Demir Energy’s Division of Renewable Resources is introducing a state-of-the-art and innovative Municipal Solid Waste (MSW) Gasification Facility Plant to be constructed in the USA by 2017/2018. Demir Energy and its strategic affiliates have received the cooperation and support of various municipalities and counties to build an innovative facility plant that can process up to 100 tons per day of MSW. The amount of carbon neutral electricity produced can be used by 3,300 homes.
Gasification has been used worldwide on a commercial scale for more than 75 years by the chemical, refining and fertilizer industries, and for more than 35 years by the electric power industry. It is currently playing an important role in meeting energy needs in the U.S. and around the world. In new settings, it is being adopted in smaller-scale applications to solve the problem of waste disposal and extract valuable energy from waste.
Each year, Americans generate about 250 million tons of MSW which translates into 4.3 pounds per person per day. This includes “trash” such as kitchen waste, electronics, light bulbs, plastics, used tires and old paint, and yard waste. Despite significant increases in recycling and energy recovery, only about one-third of the total MSW is recovered, leaving the remaining two-thirds to be disposed of in landfills or incinerated. But these traditional methods of waste disposal are becoming less viable. Many states have banned incineration or burning of waste because of the negative environmental impacts. And a number of states, such as New York, New Jersey, Massachusetts, Connecticut and California, are faced with limited landfill space, forcing them to transport their MSW hundreds of miles for disposal in other states. In addition to consuming valuable land, the decomposing MSW generates methane, a greenhouse gas, and the leaching wastes may also pose a threat to surface water and groundwater.
Faced with the expensive problem of waste disposal, a growing number of municipalities are turning to gasification, a time-tested and environmentally sound way of converting the energy in MSW into useful products such as electricity, fertilizers, transportation fuels and chemicals.
On average, conventional waste-to-energy plants that use mass-burn incineration can convert one ton of MSW to about 550 kilowatt hours of electricity. With gasification technology, one ton of MSW can be used to produce up to 1,000 kilowatt hours of electricity, a much more efficient and cleaner way to utilize this source of energy.
Gasification is a unique process that transforms any carbon-based material, such as MSW, into energy without burning it. Instead, gasification converts the materials into a gas by creating a chemical reaction. This reaction combines those carbon-based materials (known as feedstock) with small amounts of air or oxygen, breaking them down into simple molecules, primarily a mixture of carbon monoxide and hydrogen, and removing pollutants and impurities. What’s left is a clean “synthesis gas” (syngas) that can be converted into electricity and valuable products. With gasification, MSW and other types of wastes are no longer useless, but feedstock for a gasifier. Instead of paying to dispose of and manage the waste for years in a landfill, using it as a feedstock for gasification reduces disposal costs and landfill space, and converts those wastes to electricity and fuels.
Gasification can recover valuable energy from waste and convert MSW that is normally incinerated into a clean, useful syngas.
- This clean syngas can then be used to produce energy and valuable products, such as chemicals, transportation fuels, fertilizers, and electricity.
- In the gasification process, MSW is not a fuel, but a feedstock for a high temperature chemical conversion process. There’s no burning.
- Gasification does not compete with recycling; in fact, it enhances it. Metals and glass must be segregated from the waste stream prior to being sent into the gasification process. In addition, many plastics cannot be recycled and would otherwise end up in a landfill. Such plastics make excellent high energy feedstock for gasification, thereby reducing the amount of those unrecyclable materials that would end up in a landfill.
- There are significant environmental benefits of MSW gasification, including reducing the need for landfill space, decreasing methane emissions from the decomposition of organic materials in the landfill, and reducing the risk of groundwater contamination from landfills.
Gasification is not incineration, instead, 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 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 making 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 substitute natural gas. In addition, 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 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 by 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 ethanol.
Gasification is significantly different from and cleaner than incineration:
- In the high temperature environment in gasification, larger molecules such as plastics, are completely broken down into the 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 quenched, so that there is not sufficient residence time in the temperature range where dioxins or furans could re-form.
- When the syngas is primarily used as a fuel for making heat, it can be cleaned as necessary before combustion; this cannot occur in 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, taking advantage of the ability of gasification technology to enhance recycling.
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 are an excellent, high energy feedstock for gasification.
Gasification’s Environmental 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 usable 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 be shipped hundreds of miles for disposal.
- Reduces use of fossil fuels
Sources: Gasification Technologies Council