Use of microwave energy for the remediation of hydrocarbon contaminated soils John Robinson Department of Chemical & Environmental Engineering, University of Nottingham
Dec 16, 2015
Use of microwave energy for the remediation of hydrocarbon contaminated soils
John RobinsonDepartment of Chemical & Environmental Engineering,
University of Nottingham
Overview – Project Partners University of Nottingham Shanks Waste Management PERA Nelson Heat Transfer IMA Davis Decade Ltd Global Energy Associates TMD Technologies Ltd
http://waveland.pera.com/
Project Aims & Objectives
Overall aim is to develop the value proposition for ex-situ microwave treatment of hydrocarbon contaminated soils
Understand how microwaves interact with contaminated soils
Establish the mechanisms of contaminant removal and the opportunities and limitations of microwave heating
Identify an appropriate scale-up concept and construct a continuous pilot plant for soil remediation using microwave heating
Why Microwave Heating?
Selective Heating Energy savings
Volumetric Heating High throughputs Small plant footprint – mobile equipment
Electrically Operated Low Thermal Inertia
Easy to start-up and shut-down
Industrial Microwave Processing
Continuous systems
High volume/tonnage
High power microwaves
Multidisciplinary projects requiring input from process and electrical engineers, electromagnetics experts and bulk materials handling specialists
Based on a fundamental understanding of the interaction of microwaves with the process materials
MW Treatment of Soils – Lab Scale Trials
PAHUntreated Sample
Treated Sample
naphthalene 0 0.0acenaphthene 8 0.0acenaphthylene 86 0.0fluorene 52 0.0phenanthrene 619 0.0anthracene 103 0.0fluoranthene 1463 0.8pyrene 1255 0.7benzanthracene 175 1.3chrysene 2513 0.1benzo(b)fluoranthene 12 1.7Benzo(k)fluoranthene 1076 1.0Benzo(a)pyrene 1465 0.2Dibenz(a,h)anthracene 1014 0.1Benzo(ghi)perylene 771 1.7Indeno(1,2,3-cd)pyrene 673 1.7
Total 11283 9.2 Experiments carried out at 10kW for 30s in a single mode microwave cavity.
Soil samples obtained from former Gas Works site.
Significant levels of PAH removal can be achieved.
Total organic removal >99.5%
MW Treatment of Soils – Lab Scale Trials
Two classifications of contaminated soil were identified based on their interaction with microwaves (dielectric properties)
Heavy-hydrocarbon contaminated High tar concentrations High temperatures achieved
Light-hydrocarbon contaminated Remediated at low temperatures
MW Treatment of Soils – Scale-up Methodology
No one-stop shop microwave process to treat all contaminated soil types
Project scope confined to the scale-up of a process for treatment of light contaminated soils Several concepts were identified for treating heavy-hydrocarbon
contaminated soils
Organic Removal Mechanisms
Only microwave-absorbing phase in soil is water 5mm
Surface contamination: Mainly organic, some water
Pores within soil structure: mainly water,
Organic compounds are entrained in steam produced from interstitial water
Very high heating-rates are required to exploit this mechanism
Organics removed at temperatures below their normal boiling point
Key scale-up criteria
Soil must be treated with a very high heating rate to exploit the entrainment mechanism
Heating must be as even as possible throughout the entire soil sample
Batch, and commercial off-the-shelf microwave devices cannot be used Microwave applicator must be designed specifically for this
application based on the dielectric properties of the soil
Scale-up concepts
Continuous microwave processing concepts were evaluated based on a range of key criteria Materials handling Process engineering Safety Electromagnetic compatibility Ability to satisfy process requirements
00.050.10.150.20.250.30.350.40.450.50.550.60.650.70.750.80.850.90.9511.051.11.151.21.25
Scale-up Concept: Tunnel Applicator
H
L
W
Tunnel
x
y
z
Self-canceling reflection step
VIEW C-C
C
C
14
A B
y
z
(Simulations from University of Stellenbosch)
Key design challenges
Selection of appropriate material for conveyor belt Microwave-transparent and thermally stable
Control the dielectric properties of the soil to be processed Electric field distribution is sensitive to feed moisture content
Extract organic and water vapours whilst containing the electric field
Process Schematic
TREATEDMATERIAL
FEEDING SYSTEM/MIXING
CHILLER
LIQUID PRODUCTS
AUTOTUNER
MAGNETRON CIRCULATOR
FAN
MOISTURE
CONDENSER
N2
TC
O2
P
MW
DATA LOGGER
DIELECTRIC PROPERTIES
rpm
H
rpm
UNTREATED MATERIAL
L
Organic Products
Organic and water phase collected from condenser Separated by gravity settling Organic liquids can be isolated and disposed/re-used as
appropriate
Very little combustion or thermal degradation due to the low bulk temperature of the microwave process (<100°C)
Plant capabilities
Significant levels of total organic and PAH removal from all soil samples tested
Energy requirements around 100-200 kWh per tonne of soil – much less than conventional thermal processes
Small footprint Easy to start-up and shut-down Flexible throughput
Conclusions & Next Steps
This project has proved the concept of continuous microwave treatment of soil Value proposition established Ongoing assessment of performance with wider range of contaminated
soils
Process needs to be scaled further for field trials and industrially-relevant throughputs Lower microwave frequencies Integrated into standard ISO container
Mechanisms sought for scale-up and development of process for heavy-hydrocarbon contaminated soils