Sewage Sludge Drying with Microwave Irradiation:
Guray Salihoğlu*, Sibel Yenikaya, N. Kamil Salihoğlu, Gokhan Yenikaya*Department of Environmental Engineering, University of Uludag, Bursa, 16059, Turkey
Department of Electrical-Electronic Engineering, University of Uludag, Bursa, 16059, Turkey
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04•Sludge Dewatering & Drying
Introduction
Materials & Methods
•Impact of the Factors on Drying
Results & Discussion
Conclusions
Content
•Microwave Modeling
3Sludge Management
Additional fuel ?
Sludge Management
Mechanical Dewatering
•Large amounts and high moisture content•WWTP Exit: 1-4% DS
Cement plant co-
incineration•Cement plants use dried sewage sludge as a substitute for fossil fuel•Co-incineration in cement plants is possible
Drying•Increased calorific value•Easy handling•Reduced volume
Microwave Drying•Can be a preferred step in sludge management • Heats the material rapidly•Instant on/off control•Increase the calorific value
•20-35 % DS
•To investigate the efficiency of microwave technology as a sludge drying method
Objectives
•To compare the energy consumption with that of electrical heating•To investigate the influence of the addition of ionic species such as salt to the drying performance
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Materials & Methods
Mechanically dewatered sludge•Characterization experiments: Composition, dielectric constants•Salt addition : 5%
Microwave Drying•2.45 GHz : Resonance frequency of water molecules•Fixed & Rotary modes•Power: 900 W•Time intervals: 1-10 minutes•Air cure : 10 minutes
Monitoring•Moisture contents, •Evaporation rates, •Drying performances•Hot and cold regions•Energy consumption•Thermal camera images
Electrical drying to compare the energy consumption levels
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Results & Discussion
7TH INTERNATIONAL CONFERENCE ON SUSTAINABLE SOLID WASTE MANAGEMENT, 26-29 June 2019, Heraklion, Crete Island, Greece
Comparison of moisture losses in fixed and rotary operation modes
fixed mode > rotary
mode
Fixed mode provided
concentrated heating and
more evaporation
Results & Discussion
7TH INTERNATIONAL CONFERENCE ON SUSTAINABLE SOLID WASTE MANAGEMENT, 26-29 June 2019, Heraklion, Crete Island, Greece
Comparison of moisture losses in sludge with salt and without salt Salt addition resulted in a lower level of moisture
losswithout salt > with
Results & Discussion
7TH INTERNATIONAL CONFERENCE ON SUSTAINABLE SOLID WASTE MANAGEMENT, 26-29 June 2019, Heraklion, Crete Island, Greece
Comparison of temperatures in sludge with salt and without salt Higher temperatur
e levels with salt
with salt : 75.62±4.51
oC without
salt: 65.19 ±4.06oC
Low
evaporation?
Results & Discussion
7TH INTERNATIONAL CONFERENCE ON SUSTAINABLE SOLID WASTE MANAGEMENT,26-29 June 2019, Heraklion, Crete Island, Greece
Low evaporation with salt added sludge although temperature levels are high?
’ ’’ ’’/’ (×10-3)
Sludge without salt
76.22 10.18 0.134
Sludge with salt
58.18 18.90 0.325
Dielectric constant (Relative
permittivity): The ability to
store the energy
Relative dielectric loss factor:
Conversion ability of the energy into heat
Loss TangentHigh loss tangent is an indication of the use of
microwave power transferred into heat
Dielectric characteristics of the sludge studied
Measured by Network analyzer (Agilent, E506 1B)
Salt addition to the sludge
decreased the dielectric
constant and increased the dielectric loss factor, thus
increased the dissipation
factor.
Salt addition might have changed the molecular structure of the
sludge limiting the evaporation. Salt might have associated with
sludge water, thereby might have decreased the free water and converted it into bound water
(capillary or particle).
10Electric field distribution Maximum intensity
when the oven is emptywhen the sewage sludge sample was inside• Electric field is stronger near the walls of the oven
•The distribution is symmetrical relative to the XZ plane
•When the sample was placed, electromagnetic waves were reflected from the oven walls and the sample surface.•Therefore the electric field was dense on the corner points of the tray
7TH INTERNATIONAL CONFERENCE ON SUSTAINABLE SOLID WASTE MANAGEMENT,26-29 June 2019, Heraklion, Crete Island, Greece
11Energy Consumption: Electrical Microwave
Less time and less energy
with microwave
30% moisture loss duration
Microwave : 10 min.Electrical: 30 min.
30% moisture loss energy consumption
Microwave : 0.231 kW
Electrical: 0.444 kW
12Conclusions
7TH INTERNATIONAL CONFERENCE ON SUSTAINABLE SOLID WASTE MANAGEMENT,26-29 June 2019, Heraklion, Crete Island, Greece
Moisture lossFixed mode > rotary mode
Concentrated heating in the fixed mode
Salt addition •Decreased the moisture loss•Decreased the dielectric constant•Increased uniform heat distribution
Evaporation continued during air cure after drying.
Electric field was dense on the corner points of the tray, more evaporation
Electrical drying consumed more energy for a certain moisture
loss targeted in sludge.
Less Time and Less Energy with Microwave
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7TH INTERNATIONAL CONFERENCE ON SUSTAINABLE SOLID WASTE MANAGEMENT,26-29 June 2019, Heraklion, Crete Island, Greece
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7TH INTERNATIONAL CONFERENCE ON SUSTAINABLE SOLID WASTE MANAGEMENT,26-29 June 2019, Heraklion, Crete Island, Greece
References
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