www.ecn.nl
TORWASH® sewage sludge treatment Increased biogas production, highly-efficient dewatering and phosphate recovery
A.J. Grootjes, H. Kuipers, J.R. Pels, M.C. Carbo, J. Vogelaar
Symposium slibontwatering, Utrecht 14 September 2017
Table of Contents
• Introduction to TORWASH® • What can TORWASH® do for sewage sludge?
– Two process diagrams • Experimental results
– dewatering – elemental distribution of elements – digestion of effluent
• Process configuration for maximum biogas (methane) and energy yield • Controlling the fate of phosphorus recovery as fertilizer
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Waar het mee begon
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Waar het mee begon
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• Bestuur ZZL wil minder en droger slib, meer duurzame energie en grondstoffen
• 2015 1- 1,5 % droger door procesvoering • 2018 10% minder slib door Ephyra • 2018 -2020 dosering kationen ??? • 2017-2030 groei in Flevoland
• ZZL na 2018 34.000 ton slibkoek, circa € 2,5 miljoen, (nu in NL circa 110
miljoen) • Verbetering ontwaterbaarheid minimaal • Er blijft altijd slib over!!
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“haal eruit wat erin zit, doe datgene weg waar je niets meer mee kan en doe dit zo
goedkoop mogelijk”
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Hoe? “zo goedkoop mogelijk”
Kunnen we de hoeveelheid slib niet verder verkleinen? en is er nog een waarde aan toe te kennen? In 2015 mogelijk het antwoord gevonden:
TORWASH® ???
ECN acts as a bridge between science and corporate innovation
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Mission We develop knowledge and technologies that enable a transition to a sustainable energy system
Not-for-profit research institute Founded in 1955 5 Commercial licensing deals / year 500 Employees +/-20 patents a year € 80 M annual turnover
TORWASH® = Wet torrefaction + Washing
• Upgrading of biomass feedstocks that have too much water or too much salt • Under pressure in liquid water 150-250°C changes in biomass structure
that weaken fibres and releases water + ions • Unique concept:
– It enables efficient mechanical dewatering – It enables removal of salts to a high degree – Mild process conditions allow digestion of the effluent – ECN patent WO 2013/162355
• Goal: maximum energy in form of 2 fuels – Solid biomass pellets – Biogas from digestion of effluent
• Latest development: controlled recovery of phosphorus 8
TORWASH® : A multi-purpose process for green solutions
TORWASH®
clean solid fuel
biogas
reduced transport and disposal costs
biochar
densification ofsemi-finished product
hygienic animal bedding
fertilizers
grass/straw
manure
husks/shells
seaweed
sewage sludge
empty fruit bunches
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TORWASH®
clean solid fuel
biogas
reduced transport and disposal costs
biochar
densification of
semi-finished product
hygienic animal bedding
fertilizers
Why is TORWASH® unique?
Because:
• It enables efficient mechanical dewatering
• It opens up biomass and thus enables complete removal of salts
• Its mild process conditions allow digestion of the effluent to biogas
• It doesn’t use additives: – no catalysts – no pH control – no flocculants – no enzymes
• ECN patent WO 2013/162355
Why using TORWASH® at a sewage treatment plant?
• Dewatering turns wet sludge fuel – Volume reduction = saving disposal costs – Solid fuel could be directly suitable for thermal conversion – Biogas from effluent locally used in gas engine – Less costs for flocculant (polyelectrolyte = PE) – Independent plant operation – Contributes to objectives Grondstoffen en Energiefabriek
• Opportunities – P recovery from effluent – Solid fuel drying and pelleting flexibility in logistics of sludge – In future, no more incineration, but…..
– recovery of resource materials – applications in agriculture, provided that issues with heavy metals can be solved
PE may even have a negative influence on dewatering
The TORWASH® promise Almere as an example
• Amounts of sludge reduced from 21 to 3 kton/year • Potential savings on disposal costs € 1.1 million/year • Additional savings when polyelectrolyte (PE) is no longer needed: € 0.2 million/year
Dry matter Volume [ton] Disposal costs*
Centrifuge 8% 56 000
Existing Press 21% 21 000 M€ 1.3
Best Press 24% 19 000 M€ 1.1
THP 30% 15 000 M€ 0.9
TORWASH® 65% 3 100 M€ 0.2 * € 60 per ton “as received” in all cases
repeatedly obtained for various raw materials
TORWASH® Digestion
>60 wt% dry matter
Press Dewatered cake
incinerator
Anaerobic Digester
Liquids
Liquid Effluent No Solids
8-12 wt% dry matter
TORWASH® Reactor
Sewage sludge 13
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8-12 wt% dry matter
Slurry digested sewage sludge
10 wt% dry matter
Anaerobic Digester
Sewage sludge
TORWASH® Reactor
Filter
>60 wt% dry matter
Press
Dewatered cake
Liquids recycling
Liquid Effluent No Solids
Digestion TORWASH®
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Visible effect of TORWASH®
Sludge from AWZI Almere before and after TORWASH® • Left: untreated sludge • Right: TORWASHed sludge
Project TORWASH® of sewage sludge
• Experimental programme – Two kinds of sewage sludge: digested and undigested – (Three kinds of manure (cows, pigs, chicken)) – Testing in 20L autoclave with sewage sludge “as received” – Slurry pressed in Carver Die (2¼ inch) – Digestion tests, batch 18-25 days
• Highly efficient mechanical dewatering
– modern sludge presses reach 21-24% dry matter – manure separator: up to 20% dry matter
Sludge Press cake before TORWASH® after TORWASH® Undigested sludge 8-12% 67% Digested sludge 8-12% 61% Manure 5-20% 67%
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TORWASH® of undigested sludge Distribution of elements
0%
20%
40%
60%
80%
100%
120%
Mass Energy Si Al Ca Fe N P K Cl S Cr Cu Pb Zn
frac
tion
to so
lids
and
efflu
ent
fraction to effluent
fraction to solids
nutrients mostly in effluent
heavy metals stay in solids incinerator
K and Cl: >90% in effluent
Si, Al, Ca, Fe to solids
* Mass and Energy in solid product 17
TORWASH® of digested sludge Distribution of elements
0%
20%
40%
60%
80%
100%
120%
Mass Energy Si Al Ca Fe N P K Cl S Ni Cd Cr Cu Pb Zn
frac
tion
to so
lids
and
efflu
ent
fraction to effluent
fraction to solids
comparable results, e.g. > 90% Cl in effluent Si, Al, Ca, Fe and heavy metals all in solids
nutrients: • 40% K in solids • 95% P in solids
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Calorific Value (LHV, as received)
MJ/kg Non-digested Sludge (input) negative Non-digested Sludge - Product 13 Wood chips - green 16 Coal mixture 22
Fuel Quality – undigested sludge
Moisture Ash 550°C
Ash 815°C
Volatile Matter
Calorific Value (HHV, dry)
% % % % MJ/kg Non-digested sludge – input 95 16 16 69 19 Non-digested sludge – product 33 21 20 64 22 Wood chips 8 2.6 2.1 79 19 Coal mixture 3 - 12 32 24
C H N S Cl % % % % mg/kg Non-digested sludge – input 42 6.2 6.9 0.8 2100 Non-digested sludge – product 49 6.3 4.1 0.7 260 Wood chips 48 6.5 0.5 0.04 300 Coal mixture 72 4.5 1.4 0.85 260
Values are on dry basis, except moisture
municipal waste 10 MJ/kg
(LHV, wet)
TKI-BBEG EnCORE
EnCORE (Efficiente Cascadering en Opwerking Rioolslib voor Energie-neutrale bedrijfsvoering) Doel: Het doel is meer biogas en grondstoffen uit zuiveringsslib te produceren t.o.v. een klassieke slibvergister, door adaptatie en optimalisatie van de combinatie van een 'Upflow Anaerobic Sludge Blanket' (UASB) vergister van slib dat middels TORWASH® is voorbehandeld. Activiteiten: • Kleine schaal vergistingstesten • Pilotschaal TORWASH® testen (Almere) • Adaptatietesten effluentvergisting • Kwantificeren fosfaat terugwinning
Na EnCORE: opschalen naar volleschaal demo
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Digestion tests
• Batch tests at OPURE – 18-25 days – Filtered effluent after TORWASH®
• Measurements
– COD measurements before and after – biogas production – methane content methane production
• For TORWASH® assessment purposes, digestibility is defined as the COD conversion
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Digestion of TORWASH® effluent Undigested vs. digested sewage sludge
• Digestion expressed as conversion of COD
• Green = undigested sludge • Blue = digested sludge
• Effluents equally well digestible
0
10
20
30
40
50
60
70
80
90
100
COD
conv
ersi
on [%
]
Temperature [°C] Dry matter content
After centrifuge, before TORWASH®
8% w/w
After TORWASH® and dewatering
61% w/w
COD conversion 71%
Biogas yield 11.1 Nm3/m3
Methane content 69% v/v
Methane yield 7.6 Nm3/m3 22
Methane and energy yield in different configurations
• TORWASH® + digestion of only effluent gives the same amounts of biogas as TPH + full classic digestion (= +10% compared to classic digestion)
• TORWASH® of digestate after classic digestion: – Digestion of effluent gives extra biogas, solid product easy to dewater
* Energy production is sum of thermal values of two fuels, biogas and press cake, based on LHV
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Process configuration (starting with undigested sludge)
Current situation
Classic digestion Classic Digestion with TPH
TORWASH® IC(X) digestion
Classic Digestion TORWASH® IC(X) digestion
Methane Production [Nm3/kg organic dm] 0 0.13 0.14 0.14 0.19
Dry matter content of press cake after dewatering [wt%] 21 – 24 21 – 24 max. 30 > 65 > 60
Total energy production * [MJ/kg organic dm] 2.8 6.3 7.0 11.7 12.2
P-recovery via TORWASH®
• Sewage sludge and manure contain large amounts of phosphorus
• Solubility of phosphorus changes with TORWASH® chemistry – Temperature is the most important parameter
• Fate of P can be controlled in TORWASH®
– 95% P in solids is possible – 95% P in effluent is also possible
• Effluent from TORWASH® may contain double the amount of P compared to effluent from TPH
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Summary
• Lab tests have been successful for both digested and undigested sludge • Pilot TORWASH® reactor will be tested (EnCORE project)
• Main result: Sewage sludge converted into solid fuel and biogas – Chemical changes enable efficient dewatering and salt removal – Digested and undigested sludge: press cake > 60% dry matter – Effluent from TORWASH® digestible – TORWASH® of digested sludge gives extra biogas – Two TORWASH® process configurations that boost energy production
• Fate of Phosphorus can be controlled for recovery – Temperature determines fate of P and other elements
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• Input TORWASH® : non-digested sludge from centrifuge with 8-9% dry matter – Non-digested sludge from centrifuge (8-9% dry matter) – 4500 ton (dry matter)
• Output TORWASH® : – Press cakes with 65% dry matter content 3100 ton press cake – Potentially saving M€ 1.1 in disposal costs per year – Combustion at AEB waste incinerator renewable power and heat – Effluent digestible in UASB-type reactor: biogas more renewable heat and power – Effluent after digestion recycled to treatment plant – Optional: P-recovery
• Extrapolated to The Netherlands…. € 100 million per year less disposal costs
instead of 21000 ton
Back to Almere
Consortium
This presentation was made in close cooperation with Water Authority Zuiderzeeland
ECN Westerduinweg 3 P.O. Box 1 1755 LE Petten 1755 ZG Petten The Netherlands The Netherlands T +31 88 515 49 49 [email protected] F +31 88 515 44 80 www.ecn.nl
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�TORWASH® sewage sludge treatment�Increased biogas production, highly-efficient dewatering and phosphate recoveryTable of ContentsWaar het mee begonWaar het mee begonDianummer 5Hoe? “zo goedkoop mogelijk”ECN acts as a bridge between science and corporate innovationTORWASH® = �Wet torrefaction + WashingTORWASH® : A multi-purpose process for green solutionsWhy is TORWASH® unique?Why using TORWASH® at �a sewage treatment plant?The TORWASH® promise�Almere as an exampleTORWASH® DigestionDigestion TORWASH®Visible effect of TORWASH®Project TORWASH® of sewage sludge TORWASH® of undigested sludge�Distribution of elementsTORWASH® of digested sludge�Distribution of elementsFuel Quality – undigested sludge��TKI-BBEG EnCOREDigestion testsDigestion of TORWASH® effluent�Undigested vs. digested sewage sludgeMethane and energy yield in different configurations P-recovery via TORWASH®SummaryBack to AlmereConsortium
