Engineering Experiments - Innovative Chemical Engineering Teaching Experiments

Packed-Bed CO2 (or NH3) Absorber

SPECIFICATIONS: Packed bed absorber, showing air, CO2, and water/NaOH feed lines, MSA CO2 analyzer, terminal board for A/D board, Dwyer differential pressure cell, water manometer, CO2, liquid and air rotameters, stepper-motor driven liquid flow control valve, Arrick stepper control box, 4 inch ID borosilicate column with Raschig ring packing, movable liquid outlet line with conductivity cell, three thermocouples in packing, conductivity meter, tracer injection points. NaOH feed tanks and pump not shown. An NH3 absorber is also available.

Packed-Bed NH3 (or CO2) Absorber

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Hydrogen peroxide/sodium thiosulfate batch kinetics

DETAILED OVERVIEW: The apparatus consists of a 4” ID borosilicate column containing about 30 inches of ceramic Raschig ring packing. A 0.5 N NaOH solution (or water) is fed to a distributor at the top of the column. Rotameters are used to measure the air, CO2, and liquid feed rates. Two 20 L polyethylene tanks and a centrifugal pump supply the NaOH feed. The liquid flow to the top of the column is controlled by a needle valve, this valve driven by an Arrick stepper motor controlled by a computer program. The same experiment, but using ammonia and no NaOH, is also offered.

Instrumentation includes a Dwyer stainless differential pressure transducer used, in addition to a water manometer, to measure the pressure drop across the packed column. A conductivity cell mounted in the liquid effluent line is connected to a Cole-Parmer conductivity meter and measures the transient tracer level following tracer injection above or below the packing. An MSA infrared analyzer measures the CO2 concentration in the effluent air. Three thermocouples (optional) may be mounted in the packing, but show very little temperature effect due to CO2 absorption. A NI A/D board digitizes all signals, under control of LabVIEW programs. A computer (not included) is used for data acquisition and control.

The experiment operates in four modes, namely:

The pressure drop across the column is measured by the differential pressure cell and the manometer as a function of the air and water flow rates. The results can be compared to theory, and flooding behavior can be demonstrated. Each run takes about ten seconds.
The computer acquires transient effluent liquid tracer levels following conductive tracer injection above and then below the packing. A LabVIEW program calculates mean residence times and then the volume of water held up on the packing. The effects of air and water flow rates on hold up can be determined, and the onset of flooding demonstrated. Each run takes a few minutes.
The steady state effluent CO2 level is measured at selected CO2, air and NaOH feed rates. The data can be processed to yield measures of the CO2 absorption rate, for example the height of a transfer unit.
A PID control algorithm is used to control the effluent CO2 level by varying the NaOH feed rate via the stepper motor driven valve.. Students can determine the effect of the controller gains on the controller performance. Stable and oscillatory behavior can be demonstrated.

The four modes of this comprehensive experiment can easily occupy two lab periods. Please contact us at spencer@columbia.edu for more details on the experiment, and for price and delivery.