Cannabis

Vapor recovery condenser systems, comprised of a closed system of pipes, valves, compressors, and exchangers provide a safe space for vapors to be compressed without being emitted into the atmosphere. Not only is this better for our environment, but it also allows the reuse and repurposing of costly chemicals that would have otherwise been lost in vapor. Chemical and petroleum vapors can be re-condensed into a usable liquid using direct condensation and returned to their original source or repurposed for different use.

Shell and tube condensers are safe, efficient and can be designed for much higher pressures and temperatures than other heat exchanger types. When stainless steel condensers are built to ASME pressure vessel code and TEMA guidelines for best fabrication processes, they can handle design pressures up to 3000 psig and temperatures from cryogenic up to 1000F.

Surface finishes for condensers in the oil extraction market should be polished to a food grade 32Ra or better, and can be provided with finishes more commonly seen in the pharmaceutical and personal care markets of 20Ra and electropolished to a near mirror-like finish. This helps to prevent fouling and scaling inside the tubes and bonnets, while also eliminating crevices that can hold material and lead to contamination.

When solvents are in contact with the product, it is very important to keep the solvents as clean and uncontaminated as possible throughout the process. Condensing the vapors in the tubes of a shell and tube heat exchanger ensures solvent purity. The polished finish on the tubeside makes a shell and tube exchanger easier to clean between product batches. The shell side of an exchanger has many crevices where tubes and tie rods pass through baffles, which is why it is more common to use the utility fluids in the shell.

Cooling ethanol used in oil extraction down to well below 0 degrees is typical, and can be accomplished easily with the use of a shell and tube heat exchanger. The ethanol is run through the sanitary tube side of the exchanger. Coolers can be designed as single pass or multi-pass units, with removable bonnets that allow for inspection and cleaning of the tubes and other product contact surfaces. They can also be designed as U-tube exchangers with removable tube bundles. The cooling medium, which can be thermal oil or liquid nitrogen, is then run through the shell side of the cooler.

Shell and tube coolers are safe, efficient, and can be designed for much higher pressures and temperatures than other heat exchanger types. When stainless steel coolers are built to ASME pressure vessel code and TEMA guidelines for best fabrication processes, these coolers can handle design pressures up to 3000 psig and temperatures from cryogenic up to 1000F.

Shell and tube ethanol coolers can be scaled up from compact pilot scale models for small batch and R&D efforts. Mid-sized demonstration scale, and larger commercial scale coolers can be designed to handle nearly any volume required. Insulation jackets for heat conservation and personnel protection can also be added for safety and greater efficiency.

After oil extraction using ethanol or hydrocarbons, there is a need to vaporize and recover the solvents from the product. An efficient way to perform this evaporation it to feed the product stream up through a vertical shell and tube heat exchanger, often called an external calandria or reboiler. This exchanger will typically have steam or hot thermal oil running through the shell of the unit, and the oil and solvent mix is fed upward through the tubes. As the steam or thermal oil heats the solution in the tubes, the solvents in the product flash off as vapor and exit the top of the exchanger to be condensed, while the remaining product is piped to the next step in the process.

Another type of evaporator used for this type of separation is a falling film evaporator, where the product mix flows down through the tubes instead of upward. Heating medium is provided in the shell side of the exchanger, and the vapors flash off as the product drips down the inside of the tubes.

Since oil and solvent mix, and their thermal properties can vary from case to case, design of evaporators is often performed by OEM’s that specialize in evaporation. Many of them have R&D test centers where products can be tested and thermal performance confirmed, in order to properly size the shell and tube exchanger used as the evaporator. Evaporators and reboilers are not easily scalable, and can have performance issues when flow is turned down, or if flow exceeds the tested rate. Because of this, it may be necessary to have multiple evaporators sized for different flow rates on different production lines.

Evaporators and reboilers used to remove solvents from product should have product contact surfaces polished to at least food grade 32Ra levels. Better finishes like those found in pharmaceutical applications can also be provided, typically 20Ra and electropolished. Because of these finish considerations, it is best to keep the product in the tube side of the exchanger, and utilize the shell side for utility streams.

Following the separation of solvents from the product, the organic vapors are sent to a condenser to recover them for re-use. The product also needs to be cooled down before it can be tested and packaged for distribution. A shell and tube cooler works well for this process.

The product can be fed through the tube side of the exchanger, which is sanitary and typically has at least a food-grade surface finish. The cooling utility is fed through the shell of the exchanger and is directed back and forth across the tubes by utilizing baffles, wiping away the heat from the product running inside of the tubes. This occurs safely without any mixing of the product in the tubes and the utility fluids in the shell. The sanitary stainless steel design of the shell and tube cooler also makes it easier to clean and inspect than coil type coolers or plate and frame coolers.

Typically the cooling utility is chilled water, a water and glycol mix, or thermal oil provided in a closed loop system from a refrigeration glycol chiller. These chiller units typically have user friendly controls that allow you to set a temperature point for the coolant, that is consistent with the design of the shell and tube exchanger. Your shell and tube exchanger designer should be able to calculate how much coolant is needed, and help determine an optimal inlet temperature for your glycol chiller, allowing for a typical 10F rise in the coolant temperature.