Pyrolysis of sewage sludge is carried out in a fluidized bed reactor. The non-condensable gases yield is shown in the attached figure. Generally, the yield of CO2 increases as the temperature ascends to the higher degrees. But for our experiment, the yield of CO2 showed a fluctuating trend, increasing till 650, decreasing at 750, and increasing again at 850 and decreasing again at 950. I cannot understand the reason behind it. I tried looking for the reason in the research but was not able to find any logical reason behind it. We have performed every experiment three times and have used the average of the data with the standard deviation. The overall gas yield has increased as the temperature escalated to higher range, but the yield of CO2 is very confusing.
Dear A Siddiqui,
Firstly, the theoritical temperature range for pyrolysis is 400 - 600 deg C. However, you have results for temperatures as high as 950 deg C. As such it is not strange to have rather strange results for especial for CO2 or any of the product gases, as you are now operating in the gasification/low combustion region.
That said, the issue with CO2 in your results may be due to the Boudouard reaction and WGS. This strongly endothermic reaction does not favour CO but CO2 production at the temperatures > 700 C. Similarly, the Water Gas Shift reaction with also produces CO2 will be favoured.
Kindly refer to this paper by; Hunt, J., Ferrari, A., Lita, A., Crosswhite, M., Ashley, B. and Stiegman, A.E., 2013. Microwave-specific enhancement of the carbon–carbon dioxide (Boudouard) reaction. The Journal of Physical Chemistry C, 117(51), pp.26871-26880. OR
Lim, J.Y., McGregor, J., Sederman, A.J. and Dennis, J.S., 2016. The role of the Boudouard and water gas shift reactions in the methanation of CO or CO2 over Ni/γ-Al2O3 catalyst. Chemical Engineering Science, 152, pp.754-766.
These may provide more insights.
Hope this helps.
Regards,
BBN.
Presence of carbon monoxide indicate the experiment not done at complete combustion (Air:fuel ratio), i. e. the reaction need more air flow jet to convert the carbon monoxide to carbon dioxide. At increase air flow may carbon monoxide disappear and presence only carbon dioxide that indicate the complete combustion which may solve your problem.
Azka Rizwana Siddiqui Water use efficiency (WUE) is defined as the amount of carbon assimilated as biomass or grain produced per unit of water used by the crop. One of the primary questions being asked is how plants will respond to a changing climate with changes in temperature, precipitation, and carbon dioxide (CO2) that affect their WUE At the leaf level, increasing CO2 increases WUE until the leaf is exposed to temperatures exceeded the optimum for growth (i.e., heat stress) and then WUE begins to decline. Leaves subjected to water deficits (i.e., drought stress) show varying responses in WUE. The response of WUE at the leaf level is directly related to the physiological processes controlling the gradients of CO2 and H2O, e.g., leaf:air vapor pressure deficits, between the leaf and air surrounding the leaf. There a variety of methods available to screen genetic material for enhanced WUE under scenarios of climate change. When we extend from the leaf to the canopy, then the dynamics of crop water use and biomass accumulation have to consider soil water evaporation rate, transpiration from the leaves, and the growth pattern of the crop. Enhancing WUE at the canopy level can be achieved by adopting practices that reduce the soil water evaporation component and divert more water into transpiration which can be through crop residue management, mulching, row spacing, and irrigation. Climate change will affect plant growth, but we have opportunities to enhance WUE through crop selection and cultural practices to offset the impact of a changing climate.
Review Article : Article Water-Use Efficiency: Advances and Challenges in a Changing Climate
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