I’m confused by your CNG vs LNG analogy.
When you talk about CNG being better for small scale and LNG “dominating” at large scale, what exactly are you talking about? Fleets of vehicles? Or the general transmission and storage of natural gas on a global scale?
Either way your association of pumps (CNG) with smaller capital costs and smaller scale doesn’t seem to make sense here.
Recovery rate (speed) is generally not determined or provided by any pump/compressor or lack thereof. It’s determined by vapor generation in the evaporator or collection pot.
A pump that’s undersized will act as a restriction but a pump that’s oversized will generally not increase recovery rate although there may be some minor “scavenging” effect like a car’s exhaust manifold.
The recovery setup of an extractor is all about overall system design and workflow.
Generally at smaller scales in cannabis extraction the recovery pumps used (TR21, CMEPOL) often act as a major restriction due to their small pumping capacities and people see an increase in recovery rate switching to passive but sacrifice certain operating abilities.
Fluid characteristics and flow characteristics are two different things.
Just because the fluid itself is compressible, doesn’t mean the flow is.
Whether or not a flow is considered compressible is directly related to the value of the Mach number (speed) of the flow not the properties of the fluid itself.
Mach number is the ratio of flow velocity past a boundary compared to the speed of sound in that fluid.
Choked flow only occurs when the exit velocity from the orifice is at or very close to Mach 1, or 100% the speed of sound in that fluid. This is related to the critical pressure ratio across the orifice like you mentioned, but where are you thinking this is occurring in an extraction system? Why do you think the inlet of the pump would cause this?
I don’t see how the inlet to the compressors used in extraction would cause choked flow as you describe.
I think it’s possible you might be confusing choked flow through an orifice with compressor choking or stonewalling. Compressor choke is a property of dynamic (centrifugal) compressors, not positive displacement compressors like the ones we typically use in extraction.
Although some people erroneously think so, a gas compressor (pump) is not used in an extraction system to speed up recovery rate.
I agree that it’s very important to not have any restrictive orifices in the vapor recovery stream. The typical Swagelok GS series process valves that are used do indeed have a restrictive orifice size at the larger connection sizes and I make sure to use 63 series or full port valves on my vapor side to avoid flow restriction.
I’m not saying it’s impossible to have choked flow conditions in extraction systems, especially huge falling films and very large collection pots but I think it’s very unlikely.
Compressible flow and choked flow seem to be more an issue in high speed (mach 1) aircraft, jet engines, rocket nozzles and high pressure gas pipelines (I am familiar with orifice plates).
I would say this really depends on the specific situation.
For a very large batch or continuous system with intermediate tanks and falling film evaporators it could be a good choice to just go passive. Just like for ethanol and other hydrocarbons.
I personally think that for batch systems up to very large batch sizes that want to rely on a one tank closed loop system (recovering into the same tank you flood from), it will be simplest and most efficient to have a vapor recovery pump in the loop, probably as part of a hybrid recovery setup.
I think the real answer for ultimate efficiency with a balance of overall system ease of workflow and recovery rate a hybrid recovery circuit would be the best choice, see my post in the other active/passive thread.
There are definitely periods during my (active) recovery toward the top of the bell curve of the difference between vessel pressures where a passive circuit would make sense to add and I have pondered putting a simple bypass line with a one-way check valve around the pump to take full advantage.
As systems and vessels get larger, I think it becomes more difficult to keep the entire volume of solvent at low enough vapor pressure on the recovery side to keep up peak passive recovery efficiency. Not to mention vapor assisting. This is all compounded if the operator wishes to use a high propane mix.
I think your assertions about noise and hazards from recovery pumps and air compressors is somewhat moot. Obviously some people are more sensitive than others but I have worked in shops my whole life and don’t have any problems with these issues. I know the old Haskel’s can be a little loud in the operating booth with all the knocking but pumps like Corken, Blackmer and LeRoi are very quiet pumps and not a problem at all.
With respect to teflon and metal shavings, I don’t think the effect is really that bad. Especially with a proper pump like a Corken that is actually designed to pump hazardous gases like ammonia for years and years. A diaphragm pump like an MVP is probably even less prone to shedding contaminates.
Also, most extracts are filtered down to 1 micron these days with the advent of CRC which would handle any detritus that would find its way in.
Honestly, I think most contaminates come into the system on the input material itself.
I remember I was out in the hills one time and I saw some guys working on a greenhouse frame around plants and had to take a grinder to something they were working on. They had setup a blanket to act as a shield but I’m sure some metal shavings made their way onto the plants.
I understand that you’re trying to do some marketing here for your company and that’s all good.
It’s not a surprise to me that a mechanical chiller will be cheaper over time than a constant consumable like liquid air gases. That seems very obvious and I don’t think anyone is debating that fact.
However there are still several arguments for why someone would want to stick with liquid air gases over a mechanical chiller like financial ability, equipment reliability, electrical hookup availability, ability to modify the existing building, etc.
Marketing this from the angle that chiller systems like the ones you offer save money in the long run vs a constant consumable makes sense.
I think using this logic to say that passive is a better or simpler option for batch extraction systems is a stretch and may be the result of some confirmation bias you have toward the products you’re trying to sell.
The active/passive debate is much more about workflow design, throughput and system design simplicity, IMO, than it is about overall recovery rate.