GASIFICATION IS NOT INCINERATION 

The gasification process represents significant advances over incineration. In order to understand the advantages of gasification when compared to incineration, it’s important to understand the differences between the two processes: 
Incineration literally means to render to ash. Incineration uses MSW as a fuel, burning it with high volumes of air to form carbon dioxide and heat. In a waste-to-energy plant that uses incineration, these hot gases are used to make steam, which is then used to generate electricity.

Gasification converts MSW to a usable synthesis gas, or syngas. It is the production of this intermediate product, syngas, which makes gasification so different from incineration. In the gasification process, the MSW is not a fuel, but a feedstock for a high temperature chemical conversion process.

Instead of producing just heat and electricity, as is done in a waste-to-energy plant using incineration, the syngas produced by gasification can be turned into higher value commercial products such as  transportation fuels, chemicals, fertilizers, and even substitute natural gas. Incineration cannot achieve this.

One of the concerns with incineration of MSW is the formation and reformation of toxic dioxins and furans, especially from PVC-containing plastics.

These toxins end up in incinerator exhaust streams by three pathways:  

  • By decomposition, as smaller parts of larger molecules;
  • By “re-forming” when smaller molecules combine together; and/or
  • By simply passing through the incinerator without change.

Incineration does not allow control of these processes, and all clean-up occurs after combustion. One of the important advantages of gasification is that the syngas can be cleaned of contaminants prior to its use, eliminating many of the types of after-the-fact (post-combustion) emission control systems required in incineration plants. The clean syngas can be used in reciprocating engines or turbines to generate electricity or further processed to produce hydrogen, substitute natural gas, chemicals, fertilizers or transportation fuels, such as methanol.

 
 

COMPARISON  PLASMA GASIFICATION TO INCINERATION 

  • In the high temperature environment in gasification, larger molecules such as plastics, are broken down into the valuable components of syngas, which can be cleaned and processed before any further use; 
  • Dioxins and furans need sufficient oxygen to form or re-form, and the oxygen-deficient atmosphere in a gasifier does not provide the environment needed for dioxins and furans to form or reform;
  • Dioxins need fine metal particulates in the exhaust to reform; syngas from gasification is typically cleaned of particulates before being used;
  • In gasification facilities that use the syngas to produce downstream products like fuels, chemicals and fertilizers, the syngas is quickly quench-cooled, so that there is not sufficient residence time in the temperature range where dioxins or furans could re-form; and
  • When the syngas is primarily used as a fuel for making heat, it can be cleaned as necessary before combustion; this cannot occur with incineration.
  • The ash produced from gasification is different from what is produced from an incinerator. While incinerator ash is considered safe for use as alternative daily cover on landfills, there are concerns with its use in commercial products. 

  • In high-temperature gasification, the ash actually flows from the gasifier in a molten form, where it is quench-cooled, forming a glassy, non-leachable slag that can be used for making cement, roofing shingles, as an asphalt filler or for sandblasting. Some gasifiers are designed to recover melted metals in a separate stream, further taking advantage of the ability of gasification technology to enhance recycling.


WASTE PLASMA GASIFICATION ENHANCES RECYCLING RATES 

Waste Plasma Gasification does not compete with recycling. In fact, it enhances recycling programs. Materials can and should be recycled and conservation should be encouraged. However, many materials, such as metals and glass, must be removed from the MSW stream before it is fed into the gasifier.
Pre-processing systems are added up-front to accomplish the extraction of metals, glass and inorganic materials, resulting in the increased recycling and utilization of materials. In addition, a wide range of plastics cannot be recycled or cannot be recycled any further, and would otherwise end up in a landfill. Such plastics can be excellent, high energy feedstock for gasification. 
 
 


WASTE PLASMA GASIFICATION: ENVIROMENTAL AND ECONOMICS BENEFITS 

  • Reduces the need for landfill space
  • Decreases methane emissions from decomposition of MSW in landfills
  • Reduces risk of surface water and groundwater contamination from landfills
  • Extracts useable energy from waste that can be used to produce high value products
  • Enhances existing recycling programs
  • Reduces use of virgin materials needed to produce these high value products
  • Reduces transportation costs for waste that no longer needs to beshipped hundreds of miles for disposal
  • Reduces use of fossil fuels
  • Reduces pollution in the air, in the water
  • No pollution for Agricolture
  • Protect people's health

There are many types of gasifiers for waste gasification. These gasifiers vary in size and the type of MSW that they can gasify. Some gasifiers are designed to gasify construction and demolition debris, others are for MSW.

Many gasifiers require some type of pre-processing of the MSW to remove the inorganic materials (such as metals and glass) that cannot be gasified. Some gasifiers require the shredding, drying and sizing of the feedstock before it is fed into the gasifier.

WASTE PLASMA GASIFICATION: TECHNICAL DETAILS 

Plasma is an ionized gas that is formed when an electrical discharge passes through a gas. The resultant flash from lightning is an example of plasma found in nature. Plasma torches and arcs convert electrical energy into intense thermal (heat) energy. Plasma torches and arcs can generate temperatures up to 10,000ºF (5,500ºC). Plasma technologies have been used for over 30 years in a variety of industries, including the chemical and metals industries.

Historically, the primary use of this technology has been to safely decompose and destroy hazardous wastes, as well as to melt ash from mass-burn incinerators into a safe, non-leachable slag.

Use of plasma technology for gasification is much newer. While other gasifier feedstocks, such as coal and biomass, are relatively homogeneous and easily gasified, MSW and other wastes are typically  eterogeneous and may be difficult to gasify. The high temperature of a plasma gasifier initiates and supplements the gasification reactions, and can even increase the rate of those reactions, making gasification more efficient.

The high energy input from the plasma arcs or torches can be easily increased or decreased as the quantity and quality of the MSW fed into the gasifier changes. The high temperature maintains the gasification reactions, which break apart the chemical bonds of the feedstock and converts them into syngas. Some MSW gasification systems use conventional gasification technology to convert the feedstock into syngas, and then treat the syngas stream with plasma arcs or torches to ensure the efficient breakdown of any unconverted compounds into syngas.

The syngas consists primarily of carbon monoxide and hydrogen—the basic building blocks for chemicals, fertilizers, substitute natural gas, and liquid transportation fuels. The syngas can also be sent to gas turbines or reciprocating engines to produce electricity, or combusted to produce steam for a steam turbine-generator.

Because the feedstocks reacting within the gasifier are converted into their basic elements, even hazardous wastes can be converted into a useful syngas. Inorganic materials in the feedstock are melted and fused into a glassy-like slag, which is nonhazardous and can be used in a variety of applications, such as roadbed construction and roofing materials.

Dozens more plasma gasification plants are being developed worldwide, particularly where landfill costs are high, and the renewable electricity generated from the gasification facility has a high value.

GASIFICATION IS NOT INCINERATION

ADVANTAGES OF PLASMA GASIFICATION  

SYNGAS AND ENERGY PRODUCTS 

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