Development and application of a rapid sampling technique for identification and quantification of compounds in high temperature process gas streams produced from biomass gasification and pyrolysis

摘要

A commercially applicable measurement technique for measuring volatile organic compounds (VOCs) in hot process gas streams was developed. The method was validated by quantifying the amount \u22tar\u22 in a syngas stream generated from a pilot-scale gasification reactor and gas cleaning process development unit (PDU) and comparing the value to that of conventional measurements. Conventional approaches to measuring VOCs suffer from extensive amounts of equipment and require substantial preparation time in the lab before data are recovered. This makes them impractical for use in rapid process monitoring and drastically inhibits attempts to optimize new tar removal techniques for syngas. The novel method is capable of sampling directly from process piping and provides results within the time-resolution of the analytical equipment (typically 1-2 h for mass spectrometry or flame ionization detection).The method is based on time-weighted average solid-phase microextraction (TWA-SPME) theory. Testing the theory on a lab scale system for the analytes of interest (benzene, toluene, styrene, indene, and naphthalene) yielded important limitations to the technique using high temperature (\u3e115C) process environments. The TWA-SPME method was applied on the pilot-scale (20 kg/h of switchgrass feed) PDU within appropriate sample extraction conditions dictated by the lab-scale testing. The method returned results within 10% of the conventional impinger approach for most analytes, and within 20% for all analytes downstream of the gas cleaning unit. When coupled with a new rapid measurement technique for heavy tar using a pressure cooker, the new method is capable of providing the concentration of tar for any syngas stream in an hour or less compared to the conventional method that requires several days for wet-chemical analysis. Additional applications of the technique are currently underway including the measurement of key light VOCs generated in a free-fall pyrolysis reactor in an attempt to gain valuable process kinetics data. An extension of this research is based on the development of a method for measurement of VOCs at much higher temperatures (exceeding 300C) using an internally-cooled SPME fiber.