Biomass Recycling

Bio-mass is a generic term for such plant and animal material that, when treated and manipulated in certain ways, can produce man-usable energy either in a volatile gas form, a volatile liquid or, directly, as a combustible solid fuel raw material.

Gas Capture

When both animal and vegetable matter die, they rot down decomposing into various product types.

One of the several by-products of this decomposition is energy-rich volatile gases, the primary one of which, is methane, CH4. Other carbon based gases are also produced such as CO & CO2 along with many other compounds both useful and not, within the normal daily human cycle.

The gases above are also three of the most causal in terms of “global warming” and ozone layer depletion.

If captured and collected, by using anaerobic digestion for example (an activity that is more than 1000 years old in the east in its most primitive form), the Methane can be burnt as fuel in boilers, or better still, to fuel engines that could drive generators producing electricity. The hot exhaust gases from the engines then being used, through waste heat recovery techniques, to heat water for either heating or hot water production or both, dependent upon the local demand and effective exhaust availability. This process, when commercialised and “boxed-up” in a sophisticated format, is called “combined heat and power” or CHP.

Once again, it is possible to anticipate more than one useful outcome from a single potential energy source.

Such digesters can also produce energy using any biologically derived base product and food industry processing waste, outdated supermarket food and restaurant wastes. Domestic and commercial garden wastes can all be utilised as the base load for such treatments.

Various other by-products are available from the normal and aided bio-decomposition process that could prove useful in the longer-term energy use equation - one such would be to put the resultant residues of this decomposition from the digester, controlled or otherwise, back onto the land as 99.5% pathogen-free fertilisers and soil conditioning and the supernatant liquid that can be drained from the resultant sludge is potentially a perfect feed stock for hydroponic greenhouses for example. In such a set-up, the CO2, if carefully “scrubbed out” of the exhaust system and collected, can be pumped back into the same greenhouses to further enhance plant growth.

Crops

Photo-synthesis is the action by which light energy from the sun is converted and combines with carbon based matter within plant organisms to produce the leaf, stem and seed material that they are. These leaves, stems and seeds all contain recoverable energy.

A quite heavily brokered element of Bio-mass development at this time, is for crops to be specifically grown with the defined intent to use them as a solid base-load fuel for boilers to produce either steam for electricity generation and / or for heating and hot water production, preferably both.

Where such crops are grown, they can be directly utilised as a solid fuel - Miscanthus and Willow coppicing for example.

Plants can be grown and processed to produce bio-diesel (ethanol) - wheat and similar cereal based crops are those preferred for this methodology.

Finally, there is the use of forestry industry discards - formed into wood chips together with the sawdust from forestry production such as construction timber sawmills and furniture / joinery works can also be utilised.

This further fuel type is produced out of the sawdust which is highly compressed and extruded into pellets - currently, this fuel type is, almost certainly, the most high profile form of the biomass fuels in use today.

In larger boilers however, where fully automatic fuel feed systems and storage might be in place, the handling of this fuel has to be carefully controlled to prevent pellet degradation, condensation infiltration and high dust production in order to minimise plant failure and reduce maintenance.

Wood chip is not so needy of careful handling, but the chip size and moisture content do require tight specification and monitoring to ensure continual good firing performance, boiler efficiency, minimal ash production and minimal maintenance.

Different crops are more suitable than others for use commercially in the production of bio-fuels and it is the writers opinion that this approach, whilst providing an alternative energy source to fossil fuels and providing work across the entire world as these crops could be produced and used anywhere, they could still put an additional carbon load into the atmosphere. In addition, this scenario cannot be making the best use of an ever decreasing and less fertile land bank that has also to feed the ever-growing population of the world.

Biomass as a fuel, and eco-protector, is probably best served by the further development of CHP plant using possibly waste wood chip technology together with anaerobic digestion and resultant CH4 as the base-load fuels. Even so, their flue gases require to be heavily cleaned with the resultant by-products being used in other ways -iIf possible, the only final discharge from any CHP plant flue should be water vapour.

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