Steam and Mirrors or the Real Thing? Energy and Carbon Balances for Autoclaving Solid Wastes

Tudge, N.1, Boots, C.2, Mair, R.3, 1Enpure Ltd, 2Tempico Inc, 3Graphite Resources Ltd


Autoclaving, as part of an overall treatment train for mixed solid wastes, offers a number of clear benefits which enhance the recovery of organic resources and other useful materials: the waste is rendered sterile, it is safer and less offensive for downstream processing, recyclates are free from contamination and are much easier to separate and, critically, almost all of the biogenic organic component is reduced to an homogeneous fibre, allowing very high recovery rates. This paper presents a brief introduction to the history and current status of waste treatment using autoclaves, considers problems which remain to be solved and suggests some possible solutions. In particular it looks at the issues surrounding the inherently energy-intensive nature of the process and shows that by careful design the overall process can be both a net exporter of energy and have a negative carbon footprint.
To render the process both economically and environmentally sound the energy and carbon balances
must be carefully considered. Using the case of a 320ktpa plant currently being constructed in the north
of England the paper presents mass, energy and carbon balances for the process coupled with a variety
of post-autoclaving treatment options. These include:

  • Anaerobic digestion, looking at the best ways of recovering low-grade energy, and possibilities for sequestering some of the biogenic carbon
  • Production of biogenic fossil fuel, and the benefits in using low-grade heat for drying
  • Manufacture of soil amenders by composting
  • Use of cellulosic materials for board, construction and manufacturing

Unfortunately the author was unable to provide a full paper.

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