Indirectly heated biomass gasification using a latent heat ballast — 1: experimental evaluations

The objective of this study is to improve the heating value of gas produced during gasification of biomass using an indirectly heated gasifier equipped with a latent heat ballast. The latent heat ballast consists of lithium fluoride salt encased in tubes suspended in the reactor. The lithium fluoride has a melting point that is near the desired gasification temperature. With the ballast, a single, cyclically operating reactor stores energy during a combustion phase and releases it during a pyrolysis phase. Tests were carried out in a pilot-scale fluidized bed reactor to evaluate the concept. The time to cool the reactor during the pyrolysis phase from 1172 K (1650°F) to 922 K (1200°F) increased 102% by use of the ballast system. The extended pyrolysis time allowed 33% more biomass to be processed compared to an unballasted reactor. Additionally, the total fuel fraction converted to fuel gas increased from 74 to 80%. Higher heating values of 14.2–16.6 MJNm−3 (382–445 Btuscf−1) on a dry basis were obtained from the ballasted gasifier.