*5.4. Halides and H2S*

Generally, it is known that K almost exclusively volatilizes with correlation to Cl. Thus, from the results presented above, it was expected that the Cl content in syngas should be low. For baseline conditions, the amount of HCl measured in syngas was close to the detection limit of the method. In raw syngas, the mean value of HCl present was equal to 5 ppmv. To assess its removal in the gas cleaning system, the analysis of Cl content in side-products was necessary. No F or Br content in the gas was detected. Table 8 presented below depicts all results collected regarding Cl content in condensates from gas cooling. It can be seen here that, in syngas after treatment with kaolinite and dolomite, Cl concentration was so low that it reached the lower detection limit of the method.

**Table 8.** Concentration of chlorine in water–tar condensate recovered from the gas cooler.


For filter cakes, the results of Cl content are presented in Table 5. The results indicate that biomass char contained 16.9-fold higher Cl concentration than the biomass before thermochemical treatment, which supports the theory of Cl readsorption on the bed of char or its preference to remain in the concentrated solid phase composed of ash and char.

During balancing of Cl present in the system, it was noted that only up to 30 wt.% can be accounted for with all the measured inputs and outputs. The remaining stream of Cl presumably stayed in reactor bottom ash, as known from the literature [3,16]. However, due to technical limitations of the lab-scale conditions and the insufficient amount of bottom ash generated from clean biomass like wood chips, it was not possible to adequately sample and analyze this stream.

Performed analyses allowed determining the amount of HCl present in raw syngas, whereas no HCl could be measured after the last step of gas cleaning. To summarize its removal, Figure 7was prepared. The figure relates the actual streams of HCl trapped in filter cake to Cl content in condensate from syngas cooling. For T1 and T2, 90% of Cl present in syngas was recovered in the filtration/adsorption step. This value should be compared with Cl content measured for the reference case, where filtration was carried out without any sorbent and Cl was preferentially recovered in the condensate from syngas cooling.

Finally, during ion chromatography of the liquid samples, the detection of H2S was also expected. However, for all tested samples, no S ions were detected. This result indicates that the applied analytical procedure needs to be further developed in the future to give better precision in the determination of syngas composition.

**Figure 7.** Ratio of Cl recovered from syngas in filter cake and condensate from syngas cooling.
