gas analysis - anaerobic sludge digestion & - anaerobic treatment of high bod containing wastes...
Post on 31-Mar-2015
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GAS ANALYSIS - Anaerobic sludge digestion & - Anaerobic treatment of high BOD containing wastes (~1500mg/L) Methane Formation Slide 2 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 ) Anaerobic digester can be heated with this energy. Slide 3 Heating value depends on the waste strength. Composition of the gas is related with conditions in the reactor. CO 2 / CH 4 ratio Character of the substrate Slide 4 Analyze the gases produced *Determine fuel value * Monitor treatment Slide 5 * If CO 2 content increases indicates trouble in anaerobic treatment * H concentration should be low, high H Digester upset Slide 6 Methods of Analysis Volumetric Procedure : (Simple Method) Orsat Apparatus is used O 2, CH 4, H 2, CO 2, N 2 Gas Chromatography : Advantage : speed CH 4,CO 2, air (N 2 + O 2 ) Slide 7 Gas Chromatography Previously calibrated for each gas Suitable for routine work, frequent analysis TCD (Thermo Conductivity Detector) is used in GC for gas analysis Slide 8 Volumetric Analysis Combustion of hydrogen and methane Measure amount of CO 2 produced during combustion If hydrogen and methane burned together Possibility of explosion Slide 9 Volumetric Analysis (continue) Separate oxidation of H 2 and CH 4 * Hydrogen oxidized by passing the gas through a heated unit charged with cupric oxide * Methane is oxidized by bringing it and O 2 with a catalyst at a lower temperature. Slide 10 CO 2 Take 100 mL sample, contact with a solution of KOH CO 2 + 2KOH K 2 CO 3 + H 2 O Potassium Carbonate Slide 11 CO 2 (Continue) CO 2 disappears from the gaseous phase Volume reduction = V CO2 Slide 12 Hydrogen Sulfide H 2 S + 2KOH K 2 S + 2H 2 O Volume of H 2 S is too small, can be ignored Slide 13 O2O2 * Very little possibility of O 2 existence in anaerobic digester gas. Can enter during sampling. * If more than 0.1-0.2 % Indicates poor sampling technique Slide 14 O 2 (continue) * Measured by using alkaline pyrogallol Under alkaline condition pyrogallol (1,2,3-trihydroxy-benzene) is oxidized by oxygen * Measure CO 2. Volume reduction = V O2 (CO 2 present should be removed previously) Slide 15 Hydrogen * Pass the gas mixture over cupric oxide @ 290-300 o C * H 2 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 Slide 16 Methane * After removal of hydrogen oxidize methane by slow combustion or catalytic oxidation * Stoichiometry is important to calculate required amount of O 2 for combustion CH 4 + 2 O 2 CO 2 + 2H 2 O Slide 17 Nitrogen Inert gas V N2 = V T - (V CO2 + V O2 + V H2 + V CH4 ) Slide 18 Collection - Storage *Glass / metal tubes *Gum rubber balloons ( Pervious to H 2 and CH 4 !!) Use displacing fluid to transfer the gas sample to the apparatus Slide 19 Collection - Storage Temperature changes affect the analysis. If combustion is applied, measure gas volume after the temperature returns to original value. Slide 20 Collection- Storage Confining liquid: Hg (ideal, but have health hazards, used in precise inst) Water Solvent power Aqueous solution 20% Sodium sulfate, 5% H 2 SO 4 Slide 21 Hydrogen Sulfide H 2 S corrosive If gas will be used as a fuel, should contain < 1.14 mg/L H 2 S + I 2 2HI + S Excess iodine is indicated with starch indicator.