Demonstrating Commercial Hollow Fibre Membrane Contactor Performance at Industrial Scale for Biogas Upgrading at a Sewage Treatment Works

Sam Houlker,Adam Brookes,Ewan Mcadam,Marc Pidou,Daniel Herron,Tony Rutherford,Peter Vale,Andrew Moore

doi:10.3390/w13020172

Abstract

Hollow fibre membrane contactor (HFMC) technology has been developed for CO2 absorption primarily using synthetic gas, which neglects the critical impact that trace contaminants might have on separation efficiency and robustness in industrial gases. This study, therefore, commissioned a demonstration-scale HFMC for CO2 separation at a full-scale anaerobic digester facility to evaluate membrane integrity over six months of operation on real biogas. The CO2 capture efficiency identified using real biogas was benchmarked at comparable conditions on synthetic gas of an equivalent partial pressure, and an equivalent performance identified. Two HFMC were subsequently compared, one with and one without a pre-treatment stage that targeted particulates, volatile organic compounds (VOCs) and humidity. Similar CO2 separation efficiency was again demonstrated, indicating limited impact within the timescale evaluated. However, gas phase pre-treatment is advised in order to ensure robustness in the long term. Over longer-term operation, a decline in CO2 separation efficiency was observed. Membrane autopsy identified shell-side deposition, where the structural morphology and confirmation of amide I and II groups, indicated biofouling. Separation efficiency was reinstated via chemical cleaning, which demonstrated that proactive maintenance could minimise process risk.

Highlights

Anaerobic Digestion (AD) at wastewater treatment works (WWTW) can recover 34% of the initial energy of raw wastewater as biogas [1]
This study proposes to complement and build upon the limited existing literature on real gases, through implementing a demonstration-scale Hollow fibre membrane contactors (HFMC) system within a full-scale anaerobic digestion facility in order to determine technology robustness for CO2 separation on real biogas
On-site biogas upgrading was undertaken in a non-controlled environment where ambient temperature (0–30 ◦ C), gas-phase pressure (0–80 mBar) and gas-phase composition

Summary

Introduction

Anaerobic Digestion (AD) at wastewater treatment works (WWTW) can recover 34% of the initial energy of raw wastewater as biogas [1]. In the UK by the end of 2017, around 90 sites were producing biomethane, which was primarily facilitated through gas-liquid absorption columns at larger wastewater treatment installations [5,6]. Absorption columns are energyintensive, requiring up to 0.3 kWh Nm−3 biogas [7] and suffer from flooding, channelling and entrainment, which limits their operational range [8]. Hollow fibre membrane contactors (HFMC) are a promising alternative to gas-liquid absorption as the membrane extends the range of operating conditions that can be applied, due to imparting a phase change between the liquid and gas, which eliminates flooding and entrainment [8,9,10]. The increased interfacial area introduces a 15-fold process intensification into the absorption column [11,12], reducing the process footprint, capital cost and energy demand

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