energies
Article
Catalytic Temperature Effects on Conversion Efficiency of PM
2.5
and Gaseous Emissions from Rice Husk Combustion
Emmanuel Owoicho Abah
1
, Tofael Ahamed
2
and Ryozo Noguchi
2,
*
Citation: Abah, E.O.; Ahamed, T.;
Noguchi, R. Catalytic Temperature
Effects on Conversion Efficiency of
PM
2.5
and Gaseous Emissions from
Rice Husk Combustion. Energies 2021,
14, 6131. https://doi.org/10.3390/
en14196131
Academic Editors: Liwen Jin,
Wei-Hsin Chen, Aristotle T. Ubando
and Chih-Che Chueh
Received: 26 August 2021
Accepted: 23 September 2021
Published: 26 September 2021
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4.0/).
1
Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba 305-8577, Japan;
aeowoicho@gmail.com
2
Faculty of Life and Environmental Sciences, University of Tsukuba, Tsukuba 305-8577, Japan;
tofael.ahamed.gp@u.tsukuba.ac.jp
* Correspondence: noguchi.ryozo.gm@u.tsukuba.ac.jp
Abstract: Most studies on honeycomb catalysts have been conducted using simulation models and
exhaust experiments from automobiles. Very few monolithic catalyst studies have been applied to
the agricultural sector, especially the catalyst exhaust system for flue purification from the biomass
industry. The importance of exhaust gas purification and particulate removal from biomass power
plants has become critical for evaluating the performance and environmental sustainability of biomass
combustion. This is one of the first studies to investigate the performance of honeycomb catalysts
for the oxidation of flue (PM
2.5
), (CO), and (SO
2
) from a rice husk briquette combustion system.
The experimental setup comprised a fixed-bed electric furnace, the catalyst, an aerosol sampler,
and a flue gas analyzer. Rice husk (0.1 g/mL density) and rice husk briquettes (0.8 g/mL density),
were burned at 600–1000
◦
C for 3 min. From the results, the catalyst CO conversion rate was 100% at
the optimum heated temperatures of 427.4–490.3
◦
C. At these temperatures, the inhibition effect of
the chemisorbed CO was significantly minimized, enhancing the adsorption of oxygen, which reacted
with CO to form CO
2
. However, SO
2
oxidation was lower than that of CO because platinum-based
catalysts are generally more attracted to CO in the presence of oxygen. The emission of PM
2.5
decreased from its uncatalyzed-value (1169.9 mg/m
3
and 1572.2 mg/m
3
) to its catalyzed values
(18.9 mg/m
3
and 170.1 mg/m
3
). This is a significant result in ensuring cleaner production of energy
from rice husk.
Keywords: PM
2.5
; CO; SO
2
; combustion; catalytic oxidation; conversion; emission; biomass; energy
requirement; cleaner energy production
1. Introduction
Biomass energy is the oldest energy source for humans. Bioenergy is a key factor in
a low-carbon future, and its demand is projected to increase significantly, accounting for
17% of global energy by 2060 [1]. At this rate, the energy from biomass will contribute
to an increasing carbon-saving of 20% by the year 2060, cutting “greenhouse” releases
comprehensively. The utilization of biomass, such as rice husks, presents a huge potential
for increasing the quota of bioenergy in the power sector [2]. According to the Food and
Agriculture Organization (FAO) statistics, estimated global rice husk production is approxi-
mately 156.4 million tons. This is distributed among Africa (6.6 million tons), the Americas
(7.8 million tons), Asia (141.0 million tons), and Europe (4.0 million tons) [3]. The increasing
world population increases the demand for more food and, consequently, has a greater
environmental impact. Therefore, it is of great importance to explore the possibility of
introducing a metal honeycomb catalyst in biomass combustion systems to reduce future
environmental impacts and climate change effects. Pyrolysis of rice husk (separating the
bio-oil from the ash) combustion has been performed to minimize particulate matter (PM)
emissions [4]. However, the particulate matter and gaseous emissions such as carbon
monoxide (CO), nitrogenous oxide (NOx), and sulfur dioxide (SOx), from these systems
Energies 2021, 14, 6131. https://doi.org/10.3390/en14196131 https://www.mdpi.com/journal/energies