This is an energy-efficient means of transferring oxygen and methane from a gas phase into an aqueous solution using an array of 16 “U-Tubes” in a “Loop Reactor” for production of butanol automotive and aviation liquid fuel. One U-Tube consists of four 8 inch diameter inner pipes with an outer pipe diameter of 24 inches. The inner pipes carry water and injected O2 and CH4 gases downward at a water velocity 10X greater than the rise velocity of gas bubbles injected near the top of the inner pipes, ensuring efficient transfer of gases into solution. At the bottom of the inner pipes, water, along with dissolved oxygen and methane, flows upward into the space between the inside of the larger 24 inch diameter casing and the outside of the 4 inner 8 inch diameter pipes.
This “U-Tube” configuration enhances mass transfer efficiencies of injected gases. Contact duration and hydraulic pressure (65 psi) increase as gases are forced to the bottom of the 150 feet deep U-Tube. Water is pumped downward with an array of 10 to 15 HP water pumps, as oxygen and methane gas bubbles are injected into the water stream through porous gas diffusers located within the top 50 foot section of the U-Tube inner pipes. As water travels down through the inner tubes, oxygen and methane gas bubbles are forced downward as well, dissolving into the water, as downward water velocity is 10X that of a rising bubble. (A small bubble rises at 1 ft/sec). Water flow is 8 ft3/sec in each 8 inch diameter pipe.
As oxygen and methane is forced to a greater depth and pressure, they dissolve into the water. The result is an increase in dissolved oxygen concentration, to 60 to 65 mg/L, and an increase in dissolved methane concentration to 150 mg/L, depending on flow rate of the gas mixture injected into the water. The water, along with the gases in solution, then travels upward, to initial pressure and elevation, where it is immediately discharged into and re-circulated through the bio-reactor, in this case considered to be a system of about 150-193 m3. While inside the bio-reactor, the oxygen and methane undergoes microbially-mediated “gas fermentation”, a bio-chemical process that can convert methane and oxygen to butanol, a liquid fuel, according to the following reaction:
5 CH4(g) + 4 O2(g) → C4H10O(l) + 5 H2O(l) + CO2(g) ?G = -1,428 kJ (per mole butanol)
This proposal calls for the use of similar configurations of U-Tubes in arrays hydraulically connected to the volume of aqueous solution in the 150-193 m3 bio-reactor, to provide all of the required oxygen and methane (at ≥ 43 g O2/L bioreactor volume/hour and ≥ 27 g CH4/L bioreactor volume/hour) to the reactor, at an efficient electrical use of about 4.97-6.82 kW/m3 of reactor volume.
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