H2Tech - Q3 2021 - 18

SPECIAL FOCUS HYDROGEN INFRASTRUCTURE DEVELOPMENT
2. The gasification zone in the middle, where low O2
content leads to partial oxidation reactions
3. The stabilization zone on the top of the reactor,
where the further introduction of auxiliary fuel and
O2
leads to an increase in temperature, ensuring tar
degradation, full decomposition of the long-chain
organic molecules and inhibition of dioxins formation.
Multiple injections of O2
1,000°C-1,200°C
Raw syngas
600°C-800°C
Slag
RDF
and auxiliary fuel along the reactor
help maintain temperature at 1,600°C-2,000°C in the melting
zone, at 600°C-800°C in the gasification zone and up to
1,100°C-1,200°C at the top. Such a temperature profile ensures
the full conversion of waste into two products: a highly valuable
syngas that is rich in H2
and CO and is free of char, tar, dioxin
The high temperaand
furans discharged from the top of the reactor; and an inert
vitrified material discharged on the bottom.5
ture in the melting zone allows for discharge of the inert components
of waste (minerals and metals) in a granulated and vitrified
state, ideally carbon-free. Depending on local legislation,
such material can be valorized into the cement or construction
industry, or otherwise disposed as standard waste.
As reported by Salladini et al.,6
the syngas yield and relevant
composition are mainly affected by the lower heating value
(LHV) and the carbon-to-oxygen (C/O) ratio. In general,
higher LHV results in higher syngas yield, higher CO and H2
content and lower concentration of CO2
tains, as the major components, CO, H2
. Produced syngas con,
CO2, as well as minor
quantities of volatile metals and other particles. FIG. 2 shows a
block diagram of the gasification section, together with the preliminary
cleaning and syngas purification section.
As a first step, the hot gas exiting the reactor is routed to an
1,600°C-2,000°C
FIG. 1. High-temperature gasification reactor.
Waste
NG
O2
O2
HT-Gasification
and acid cleaning
O2
HT-Gasification
and acid cleaning
O2
Compression
HT-Gasification
and acid cleaning
Raw syngas
Vitrified
granulate
Alkaline scrubbing
Sludge to wastewater treatment
Wet electrostatic precipitator
Subcooled washing
Syngas storage
FIG. 2. Block scheme for gasification and syngas preliminary cleaning and purification.
18 Q3 2021 | H2-Tech.com
Residual HCI and HF removal
Residual metals removal
Hydrolysis of COS (HCN)
Hg removal
H2
S removal
H2S deep polishing removal
Purified syngas
NG
NG
evaporative quench, where temperature is abruptly reduced to
85°C-90°C by direct injection of water. Although a loss of hightemperature
heat is observed, this rapid cooling freezes the chemical
composition achieved at high temperature, thereby avoiding
undesired reactions. The two-phase mixture at the bottom exit of
the quench is routed to a sedimentation tank. This unit allows for
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