Historically one of the most widely used means of generating both heat, energy and now biofuels, bio-energy figures strongly in the list of those energy technologies with the greatest potential for the future and is therefore a central plank of the research and development effort in Scotland.
Even at its most basic level bio-energy, in the form of simple technologies such as wood burning stoves, is much more widely used.
Over the past couple of decades even the simple stove has evolved into much more sophisticated wood fired boilers used for heating and hot water supply to replace oil or gas fired systems. These mainly require wood fuel pellets produced to particular and consistent standards of density and humidity and has required a great deal of innovation in forest management, harvesting methods, timber processing and pellet production.
Bio mass fired power stations
The use of biomass fired power stations is also increasing. While these are also fuelled mainly by timber or timber products using fast growing forms of tree a number can also use domestic waste material collected and sorted and burnt to produce steam that can be used for generating electrical power and/or hot water for district or local heating systems.
Improving the efficiency of biomass firing which includes improving the quality of the feedstock as well as the combustion process itself is an essential requirement. Similarly, ensuring the flue gases produced are both clean of toxic elements and particle free is a priority.
Some biomass power plants use a technique known as Gasification. Here the material is burnt at high temperatures but using a controlled amount of oxygen and/or steam. This produces a gas mixture called syngas which is made up mainly of carbon monoxide and hydrogen and is itself a fuel. A similar technique called Pyrolysis also uses high temperature burning but in the absence of any air. The process can be optimised to produce charcoal, gases or liquid fuels.
With both Gasification and Pyrolysis the syngas can be used to fuel an internal combustion engine, a gas turbine or – given the high level of hydrogen of circa 85% – a fuel cell. Syngas can also be processed using Fischer Tropsch technology to liquid fuels such as methanol or diesel.
Conversion of wet waste material
Biological conversion processes include Anaerobic Digestion where wet waste materials are “encouraged” to decompose as efficiently as possible to produce primarily methane. This may appear superficially simple, however, the use of selected microorganisms can improve the process significantly resulting in much higher methane yields and a higher quality co-product which is used as a fertiliser. The methane produced is generally used for power generation by burning it in an internal combustion engine or small gas turbine connected to a generator. More recent developments see the gas cleaned and distributed through the natural gas mains.
Understanding the process of anaerobic digestion and which bacteria are most effective on the various types of waste that might be used is essential to maximising gas production from the wide range of waste materials available.
Bio-fuels
Liquid fuel availability is a much larger issue than power generation and there is considerable interest in Bio-fuel which has become perhaps the most familiar recent outcome of bio-energy research and development work with the best known bio-fuel products being probably bio-ethanol and bio-diesel.
Both these can be produced from a range of plant sources and considerable effort is going into maximising the “oil production” from particular plants and in the process of producing the fuels.
The pace of bio-fuel development is quickening. Already, a Scottish university project has resulted in the successful production of Bio-Butanol from distillery waste and another institution is working on producing bio-fuels from seaweed and marine micro-algae. Butanol is a higher octane fuel than ethanol and will run in standard engines. Many countries are also now working on a Bio-Kerosene to be used as jet fuel and trial flights have already been made successfully.
Synthetic biology
Even more interesting in terms of bio-fuel production is the development of Synthetic Biology which – for example - has resulted in bacteria that can consume sugars and excrete pure diesel. Other developments in this area include bacteria that can produce hydrogen whilst at the same time absorbing or “fixing” other gases including carbondioxide.
The question has to be asked as to what else might be possible using Synthetic Biology techniques. Another important development is the use of algae to capture carbon dioxide and produce oils capable of being processed into biofuels and other products including proteins. It is possible this technology might be used to remove carbon dioxide from the gases produced by coal or gas fired power stations and a small scale demonstrator aimed at proving this concept is already in operation in Scotland. Again, this is an area that could well benefit from Scotland’s synthetic biology capabilities.