comparison of different air treatment methods with plasma treatment

transcript

Part-financed by the European Union (European Regional Development Fund

COMPARISON OF DIFFERENT AIR TREATMENT METHODS WITH PLASMA TREATMENT

PlasTEP 3rd Summer school and trainings course 2012 Vilnius / Kaunas

Saulius Vasarevicius, VGTU

Two Types of Air Pollutants

Particulate (Visible)

Gaseous

Stationary Source Control

• Philosophy of pollution prevention (3P’s)

– Modify the process: use different raw materials

– Modify the process: increase efficiency

– Recover and reuse: less waste = less pollution

• Philosophy of end-of-pipe treatment

– Collection of waste streams

– Add-on equipment at emission points

• Control of stationary sources

– Particulates

– Gases

Three Types Of Control

Mechanical

Chemical

Biological

Particulate Control

(Mechanical)

• Electrostatic precipitator

• Bag house fabric filter

• Wet scrubber

• High efficiency cyclones

Particulate Control Technologies

• Remember this order:

– Settling chambers

– Cyclones

– ESPs (electrostatic

precipitators)

– Spray towers

– Venturi scrubbers

– Baghouses (fabric filtration)

• All physical processes

Settling Chambers

• “Knock-out pots”

• Simplest, cheapest, no moving parts

• Least efficient

– large particles only

• Creates solid-waste stream

– Can be reused

• Picture on next slide

Gravity settler

Disadvantages

• Large space requirement

• Relatively low overall collection

efficiencies (typical 20 - 60 %)

Flue Gas Cleaning – The state of the art

Selection criteria

ESP Bag house Scrubber Cyclones

(normal)

Spraycone

Cyclones

Emission

mg/Nm3 100 30 200 250 < 100

Reliability ++ + ++ ++++ ++++

Cost ++++ ++++ +++ + +

Gas Cleaning – The state of the art

Evaluation of ESP for industrial boilers: • High cost (investment, maintenance & operation)

• Complex large size plant with sub-systems

• Requires constant gas conditions (sulphur, temp, moisture)

Evaluation of bag filters for industrial boilers: • High cost (investment, maintenance & filter bags)

• Difficult to handle sulphur and sparks

• Not robust (one faulty bag destroys efficiency

Evaluation of wet scrubbers for industrial boilers: • High cost (large water treatment plant)

• Difficult to separate fine particulate

• Sulphur control costly & difficult

Evaluation of cyclone “grid arrestor” :

• Low collection efficiency due to:

• Wrong design (see velocity analysis)

• Air ingress

• Bad manufacturing quality

• Lack of maintenance (blockage of cyclone cells)

But cyclone system advantages are low cost and robust installation

Can a cyclone reach efficiencies of ESP / Bag filter / Wet scrubber?

This question triggered our cyclone development Program

in 1994 to improve cyclone efficiency and to invent the

“dry spray agglomeration principle”

Cyclone

•Most Common

•Cheapest

•Most Adaptable

Mechanical Collectors –

Cyclones

Advantages: Good for larger PM

Disadvantages: Poor efficiency for finer PM

Difficult removing sticky or wet PM

Cyclone Operating Principle

“Dirty” Air Enters The Side.

The Air Swirls Around The

Cylinder And Velocity Is Reduced.

Particulate Falls Out Of The Air To The Bottom Cone And Out.

Commercial applications of high efficiency cyclones:

BurnerMax Fluidized bed furnace

High efficiency cyclones

operating at 400 C

Multiple Cyclones

(Multi clone)

Smaller Particles Need Lower

Air Flow Rate To Separate.

Multiple Cyclones Allow Lower Air Flow Rate, Capture Particles to 2 microns

Air Filtration

Filtration Mechanisms • Diffusion

Q: How does efficiency change with

respect to dp?

a. Efficiency goes up as dp decreases

b. Efficiency goes down as dp decreases

Filtration Mechanisms • Impaction

Q: How does efficiency change

with respect to dp?

a. Efficiency goes up as dp decreases

b. Efficiency goes down as dp decreases

Filtration Mechanisms • Interception

Fat Man’s Misery,

Mammoth Cave NP

Filter efficiency for individual mechanism and combined mechanisms

dp (m)

0.01 0.1 1 10

Interception

Impaction

Diffusion

Gravitation

FILTRATION

Fiber filter

Q: Do filters function just as a strainer,

collecting particles larger than the strainer

spacing?

a: yes

Filter Drag Model

spf PPPP

VLVtKVK 21

Areal Dust Density LVtW

Filter drag

WKKS 21

Ke & Ks to be determined empirically

Pf: fabric pressure drop

Pf: particle layer pressure drop

Ps: structure pressure drop

Time (min)

10 505

20 610

30 690

60 990 Q: What is the pressure drop after 100 minutes of

operation? L = 5 g/m3 and V = 0.9 m/min.

Case A: Pore blocking

Case B: Pore plugging

Case C1: Pore narrowing

Case C2: Pore narrowing w/lost pore

Case D: Pore bridging

Air Filtration

• Impaction

• Diffusion

• Straining (Interception)

• Electrostatics

Fabric Filter

(Baghouse)

•Same Principle As Home Vacuum Cleaner

•Air Can Be Blown Through Or Pulled Through

•Bag Material Varies According To Exhaust Character

Cleaned gas

Dirty gas

Baghouse Filter – only one to remove hazardous fine particles

Dust discharge

Advantages/Disadvantages

• Very high collection efficiencies

• Pressure drop reasonably low (at beginning of operation,

must be cleaned periodically to reduce)

• Can’t handle high T flows or moist environments

Pulse-Air-Jet Type

Baghouse

About Baghouses

Efficiency Up To 97+%

(Cyclone Efficiency 70-90%)

Can Capture Smaller Particles Than A Cyclone

More Complex, Cost More To Maintain Than Cyclones

Types of Baghouses

• The three common types of baghouses based on cleaning methods a. Reverse-air

b. Shaker

c. Pulse-jet

Electrostatic Precipitators

Types include:

• Dry, negatively charged

• Wet-walled, negatively charged

• Two-stage, positively charged

• ELECTROSTATIC PRECIPITATOR

• Advantages of Electrostatic Precipitators Electrostatic precipitators are capable very high efficiency, generally of

the order of 99.5-99.9%.

Since the electrostatic precipitators act on the particles and not on the air, they can handle higher loads with lower pressure drops.

They can operate at higher temperatures.

The operating costs are generally low.

• Disadvantages of Electrostatic Precipitators

The initial capital costs are high.

Although they can be designed for a variety of operating conditions, they are not very flexible to changes in the operating conditions, once installed.

Particulate with high resistivity may go uncollected.

http://www.ppcbio.com/ppcdespwhatis.htm

Electrostatic Precipitator Drawing

How An ESP Operates

• Electrostatic precipitator

• More expensive to install,

• Electricity is major operating cost

• Higher particulate efficiency than

cyclones

• Can be dry or wet

• Plates cleaned by rapping

• Creates solid-waste stream

• Picture on next slide

Electrostatic Precipitator Concept

Electrostatic Precipitator

Electrostatic Precipitator – static plates collect particles

Dirty gas

Dust discharge

Electrodes

Cleaned gas

Wet Type

• Venturi

• Static packed

• Moving bed

• Tray tower

• Spray towers

Scrubbers

•Gas Contacts A Liquid Stream

•Particles Are Entrained In The Liquid

•May Also Be A Chemical Reaction

–Example: Limestone Slurry With Coal Power Plant Flue Gas

Wet Particle Scrubbers

• Particulate control by impaction,

interception with water droplets

• Can clean both gas and particle

phases

• High operating costs, high

corrosion potential

• WET SCRUBBERS (CONTD.) • Advantages of Wet Scrubbers

• Wet Scrubbers can handle incoming streams at high temperature, thus

removing the need for temperature control equipment.

Wet scrubbers can handle high particle loading.

Loading fluctuations do not affect the removal efficiency.

They can handle explosive gases with little risk.

Gas adsorption and dust collection are handled in one unit.

Corrosive gases and dusts are neutralized.

• Disadvantages of Wet Scrubbers

High potential for corrosive problems

Effluent scrubbing liquid poses a water pollution problem.

Venturi Scrubber

Detail illustrates cloud atomization from high-velocity gas stream shearing liquid at throat

Vertical Venturi Scrubber

Packed Bed Scrubber

Dry Scrubber System

http://www.fkinc.com/dirctspraydry.htm#top

Tower Scrubber

Spray Towers

• Water or other liquid “washes out” PM

• Less expensive than ESP but more than

cyclone, still low pressure drop

• Variety of configurations

• Higher efficiency than cyclones

• Creates water pollution stream

• Can also absorb some gaseous

pollutants (SO2)

Spray Tower

Gaseous Pollutant Control

•Absorption

•Adsorption

•Combustion

Control of Air Pollutants

Gaseous pollutants - Combustion

• 3 types of combustion systems commonly

utilised for pollution control

– direct flame,

– thermal, and

– catalytic incineration systems

Gaseous pollutants - Adsorption

• physical adsorption to solid surfaces

• Reversible - adsorbate removed from the adsorbent by increasing temp. or lowering pressure

• widely used for solvent recovery in dry cleaning, metal degreasing operations, surface coating, and rayon, plastic, and rubber processing

Gaseous pollutants - Adsorption

• limited use in solving ambient air pollution

problems – with its main use involved in the

reduction of odour

• Adsorbents with large surface area to

volume ratio (activated carbon) preferred

agents for gaseous pollutant control

• Efficiencies to 99%

Carbon Adsorption

• Will do demonstration shortly

• Good for organics (VOCs)

• Both VOCs and carbon can be

recovered when carbon is

regenerated (steam stripping)

• Physical capture

– Adsorption

– Absorption

Adsorb

Absorb

Gaseous pollutants - Absorption

• Scrubbers remove gases by chemical

absorption in a medium that may be a liquid

or a liquid-solid slurry

• water is the most commonly used scrubbing

medium

• Additives commonly employed to increase

chemical reactivity and absorption capacity

Pollutants Of Interest

•Volatile Organic Compounds (VOC)

•Nitrogen Oxides (NOx)

•Sulfur Oxides (SOx)

Controlling Gaseous Pollutants: SO2 &

• Modify Process (recall 3P’s)

– Switch to low-sulfur coals

– Desulfurize coal (washing, gasification)

• Increase efficiency

– Low-NOx burners

• Recover and Reuse (heat)

– staged combustion

– flue-gas recirculation

Scrubbers / Absorbers

• SO2 removal: “FGD” (flue gas desulfurization)

– Lime/soda ash/citrate absorbing solutions

– Can create useable by-product OR solid waste

stream

• NOx removal—catalytic and non-catalytic

– Catalyst = facilitates chemical reaction

– Ammonia-absorbing solutions

– Process controls favored over this technology

• CO & CO2 removal

• Some VOC removal

Flue Gas SOx Control

SOx Forms Sulfuric Acid With Moisture In Air Producing Acid Rain.

Remove From Flue Gas By Chemical Reaction With Limestone

Control Technologies for Nitrogen

Oxides

• Preventive – minimizing operating

temperature

– fuel switching

– low excess air

– flue gas recirculation

– lean combustion

– staged combustion

– low Nox burners

– secondary combustion

– water/steam injection

• Post combustion – selective catalytic reduction

– selective non-catalytic reduction

– non-selective catalytic reduction

Thermal Oxidizers

For VOC Control

Also Called Afterburners

Thermal Oxidation

• Chemical change = burn

– CO2 and H2O ideal end products of all processes

• Flares (for emergency purposes)

• Incinerators

– Direct

– Catalytic = improve reaction efficiency

– Recuperative: heat transfer between inlet /exit gas

– Regenerative: switching ceramic beds that hold

heat, release in air stream later to re-use heat

Two Types Of Oxidizer

•Catalytic

•Non-Catalytic

Thermal Oxidizer

(Non-Catalytic)

Catalytic Thermal Oxidizer

Biological Method

•Uses Naturally Occurring Bacteria (Bugs) To Break Down VOC

• “Bugs” Grow On Moist Media And Dirty Gas Is Passed Through. Bugs Digest The VOC.

•Result Is CO2 And H2O

A Bio Filter For VOC Removal

Other Technologies

• High-temp ceramic filter

• Operates at T > 500 F (limit for

baghouses)

E-beam flue gas treatment process (Prof. A.Chmielewski)

Pollutants removed by EB method

The method has been designed for simultaneous removal of:

• SO2

• NOx

• Cl, HF etc.

• Volatile Organic Hydrocarbons (VOC)

• Dioxins

• Mercury

• Others…

Electron beam effect on gas, primary radiolysis products:

• 4.43N2 -› 0.29N2* + 0.885N(2D) + 0.295N(2P) + 1.87N(4S) + 2.27N2+ +

0.69N+ + 2.96e-

• 5.377O2 -› 0.077O2* + 2.25O(1D) + 2.8O(3P) + 0.18O* + 2.07O2+ +

1.23O+ + 3.3e-

• 7.33H2O -› 0.51H2 + 0.46O(3P) + 4.25OH + 4.15H +1.99 H2O+ + 0.01H2+

+ 0.57OH+ + 0.67H+ + 0.06O+ + 3.3e-

• 7.54CO2 -› 4.72CO + 5.16O(3P) + 2.24CO2+ + 0.51CO+ + 0.07C+ +

0.21O+ + 3.03 e-

Electron beam effect on gas, secondary reactions:

• O(1D) + H2O͢͢͢͢͢͢͢͢͢͢͢͢͢͢͢͢ -› 2OH*

• N2+ + 2H2O -› H3O+ + OH*+ N2

• O(3P) + O2+ M -› O3+ M

• e-+ O2 + M -› O2-+ M

• H3O+ + O2- -› HO2*+ H2O

As a result of these primary and secondary reactions OH*,

HO2 *, O*radicals, O3and other oxidizing species are

formed, that can oxidize NO, SO2 and Hg.

SO2 removal pathways

Radiothermal:

• SO2 + OH* + M -› HSO3 + M

• HSO3 + O2 -› SO3 + HO2*

• SO3 + H2O -› H2SO4

• H2SO4 + 2NH3 -› (NH4)2SO4

Thermal:

• SO2 + 2NH3 -› (NH3)2SO2

• (NH3)2SO2 -› (NH4)2SO4

NOx removal pathways

NO oxidation

• NO + O(3P) + M -› NO2+ M

• O(3P) + O2+ M -› O3+ M

• NO + O3+ M -› NO2+ O2+ M

• NO + HO2* + M -› NO2+ OH* +M

• NO + OH* + M -› HNO2+M

• HNO2+ OH* -› NO2+ H2O

NO2removal

• NO2+ OH* + M -›HNO3+ M

• HNO3+ NH3-›NH4NO3

Reaction mechanisms and sequenceof E-beam process

H. Namba: Materials of UNDP(IAEA)RCA Regional Training Course on

Radiation Technology for Environmental Conservation TRCE-JAERI,

Takasaki,

VOC-decomposition and deodorization methods

Thermal Processes: 1-TO, Thermal Oxidation; 2-RTO, Regenerative Thermal Oxidation; 3-

Catalytic Oxidation with Recuperation. Filtering/Adsorption: 4-Biofilters; 5-Scrubber; 7-

Adsorption Container; 8-Concentrator Unit with TO; 9-Filtering. Non-thermal Oxidation: 6a-

Electrical Non-thermal oxidation; 6b-UVS Non-thermal Oxidation.

VOC-decomposition

Non-thermal plasmas:

• Decomposition of contaminants without heating

• Wide range of pollutants (Gases ... Particulate Matter PM)

• Decomposition of organic PM

• High efficiency for low contamination (e.g. deodorization), ([VOCs] < 1 g

Corg/m3)

Negative aspects:

• High energy cost/molecule_ high energy for high concentrations

• Uncompleted conversion and by-products _ low selectivity (CO2)

• Deposition of polymer films in reactors _ unstable plasma source

Possibilities - indirect treatment, hybrid methods = combination of plasma with:

catalysts, scrubbing, adsorbents…

VOC decomposition by O2 plasma

Aromatic VOC decomposition mechanism. Positive ions’

charget transfer reactions

• M++ RH = M + RH+

• Radical –neutral particles reactions

• OH radical reactions

• ˙OH + C6H5CH3= R1˙(OH radical addition)

• C6H5CH3+ ˙OH = R2˙ + H2O ( H atom abstraction)

• C6H6+ ˙OH = C6H5OH + H (H atom elimination)

• Organic radicals’ reactions

• R˙ + O2= RO2˙

• 2 RO2˙ = 2RO˙ + O2

• RO2˙ + NO = RO˙ + NO2

• RO˙ + O2= HO2˙ + products ( aromatic-CHO, -OH)

• RO˙ -› aliphatic products

R. Atkinson: Chem. Rev. 85(1985) 69

Non thermal plasma

PDC for deodorization (commercial)

Total weighed environmental impact of plasma and non-plasma end-of-pipe

pollutant treatment technologies: the comparison of technologies for SOx/NOx

removal. 1) Electron Beam Flue Gas Treatment (EBFGT) versus 2) Wet Flue Gas

Desulphurization with Selective Catalytic Reduction (WFGD+SCR

1099.7

EBFGT WFGD + SCR

001, E

By-products

Material resources

Electricity

Total weighed environmental impact of plasma and non-plasma end-of-pipe

pollutant treatment technologies: the comparison of technologies for VOCs

removal. 1) Dielectric barrier discharge (DBD) versus 2) adsorption by zeolite (for

LCA) and molecular sieves (for CBA), 3) biofiltration,

DBD plasma Adsorption

(zeolite rotor)

Biofilttration

001, E

By-products

Material resources

Electricity

Flue gas treatment method >300

MW unit

Investment costs

€/kW

Annual operation costs

€/MW

EBFGT 32-45 1290-1577

Wet deSO2 + SCR 176-247 4786-5350

Wet deSO2 + SNCR 144-190 3870-4223

Emission control method 120 MW

Investment costs

€/kW

Annual operation costs

€/MW

EBFGT 113 5167

WFGT+SCR 162 5343

Investment and operation costs of EBFGT and combination of conventional deSO2 and deNOx

Full “Report on Eco-Efficiency of Plasma-Based technologies for Environmental Protection” and

“Report on cost-benefit analysis of plasma-based technologies“ are available at the PlasTEP

project website (http://www.plastep.eu/fileadmin/dateien/Outputs/OP3-2.1_Eco-

efficiency_report.pdf, http://www.plastep.eu/fileadmin/datein/Outputs/120208_CBA.pdf).

Thank You for Your attention!

comparison of different air treatment methods with plasma treatment

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