gas analysis
DESCRIPTION
GAS ANALYSIS. - Anaerobic sludge digestion & - Anaerobic treatment of high BOD containing wastes (~1500mg/L) Methane Formation . Gas produced contains; CO 2 33-38% CH 4 55-65% N 2 H 2 S Heating value: 600 Btu / ft 3 (5330 kcal/m 3 ) - PowerPoint PPT PresentationTRANSCRIPT
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GAS ANALYSIS
- Anaerobic sludge digestion &- Anaerobic treatment of high BOD containing wastes (~1500mg/L)
Methane Formation
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Gas produced contains; CO2 33-38% CH4 55-65% N2
H2S • Heating value: 600 Btu / ft3 (5330 kcal/m3 )
• Anaerobic digester can be heated with this energy.
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• Heating value depends on the waste strength.
• Composition of the gas is related with conditions in the reactor.
CO2 / CH4 ratio
Character of the substrate
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Analyze the gases produced
*Determine fuel value* Monitor treatment
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* If CO2 content increases
indicates trouble in anaerobic treatment
* H concentration should be low, high H Digester upset
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Methods of AnalysisVolumetric Procedure : (Simple Method) Orsat Apparatus is used O2 , CH4, H2, CO2, N2 Gas Chromatography : Advantage : speed CH4 ,CO2 , air (N2 + O2 )
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Gas Chromatography
• Previously calibrated for each gas • Suitable for routine work, frequent
analysis
• TCD (Thermo Conductivity Detector) is used in GC for gas analysis
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Volumetric Analysis
• Combustion of hydrogen and methane Measure amount of CO2 produced during
combustion
• If hydrogen and methane burned together
Possibility of explosion
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Volumetric Analysis(continue)
Separate oxidation of H2 and CH4
* Hydrogen oxidized by passing the gas through a heated unit charged with cupric oxide
* Methane is oxidized by bringing it and O2
with a catalyst at a lower temperature.
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CO2
• Take 100 mL sample, contact with a solution of KOH
CO2 + 2KOH K2CO3 + H2O
Potassium Carbonate
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CO2 (Continue)
CO2 disappears from the gaseous phase
Volume reduction = V CO2
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Hydrogen Sulfide
H2S + 2KOH K2S + 2H2O
Volume of H2S is too small, can be ignored
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O2
* Very little possibility of O2 existence in anaerobic digester gas.
Can enter during sampling. * If more than 0.1-0.2 %
Indicates poor sampling technique
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O2
(continue)* Measured by using alkaline pyrogallol Under alkaline condition pyrogallol (1,2,3-trihydroxy-benzene) is oxidized by oxygen * Measure CO2 . Volume reduction = VO2
(CO2 present should be removed previously)
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Hydrogen
* Pass the gas mixture over cupric oxide @ 290-300 o C
* H2 is oxidized to water (methane is not)Water vapor formed condenses at lower temperature
Cool the sample Measure volume loss after contact with heated cupric
oxide
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Methane
* After removal of hydrogen oxidize methane by slow combustion or
catalytic oxidation * Stoichiometry is important to calculate
required amount of O2 for combustion CH4 + 2 O2 CO2 + 2H2O
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Nitrogen
Inert gas
VN2 = VT - (VCO2 + VO2 + VH2 + VCH4 )
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Collection - Storage
*Glass / metal tubes *Gum – rubber balloons ( Pervious to H2 and CH4 !!)
Use displacing fluid to transfer the gas sample to the apparatus
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Collection - Storage
Temperature changes affect the analysis. If combustion is applied, measure gas
volume after the temperature returns to original value.
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Collection- Storage
Confining liquid: • Hg (ideal, but have health hazards, used in
precise inst)
Water Solvent power Aqueous solution 20% Sodium sulfate, 5% H2SO4
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Hydrogen Sulfide
H2S corrosive • If gas will be used as a fuel,
should contain < 1.14 mg/L
H2S + I2 2HI + S • Excess iodine is indicated with starch
indicator.