Gasification benefits are numerous, here are a list of questions and answers that will shed some light on this energy source:
Q: Why gasify?
A: It’s a solution that can take a problem feedstock such as waste, and convert it into valuable products (e.g. chemicals, fuels, heat, fertilisers, electricity etc)
Q: Is the feedstock burnt?
A: No – gasification is not incineration. Combustion is not employed which is why dioxins are minimized
Q: Are there environmental benefits to gasification?
A: Yes – significant benefits including reducing the need for landfill space, decreasing methane emissions from decomposing material in landfill and reducing the risk of groundwater contamination from landfills. Gasification also reduces transportation costs for waste that no longer needs to be shipped for disposal. This reduces carbon footprint. Furthermore, if the feedstock is renewable (e.g. waste), converting this feedstock to energy will actively replacing fossil fuels.
Q: What is Incineration and how is it different?
A: 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.
Q: Is Gasification more efficient than Incineration?
A: On average, conventional waste-to-energy plants that use mass-burn incineration can convert one ton of MSW to about 550 kwh of electricity. With gasification technology, one ton of MSW can be used to produce up to 1,000 kwh of electricity, a much more efficient and cleaner way to utilize this source of energy (up to almost twice as efficient).
Q: Is Gasification new?
A: No – it is tried and tested, and has been used industrially for over 100 years.
Q: Is Gasification cleaner than Incineration?
A: One of the concerns with incineration of MSW is the formation toxic dioxins and furans, especially from plastics. These 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 this to occur.
Q: What about Cost?
A: A gasification plant will typically cost less than half the cost of an equivalent Incinerator. This is because expensive steam handling equipment is not needed. Also, since an incinerator produces large volumes of hot gas, this gas needs large and expensive cleaning equipment prior to discharge. Since gasification produces a concentrated low volume gas stream, the gas volumes are lower, and hence the cleaning equipment is far more compact.
As another side benefit, the low gas volumes mean low gas velocities and less dust carryover. It is the fine metallic particulates in these dusts that often promote the formation of dioxins in incinerators. This is not the case in gasifiers.
Q: What about the Ash?
A: 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.
Q: What about Recycling?
A: 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.