Nuevos procesos de depuración con menores costes y aprovechamiento energético del biogás JORNADA BIOGAS GALICIA 29/01/2015 Alberto Sánchez Biogas general background WHY RECOVER ENERGY FROM BIOGAS? Sewage treatment is a high-energy consuming process (pumping & aeration): 0,4 – 0,6 kWh/m3 Electricity costs are rising Climate change awareness: reduction of the carbon footprint Use of renewable energies: target of 20% of the total in the UE by 2020 HOW IS IT DONE TODAY? Energy Conversion Systems (ECS): flare, boilers and some ICE Biogas treatment: very light (FeCl3 dosing, moisture condensation…) SE water branch (2011) Energy balance in a WWTP 28% (CO2) 1 kg COD 3,5 kWh 30% 30% BIOGAS 35% aireation & pumping Boosting biogas production Energy from byproducts 7% Effluent Energy consumption 35% Final sludge High efficient energy recovery Energy production ENERGY SELFSUFFICIENCY ? Biogas: Value chain • Include external sources • Reduce operation risk • Quantify correctly • Select correctly •Reduce cost •Reduce operation risk Energy production INCREASE • Enhance productivity Biogas cleaning REDUCE INCREASE Biogas production • Increase electricity production • Increase heat use Biogas: Value chain ADVANCED DIGESTION • Anaerobic digestion at low temperatures sludge • Anaerobic digestion at ambient temperatures sewage • Anaerobic digestion control Advanced digestion rationale • Sewage sludge anaerobic digestion has limited performance (VSR at around 40%) and is far from the stoichometric ratio of 0.35 Nm3CH4/kg COD boosting production through add-on processes/different operating conditions • Some digesters are not operated at full load boosting production through co-digestion Sludge AD at Low Temperature Typical anaerobic digesters operate in: 30% Biogas produced : Maintain digester temperature around 37ºC Mesophilic conditions (30 – 40 ºC) Thermophilic conditions (50 – 70 ºC) Underloaded digesters need the same energy PRESENT STATUS FUTURE STATUS Electric energy Electric energy Biogas 30% Sludge 35ºC Biogas Grid injection Boiler Grid injection 7% Others Sludge 20 ºC Boiler Anaerobic digestion at psychrophilic temperatures Reduction of the energy input required for heating the bioreactor Lower temperatures lead to more stable conditions of operation Improvement of the operational performance by reducing costs Others Sewage AD at ambient temperature «Integrated System of Anaerobic Methanogenic reactor and Membrane bioreactor» ES 2 401 445 B2 - 0.25 kw/m3 600 mgCOD/L SIAM • 50% lower sludge production • 70 % NT removal • 90 % dissolved methane removal (GHG) • High quality effluent (Reuse) SIAM 50-75% CH4 (biogas) CH4 (GHG) N2 NO3- 25-50% CH4 (dissolved) Anaerobic CH4 + NO3 Anoxic Aerobic NH4+ Aerobic NH4+ permeate wastewater O2 AD control Oversized Unstable «Control System for Anaerobic Codigestors» ES 2 516 615 A1 Biogas: Value chain BIOGAS CLEANING • Desulphurisation by micro-aeration • Biogas deep polishing Biogas cleaning rationale • Gas treatment line should be designed according to CHP technologies • Combination of treatment technologies is necessary • The entire line should be considered altogether H2S CO2 CH4 Internal Combustion Engine NA > 45% µ-turbine NA > 30% Stirling NA > 30% Fuel cells NA > 50% Biomethane Si 96 – 99% Desulphurisation by Microaeration H2S removal Polishing Inside digester Microaeration FeCl3 dosing NaOH Scrubbers Main removal Bio-scrubber Outside digester Iron based sorbents Bio-trickling filter Activated carbon Desulphurisation by Microaeration Injection in the sludge loop Injection in the biogas loop Injection in the headspace Patented (FR13.55.538) Key issues H2S removal efficiency (i.e.: residual content of H2S in the treated gas) CH4 and CO2 content in the treated gas Residual content of O2 in the treated gas (problems injection + S formation on piping) Elemental sulphur accumulation (digester; aeration chamber; other locations) Biogas deep polishing • Pilot plant in real WWTP for biogas polishing • Characterization of adsorbent materials for H2S and Siloxanes removal (virgin activated carbon, impregnated activatd carbon, iron-based adsorbent, silica gel, etc.) • Study the reaction mechanisms Activated carbon adsorbent (top: virgin; bottom: saturated) Iron-based adsorbent (bottom: virgin; top & middle: saturated) Biogas: Value chain BIOGAS END-USE • Cogeneration with fuel cells • Fuel: Biomethane Biogas end-use rationale Raw biogas Cleaning (removal of water,H2S, siloxanes, …) Cogeneration (ICE, µ-cogen, ICE+ORC) Combined Heat & Power (CHP) High temperature fuel cells Reforming + Low temperature fuel cells Clean Biogas CO2 removal FUEL biogas upgrading Waste heat Jan-15 Cogeneration with fuel cells • Chemical combustion External combustion Internal combustion • Electrochemical combustion Cogeneration with fuel cells Key issues • High temperature fuel cells are more efficient for biogas applications • Net electrical efficiencies of 40 – 50% can be obtained • Heat integrated systems; with thermal efficiencies of 30 – 35% • Stack durability is an issue but guarantees are given • CAPEX around 3 – 4 times compared to ICE/micro-turbines Cogeneration with fuel cells 78 biogas-powered fuel cell references accounting for 53.5 MW Fuel: Biomethane Car fuel Natural gas grid Fuel: Biomethane Quality monitoring Definition of sampling points and frequency of monitoring Parameters Temperature Pressure Dew point CH4 - CO2 N2 - O2 H2S Linear hydrocarbons BTEX Siloxanes Sulphur compounds Ammonia Halogenated compounds CO HCN Mercury Density Water Low/high heating value Wobbe Index Different on-line analysers assessed Conclusiones Biogas production Biogas cleaning Energy production • Utillization of existing installations • New operational strategies/processes • Integration of biogas treatment • Solutions for specific requirements • High development potential THANKS QUESTIONS?
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