Contaminant transfer in run-around membrane energy exchangers

Abstract

The run-around membrane energy exchanger (RAMEE) is a novel membrane-based energy recovery system, which uses liquid desiccant to transfer heat and moisture between air streams. VOCs may transfer from the exhaust air to supply air due to (i) air leakage and (ii) dissolution of VOCs into liquid desiccant in the exhaust exchanger and subsequent evaporation into air stream in the supply exchanger. Experimental tests were conducted at different operating conditions using two RAMEE prototypes. Sulfur hexafluoride (SF6) was used as tracer gas to test air leakage, and toluene (C7H8) and formaldehyde (HCHO) were used to test VOC transfer fraction. Results show that the exhaust air transfer ratio (EATR) of SF6 was 0.0±3.6% for both prototypes, which means the air leakage is negligible. The transfer of C7H8 was 2.3–3.4±3.5%, while the transfer of HCHO was 4.5–6.4±3.6% in the prototypes. It implies that there is a negligible transfer of low water soluble VOCs (i.e. C7H8), but possibly a small detectable transfer of very water soluble VOCs (i.e. HCHO) between the exhaust and supply air streams in RAMEEs. Moreover, the EATR values for both prototypes were insensitive to changes in air flow rate, liquid desiccant flow rate, latent effectiveness and environmental conditions.