Boka Reflux Still - How To Build
Posted: Sat Feb 02, 2013 5:59 am
Here is the data FROM the wiki. From time to time, that resource hog may need to be taken down. This seems to be the one post everyone requires, so I will try my best to put the full 'proper' post here. The siki link is: http://homedistiller.org/wiki/index.php/index.php ... w_To_Build" onclick="window.open(this.href);return false;" rel="nofollow but when we have more 'guest' traffic than the site can handle, the first thing to be shut down is the wiki (since it uses SO much of our server's CPU, and we have no way to properly throttle robotic site suckers). Thus, this page contains ALL of the information from the wiki page. It may not be quite as 'pretty' as the wiki, but the content is fully here, including all pix and links.
Husker:
Boka Reflux Still - How To Build
The Bokakob (Boka or Bok for short) is the common name for a Dual Slant-Plate Single Column In-line Reflux Still designed by Alex Bokakob in 2001. The still was originally designed with a fairly small reflux column to sit atop a stove-top boiler, and has seen significant modifications and improvements over the years. This still is popular with many novices for its simplicity to build and operate, while being able to yield 95% ABV neutral spirits. It can also have its packing material removed and function as an adequate pot still. It is classified as a Liquid Management or LM Column reflux still. History
Bokakob created a series of reflux still design drawings that were widely circulated after they were created in 2001. http://homedistiller.org/equip/photos-alex" onclick="window.open(this.href);return false;" rel="nofollow This particular still featured a short (2ft/.67m) column made of 1.5" copper pipe attached to a stove-top pot boiler, and only required three joints to be soldered (the upper and lower plate, and take-off tube). Various discussions on Yahoo and HomeDistiller.org resulted in many design variations and improved efficiencies.
The still was named after its designer Alex, who had a Yahoo username of Bokakob, but web discussions with poor spelling or simple abbreviation led many to refer to the still as a Bokabob, Boka and Bok.
Column and Slanted Plates
General Theory
The single in-line reflux column of the Boka is meant to carry vapors from the boiler up through packing material for reflux and up to the condenser. Some of the distillate will fall to the dual slanted plates which can then overflow (allowing the distillate to fall back into the packing, which is the basis of the reflux design) or be drawn-off for collection. Materials
The column of your still should be made from copper or stainless steel. Stainless is inert, and copper actually assists in creating a clean flavor in the final product by removing sulfides as vapors come in contact with the copper as they travel through the column. http://homedistiller.org/forum/viewtopic.php?f=2&t=749 Availability and local price will probably be the greatest determiner of which material to use. Also note that stainless steel may require more industrial type of equipment and skill to weld than copper which requires simple soldering. Stainless does not suffer as greatly from heat loss, so insulation is less critical. Also note that well polished copper is very pretty. All other things being equal, choose the copper. Synthetic materials other than PTFE are unsuitable. http://homedistiller.org/forum/viewtopic.php?f=2&t=3662 See rule #8 http://homedistiller.org/forum/viewtopi ... =35&t=5090
Most pipe also comes in varying thicknesses: K, L, M and DWV. http://homedistiller.org/forum/viewtopi ... 46&t=18123 and http://www.sizes.com/materls/pipeCopper.htm" onclick="window.open(this.href);return false;" rel="nofollow K is the thickest but is commonly not found at retail outlets. L is the most common and is a standard thickness, meaning that it fits the couplers, caps, etc that are sold retail. M is the thinnest and is a better value of pipe for our purposes, but may make attachments more difficult to fit. DWV (which stands for Drain Waste Valve) is the thinnest by far, and subsequently cheapest and best value. Due to its thin walls, it has temperature and pressure ratings and warnings which do not apply to our neutral pressure systems http://homedistiller.org/forum/viewtopi ... 15&t=18093 Your column should ALWAYS be properly vented and no pressure buildup should be possible, even in full reflux. If you have pressure buildup in your column it could explode, regardless of the thickness of the pipe. If you are going to use DWV, made sure that you check the accompanying fittings before you buy to make sure it will all assemble easily and be solderable.
Column Width
The original Boka was built with a 1.5" (38 mm) column. The width of the column directly impacts the speed at which distillate can be collected, all other things being equal. In actuality, with a narrow column, the heat put into the still has to be lower to keep the vapor speed in the column at an appropriate speed so the reflux can occur properly. With a wider column, more heat can be applied while maintaining proper vapor speed, and the overall yield of properly refluxed distillate will increase. Many Boka builders quickly realized that a 2" (50mm) column yielded almost twice the distillate as the 1.5" (38mm), and was still reasonably cost effective. http://homedistiller.org/forum/viewtopi ... 17&t=18926 A 3" (76 mm) column allows for even more speed, but the cost of materials increases exponentially and availability diminishes.
The first decision you'll make when making a Boka is usually the width of your column. This will impact the condenser and boiler sizes you need, and is usually impacted by costs and local availability. Don't forget to look at connectors which can be harder to procure than pipes. (ie, 3" copper male and female screw adapters are pretty rare.) The most common and recommended size for simple hobby distillation is a 2" width. A 2" column will allow for around 1 to 2 quarts or litres output an hour, (depending on column height and desired purity) while a 3" column can almost double that.
Column height
One you've figured out which width of pipe you are getting, the next step is to figure out how much pipe you'll need. The packed height (the amount of column height taken up by packing) of the column directly impacts the purity of the distillate you are able to produce. A taller column allows for more packing material, which allows more distance for the vapour to travel while mingling with downcoming reflux and form a temperature gradient, which means higher alcohol content in the distillate and better separation of undesirable fractions (heads; tails).
The recommended packed height of a reflux column is 48" to 60" (120cm to 150cm). Beyond that there is very little benefit in additional packed height. It is possible to make the column shorter than that, however. You can build it as short as you like, but as the packed height is reduced, the capacity of the column to produce high alcohol distillate is reduced, and reflux would need to be increased to maintain pure output, which will slow down operation. Columns with as little packed height as 12" (30cm) can still achieve near azeotrope, but are very slow to run at those purities.
Some people like to talk about column height in a ratio with column diameter. These are accurate in a 2" column, but they break down quickly when diameter changes to other values, and also mislead new distillers into thinking that wider columns require more height - they are independent variables http://homedistiller.org/forum/viewtopi ... 17&t=15467 . The recommended column height to width ratios for a 2" column are between 12:1 to 30:1. http://homedistiller.org/forum/viewtopi ... 17&t=15467 For some detailed expaination on the theory behind how packing height and reflux influences column efficiency, and also varies with different packing materials read more at the reflux still design page on the Homedistiller parent site http://homedistiller.org/theory/refluxdesign" onclick="window.open(this.href);return false;" rel="nofollow. The interactive design calculators are especially useful for determining how your still will behave and where it's theoretical performance limits lie. http://homedistiller.org/calcs/reflux_calc" onclick="window.open(this.href);return false;" rel="nofollow
Most 2" (50mm) columns would have between 36" (90cm) and 50" (125cm) of packed height, plus another 8-10" (20-25cm) for the plates and condenser. All else being equal, and if you have the space and money for the materials, it is better to have a taller column, until you run into the 50"-60" (125cm- 150cm) range, beyond which there is little benefit building taller, and ceiling height also becomes an issue.
Plate angle, placement, and spacing The slanted plates (not to be confused with reflux plates or trays such as bubble caps or perforated plates discussed elsewhere) in the Bokakob design are set at an angle below the condenser coil so that the upper plate collects distillate from just over half of the column and directs it onto the other lower plate. The lower plate is angled towards the wall of the column and collects a "pool" of distillate. At the bottom of the "pool" there is a take-off tube which can be opened to collect the distillate. If the take-off tube is only partially opened or is left closed, the "pool" overflows and a notched recess in the lower plate allows this overflow to fall back into the middle of the packing material of the column below. This allows for further reflux and purification of the distillate.
The ideal placement for the plates should be such that the upper plate is just below the condenser, about 0.5" to 1" (15-25mm). In earlier designs the upper plate was connected to the bottom of the condensing coil, but distillate was able to drip down the sides of the column and then would not properly mingle with upcoming vapour. The original design also required the condenser/plate assembly be perfectly rotated to align with the lower plate or collection would suffer. Later designs have the upper plate soldered to the column independent of the coil. So, for proper placement of the slanted plates, you need to know the size of your condenser coil. Building your coil and deciding its placement and measuring where it will end in the column need to be completed before deciding on placement of your slanted plates.
The angle of the slanted plates has traditionally been at 30 degrees of angle from horizontal. The angle is only important to the extent that the take-off tube is submerged in the "pool" of distillate. http://homedistiller.org/forum/viewtopi ... =17&t=1757 More extreme angles (>30º) will require more material to construct and will not provide any benefit, though those using a compound mitre box may only have a 45º slot. You also need to ensure that both plates pass the center of the column, or overlap in a vertical plane. If your plates do not overlap then distillate will fall of the upper plate back into the column, missing the lower plate and collection "pool".
The spacing of the plates, (ie, the vertical space that is left between them) needs to be sufficient to not constrict flow of vapor up the column. Too small of a space may increase vapor speed in the column after the constriction and minimize the time the vapor spends condensing at the condenser coils. The general consensus is that 0.75 to 1" (17-25mm) is best in a 2" (50mm) column. This approximates the cross-sectional area of the column with the packing material in place. http://homedistiller.org/forum/viewtopi ... 17&t=17857 http://homedistiller.org/forum/viewtopi ... 32&t=15948 There is a nice diagram of the Boka head here. http://homedistiller.org/forum/download ... &mode=view
The plates are typically made from a scrap section of copper pipe, which is cut along its edge )parallel to direction of the pipe) and beaten flat with a hammer. Once the column has grooves cut to accommodate the plates, the rectangular plates can be inserted into the grooves and marked with the correct shape, then ground or cut to be smooth. There is no need to pre-cut the plates into elliptical shape before the grooves have been cut. Once to proper shape they can be soldered or brazed into place. http://homedistiller.org/forum/viewtopic.php?f=2&t=8794
Templates
For those who don't want to go through the trouble of measuring and marking their column with the proper placing of the plates, several generous souls have created easy to use templates that are pre-marked with the proper plate positions for a 2" column. These can be printed and taped to your column in the proper position and the cuts can be made through the template. They can be scaled up 50% for a 3" column, or shrunk down for smaller columns. For a 2" column, ensure that your printer isn't scaling the image at all. This link is to a revised 2010 template http://homedistiller.org/forum/download ... hp?id=7005 Cutting, mitres and saw box
Cutting the slanted plate grooves in the column can be difficult. If you are using a template or your column has been pre-marked with the desired cut locations, you can use a Dremel or hand-drill with a black Dremel cutting wheel to cut the column grooves. Others have found success using a hacksaw or two hacksaw blades side by side to accommodate the width of the plates. If you are lucky enough to have a chop saw with a compound mitre box, you may be able to cut the grooves with that. A standard mitre box will not work since you need the angle to be cut around a different axis than a standard mitre box can provide. (A normal one only allows 'yaw', while you need to adjust the 'roll') http://homedistiller.org/forum/viewtopi ... &start=165 Summary of building process
Find a suitable pipe for your column of proper width and length for your needs. Skip to next section and build a condenser. Measure the height of the condenser installed on the column and mark your column. Measure and cut the grooves for the slanted plates just below the condenser, then install the plates and solder into place. (If you are using later plate designs, you may need to install the lower plate first, then bend down its reflux drip tab, and only then install the upper plate.) Drill holes for temperature port and output tube and solder them into place. You probably want to solder each plate and its corresponding tube at the same time so you don't melt nearby solder. Check to ensure the slanted plates overlap inside your column. Check your soldering to ensure the column has no leaks and the output tube functions properly.
Husker:
Boka Reflux Still - How To Build
The Bokakob (Boka or Bok for short) is the common name for a Dual Slant-Plate Single Column In-line Reflux Still designed by Alex Bokakob in 2001. The still was originally designed with a fairly small reflux column to sit atop a stove-top boiler, and has seen significant modifications and improvements over the years. This still is popular with many novices for its simplicity to build and operate, while being able to yield 95% ABV neutral spirits. It can also have its packing material removed and function as an adequate pot still. It is classified as a Liquid Management or LM Column reflux still. History
Bokakob created a series of reflux still design drawings that were widely circulated after they were created in 2001. http://homedistiller.org/equip/photos-alex" onclick="window.open(this.href);return false;" rel="nofollow This particular still featured a short (2ft/.67m) column made of 1.5" copper pipe attached to a stove-top pot boiler, and only required three joints to be soldered (the upper and lower plate, and take-off tube). Various discussions on Yahoo and HomeDistiller.org resulted in many design variations and improved efficiencies.
The still was named after its designer Alex, who had a Yahoo username of Bokakob, but web discussions with poor spelling or simple abbreviation led many to refer to the still as a Bokabob, Boka and Bok.
Column and Slanted Plates
General Theory
The single in-line reflux column of the Boka is meant to carry vapors from the boiler up through packing material for reflux and up to the condenser. Some of the distillate will fall to the dual slanted plates which can then overflow (allowing the distillate to fall back into the packing, which is the basis of the reflux design) or be drawn-off for collection. Materials
The column of your still should be made from copper or stainless steel. Stainless is inert, and copper actually assists in creating a clean flavor in the final product by removing sulfides as vapors come in contact with the copper as they travel through the column. http://homedistiller.org/forum/viewtopic.php?f=2&t=749 Availability and local price will probably be the greatest determiner of which material to use. Also note that stainless steel may require more industrial type of equipment and skill to weld than copper which requires simple soldering. Stainless does not suffer as greatly from heat loss, so insulation is less critical. Also note that well polished copper is very pretty. All other things being equal, choose the copper. Synthetic materials other than PTFE are unsuitable. http://homedistiller.org/forum/viewtopic.php?f=2&t=3662 See rule #8 http://homedistiller.org/forum/viewtopi ... =35&t=5090
Most pipe also comes in varying thicknesses: K, L, M and DWV. http://homedistiller.org/forum/viewtopi ... 46&t=18123 and http://www.sizes.com/materls/pipeCopper.htm" onclick="window.open(this.href);return false;" rel="nofollow K is the thickest but is commonly not found at retail outlets. L is the most common and is a standard thickness, meaning that it fits the couplers, caps, etc that are sold retail. M is the thinnest and is a better value of pipe for our purposes, but may make attachments more difficult to fit. DWV (which stands for Drain Waste Valve) is the thinnest by far, and subsequently cheapest and best value. Due to its thin walls, it has temperature and pressure ratings and warnings which do not apply to our neutral pressure systems http://homedistiller.org/forum/viewtopi ... 15&t=18093 Your column should ALWAYS be properly vented and no pressure buildup should be possible, even in full reflux. If you have pressure buildup in your column it could explode, regardless of the thickness of the pipe. If you are going to use DWV, made sure that you check the accompanying fittings before you buy to make sure it will all assemble easily and be solderable.
Column Width
The original Boka was built with a 1.5" (38 mm) column. The width of the column directly impacts the speed at which distillate can be collected, all other things being equal. In actuality, with a narrow column, the heat put into the still has to be lower to keep the vapor speed in the column at an appropriate speed so the reflux can occur properly. With a wider column, more heat can be applied while maintaining proper vapor speed, and the overall yield of properly refluxed distillate will increase. Many Boka builders quickly realized that a 2" (50mm) column yielded almost twice the distillate as the 1.5" (38mm), and was still reasonably cost effective. http://homedistiller.org/forum/viewtopi ... 17&t=18926 A 3" (76 mm) column allows for even more speed, but the cost of materials increases exponentially and availability diminishes.
The first decision you'll make when making a Boka is usually the width of your column. This will impact the condenser and boiler sizes you need, and is usually impacted by costs and local availability. Don't forget to look at connectors which can be harder to procure than pipes. (ie, 3" copper male and female screw adapters are pretty rare.) The most common and recommended size for simple hobby distillation is a 2" width. A 2" column will allow for around 1 to 2 quarts or litres output an hour, (depending on column height and desired purity) while a 3" column can almost double that.
Column height
One you've figured out which width of pipe you are getting, the next step is to figure out how much pipe you'll need. The packed height (the amount of column height taken up by packing) of the column directly impacts the purity of the distillate you are able to produce. A taller column allows for more packing material, which allows more distance for the vapour to travel while mingling with downcoming reflux and form a temperature gradient, which means higher alcohol content in the distillate and better separation of undesirable fractions (heads; tails).
The recommended packed height of a reflux column is 48" to 60" (120cm to 150cm). Beyond that there is very little benefit in additional packed height. It is possible to make the column shorter than that, however. You can build it as short as you like, but as the packed height is reduced, the capacity of the column to produce high alcohol distillate is reduced, and reflux would need to be increased to maintain pure output, which will slow down operation. Columns with as little packed height as 12" (30cm) can still achieve near azeotrope, but are very slow to run at those purities.
Some people like to talk about column height in a ratio with column diameter. These are accurate in a 2" column, but they break down quickly when diameter changes to other values, and also mislead new distillers into thinking that wider columns require more height - they are independent variables http://homedistiller.org/forum/viewtopi ... 17&t=15467 . The recommended column height to width ratios for a 2" column are between 12:1 to 30:1. http://homedistiller.org/forum/viewtopi ... 17&t=15467 For some detailed expaination on the theory behind how packing height and reflux influences column efficiency, and also varies with different packing materials read more at the reflux still design page on the Homedistiller parent site http://homedistiller.org/theory/refluxdesign" onclick="window.open(this.href);return false;" rel="nofollow. The interactive design calculators are especially useful for determining how your still will behave and where it's theoretical performance limits lie. http://homedistiller.org/calcs/reflux_calc" onclick="window.open(this.href);return false;" rel="nofollow
Most 2" (50mm) columns would have between 36" (90cm) and 50" (125cm) of packed height, plus another 8-10" (20-25cm) for the plates and condenser. All else being equal, and if you have the space and money for the materials, it is better to have a taller column, until you run into the 50"-60" (125cm- 150cm) range, beyond which there is little benefit building taller, and ceiling height also becomes an issue.
Plate angle, placement, and spacing The slanted plates (not to be confused with reflux plates or trays such as bubble caps or perforated plates discussed elsewhere) in the Bokakob design are set at an angle below the condenser coil so that the upper plate collects distillate from just over half of the column and directs it onto the other lower plate. The lower plate is angled towards the wall of the column and collects a "pool" of distillate. At the bottom of the "pool" there is a take-off tube which can be opened to collect the distillate. If the take-off tube is only partially opened or is left closed, the "pool" overflows and a notched recess in the lower plate allows this overflow to fall back into the middle of the packing material of the column below. This allows for further reflux and purification of the distillate.
The ideal placement for the plates should be such that the upper plate is just below the condenser, about 0.5" to 1" (15-25mm). In earlier designs the upper plate was connected to the bottom of the condensing coil, but distillate was able to drip down the sides of the column and then would not properly mingle with upcoming vapour. The original design also required the condenser/plate assembly be perfectly rotated to align with the lower plate or collection would suffer. Later designs have the upper plate soldered to the column independent of the coil. So, for proper placement of the slanted plates, you need to know the size of your condenser coil. Building your coil and deciding its placement and measuring where it will end in the column need to be completed before deciding on placement of your slanted plates.
The angle of the slanted plates has traditionally been at 30 degrees of angle from horizontal. The angle is only important to the extent that the take-off tube is submerged in the "pool" of distillate. http://homedistiller.org/forum/viewtopi ... =17&t=1757 More extreme angles (>30º) will require more material to construct and will not provide any benefit, though those using a compound mitre box may only have a 45º slot. You also need to ensure that both plates pass the center of the column, or overlap in a vertical plane. If your plates do not overlap then distillate will fall of the upper plate back into the column, missing the lower plate and collection "pool".
The spacing of the plates, (ie, the vertical space that is left between them) needs to be sufficient to not constrict flow of vapor up the column. Too small of a space may increase vapor speed in the column after the constriction and minimize the time the vapor spends condensing at the condenser coils. The general consensus is that 0.75 to 1" (17-25mm) is best in a 2" (50mm) column. This approximates the cross-sectional area of the column with the packing material in place. http://homedistiller.org/forum/viewtopi ... 17&t=17857 http://homedistiller.org/forum/viewtopi ... 32&t=15948 There is a nice diagram of the Boka head here. http://homedistiller.org/forum/download ... &mode=view
The plates are typically made from a scrap section of copper pipe, which is cut along its edge )parallel to direction of the pipe) and beaten flat with a hammer. Once the column has grooves cut to accommodate the plates, the rectangular plates can be inserted into the grooves and marked with the correct shape, then ground or cut to be smooth. There is no need to pre-cut the plates into elliptical shape before the grooves have been cut. Once to proper shape they can be soldered or brazed into place. http://homedistiller.org/forum/viewtopic.php?f=2&t=8794
Templates
For those who don't want to go through the trouble of measuring and marking their column with the proper placing of the plates, several generous souls have created easy to use templates that are pre-marked with the proper plate positions for a 2" column. These can be printed and taped to your column in the proper position and the cuts can be made through the template. They can be scaled up 50% for a 3" column, or shrunk down for smaller columns. For a 2" column, ensure that your printer isn't scaling the image at all. This link is to a revised 2010 template http://homedistiller.org/forum/download ... hp?id=7005 Cutting, mitres and saw box
Cutting the slanted plate grooves in the column can be difficult. If you are using a template or your column has been pre-marked with the desired cut locations, you can use a Dremel or hand-drill with a black Dremel cutting wheel to cut the column grooves. Others have found success using a hacksaw or two hacksaw blades side by side to accommodate the width of the plates. If you are lucky enough to have a chop saw with a compound mitre box, you may be able to cut the grooves with that. A standard mitre box will not work since you need the angle to be cut around a different axis than a standard mitre box can provide. (A normal one only allows 'yaw', while you need to adjust the 'roll') http://homedistiller.org/forum/viewtopi ... &start=165 Summary of building process
Find a suitable pipe for your column of proper width and length for your needs. Skip to next section and build a condenser. Measure the height of the condenser installed on the column and mark your column. Measure and cut the grooves for the slanted plates just below the condenser, then install the plates and solder into place. (If you are using later plate designs, you may need to install the lower plate first, then bend down its reflux drip tab, and only then install the upper plate.) Drill holes for temperature port and output tube and solder them into place. You probably want to solder each plate and its corresponding tube at the same time so you don't melt nearby solder. Check to ensure the slanted plates overlap inside your column. Check your soldering to ensure the column has no leaks and the output tube functions properly.