potential opportunities for hydrothermal carbonisation of
TRANSCRIPT
School of Chemical and Process EngineeringEnergy Research Institute
Potential opportunities for hydrothermal carbonisation of biomass wastes
Aidan SmithThermal Processes for Resource Recovery from Waste
Aqua Enviro
10.09.15
Conversion of organic material in hot compressed water at high temperature and pressure (200-250oC, 15-40 bar)
Products are dependent upon process severity
Simulates natural coal formation to convert biomass into a coal like product
Hydrothermal Carbonisation (HTC)
Utilises changes in the properties of water under hot compressed conditions
Polar > non-polar solvent
Physical properties of water
(Source: Kritzer and Dinjus, 2001)
Methanol Acetone
Biomass + water bio–coal +
Hydrothermal Carbonisation (HTC)
200-250°C
14-40 bar
Biomass
HTC Coal
Water and TOC
GasMainly CO2
Sugars, organic
acids, furans,
phenols and
inorganic salts
Carbon dense lignite like
material (retains app. 80%
biomass energy)
aqueous products
Bulk and energy density (GJ/m3 and GJ/tonne) You are paid per GJ but logistics are based on mass and volume!
Moisture content increases transport costs
Reduced energy density
Storage issues (decomposition, spontaneous combustion, emissions)
Thermal drying (energy intensive)
Biomass reabsorbs moisture once dried
Fuel preparation? Cutting, grinding, blending, palletising (energy intensive and difficult
with fibrous material)
Combustion behaviour Will it burn?
Variable quality? (consistency = higher price)
Slagging and fouling propensity
Commercial considerations when handling solid biomass fuels
Biomass
• Low bulk density
• High moisture
• Low calorific value
• Hydrophilic
• Difficult to mill
• Slagging and Fouling propensity
Bio-Coal
• Higher bulk density
• Low moisture
• High calorific value
• Hydrophobic
• Easily friable
• Reduces Slagging and Fouling propensity
HTC = potential pre-treatment for biomass• Combustion and gasification• Biomass based synthetic chemicals
Why interest in HTC?
Energy densification in range of biomass via HTC
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
HH
V (
MJ/
kg)
Unprocessed
HTC 200
HTC 250
De-oxygenation: removal of hydroxyl (-OH), carboxyl (C=O) and carbon-oxygen bonds (C-O)
(Source: Smith et al.,) GHW = Commercial Greenhouse Waste; MSW = Municipal Solid Waste
Bio-coal yield
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
100.0
Yie
ld o
f h
ydro
char
(w
t %
db
)
ash
(Source: Smith et al.,)
Coals
Lignite & HTC 250
HTC 200
Raw biomass
Van Krevelen
(Derived from: Smith et al.,)
0
10
20
30
40
50
60
% A
sh
Coal Ash Willow
Inorganics: Biomass vs Coal
Coal
Fouling + Slagging
Biomass
Inorganics = ash = metal oxides in fuel
Problematic in combustion
Slagging = sticking, melting and fusion of ash in furnace
low temp =
high temp =
K + Na lower melting temperature
Ca + Mg increase melting temperature
Fouling = formation of corrosive alkali chlorides on heat exchangers
K + Na + Cl + S problematic
Influence of inorganics on combustion
Ionic Salts
Na = Nitrate + Chloride >90%
K = Nitrate + Chloride >90%
Ca = Nitrate + Chloride + Phosphate (20-60%)
Mg = Nitrate + Chloride + Phosphate (60-90%)
Ionic = SO42-, PO4
3-, Cl-
Organically Associated
• Organically associated Mg (8-35%)
• Organically associated and crystalline Ca (30-85 %)
Inorganic materials in higher plants
Additives + intelligent blending + combustion temperature control can reduce impacts
Ideally problematic elements (K, Cl, Na, S) avoided or reduced
Interest in fuel pre-treatment – demineralisation
Biomass washing:
1. Deionised water > easily available ionic salts
2. Ammonium acetate > ionic salts via ion exchange
3. HCl > dissolve alkali earth CO32-, SO4
2-, S2-
Or…
HTC
Control of inorganics in combustion
HTC uses hot compressed water!
Water soluble = NaNO3 NaCl, KNO3, KCl, Ca(NO3)2, CaCl2, Ca3(PO4)2, Mg(NO3)2, MgCl2, Mg3(PO4)2, SO4
2-, PO43-, Cl-
HTC modifies biomass structure
Organic acids major product of HTC
Lower water viscosity
Subcritical water: increased dielectric content, and ionic dissociation constant and acidic conditions
- aid removal of Ionic bonded metals
- dissolve inorganics
Inorganics and HTC
0
500
1000
1500
2000
2500
Potassium Sodium Calcium Magnesium Posphorous Ash
mg/
kg f
ue
l
Miscanthus
Raw HTC 200 HTC 250
Inorganics in fuel
2.5
5.0
0
7.5
12.5
10.0
% A
sh in
fu
el
Inorganics in fuel
0
10000
20000
30000
40000
50000
60000
70000
80000
Potassium Sodium Calcium Magnesium Chlorine Ash
mg/
kg f
ue
l
Brown Kelp
Raw HTC 200 HTC 250
5
15
10
0
20
40
35
30
25
% A
sh in
fu
el
Original sample
Shrinkage Deformation Hemisphere Flow
Ash fusion test using an ash fusion oven
Analysing ash behaviour
Ash Fusibility
550
750
950
1150
1350
1550
Srinkage Deformation Hemisphere Flow
Tem
pe
ratu
re (
cels
ius)
Transition
Ash Transition Temperatures for MiscanthusFurnace Limit - 1570°C
440 ⁰C increase in safe combustion temperature
Ash Fusibility
550
750
950
1150
1350
1550
Shrinkage Deformation Hemisphere Flow
Tem
pe
ratu
re (
cels
ius)
Transition
Summer Harvest Kelp (L. Hyperborea)Furnace Limit - 1570°C
>1020 ⁰C increase in safe combustion temperature
Key plant nutrients in aqueous phase:• Phosphate = 30 g/kg feed• Potassium = 30 g/kg feed• Magnesium = 6 g/kg feed
Aqueous Phase
1) Large molecules: 1280 Mw = 0-5 % of material
2) Sugars and organic acids:5-HMF (5 wt %), furfural, galactose, xylose and mannose. Lactic acid, succinic acid and glutaricacid
3) Small organic acids: formic acid, acetic acid = ~10 % of material
Size Exclusion Column Chromatogram
Aqueous Phase Total sugars and organic acids in aqueous phase products
Feedstock
TM LP PJ SC CS RH TM LP PJ SC CS RH TM LP PJ SC CS RH TM LP PJ SC CS RH TM LP PJ SC CS RH TM LP PJ SC CS RH
% S
tart
ing D
ry F
eedsto
ck
0
2
4
6
8
10
12
14
16
Organic Acids
Sugars
175oC 215
oC 235
oC 255
oC 275
oC 295
oC
(Source: Hoekman et al., 2013)
Sugars Organic acids
Temperature
Reuse of process water in HTC Increased process water organic carbon loading increases char yields
‘Catalytic’ affects of organic acids and certain salts
Removal of inorganics and heteroatoms required
Extraction of high value chemicals Process water compounds more valuable than bio-coal
Extraction and purification challenges?
Anaerobic digestion of process waters Commercially available solution
Relatively simple/ cheep
Potential inhibition of methanogenic bacteria (nitrogen and salts) Hydrogen or carboxylate platform routes?
Enhanced recovery from process water
ANAEROBIC DIGESTION
HTC
process water
Bio-Coal
Methane? or Hydrogen? Low pH
1. Benefits? Optimise for Bio-coal Remove contaminants
Feed
2. challenges Inhibition? Yields?
Anaerobic digestion of process waters
TOC measured and analysed – compared to reported yields The process water can be evaporated and analysed The Buswell equation can be used to estimate biogas yields based
on assumed conversion
Digestate
Wirth B., Mumme J., Anaerobic digestion of waste water from hydrothermal carbonization of corn silage, Appl. Bioenergy, 2013, 1, 1-10.
HTC water Biogas yields Reference
Sewage sludge 0.5 L g TOC-1 Blöhse (2013)
Digestate 1 L g TOC-1 Blöhse (2013)
Corn silage 0.6 L g TOC-1 Wirth et al. (2013)
AD tests of HTC process water using mesophilic (35-37°C) batch digester tests
AD test data
Experimental data
0
5
10
15
20
25
Ene
rgy
(MJ/
kg o
rigi
nal
fe
ed
sto
ck)
Char (200) Methane (200)
Char (250) Methane (250)
HTC mimics natural coal formation and can be used as a pre-treatment to improve biomass handling properties higher bulk density lower moisture content higher calorific value less hydrophilic easily friable
Inorganic extraction via HTC reduces fouling and slagging propensity of fuel enable commercialisation of otherwise unsuitable combustion fuels
Homogenises product higher value lower risk!
Aqueous co-product containing key plant nutrients and high value organic acids and sugars
Recovery of high value products or water treatment via AD will further improve the economics of HTC
Conclusions
