59
4.5.3 Environmental and Health Impacts
Among the thermal conversion technologies, pyrolysis results in the least emissions
since all products can be used as energy sources or marketable nonenergy products.
Studies also show that carbon can be sequestered in the soil by using char as a soil
enhancer or fertilizer thus reducing GHG emissions (Roos 2009; Ahmad et al.
2014). Moreover, the use of char as fertilizer can reduce the need for chemical fertilizers and increase nutrient uptake efficiency. However, these positive impacts may
be offset if the energy input to the process will come from fossil fuels. This provides
motivation for the recirculation of heat from syngas combustion as suggested by
Agarwal (2014). Upgrading of the bio-oil, on the other hand, may render it as a
comparable replacement to petroleum-derived liquid transport fuels.
Compared to combustion, gasification has lower carbon and NOx emissions
since NOx are produced at temperatures higher than the gasification range.
Combustion only produces heat, while gasification produces excess heat and gaseous fuel, which can be used in a reciprocating engine, gas turbine, fuel cells or in
an integrated gasification combined cycle resulting to higher energy efficiency and
lower GHG emissions (Roos 2009). Also, direct combustion may result in emission
of toxic substances such as dioxins and furans especially if chlorinated compounds
are present in the feedstock. Untreated rice straw has about 0.4% Cl (Roos 2009).
Pyrolysis, on the other hand, has the advantage of producing gaseous product that is
free from such pollutants due to its inert atmosphere (Agarwal 2014).
More attention is needed by the research community to find solutions to potential
health hazards from small-scale gasification. To minimize investment costs to make
gasification economically viable, often simple filters are installed for tar removal in
small gasification plants, which often produce much carcinogenic waste, especially
in the case of wet stripping of the gas. This causes severe environmental and health
threats (Dimpl 2010). None of the small-scale plants that were repeatedly monitored in studies since 1995 (Stassen 1995; Dimpl 2010, IRRI unpubl. Trip reports
from Myanmar and Cambodia, 2008–13) took adequate measures to deal with the
condensates; instead the pollutants were freely discharged into the environment. In
addition, the operators dealing with these contaminated condensates often did not
use protective clothing or gloves and some complained about frequent headaches.
Shackley et al. (2011) studied soil improvement and carbon sequestration using
gasification biochar from rice husk gasifiers installed in Cambodian rice mills and
ice factories and highlight that questions remain regarding the safety of the biochar
for human health.
4 Thermochemical Conversion of Rice Straw
4.5.3 Environmental and Health Impacts
Among the thermal conversion technologies, pyrolysis results in the least emissions
since all products can be used as energy sources or marketable nonenergy products.
Studies also show that carbon can be sequestered in the soil by using char as a soil
enhancer or fertilizer thus reducing GHG emissions (Roos 2009; Ahmad et al.
2014). Moreover, the use of char as fertilizer can reduce the need for chemical fertilizers and increase nutrient uptake efficiency. However, these positive impacts may
be offset if the energy input to the process will come from fossil fuels. This provides
motivation for the recirculation of heat from syngas combustion as suggested by
Agarwal (2014). Upgrading of the bio-oil, on the other hand, may render it as a
comparable replacement to petroleum-derived liquid transport fuels.
Compared to combustion, gasification has lower carbon and NOx emissions
since NOx are produced at temperatures higher than the gasification range.
Combustion only produces heat, while gasification produces excess heat and gaseous fuel, which can be used in a reciprocating engine, gas turbine, fuel cells or in
an integrated gasification combined cycle resulting to higher energy efficiency and
lower GHG emissions (Roos 2009). Also, direct combustion may result in emission
of toxic substances such as dioxins and furans especially if chlorinated compounds
are present in the feedstock. Untreated rice straw has about 0.4% Cl (Roos 2009).
Pyrolysis, on the other hand, has the advantage of producing gaseous product that is
free from such pollutants due to its inert atmosphere (Agarwal 2014).
More attention is needed by the research community to find solutions to potential
health hazards from small-scale gasification. To minimize investment costs to make
gasification economically viable, often simple filters are installed for tar removal in
small gasification plants, which often produce much carcinogenic waste, especially
in the case of wet stripping of the gas. This causes severe environmental and health
threats (Dimpl 2010). None of the small-scale plants that were repeatedly monitored in studies since 1995 (Stassen 1995; Dimpl 2010, IRRI unpubl. Trip reports
from Myanmar and Cambodia, 2008–13) took adequate measures to deal with the
condensates; instead the pollutants were freely discharged into the environment. In
addition, the operators dealing with these contaminated condensates often did not
use protective clothing or gloves and some complained about frequent headaches.
Shackley et al. (2011) studied soil improvement and carbon sequestration using
gasification biochar from rice husk gasifiers installed in Cambodian rice mills and
ice factories and highlight that questions remain regarding the safety of the biochar
for human health.
4 Thermochemical Conversion of Rice Straw