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

Microwave Processing

XMisconceptions

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

Pilot Plant

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

Treated Soil

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