ACTIVATED CARBON FILTER.pdf

8/17/2019 ACTIVATED CARBON FILTER.pdf

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THERMAX LTD | C & W SERVICE & SOLUTIONS GROUP OC No: 200134

OPERATION & MAINTENANCE MANUAL

FOR ACTIVATED CARBON UNIT – CONDENSATE POLISHING UNIT 1

OPERATION, MAINTENANCE

&

TROUBLESHOOTING

MANUAL

CLIENT : IFFCO PHULPUR

PROJECT : ACTIVATED CARBON FILTER

FOR AMMONIA & POWER PLANT

PLANT : CONDENSATE POLISHING UNIT

CAPACITY : 150M3/HR

REFERENCE : OC NO 200134

Thermax Limited, (C&W Service & Solutions Group)

Thermax House, Mumbai Pune Road,

Shivaji Nagar, Pune - 411005

Tel. : 020-25511010, Fax. : 020-25511236.

WATER TREATMENT PLANT


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Improving Your Business Is Our Business On Thermax Group:

Thermax’s vision is to be a globally respected high performance company offering sustainable

solutions in energy and environment. The Thermax Group provides business to business

solutions in the areas of heating, cooling, captive power, water treatment, air pollution control,

waste management & resource recovery, and chemicals to a wide range of industry in Indian

and international markets.

In the energy business, Thermax executes projects in the areas of process heat, captive power

and waste heat recovery. It also offers a range of heating equipment; energy efficient chillers

and customized products such as waste heat and exhaust gas boilers.

Thermax’s integrated expertise in energy has made GE to choose it as the ‘vendor on first call’

for its global Combined Heating Power and Cooling (CHPC) projects...

Thermax offers industry its expertise over a hundred fuels including oil, gas and a wide variety

of solid fuels including biomass. The Group’s Joint Venture, Thermax Babcock & Wilcox (TBW)

has emerged as a leading and reliable project management companies with installations the

world over; in the US, Saudi Arabia, Thailand, Egypt, Philippines and several other countries.

Leveraging its leadership position in electricity saving vapor absorption technology, it offers

process industries and commercial establishments like hotels, shopping malls and offices vapor

absorption chillers a boon in power‐starved areas. These Eco‐friendly, energy efficient

equipment have found prestigious customers such as BBC, Mercedes Benz, Audi, Bosch,

Panasonic, Henry Ford Museum.

In the environment area Thermax offers waste management expertise for solid, liquid and air

pollution. Thermax provides solutions from pre‐treatment to waste water treatment and

chemical conditioning of water for boiler and cooling water systems. Water recycling is a thrust

area for Thermax. Hi‐grade resins from Thermax have found niche customers in US and

Japanese markets.

Thermax has an extensive international marketing network. Headquartered in Pune (Western

India), Thermax's eleven international offices are located in South East Asia, Middle East, Africa,

Russia, UK and the US. Thermax’s 4 overseas subsidiaries play a significant role in generating

business in the International market: Thermax (Rus) Ltd., Thermax (Europe) Ltd.,


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Thermax Inc., USA and ME Engineering, UK. Around 20 per cent of the group’s turnover come

from exports – to the US and European markets, Japan, East Africa, the Middle East, South East

Asian and CIS countries.

The Thermax group’s manufacturing facilities. Spread over 14 plants, measuring a covered area

of over 65,000 sq. Mts., are ISO 9000 and ISO 14001 accredited. Thermax manufactures to

international standards like ASME, BS, DIN, and GOST. The facilities have been inspected by

Lloyds, Bureau Veritas, SGS, and TUV.

Thermax’s business is inspired by the conviction that ‘Improving your business is our business.’

Water & Waste Solutions

MAKING INDUSTRY

GREEN

AND

COMPETITIVE

Cost competitive and Environment friendly technology innovated and developed through

continuous research to keep industry green and competitive. Excellence in Technology and

stringent quality control measures are the hallmarks in all projects undertaken by Thermax

Water & Waste Solutions Division. Thermax Water & Waste solutions division takes on

Retrofitting and Revamping orders to extend life of all aging plants. Our comprehensive service

program is the first of its kind in India. It is a program that evaluates and then enhances the

economical performance of all water & waste treatment plants.

Thermax Water & Waste Solution Division’s wide spectrum of products and technology covers

Pretreatment

Process Water Treatment

Ion Exchange Resins

Reverse Osmosis and Electro dialysis

Condensate Polishing

Thermal Desalination

Waste Water Treatment

Sewage Treatment

Recycling of water

Range of Cooling Water Chemicals

Range of Polyelectrolyte

Incinerators.


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I N T R O D U C T I O N

The Operation & Maintenance Manual gives a brief introduction to the total system supplied

and gives instructions and guidelines for smooth, long lasting and trouble free operation of the

plant. The O&M manual is prepared to make the operator familiar with the system/plant

supplied (ACF unit) and its operation and maintenance of the Plant.

The chapter Chemical Control describes the various laboratory tests and their procedures, to be

carried out in the laboratory to understand quality of feed water to the plant and quality of

product water. The regular analysis also helps in analyzing individual units' performance and

total plant performance vis‐à‐vis output water produced and chemicals consumed.

The maintenance of various equipment in general and resin units in particular are detailed in

this O&M manual along with details of trouble shooting, safety precautions, etc. It is also to be

noted that this O&M manual covers all areas relevant to the system supplied in general and

certain problematic areas, in particular, with respect to operation and maintenance, based on

our experience, as far as possible. In case of problems, which are not covered, and peculiar, the

same can be referred to us or the various manufacturers as and when they arise.


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1. WATER TREATMENT FUNDAMENTALS

1.1 WATER TREATMENT GENERAL WRITE – UP & BASIC WATER CHEMISTRY:

INTRODUCTION:

The natural water contains solid, liquid and gaseous impurities and therefore, this water cannot

be used for the generation of steam in the boilers. The impurities present in the water should

be removed before it’s use in steam generation The necessity for reducing the corrosive nature

& quantity of dissolved and suspended solids in feed water has become increasingly important

with the advent of high pressure, critical & supercritical boilers.

IMPURITIES IN WATER: ‐

The impurities present in the feed water are classified as given below

• Undissolved and suspended solid materials.

• Dissolved salts and minerals.

• Dissolved gases.

• Other materials (as Oil, Acid) either in mixed or Unmixed forms.

• Undissolved and suspended solid materials.

a) Turbidity and Sediment

Turbidity in the water is suspended insoluble matter including coarse particles (mud, sediment,

sand etc.) That settles rapidly on standing. Amounts ranges from almost zero in most ground

waters and 60,000 ppm in muddy and turbulent river water. The Turbidity of feed water should

not exceed 5 ppm. These materials can be removed by settling, coagulation and filtration. Their

presence is undesirable because heating or evaporation produces hard stony scale deposits on

the heating surface & clog fluid system. Both are objectionable as they cause damage to the

Boiler system standard amount of measurement of hardness is taken as being the amount of

Calcium Carbonate (CaCO3) in the water and is referred to in part per million (ppm) or grains

per gallon (grains/gallon * 17.1 = ppm).

b) Sodium and Potassium Salts

These are extremely soluble in water and do not deposit unless highly concentrated.

Their presence is troublesome as they are alkaline in nature and accelerate the corrosion.


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c) Chlorides

Majority of the chloride causes increased corrosive action of water.

d) Iron

Most common soluble iron in water is ferrous bicarbonate. The water containing ferrous

bicarbonate deposits becomes yellowish and reddish sediment of ferric hydroxide if exposed to

air. Majority of ground surface water contains less than 5 ppm but even 0.3 ppm can create

trouble in the feed water system by soft scale formation and accelerating the corrosion.

e) Manganese

It also occurs in similar form as iron & it is also equally troublesome.

f) Silica

Most natural water contains silica ranging from 1 to 100 ppm. Its presence is highly

objectionable as it forms very hard scale in Boilers and forms insoluble deposits on turbine

blades. In modern high pressure Boilers its presence is reduced as low as 10‐50 ppb.

g) Microbiological Growth

Various growths occur in surface water (lake & river). The microorganisms include diatons,

moulds, bacterial slimes, algae, manganese & sulphate reducing bacteria and many others.

These can cause coating on Heat Exchanger and clog the flow passages and reduce the heat

transfer rates.

h) Colour

Surface waters from swampy areas become highly coloured due to decaying vegetation. Colour

of feed water is objectionable as it causes foaming in Boilers and may interfere with treatment

processes. It is generally removed by chlorination or adsorption by activated carbon.

Dissolved Salts and Minerals

Calcium and Magnesium Salts

The Calcium and Magnesium salts present in the water in the form of carbonates, bicarbonates,

and sulphates and chlorides. The presence of these salts is recognized by the hardness of the

water (hardness of water is tested by soap Test). The hardness of water is classified as

temporary and permanent hardness. The temporary hardness is caused by the bicarbonates of

calcium and magnesium and can be removed by boiling.


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The boiling converts the soluble bicarbonates into less soluble carbonates, which can be

removed by simple blow down method. The permanent hardness of the water is caused by the

presence of chlorides, sulphates and nitrates of calcium and magnesium and they can not be

removed just by boiling because they form a hard scale on heating surfaces.

Dissolved Gases

Oxygen

It presents in surface water in dissolved form with variable percentage depending upon the

water temperature and other solid contents in water. Its presence is highly objectionable, as it

is corrosive to iron, zinc, brass and other metals. It causes corrosion and pitting of water lines,

boiler exchangers. Its effect is further accelerated at high temperatures.

b) Carbon Dioxide

The river water contains 50 ppm and well water contains 2 to 50 ppm of CO2. It also causes the

corrosion of stream, water and condenses lines. It also helps to accelerate the corrosive action

of oxygen. The other gases are H2S, CH4, N2 and many others but their percentages are

negligible, therefore, their effects are not discussed here.

4. Other Materials

Free Mineral Acid

Usually present as sulphuric or hydrochloric acid and causes corrosion. The presence is reduced

by neutralization with alkalis.

b) Oil

Generally, the lubricating oil is carried with steam into the condenser and through the feed

system to the Boiler. It causes sludge, scale and foaming in Boilers. It is generally removed by

strainers and baffle separators.

The effects of all the impurities present in the water are the scale formation on the different

parts of the Boiler System and corrosion. The scale formations reduces the heat transfer rates

and clog the flow passage and endanger the life of the equipment’s by increasing the

temperature above safe limit. The corrosion phenomenon reduces the life of the Plant rapidly.

Therefore, it is absolutely necessary to reduce the impurities below a safe limit for the proper

working of the power plant.


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1.2 Importance of Water Analysis

Water analysis

The process of determining how much of various substances (impurities) are present in given

sample of water is known as Water Analysis.

Need for Water Analysis

Water analysis is essential for the following reasons:

a) Raw water source selection.

b) Analysis of raw water determines the type of treatment and unit size.

c) Treated water analysis indicates the efficiencies of various units of water treatment.

d) Designing of most economical water treatment plant.

To design a water treatment plant knowing the impurities present in the water to be treated is

needed. Complete analysis helps in determining the degree of pretreatment required in Ion

Exchange and other process like reverse osmosis etc.

Minor constituent like silica is very important since it may have influence on the regeneration

technique used and can affect the capacities that can be obtained.

Analysis of Iron and chlorine is important for reverse osmosis design.

Definition used in water analysis

pH:

It is common practice to express hydrogen ion concentration in terms of pH. By definition the

pH is the negative logarithm of hydrogen ion concentration to the base of l0.

pH = ‐ log10 (H+) = log (1/H+)

Ionic product of water Kw has a value of 1 x 10 ‐ 14 and in neutral water H + concentration is

equal to OH ‐ concentration.

Kw = H + x OH‐ = 1 x 10‐ 14 ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ (1)

For neutral water = (H+) = (OH‐) = 1x10 ‐7

The equilibrium represented by equation (1) occurs universally in aqueous solution regardless

of the equilibrium or the solutes present. Hence equation (1) should always be satisfied.

Thus the terms pH expresses the acidity or basicity of water.

Neutral water has a pH of 7. pH lower than 7 indicates acidity and greater than 7 is alkaline.


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Alkalinity:

As mentioned earlier alkalinity in water is due to presence of HCO‐3. CO‐3 and OHions. In raw

water alkalinity is mostly due to HCO‐3, but in some cases CO‐3 ions also may be present. It is

important to note that out of the three ions only two ions can exist in any system. That is HCO‐

3, CO‐3 or OH‐ can exist alone or in combination with one more ion. Any water analysis

reporting the presence of all three ions should be discarded.

Alkalinity of water is determined by titration with phenolpthalein and methyl orange indicator.

The result of titration with methyl orange indicator is called Total Alkalinity or MAlkalinity.

M. Alk. = Total Alk = HCO‐3 + CO‐3 + OH‐.

The result of titration with phenolpthalein indicator is called P‐Alkalinity.

P. Alk = OH + 1/2 CO3.

Hardness

Calcium and Magnesium salts impart hardness to water. Hard water is defined as a water which

does not lather or foam with soap easily. The salt of calcium and magnesium which causes

hardness is divided in two parts.

1. Temporary hardness or carbonate hardness.

2. Permanent hardness or non‐carbonate hardness.

The sum of temporary and permanent hardness is called Total Hardness.

Total Hardness = Carbonate hardness + Non Carbonate hardness

Carbonate Hardness

It is mainly due to presence of bicarbonates of Calcium and Magnesium.

Alkalinity in raw water is normally due to bicarbonate ions. Therefore, carbonate hardness

(Alkalinity) plus Non Carbonate hardness is equal to total hardness.

1) Carbonate hardness = Alkalinity, when alkalinity is less than total hardness.

2) Carbonate hardness = Total hardness, when alkalinity is greater or equal to total hardness.

Conductivity:

The conductivity of water is dependent on the ionic content of water, specifically on the ability

of ionic impurities in the water to conduct electricity. Ionic impurities have the ability to

conduct electric current and thus there is direct linear relationship between ionic impurities

and conductivity which help in determining the ionic impurities in water.


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Conductivity is also related to TDS empirically = Conductivity x 0.65 = TDS.

Total Dissolved Solids

This represents all the soluble inorganic solids in water expressed in ppm.

Total Solids

Total solid is defined as SUM of soluble and insoluble solids.

Electrolytes

This is total ionizable dissolved solids in water. Total electrolyte is numerically equal to total

cation or total anions (not sum of both). Total electrolyte does not include CO2 and silica.

Total Cations

Sum of calcium, magnesium, sodium and potassium all measured in the same unit.

Total Anions

Sum of alkalinity (HCO‐3 + CO‐3 + OH‐) + Cl + SO4 + NO3 all measured in the same unit.

Total Cation = Total Anion = Total Electrolyte

Equivalent Mineral Acidity (EMA)

The equivalent mineral acidity, EMA is equal to the sum of equivalent concentration of

sulphates, chloride and nitrate. It is also called sometimes as Total Mineral Acidity.

Free Mineral Acidity (FMA)

Free mineral acidity is equal to (EMA ‐Sodium leakage).

EMA ‐Sodium leakage = FMA

EMA ‐FMA = Sodium leakage.

Method of reporting water analysis

There are various ways of reporting water analysis, but in general four methods which are

commonly used are,

1. As ppm ion or mg/litre.

2. EPM or M.Eq./litre (Mill equivalent per litre)

3. ppm as CaCo3.

4. Grains per gallon as CaCo3.


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Water analysis Report

Water analysis can be reported in many ways but most laboratories give in the format as given

below.

WATER TREATMENT PLANT

Format for Reporting water Analysis

Physical

pH ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐

Colour ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐Hazen Unit

Taste and Odour ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐

Turbidity ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐NTU

Conductivity ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ μmhos or milli mhos

Chemical

Suspended Solids ‐ in ppm

Calcium ‐as ppm CaCO3.*

Magnesium ‐as ppm CaCO3.*

Hardness ‐as ppm CaCO3.*

M.Alkalinity ‐as ppm CaCO3.*

P.Alkalinity ‐as ppm CaCO3.*

Chloride ‐as ppm or mg./litre.

Sulphate ‐as ppm or mg./litre.

Nitrate ‐as ppm or mg./litre.

Silica ‐as ppm or mg./litre.

Iron ‐as ppm or mg./litre.

TDS ‐as ppm

CO2 ‐as ppm

* Sometimes calcium and Magnesium can be reported as in ppm as Ca or Mg.


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2. PLANT CONFIGURATION AND DETAILS

2.1 SYSTEM DETAILS ‐ PLANT DATA

DESIGN DATA

S.No Description Design Value

1 Unit Name Activated Carbon Filter

2 No of Stream 01

3 Design Flow rate 150 M3/Hr

4 Specification 4 M Dia & 2.6 HOS

4 Design pressure 12.5 Kg/cm

2

6 Design temperature 80C

OPERATING DATA

S.No Description Design Value

1 Unit Name Activated Carbon Filter

2 No of Stream 01

3 Flow rate 150 M3/Hr

4 Operating Time 20 Hrs

5 Operating pressure 9 – 11 Kg/cm2

6 Operating temperature 60C

7 Operation Mode Manual

8 Backwash Time 30 min

9 Feed Water Condensate outlet water

10 Differential pressure in vessel 0.6 Kg/cm2

11 Differential pressure in Basket filter 1.5 Kg/cm2

12 Blower for ACF 600m3/Hr at 0.4 Kg/cm

2


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3. CONTROL PHILOSPHY

3.1 SYSTEM DESCRPTION:

ACTIVATED CARBON FILTER BASICS

Activated Carbon works by attracting and holding certain chemicals as water passes through it.

Because AC is a highly porous material, it has an extremely high surface area for contaminant

adsorption. The contaminant is more likely to diffuse into a pore and become adsorbed.

The two principal mechanisms by which activated carbon removes contaminants from water

are adsorption and catalytic reduction. Organics are removed by adsorption and residual

disinfectants are removed by catalytic reduction.

Activated carbon is proven technology for the removal of naturally occurring organics and

residual disinfectants. Activated carbon filters are using granular activated carbon as media.

Activated carbon filtration is most effective in removing organic contaminants from water.

Organic substances are composed of two basic elements, carbon and hydrogen. Because

organic chemicals are often responsible for taste, odor, and color problems.

AC filtration can generally be used to improve aesthetically objectionable water. AC filtration

will also remove chlorine. AC filtration is recognized by the Water Quality Association as an

acceptable method to maintain certain drinking water contaminants within the limits of the

EPA National Drinking Water Standards.

Overall this study showed that activated carbon filters are extremely effective as primary filters

and have the added benefit of organics reduction resulting in cost savings with reduced

chlorine demand and safer water with reduced THM formation and cleaner distribution

systems.

Activated carbon beds are filters and need to be backwashed periodically.


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3.2 PROCESS (ACF)

The ACF filter has a Activated Carbon Media, one of the most widely used media for adsorption

of impurities.

The Activated carbon is employed for_

• Dechlorination

• Removal of Organics

• Removal of Odour

The residual chlorine in the water, where chlorination is used for Organics removal, as

adsorbed by Activated Carbon Filter. Chlorination of water is widely used in Drinking Water

Plants, Pretreatment of DM plant and Ro plants and effluent treatment plants. The VERSA ACF

removes almost all of the residual chlorine in the water.

The VERSA ACF also helps in removal of Organic matter from the water. It is used in treatment

plants for Drinking water as polisher unit at the outlet of the plant and removes objectionable

odours. The Activated carbon media has finite capacity of absorption and shall exhaust on

prolonged usage depending upon the inlet impurity load.


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4. OPERATION AND MAINTENANCE OF ACF FILTER

4.1 SYSTEM OPERATION FOR ACTIVATED CARBON FILTER (ACF)

The ACF unit for manual operation shall be divided into the following operations:

1. SERVICE cycle of ACF unit

2. BACKWASH operation of ACF unit

3. AIR RELEASE operation of ACF unit

SERVICE CYCLE OF ACF UNIT:

•

Ensure that the ACF filter is backwashed and is ready for service.

• Ensure feed water is available in rated quantity/quality and pressure.

• In the service mode Service Inlet Valve VM‐1 and the service outlet valve VM‐2 remain

open.

The service cycle of ACF is 20 hours or differential pressure across the filter 0.6kg/cm2.

SERVICE STEPS

1. RINSE

2. REFILL

3. SERVICE

1. RINSE:

In this step Service inlet valve VM‐1 and Rinse outlet valve VM‐6 remains open. The step is

carried out with the condensate outlet water for 5 minutes at the flow rate is 150 m3/Hr.


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2. REFILL:

In this step the service inlet valve VM‐1 and air release valve VM‐12 remain open. All the

other valves are in closed condition. Refill is carried out at the service flow rate till full bore

of air comes from the air release line. The time set for refill is 2 minutes.


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3. SERVICE:

The unit is taken into service. It remains in service for a cycle of 1200 min. After this it is

taken into regeneration mode. Service inlet valve VM‐1 and Service outlet valve VM‐2

remain open.


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BACKWASHING OF ACF

After completion of design service run hours (20 hours) or depending up on the differential

pressure across the filter i.e Difference between inlet and outlet pressure gauge readings of 0.6

kg/cm2, the vessel is taken in backwash mode.

BACKWASHH IMPORTANCE:

The waste wash water drains should be kept free of clogging or sediment. The requisite up‐flow

velocity of backwash water should be maintained at the design rate for proper cleaning of the

media.

Backwashing of filters should not be based on arbitrarily fixed time scheduled but the

frequency should be in accordance with the filtrate quality and head loss measurement.

Duration of cleaning should be dependent upon the turbidity of the wasted water.

For better performance, carry out extended backwash for 30‐45 minutes once in a week or till

backwash effluent is clear.

BACKWASH STEPS

Backwash steps are as follows,

1. DRAIN

2. AIR SCOURING

3. STEAM

4. BACKWASH

5. SETTLE BED

6. RINSE STEP


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BACKWASH STEPS

1. DRAIN:

The backwash mode is initiated with the drain step. In this step Backwash Outlet Valve (VM‐

4) and drain outlet valve or rinse outlet valve (VM‐6) remains open. All the other valves

remain closed. The drain step is for a period of 5 minutes.


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2. AIR SCOURING:

Air scouring step starts and is done through ACF Blower (ACFB‐1). Backwash outlet valve

(VM4), Air Inlet valve (VM‐5) and Air release valve (VM‐12) remain open in this step. The

step is carried for 5 minutes.


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3. STEAM:

Steam scouring step starts and is done through steam inlet line. Backwash outlet valve

(VM4), Steam Inlet valve (VM‐30) and Air release valve (VM‐12) remain open in this step.

The step is carried for 10 minutes.


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4. BACKWASH:

In this step the Backwash Inlet Valve (VM‐3) and Backwash Outlet Valve (VM‐4) remain

open. The backwash is done through the Condensate outlet valve. The backwash is carried

out at a flow rate of 150 m3/hr for 10 minutes.


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5. SETTLE BED:

In this step the bed is allowed to settle for a period of 2 min. All the valves remain closed in this

step.

6. RINSE STEP:

The rinse step of ACF in backwash mode is carried out with the condensate outlet water. In this

step VM‐1 of ACF remains open & rinse water is drained out through the rinse outlet valve VM‐

6 of ACF. The rinse step is carried out for 5 minutes at the flow rate of 150m3/hr.


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AIR RELEASE OPERATION:

Air release operation is an independent operation carried out to release the entrapped air from

within the vessel. This single operation; when opened the Air release valve VM 12 in 2 min and

the air release valve also gets closed manually after 2 mins.

BASKET STRAINER IMPORTANCE:

The Filtered/Treated Water is first passed to Basket Filter. This unit is provided for removal of

fine suspended particles. This is a SS vessel housing with the SS screen Filter elements which

prevents micron size particles up to 100 µ. If the differential pressure on the inlet to Basket

Strainer sensed by DPT 352 is high value alarm is 1.5 Kg/cm2. ACF feed water valve close/trips in

this case.

ACF OUTLET FILTERED/TREATED WATER

After Filtered/Treated water of ACF outlet water is sent directly to make up water day tank of

the power plant for BFW make up in boiler through deaerator.

After Filtered/Treated water of ACF outlet water is sent directly to make up water day tank of

the ammonia plant for BFW make up in waste heat boiler through deaerator.


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4.2 PROCESS FLOW DIAGRAM

SCHEMATIC DIAGRAM FOR ACTIVATED CARBON FILTER UNIT

SURFACE

CONDENSER

CONDENSATE

WATER INLET BASKET FILTER 1

TREATED WATER OUTLET

BASKET FILTER 2

TO DEAERATOR

ACF

PROCESS STEPS:

Process condensate water from surface condenser outlet to deaerator.

SURFACE CONDENSER – ACF – BASKET FILTER – DEAERATOR.


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4.3 OPERATING CONDITION CHECKS FOR ACF YNIT

PRE‐REQUISITE CONDITION ‐ OPERATION (MANUAL) ‐ ACF UNIT

• Check the all manually operated valves open or close condition such as VM‐1, VM‐2, VM‐3,

VM‐4, VM‐5, VM‐12, VM‐30 & VM‐26.

• Ensure all Pressure Gauge isolation valve (VM‐41) are open for all the Units & of Rotary

equipment’s.

• Ensure all Flow Indicators’ / Flow transmitter DP transmitter isolation valves (VM‐46) are

open for all the Units.

• While in service Condensate outlet header valve and ACF outlet header valve is open.

• Inlet water pressure should not exceed 12 kg/cm2. Do not exceed the Max Operating Flow

rate of 150 m3/hr, as this may deteriorate the quality of outlet water.

• Inlet water temperature should not be more than 80 Deg.C

• Check the differential pressure across the vessel & across the basket filter before start up

the unit.

Now ACF unit is ready to take in to operation.

MAINTENANCE CHECKS:

• Analyze inlet / outlet water in periodically i.e., hourly, shift basis, daily, weekly basis.

• Ensure Air blower are sufficiently lubricated and continued oil levelers are filled up.

• Inspect the vessel, piping externally once in year for damage to the painting.

• Inspect the filter media every year, and replaced if required.

• Give extended backwash to the filter once in a week for more than 45 min or till clear

water.

• Give air scouring to the filter media once in six months or if the filter is found heavily

chocked, as described in maintenance section.

• Use genuine spares (THERMAX SPARES).

• Repaint as necessary.

• Inspect vessel internally once in a year for any damaged in internals system or not. And

repair the internals if found damaged.

• If found consistently more than the design limit, consult THERMAX representatives.


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4.4 TROUBLESHOOTING GUIDE (ACF)

S.No DEFECT CAUSE REMEDY

1 Condensate water

quality not up to

the standard

a. Filter not backwashed

b. Inlet Suspended Solids load

increased

c. Excessive Flow Rate

d. Channeling Collection/distribution

e. Disturbed media layers.

a. Backwash filter regularly

b. Check inlet water quality.

You may have to increase backwash

frequency. Also Consult Thermax.

c. Please do not cross unit max service

flow rate.

d. Check and ensure sufficient

pressure.

e. Check and ensure proper

segregated media layers

2 Backwash Frequency

Required is high

a. Inlet Suspended Solids load

increased

a. Check inlet water quality. You may

have to increase backwash frequency.

Also Consult Thermax.

3 Unit Rinse takes long time a. Flow rate too low

b. Improper Backwash

a. Adjust the flow rate to the normal

b. Give proper backwash as given in

OPERATION section till clear water is

observed.

4 Pressure Drop across bed

is increasing day by day

a. No or Insufficient backwash

b. Inlet Suspended Solids load

increased

a. Backwash filter regularly.

b. Check inlet water quality.

You may have to increase backwash

frequency. Also Consult Thermax.

5 Media comes out

from bottom outlet

a. Improper media charging at

the time of erection

b. Too much excessive backwash

flow rate/Pressure

c. The gap in collection box and dish

is more than 5 mm. ( This should

have been checked before

installation)

a. Remove and recharge media

properly

b. Always maintain backwash flow.

Too much backwash flow rate/

Pressure can disturb media layers.

c. Remove the entire media, adjust

the gap to 5 mm, segregate the media

by type and recharge the media.

TREATMENT PLANT


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4.5 MAINTENANCE (ACF)

The routine maintenance of the filters should include the following _

VALVES

At periodic intervals (say one month) open out the valves and check seating, gate, etc. Attend

to gland packing. Replace if necessary, do routine lubrication of spindle.

EXTENDED BACKWASH

Once in a week extend the backwash operation to at least 45 minutes to keep the bed clean.

AIR SCOURING AND CLEANING OF THE FILTER MEDIA

Once in six months, open the manhole and examine the condition of the media. Throw away

any lumps formed on the top of the bed. On units where no regular air scouring facilities are

provided, air scouring should be done as follows –

a. If compressed air supply is available, take a temporary tapping (say 1” hose).

Attach the hose to a M.S. pipe about 1 M long with water level inside vessel about 3“above the

level of the bed, insert the pipe into the bed till it is about halfway through. The media will be

seen getting violently agitated. Move the pipe all over the bed. Carry out the air scour for a

period of about 10 minutes.

b. Drain the water till the surface of the bed and scrape off any fine dust.

c. Close the manhole.

TREATMENT PLANT

DO’S AND DON’T’S

• Never exceed the filter service flow

• Analyses Inlet water for Turbidity regularly

• Always check Inlet water for Oil & Grease content. Don’t allow exceed the limit.

• Inlet Water Temp should not exceed 80 Deg.C

• Do annual Media Check up and replacement as required.

• Backwash the filter regularly as per Manual

• Never allow corrosive liquids to pass through the Filter.


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5. LABORATORY DETAILS

5.1 LABORATORY ANALYSIS

CONTENTS

1. pH

2. TURBIDITY

3. COLOUR

4. ELECTRICAL CONDUCTANCE

5. TOTAL DISSOLVED SOLIDS

6. SUSPENDED MATTERS

7. HARDNESS

8. SILICA

9. CHLORIDE

10. OILS AND GREASE

11. RESIDUAL CHLORINE

12. REAGENTS


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1. pH:

It is common practice to express hydrogen ion concentration in terms of pH. By definition the

pH is the negative logarithm of hydrogen ion concentration to the base of l0.

pH = ‐ log10 (H+) = log (1/H+)

Ionic product of water Kw has a value of 1 x 10 ‐ 14 and in neutral water H + concentration is

equal to OH ‐ concentration.

Kw = H + x OH‐ = 1 x 10‐ 14 ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ (1)

For neutral water = (H+) = (OH‐) = 1x10 ‐7

WATER TREATMENT PLANT The equilibrium represented by equation (1) occurs universally in aqueous solution regardless

of the equilibrium or the solutes present. Hence equation (1) should always be satisfied.

Thus the terms pH expresses the acidity or basicity of water. Neutral water has a pH of 7. pH

lower than 7 indicates acidity and greater than 7 is alkaline.

METHOD A – pH Indicator:

A pH indicator is a halochromic chemical compound that is added in small amounts to

solution so that the pH(acidity or basicity) of the solution can be determined visually. Hence a

pH indicator is a chemical detector forhydronium ions (H3O+) or hydrogen ions (H

+) in

the Arrhenius model. Normally, the indicator causes the colour of the solution to change

depending on the pH.

These commercial indicators (e.g., universal indicator and Hydrion papers ) are used when only

rough knowledge of pH is necessary.

METHOD B‐ PPH CELL ( pH Meter):

A pH meter is an electronic device used for measuring the pH (acidity or alkalinity) of a liquid

(though special probes are sometimes used to measure the pH of semi‐solid substances). A

typical pH meter consists of a special measuring probe (a glass electrode) connected to an

electronic meter that measures and displays the pH reading.

This is containing a pair of electrodes. The sample to be tested is poured into this cell. There are

many forms of cell.

There are several satisfactory commercial models. Operators, less they have adequate facilities,

would be well advised to purchase a readymade instrument.

http://en.wikipedia.org/wiki/Halochromismhttp://en.wikipedia.org/wiki/Chemical_compoundhttp://en.wikipedia.org/wiki/Chemical_compoundhttp://en.wikipedia.org/wiki/Chemical_compoundhttp://en.wikipedia.org/wiki/Solutionhttp://en.wikipedia.org/wiki/PHhttp://en.wikipedia.org/wiki/Acidhttp://en.wikipedia.org/wiki/Base_(chemistry)http://en.wikipedia.org/wiki/Chemicalhttp://en.wikipedia.org/wiki/Hydroniumhttp://en.wikipedia.org/wiki/Acid-base_reaction_theorieshttp://en.wikipedia.org/wiki/Acid-base_reaction_theorieshttp://en.wikipedia.org/wiki/Acid-base_reaction_theorieshttp://en.wikipedia.org/wiki/Colourhttp://en.wikipedia.org/wiki/Universal_indicatorhttp://en.wikipedia.org/wiki/Universal_indicatorhttp://en.wikipedia.org/wiki/Universal_indicatorhttp://en.wikipedia.org/wiki/Hydrion_paperhttp://en.wikipedia.org/wiki/Hydrion_paperhttp://en.wikipedia.org/wiki/Hydrion_paperhttp://en.wikipedia.org/wiki/PHhttp://en.wikipedia.org/wiki/Acidhttp://en.wikipedia.org/wiki/Base_(chemistry)http://en.wikipedia.org/wiki/Glass_electrodehttp://en.wikipedia.org/wiki/Glass_electrodehttp://en.wikipedia.org/wiki/Glass_electrodehttp://en.wikipedia.org/wiki/Glass_electrodehttp://en.wikipedia.org/wiki/Base_(chemistry)http://en.wikipedia.org/wiki/Acidhttp://en.wikipedia.org/wiki/PHhttp://en.wikipedia.org/wiki/Hydrion_paperhttp://en.wikipedia.org/wiki/Universal_indicatorhttp://en.wikipedia.org/wiki/Colourhttp://en.wikipedia.org/wiki/Acid-base_reaction_theorieshttp://en.wikipedia.org/wiki/Hydroniumhttp://en.wikipedia.org/wiki/Chemicalhttp://en.wikipedia.org/wiki/Base_(chemistry)http://en.wikipedia.org/wiki/Acidhttp://en.wikipedia.org/wiki/PHhttp://en.wikipedia.org/wiki/Solutionhttp://en.wikipedia.org/wiki/Chemical_compoundhttp://en.wikipedia.org/wiki/Halochromism


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2. TURBIDITY

OUTLINE OF

THE

METHOD

The sample is matched against standard suspensions of fullers earth in water.

TERMINOLOGY

For the purpose of this test, the following definition shall apply. Scale Unit ‐ Turbidity imparted

by 1 mg of fullers earth when suspended in 1000 ml of distilled water.

PREPARATION OF TURBIDITY STANDARDS

Mix slowly with constant stirring 5.000 g of fullers earth previously dried and shifted through 75

micron IS Sieve with distilled water and dilute it to 1000 ml. Agitate intermittently for one hour

and then allow to stand for 24 hours. Withdraw the supernatant liquid without disturbing the

sediment. Vaporate about 50 ml of the removed liquid, dry the residue at 105 + 2 Deg. C and

weigh the residue to determine the amount of clay in suspension. Prepare turbidity standards

with this standardized stock suspension with distilled water. A drop of saturated mercuric

chloride solution may be added as preservative. The standards are stable for three months.

PROCEDURE

Pour the sample after thorough shaking into a clear glass bottle of suitable capacity, say 1 lit.

Compare it with the turbidity standards contained in similar bottles, holding them against a

suitable background and using a source of light which illuminates them equally and is placed so

that no rays reach the eye directly. The sample and the standards shall be shaken

simultaneously immediately before comparison. If the sample has turbidity over 100 units,

dilute it with distilled water before testing and multiply the result with an appropriate factor.

NOTE Comparison of turbidity may also be done with the help of suitable instruments.


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3. COLOUR

OUTLINE OF THE METHOD

The colour of the sample is matched against a series of standards containing potassium

chloroplatinate and cobalt chloride.

TERMINOLOGY

For the purpose of this test, the following definitions shall apply:

True Colour Colour due to substances in solution, after removal of suspended matter.

Apparent Colour Colour due to substances which are in solution as well as in suspension.

Hazen Unit

Colour obtained in a mixture containing either on milligram of Patinum or

2.49 mg of potassium chloroplatinate along with 2 mg of cobalt chloride

(CoCl2.6H2O) in 1 litre of the solution.

APPARATUS

Nessler Tubes ‐ Flat‐bottom tube of thin colourless glass. Two types of tubes are required. The

longer tubes shall be 45 cm tall and 2.5 cm in internal diameter. The shorter tubes shall be 30

cm tall and 1.7 cm in internal diameter. Tubes of any one type shall be identical in shape, and

the depth measured internally from the graduation mark to the bottom shall not vary by more

than 2 mm in the tubes used.

REAGENTS

Platinum or Potassium Chloroplatinate Aqua Regia ‐ prepared by mixing one part by volume of

concentrated nitric acid (conforming to IS: 264‐1950) with three parts by volume of

concentrated hydrochloric acid (conforming to IS: 265‐ 1962). Cobalt Chloride‐Crystalline, with

the molecular composition CoCl2.6H2).

TREATMENT PLANT


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PROCEDURE

PREPARATION OF COLOUR STANDARDS

Dissolve 0.500 g of metallic platinum in aqua regia and remove nitric acid by repeated

evaporation to dryness on water bath after addition of excess of concentrated hydrochloric

acid (conforming to IS:265‐1962). Dissolve the residue with 1.0 g of cobalt chloride in 100 ml of

concentrated hydrochloric acid to obtain a bright solution, if necessary by warming. Dilute the

solution to 1000 ml with distilled water. This stock solution has a colour of 500 Hazen units. A

more convenient way of preparing the same solution is by dissolving 1.245 g of potassium

chloroplatinate and 1.0 g of cobalt chloride in distilled water and diluting to 1 litre. Prepare a

set of colour standards having colour 5, 10, 15, 20, 25, 30, 35, 40, 50, 60 and 70 Hazen units by

diluting the stock solution with water. Protect these colour standards from evaporation and

contamination when not in use. The colour standards shall be freshly prepared for each

determination. But in routine practice, they may be used repeatedly, provided they are

protected against evaporation and contamination when not in use.

PROCEDURE FOR CLEAR SAMPLES

For samples having turbidity under 5 mg/l, match the colour of the sample against the standard

colours in the longer Nessler Tubes. Fill the tubes to mark and compare the colour by looking

vertically downwards against a pure white surface. If the colour is found to exceed 70 units,

dilute the sample with distilled water before comparison and multiply the result by appropriate

factor. As matching is very difficult when the colour of the sample is below 5 Hazen units,

report the colour as less than 5 Hazen units in such cases. When the colour of the sample

exceeds 30 Hazen units, the comparison may, if desired, be made in the shorter Nessler tubes.

TREATMENT PLANT

PROCEDURE FOR TURBID SAMPLES

If the sample has turbidity over 5 mg/l it becomes impossible to measure the true colour

accurately by the method prescribed in PROCEDURE for clear samples and if an attempt is

made, the value found shall be reported as "apparent colour". In the presence of turbidity, the

true colour shall be determined after centrifuging. The sample shall be centrifuged until the

supernatant liquid is clear. The centrifuged clear sample shall be compared by the method

prescribed in PROCEDURE for clear samples.


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NOTE

For estimating true colour, filter paper shall not be used since that leads to erroneous results.

REPORT

The results of colour determination shall be excess in whole numbers and shall be recorded as

follows:

Hazen Units

Less than 5 Reports as "Less than 5 Hazen Units"

5 to 50 Reports to the nearest 1 Hazen Unit




NOTE

The colour determination shall be made as early as possible after the collection of samples as

certain biological change occurring in storage may affect the colour.


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4. ELECTRICAL CONDUCTANCE

GENERAL

The unit of conductance is the mho or reciprocal ohm. Specific conductivity is the conductance

at a specified temperature across a column of a liquid 1 cm2

in area and 1 cm long, and is

expressed mhos per centimeter. This is an inconveniently large unit for water testing and it is

usual to use the micromho per centimeter known as the "dionic unit", which is one‐millionth

part of a mho per centimeter.

APPARATUS

Several kinds of apparatus are available. They generally consist of two parts.

CONDUCTIVITY CELL

This is containing a pair of electrodes. The sample to be tested is poured into this cell. There are

many forms of cell. One of the most convenient types is provided with a funnel for filling, a

drain for emptying, and an overflow for maintaining constant level. Electrodes for use with

samples having very low dissolved solids (such as condensates) should not be coated with

platinum black. Platinum black which has been heated to redness until it is grey is suitable.

Bright platinum or gold or heavily gold plated electrodes may be used. Some instruments are

designed to work with particular form of conductivity cell, and are then calibrated directly in

conductivity units.

Other instruments, primarily introduced for more general application, are calibrated on

conductance units and their readings require multiplication by a factor known as the "cell‐

constant" which shall be determined by experiment. Measuring Instrument ‐For measuring the

electrical conductance (or the resistance which is the inverse of conductance) between the

electrodes of the cell. There are several satisfactory commercial models. Operators, less they

have adequate facilities, would be well advised to purchase a readymade instrument.

TREATMENT PLANT


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PROCEDURE

Determine the cell constant if necessary, either directly with a standard potassium chloride

solution (say 0.002 N) or by comparison with a cell the constant of which is known accurately.

(In the latter case, the concentration and nature of the electrolytes in the liquid which is used

for the comparison should be the same and should be similar respectively to those of the

liquids with which the cell is likely to be used in practice). Use some of the samples to wash out

the conductivity cell thoroughly. Fill the conductivity cell with the sample.

Calculations

FOR INSTRUMENT READING RESISTANCE :

1 x 106

Electrical conductance, in dionic units (or micromhos per centimetre) =

rk

Where r = Resistance in ohms, and k = Cell constant

FOR INSTRUMENT READING CONDUCTANCE :

Electrical conductance, in dionic units (or micromhos per centimetre) = ck

Where

c = conductance in micromhos, and k = cell constant

CORRELATION OF ELECTRICAL CONDUCTANCE TO TOTAL DISSOLVED SOLIDS

For water containing a given mixture of mineral salts, the electrical conductance is closely

proportional to the dissolved solids. When the samples are known to be free from wide

fluctuation in mineral content, the electrical conductance offers a quick means of computing

the total dissolved solids.

Electrical conductance

Dissolved Solids

TREATMENT PLANT


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5. TOTAL DISSOLVED SOLIDS (TDS)

A well mixed filtered sample is evaporated in a weighed dish and dried to constant weight in an

oven at 103 to 105 Deg. C. The increase in weight over that of the empty dish represents the

total residue.

APPARATUS

1. Silica or porcelain dish of 100 ml capacity

2. Desicator

3. Oven

PROCEDURE

Ignite the clean evaporating dish at 550 + 50 Deg. C for 1 hour. Cool, desiccate and weigh.

Transfer the measured sample to the pre weighed dish and evaporate to dryness on a steam

bath. Choose a sample volume that will yield a minimum residue of 25 mg to 250 mg. If

necessary, add successive portions of sample to the same dish. Dry the evaporated sample for

at least 1 hour at 103 to 105 Deg.C. Cool the dish in a desiccators and weigh. Repeat the cycle

of drying, cooling and weighing until a constant weight is obtained.

Calculations

Wt of residue x 1000

Total dissolved solid, mg/L =

ml. of sample taken


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6. SUSPENDED MATTERS

Suspended matter is the material retained on filter after filtration of a well mixed sample of

water. The residue is dried at 103 to 105 Deg. C.

APPARATUS

1. Gooch crucible

2. Silica or porcelain evaporating dish of 100 ml capacity

3. Desiccators

4. Oven adjustable to constant temp of 103 ‐105 Deg. C.

5. Water batch

PROCEDURE

Prepare a gooch crucible with asbestos (20 to 30 ml of 0.5% suspension of gooch asbestos

added and washed under suction), dry and ignite at 500 Deg. C for at least 30 minutes, cool and

weigh. Filter a suitable volume of the well mixed sample through the crucible. Wash with

distilled water, dry at 105 Deg. C for one hour.

Weigh.

Calculations

W x 106

Suspended matters in mg/L =

V

Where,

w = wt. in g of the suspended matter

V = vol. in ml. of the sample taken for filtration

NOTE

If Gooch Crucible is not available, standard "Whatman" filter paper may be used.


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7. HARDNESS

Hardness in water is due to the presence of bicarbonates, chlorides and sulphates of calcium

and magnesium. Temporary hardness is due to the presence of bicarbonates and permanent

hardness due to the presence of chlorides and sulphates. Sometimes, hardness may include

iron, aluminum, zinc, manganese, etc.

METHOD A ‐ OMPLEXAMETRIC METHOD (EDTA METHOD)

EDTA forms a chelated soluble complex when added to a solution of certain metal ions. If a

small amount of EBT is added to an aqueous solution containing calcium and magnesium ions

at pH of 10.0 + 0.1, the solution will become red wine. If EDTA is then added as a titrant, the

calcium and magnesium will be complexes. After sufficient EDTA has been added to complex all

the calcium and magnesium, the solution will turn blue from red wine.

REAGENTS

1. Ammonia buffer of pH 10.

2. M solution of disodium salt of ethylenediamine tetra acetic acid.

3. Eriochrome black T indicator solution.

PROCEDURE

Take 50 ml of sample in an Erlenmeyer flask; add 4 to 6 drops of Eriochrome black T indicator

solution. Add 1 ml of buffer solution and mix. Titrate immediately with EDTA solution till the

colour changes from red to blue.

Calculations:

Total hardness as CaCO3 mg/lit = Vol. of 0.01 M EDTA solution x 1000 ml of sample

ATER TREATMENT PLANT

NOTE

For checking hardness in soft water use 500 ml of the sample into 750 ml evaporating dish and

add 3 ml of buffer solution followed by 10‐12 drops of indicator solution.


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METHOD B

SOAP SOLUTION METHOD FOR HARDNESS TESTING

This is a quick method for checking hardness of treated water or an accurate determination of

the hardness of treated water, EDTA method for hardness should be used.

REAGENTS

1. “B” soap solution

2. 40 ml shaking bottle

PROCDURE

Take water sample up to 40 ml mark in shaking bottle. Add 10 drops of the "B" soap solution.

Shake vigorously. If lather is obtained which will last for 1 to 2 minutes, the water is soft. If no

lather is obtained, or if the lather does not last, the water is hard.

NOTE

1. Rinse the shaking bottle clean with soft water thoroughly.

2. The soap solution bottle should be kept tightly stoppered. It will otherwise evaporate and

give false reading.


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CALCIUM HARDNESS

The water sample is titrated against EDTA solution using Murexide indicator (ammonium

purpurate) in highly alkaline medium.

REAGENTS

1. Approximately 1 N sodium hydroxide solution

2. 0.01 M standard EDTA solution

3. Murexide indicator

PROCEDURE: Prepare a colour comparison blank in a white porcelain basin by stirring 2.0 ml of

1 N. NaOH, 0.2 g solid indicator mixture (or 4 to 6 drops of indicator solution) into 50 ml of

distilled water and sufficient EDTA titrant (0.05 to 0.1 ml) to produce an unchanging purple

colour. Pipette into a similar basin 50 ml. of sample, neutralize the alkalinity with 0.02 N. HCl,

boil for 2 to 3 minutes to expel the CO2 and cool to room temperature. Add 2.0 ml 1 N NaOH, or

a volume sufficient to produce a pH of 12 to 13 and mix. Add 0.2 g of powdered indicator.

Stirring constantly titrate with standard EDTA solution to the colour of comparison blank. Check

the end point by adding 1 or 2 drops of titrant in excess to be sure that no further deepening of

the purple colour takes place.

Calculations

Calcium, as CaCO3, mg/L = (A ‐) x C x 1000 ml of Sample

Where A = ml of EDTA required for titration of sample

B = ml of EDTA required for blank

C = mg of CaCO3 equivalent to 1.0 ml of EDTA

NOTE: The only serious interference with the EDTA titrant of calcium is that of orthophosphate

ion. If the calcium hardness exceeds about 60 ppm CaCO3, and the concentration of

orthophosphate is 10 ppm, or more, calcium phosphate is precipitated when the pH is raised to

12, giving low results.

Phosphate, if present, can be removed by ion exchange. WATER TREATMENT PLANT


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8. SILICA

The silica content of natural water will vary to a considerable extent depending on the locality.

The presence of silica is particularly objectionable in water used for boiler feed purpose as it

may lead to the formation of hard dense scale. In addition, a very serious problem encountered

in high pressure operations is the deposition of siliceous materials on turbine blades & super

heaters. The gravimetric method is the standard applicable above 20 mg / lit SiO2 content. This

method should be followed for standardization of standard silicate solution used in colorimetric

methods. The heteropoly blue colorimetric method is adaptable for the range of 0 to 2 mg / lit

SiO2 & yellow molyb silicate method in the range of 0 to 20 mg / lit. Reagent blank should

always be used in all the three methods.

METHOD A ‐ GRAVIMETRIC METHOD

PROCEDURE

Take a sample to contain at least 10 mg of SiO2 . If necessary clarify by filtration. Acidify with 2

or 3 ml of conc. HCl & evaporate to dryness in a platinum dish on a water bath. At regular

intervals add 2 or more portions of 2 to 3 ml of conc. HCl as an additional quantity of sample is

added to the dish. Bake the evaporated residue in an oven ad 110 Deg. C for about an hour.

Add 5 ml. of conc. HCl warm & add 50 ml distilled water. Loosen the clinging residue from the

sides & the bottom of the dish & filter collecting the filtrate. Wash the dish & residue with hot

1 : 50 HCl & finally with distilled water until the washings are free from chloride. Return the

filtrate & washings to the platinum dish & again evaporate to dryness. Repeat as previously,

collecting the residue in another filter paper. Dry the two filter papers with residue, burn, ignite

at 1000‐1200 Deg.C in a platinum crucible & weigh. Moisten the residue with a few drops of

distilled water; add 2 drops of H2SO

4 & 10 ml. 48% HF. Cautiously evaporate to dryness on a

steam bath in a fume cupboard. Again ignite at 1000‐1200 Deg.C Cool & weigh. Carry out a

blank.


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Calculations

( A ‐ B ) ‐ ( C ‐ D ) x 1000 SiO2 , as SiO2 mg / lit = ml of sample

Where A = Weight of crucible & sample residue in mg. after first ignition

B = Weight of crucible & sample residue in mg. after HF treatment & second ignition.

C = Weight of crucible & blank residue in mg. after first ignition

D = Weight of crucible & blank residue in mg. after HF treatment & second ignition.

METHOD B ‐ REACTIVE SILICA

COLOMETRIC ESTIMATION OF SILICA

Ammonium molybdate at approximately pH 1.2 reacts with silica & any phosphate present to

produce hteropoly acids. Oxalic acid is added to destroy the molybdophosphoric acid but not

the molybdosilicic acid. Even if phosphate is known to be absent, the addition of oxalic acid is

highly desirable & is a mandatory step. The intensity of the yellow colour is proportional to the

concentration of molybdate‐ reactive silica. The yellow molybdosilicic acid is reduced by means

of 1 Amino ‐ 2‐ naphthol ‐ 4 ‐ sulphonic acid to heteropoly‐ blue. The blue colour is more

intense than the yellow colour & provides increased sensitivity. In at least one of its forms ,

silica does not react with molybdate even though it is capable of passing through filter paper &

is not noticeable turbid. The presence of such a molybdate unreactive silica is undesirable in

raw water .It will not be removed in the water treatment plant & will find its way to highly

pressure stream system, where it will be converted to “molybdate‐reactive " silica. Such

increase in silica content will give rise to scale problem.

PLANT

Chromate & large amounts of Fe, PO4, sulphide, tannin, colour & turbidity are potential

interferences. Oxalic acid treatment suppresses PO4

& reduces tannin interference. Inorganic

sulphide can be removed by boiling an acidified sample. The addition of 1 ml. of 1% EDTA

solution after molybdate reagent overcomes high Fe & Ca concentrations.


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COLOMETRIC ESTIMATION OF SILICA 0‐2 PPM SiO2

REAGENTS

1. Acidified ammonium molybdate solution.

2. 10 % oxalic acid.

3. Amino ‐naphthol reducing agent.

4. Lovibond comparator with standard silica disc or spectrophotometer suitable for

measurement at 815 micro siemens wave length.

PROCEDURE

1. Fill one of Nessler tubes to the 50 ml. Mark with sample, & place in the left hand

compartment of Lovibond comparator.

2. Fill the other Nessler tube with 50 ml. of sample, at 25 ‐30 Deg.C. Add 2 ml. of acidified

ammonium molybdate solution. Mix thoroughly, stand for 5 minutes. Add 4 ml of oxalic acid &

mix well. Then 2 ml. of reducing agent, mix well compared with that of a blank comprising the

same water without reagents, using Lovibond comparator or read the absorbance using a

spectrophotometer (wave length 815 micro siemens). Compute the silica content from the

standard graph prepared from the standard silica solution.

TREATMENT PLANT


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METHOD C :

DETERMINATION OF TOTAL SILICA (MOLYBDATE REACTIVE & UNREACTIVE SILICA)

The molybdate unreactive silica is converted to the reactive form or state by digesting the

sample with sodium bicarbonate.

REAGENTS

1. Sodium bicarbonate.

2. 1 N sulphuric acid.

3. Other reagents as per previous method.

PROCEDURE

Take 100 ml. of sample or lesser quantity ( 20 ‐ 100 micrograms SiO2 ) but made up to 100 ml.

distilled water in a platinum dish. Add 200 mg. of silica free sodium bicarbonate & digest on a

stream bath for one hour. Cool & add slowly, with stirring, 2.5 ml. sulphuric acid ( 1 N ) . Do not

interrupt the analysis but proceed at once with the remaining steps. Transfer quantitatively

into a plastic container. For development of colour & CALCULATIONS refer the previous

procedure.

TREATMENT PLANT


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9. CHLORIDE

METHOD A ‐ SILVER NITRATE METHOD

Chloride is determined by titration with std. silver nitrate solution in the presence of potassium

chromate indicator at neutral Ph. Silver chloride is precipitated and at the end point red silver

chromate is formed.

REAGENTS

1. N Std. silver nitrate solution

2. Potassium chromate indicator

3. Phenolthalein Indicator solution

4. N Nitric Acid solution

5. Calcium carbonate

PROCEDURE

Take 50 ml. or 100 ml of sample in an Erlenmeyer flask. Add five drops of phenolthalein. If the

sample turns pink, Neutralize with 0.02 N Nitric acid. If Acidic (as in the case of decationised

water) add a small amount of A.R. calcium carbonates. Add 1 ml of potassium chromate

indicator and titrate with std. silver nitrate solution wi

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