generates different chemistry which yields higher carbon conversion to produce more energy and cleaner results.
An introductory article on plasma gasification that can be helpful for understanding the technology in general, can be found on the “How Stuff Works” website.
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 feedstocks 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 we are proposing for the city of Sacramento, California is provided in an independent analytical report by Juniper Consultancy Services, Ltd. It 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 (and reviewed in the analytical report) makes significant improvements compared to the design of the existing facilities operating today.