The utilization of coal and other fossil fuels is becoming
increasingly
restricted. Biomass, as a clean and renewable energy, plays a significant
role in achieving zero carbon emissions. However, biomass is prone
to slagging in the combustion process due to its high alkali metal
content. The ash slagging rate and pollutant emission level of flue
gas can be reduced by optimizing the air distribution, in order to
decrease the fuel layer temperature in the combustion chamber. The
results reveal opposite change trends of CO and NO
x
concentrations
in the flue gas. The NO
x
emissions of corn stalk combustion
under the multilayer secondary air distribution are obvious compared
with those of rice husk combustion. The slagging rate of corn stalks
is highly correlated with temperature
T
1
of the fuel bed. The silica ratio (
G
), alkali/acid
ratio (
B
/
A
), Na content index (Na
(index)), and alkaline index (Al
c
) cannot
accurately predict the slagging tendency when temperature
T
1
changes. Therefore, the modified predictive
index (
G
t
) was proposed to predict the
slagging tendency of corn stalks with the combustion zone temperature
T
1
effectively. The experimental results can
contribute to the efficient combustion and low pollutant emissions
of biomass.
Three kinds of pore-forming agents (corn flour, starch, and biochar) were selected to prepare dolomite-based porous ceramic catalyst carriers with good mechanical properties. Pore-forming agents occupy space within preformed agglomerates, such that after the pyrolysis and sintering have been completed there are spaces within the resulting ceramic material. Porous ceramic samples prepared with biochar exhibited high apparent porosity and water absorption. By contrast, the apparent porosity of the porous ceramic samples prepared with starch as the pore-forming agent was low. When the ratio of the dolomite to quartz sand in the ceramic aggregate was changed from 4:6 to 3:7, the change of the apparent porosity of the porous ceramic samples made with starch as a pore-forming agent was very small, with high bulk density and compressive strength. Compared with corn flour and biochar, starch was less suitable as a pore-forming agent for porous ceramics. The apparent porosity and water absorption of the porous ceramics prepared with biochar as a pore-forming agent decreased slightly. But its bulk density and thermal conductivity were increased. This is mainly attributable to the fact that biochar is lighter, but it performs well in terms of mechanical strength and thermal conductivity.
This study aimed to investigate the effect of the urea content on the characteristics and distribution of nitrogen-rich biooil and nitrogen-doped biochar. Cellulose, cellobiose, and glucose were used as feedstock. Urea was used as the exogenous nitrogen source in nitrogen-rich pyrolysis at 500 °C. The order of the nitrogen increase in the nitrogen-doped biochar was cellulose < cellobiose < glucose. Nitrogen-doped biochar consisted of abundant nitrogen and nitrogenous functional groups, and the stability of biochar was optimal. The nitrogen-doped biochar obtained from cellulose showed the optimal adsorption performance for diethyl phthalate with 50% urea addition. When the proportion of urea was 20%, the content of anhydro-sugars in biooil reached the maximum value (61.86%). Furans and other smallmolecule oxygenates were intermediates to produce nitrogenous heterocyclic compounds (NHCs) from cellulose. When the proportion of urea was 40%, the bio-oil had the highest selectivity (91.63%) of NHCs. The NHCs in the obtained bio-oil mainly consisted of pyrroles, pyrimidines, pyridines, imidazoles, and pyrazines. Therefore, the excellent proportion of urea in the blend could promote the generation of high-value NHCs and nitrogen-doped biochar from the nitrogen-rich pyrolysis of cellulose (and its model compounds).
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