Membrane Gas Absorbers for H₂S Removal – Design, Operation and Technology Integration into Existing Odour Treatment Strategies

Abstract

A hollow fibre (HF) polypropylene membrane gas absorber was investigated for the removal of hydrogen sulphide (H2S) from gas streams. Gas concentrations between 25-2010 ppmV were fed into the shell side of a membrane module whilst water-NaOH solutions flowed counter-currently in the fibre lumens. The process was effective at removing the H2S (96% at G:L ratios up to 50 and pH 13) from the gas phase in a single pass through the membrane at all the concentrations of HaS investigated. Analysis of the mass transfer process revealed the rate of transfer to be controlled by the gas phase transfer coefficient with a value between 1 and 25 x 10(-4) m.s(-1). The possible integration of a membrane absorber system into existing odour treatment strategies was assessed by comparing the membrane system, based on the experimentally determined mass transfer coefficient, with existing full scale biofiltration plants. The membrane system became economically favourable at gas flow rates lower than 1630 m(3) x h(-1).

Influence of pH on gas phase controlled mass transfer in a membrane contactor for hydrogen sulphide absorption

“…Consequently, K G increased with an increase in V G . As V G increased, the resistance associated with the gas phase decreased as the thickness of the boundary layer tended toward a minimum and is consistent with the literature [1,6]. At a solvent pH of 10 and higher, this was evidenced as a plateau in the overall mass transfer coefficient as V G increased.…”

“…The independence of Sherwood could be described (11) which provided a satisfactory analytical solution to approximate the enhancement of chemical reaction on gas phase controlled mass transfer in the laminar regime. The overall mass transfer coefficient (K G ) values of up to 2.4Â 10 À 3 m s À 1 recorded for pH 13 (0.1 M) compared favourably to previous HFMC H 2 S studies using up to 1 M NaOH solvent [1,22]. This finding suggests that less concentrated chemical solvents can be used without demanding further membrane area to counterbalance the lower reactivity since [OH À ] ions are already in excess at lower solvent concentrations.…”

“…This linear relationship between pH and H 2 S flux can be correlated to the increase in excess [OH À ] ions enhancing the rate of reaction. At the higher solvent pH conditions tested, enhanced reactivity offsets the low H 2 S solubility constant and negated the liquid side resistance [1,13] thus the process was predominantly gas phase controlled. There are few hollow fibre membrane contactor studies in which the process is gas phase controlled.…”

“…Sources of odour complaint during wastewater treatment include the degradation of sewage during transportation [1] and industrial discharges to sewer [2]. The dominant odorous gas is hydrogen sulphide (H 2 S) for which regulatory compliance demands a target concentration of approximately 3 ppmv H 2 S. To conform to standards, odour abatement technology is frequently applied to air flows typically comprising low H 2 S concentrations of o50 ppmv [3,4].…”