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Use of microwave energy for the remediation of hydrocarbon contaminated soils John Robinson Department of Chemical & Environmental Engineering, University.

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Presentation on theme: "Use of microwave energy for the remediation of hydrocarbon contaminated soils John Robinson Department of Chemical & Environmental Engineering, University."— Presentation transcript:

1 Use of microwave energy for the remediation of hydrocarbon contaminated soils John Robinson Department of Chemical & Environmental Engineering, University of Nottingham

2 Overview – Project Partners University of Nottingham Shanks Waste Management PERA Nelson Heat Transfer IMA Davis Decade Ltd Global Energy Associates TMD Technologies Ltd

3 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

4 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

5 Microwave Processing X Misconceptions

6 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

7 MW Treatment of Soils – Lab Scale Trials 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%

8 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

9 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

10 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

11 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

12 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

13 Scale-up Concept: Tunnel Applicator H L W Tunnel x y z Self-canceling reflection step VIEW C-C C C A B y z (Simulations from University of Stellenbosch)

14 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

15 Process Schematic

16 Pilot Plant Process throughputs up to 500 kg/hr depending on soil type and contaminant levels

17 Treated Soil

18 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)

19 Plant capabilities Significant levels of total organic and PAH removal from all soil samples tested Energy requirements around kWh per tonne of soil – much less than conventional thermal processes Small footprint Easy to start-up and shut-down Flexible throughput

20 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


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