CMPS&F - Environment Australia
Appropriate technologies for the treatment of scheduled wastes
Review Report Number 4 - November 1997
The Viking Gasification System (VGS) is a gasification technology under development by Phoenix Consortium Limited (PCL) by which carbon based waste streams are processed in a spouted bed reactor to produce a clean commercial quality gas. A spouted bed reactor is a form of fluidised bed reactor. The process consumes wastes during a high temperature, steam reformed, closed loop gasification process. The process achieves high efficiencies through indirect heating of feedstocks, thermochemical reaction (in a spouted or fluid bed reactor) and high heating rates.
PCL is represented in Australasia by Fostex Pty. Ltd; Fostex provided the information for this review (Fostex, 1995).
The process uses low pressure steam at a high temperature (approximately 1600oC), and a thermochemical reaction to vaporise and separate feedstocks into their constituent chemical elements. A reduction process takes place in the reaction vessel which is indirectly heated by radiant tube heaters. A reductive process, rather than combustion takes place within the reaction system. The process is continuous and yields a mixture of hydrogen and carbon monoxide that is consistent across a wide range of feedstocks and is of a commercial quality (10.6 MJ/m3 or 285 BTU/std. ft3).
The process includes a computer based control system which monitors feedstock mixing and monitors and updates process results for future reference.
The output streams of the reaction vessel are stripped of entrained carbon particles and cooled for further processing or use. When treating scheduled wastes, the gas stream would be scrubbed to remove hydrochloric acid. There is no reactor gas stack and no wastewater discharge.
The product gas can be compressed and stored for later use, fed into an electrical cogeneration system, or used as a feedstock for reformer columns that produce derivatives such as propane, butane, methane, methanol, diesel fuel, other hydrocarbon based products, ammonia and urea.
Metals such as tin, lead and mercury are collected in a waste ash along with unreacted material, such as steel particulates, soil and stable inorganic compounds.
It is claimed that the VGS may be used to process the following:
Fluidised bed systems have been in widespread use and can be regarded as proven technology for treatment of waste materials. It can be expected that a spouted bed system will act as an efficient desorber as required for gasification of organic waste. However, insufficient information was provided to properly evaluate the performance of this process and its application to scheduled waste. While Fostex claims that the process has application in the treatment of a variety of scheduled wastes, insufficient information was provided to substantiate this claim.
By operating as a closed loop system and avoiding stack gas emissions and wastewater discharges, the process avoids the normal performance requirements for discharge to the environment, although the product gas (which will be combusted) can be expected to be required to comply with specified quality objectives, no information was provided regarding the product gas quality achieved by the system.
Fostex advises that the VGS recovers and converts waste stream energy at a mean process efficiency of around 75%. The process uses fossil fuels or electric power to reach the required operating temperature. When this temperature has been reached, approximately 20% of the product gas internally produced is used to maintain the reaction. A VGS "standard" module can be expected to process 25 tonnes/day of organic waste material.
Fostex states that the VGS can process solid, liquid or gas carbonaceous wastes; in practice pre-treatment will be required to ensure that the waste is in a form which can be processed in the reaction vessel. This can be expected to require size range restrictions, the avoidance of substances which may slag or agglomerate at the reaction temperature, and restrictions on wastes with a high inert component such as soil.
VGS technology is claimed to offer saleable byproducts such as electricity, thermal energy, product gas, reformed hydrocarbon, inorganic chemicals and ash products (metals etc.). In the case of scheduled waste processing such byproducts are unlikely to be an important factor in the process application.
The technology has not been trialed or demonstrated in Australia. A submission was made in early 1994 to the Senate Waste Disposal Inquiry and ICI regarding the specific application of a spouted bed reactor configuration of the VGS to process ICI's hexachlorobenzene (HCB) waste. ICI , however, did not consider the process further (Manson, 1994).
Fostex advises that the US Departments of Energy and Agriculture have recently allocated further funding for a prototype spouted bed reactor configuration of the VGS aimed at the pyrolytic removal of fugitive plastics from municipal solid waste (MSW) streams. Testing of the spouted bed reactor for this purpose is currently under way.
Fostex Pty Ltd (Melbourne).
Range of waste types subject to limitations on size range, inert solids fraction and slagging materials.
All scheduled compounds, although insufficient information is available to confirm this.
This technology has not been trialed or demonstrated in Australia. Prototype spouted bed reactors are currently being tested in the US.
As the technology has not been demonstrated in Australia yet, it is expected that commercialisation will not occur in the foreseeable future (ie 5 years).
None provided. Forecast paybacks for larger VGS installations are in the 5-8 year range. However, this projection has little relevance to scheduled waste processing in Australia.
The process avoids the direct discharge of gaseous emissions and wastewater, however, systems will be required to ensure product gas quality objectives are achieved. The process produces a gas which, if mixed with air, is potentially explosive and appropriate design and operation is required to ensure safety of the process.
Insufficient information has been provided at this point in time to determine this.
Preprocessing will be required for some wastes to ensure that the material to be treated is in a form which can be processed in the reaction vessel. This includes wastes with a high inert component such as soil. It is expected that size range restrictions will apply and substances which may agglomerate at the reaction temperature need to be avoided.
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