Process analysis of chemical looping gasification (CLG) of biomass for liquid fuel production with net-negative CO₂ emissions
Typ
Examensarbete för masterexamen
Program
Publicerad
2019
Författare
Roshan Kumar, Tharun
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
Biomass gasification integrated with downstream Fischer-Tropsch (FT) synthesis for
the production of liquid biofuel is a potential pathway to decarbonize growing transportation
sectors such as aviation and maritime sectors. Chemical Looping Gasification
(CLG) is a novel gasification technology that resembles indirect gasification
in circulating fluidized bed, but instead of inert bed material (e.g. olivine), so-called
oxygen carrier (OC), metal-oxide particles are utilized. The OC particles undergo
cyclic oxidation and reduction in the air reactor and the fuel reactors, respectively,
providing heat and oxygen for gasification. Thus, the raw syngas produced is more
oxidized than in a conventional gasifier, with a lower concentration of tar and a
higher concentration of CO2. Capturing and storage of CO2 during the subsequent
gas cleaning stages would result in FT-crude production with net-negative CO2 emissions.
For evaluating the performance of an integrated biomass-to-liquid (BTL) process
with CLG as the primary gasification technology, an integrated process model
was developed and analyzed using Aspen Plus® simulation software. The CLG process
model was modelled with a thermal input of 100 MWth of waste biomass and
was complemented with Fortran statements to calibrate thermodynamic equilibrium
deviations, experienced during associated experimental activities or reported in the
literature. LD-slag, an inexpensive and readily available by-product from steel production,
was used as the primary oxygen carrier in the process models. The core
gasification models were validated with experimental data from the chemical looping
gasification tests done at Chalmers research boiler/gasifier with wood pellets
and LD-slag as bed material. The gasification model predicts syngas composition,
energy content and cold gas efficiency in good agreement with published data. Syngas
with a high energy content of 12 MJ/Nm3 (LHV basis) is predicted with an
average cold gas efficiency of 56.6%. A high CO2/CO ratio is also predicted in
the syngas produced, which would be suitable for carbon capture. The integrated
model estimates an FT-crude production of approximately 359 barrels per day with
a CO2 capture capacity of 138.5 ktCO2/year. The integrated model has an average
chemical efficiency, i.e. the conversion efficiency of biomass-to-FT crude of 22.8%
with the chosen operating conditions. Heat integration studies show that there are
adequate heat recovery possibilities for co-generation of steam and power.
Beskrivning
Ämne/nyckelord
chemical looping , biomass , gasification , Fischer Tropsch Synthesis , oxygen carriers , LD-slag