Supercritical CO2 oilseed extraction in multi-vessel plants. 2. Effect of number and geometry of extractors on production cost

Extraction of natural compounds using supercritical CO2: Going from the laboratory to the industrial application

“…They made a detailed costing of the main components of the SFE plant and applied a large installation factor (2.5), and estimated the cost of larger plants that increased the production capacity four times by using equipment-specific scaling factors. This resulted in an overall exponent of 0.57 that is close to the 0.60 rule-of-thumb exponent [12] but is higher than the value estimated by Núñez & del Valle [13] for SFE plants (0.48). The estimated production cost for an average spice was USD 1.1/kg and decreased to USD 0.50/kg when increasing SFE plant size and productivity by a factor of four [12].…”

“…The mass flow rate of CO 2 through every vessel was very large (30 ton/h) to ensure the short residence time of a small-scale unit (about 2 min). This resulted in a superficial CO 2 velocity of 32.8 mm/s that would fluidize 6-mm particles of a dense material (ρ s = 1400 kg/m 3 ) at the stated extraction conditions (40 °C and 28 MPa) [13]. Under the assumed extraction conditions (details of the mass transfer model were not revealed by Bravi et al [15]), the extraction process was fully controlled by the solubility of the oil in scCO 2 at 40 °C and 28 MPa for about 6-7 min, a time in which the oil content dropped to 76% of the original.…”

“…Extraction times were 20 min for a 3-vessel SFE plant using 60 ton/h of CO 2 to produce 8.28 ton/day of oil (45.1% yield), 10 min for a 4-vessel SFE plant using 90 ton/h of CO 2 , and 6.67 min for an optimal 5-vessel SFE plant using 120 ton/h of CO 2 to produce 13.3 ton/day of oil (29.7% yield). A merit of the article of Bravi et al [15] is the proposal of a three-stage CO 2 recovery and compression system that may dramatically reduce the requirement of energy for the recompression of CO 2 from a residual pressure of 1 MPa up to the operating pressure of a typical buffer tank (e.g., 6.43 MPa [13]). …”

“…As done by Clavier et al [7] before, our group is tackling the problem of optimizing extraction time by computer simulation of an industrial SFE plant using a mass transfer model of the extraction process [13,17,40], rather than experimentally. For those industrial SFE plants equipped with three or more extraction vessels, computer simulation of the plant requires a time-dependent border condition to account for the variable concentration of extract in the scCO 2 stream entering the extraction vessel.…”

“…Potential customers may require committing to a company that sells SFE plants prior to process optimization, leading to potentially suboptimal solutions. There have been several isolated efforts to establish the economic feasibility of several SFE processes dealing with food materials and applications [3,7,[12][13][14][15][16] that are briefly summarized in the next section.…”