Unit 3 Flashcards
(108 cards)
1
Q
Design variables for continuous stills
A
- Capacity
- Feed composition
- Material (copper/steel)
- Shape (rectangle/circular)
- Operation
- Cleaning frequency
- Thermal energy
- Condensation method
- Product/Intermediate stream collections.
- Pipework, etc
- Integrated safety/alarms.
2
Q
First column of 2 stage continuous distillation (Names)
A
Analyser
Beer column
Wash still
Stripping column.
3
Q
Components of hot feints
A
Fusel oils, iso-amyl alcohols.
4
Q
Describe a single column layout
A
Pre-heated continuous feed inputs halfway up.
Thermal energy input from the base.
Perforated plates throughout the column.
Above input = rectifier
Below input = stripper
Overhead condenser - distillate collected and returned as reflux.
Water exits from the bottom to waste and/or a reboiler.
5
Q
Why can a single column not be used for potable spirits?
A
Many flavour congeners
Too many plates required (too tall).
Some very volatile congeners must be vented.
Reboiler cannot be used with solids.
6
Q
Wash feed speeds and strengths
A
1500-60000L/hr
8-16%
7
Q
3 basic column still designs
A
Coffey (specific atmospheric design)
Atmospheric
Vacuum.
8
Q
Primary function of the stripping column
A
Strip alcohol and congeners from the wash
9
Q
Primary function of a rectifying column
A
Concentrate alcohol and congeners
10
Q
Reboiler design festures
A
Feed from overflow in column base.
Constant level maintained by weir.
Vapour disengagement area.
Steam heating tubes
11
Q
Pros of reboilers
A
Economical - condensate returned to boiler.
12
Q
Cons of reboiler
A
Inlet can choke - maintain and clean.
No solids - bake on to heating elements - transfer issues and off odours.
13
Q
2 main types of thermal energy provision
A
Reboiler
Thermocompressor/live steam.
14
Q
How does a thermocompressor work?
A
Stillage from stripping column collected in a vessel, then steam is flashed off from the liquid by creating a partial vacuum.
The mix of flashed off steam and lower pressure steam is fed to the base of the stripper column.
15
Q
How is a vacuum generated in a thermocompressor?
A
High pressure steam passed through a venturi connected to the flash vessel.
16
Q
Results of a thermocompressor?
A
Spent wash is cooled, heat energy recycle into steam. Spent wash volume increases 10% from added steam.
17
Q
Key points of tray design
A
Enough space for foam
Minimise pressure drop between trays
18
Q
Pros of a Coffey still?
A
Extra reflux in rectifier due to wash pre-heat coil.
Top condenser can be used to heat other distillery processes.
19
Q
Processing issues caused by abnormal conditions in columns
A
Coning
Dumping
Weeping
Flooding
Entrainment
20
Q
Coning
A
Liquid downflow rate is too low, and it is driven off.
No liquid/vapour interaction.
21
Q
Dumping
A
Ascending vapour is too slow, and liquid id dumped between plates with no vapour passage.
22
Q
Weeping
A
A combination of pulsing vapour flow and dumping.
23
Q
Flooding
A
Ascending vapour rate is too high, holding up liquid on the plates and creating pressure drop across the plates
24
Q
Entrainment
A
Vapour carries liquid up the column.
25
Column still condensers
Horizontal shell & tube.
Stainless steel.
Pairs.
Temp & pressure monitoring (effectiveness, and fouling alarm)
Can be used to pre-heat incoming wash.
26
Pros of wash chargers
2-3 FVs
Consistent
- feed temp
- wash strength
- wash pH
- amount of solids.
27
Tanks needed in a column systems
Wash charger
Intermediate process tanks
Product tank
Iso-amyl alcohol/fusel oil tank.
28
Tanks must have (6)
Sufficient capacity
Suitable materials
Sampleable
Volume calibrated
Cleanable
High alcohol safety precautions.
29
How many plates are typically in a Coffey still?
25 in stripper
42 in rectifier.
30
How is wash pre-heated in a Coffey still?
Pipework through rectifying column - also increases reflux in rectifier.
31
Coffey still plate design
Downpipes on opposite sides of perforated plate.
32
Coffey still heating
Thermo-compressor input at the base of the stripper.
Flash steam from boiling wash at base = reduced steam input + 10% extra condensate in spent wash.
33
How is distillation controlled in a Coffey still?
Historically, consistent steam + adjustments to wash flow.
Now controlled to give low alcohol concentration/high water concentration at base of rectifier.C
34
Coffey still spirit plate
Near top of rectifier.
Less perforated, with spirit collection cup.
35
How are incondensable gases removed?
Carbon dioxide and highly volatile compounds vented from secondary ether condenser.
36
What is hot feints?
Liquid leaving the bottom of the rectifier at 10-15%
Fed back into the top of the stripper at a controlled rate.
37
What are cold feints?
Liquid from condensing at the top of the rectifier/excess off character distillate, and alcohol from fusel oil distillation.
It is fed back into the stripper at a controlled rate, or refluxed back to the rectifier.
38
What is spent wash used for?
Animal feeds.
Carbon source from renewable energy production.
39
Downsides of a Coffey still?
Operates at a fixed throughput, dictated by pipework diameter.
Complex design, can require more frequent internal cleaning.
If copper used in pre-heat loop it must be turned off to allow for regeneration.
40
Number of plates in an atmospheric still?
Stripper - 50
Rectifier - 80
41
How does an atmospheric still pre-heat wash?
Passed through the heads condenser of the stripping column.
A de-gassing process removes carbon dioxide.
42
How can you increase efficiency of an atmospheric still (heating)?
Pass wash through both stripping and rectifying condensers.
Use a reboiler.
43
Cooling in atmospheric stills
2 x condensers on each column.
Portion of distillate returned as reflux.
Non-condensable gases vented from condensers.
44
Can throughput be adjusted for atmospheric stills?
Yes, up or down depending on requirements.
45
What is the main difference between atmospheric and vacuum stills?
In vacuum stills a vacuum is created in the overhead system at the top of the columns.
Pumps in between the 2 sets of condensers.
46
What is the effect of the vacuum pumps in a vacuum still?
Lowers the boiling point of the liquid streams, therefore decreasing the temperature and energy input required.
47
2 main inputs of a continuous system
Wash
Thermal energy.
48
5 variables that should remain consistent in wash feed
pH
ABV
Congeners
Temperature
Solids
49
What contaminant form fermentation would give a peppery, pungent character to distillate?
Acrolein
50
4 main outputs of a continuous system
Product distillate
Spent wash
Incondensable vent gases
Fusel oil
51
What ABV must Scotch grain whisky be distilled below?
94.8
52
2 methods to remove incondensable carbon dioxide
De gassing in wash pre-heat
Venting from condensers
53
Why must condenser temps be carefully monitored?
To allow venting of incondensable gases, but preserve alcohol.
54
3 recycled liquid streams in a continuous system
Hot feints (10-15% ABV)
Cold feints (96%+ ABV)
Reflux from overhead condenser
55
Liquid level maintained on a Coffey still plate?
4.5-5cm
56
What spirits does a Barbet still produce?
Light rums, and other light flavoured spirits.
57
Barbet features
Steam to both columns - limits recycling and reduces build up of unwanted congeners.
Stripper split into 3.
Rectifier column made of small stripper and concentrator.
58
How many plates in a Barbet still stripping column?
Main stripping column (20-35)
Pre-stripper (4-10)
Heads Concentrator (4-10)
59
How many plates in a Barbet still Concentrator?
Small stripper (20)
Rectifying section (50)
60
Where is product drawn from a Barbet still?
5 plates from top of concentrator column. 95-96% ABV
61
Objective of neutral spirit production
Go from 10% to >96%
Clear, clean spirit with no flavour compounds.
62
Columns/Actions in neutral spirit distillation
Primary Stripper
Extractive Distillation (hydro-selection)
Secondary Stripper
Fusel Oil Recovery
Alcohol recovery from off-take streams.
Methanol Removal.
63
Overall still design points for NGS
Steel
Circular
Thermal energy supply + plate design depends on wash.
After primary distillation - reboilers - energy consumption.
Each column has an overhead condenser - further distilled in heads column.
64
Why is hydro-selection used?
At high ABV some flavour compounds have similar volatility to alcohol.
65
Congener/flavour removal methods
Hydro-selection/extractive distillation.
Secondary rectification
Methanol column
Fusel oil column (amyl alcohols)
66
What compounds can be monitored through NGS production to indicate if the process is working efficiently?
n-Propanol
67
Describe the primary rectification step of NGS production
Stripping and rectifying column.
Strips all alcohols and volatiles from wash.
Rectifies to 60-96% ABV
Removes as many unwanted compounds and congeners as possible.
Typical Coffey or 2-column system.
68
Describe the hydro-selection/extractive distillation step of NGS production
Between primary and secondary rectification processes.
Hot water added to top of column, or diluted into feed 2/3 up column.
Steam feed from bottom, strips impurities from descending liquid.
Past input point the vapour is in contact with only water, which selectively removes alcohol from the vapour, and impurities continue up.
Clean, diluted alcohol leaves the base at 15-20%
69
Condition for continuous operation of a hydro-selection column?
Steady feed of hot water.
Stead feed on intermediate product from primary rectification.
Steady feed of steam to base of column.
70
Describe the secondary rectification step of NGS production.
Dilute alcohol (15-20%) concentrated back to 96.2%.
Column has 50-80 plates, feed enters 1/4 way up.
Thermal energy from steam at the base.
Steam strips alcohol and volatiles.
Hot water from base recycled to input for hydro-selection.
71
What impurities are removed during NGS production?
Fusel Oil - from rectification column in primary recitification.
Methanol
Volatile compounds - from heads condensers.
Unwanted compounds - hydro-selection.
72
What is the main factor in methanol content?
Raw material.
73
Describe a de-methylation column?
Fed from secondary rectification 1/2 way up column.
40-65 plates.
Reboiler
At >40% ABV methanol is more volatile than alcohol, so is stripped by rising hot vapour.
Reflux condenser back to column
Second heads condenser removes methanol as condensate.
74
Why might a continuous distillation need to shut down?
Cleaning solids from stripper plates.
Congeners accumulate to unacceptable levels.
Copper surfaces exhausted.
75
How to refresh copper?
Air flow to re-oxidise and re-activate surfaces.
76
2 options for column start up
Hot feints
water
77
How to shut down a continuous column still.
Swap wash to water (same temp)
Assess product quality until it drops.
Direct flow to cold feints tank.
Once spent wash is free of solids, divert to drain.
Cut steam supply.
Either discharge to hot feints, or keep remains in still.
Turn off cooling to condensers.
78
How to start up a continuous column still using hot feints
Pump hot feints at usual wash rate.
Adjust to usual wash ABV using water.
Turn on steam.
Once the temperature of the feints is at usual operating temperature, switch input to wash.
Adjust hot feints flow rate to normal for running.
Distillate collected as cold feints until it reaches required quality.
Distillate quality must be carefully monitored up to steady state conditions.
79
How to start a continuous still with water?
Feed water in to feed plate. Run steam until the two columns and condenser reach usual working temperatures.
Run product to cold feints until regular nosing indicates sufficient quality.
80
How to start up a Coffey still?
Pump water at wash temp through wash coils at normal feed rate.
Hot feints or water can be used.
Hot feints go up, or water goes down, until normal temperatures are reached.
Wash flow is started.
Hot and cold feints returns set to normal rates.
Initial spent wash recovered for further treatment.
Product distillate run to cold feints until of sufficient quality.
81
How to fix bad continuous product
Dilute to usual wash strength and temp and feed back into system.
82
Potential issues with continuous distillation system
High levels of fusel oils or sulphur.
Cold feints rate inconsistent - inconsistent ABV and potential alcohol loss in waste.
83
Important points for maintaining continuous stills
- All safety systems, inc pressure, vacuum, flow, and temperature systems.
- Regular cleaning, inspection, and servicing.
- Preventative maintenance.
- Achieve steady state operation.
84
How can a stripper column's performance be checked?
Check for alcohol in the spent wash.
Monitor temperature gradient up column.
85
What is the max ABV to which Scotch whisky can be distilled?
94.8%
86
Consequences of a weak wash
Higher concentrations of less volatile compounds in rectifier, leading to more reflux.
Little alcohol in hot feints.
87
Consequences of a strong wash
Decreased reflux, increase in alcohol in hot feints.
Possible loss of alcohol in spent wash if stripper becomes overloaded.
88
1Mla
1 000 000L
89
Key areas where alcohol loss can occur in a continuous distillation
Spent wash - overloaded stripper.
Intermediate product tanks - fitted with vent condensers.
Fusel oil system - incorrect or unbalanced operation.
Vapour condensers - inadequate cooling = venting of vapour.
Physical loss of distillate.
90
How to work out cost of losses?
Loss %
% of LPA
La/t = cost of grain.
+ energy, production team, etc.
91
Wash congeners
Acetaldehydes
Ethyl acetate
Methanol
Di-acetyl
Iso-butanol
Iso-amyl alcohol.
N-propanol
92
More volatile at high ABV
Methanol
93
Highly volatile at all ABVs
Acetaldehyde
Diacetyl
94
Less volatile at high ABV
Ethyl acetate (but still high)
Iso-butanol
Iso-amyl alcohol.
95
What happens to compounds more volatile than alcohol?
Vented from condensers
96
What happens to less volatile compounds?
Left in stripper and come out in spent wash.
97
Why do compounds accumulate in the rectifier at certain points?
The ABV is different up the column, compounds accumulate where their volatility at that ABV is the same as alcohol.
98
What are the primary focusses of grain whisky production by continuous distillation?
Recover the iso-butanol and n-propanol into product distillate, and remove the majority of iso-amyl alcohol.
99
How might a change in wash rate or composition affect congeners?
Reflux and alcohol concentrations at specific points in the rectifier will be altered, so will impact the accumulation of 'group B' congeners.
100
Steady state conditions for a full continuous still system
Wash composition and feed rate.
Hot & cold feints returns.
Operation of fusel oil column.
Draw off of product distillate.
Thermal energy supply.
Overhead condensing.
Regular cleaning.
101
How might congeners be lost during distillation?
Condenser too hot - lost volatiles.
Excess removal to fusel oil column, or lack of capacity in column to recover, separate and return alcohols.
Poorly maintained recycling of hot and cold feints - physical losses.
Vent leaks on intermediate storage tanks.
102
Why must iso-amyl alcohol be removed?
Can cause a vapour flow blockage due to foaming.
103
Fusel oil volatility
More volatile in lower ABV - therefore removed further down the column.
104
Key elements of fusel oil column distillation
Continuous still in its own right.
Small diameter, not copper.
Can be plateless.
Plates or rings can be surface area for reflux & separation.
Liquid feed, or reboiler or live steam.
Feed drawn from about plate 6 - monitored.
Top product returned to column as reflux, or to hot/cold feints.
Bottom product is mostly fusel oil to decanter.
105
Ways to remove DMS/DMDS/DMTS in continuous stills
Copper stills
Sacrificial copper - hot vapour pipes top plates (below product plate)
Venting via overhead condensers.
106
How is ethyl carbamate removed?
Sacrificial copper in the hot feints tank, and aeration of the hot feints.
Copper enriched, aerated hot feints steam is fed to near the bottom of the rectifier, where it traps volatile pre-cursors
107
Balance between 'easy' 'medium' and 'difficult' distillation patterns.
Easy - low ABV to rectifier. More reflux, rapid rectification.
Difficult - More alcohol = less reflux, but less energy required. More alcohol in hot feints (potential to overload stripper)
Medium - balance between the 2.
108
Options for dealing with out of spec input (wash)
- adjust cold feints to compensate (ABV)
- Blend with in spec to decrease change (wash charger)
- Monitor and adjust iso-amyl plate draw off and product quality.
- Adjust thermal energy input to normalise temperatures.
