Pyrolysis Technologies
Pyrolysis is a process in which oxygen is excluded from the reactor, which is heated externally to produce the elevated temperature environment that causes the organic solids (waste input) to breakdown via physical and chemical processes into three products; solid char, pyrolysis oil and pyrolysis gas with the proportions of each being governed by the operating temperature within the pyrolysis reactor.
There is a certain amount of misunderstanding concerning the differences between pyrolysis and gasification with some people believing that they are the same. True pyrolysis is a low temperature thermal conversion technology that operates with an air free environment and produces a primary liquid product as well as gas and solid phase products. If pyrolysis is operated at high temperature (>800oC) then the primary product becomes syngas but the process will also produce liquid and solid phase products in lesser amounts.
By increasing the operating temperature the thermodynamics governing the reactions taking places cause a greater production of pyrolysis gas (syngas) at the expense of pyrolysis oil. The quantity of char produced at low and high temperatures does not vary greatly.
For biomass processing the lower temperature pyrolysis processes have been used with the objective of maximising the production of pyrolysis oil, referred to as bio-oil, which was seen as a pre-cursor to the production of many other chemicals in a bio-refinery context.
In a waste processing context the higher temperature pyrolysis processes have been developed in order to maximise the production of syngas, which is more easily converted to electricity.
WHY OYROLYSIS?
Incineration (combustion/burning) of waste material converts input waste into energy and ash but is always associated with emissions of greenhouse gases, unhealthy particulate matter and toxic residues. Even with the most advanced and sophisticated emission controls, combustion can never achieve the environmental standards available with the best engineered pyrolytic platforms. In contrast to combustion/incineration, pyrolytic/gasification "bakes" waste materials at relatively low temperatures (generally, 300 to 650 degrees centigrade) under highly controlled conditions that reduce or eliminate oxygen - so waste conversion is conducted without combustion.
Instead, a variety of waste materials are broken down into smaller carbon-containing compounds; these molecules are collected and sold "as is" or further cost-effectively transformed into valuable end-products that can be used to generate energy (electricity, heating and cooling), oils/solvents, recyclable materials for resale (such as metals) and other bio-products such as biochar - all of which can create substantial profits and new jobs while generating carbon credits and environmental benefits.
The process of pyrolysis (or thermolysis) of waste materials takes place in special chambers with reduced or no oxygen, resulting in thermal decomposition of all organic materials without combustion. Most pyrolytic processes produce solids (char and ash), gases and oils. Depending on the waste feedstock and pyrolysis technology used, these end-products can be sold "as is" or cost-effectively converted into other by-products of greater commercial value. When pyrolysis (a relatively low temperature process) is coupled with gasification (a higher temperature process, but still combustion-free), organic waste compounds into a clean "synthetic gas" (often called syngas or producer gas) that can then be combusted to create steam to generate electricity in special gas engines or turbines.
Conventional incineration/combustion in conventional power plants - whether burning coal or natural gas - also produce steam to drive turbines to generate electricity; however, they operate at lower efficiency and produce environmentally destructive emissions. Coal burning also produces significant amounts of "fly ash", an unavoidable consequence of combustion that can contain toxic metals (including arsenic and mercury); the recent accidental spillage of millions of gallons of stored fly ash in Tennessee underscores the many environmental threats associated with coal burning.
In contrast to incineration/combustion, pyrolysis is the decomposition of organic materials during heating in oxygen-free atmosphere to produce gas, liquid and solid residuals. Decomposition products of the pyrolysis depend upon the heat, pressure and time the material is held within the vessel.
There are many variations of pyrolysis technologies in commercial operation; they vary greatly in their efficiency, cost-effectiveness, environmental impact and range of converting waste materials to profitable products. Some of the advantages of pyrolysis over incineration/ combustion include:
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Greatly increased possibilities for recycling:
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with incineration, the only practical product is energy;
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carbonized material can be pelletized for use as fuel, carbon black for industry, and activated carbon for smokestack scrubbing.
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in pyrolysis, gases, oils/solvents and carbonized materials are produced;
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gas and liquid products can be used as a combustion fuel;
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Emissions from pyrolysis are considerably lower:
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depending on the technology variant employed, up to 99% of the material treated is recovered, with virtually no effluents escaping into the environment;
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no smokestack is necessary.
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By displacing fossil-fuels, waste pyrolysis can help meet renewable energy targets, address concerns about global warming, contribute to achieving Kyoto Protocol commitments and generate renewable energy/carbon credits for sale or trading.
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Pyrolysis systems have been developed for a wide range of capacities and wastes, including recovering materials and energy from residues left from materials recycling e.g. electrical and electronic scrap, tires, mixed plastic waste and packaging residues.
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Pyrolysis is the only process that is basically insensitive to its input material:
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if properly engineered, pyrolysis equipment can accept unsorted MSW (municipal solid waste), dioxins, contaminated soils, medical wastes and liquid materials such as municipal sluedge with high levels of water content.
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Pyrolysis facilities require lower capital investment and have lower operating costs than combustion plants and can be operational within 5 to 6 months of breaking ground:
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These facilities have excellent operator safety records and function continuously at very low noise levels;
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Combined with low profile building requirements and no smokestack, these characteristics allow faclities to be placed in senstive locations.
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The pyrolytic technologies employed by BioSynEnergy are modular and scalable from 10 tons up to hundreds of tons of waste processing capabilities daily.