Packing material creates a large surface area for the vapor and liquid to interact. The more interaction, the more reflux, and the more reflux, the higher the ABV and purity. But what is the best packing for a distillation column? Common choices for most home distillers are:
- Pot scrubbers
- Raschig rings
- Spiral prismatic packing (SPP)
This begs the question: how do you choose among different types, shapes, and sizes? And what are the advantages and disadvantages of using them over plates or trays? These are some of the questions I’ll answer in this post.
What Is Packing
Packing is a type of material placed inside a column. It increases the surface area for interaction and separation of components between vapor and liquid.
There are two main types of packing: random and structured packing. Random packing is made up of pieces of material randomly distributed in the column. Structured packing comprises larger, more uniform pieces arranged in a specific pattern.
Why Is Packing Used In Distillation Column
Packing increases the surface area for vapor and liquid contact. This allows for the efficient separation of volatile compounds in a wash, resulting in a pure spirit with a high ABV (proof). Some advantages of using packing include:
- Lower pressure drop than trayed columns.
- Often cheaper and easier to maintain.
How Do Different Packing Materials Affect Reflux
Here’s an explanation of how different packing materials affect reflux.
- Surface Area: Packing materials have larger surface areas, which provides enough room for vapor and liquid to interact. This increases the reflux action and enhances separation.
- Void Fraction: The void fraction refers to the empty spaces between the packing material. For example, marbles and spiral prismatic packing have a higher void fraction. This allows for continuous vapor flow and better distribution throughout the column.
- Turbulence: Turbulence promotes better mixing between vapor and liquid, facilitating more efficient separation. Because of their hollow design, raschig rings efficiently generate turbulence, leading to increased reflux.
What Is HETP: Height Equivalent To A Theoretical Plate
Height equivalent to a theoretical plate (HETP), is a measure of the distillation efficiency of a column. It’s the height of packing required to achieve the same separation as one theoretical plate and is the perfect stage where the gas and liquid are in equilibrium.
Understanding HETP (and the performance of your still) can help you choose suitable packing material, measure how close the column is to achieving separation, and ultimately, gauge the alcohol content yield.
Apart from your packing material, other factors that influence HETP include:
- The flow rate of the vapor and liquid.
- The temperature of the column.
Packing Vs Trays Vs Bubble Plates
Packing, trays, and bubble plates are similar in that they’re placed in columns and provide a surface area for gas and liquid to make contact. But there are some nuances to how these materials achieve this.
Packing, as discussed earlier in the post, comprises individual pieces arranged in a random or structured pattern. They work as contacting devices by allowing gas and liquid to come in contact.
Trays are solid plates with holes and they work as containing devices by holding a fixed amount of liquid or vapor at a certain temperature and pressure. The vapor rises up the column and passes through the holes or slots. The liquid is distributed evenly across the plate, and the gas bubbles through the liquid. As the trays fill up with the distillate, the distiller opens a valve to collect it. The two main types of trays are:
- Sieve: Have slots for gas to flow through and is ideal to use when distilling solids.
- Valve: Comprise holes with opening and closing valves that regulate the vapor flow.
Bubble (cap) plates are a type of tray with caps, or what is commonly referred to as standoffs. Similar to trays, they work as containing devices. Here’s a breakdown of how they operate:
- The vapor rises through the holes and into a reflux condenser.
- Once pre-condensed, the liquid drops and is evenly distributed across the plate.
- When the plate is filled with liquid it re-vaporizes, which creates the bubbling effect. The same action happens on each of the plates.
- The excess liquid drops past a downward-facing standoff called the downcomer, while the pure liquid (ethanol) exits the condenser.
The table below summarizes the differences between packing, trays, and bubble plates
|Types||Random or Structured||Mainly sieves or valves||A type of tray with caps or valves|
|Pressure Drop||Lower (reduced energy consumption)||Higher (may require more energy)||Higher (may require more energy)|
|Capacity||Lower (may have limitations on liquid and vapor flow rates)||Higher (less susceptible to flooding)||Higher (less susceptible to flooding)|
|Efficiency||Higher (better separation with fewer stages or shorter column height)||Lower (may require more stages or taller column height)||Lower (may require more stages or taller column height)|
|Fouling Resistance||More susceptible to fouling||Less prone to plugging or reduced performance||Less prone to plugging or reduced performance|
|Cost||Cheaper||More expensive||More expensive|
The Best Column Packing Material
These everyday kitchen cleaning tools are probably what most home distillers started with when they first embarked on the hobby. Pot scrubbers are made of stainless steel or copper and their coarse, mesh-like structure provides a lot of surface area for compounds to make contact. They’re budget-friendly and readily available.
TIP: When purchasing pot scrubbers, try to get your hands on pure copper. Some are copper-coated steel and when the chemicals in your wash interact with the material, the coating can leach into your spirit.
Marbles aren’t just for kids’ games! These glass spheres can be an excellent choice for packing material. They occupy a relatively small volume within the column, allowing for simpler gas and liquid flow. Their smooth surface and spherical shape contribute to effective mass transfer. Marbles are also readily available and inexpensive.
Mesh is often made from stainless steel or copper that’s interwoven to create a network of open spaces. When wrapped loose enough to hold itself in place and tight enough for refluxing to happen, it does provide a large surface area for vapor-liquid interaction. Mesh is available in various wire thicknesses and can handle high liquid and gas flow rates.
Raschig rings are cylindrical, hollow materials made of ceramic, metal, plastic, or glass. They’re resistant to corrosion and thermal shock, and their hollowness allows for effective vapor-liquid contact.
Spiral prismatic packing (SPP)
As the name suggests, spiral prismatic packing (SPP) is spiral-shaped pieces made of copper or stainless steel. Its feature (combination of spiral and prism shape) creates more turbulence, resulting in more efficient separation. Though it’s durable, it’s more expensive compared to pot scrubbers and marbles.
Saddles are concave-shaped (similar to the seat of a horse saddle) perforated discs, and the perforations allow for optimal separation. Similar to most packing materials, they’re made from copper or stainless steel, but copper is a common choice.
Copper Vs. Stainless Steel
Copper is an excellent conductor of electricity, making it easier to transfer heat between liquid and vapor. It’s also revered for its ability to remove sulfur in a wash and improve purity. When the gas comes into contact with copper, a chemical reaction occurs. This reaction helps to remove the rotten egg smell and taste, for a cleaner final product. The downside to using copper is that it’s very expensive.
The best feature of stainless steel is that it’s corrosion-resistant. It does not react with most substances and can withstand a wide range of temperatures and pressures. The result is often a pure distillate. But, it doesn’t have a strong affinity for sulfide, so it might not effectively remove sulfur compounds. Compared to copper, stainless steel is more budget-friendly.
Glass is chemically inert, so it will not interact with or contaminate your distillate. This is beneficial because it helps maintain the purity of the distilled product without introducing any unwanted flavors or contaminants. It can also withstand high temperatures without deforming. Glass packing, like glass distilling beads, can be costly. But, depending on where you purchase them, you can get glass marbles at around $7 a pack.
Ceramic packing, like raschig rings, is stable and durable. It’s extremely heat-resistant and provides rapid heating and cooling efficiency. It can also withstand prolonged use without breaking down or degrading. Similar to copper, ceramic doesn’t come cheap. But because they last longer, they are cost-effective in the long run.
How Do You Choose Packing For A Distillation Column?
Price and availability
As home distillers, we often operate on a budget and are always seeking equipment that provides great performance without breaking the bank. This is not any different from packing material. Also, it can be frustrating to find the perfect packing material, only to realize it’s not available in your area.
To save you time, effort, and money, we suggest you purchase marbles or pure copper pot scrubbers. Mesh is another fantastic option you can get at your local hardware. If you decide to opt for marbles, couple them with copper scrubbers to hold them in place and remove sulfur during distilling.
The whole point of packing is to achieve efficient separation. Pot scrubbers and SPP not only yield the desired result with fewer stages, but they improve the overall efficiency of the distilling process too.
Copper or not copper
We know copper doesn’t come cheap, but it’s a necessary catalyst during distillation. It strips off any sulfur odors, while you wind up with a clean and pure spirit. If you’re on a tight budget, we recommend you fill the bottom half of your column with copper pot scrubbers or mesh and the rest with marbles or stainless steel mesh.
Placing packing materials within the column of your still can improve gas and liquid transfer and increase the ABV of your product. Most have high resistance to thermal shock and corrosion. But, not all packing materials are created equal. Pot scrubbers are a good choice if you’re looking for reasonably priced but effective material.
They provide good surface area, easy cleaning, and anti-corrosive benefits. If you have enough money at your disposal, you can explore SPP, raschig rings, or saddles. Their design allows for more turbulence, without the likelihood of flooding, resulting in a more refined separation.
Frequently Asked Questions
Q. What is the best packing material for a distilling column?
The best packing material for a distilling column are:
- Pot scrubbers
- Raschig rings
- Spiral prismatic packing
Q. What does copper mesh do for distilling?
Copper has several uses in distilling. Common ones include
- Increases the surface area for the vapor and liquid to make contact. This allows for the efficient separation of volatile compounds, resulting in a pure final product.
- Reduces sulfur compounds, which prevents the likelihood of any off flavors (rotten egg smell).
- Because copper has antibacterial properties, it prevents potential contamination.
Q. What can I substitute for copper mesh?
If you can’t get your hands on copper mesh, fantastic substitutes are:
- Stainless steel mesh
- Pure copper pot scrubbers
- Raschig rings
- Spiral prismatic packing
- Glass marbles
Q. Is copper mesh the same as steel wool?
Copper mesh and steel wool are not the same. They are both made of metal but have different properties.
Copper mesh is made of pure copper that’s interwoven to create a network of open spaces and it’s more durable. Steel wool is more compact because it’s made of fine strands of alloy steel–a mixture of iron and carbon. It can rust and break down, especially when mixed with chemicals.
Q. What are ceramic balls for in distilling?
Ceramic balls are used as column packing material in distilling. They provide a large surface area for gas and liquid to interact and separate different components of a wash. They don’t react with the vapor or liquid, which means your distillate remains free from off-flavors.