TITLE : - SEGREGATION AND THERMAL TREATMENT OF HIGH STRENGTH

EFFLUENTS

AUTHOR : - Mr. Jayesh Parikh

Managing Director

CHEM Process Systems Pvt. Ltd.

15, Natraj Industrial Estate, Sanand – Viramgam Road

Sanand, Ahmedabad – 382170

Ph: - 02717 – 284148 / 149

Email: - chem@chemprosys.com

Website:-www.chemprosys.com

ABSTRACT : - High Strength Effluents can be treated by Thermal Treatment, or thermal

treatment with combination of traditional treatment system. Such Effluents

can be separated, segregated, and converted in recyclable and disposable

liquids. Functioning of such systems need to be properly selected and

maintained. The Segregation of High Strength Effluent and its Treatment is

mandatory to overcome the failure of conventional ETP and Biological

Treatment. The Removal of High TDS and High COD from the waste water

make the water cycle viable and functional. The objective of Water

conservation and recycling becomes more practical by removal of inorganic

salts and organic compounds from the industrial waste.

OBJECTIVES OF THERMAL TREATMENT OF HIGH STRENGTH EFFLUENTS

• Water recycling

• Separation of dissolved Solids from Effluent

• Enhance Efficiency of Biological System –by removal of TDS

• Removal of heavier organics compound

• Reduction of COD by thermal stripping

• Recovery of Valuable inorganic and Organic matters

• Elimination/Reduction of incineration energy requirement.

HOW THESE HIGH STRENGTH EFFLUENT STREAMS ARE FORMED

� Reaction and unit operation waste - High TDS and High COD

� RO Reject (Process & Drinking Water) - High TDS

� Scrubber Blowdown - High TDS

� Cooling Tower Blowdown - High TDS

� Boiler Blowdown - - High TDS

� Equipment Cleaning & washing Liquids, Floor & Canteen Wash waste – Low TDS

and Low COD

� Softener Regeneration waste - High TDS

� Demineralization waste - High TDS

TYPES OF THERMAL TREATMENT

• THERMAL EVAPORATION: In Engineering Practice Evaporation Plants are

described as an apparatus for efficiently using the heat from Steam / Thermic Fluid /

Flue Gases / Waste Heat to Evaporate Water.

It is one of the most Efficient and Acknowledged methods of High TDS Treatment,

whereby most of the dissolved solids in form of High Boiling Inorganic matters or

Dissolved Salts are removed Evaporation and Crystallization Methods..

Thermal Evaporation can be carried out by using one of the following ways.

� Evaporation Plants with or Without Thermal Vapor Recompression (TVR)

� Evaporation Plants with or Without Mechanical Vapor Compression (MVC)

Evaporation Plants are generally of following type:

� Natural Circulation Evaporation Plants

� Falling Film Evaporation Plants

� Rising Film Evaporation Plants

� Forced Circulation Evaporation Plants

� Plate Type Evaporation Plants

� Multi – Effect Evaporation Plants

• THERMAL STRIPPING: Thermal Stripping is used to separate High COD (Usually

through Low Boiling Organic – Inorganic Liquids, Solvents. Here we can recover some

inseparable valuable materials, before being sent to thermal treatment in

Evaporation Plants

• THERMAL DRYING: Thermal drying in generally utilized to Eliminate residue

moisture that get carried over after the Evaporation Process, or if it is some valuable

matter which is recovered and can be directly utilized for industrial process after

drying. Commonly used methods of Drying are,

� Spray Drying

� Thin Film Drying

� Fluidized Bed Drying and other conventional methods

• CRYSTALLIZATION: This is a process of Solid liquid separation obtained by

variation of solubility conditions of solute and solvent either by natural

Sedimentation, Precipitation or by use of Artificial Crystallizers.

Artificial Crystallizers are generally of following types,

Cooling type Crystallizers (Retention and Nucleate Growth method)

Oslo Type Crystallizer

Draft Tube and Baffle Type Crystallizers

• INCINERATION : It is a Final waste treatment process that involves the

combustion (Burning) of organic substances contained in the waste materials

WHY THERMAL TREATMENT OF THE HIGH STRENGTH EFFLUENTS IS REQUIRED

High TDS:

Traditional ETP’s and Membrane Separation is mainly reduces COD, BOD, Color,

Hardness and other undesirable toxic ions with suitable Primary & Secondary treatment.

Membrane Filtration is converting medium Concentration Water to Low Concentration Liquid

and generating high concentration water. For high TDS Effluent ETP’s and Membrane

Separation are not suitable and hence Thermal Treatment of Effluent is required.

High COD (Volatile) with High TDS:

High COD effluent is not treatable in ETP’s when it contains high TDS due to

instability of Biological system at high TDS. Hence TDS is the problem in treatment of High COD

effluent. In these circumstances it is mandatory to remove TDS from the High COD effluent to

Convert Effluent to treatable Effluent in ETP. In these conditions Thermal Treatment followed

by Biological / other suitable treatment is desirable. Stripping as pretreatment of such Effluent

extremely reduces Organic contains in the Effluent and separate Solvent/ mixed solvent for

recovery or incineration.

High COD (Low Volatile) with High TDS:

High COD effluent is not Treatable in ETP’s when contains high TDS. When COD is

because of Low volatile organic it required to separate treatable water from the system to

make drying / incineration economical with lower volume/ high calorific value. Recovered

water can be recycled back after minor polishing with ETP/MBR/ACF.

THERMAL TREATMENT PROCESS:

BRIEF ON TYPES OF EVAPORATION PLANTS

Natural Circulation Evaporation Plants: Natural Circulation Evaporation Plants are based on the

natural circulation of the product caused by the density differences that arises from heating. In

an Evaporator using tubing, after the water begins to boil, bubbles will rise and cause

circulation facilitating the separation of the liquid and the vapor at the top of the heating tubes

(or in provision of Vapor Liquid Separator).

Falling Film Evaporation Plants: These types of evaporators are made up of long tubes which

are surrounded by Steam jackets. The solution enters and gains velocity while moving

downwards. This gain in velocity is attributed to the vapor being evolved against the heating

medium which flows downwards as well. These types of evaporators are applied generally in

highly viscous solutions.

Rising Film Evaporation Plants: In this type of evaporator boiling takes place inside the tube due

to the heating arrangement made outside the same. The creation of this water vapor bubbles

due to boiling inside the tubes creates an upwards flowing, hence enhancing the heat transfer

coefficient.

Forced Circulation Evaporation Plants: By inserting a Pump in the natural circulation loop, we

create a forced circulation type evaporator by increasing pressure and circulation rate. Forced

circulation occurs when hydrostatic head prevents boiling at the heating surface. The pump

suppresses the bubble formation and hence avoiding the fouling caused due to the boiling of

liquid inside the tubes. Since the steam consumption is high and hence the temperature

generation is high causing higher effective evaporation and low residing time.

Plate type Evaporation Plants: Here corrugated plates supported by solid strong frames are

used instead of tubes, which have relatively higher heating surface area. During evaporation,

Steam flows through the channels formed by the free spaces between the plates. Here the

steam falls and rises parallel to the concentrated liquid to be evaporated.

Multiple-Effect Evaporation Plants: This sort of Evaporation system is created by combination of

different or same type of above mentioned evaporators. The product is partially concentrated

in the 1st

evaporator, here it is generally termed as 1st

effect, and then subsequently passed on

to the next effect for further concentration and further to the number of effects designed or

decided. Multi staging of evaporation is done to save the cost incurred due to the steam being

utilized for evaporation. This is done by utilizing heated vapor in the former stage as heating

source, which can be there by forwarded to the next stages for further heating and hence

saving on energy expenditure.

APPLICATION OF DIFFERENT TYPES OF EVAPORATION PLANTS

FACTORS AFFECTING PROPER FUNCTIONING OF AN EVAPORATION SYSTEM

• DESIGNING FACTOR:

� Thermal engineering and Chemical Engineering are two

different fields. Only perfect estimation of properties of the High Strength

Effluent in both the fields will help generate a most appropriate design for a

Evaporation Plant.

� Skilled, Experienced and Good Engineering practices help

develop such designs in to the most relevant Actual product, and hence a more

actual and designed performance.

• EFFECTIVE PRETREATMENT:

� By proper filtration method, removal of suspended solids

is a must for minimizing choking of Heat Exchangers and effective solid

separation.

� Hardness removal for eliminating high scale formation

� Removal of Volatile organics, for eliminating the COD

factor, by proper stripping application

� Proper pH adjustment to ensure stabilized ions in

effluent having minimum corrosion effect, to enhance equipment life.

• PROPER UTILITY SUPPLY

� For achieving Good performance to the designed

capacity, it is of utmost importance that the utilities provided, like Heat media,

Cooling Water and Electrical supply are consistent and as per requirement

• PROPER CLEANING AND MAINTENANCE

� Scaling and fouling are unavoidable phenomena in the

operations of a Evaporation Plant, which not only affect the performance of the

plant, but heavily affects the life of plant and the cost involved for running it.

� Periodic and Frequent maintenance activity including

cleaning activity of all Effluent and concentrated slurry exposed parts, will help

eliminate the risks of low performance of plant and ensure longer life of the

system

• PROPER OPERATIONS:

� Skilled operations, monitoring and handling of plant

plays an important role in the Optimized performance of the plant.

• DOSING OF ANTISCALANT AND ANTIFOAMING AGENTS

� Silica and hardness are the main reasons for the forming

of scales on the heat transfer areas. Antiscalant dosing will help minimize scale

formation, or scale formation can be of soft nature which can be easily removed

by cleaning

� Foaming occurs due to presence of certain chemicals

which can adversely affect the performance of the Evaporators and affect the

quality of the condensate. Antifoaming agents can help trouble shoot this

matter.

• PROPER SELECTION & MAINTENANCE OF ACCESSORIES

OF PLANT

� The Pumps, Seals, Gauges, and Instruments play a vital

role in terms of plant operations by deciding and controlling the desired and

designed input and output parameters. Proper selection and maintenance of

these accessories help check the performance of the plants

MAJOR CONCERNS OF PUTTING AN EVAPORATION PLANT

• CAPITAL INVESTMENT

• OPERATIONAL COST

• SCALING AND DEPOSITION

• CORROSION

• MAINTENANCE

• OPERATIONAL SKILLS

REMEDIES TO THE CONCERNS FOR EVAPORATION PLANTS

• PROPER DESIGNING AND ENGINEERING OF

EVAPORATION PLANT

• PROPER STUDY OF CHEMISTRY OF OPERATIONS

• GOOD PRETREATMENT PRACTICE

• FEED AND UTILITY CONTROLS

• SKILLED OPERATIONS

• PERIODIC AND FREQUENT PREVENTIVE MAINTENANCE &

CLEANING

• PROPER OPERATIONS

• GOOD MONITORING OF THE PERFORMANCE

PARAMETERS

EVAPORATION PLANT COST OPTIMIZATION (REFERENCE FIGURE)

No. of

Effect

Feed capacity

(kg/hr)

Water evaporation

/kg of steam

without Thermo

compressor

Approx

Utility cost

per M3 of

feed (Rs.)

Water evaporation/kg

of steam with Thermo

compressor

Approx Utility

cost per M3 of

feed (Rs.)

1 0-500 0.95 1010 2 560

2 300-1000 1.9 600 3 385

3 800-2500 2.8 410 4 290

4 2000-6000 3.65 320 5.5 215

5 4000-10000 4.4 265 6.6 180

6 >7000 5.25 225 7.7 160

7 >10000 6.1 195 8.9 140

CONCLUSION

The Moral responsibility to secure the Nature for future existence, by minimizing the toxic and

hazardous disposal is of prime concern in today’s time. Marine pollution, aquatic life

conservation, and preserving the land fertility can be achieved by either lowering or nullifying

the waste water / effluent disposal. Thermal Treatment of such water is one of the most

effective tools for achieving the Green Earth motto.