Siva Sankar Thanapal

Ranking Renewable and Fossil Fuels on Global Warming Potential Using Respiratory Quotient Concept

Carbon dioxide (CO2) is one of the greenhouse gases which cause global warming. The amount of fossil fuels consumed to meet the demands in the areas of power and transportation is projected to increase in the upcoming years. Depending on carbon content, each power plant fuel has its own potential to produce carbon dioxide. Similarly, the humans consume food containing carbohydrates (CH), fat, and protein which emit CO2 due to metabolism. The biology literature uses respiratory quotient (RQ), defined as the ratio of CO2 moles exhausted per mole of O2 consumed within the body, to estimate CO2 loading in the blood stream and CO2 in nasal exhaust. Here, we apply that principle in the field of combustion to relate the RQ to CO2 emitted in tons per GJ of energy released when a fuel is combusted. The RQ value of a fuel can be determined either from fuel chemical formulae (from ultimate analyses for most liquid and solid fuels of known composition) or from exhaust gas analyses. RQ ranges from 0.5 for methane (CH4) to 1 for pure carbon. Based on the results obtained, the lesser the value of “RQ” of a fuel, the lower its global warming potential. This methodology can be further extended for an “online instantaneous measurement of CO2” in automobiles based on actual fuel use irrespective of fuel composition.

Updraft gasification of juniper wood biomass using CO2–O2 and Air (N2–O2)

ABSTRACT Biomass gasification is being considered as one of the most promising technologies for converting low-quality solid biomass fuel into gaseous fuel. Redberry juniper (Juniperus pinchotii), one of the woody species that dominate uncultivated lands in the southern great plains, USA, may have a great potential for bioenergy utilization. In this study, the results of gasification of juniper are presented. Juniper wood chips were gasified in an adiabatic fixed bed updraft gasifier using air and the mixture gas of carbon dioxide and oxygen (CO2:O2) as gasification medium. The effect of gasification parameters such as moisture contents, gasification mediums, and gasification temperature on produced gas properties and the tar yield were investigated. It was observed that oxy fuel gasification (the reaction of woody fuels with carbon dioxide) of juniper resulted in the increase of production of carbon monoxide, especially at higher peak gasification temperatures. As a result, the CO2 gasification resulted in producing higher heating value gas (6264 kJ/nm3 with dilution of CO2 and 19,750 kJ/nm3 inert free) compared to air gasification. For air gasification, it was observed that the updraft gasification produced large amount of the tar in the product gas (more than 100 g/nm3) for the fuels with moisture content between 6% and 11%. Generally, the tar yield increased with the increase of equivalence ratio (er) and moisture content. However, when the fuel moisture content reached 23.5%, the tar yield reduced significantly due low gasification temperature which reduced the less tar cracking.

Biomass Fuel Quality Enhancement and Respiratory Quotient (RQ) for Ranking Fossil and Biomass Fuels Based on CO2 Emissions

Torrefaction is one of the thermo-chemical pretreatment techniques used to enhance the properties of biomass fuels. An inert environment is maintained during torrefaction process. Effect of using carbon dioxide (CO2) as torrefaction medium for mesquite and juniper woody biomass was investigated in the current study. CO2 torrefaction resulted in improved grindability and comparable energy retention in the case of mesquite and juniper. A three component model based on independent parallel reactions was developed to model the torrefaction process. Effect of torrefaction on behavior of the three components in the biomass: hemicellulose, cellulose and lignin was studied. Kinetic parameters for the three biomass components were obtained from literature. Results from the TCM were compared with the results obtained from TGA experiments carried out on mesquite and juniper samples. Further, concept of respiratory quotient (RQ) used in biological literature was applied to combustion applications. Global warming potential (GWP) of different fuels were estimated based on respective RQ. Higher the RQ of fuel, higher is its GWP. A term RQ Process,Biomass was introduced to estimate the amount of CO2 produced during processing a renewable fuel for combustion applications.

Updraft Fixed Bed Gasification of Mesquite Fuel Using Air-Steam Mixture

The mesquite woody species that dominate uncultivated lands in the south central Great Plains, U.S.A. (Texas, Oklahoma) may have the potential for bioenergy utilization. Gasification of woody biomass is an environmentally promising technology that provides an alternative to the use of fossil fuel. The objective of this study is to study enhancement of heat values of mesquite (Prosopis glandulosa) using an adiabatic fixed bed gasifier using air-steam as gasification medium and compare these values with those from other methods which include: air (N2:O2), CO2-O2 mixture, enriched air, blending biomass with high quality coal etc. The effects of steam/fuel ratio (S:F) and equivalence ratio (ER) on the gasification peak temperature (Tpeak), gas compositions, and gas higher heating value (HHV) were investigated. It is found that the Tpeak in air-steam gasification is lower than that of air gasification and the Tpeak decreased with the increase in the steam to fuel ratio (S:F). In addition, when S: F ratio increased from 0 to 0.45, the CO2 and H2 concentration increased while the CO percentage decreased. The mole composition of the end product gas contained: 8–19% CO, 4–15% H2, 1–3% CH4, and 10–18% CO2. The HHV of the mesquite gas was estimated to be in a range of 2800 kJ/Nm3 to 3800 kJ/Nm3. The HHV increased when the S: F increased from 0.15 to 0.3, and then it decreased when the S: F was increased from 0.3 to 0.45 and the highest value was obtained at S: F = 0.3 and ER = 2.7 (optimum). The HHV of the producer gas from air-steam gasification is found to be almost same as that produced from pure air gasification (2800–4000 kJ) and lower than that obtained from CO2:O2 mixture (79:21) gasification (4000 to 6000 kJ/Nm3). However, H2 rich producer gas was obtained with air steam mixture.Copyright

Comparative Evaluation of CO2-O2 and Air (N2-O2) Gasification of Agricultural Biomass Fuels

Biomass gasification is being considered as one of the most promising technologies for converting biomass into gaseous fuel. Here we present the results of gasification, using an adiabatic fixed bed updraft gasifier with air and carbon dioxide as gasification medium, for redberry juniper (Juniperus pinchotii), one of the woody species that dominate uncultivated lands in the Southern Great Plains, U.S.A., that may have potential for bioenergy utilization. The effect of gasifying the woody fuels with carbon dioxide (oxy fuel gasification) was carried out to study for increased production of carbon monoxide through Boudouard reaction. The effect of three different moisture contents: 5–6%, 11–12%, and 23–24%, on the tar yield was investigated for juniper using air as the gasification medium since the amount of tar in the gas produced impacts the way the gas is utilized for different applications. It was observed that oxy fuel gasification of juniper resulted in increased production of carbon monoxide at higher peak temperatures and hence increased heating value of the resulting gas mixture (6264 kJ/ Nm3 with inerts CO2 and N2, 19750 kJ/Nm3 inert free). It was found that the tar yield was more than 100 g/Nm3 of the gas produced using air as gasification medium for juniper fuels with moisture content between 5–6% and 11–12%. Also, the tar yield increased with the increase of equivalence ratio (ER). At a fixed ER, tar increased with the increasing moisture content. However, when the fuel moisture content reached 23–24%, the tar yield reduced significantly due low gasification temperature which reduced the pyrolysis and other gas phase reaction rates within the gasifier.© 2012 ASME