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Superheated steam drying and processing?
Stefan Cenkowski
Department of Biosystems Engineering University of Manitoba
Nov. 17, 2014
Overview • History of SS drying • What is superheated steam drying? • How does it work? • What are the (dis)advantages? • Where are the potential opportunities? • Our experimental results
History • Hausbrand (1912)
– Heat transfer textbook – Considered drying with steam alone and wide application
attainable once advantages known • Use of SS kilns for lumber (on the West Coast of US 1908)
• WWI produced a high velocity, low superheat kiln – Inefficiencies and corrosion caused decline in use
• WWII saw kilns with SS or air-steam mixtures, with 2 companies supplying kilns
• Brown coal (low grade, high mc) drying – Introduction of the Fleissner process (1920’s)
• In addition to lumber and coal, there was foundry sand drying, and resin production – Yoshida and Hyodo (Osaka, Japan) looked at synthetic
fibers and potato slices
Industrial Applications • Greatest number of units for lumber
– Brunner/Hildebrand and WWT account for over 250 units • Outside of the lumber industry suppliers are :
– GEA/Barr-Rosin drying pulpy materials – BMA AG to dry sugar beet pulp – W. Kunz dryTec AG – Swiss Combi Ecodry dryers (dry sludge, sawdust, wood chips, and
other products on a rotary drum dryer with recirculating SS) – Maschinenfabrik Gustav Eirich GmnH & Co KG for processing sludge,
brake linings, pigments, wash powder additives, and ferrites – Moenus Artos Textilmaschinen GmbH (Textile dryer - impingement – Keith Engineering New Zealand (Pinches Industries of Melbourn)
• rendering industry, animal b-products, blood, wood chips, and sewage sludge
– Sharp Coroperation (Japan) • “Healsio” SS oven to cook and roast food
Drying Systems: Batch Fixed Bed SS Dryer
• On the industrial scale: – Lumber
• On the laboratory scale: – Spent grains – Sugar-beet pulp – alfalfa – Potatoes, flour – Molasses, clay – Wheat, corn, oilseed – Instant foods, Asian – Meat (ham, chicken) – Shrimp, fishmeal – Silkworm cocoons
– Vegetables (carrot, cauliflower, asparagus, leek)
– Citrus pulp/peel, apple pomace.
– Herbs (oregano, parsley, green tea)
– Spices (paprika, onion powder)
§ Sterilization - enhanced microbial destruction (spores), product sterilization (hemp seed)
Hot air vs SS - Advantages Summary
• Closed-loop system reduces the energy • Evaporated moisture can be recovered • High heat transfer – high drying rate, reduction in the
equipment size and capital cost • No oxidation can eliminate fire and explosion
hazards • Elimination of environmental pollution • Valuable volatile organic compounds could be
recovered
Main Limitations: • High temperature for temperature sensitive products
– Browning reactions, Discolouration, Starch gelatinization, Enzyme destruction, Protein denaturation
• Drying systems are more complex but… • Simultaneous drying and cooking • Change in textural properties could be beneficial (e.g. baking • potatoes, instant pastas and noodles) • Microbial destruction
What is Superheated Steam?
§ Steam that has additional sensible heat added so that its temp. is above the saturation temp. at a given pressure.
How does it work? • SS drying relies on:
– saturated steam equilibrium – superheat of steam
P=Pa+Pv
ΔS=---- ΔQ T
30oC
s
Tdp
T1
100oC tsat
Wet steam
Super- Heated Steam
1
2
1
2 50°C
s
• Conventional air drying depends on: – psychrometric equilibrium
Superheated Steam Processing System
condensate steam out
water
processing chamber
condenser
steam generator superheater
sup
supe
rhea
ted
st
eam
Sample tray
Three distinct periods in SS drying • Preheating and condensation period • Constant drying rate period, and • The falling rate period.
mc
Temp
mc(t)
Drying time
Product temp(t)
SS temp condensation
SS Research U of M
Sugar-beet pulp
Drying kinetics
SS Research at U of M
Temp
Temp
Temp
Temp
Temp Temp
Moisture Moisture
Drying kinetics
Potatoes
` SS Research at U of M
aw for brewers’ grain and distillers grain
aw for sugar beet pulp SS vs hot air
Drying Asian Noodles
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0 100 200 300 400 500 600 700 800 900 1000
Drying time (s)
Moi
stur
e ra
tio, M
R
Measured (0.5 m/s)
Measured (1.0 m/s)
Measured (1.5 m/s)
Predicted
120°C SS temperature
SS Research at U of M • Decontamination of oat groats
– Bacillus stearothermophilus • Spore-forming microorganism • Spores are heat resistant and used to monitor
sterilization of moist heat
Table 5. D-values of Bacillus stearothermophilus treated in superheated steam
Temperature (ºC)
D-value (min) for 103
(cfu•g-1) inoculum levelD-value (min) for 106
(cfu•g-1) inoculum level[a]
105 23.5 -130 65.9 -145 63.0 29.0160 9.3 2.1175 2.2 1.5
[a] D-values at 105 and 130ºC could not be calculated even after 80 min of processing
D-value of bacillus stearothermophilus treated with SS
• Distillers’ and Brewers’ spent grain – Modeled drying process in SS
• Results favorable with benefits of reduced fire risks, and better aroma with acetic acid removal
– Pentosan, β-glucan, and protein levels not affected with increase in drying time and temperature,
– Starch content low due to partial starch gelatinization and/or formation of amylose-lipid complexes
Developing Manitoba’s Ethanol Industry
Steam
Steam
Steam Thermal/Steam
Disintegra*on of biomass compacts
Crumbled compacts and fines may
interrupt the drying system
Superheated steam dryer
Compacted biomass
Densification and drying of DSG
S*llage (Corn and wheat
ra*o 9:1)
Thin s*llage
Wet dis*ller’s spent grain (WDG) MC: 69.0% wb
d(0.9)= 1283.6 µm
d(0.9)= 1069.3 µm
Raw Materials and Ini/al Sample Prepara/on
Grinding
Centrifuga*on Solubles (CDS) MC: 79.4% wb d(0.9)= 563.9
d(0.9)= 812.8 µm
Effect of SS at 220oC on moisture content of wheat straw (i) boiled at 119C for 15 min followed by SS treatment and (ii) processed in SS alone.
Time, s
Moi
stur
e co
nten
t, %
db BW
SS
Drying Characteristics of WDG Compacts during SS Drying
ü Approximately 78 to 130% percentage increase in volume was observed while drying the compacts in SS.
SS processing
Before
Percent increase in volume
Percent decrease in density
Oven drying temp
Per
cent
age
chan
ge
After
Solubles (%)
Solubles (%) H
ardn
ess
(N)
Hardness and Asymptotic Modulus
Before processing
5s SS processing
Har
dnes
s (N
)
Moisture content (% wb)
Asy
mpt
otic
mod
ulus
(MP
a)
Moisture content (% wb)
Conclusions
• SSD technology can provide: – Product benefits
• increased drying rate • specific product quality
– Pelleting moist product before drying • Developing surface area • Condensation period affecting hardness • Volume increase
– Environmental advantages
Processing with superheated steam
Dave Barchyn & Stefan Cenkowski University of Manitoba Department of Biosystems Engineering November 17th, 2014
Pre-‐treatment of lignocellulose
• Disrup*on of lignin structures / delignifica*on • Hydrolysis of 5-‐ and 6-‐carbon sugars • Minimize genera*on of inhibitors, destruc*on of sugars
• Maximize poten/al conversion to end product
2-‐Phase pre-‐treatment
• Treatment in pressurized hot water • Treatment with atmospheric SS at 220˚C
0%
10%
20%
30%
40%
50%
60%
70%
Raw 15HW 15HW2SS 15HW5SS 15HW10SS
% Con
version
Treatment
Glucose yield (%)
Xylose yield (%)
0%
10%
20%
30%
40%
50%
60%
70%
80%
Raw 15HW 15HW2SS 15HW5SS 15HW10SS
% xylose conversion
Treatment
With xylose recovery Without xylose recovery
Treatment Change in
moisture content (kg/kg)
Corresponding energy demand*
(kJ/kg)
Total energy demand (kJ/kg)
15 min. HW 0 0 930
15 min. HW + 2 min. SS 0.368 1068 1998
15 min. HW + 5 min. SS 0.611 1772 2702
15 min. HW +10 min. SS 0.809 2348 3278
* Associated with SS phase of treatment
Energy Balance Steam explosion
Process energy
Energy in ethanol
Superheated steam (no xylose recovery)
Process energy
Energy in ethanol
Superheated steam (xylose recovery)
Process energy
Energy in ethanol
Cost of produc*on
Process efficiency
$0.73
$0.74
$0.75
$0.76
$0.77
40 45 50 55 60 65 70 75 80 85
MESP ($/L)
Glucose conversion efficiency (%)
MESP
MESP w/ xylose recovery
Conclusions
• Processing with SS can provide energy savings for the pre-‐treatment of lignocellulosic substrates
• Subject to op*miza*on of the process to increase the efficiency of glucose and xylose conversion
Recommended