U.S. Water’s Ethanol Process Technologies (EPT) team engaged in a CO2 Scrubber performance comparison evaluation in an Eastern United States dry grind fuel ethanol plant with a 100 MMgpy nameplate.
Parameters compared were:
- Compliance Reliability
- Application Cost
- Residual Bisulfite – and its impact on both yeast vitality and final product sulfur content
- Accompanying Value
Recommendations were delivered that enabled improved performance. Comparative testing was scheduled with three (3) acetaldehyde control additives:
- VOxOUT 70C
- Commodity Ammonium Bisulfite (“ABS”)
- Commodity Sodium Bisulfite (“SBS”)
The plant implemented the EPT equipment and procedure recommendations prior to the primary engineering study. Adoption of the recommendations resulted in a 4% higher rate of ethanol recovery – even with a reduction in scrubber feed water of 25 gallons per minute. During scrubber additive testing, an emission limit of 10 ppm(V) of acetaldehyde was adopted to ensure that State permit compliance was achieved. Testing over the period of complete fermenter drop cycles was performed with each additive to replicate as consistent operation as achievable.
RESULTS & CONCLUSIONS
Compliance with State permit was achieved in all cases, with a 10 ppm(V) acetaldehyde target maintained throughout.
On a calculated use cost basis, the scrubber additive products performed as follows:
- VOxOUT 70C – $154,000 per year
- Commodity Ammonium Bisulfite – $158,000 per year
- Commodity Sodium Bisulfite – $191,000 per year
Also, the reduced volume of VOxOUT 70C resulted in the lower calculated freight costs:
- VOxOUT 70C freight cost was calculated to be 77% lower than that of SBS
- VOxOUT 70C freight cost was calculated to be 42% lower than that of ABS
Residual (unconsumed) bisulfite was measured during the engineering study at corresponding points in the fermenter drop curves during application of the three scrubber additives. Residual bisulfite is not only wasted, but also adds to yeast stress and to potential sulfate carryover into the final product ethanol.
Comparative average residual bisulfite values measured were:
- VOxOUT(R) 70C ~ 10ppm
- ABS ~ 30ppm
- SBS ~ 55ppm
Further, the plant placed value in the support and experience provided by the U.S. Water Ethanol Process Technologies team.