THERMOCHEMICAL CONVERSION: (CO)GASIFICATION AND HYDROTHERMAL GASIFICATION - Biomass as a Sustainable Energy Source for the Future - page 338

￿ Sulfur species (e.g., H 2 S, COS, thiophenes, mercaptans)

￿ Chlorine species (e.g., HCl)

￿ Alkali and other trace elements (e.g., KCl, KOH, NaCl)

￿ Nitrogen compounds (e.g., NH 3 , HCN, aromatic nitrogen compounds such as

pyrroles and pyridines)

Feedstock composition as well as gasification process layout and conditions deter-
mine the concentration of such species in the raw product gas. Also, certain com-
pounds of these classes have impact on the effective emission of other species,
e.g., particulate matter can capture alkali and trace species (e.g., Hg compounds)
depending on the concentration and on the process conditions.
An overview of typical gas cleaning demands concerning the aforementioned spe-
cies classes for different prime movers (engines) and biofuel production processes is
presented in Table 10.7 (Knoef, 2012). Concerning high-temperature fuel cell appli-
cation, gas cleaning requirements are extensively dealt with in Chapter 16 and in
Aravind and De Jong (2012).
Different end uses of the raw synthesis gas generated demand different gas treating
sections. A generic scheme of such part of a BTL technology chain is presented in
Figure 10.14. The dashed circle points to the opportunity of integration of particle
removal and tar/hydrocarbon removal. Leibold et al. (2008) have suggested an even
further simplification by addition of sorbent materials for removal of H 2 S and HCl

TABLE 10.7 Overview of important gasification product gas applications and
compound restrictions

Application

Methanol
synthesis

FT
synthesis

Contaminant IC engine Gas turbine

<50 mgm n −3
(PM10)

<30 mgm n −3
(PM10)

<0.02 mgm n −3

n.d. ∗

Particulate matter
(soot, dust, char, ash)

<100 mgm n −3 <0.1 mgm n −3

Tars
￿ Condensables
￿ Inhibitory species
(class 2 heteroatoms,
benzene, toluene,
xylenes)

<10 ppb
<1 ppm

<1 mgm n −3 <20 ppm <10 ppb

Sulfur species
( H 2 S, COS)

<0.1 mgm n −3 Nitrogen species

( NH 3 , HCN)

<50 ppm <20 ppb

Alkali compounds <24 ppb <10 ppb

<0.1 mgm n −3 Halides (mostly HCl) 1 ppm <10 ppb

(Source: Adapted with permission from Knoef (2012). © Biomass Technology Group (BTG).)
∗ n.d., not detectable.