Removal of siloxanes from biogas upgraded to biomethane by Cryogenic Temperature Condensation System

Abstract

An eco-friendly system based on Cryogenic Temperature Condensation System (CTCS) that was designed to remove siloxanes as well as another organic and inorganic impurities from biogas was investigated. Moreover, the analyzed biogas was theoretically upgraded to biomethane and the CTCS was implemented as a part of biogas upgrading pre-treatment process. Testing was conducted during three stages of biogas treatment, and the off-heat from the CTCS for chilling column regeneration was arranged. The CTCS was monitored in terms of its capability to operate a real landfill biogas plant; it worked according to the principle of temperature swing in temperatures ranging from +40 to −50 °C. Biogas along with methylsiloxanes (incl. L2, L3, L4, D3, D4, D5, D6), trimethylsilanol (TMSOH), CH4, CO2, H2, O2, N2, H2S, NH3, relative humidity (rH), halogenated compounds (including organic chlorine and fluorine), and volatile organic compounds (VOCs) was investigated; moreover, the samples were tested under both laboratory and real landfill biogas plant conditions. The CTCS removal performance was tested by applying gas chromatography techniques coupled with different types of detectors (MS, flame ionization detector [FID], and electron capture detector [ECD]). In the analyzed biogas, high concentrations of siloxanes and TMSOH were observed:109.4 mg/m3 and 21.1 mg/m3, respectively. Moreover, the concentration of impurities in shape of halogenated compounds and VOCs (including all organic compounds C5–C12) ranged from 108.5 to 111.3 mg/m3 and from 186.2 to 191.0 mg/m3, respectively. The biogas rH and inorganic impurities were observed to be up to 95.3%/113.7 mg/m3. The CTCS was operated in nine independent approaches characterized on the basis of different biogas flow sequences. Finally, the performance in terms of removal of siloxanes and other impurities was observed to be up to 99.87% and 78.36%, respectively, in contrast to raw biogas before using CTCS. This study highlights and compares the concentrations of silica impurities with Polish standards for biomethane, combined heat and power (CHP) manufacturers limits, EU requirements for biomethane, and Polish Standards for biogas. Moreover, it calculates volatile methylsiloxane emission from landfill gas on the example of landfill gas life cycle assessment.