2013-01(Jan)-12: Status of scCO2 extractions

Although I've done a couple of extractions so far (coffee and cardamom), the SFT-110XW isn't quite ready for routine use yet. The biggest issue is hooking up the 220V outlet so the oven can be adequately heated. So far the oven has been plugged into a 110V outlet, which sort of works because the oven circuitry has a voltage sensor, allowing either 110V or 220V. But although the main oven gets up to an acceptable temperature (40C), the restrictor block, which needs to be hotter, does not.

When CO2 flows out of the system, it rapidly expands as it turns from a liquid to a gas. This is the same principle as is used for air conditioners. In order to keep the restrictor block from freezing up, which leads to inconsistent flow. The CO2 itself can freeze, turning into dry ice, which sputters out and melts like snow. The dissolved compounds from the botanical material can also freeze. Since the rate of heat into the block needs to keep up with the rate of heat absorbed by the rapidly expanding CO2, having an underheated restrictor block means the flow rate must be low. I hope to have the 220V connector installed later today, which will solve this problem.

The other variable that affects the maximum flow rate is how fast the CO2 pump can repressurize the extraction vessel with liquid or supercritical CO2 as gaseous CO2 exits the system. The pump's efficiency is related to the pressure in the CO2 tank, which is related to the tank temperature. At temperatures around room temp. (~20-25C, or ~68-75F) or below, a 55 lb. CO2 tank will not have enough pressure to allow the pump to work efficiently, meaning the tank needs to be heated. I have ordered a silicone heating pad, but until it arrives a space heater is sitting next to the tank. Luckily CO2 isn't flammable, so no safety worries there.

Last Modified:
10 November 2013

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