primary focus will be on the grain whisky distillation processes currently found in Scotland. Continuous distillation is a form of distillation where a mixture is con- tinuously fed into the process – and separated fractions are continuously removed as output streams. Distillation is the separation, or partial separation, of a liquid feed stream into individual components or fractions by selective boiling, evaporation and condensation. These continuous processes are generally driven by thermal energy in the form of steam and produces at a minimum two output fractions – at least one volatile distillate fraction which has been boiled and separately recovered as a vapour condensed to a liquid and a bottoms fraction which is the least vola- tile residue which has not been sepa- rately captured as a condensed vapour. Continuous distillation is used widely in the chemical process industries where large quantities of liquid have to be distilled and separated either into single individual components or fractions. This article concentrates on this chemical engineering process as it re- lates to the potable alcohol industry. This is also used extensively in the very large capacity fuel alcohol industry. Continu- ous distillation in the potable alcohol industry has its roots in the early 1820s- 30s when different types of plant were designed, built, installed and operated Stripping and rectifi cation columns at to signifi cantly increase product output Adnams Copper House Distillery (© Adnams) which to that time had been limited to the small batch pot still distillation Continuous distillation processes in the lowlands of Scotland. Continuous distillation The early continuous stills were de- Grappling with grain whisky signed and patented by Robert Stein and Aeneas Coffey, two enterprising production engineers and designers of the time. These early designs, particularly the By Billy Mitchell Coffey stills, form the basis of many of the plants remaining in operation in This is the sixth article in the series to support those Scotland today. The main distillation plant found in studying for the General Certifi cate in Distilling and builds use today will consist of a large wash on the previous article in the series around the batch/pot charger, beer, analyser or stripper column, a rectifying column, various still distillation process. This type of continuous process is overhead condensing process, pumps, widely used, in various forms, in the production of whisk(e)y, pipe work, a fusel oil removal system, heat recovery and reuse, product potable neutral alcohol and non-potable fuel alcohol. off-take streams including systems to remove spent wash, product spirit, and t is also widely used in many other raw material input and pre-distillation fusel oils. Itypes of spirits production around the processes may be very different. The process will also include the world. Although the main focus of this This article will cover the theory, provision of thermal energy in the form article will be grain whisky produc- principles and practicalities – and of steam supplied either through live tion, the theory and risks are common general risks – associated with the steam injection, thermo compressor or across all distilled liquid types – and continuous distillation processes. The re-boiler systems. This is a very ener-

50 z Brewer and Distiller International June 2017 www.ibd.org.uk BASICS OF SPIRITS PRODUCTION l

gy-intensive continuous process which Hopefully some, if not all of these can be designed, built and operated on will be more recognisable once you a range of input capabilities ranging have completed this article. from ~1500 litres/hour to larger plant operating at input capacities of well Distillation theory over 60,000 litres/hour. Distillation can be described as a These continuous distillation pro- process for separating the compo- cesses when operated in steady-state nent substances in a liquid mixture conditions are very efficient at recovery by evaporation and condensation. The of ethyl alcohol and various flavour principle of continuous distillation is components from the input wash feed the same as for pot still distillation and are designed to recycle and re- – when a liquid mixture is heated to cover various liquid streams to ensure boiling point, the composition of the ethyl alcohol recovery is maximised vapour above the liquid differs from with little or no loss of alcohol. the liquid composition – and if this In potable alcohol production there vapour is separated and condensed is no one design or layout of plant. into a liquid, it becomes richer in the Designs have evolved from the early lower boiling point compound(s) of the rectangular, wood and copper stills – original liquid. and can now be found as rectangular, This is the basis for continuous circular or a combination of both, and distillation. The liquid/solids mixture is constructed either in stainless steel or Coffey still from Kilbeggan Distillery in heated up and fed into the distillation copper – or a combination of both. As County Westmeath in Ireland. (Photo: column, where the feed initially starts already stated they can be designed, HighKing on Wikimedia Commons) to flow down the column but where constructed, installed and operated as it is in the small-batch pot still the higher volatile (lower boiling point) at a huge range in wash feed input processes. Use of this metal in the compounds are vaporised and rise up rates and product spirit recovery rates. relevant areas of this plant will remove the column. These processes can be operated these undesirable flavour compounds, As this vapour rises it eventually under normal atmospheric pressure, ensuring production of a good consist- cools and while a portion continues under vacuum, at high pressure or a ent quality of product. These off-odour up as vapour, some of it enriched in combination of these. removal reactions are not required in the less volatile components beings Each of these conditions will the large fuel-alcohol plants. to descend as liquid. Figure 1 gives an have variations in energy input and Continuous distillation plants, example of a distillation apparatus for in general will have been chosen to whether operating at low- or high- separating some form of feed into two deliver best fit with your other process input rates lend themselves readily to plant and how they are configured. semi- or fully-automated control. The Condenser Their key task is the same whether key to delivery of product at optimised operating under pressure, vacuum or energy consumption is best achieved atmospheric – to separate the alcohol when operating under steady condi- Cooling Water Re ux and other required flavour compounds tions with consistent wash feed, ther- Drum from the fermented wash in a con- mal energy supply, clean condensing Re ux tinuous process and to recover the systems, consistent spirit off take and required volume and quality of final recovery and return of recycled liquid product with optimum energy input. streams. Pump The feed material for this process As is the case within the whisky is fermented wash containing ethyl al- industry there is a list of terminologies Overhead product cohol and other minor flavour constit- which are aligned to this continuous pro- Feed uents (which can be either desirable cess – these may include the following: or undesirable in final product), water Fermented wash, wash charger, hot and solid material (mainly unferment- and cold feints, spirit safe, fusel oil Distillation Column Distillation plate ed cereals and yeast.) This fermented column or fusel oil decanter, steam Vapour wash may contain all the solids from thermo compressor or re-boiler, wash Reboiler the cooking, mashing and fermenta- coils or other external heat recovery tion processes, or can be relatively processes, spirit plate, the bend, the Steam solids free where the primary solids bend temperature, overhead con- Condensate have been removed and recovered denser, re-ascending wash lines, down after mashing. comers, valves and triangular pitch, Bottoms Bottom These cereal solids have come rectifier and analyser plates, conge- liquid product from the maize, wheat or malt element ners, on water, on wash, on spirit, off of the mash bill which is governed by spirit, spent wash, pressure relief and Up owing vapour Down owing liquid the capability of the pre-distillation anti vacuum systems, spirit charges processes. and spirit receiver, feints receivers… Figure 1: Separation into two fractions: overhead distillate The use of copper in the manufac- as well as temperature, pressure and product and bottoms product. Note the column itself is ture of these continuous stills is as flows associated with this continuous divided into two sections: Rectifying (above feed) and important in these production plants operation. Stripping (below feed) www.ibd.org.uk Brewer and Distiller International June 2017 z 51 l BASICS OF SPIRITS PRODUCTION

0.75 – they are much less effective than wash is alcohol-free if the process is top vapor any ideal model stage thus the actual fully optimised. There should be no fraction to number of plates required is calculated alcohol loss through this stream. This condenser by dividing the number of theoretical material is boiling water containing reux stages by the plate efficiency. non-fermentable material in solution In principle both the stripping and with grain and yeast debris. It can then rectification processes could take be removed via heat recovery processes place within the one column but in for further processing as animal feed or downcome r practice these are split into two sepa- potentially as a ‘green’ energy source. Trays rate processes primarily due to the

downcome r overall height and practical civil and Rectifier column recti cation mechanical engineering difficulties These columns also vary in shape and Feed encountered in building and erecting size and also in the number of plates. downcome r Feed tray a single tall column. Figure 4 shows Hot vapour from the top of the stripper the construction of a McCabe-Thiele column passes through the vapour pipes

downcomer model for ethanol-water separation. entering the base of the rectifier where For a detailed description see Brewer it condenses and evaporates the liquid and Distiller International, Shortcut on the plates as it passes from plate to downcomer distillation design methods, April 2016. plate up the column. These hot vapours Trays strippin g from the stripper column are the only

downcomer Stripper column (beer column, source of thermal energy within the analyser column) rectifier and act in the same manner as Stripper columns vary in shape and the steam in the stripper column. downcomer size but generally contain anything The least volatile components col- from between 15 to 30 plates. Fermented lect in the base of the rectifier as a liq- Reboil wash is fed from a large wash charger uid called feints or hot feints which are to to ensure an uninterrupted steady flow fully recycled to the top of the analyser Reboiler to the still. The use of such a large for further distillation. vessel evens out any major tempera- Liquid product is collected at a ture and alcohol strength variations in solid plate near the top of the rectifier Figure 2: Major flows and components of a column individual fermentations in attempts to at the required spirit strength, this can fractions, namely an overhead distil- operate under steady conditions. be in the range 92%-96% alcohol by late product and a bottoms product. The wash can be preheated in a volume – but for grain whisky must not As explained earlier these lower- number of different ways depending on be below 94.8% alcohol by volume. The boiling, higher-volatility products exit the process plant layout – and in the strength of final product can also have a from the top of the column and are case of the Coffey still within the wash significant impact on the concentration condensed and recovered while the coils themselves. In other non-Coffey of the recovered congeners with lower higher-boiling compounds exit from still designs it is generally preheated strengths giving a product containing the bottom of the column. Thermal by high-temperature overhead vapours relatively high concentrations while energy is provided to the base of the from the rectification column and from higher strengths tending towards neu- column to drive this process. This type high-temperature spent wash. The trality with very low levels of congeners. of continuous distillation plant has a feed plate is located at or very near the Vapours which pass out the top of constant flow of feed mixture and not top of this column. In the case of grain the rectification column contain the very filled all at once like a batch pot still whisky production the target incoming volatile components including alcohol operation – and therefore does not wash feed temperature is in excess of and a very small portion of water. This require a large distillation reservoir for 85o C and the feed alcohol concentra- vapour is condensed in the overhead each batch fill. tion is in the range of 7.0% to 14.0% condenser arrangements where some The design, build and operation alcohol by volume. of the condensate is returned to the of a continuous distillation process Thermal energy enters the bottom top of the rectifier as reflux while the depends on the composition of the of the stripper column and proceeds to balance is collected as cold feints which feed and desired products. There are mix with the liquid pouring down the are recycled via the hot feints system to many computerised simulation model column. The steam and the vapours it the analyser. The temperature of opera- systems which are used to establish generates strip the wash of the ethanol tion of the overhead condenser is set both design and operational criteria. and most of the other congeners which to control the venting of unwanted very One of the most common methods flow forward to the rectifier. This volatile compounds whilst also ensur- used in the design to distil a binary vapour leaving the analyser or stripper ing maximum recovery of ethanol as component feed is the McCabe-Thiele column will contain between 15-30 % reflux or cold feints. method, first published in 1925 and alcohol by volume – this being driven by The removal and further process- still valid today. wash feed composition and the opera- ing of side streams from the rectifier These design models will calculate tional conditions of the process. will be discussed later. Needless to say the number of theoretical plates for both The wash continues to cascade this is a very important process in re- the vapour stripping and rectification down the stripper column from plate moving iso-amyl alcohol (feints) from sections within the continuous distil- to plate mixing with the rising vapours. the final product thus ensuring a clean lation plant. Actual tray efficiency for The liquid that flows to the bottom of spirit recovery. installed operations is in the range 0.5 to the column known as stillage or spent The design of the trays or plates

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in the analyser and rectifier column is governed by the composition of vapor the feed. Trays and plates encourage bubble bubble caps caps liquid vapour liquid contact so that falling liquid partially vaporises and rising weir vapour partially condenses to create liquid more equilibrium phases. This involves downcomer tray heat transfer which takes time to achieve and the plate or trays provide panel

the mechanism for this to happen. downcomer vapor

A key feature of any tray design is to liquid minimise pressure drop. This design could include incorpo- active tray area ration of the following types: weir Bubble cap trays: where each riser liquid has a riser or chimney fitted over each hole and a cap which covers the riser tray downcome r to allow passage of vapour. Vapour rises through the chimney and is pane l

vapor downcome r directed downward by the cap finally liquid discharging through slots in the cap into the liquid on the tray. Sieve trays: which are simply metal plates with holes in them – vapour pass- Figure 3: Bubble cap trays in a column. Note the liquid and vapour paths along the column es straight upward through the liquid on the plate. The exact number and size of modifications and adjustable vapour (wash coils) were all made of copper the holes are established during overall rate flows. and rectangular in shape. New designs column design including the triangular Sieve trays are the preferred choice have seen analysers being replaced with pitch of the centre of the holes. in the stripper column where the feed either circular or rectangular stainless- Valve trays: where the perforations in material contains solids which could steel columns and the traditional copper the plate are covered by liftable caps. result in choking both bubble caps wash coils in the rectifier being replaced Upward vapour flow lifts these caps and valve trays. This is less important by stainless-steel wash coils. creating a flow area for passage of this in rectifier columns where solids are Use of stainless steel has led to a vapour. The lifting caps directs the flow generally excluded. reduction in the manufacturing costs of vapour horizontally into the liquid Distillation columns can be packed and to longer plant life. The reduc- providing a better method of mixing as an alternative to the use of trays. This tion in copper surface area has been than in traditional sieve trays. metallic, plastic or ceramic packing overcome by the use of sacrificial could include pall rings, raschig rings or copper installed in key quality control- Some form of weir is required to en- saddles which provide a large interfacial ling areas of the process. To maintain sure there is always some liquid on the area and minimises short circuits of quality this ‘sacrificial copper must be tray for any of these tray types. flow. They are useful for small-diameter replaced at regular intervals. Adverse vapour flows within the columns where tray installation is dif- The two feeds to the still are: stripper and rectifier columns can ficult. Vapour/liquid contact may be less fermented wash at approximately 8.0% cause a variety of processing issues. efficient when compared with trays as ethanol by volume entering through These can include: the liquid moves towards the column wash coils at the top of the rectifier at Coning: where the liquid rate is too walls and the vapour flows move readily around 30-340C and thermal energy in low allowing vapours to drive the liquid in the liquid free area – this can be over- the form of steam entering the base of away passing through as a continuous come by the use of some form of liquid the analyser to drive the process. stream resulting in little or no mixing, redistribution process. The stills are divided into a number Dumping: where the vapour rate is of sections separated by perforated too low allowing some plates to dump Grain whisky distillation trays on which we have counter flows liquid with no vapour passage. The Coffey still is the most common of liquid and vapour. Typically the Weeping: which is a combination of pul- type in use in Scotland for the produc- analyser will have around 30 and the sating vapour flow and liquid dumping. tion of grain whisky. This is a two-col- rectifier around 40 trays. The ferment- Flooding: where the vapour rate is too umn system consisting of an analyser ed wash flows down the rectifier within high creating hold up of liquid on the and rectifier containing sieve plates, the stainless-steel or wash coils which plates creating increases in column designed to operate continuously wind their way between the trays con- pressure drop. under steady-state conditions. A much nected from one section to the other Entrainment: where high vapour flow smaller packed column (or fusel oil by external bends protruding from the carries liquid back up the column to decanter process) is used to separate, rectifier frame. the previous tray. recover and remove the highly potent, As it descends the wash, tempera- feinty, iso-amyl alcohol. A diagram of a ture is increased by the contact of hot Most of these issues can be designed simple Coffey still is given in Figure 5. vapours from the analyser. By the time out at the modelling stage although Traditionally these columns, trays it reaches the bottom of the rectifier the they can also be overcome by plant and ancillary condensers and pipework wash temperature will have increased www.ibd.org.uk Brewer and Distiller International June 2017 z 53 l BASICS OF SPIRITS PRODUCTION

to around 90-940 C, the boiling point of becomes richer in alcohol and volatile fier and rises through the trays heating an ~ 8% ethanol by volume solution. congener as it rises. the descending wash pipe. This vapour This hot wash is then redirected to Spent wash will contain little or is progressively condensed as it rises, the top of the analyser via the reas- no ethanol as it leaves the base of the providing the down-flow of liquid and cending wash pipe where it is then analyser at boiling point where flash vapour/liquid. Equilibrium is reached cascaded down the analyser through steam is recovered through a thermo- on each tray for that particular tem- the system of weirs, plates and down compressor to augment the live steam perature. This can be viewed as a series comers. This liquid passing from tray feed. The addition and condensation of batch distillations progressing up the to tray meets vapour forcing itself of pure, clean live steam within this rectifier with increasing concentrations upwards through the plate perfora- process adds approximately 10% to the of ethanol and the more volatile compo- tions through the liquid layer. Gradu- actual input liquid feed to the still. nents at each higher tray. ally the wash is stripped of its more The alcohol-enriched vapour at On condensing at the lower plates volatile components as it descends the around 15-30% alcohol transfers via the of the rectifier the liquid concentration analyser and conversely the vapour vapour pipes to the base of the recti- of alcohol can range between 10-

Ethanol/water at 14.70 psia by NRTL Ethanol/water at 14.70 psia by NRTL 1 1 0.9 0.9 0.8 0.8 0.7 0.7 0.6 0.6 0.5 0.5 0.4 0.4 0.3 0.3 0.2 0.2 Ethanol vapour mole fraction Ethanol vapour Ethanol vapour mole fraction Ethanol vapour 0.1 0.1 0 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Ethanol liquid mole fraction Ethanol liquid mole fraction 1: Ethanol-Water X-Y diagram 2: Rectifying Line added to X-Y diagram

Ethanol/water at 14.70 psia by NRTL Ethanol/water at 14.70 psia by NRTL 1 1 0.9 0.9 0.8 0.8 0.7 0.7 0.6 0.6 0.5 0.5 0.4 0.4 0.3 0.3 0.2 0.2 Ethanol vapour mole fraction Ethanol vapour 0.1 mole fraction Ethanol vapour 0.1 0 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Ethanol liquid mole fraction Ethanol liquid mole fraction 3: Stripping line added to X-Y diagram 4: Rectifying, stripping, and Q-Line

Ethanol/water at 14.70 psia by NRTL 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 Ethanol vapour mole fraction Ethanol vapour 0.1 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Ethanol liquid mole fraction 5: McCabe-Thiele diagram for Ethanol-Water separation

Figure 4: Constructing the McCabe-Thiele model for ethanol/water separation

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Analyser vapour pipe Rectifier the final product. With the still operating as in Figure 6, a small side-stream flow can be wash pipe vapour vent feints inlet withdrawn from plate 4 to the fusel oil column for further distillation where wash fusel oil (iso-amyl alcohol) is sepa- inlet rated from the ethyl and iso-butyl alco- hols, which could also be in this side stream. The spirit/butanol top product is returned to the still via the hot feints system while the fusel oils can be recovered and sold. Figures 7 and 8 show the potential distribution of these three congeners under abnormal operating conditions. The graphs show the iso-amyl alcohol either being driven lower down the spirit to rectifier into the hot feints or even the receiver top of the analyser and significantly higher up the column with the poten- tial to overflow into the product spirit. Maintaining steady, consistent operating conditions is essential if you are to produce the required quality of spent hot feints product at the designed output with steam inlet wash outlet to receiver optimum energy consumption. Good operating conditions will have been established for each still currently in Figure 5: A simple Coffey still production. These could include: 15%wt/wt with the vapour in equilibri- solid plates and can be referred to • Wash temperature and strength um with the liquid. This liquid, known as the spirit plate. Spirit off-take is • Bend temperature – which controls as hot feints, is recycled to the top of controlled by some form of density the wash throughput – the lower the the analyser generally via a hot feints measurement and is set at between bend the higher will be the throughput storage tank for further distillation. 94.2-94.7% alcohol by volume. and vice versa Vapour progresses upwards Off-specification high-strength • Overhead condenser operating tem- condensing in both the liquid on the product produced at ‘start up’ or ‘shut peratures and general conditions plate and the wash coils. This releases down’ of the distillation process is re- • Re-ascending wash temperature latent heat to both the incoming wash covered after cooling in the cold feints pipe and to the liquid at each plate. receiver and recycled in a controlled The latent heat is the heat released manner via the hot feints to the top of or absorbed during a change in state the analyser. (re liquid to vapour or vapour to liquid) Rapid dumping of this high-strength without incurring a change in tem- liquid to the top of the analyser in an perature. The incoming wash thus re- uncontrolled manner will add a consid- ceives preheating whilst condensation erable increase in alcohol feed and will Spirit plate in the liquid on the plate generates result in abnormal operations. 32 more vapour for fractional distillation. Concentrations of the main con- 30 28 The most volatile components rise geners in the liquid phase on each 26 to the top of the column and out into rectifier plate can be measured by gas 24 the overhead condenser system. These chromatography and can be graphed 22 vapours contain some highly volatile, as in Figures 6, 7 and 8. These show 20 Spirit obnoxious unwanted compounds and the three main components of ethyl 18 this system should be set at a tem- alcohol, iso-butyl alcohol and iso- 16 Butanol perature to vent off these compounds amyl alcohol. The removal of iso-amyl 14 whilst recovering the maximum volume alcohol is a key function of this type of 12 of high-strength alcohol. This alcohol rectification. 10 is recycled as reflux to the rectification The fusel oil or iso-amyl alcohol 8 column or after cooling into the cold distribution will be as in the green line 6 Fusel oil feints receiver and thereafter via the of Figure 6 under good, average oper- 4 hot feints system to return for further ating conditions. The concentration in 2 1 processing at the top of the analyser. the hot feints will be low but will rise 0 20 40 60 80 100 rapidly to 20-30% wt/wt by Plate 4-6. Concentration % w/w Control of congeners The concentration will then fall away to Two to three perforated plates at the almost zero by plate 16 or so and there Figure 6: Main congeners on each rectifier plate – good top of the rectifier are replaced with should be very little or no fusel oil in average running conditions www.ibd.org.uk Brewer and Distiller International June 2017 z 55 l BASICS OF SPIRITS PRODUCTION

(stripper and rectifier) along with some and explosion, COSHH arrangements, form of fusel oil removal and recovery. DSEAR/ATEX and personal protective These differ from the Coffey stills in equipment to name but a few. that they do not generally have internal Over and above the process issues wash coils and inlet wash temperature you have a wide range of legislation to is increased by heat transfer with hot comply with – taxation authorities also Spirit plate process liquid or vapour streams – place a major duty on each distiller to 32 and also generally operate re-boiler accurately account for all raw materi- 30 systems at the base of the analyser als processed and all spirit streams 28 to provide the thermal power for the recovered – this can be a relatively 26 distillation process. The theory and simple or complex process depending 24 general operating and control princi- on the physical layout and capacities of 22 ples and practices also apply. your plant. 20 Hopefully, you should now have 18 Spirit Safe operation of a continuous some indication of the potential vari- 16 system ables in the overall production pro- 14 Butanol cess, along with those making a major 12 Distillation plant is a major asset in 10 any grain distillery. It is in operation contribution within the distillation pro- 8 twenty four hours per day over extend- cess – which can have a real impact on 6 ed still runs ranging from several days your spirit quality and overall distillery 4 to several weeks. Unexpected failure efficiency. Fusel oil 2 of this asset will have profound impact 1 0 20 40 60 80 100 on the site’s ability to meet production More follow-ups: Concentration % w/w target volumes – so all plant must be There is no one size or design of plant regularly cleaned, inspected, main- fits all producer’s requirements. Here tained and replaced as components are some follow-up pointers to help Figure 7: Main congeners on each rectifier plate – difficult distilling conditions become obsolete. embed your learning around your yeast A comprehensive planned main- and fermentation processes :- tenance system is a pre-requisite in • How are the major risks associated ensuring the plant is always fit for the with the operation of the overall distil- purpose it was designed, operates lation plant assessed and controlled? efficiently and safely and produces the Who is responsible for this? quality of product which meets your • Talk with your quality department or business requirements. blender to fully understand how your Spirit plate There are a number of regulations spirit quality is defined. What are the 32 relating to the safe operation of this key attributes throughout the distillery 30 plant which must be fully addressed which, if controlled, will deliver the 28 during the design, build and operation desired quality of final product? 26 of the distillation equipment. These • Fully understand the capacities and 24 will include pressure systems regula- capabilities of all the plant associated 22 tions relating to your steam produc- with the distillation process and fully 20 tion, supply, distribution and recovery, understand your accounting processes Spirit 18 location of vents and testing of pres- to ensure compliance with the excise Butanol 16 sure relief and anti-vacuum systems, tax/duty controls. 14 overfill protection of the receivers, any • What are the key maintenance and 12 potential loss of containment and fire cleaning procedures employed in the 10 and protection systems. distillery? How can they impact on your 8 This is not an exhaustive list but production activities? What evidence 6 Fusel oil should give an idea of the range of shows that they require maintenance? 4 controls required and the testing of How does poorly-maintained equip- 2 1 these controls to ensure they work as ment impact on distillation perfor- 0 20 40 60 80 100 designed. mance? Concentration % w/w Anti-vacuum, pressure-relief and • What are the key control points to overfill protection systems are also be followed on your distillation plant Figure 8: Main congeners on each rectifier plate – easy safety systems installed in this plant – i.e. timings, liquid strengths, testing distillation conditions – the anti-vacuum and pressure-relief protocols etc. What is the frequency of • Steam flow and pressure systems are generally vented exter- these tasks? • Fusel oil removal rate. nally to atmosphere to negate any • Hot and cold feints recycle and potential release of ethanol vapour. Answering these questions and posing return rates. Regulations relating to general a few more of your own will ensure a health and safety could include entry more detailed understanding of how Other grain whisky distillers in Scot- into confined spaces, isolation pro- and where the distillation and as- land and Ireland operate alternative cedures, risk assessments, work in- sociated processes fit in your overall distillation plant. These are gener- structions, permit to work procedures, production plant. I wish you well in ally circular, stainless-steel columns controls around the major risks of fire your endeavours.

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