Biomedical Engineering Reference
In-Depth Information
Biomass
Gasification
Air, Steam
Gas cooling
Carbon dioxide
Gas cleaning
Hydrogen
Fig. 6.4
The main process of biomass gasification to produce hydrogen [
56
]
air, resulting in the decrease of the H
2
content in the product gas. The downdraft
gasifier improves the H
2
content of the product gas, but its structure is complex and
difficult to operate. In recent years, the fluidized bed gasifier has been a study focus.
It is able to handle fuels with different shapes and sizes and transfer heat and mass
quickly. Therefore, it is more suitable for continuous large-scale production [
59
].
At present, although biomass gasification technology has been maturing, there
are still many problems, such as high tar content. Unneeded tar would form tar
aerosols and polymerize into a more complex structure, which is not conducive for
steam re-forming to hydrogen. Three methods are generally used to reduce tar gener-
ation. They are appropriate setting of the gasifier, appropriate control and operation,
and addition of catalyst. The operating parameters, such as temperature, gasifying
agent, and residence time, play major roles in tar formation and decomposition. In
addition, the added catalyst not only can reduce tar content but also can improve
the product gas quality and conversion efficiency. Wei et al. [
60
] have studied the
effects of different naturally occurring catalysts, limestone, olivine, and dolomite in
the same unit, and found that dolomite reveals a comparably good performance in
terms of catalytic activity of tar destruction and the consequential increase in the
production of gases [
54
].
Generally, biomass-catalyzed gasification is still in the stage of laboratory
research worldwide. In addition, both gasification and catalytic processes need
to consume a great deal of energy, which is an important aspect that needs
improvement.
(2) Microbial metabolism for hydrogen production
Microbial metabolism to produce hydrogen utilizing organics is a new method of
hydrogen production. This method not only is environmentally friendly, clean, and
energy saving but also can take advantage of wastewater, solid waste, urban waste,
and lignocellulose, combining waste utilization with energy recovery. Therefore, it
has a broad application prospect. Next, the status quo and the existing problems of
microbial metabolism for hydrogen production are analyzed.
