Steam was one of the great drivers of the Industrial Revolution. British engineers Smeaton, Savery, Newcomen, Boulton & Watt and Trevithick were able to harness the power of steam with the strength of iron and steel to create the engines that drove the revolution for a hundred years.
STILLS FROM “BRIEF ENCOUNTER” — 1945
One application was the railway engine. Essentially a boiler on wheels, the coal-fired furnace heated up a water tank, the evaporating steam piped into cylinders, expanded, pushing the pistons that drove a crank shaft and thus the wheels providing locomotion.
Distilleries have similar boilers, without the wheels or the pistons of course, to provide the heat for distillation. But rather than using fossil fuels like oil or coal, we use our bagasse, the organic, shredded cane debris leftover after milling.
That iconic image of a steam train belching out smoke and soot clearly will not do. Consequently we commissioned a complex three-part system to generate steam from biomass without pollution.
OUR BIOMASS BOILER HOUSE
This bespoke boiler system – our single most expensive piece of kit – was manufactured for us by John Thompson in South Africa. Unusually, it is made of two parts: firstly a water-cooled furnace that combusts the bulky bagasse; secondly, the 35 ton evaporator, a fire tube bank that separates the steam from the super-heated water.
The bagasse is fed in to the furnace via a box ram feeder. Here it burns at very high temperatures in order to dry out the bagasse’s moisture. A waterwall surrounding the furnace mediates it’s high heat. There is also a vibrating ‘grate’, which forces coarse ash and cinders to fall out into a hopper underneath ensuring continually efficient, optimum combustion.
The hot exhaust gases (260˚C) pass from the furnace through a fancy air heat exchanger that captures the waste heat and cunningly re-uses the heated air to pre-dry the damp bagasse entering the combustion chamber, reducing energy usage, generating more steam.
Now down at 192˚C, the hot gas passes another heat exchanger, known as an economiser, that pre-heats the incoming water into the boiler, again reducing energy usage.
The steam generated in the evaporator goes to a manifold, a switch board, that directs it where needed, primarily the stills, but also to the Orc. More turbo generator than Tolkien ogre, the Organic Rankine Cycle steam-powered turbine generates electricity to help run the site.
But we still have the sooty combustion gases from the furnace to deal with. We have a two part cleansing operation before the exhaust air reaches the chimney. First, the grit collector, where a series of cyclones spin creating differential pressure forcing heavier soot particles to separate out in to a hopper.
Finally, the exhaust air is pulled through a baghouse filter for the final clean by an induced draught fan. The baghouse works like 129 vacuum cleaners – long fabric filter ‘bags’ in a cylindrical holding cage – where the exhaust air on a reverse jet principle is sucked through removing the remaining very fine ash particles ensuring the exhaust air exits the chimney clear.
The ash, composted with other by-products such as dead yeast and excess bagasse, is applied to the cane fields as fertiliser.
Such is the exceptional efficiency of this electronically controlled system there is nigh-on total combustion in the furnace. This perfect state is known as Stoichiometric – or Theoretical Combustion – and results in exceptionally clean exhaust gases.
Further, as cane has no sulphur content, the emissions are substantially cleaner than any commercial coal-fired boiler, significantly lower even than the latest World Health Organisation guidelines.
WORLD HEALTH ORGANISATION AIR QUALITY GUIDELINES
This doesn’t come cheap. We sought out the very latest thinking, the most sophisticated engineering to provide the maximum environmentally-responsible solution possible. At a fifth of WHO limits this we have achieved.