Assessment of the Solid-Phase Adsorption Method for Sampling Biomass-Derived Tar in Industrial Environments

Artikel i vetenskaplig tidskrift, 2013

Low-temperature gasification of biomass is a primary process step for production of biofuels or electricity using gas-fired engines or turbines. In addition to the desired product gas, the raw gas produced through gasification inevitably contains condensable hydrocarbons, known collectively as tar. The amount and composition of the tar have relevance for the efficiencies of the downstream processes. Tar can be measured using both online and off-line methods. However, many of these methods currently lack information regarding their implementation and accuracy levels for large-scale systems. In this work, the Solid-Phase Adsorption (SPA) method for measuring tar in industrial applications is evaluated. The individual steps of the method were examined for their effects on the overall performance of the analysis. Sample collection was found to be the most prominent source of error, and this was mainly due to human factors. Omitting to determine the temperature and pressure of the sampled gas contributed to this error, as the sampled volume of gas under normal conditions could not be correctly calculated. Inconsistencies in the treatment and storage of the collected samples were shown to affect the more volatile species with boiling points similar to that of benzene. The gas chromatography (GC) analysis was performed with satisfying accuracy. However, the reliability of the estimations of the average composition and dew-point of the tar mixture were dependent upon the amount of the identified species. The current implementation of the SPA method yields values with a relative standard deviation within 10% for the majority of the compounds in a given sample. However, in line with the result of previous studies, the tar species with boiling points between those of benzene and xylene (i.e., the BTX compounds) were measured with a lower accuracy than those of heavier tars.