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WET AIR OXIDATION. Dr. V.V MAHAJANI Professor of Chemical Engineering, Institute of Chemical Technology, Matunga, Mumbai 400 019 . E.mail :vvm@udct.org vvmahajani@gmail.com Phone : (022) 2414 5616 (Extn 2015 ). V V M 0. WELCOME TO ALL. v.v.mahajani, uict .

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slide1

WET AIR OXIDATION

Dr. V.V MAHAJANI

Professor of Chemical Engineering,

Institute of Chemical Technology, Matunga, Mumbai 400 019

E.mail :vvm@udct.org

vvmahajani@gmail.com

Phone : (022) 2414 5616 (Extn2015)

V V M 0

slide2
WELCOME

TO ALL

v.v.mahajani, uict

slide3

CHEMICAL PROCESS INDUSTRY ( CPI)

BIRD’S EYEVIEW

UTILITIES GASEOUS WASTE

RAW MATERIALS PRODUCTS, By PRODUCTS,

INTELLECTUAL SOLID WASTE

INPUTSLIQUID WASTE (~ 90 % of water in)

CPI

V V M 1

slide4

Chemical Engineer’s View

  • BIO PROCESSESPHYSICO CHEMICAL PROCESSES
  • Aerobic 1. SEPARATION 3. BULK MINERALIZATION
  • Anaerobic Liquid / Liquid Extraction Incineration
          • Precipitation Wet Air Oxidation
          • Adsorption 4. POLISHING PROCESS
          • Membrane Photo Chemical
          • 2. REACTIVE DESTRUCTIONFenton
          • HydrotreatmentSonication
          • Ozonation
        • HYBRID PROCESSES : INNOVATIVE COMBINATION OF ALL

V V M 2

process pre view
PROCESS PRE-VIEW

BIO-PROCESSES

MOST POPULAR PROCESSES OPERATING AT NEAR ATM PRESSURE AND

AMBIENT TEMPERATURE.

BIO GAS GENERATION FROM SPENT WASH OF A DISTILLERY UNIT

  • LIMITATIONS

SLOW RATES, LARGE VOLUME. HENCE, MORE FLOOR AREA REQD.

OFTEN NEED ENGINEERED MICRO-ORGANISMS

DO NOT PERMIT, INVARIABLY, SHOCK LOADS, TOXIC WASTES

NEEDS ELABORATE POLISHING TREATMENT FOR WATER RECYCLE

V V M 3

slide6

WATER COSERVATION RESULTS IN

CONCENTRATED WASTE

X NOT SUITABLE FOR BIO PROCESS

  • OPTIONS AVAILABLE:
  • INCINERATION
  • WET AIR OXIDATION

V V M 4

slide7

INCINERATION :

  • HIGH OPERATING COST.
  • LOWER CAPITAL INVESTMENT..
  • WATER CAN NOT BE RECYCLED UNLESS TREATED.
  • DEPRECIATION BENEFIT IS ONLY FOR CAPITAL
  • INVESTMENT AND NOT FOR OPERATING COST.

V V M 5

slide8

WET AIR OXIDATION

  • MORE APPROPRIATELY : THERMAL PROCESS.
  • IT IS SUBCRITICAL OXIDATION PROCESS IN AN AQUEOUS MEDIUM

WaterTc = 374 0C & Pc = 217.6 atm

  • OXIDATION OF ORGANIC INORGANIC SUBSTRATE IN PRESENCE OF MOLECULAR O2 T = 100 _ 250 0C; Pressure: O2 pressure 5 to 20 atm
  • O2 Solubility in water is minimum at near about 100oC. Above 100 oC it is increasing with increase in temperature.

V V M 6

slide9

OXIDATION REACTIONFREE RADICAL MECHANISM

O2 + H2O OH* via OH* radical formation

NON SELECTIVE OXIDATION TO MINERALIZE OXIDIZABLE CONTAMINANTS

ORGANICS

O2

Ca Hb Nc Pd Xe Sf Og C CO2

H2O N N2, NH3, NO3, H H2O

P PO4

X HX (halogen)

S SO42-

O2 O2

Inorganic substances

O2

Na2S Na2SO4

Na2SO3 Na2SO4

V V M 7

oxidation power of common oxidizing agents relative to oxygen
OXIDATION POWER OF COMMON OXIDIZING AGENTSRELATIVE TO OXYGEN

O2 1.00

Cl2 1.06

ClO2 1.06

HOCl 1.24

H2O2 1.48

O3 1.68

OH* (hydroxyl radical) 2.33

F2 2.50

V V M 8

slide11

HIGHER OXIDATION POWER MEANS A RELATIVE LACK OF

  • SELECTIVITY.
  • This property IS USELESS for organic synthesis but the most desirable in waste treatment.
  • SHE management does not allow use of “F”
  • WET Oxidation Technology is centered around OH* radical as non-selective but powerful oxidizing agent.

V V M 9

slide12

INSIGHT INTO REACTION MECHANISM

Large molecular wt O2 CO2 + H2O

organic substrate

low mol. wt organic acids

(Acetic, Propionic, Glyoxalic, Oxalic)

Complex Reactions

Intermediates are formed and can be slow to oxidize or mineralize to CO2

V V M 10

slide13

KINETICS

The waste is characterized as: BOD (bio-chemical oxygen demand), COD ( chemical oxygen demand ) & TOC ( total organic carbon )

Kinetics is presented in terms of COD / TOC reduction

Instead of having complex kinetics representing series and parallel reactions, a series

reaction approach is considered. We have found that a lumped parameter series

reaction in terms of COD is more design friendly

k1 k2

(COD) (COD) CO2 and H2O

Original low mol. wt

Waste intermediates

In majority of cases, the second reaction step (k2) is the rate limiting step.

V V M 11

slide14

The kinetics is then given as

  •  d(COD) = k (COD)m (O2)n

dt

m  1 ; n varies with 0.5 to 1.0

CATALYSTS

Wet air oxidation reactions can be catalyzed by

  • homogeneous catalysts
  • heterogeneous catalysts

to reduce SEVERITY of operating conditions.

V V M 11

slide15

CATALYST CHARACTERIZATION

  • Homogeneous catalysts
  • The catalyst should be such that complete oxidation of substrate is possible to CO2 and H2O.
  • It should be compatible with MOC of the reactor.
  • It should be easily recoverable.

CATALYST RECOVERY

  • Homogeneous catalysts could be recovered by
  • Precipitation
  • Ion exchange technique
  • Liquid emulsion membrane process
  • The leached catalyst and support can be recovered also by the above techniques.

V V M 12

slide16

Heterogeneous catalysts

  • Cu, Co, Mn, Fe, Ru could be supported on suitable support such as Al2O3, SiO2 and TiO2
  • Temperatures are around 200 oC and there exists acetic acid as an intermediate. This could result in extraction/leaching of the catalyst element into treated aqueous stream.
  • Leaching of support also may take place.

We have observed:

  • Cu salts are very good for complete mineralization
  • Co and Fe are not able to oxidize acetic acid as effectively as copper

V V M 13

slide17

Advantages and Limitations

Advantages

  • It can handle concentrated waste COD 10,000-500,000 mg/l
  • It can handle toxic chemicals cyanides, sulphides and priority pollutants
  • Waste with high TDS can be handled
  • Energy integration possible
  • Very less space, even it can be underground.
  • Lower operating cost

V V M 14

slide18

Limitations

  • Capital intensive due to exotic MOC.

However, depreciation benefit makes it attractive!

V V M 15

slide19

STEAM

ENERGY RECOVERY

SYSTEM

AIR COMPRESSOR

AIR

BFW

WET OXIDATION

REACTOR

AIR

SATURATOR

BFW

EFFLUENT

TREATED

WATER

ENERGY RECOVERY

SYSTEM

Typical Continuous Wet Oxidation System for Liquid Waste

OFFGAS

V V M 16

slide20

Integration with other waste treatment processes:

It is possible to have hybrid systems to realize economic advantage

of the waste treatment process.

1 Membrane – WAO

2 WAO - Membrane

3 Sonication – WAO

4 Fenton – WAO

5 Biological treatment – WAO

6 WAO - Biological treatment

V V M 17

slide21

A SYSTEMATIC APPROACH FOR WATER TREATMENT FOR RECYCLE

  • We can use following guidelines for water recycle in a chemical plant
  • Identify contribution of water bill in the cost of production.
  • Identify the scenario around your project with special reference to availability of water in future, considering your future requirements due to expansion.
  • Take water balance in your plant.
  • Identify all water outlets such as plant effluent, utility blow downs, water used in administrative block, canteen etc. Please note that one can do little to evaporation loss in cooling tower.
  • Have detailed analysis of each effluent stream and decide which can be used for recycle and which can be used for purging. It may be possible to use purge water for gardening and horticulture.

V V M 18

slide22

Have specifications for water use at all process blocks in the project. For instance, specifications for water used for washing filters would be totally different from that used as boiler feed water generating steam for captive power generation also.

  • Decide on treatment strategy.
  • Since each effluent stream is unique, carry out bench scale studies.
  • Carry out detailed technoeconomic feasibility study to ensure that set goals or targets could be achieved / realized.
  • Implement the project without any delays.

*********************************************

V V M 19

slide23

SUSTAINABLE DEVELOPMENT OFMANKIND

IS POSSIBLE ONLY WHEN

WE LEARN TO RESPECT THE DIGNITY

OF ENVIRONMENTAL PROTECTION