Passive vs. Active Closed Loop
Kind Garden Supply offers a wide array of options for closed loop hydrocarbon extraction. You have chosen the unit that best fits your needs, but are unsure if you need a passive or active system. What is the difference and how can you determine which will work best for you? Let’s first discuss how each style works.
Passive recovery works by manipulation of temperature and pressure. In a closed system, gas will always seek the lowest pressure it can. Using this simple bit of knowledge, hydrocarbon gas can be moved from one part of the system to another by making sure the pressure on the receiving end is lower. This is accomplished by manipulating temperature. The pressure of a hydrocarbon is directly correlated to the temperature. If you refer to the graph below, you can see temperature and the corresponding pressure for butane and iso-butane. By heating the butane liquid in the collection base and cooling the receiving LP tank, butane vapor will naturally move to the cooler area. If the temperature is below the boiling point of the solvent, vapors will re-condense into a liquid. This method is a simple solution to recovering solvent and is often the way beginning users learn how to operate a closed loop system. Passive systems tend to leave more solvent behind, so solvent loss per run is usually higher.
Active recovery will follow the same principals as passive with the addition of a recovery pump. This pump will aid the movement of solvent vapors by utilizing a push/pull action. By utilizing a pump, solvent recovery is sped up. This method also helps reduce continuing cost by minimizing the need for expensive chilling options, such as dry ice. The solvent is condensed into a liquid by using a coil located on the output port of the pump. This method reduces the amount of dry ice needed to have a fast, efficient recovery. The combination of efficient condensing of vapors and the force created by the pump, solvent recovery tends to be faster when using a pump. This method does not require the LP tank to be chilled, so active systems cost-effectiveness becomes greater as the capacity of the closed loop increases. Being that a recovery pump can pull into the vacuum, less solvent can be left behind in the extract. These systems tend to have less solvent loss per run. The major downfall of active systems is that the pumps do need to be maintained and rebuilt periodically, so more attention is required with these systems.
Which Option Should I Choose?
Passive systems are a great for the beginner, being that there is no need for electrical equipment to move the solvent. These systems can be efficient with recovery speeds, however, a large amount of dry ice is needed to do so. Regular ice can be used instead, but recovery times will be much larger. This option is great for units with 1lb capacity or lower. They are also a good option if large production is not a concern. If you have plenty of time to process and/or have easy access to bulk dry ice, passive is a great option for you.
Active systems will reduce the need for large amounts of dry ice, but have a larger start up cost. These systems give faster recovery times per lb. of solvent used. These become especially attractive to those who need to have large amounts of production or using large systems. These systems can also pull the collection base into a vacuum when completed, so more advanced options for extract removal (i.e. cold muffin technique) can be accomplished. If speed and production amount is a requirement or dry ice is hard to come by, an active system should be your chosen option.