Sewage Sludge Inevitable production of a renewable resource

Transcription

1 Sewage Sludge Inevitable production of a renewable resource Dr Bill Barber 23 February 2012 Geelong Traditional wastewater treatment Primary Sludge 1

2 Stricter wastewater standards Secondary Treatment Primary Sludge Secondary Sludge Nutrient removal Chemical Dosing Ferric alum Ferric alum Chemical Sludge Chemical Sludge 2

3 World-wide Sludge Production World Sludge Production 1 every 40 seconds 3

4 World Sludge Production Increasing sludge production in Europe mainly due to stricter environmental standards TTDSA

5 Sludge Processing Wastewater treatment Sludge Type Thickening Pre-treatment Mechanical ATAD Series Biological Acid TAD Liquid Thermal Digestion Chemical Pasteurisation Thermal Hydrolysis Other Anaerobic Digestion MAD Composting Liming Dewatering Drying Gasification Lime + Supp Heat Oil from Sludge Transport (Super Critical) Wet Air Oxidation with digestion without digestion Outlets What can you do with it? Environmental Drivers Wastewater Treatment Biosolids Production Removal of pathogens, organics, metals etc Biosolids Treatment Other Wastes Land Application Combustion Other Landfill Land Reclamation Wet Stockpiling Forestry SC(WAO) Building aggregates Recycling Food crops Non-food crops Energy crops Dry Monoincineration Co-firing Power stations Resource recovery Protein extraction Factories 5

6 What else can you do with it? European Sludge Outlets 50% 40% 30% % 10% 0% Land recycled Landfill Compost Incineration Hamburgers 6

7 Energy Recovery Energy Price Oil Price [$ US/barrel] Dec- 81 Juṉ 83 Dec- 84 Juṉ 86 Dec- 87 Juṉ 89 Dec- 90 Juṉ 92 Dec- 93 Juṉ 95 Dec- 96 Juṉ 98 Dec- 99 Juṉ 01 Dec- 02 Juṉ 04 Dec- 05 Juṉ 07 Dec- 08 Juṉ 10 Dec- 11 7

8 Energy Security Energy Security Natural Gas [Trillion cubic metres] at end 1990 at end 2000 at end 2009 Proved World Reserve Former Soviet Union Reserve 8

9 Anaerobic Digestion in the Water Industry Traditional Configuration Two stage process Secondary Digesters Primary Digesters Primary digestion HRT ~ 16 d Covered Biogas collected and used in CHP Secondary digestion HRT ~ 14 d Uncovered For additional stabilisation Biogas lost to atmosphere Not originally designed for energy generation or carbon footprint reduction 18 9

10 Energy recovery from sludge MAD with CHP Energy in kwhr In pure biomass 6480 In pure biomass 6480 In dry solids 4860 In dry solids 4860 In biogas 3159 In biogas 2187 After fugitive gas losses 1935 After heat losses 1529 After efficiency losses 658 Export as Renewable Power 658 Things which influence gas production Wastewater Treatment Maintenance Equipment Selection 10

11 Water Industry Advanced Anaerobic Digestion Ultrasonics High Pressure Shear Electric Pulse Chemical Lysis Medium Pressure Maceration Rapid Decompression Thermal Hydrolysis Acid Phase Biological Hydrolysis Benefits of Advanced Digestion Higher biogas production Smaller Digestion Plants Greater Stability Better dewatering Reduced secondary emissions Advanced treated 11

12 Performance Biological Thermal Acoustic Pressure Sludge Organics Standard Advanced Sterilisation (ABP) High DS (OLR) VS destruction 58% 62% 62% 70% Complexity Energy Demand Dewaterability (NH 3 ) (NH 3 ) In pure biomass 6480 Energy recovery from sludge - Advanced MAD with new CHP In dry solids 4860 In biogas 3159 After fugitive gas losses 3023 After heat losses 2426 After efficiency losses 1213 Energy in kwhr Export as Renewable Power

13 Alternative Biogas Uses Biogas CH 4 65% CO 2 35% Cogeneration Anaerobic Digestion Facility Heat Alternative Biogas Uses Biogas CH 4 65% CO 2 35% Biomethane CH 4 96% CO 2 4% Further Processing Clean-Up Anaerobic Digestion Facility Heat Compression 13

14 Alternative uses for Biogas Davyhulme - Biogas to Grid m 3 biogas/hr Pressure Swing Adsorption preferred technology to produce 96% CH 4 biomethane 230 m 3 /hr biogas cleaned Injection to grid Compression and vehicle use 14

15 Energy Recovery Thermal Calorific Value of Substances Calorific Value (GJ/kg)

16 Thermal sewage sludge treatments Incineration Drying Co-combustion Benefits Total destruction Energy recovery Fly ash may be recycled Proven at full-scale Reduces reliance on landfill Proven at full-scale High volume reduction Partial pasteurisation Storage and handling of product may be easier than sludge cake (especially if pelletised) Long storage times possible Fraction of the costs and plant of incineration Commercially proven at full scale with both sludge and numerous refuse derived fuels (such as chicken litter) Can take dewatered or dry cake Reduces fossil fuel requirements Larger range of disposal options than sludge cake Sludge burnt by company who have expertise in burning materials Increases calorific value of sludge prior to thermal destruction Thermal sewage sludge treatments Incineration Drying Co-combustion Planning High capital and operating costs Critically dependent on third parties Disadvantages Public Perception Very low on waste hierarchy Requires complex gas cleaning Removes phosphorous from ecosystem Produces a number of hazardous wastes High capital cost Needs auxiliary fuel such as natural (or bio)gas Potentially complex operation Potential handling problems Very sensitive to fluctuations in load (especially dry solids) Issue with fibres and other materials With direct driers, production of gas which may require further treatment. May result in tightening regulations at power station Public perception Limited to power stations with advanced flue gas treatment facilities Methane build-up problems May be forced to dry cake Competition from other refuse derived fuels High operating cost Critically reliant on gas prices Rewetting of raw dried sludge has resulted in pathogen regrowth Numerous take-overs of power station companies may disrupt long term contracts Fluctuations in sludge quality may discourage power plant owners from accepting sludge 16

17 Drying Theory - Two falling rate curves - 1 MW/t we (0.72 MW for water evaporation) - 50 kwe/t we - Pelletiser - Operational breakdown Energy 55% Staff 30% Maintenance 10% Other 5% Drying Technology Drying Conductive Convective Hybrid Direct Belt Drum Thin Film Solar Indirect Paddle Tray Hybrid Fluidised bed 17

18 Direct Dryers: Rotary Drum Dryer - Andritz, Siemens, Baker-Rullman - Medium to Large - High operating temperature, Complex - Multipass Design - High Pellet Quality In-Direct Dryers - Paddle Dryer - Komline Sanderson, Fenton, Therma-Flite - Small to Medium C - Can use waste heat - Single Pass Design - No need for biosolids recycle 18

19 Fluidized Bed Dryer, Hybrid - Andritz, Schwing - Medium to Large - Can use waste heat - Low operating temp (85 C) Solar Drying - Veolia, Wendewolf, Parkson, Huber - Large footprint, low energy kg/m 2 /yr in Europe m 2 /t we/yr kg we/m 2 /d - Thickness 100 > 350mm - Largest plant 150 MLD 19

20 Economic and carbon analysis (long transport distance) Cost Carbon Footprint MAD Adv MAD+TH Drying MAD Adv MAD+TH Drying Economic and carbon analysis (short transport distance) Cost Carbon Footprint Adv MAD Adv MAD 20

21 Impact of transport on processing costs MAD TH Adv + MAD Drying Cost Biosolids transport distance Impact of transport on carbon footprint MAD TH Adv + MAD Drying Operating Carbon Footprint Biosolids transport distance 21

22 Heilbronn Power Station Co-firing of sludge at coal-fired power station 1. Sludge cake enters system and is screened (400 mm) mesh. Silo holds 70 m 3 2. Material is pumped (45 m 3 /hr) to storage silo which holds 240 m 3 3. Sludge is pumped (<30 m 3 /hr at 80 bar) distance of 150 m to storage hoppers 4. Controlled amounts of dewatered cake (0.5 4%) are fed into 4 boilers, each of which have 4 t/hr spare water evaporation capacity 5. Methane and air are extracted from all areas containing sludge to prevent build-up of hazardous gases 22

23 Sludge reception station Sludge reception station Sludge cake storage silo 23

24 Sludge cake pump Nutrient recovery 24

25 Fertiliser Costs Phosphorus Cost [$ US/t] Super-phosphate 20% phosphate Super-phosphate 44-46% phosphate Diammonium phosphate ( ) Potassium chloride 60% potassium Fertiliser Costs Nitrogen Cost [$ US/t] Anhydrous ammonia Nitrogen solutions (30%) Urea 44-46% nitrogen Ammonium nitrate

26 Phosphorous - World population increasing Becoming urbanized Changing food habits Global demand increased 4.7 million tones in 3 years (equivalent to USA consumption) kg P/person.year Demand - Peak P predicted at 2035? years of easily mined P remain >60% of all reserves in Morocco China imposed P export tax (+110%) Supply Phosphorous Balance 17.5 Phosphate Rock Reserves Natural Environment Mined P Rock P Fertilizer Production Animal Manure Other Uses 0.9 Arable Soil 15 Crops Domestic Animals Harvested Crops Non-food Anthroposphere 0.6 Food Commodities Organic Waste 3 Humans Excreta Mining losses Distribution losses Annual figures in millions of tones Erosion losses Crop losses Harvest losses Food-chain losses Inland Coastal Waters 1.5 Adapted from Cordell et al., The story of phosphorus: Global food security and food for thought 26

27 Phosphorus - 90% of phosphorus consumed by humans is wasted - If recovered, this phosphorus could meet 20% of current global demand - Over half of this phosphorus is in sludge Generally this is a nuisance at a sewage works - This is lost during thermal processing Incineration Struvite Mg 2+ + NH 4+ PO H 2 O MgNH 4 PO 4.6H2O Heizmann and Engel,

28 Phosphorus Biosolids as a resource 1 tonne sewage sludge 0.42 tonne oil equivalent 0.08 kw electricity 200 m 3 biomethane 50 kg N 25 kg P 15.3 oz troy $305 $70 $25 $40 $26,000 28

29 Summary - Sludge production is increasing globally Stricter legislation; Population increase; Greater urbanization - It is also becoming increasingly difficult to treat - Many ways which energy can be recovered from sludge Anaerobic digestion; biogas upgrading; thermal recovery (mono- and co-firing as cake or dried material) - Nutrient recovery becoming more important to address phosphorous requirements and to assist with carbon reduction Thank you bill.barber@aecom.com 29

30 Case-study Energy Recovery using Super Critical Wet Air Oxidation (SCWAO) Alternative to Incineration Super Critical Wet Air Oxidation (SCWAO) Super Critical 221 bar Solid Liquid Gas 374 C 30

31 SCWAO Bruxelles Nord Thermal Hydrolysis with WAO TDSA Operational 2006/7 - Mixed primary and secondary sludge - Sub-critical oxidation 50 bars 250 C Uses catalyst - Less than 5% organics in solid residue - Effluent contains 25% COD load 31