Madam, - Mary White is to be commended for her attempt to link the Carlow sugar factory closure to the need to process energy crops into substitutes for fossil fuel. May I, however, comment on Mary White's arguments, and adapt them constructively to the technological realities.
Ethanol by fermentation of beet sugar as a petrol substitute is a non-starter, due to the amount of energy required by the necessary distillation process. For a time this was tried in Brazil, but the energy balance was negative, even though they had access to the crushed sugar-cane as fuel.
Bio-energy to be sustainable must be produced by a dry process, and the challenge for process technologists is to devise one which will convert bio-sources into a manageable mix of combustible gases and/or liquids, leaving a residue of char as a clean solid fuel.
In the case of rape-seed oil, the pressed cake is good cattle-feed, and the oil is an excellent diesel substitute. This would be economic with currently available technology if the tax penalty were to be lifted. I understand it is actively under consideration by a farmer group in Wexford.
In the case of wood chips from forestry waste, and from dedicated short-rotation coppicing, the indications are that with high-temperature pyrolysis one can get a mix of gases from which methanol can be produced catalytically, and this is one route to liquid fuel.
To obtain high-calorific gas, suitable for the gas grid, however involves dealing with the problem of nitrogen dilution in the oxidation process, and the problem of pollution by nitrogen oxides, where the oxidation source is air. This could perhaps be resolved with the aid of pure oxygen available as a by-product in the production of hydrogen by electrolysis of water, a process being promoted elsewhere in the context of energy from renewable sources such as wind, wave and tide.
Much work was done in the US in the 1970s in the aftermath of the first oil crisis, and I attended a conference in Golden, Colorado at which the possibilities were discussed at length, reporting for the National Board for Science and Technology. The scenarios which began to be considered then have again become relevant, and the various identified development threads need to be picked up and explored systematically for their current techno-economic feasibility, in the light of updated technology.
There are many factors involved in making the transition to multi-source renewable energy, and the adaptation of the Carlow factory to renewable energy production needs to be embedded in an overall strategic energy development plan, looking decades ahead.
There is, alas, more to it than simply fermenting sugar to get ethanol. - Yours, etc.,
Dr ROY H W JOHNSTON,
Belgrave Road,
Rathmines,
Dublin 6.