WATER and BASICS OF CORROSION

The pH value of boiler feed water plays very important role in controlling the corrosion. To understand the importance of pH value for controlling the corrosion it is necessary to know little about electro chemical corrosion.

ELECTROCHEMICAL THEORY OF CORROSION; Each substance even metals dissolve in water to a certain extent like sugar and salt . No doubt the amount of dissolved substance required for saturation varies considerably according to the nature of the substance. A limited amount of any given substance dissolved in water no matter how much the substance is added.

All metals also tend to dissolve in water to a certain extent according to electrochemical theory. Water in contact within iron dissolves very small quantity of iron into solution. The water quickly becomes saturated with iron which stops further dissolving. The dissolved iron remains in different conditions from that in the solid metallic state . Every iron particle going into solution takes on an electric charge and is known as ferrous ion.



Fe(metallic state) = Fe ++ (Ferrous ion when goes into solution)



Water 9in natural condition also ionizes to a very small extent and forms positive H2 ions and negative hydroxyl OH _ as given in the following equation





H2O = H(+ ) + OH( -)



The ferrous ions combine with negatively charged Hydroxyl ions to form ferrous hydroxides.



Fe ++ + 2 OH - = Fe (OH) 2 (ferrous hydroxide)



The dissolved oxygen in water oxidizes formed ferrous hydroxides to ferric hydroxide as given by the following equation



4 Fe(OH) 2 + O2 + 2 H2O = 4 Fe(OH)3 ( insoluble ferric hydroxide)

The formed ferric hydroxides is much less soluble than the ferrous hydroxides and tend to precipitate. This in turn allow s more iron to go into the solution.



The another important role is played by excess hydrogen ions that form on the metal surface to accelerate corrosion. Hydroxil ions form the water unite with the ferrus ions and hydrogen ions are left free in the water as given by the following chemical equation



Fe++ + 2 HOH = Fe(OH)2 + 2H+



These excess hydrogen ions form a protective coating over thye metallic surface and tend to prevent further solution of metallic ions. The dissolved oxygen in the water also tends to combine with free excess hydrtogen ions and forms water

Therefore the dissolved oxygen also removes the protective layer of hydrogen ions and allows more iron to dissolve in the water.

The above explained electrochemi9cal theory of corrosion states that the corrosion is controlled by the free Hydrogen ions present in water. Higher hydrogen content means increased acidity. The acidic or alkaline nature of water is also responsible for the corrosion .





pH and its role in corrosion

The pH is a number denoting the degree of acidity or alkalinity of a substance. It does not indicated the quantity of acid or alkaline as found by titration method. It is derived by measuring the amount of Hydrogen ion (H+) in grams per liter of solution.



For example Pure water ionizes to produce ( 10 -7) grams of H2 ions per liter. Therefore any substance producing 10( -7) grams of Hydrogen ions per liter considered to be neutral solution.

The greater the amount of Hydrogen ions present in solution its acid reaction becomes stronger. Therefore pure water being neutral solution any solution producing more hydrogen ions than pure water will be acidic and degree is governed by the difference.

Other solution producing less hydrogen ions than pure water will be alkaline and the degree is also governed by the difference.

The law of mass action in mass dissociations is OH (-) + H(+) = 10 (- 14)

The pH value of water is the logarithm of the reciprocals of Hydrogen ion concentration. It is numbered from 0 to 14 indicating 7 for neutral water. As the pH is a logarithmic function solution having a pH as 6, 5 or 4 are respectively 10 ,100, 1000 times more acidic than one with pH value as 7



THE ROLE OF pH in CORROSION OF METALS

The role of pH in corrosion of metals is extremely important . The corrosion rate of iron in the absence of oxygen is proportional to pH up to a value of 9.6. At this point hydrogen gas formations and dissolving of iron practically stops . This is the same pH produced by a saturated solution of Ferrus Hydroxide ( Fe(OH)2.

Alkalinity adjustment and film formation are closely related. The pH value of feed water should be maintained greater than 9.6 to reduce the corrosion effects caused by the reason. Film formation occurs when the alkalinity is kept in the desired range The simplest film is composed of the iron hydroxide initially formed on the metal surface . As long as the alkalinity is high the iron hydroxide remains insoluble and acts as a protective layer.

FLUE GAS ANALYSIS BY VOLUME : ORSAT APPARATUS

Orsat apparatus is a very convenient apparatus for analysing the flue gas on the spot asnd by proper handling gives accuracy upto +- 0.5% of the CO2 content. Many types of this apparatus for analysing the volumetric composition  of a mixture of gases are available . In its simplest form the apparatus is arranged for determining the volumetric composition of the flue gases containing  CO2, CO, O2 and N2 by difference .  Fig showws a three bulb Orsat apparatus . A is a water jacketed eudiometer graduated upto 100 cc. The base of the eudiometer is connected by a fle4xible rubber pipe to an aspirator bottle B. purpose of the aspirator bottle is to charge or discharge the eudiometer.

The flasks 1.2.3 with duplicate flasks behind them contain respectively the solutions of caustic potash ( KOH)   ( one paret of KOH to 2 part of water by weight) for absorbing CO2. alkaline solution of pyrogalic acid ( 5 grams of pyrogalic acid in 15 cc of water mixed with 120 grams of KOH in 80 cc of water) for absorbing O2 and Cuprous Chloride ( CuO dissolved in twenty times its weight of concentrated HCl acid with copper wire immersed till it becomes colorless for absorbing CO.

In order to accelerate absorbtion of the gases in flasks 1 2 3 they are packed with small glass tubes.wetted surfaces of the glass tubes are bare  by raising the aspirator bottle and opening the cock communicating with a particular flask. The gas sample is introduced in the flask and is protected from reaction with atmosphere by a film of oil.

Testing procedure
To start with it is to be ensured the the chemicals reagents in the flasks are freshly prepared water is filled in the Eudiometer jacket  Salt water is filled in the Aspirator Bottle  B .
Three Way Cock  D is opened to the atmosphere and the aspirator bottle is raised to fill the eudiometer
(Send a mail  at kaacconsultant@gmail.com   for detail)

kaaccentre Q&A students ask at kaacconsultant@gmail.com

2. What do you mean by following items?


i. )ISLB-400 ii) ISMB-600 iii) ISHB-350 iv) ISMC-300 v) ISJB-150 vi) ISLB-200

vii)ISMB-450 viii)ISWB-400 ix) ISJC-200 x) ISLC-350 xii) ISMC-250

Answer:

i. Indian STD light weight beam, Web size – 400

ii. Indian STD medium weight beam, Web size – 600

iii. Indian STD ‘H’ beam, Web size – 350


students ask at   kaacconsultant@gmail.com    get answer

iv. Indian STD medium weight channel, Web size –300

v. Indian STD junior beam, Web size – 150

vi. Indian STD light weight beam, Web size – 200

vii. Indian STD medium weight beam, Web size – 450

viii. Indian STD wide flange beam, Web size – 400

ix. Indian STD junior channel, Web size – 200

x. Indian STD light weight channel, Web size – 350

xi. Indian STD medium weight channel, Web size – 250



3. What is this item?

i. ISA-100X100X12     ii) ISA-80X50X10       iii)ISLT-100X100

Answer:

i. Equal angle size 100x12 THK

ii. Unequal angle size 80x50x10 THK

iii. Indian STD light weight tee bar size 100x100


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ION EXCHANGE PROCESS

Basic ion exchange processes


in water treatment

Introduction

The ion exchange technology is used for different water treatment applications:



•Softening (removal of hardness)

•De-alkalisation (removal of bicarbonate)

•Decationisation (removal of all cations)

•Demineralisation (removal of all ions)

•Mixed bed polishing

•Nitrate removal

•Selective removal of various contaminants

Natural water contains calcium and magnesium ions (see water analysis) which form salts that are not very soluble. These cations, together with the less common and even less soluble strontium and barium cations, are called together hardness ions. When the water evaporates even a little, these cations precipitate. This is what you see when you let water evaporate in a boiling kettle on the kitchen stove.


Hard water also forms scale in water pipes and in boilers, both domestic and industrial.  Calcium salts deposit on the glasses in your dishwasher if the city water is hard and you have forgotten to add salt.

Strongly acidic cation exchange resins (SAC, see resin types) used in the sodium form remove these hardness cations from water. Softening units, when loaded with these cations, are then regenerated with sodium chloride (NaCl, table salt).

Reactions



Here the example of calcium:


2 R-Na + Ca++   =   R2-Ca +   2 Na+



R represents the resin, which is initially in the sodium form. The reaction for magnesium is identical.



The above reaction is an equilibrium. It can be reversed by increasing the sodium concentration on the right side. This is done with NaCl, and the regeneration reaction is:



R2-Ca + 2 Na+ 2 R-Na + Ca++



What happens to the water

Raw water SAC (Na)

Softened water

The water salinity is unchanged, only the hardness has been replaced by sodium. A small residual hardness is still there, its value depending on regeneration conditions.

Uses



Examples for the use of softeners:



•Treatment of water for low pressure boilers

•In Europe, most dishwashers have a softening cartridge at the bottom of the machine

•Breweries and soft drink factories treat the water for their products with food grade resins

Softening the water does not reduce its salinity: it merely removes the hardness ions and replaces them with sodium, the salts of which have a much higher solubility, so they don't form scale or deposits.

De-alkalisation

This particular process uses a weakly acidic cation resin. This resin type is capable of removing hardness from water when it also contains alkalinity. After treatment, the water contains carbon dioxide, that can be eliminated with a degasifier tower. The cation resin is very efficiently regenerated with an acid, usually hydrochloric acid.



Reactions



Here the example of calcium:



2 R-H + Ca++(HCO3–)2  =    R2-Ca + 2 H+ + 2 HCO3–



and the hydrogen cations combine with the birarbonate anions to produce carbon dioxide and water:



H+ + HCO3–   =    CO2 + H2O


What happens to the water


Raw water WAC (H)



Decarbonated water

Recombination of hydrogen and bicarbonate and removal of carbon dioxide with the degasifier:



Decarbonated water DEG


Degassed water

The salinity has decreased. Temporary hardness is gone.



Uses

De-alkalisation is used:



•In breweries

•In household drinking water filters

•For low pressure boilers

•As a first step before the SAC exchange in demineralisation

De-alkalisation reduces the salinity of water, by removing hardness cations and bicarbonate anions.

Decationisation

The removal of all cations is seldom practiced, except as a first stage of the demineralisation process, or sometimes in condensate polishing where the decationiser precedes a mixed bed unit. A strongly acidic cation exchange resin (SAC) is used in the H+ form.



Reactions



Here the example of sodium, but all cations react in the same way:



R-H + Na+   =   R-Na + H+


The equilibrium reaction is reversed for regeneration by increasing the hydrogen concentration on the right side. This is done with a strong acid, HCl or H2SO4:



R-Na + H+ =   R-H + Na+



What happens to the water





Raw water SAC (H)



Decationised water DEG



Decat + degassed water



In the second step, a degasifier is used again to remove the carbon dioxide formed by combining the bicarbonate anions and the released hydrogen cation. The water salinity is reduced, and the water is now acidic. A small sodium leakage is shown.





Demineralisation

For many applications, all ions in the water must be removed. In particular, when water is heated to produce steam, any impurity can precipitate and cause damage. As there are cations and anions in the water, we must use two different types of resins: a cation exchanger and an anion exchanger. This combined arrangement produces pure water, as presented in the general introduction. Demineralisation is also called deionisation. The cation resin is used in the hydrogen form (H+) and the anion resin in the hydroxyl form (OH–), so that the cation resin must be regenerated with an acid and the anion resin with an alkali.



A degasifier is used to remove the carbon dioxide created after cation exchange when the water contains a significant concentration of bicarbonate.



The cation resin is usually located before the anion resin: otherwise if the water contains any hardness, it would precipitate in the alkaline environment created by the OH— form anion resin as Ca(OH)2 or CaCO3, which have low solubility.



Layout SAC – (DEG) – SBA

Let us first consider a simple deminineralisation system comprising a strong acid cation exchange resin in the H+ form, a degasifier (optional) and a strong base anion exchange resin in the OH– form. The first step is decationisation as shown above:

RSAC-H + Na+ RSAC-Na + H+



With calcium insead of sodium (also valid for magnesium and other divalent cations):



2 RSAC-H + Ca++ (RSAC)2-Ca + 2 H+



In the second step, all anions are removed with the strong base resin:



RSBA-OH + Cl– RSBA-Cl + OH–



The weak acids created after cation exchange, which are carbonic acid and silicic acid (H2CO3 and H2SiO3) are removed in the same way:



RSBA-OH + HCO3– RSBA-HCO3– + OH–



And finally, the H+ ions created in the first step react with the OH– ions of the second step to produce new molecules of water. This reaction is irreversible:



H+ + OH– H2O



What happens to the water



Cation exchange (as in the decationisation process above):



Raw water SAC (H)



Decationised water DEG



Decat + degassed water

Anion exchange:



Decat + degassed water SBA (OH)



Demineralised water



Demineralised water is completely free of ions, except a few residual traces of sodium and silica, because the SAC and SBA resins have their lowest selectivity for these. With a simple demineralisation line regenerated in reverse flow, the treated water has a conductivity of only about 1 µS/cm, and a silica residual between 5 and 50 µg/L depending on the silica concentration in the feed and on regeneration conditions.



Regeneration



The SAC resin is regenerated with a strong acid, HCl or H2SO4:



R-Na + H+ =    R-H + Na+



And the SBA resin is regenerated with a strong alkali, NaOH in 99 % of the cases:



RSBA-Cl + OH– ==   RSBA-OH + Cl–



Layout WAC/SAC – DEG – WBA/SBA

Because weakly acidic and weakly basic resins offer a high operating capacity and are very easy to regenerate, they are used in combination with strongly acidic and strongly basic resins in large plants. The first step with the WAC resin is dealkalisation (removal of bicarbonate hardness), and the second step with the SAC removes all the remaining cations. A WAC resin is used when both hardness and alkalinity are present in large relative concentrations in the feed water.

WBA resins remove only the strong acids after cation exchange. They are not capable of removing the weak acids such as SiO2 and CO2. In the regenerated, free base form, they are not dissociated, so no free OH– ions are available for neutral anion exchange. On the other hand, their basicity is enough to adsorb the strong acids created after cation exchange:



RWBA + H+Cl– =   RWBA.HCl

In the last step, a SBA resin is thus required to remove the weak acids, as shown in the preceding section:

RSBA-OH + HCO3–  =  RSBA-HCO3– + OH–

What happens to the water

Cation exchange beginning with dealkalisation followed by the removal of all remaining cations:

Raw water WAC (H)

Decarbonated water SAC (H)

Decationised water

Anion exchange begins with the removal of strong acids after degasification:

Decat + degassed water WBA (FB)

Partially demineralised SBA (OH)

Demineralised water

A full demineralisation line is shown below, with a cation exchange column (WAC/SAC), a degasifier, an anion exchange column (WBA/SBA) and a polishing mixed bed unit. The use of a weakly acidic resin and the degasifier column are conditioned by the presence of hardness and alkalinity in the feed water, as explained in the previous sections.





A demineralisation line (click to enlarge)

Regeneration



Regeneration is done in thoroughfare, which means that the regenerant first goes through the strong resin, which requires an excess of regenerant, and the regenerant not consumed by the strong resin is usually sufficient to regenerate the weak resin without additional dosage.



The cation resins are regenerated with a strong acid, preferably HCl, because H2SO4 can precipitate calcium.

The anion resins are regenerated with caustic soda.





Regeneration of the demineralisation line (click to enlarge)

The quality obtained is the same as in the simple SAC-SBA layout, but because the weak resins are practicallly regenerated "free of charge", the regenerant consumption is considerably lower. Additionally, the weak resins have a higher operating capacity than the strong resins, so the total volume of ion exchange resins is reduced.



Uses



Examples of demineralisation:



•Water for high pressure boilers in nuclear and fossil fuelled power stations and other industries

•Rinse water used in production of computer chips and other electronic devices

•Process water for many applications in the chemical, textile and paper industries

•Water for batteries

•Water for laboratories



Mixed bed polishing


Mixed bed unit in service

and in regenerationThe last traces of salinity and silica can be removed on a resin bed where highly regenerated strong acid cation and strong base anion resins are mixed.

Mixed bed units deliver an excellent treated water quality, but are complcated to regenerate, as the resins must first be separated by backwashing before regeneration. Additionally, they require large amounts of chemicals, and the hydraulic conditions for regeneration are not optimal. Therefore, mixed beds are usually only used to treat pre-demineralised water, when the service run is long.



What happens to the water



Practically nothing is left:



Demineralised water SAC (H) + SBA (OH)



Nothing is left



Mixed bed polishing produces a water with less than 0.1 µS/cm conductivity. With sophisticated design, the conductivity of pure water (0.055 µS/cm) can be achieved. Residual silica values can be as low as 1 µg/L.



Uses



•Treatment of water pre-demineralised with ion exchange resins

•Polishing of reverse osmosis permeate

•Polishing of sea water distillate

•Treatment of turbine condensate in power stations

•Treatment of process condensate in various industries

•Production of ultra-pure water for the semiconductors industry



Nitrate removal

Nitrate can be removed selectively from drinking water using strong base anion resins in the chloride cycle, i.e. regenerated with a NaCl brine. The reaction is:



RSBA-Cl + NO3– = RSBA-NO3 + Cl–

What happens to the water

Raw water SBA (Cl)

Denitrated water



Conventional SBA resins can be used, but they also remove sulphate from water. See the selectivity table. Depending on the resin type, some (selective resins) or all (non-selective) sulphate is removed. Bicarbonate is only removed partially at the beginning of the service run.



Uses



•Treatment of water pre-demineralised with ion exchange resins

•Polishing of reverse osmosis permeate

•Polishing of sea water distillate

•Treatment of turbine condensate in power stations

•Treatment of process condensate in various industries

•Production of ultra-pure water for the semiconductors industry



Selective removal of various other contaminants

Selective removal of metals and other contaminants is mainly used for drinking water and for waste. Many of these applications require special resins: chelating resin making stable metal complexes, for instance.



Examples



•Removal of boron (boric acid) from drinking water

•Removal of nitrate from drinking water (shown above)

•Removal of perchlorate from drinking water

•Removal of heavy metals from waste: Cd, Cr, Fe, Hg, Ni, Pb, Zn

In many of these applications, a residual concentration in the µg/L range is possible.

Some contaminants are difficult to remove with ion exchange, due to a poor selectivity of the resins. Examples: As, F, Li. See the periodic system of the elements with some ion exchange data. See also the page about resin types (selective resins) and a separate page about ion exchange processes for drinking water.





Other information

Abbreviations

Resin types are usually abbreviated in these pages:



•SAC: strongly acidic cation exchange resin

•WAC: weakly acidic cation exchange resin

•SBA: strongly basic anion exchange resin

•WBA: weakly basic anion exchange resin

See a table with a complete list of abbreviations and units.

Water

See details about the water analysis as required for the above processes.



Ion exchange columns

Various column types are described in a separate page.



Regeneration

See details about regeneration processes, quantities and concentrations of regenerants.



Ion exchange reactions

A full page describes reaction equilibrium and chemical reactions of these resins.



--------------------------------------------------------------------------------

Ion-Exchange


The Process of Ion-exchange

In the context of water purification, ion-exchange is a rapid and reversible process in which impurity ions present in the water are replaced by ions released by an ion-exchange resin. The impurity ions are taken up by the resin, which must be periodically regenerated to restore it to the original ionic form. (An ion is an atom or group of atoms with an electric charge. Positively-charged ions are called cations and are usually metals; negatively-charged ions are called anions and are usually non-metals).



The following ions are widely found in raw waters:



Cations                                                                                             Anions



Calcium (Ca2+)                                                                         Chloride (Cl-)

Magnesium (Mg2+)                                                                Bicarbonate (HCO3-)

Sodium (Na+)                                                                           Nitrate (NO3-)

Potassium (K+)                                                                          Carbonate (CO32-)

Iron (Fe2+)                                                                                 Sulfate (SO42-)



Ion Exchange Resins

There are two basic types of resin - cation-exchange and anion-exchange resins. Cation exchange resins will release Hydrogen (H+) ions or other positively charged ions in exchange for impurity cations present in the water. Anion exchange resins will release hydroxyl (OH-) ions or other negatively charged ions in exchange for impurity anions present in the water.



Today’s modern ion-exchange resins are prepared from synthetic polymers such as styrenedivinylbenzene copolymers which have either been sulphonated to form strongly acidic cation-exchangers or aminated to form strongly basic or weakly basic anion-exchangers.



The application of ion-exchange to water treatment and purification

These are three ways in which ion-exchange technology can be used in water treatment and purification: first, cation-exchange resins alone can be employed to soften water by base exchange; secondly, anion-exchange resins alone can be used for organic scavenging or nitrate removal; and thirdly, combinations of cation-exchange and anion-exchange resins can be used to remove virtually all the ionic impurities present in the feedwater, a process known as deionization.



The first two technologies are forms of water treatment in which either the chemical nature of the impurities is changed (as in base-exchange softening) or certain impurities are selectively removed (as in organic scavenging or nitrate removal). By contrast, deionization is a purification process which can produce water of exceptionally high quality.



Base-Exchange Softening

Softening was the first industrial application involving ion exchange. The process was first proposed by Gans in 1905. Except for certain improvements in the type of ion exchange material and the equipment, Gans’ process is still one of the simplest methods for softening water.



The process involves passing water containing hardness ions, namely calcium (Ca2+) and magnesium (Mg2+) through a column containing a strongly acidic cation exchange resin in the sodium (Na+) form (i.e. the exchangeable cations are sodium). The calcium and magnesium ions are exchanged for an equivalent number of sodium ions. The resin, once exhausted, (i.e. all the available sodium ions have been exchanged) must be re-charged. This entails passing a solution containing a high concentration of sodium salts such as brine (sodium chloride) through the ion exchange resin - a process known as regeneration.



Main Usages of Softened Water



To prevent scale formation in boilers, water heaters, steam irons and dish-washing machines etc.





To eliminate the production of insoluble ‘scums’ formed as a result of the reaction between calcium and magnesium ions with fatty acids found in soaps - in the textile industry, washing machines etc.





To prevent unsightly stains on glassware, mirrors, etc.





To pre-treat reverse osmosis feed water to prevent fouling of reverse osmosis membranes.

Organic Scavenging

Organic scavengers are fully automatic plants designed primarily to remove naturally-occurring organic contaminants - mainly humic and fulvic acids - from water supplies. These are weakly-ionised compounds which can irreversibly foul normal anion resins and reverse osmosis membranes, but which can readily be removed from water by a combination of adsorption and ion-exchange.



Organic scavengers contain special macroporous anion-exchange resins operated in the chloride form. They have an open structure with large pores that allow the bulky organic anions to be removed from the feedwater and then eluted out again during regeneration.



Regeneration is initiated automatically by a clock cycle timer. The regenerant is sodium chloride in the form of a 10% brine solution which is drawn into the scavenger from a brine tank.



Nitrate Removal

Nitrates are a particular hazard to infants under six months old. The nitrates are reduced to nitrites in the child’s gastro-intestinal system, reducing the capacity of the blood to carry oxygen (‘blue baby syndrome’). The simplest and most cost-effective method of removing nitrates from water is by anion-exchange, using resins operated in the chloride form and regenerated with brine. Special resins are available to treat sulphate-rich waters. (Conventional resins have a stronger affinity for sulphate than nitrate, reducing their capacity for nitrate removal).



Deionization

For many laboratory and industrial applications, high-purity water which is essentially free from ionic contaminants is required. Water of this quality can be produced by deionization.



The two most common types of deionization are:



Two-bed deionization





Mixed-bed deionization

Two-bed deionization

The two-bed deionizer consists of two vessels - one containing a cation-exchange resin in the hydrogen (H+) form and the other containing an anion resin in the hydroxyl (OH-) form. Water flows through the cation column, whereupon all the cations are exchanged for hydrogen ions.



To keep the water electrically balanced, for every monovalent cation, e.g. Na+, one hydrogen ion is exchanged and for every divalent cation, e.g. Ca2+, or Mg2+, two hydrogen ions are exchanged. The same principle applies when considering anion-exchange.



The decationised water then flows through the anion column. This time, all the negatively charged ions are exchanged for hydroxide ions which then combine with the hydrogen ions to form water (H2O).



Mixed-bed deionization

In mixed-bed deionizers the cation-exchange and anion-exchange resins are intimately mixed and contained in a single pressure vessel. The thorough mixture of cation-exchangers and anion-exchangers in a single column makes a mixed-bed deionizer equivalent to a lengthy series of two-bed plants. As a result, the water quality obtained from a mixed-bed deionizer is appreciably higher than that produced by a two-bed plant.



The vessel can be in the form of a large stainless steel or reinforced fibreglass column containing many hundreds of litres of resin, or a small disposable/regenerable cartridge which, when exhausted, can either be thrown away or sent back to the original supplier for regeneration. The large deionizers - whether two-bed or mixed-bed - regenerate themselves automatically, in situ, when the water quality drops to a pre-set level.



Although more efficient in purifying the incoming feedwater, mixed-bed plants are more sensitive to impurities in the water supply and involve a more complicated regeneration process. Mixed-bed deionizers are normally used to ‘polish’ the water to higher levels of purity after it has been initially treated by either a two-bed deionizer or a reverse osmosis unit.



The deionizers used in laboratory applications are almost invariably small mixed-bed units containing exchangeable or disposable cartridges of resin. Large, self-generating deionizers are sometimes used in water purification systems supplying substantial volumes of water to suites of laboratories, or providing large quantities of industrial process water.

WATER TREATMENT AND DE MINERALISATION

ASK  kaacconsultant@gmail.com  
one mail is sufficient.

Ion exchange is an effective,versatile means of conditioning  boiler feedwater. The term “ion

exchange” describes the process:

as water flows through a bed of ion exchange material, undesirable ions are removed and

replaced with less objectionable ones.

For example, in softening processes,

calcium and magnesium  ions (hardness) are exchanged for sodium ions.

In dealkalization, the ions contributing to alkalinity (carbonate, bicarbonate, etc.) are removed and

replaced with chloride ions.

Other dealkalization processes

utilizing weak acid cation resin or strong acid cation resin in a split stream process, exchange cations with hydrogen.
This forms carbonic acid which can be removed in a decarbonator tower.

Demineralization is simply replacing all cations with hydrogen ions (H+) and all anions with hydroxide ions (OH–).
Ion exchange materials are like storage batteries; they must be recharged (regenerated) periodically

to restore their exchange capacity. With proper design and operation, ion exchange processes are capable of removing  selected ions almost completely (in some cases to a fraction of a part per million).

Ion exchange processes

Table 1 — Types of ion exchange materials

Capacity Exchangers kgr/ft3

CATION

Inorganic (zeolites)

Natural (greensand) 3–5

Synthetic 12–16

Organic

Sulfonated coal — 5–7

(carbonaceous)

Synthetic – (phenolic types) 6–18

(styrene base) 20–30

ANION

Inorganic Not widely

Metallic oxides used

Organic

Synthetic resins 10–22

Cation exchangers

There has been constant improvement in ion exchange materials since the first use of natural and

synthetic inorganic products.  Sulfonated coal, styrene-base resins, phenolic resins and acrylic

resins are some that have been developed. Exchange capacities were greatly increased with the

development of the styrene-base exchangers. These resins are manufactured in spherical, stress

and strain-free form to resist physical degradation. They are stable at temperatures as high as

300°F and are applicable over a  wide pH range. More dense ION EXCHANGE MATERIALS

Ion exchange processes are versatile — specific types of ions can be removed from water depending on the choice of exchange material and regenerant used.

Development

Slightly more than 100 years ago,two English agricultural chemists, H. S. Thompson and J. Thomas Way, noted that certain soils had a greater ability than others to absorb ammonia from fertilizers.

They found that complex silicates in the soil performed an ion exchange function. They were able to prepare materials of this type in the laboratory from solutions of sodium aluminate and sodium silicate. In 1906,

Robert Gans used materials of this type for softening water. The early materials used were slow in

regenerating and lacked physical stability. These first synthetic,inorganic exchangers were called

zeolites. Today, zeolites are almost totally replaced by synthetic ion exchange materials. The basic types of ion exchangers in use for water conditioning are



Anion exchangers

Anion exchange materials are classified as either weak base or strong base depending on the

type of exchange group. Weak base resins act as acid adsorbers,efficiently removing strong acids

such as sulfuric and hydrochloric.

However, they will not remove carbon dioxide or silica. They are used in systems where strong

acids predominate, where silica reduction is not required, and where carbon dioxide is removed

in degasifiers. Preceding strong base units in demineralizing  processes, weak base resins give

Typical Minerals Types of Minerals in Influent Exchanger Converted to

Cation

(A) Ca(HCO3)2 ® Na+ ® NaHCO3

CaSO4 ® Exchanger ® Na2SO4

Cation

(B) Ca(HCO3)2 ® H+ ® H2CO3

CaSO4 ® Exchanger ® H2SO4

Cation

(C) Ca(HCO3)2 ® H+ ® H2CO3

Exchanger

(Weak Acid)

Anion

(D) Na2SO4 ® Cl– ® NaCl

NaHCO3 ® Exchanger ® NaCl

Anion

(E) H2CO3 ® OH– ® H2O

H2SO4 ® Exchanger ® H2O

Conventional softening — process (A)

Dealkalization by split stream softening — blending effluents from (A) and (B)

Dealkalization by anion exchange — process (D) proceded by (A)

Dealkalization by weak acid cation exchanger followed by conventional softening

process (C) followed by (A)

Demineralizing — combination of (B) and (E)

Table 2 — Types of ion exchange processes

more economical removal of  sulfates and chlorides.

These are two general classes of  strong base anion exchangers,

Types I and II, denoting differences in chemical nature. Both remove silica and carbon dioxide

as well as other anions.
Type I is more effective in removing silica,and is used when the combined

silica and carbon dioxide content of the water contacting the exchanger is more than 25% of

the total anions. When there is contamination of the water with organic matter, a more porous

form of Type I resin is recommended.

The Type II anion

material is used in treating waters where the combined carbon dioxide and silica content is less

than 25% of the total anions. This is often the case when carbon dioxide is taken out in a degasifier

ahead of the anion exchanger unit.

2

Figure 1 — Typical ion exchange unit

Equipment operation Ion exchange material is housed in specially constructed tanks (Figure 1) where it forms a bed,

usually 30–60 inches deep. In some cases, it is supported by another bed of graded gravel or anthracite filter media. In other cases, some special methods of support, without gravel or anthracite, are used. During normal operation, water enters the top of the tank through a pipe, which distributes it over the surface of

the exchanger bed. The treated water is drawn off by collector piping at the bottom.

Several newer designs for ion exchange are now coming into common use. These are becoming

popular because of their advantages of higher operating efficiencies and lower leakage rates. In

countercurrent regeneration procedures, the regenerant flow is opposite in direction to the service

water flow. Therefore, the resin located in the bed where the finished water leaves the vessel, is

the most highly regenerated. This results in lower leakage rates and slightly higher operating capacities

at equal regenerant dosages to cocurrent operated vessels.

Physical Characteristics of

Resin

Anion and cation resins can be obtained in several different physical forms. They can be

obtained with different ions located on the exchange site.

This has importance in applications such as mixed beds where minimal leakage rates are

required even from a newly installed bed.

Particle size can also be specified.

Uniform particle sized (UPS)

resins are now available where all beads fit into a very close particle size range. For practical

purposes, all of the beads are the same size. Beds of UPS resins have some unique operating

characteristics which offer advantages

when they are used in mixed bed, layered bed, and packed bed applications. Macroporous resins are highly porous which give them advantages when used in processes that have high fouling potential.

ION EXCHANGE PROCESSES

Ion exchange processes fall into several categories: softening  (including removal of iron and

manganese), dealkalization, and demineralization. Examples of these processes are listed in

Table 2.

3

Figure 2 — Cocurrent vs. countercurrent regeneration

Cocurrent vs countercurrent: With downflow operation, ion distribution at end of operating cycle

is the same for cocurrent and countercurrent operation. But at end of regenerating cycle, ion

distribution is revised when cocurrent is compared with countercurrent regeneration. Key to

optimum results is quality of rinse water used with countercurrent regeneration.

R– H+ R– H+

R–2 Ca+2

R–2 Mg+2

R– Na+

R–2 Ca+2

R–2 Mg+2

R– Na+

R– H+

R– H+

R–2 Ca+2

R–2 Mg+2

R– Na+

R–2 Mg+2

R–2 Ca+2

R– Na+

4

However, countercurrent vessels are more sensitive to operating problems. The bed must be immobilized during the regeneration process and the influent water must be very low in suspended solids.
Figure 2  illustrates what happens in the two regeneration modes at exhaustion and after regeneration.

Packed bed systems essentially fill the vessel with resin. The systems are countercurrent in design and offer the low leakage rate advantage. However, packed beds also offer the advantage of reduced waste generation. Since there is no space for proper backwash, packed bed systems usually are built with external backwash tanks which allow the resin to be backwashed after it is sluiced out of the operating

vessel. All countercurrent ion exchange systems require feedwater that is very low in suspended solids.

Regeneration of the exchange material involves three steps: backwash, introduction of the regeneration chemicals, and rinse.

Figure 3 shows valve arrangements on a salt regenerated unit.

Backwash is simply a reversal of the normal flow to wash out any suspended matter in the bed and

to “fluff” the bed, to break up packed areas. This is done just before the unit is regenerated.

During regeneration, chemicals are introduced at the top surface of the bed and removed through

the bottom outlet. The rinse washes out the last traces of regenerant chemical.

Figure 3 — Valve arrangements for regeneration with salt

Ion exchange units are usually installed in duplicate to permit continuous service during regeneration. Some typical equipment arrangements are

shown in Figure 4.

Regeneration procedures When regeneration is ineffective, the bed is usually fouled with suspended matter. This emphasizes the importance of proper backwash procedures. During backwash, the cation exchanger bed should expand at least 50%, while the anion exchanger bed should expand at least 75%.

How much the bed expands depends on the backwash water temperature, backwash rate and density of the ion exchanger.

Figure 5 shows the expansion characteristics of typical cation and anion resins.

The capacity of ion exchange material varies according to the amount and concentration of regenerating chemical used and the time the chemical contacts the exchanger. Table 3 shows this variation in capacity with regenerant dosages.

Selecting the optimum dosage level depends mainly on the quality of finished water required, considering both economic and operating factors.

5

KEY:

WAC – Weak acid cation WBA – Weak base anion SAC – Strong acid cation SBA – Strong base anion

6

Figure 4 — Typical equipment arrangements

CONCLUSIONS

The use of ion exchange processes affords numerous efficient and effective means of conditioning

feedwater. The proper selection of the specific ion exchange process depends on water quality needs, operating convenience, and economic considerations. For effective results, the system must be

carefully selected, designed, operated and maintained. Because m
the decision is complex,

an experienced ion exchange

engineer should be consulted to

Regenerant Operating assist in selection and design.

Exchanger Dosage Capacity

Type Regenerant (lb/ft3) (kgr/ft3)

Cation (high capacity) Salt 6 – 8 20 – 24

10 – 15 25 – 30

Cation (high capacity) Sulfuric acid 4 – 6 10 – 12

8 – 10 14 – 16

Anion (weak base) Ammonia 1.5 – 2 20 – 22

Caustic 3 – 4 20 – 22

Soda ash 3 – 5 12 – 15

Anion (strong base) Caustic 3.5 – 5 10 – 12

7

Figure 5 — Expansion characteristics of exchange beds

Table 3 — Effect of regenerant levels on exchange capacity

TIPS ON ENERGY SAVING SAVINGS

Tips on Energy Savings Page 1 of 5

TIPS ON ENERGY SAVING

IN HOME APPLIANCES AND ELECTRICITY SAFETY

The Domestic Sector accounts for 30% of total energy consumption in the country. There is a

tremendous scope to conserve energy by adopting simple measures.

This information is a guide, which offers easy, practical solutions for saving energy in Home

Appliances. Please, take a few moments to read the valuable tips that will save energy & money

and ultimately help conserve our natural resources.

It would be useful to know which gadget consumes how much electricity. Economic use of home

appliances can help in reducing electricity bills.



By following these simple tips one can save energy to a large extent.

Lighting

Ø Turn off the lights when not in use

Ø Take advantage of daylight by using light-colored, loose-weave curtains on your windows

to allow daylight to penetrate the room. Also, decorate with lighter colors that reflect

daylight

Ø De-dust lighting fixtures to maintain illumination

Ø Use task lighting; instead of brightly lighting an entire room, focus the light where you need

it

Ø Compact fluorescent bulbs are four times more energy efficient than incandescent bulbs

and provide the same lighting

Ø Use electronic chokes in place of conventional copper chokes

Fans

Ø Replace conventional regulators with electronic regulators for ceiling fans

Ø Install exhaust fans at a higher elevation than ceiling fans

Electric iron

Ø Select iron boxes with automatic temperature cutoff

Ø Use appropriate regulator position for ironing

Ø Do not put more water on clothes while ironing

Ø Do not iron wet clothes

Kitchen Appliances

Ø Mixers

§ Avoid dry grinding in your food processors ( mixers and grinders) as it takes longer

time than liquid grinding

Ø Microwaves ovens

§ Consumes 50 % less energy than conventional electric / gas stoves

§ Do not bake large food items

§ Unless you're baking breads or pastries, you may not even need to preheat

§ Don't open the oven door too often to check food condition as each opening leads to a

temperature drop of 25°C

Ø Electric stove

§ Turn off electric stoves several minutes before the specified cooking time

§ Use flat-bottomed pans that make full contact with the cooking coil

Tips on Energy Savings Page 3 of 5

Ø Gas stove

§ When cooking on a gas burner, use moderate flame settings to conserve LPG

§ Remember that a blue flame means your gas stove is operating efficiently

§ Yellowish flame is an indicator that the burner needs cleaning

§ Use pressure cookers as much as possible

§ Use lids to cover the pans while cooking

§ Bring items taken out of refrigerators (like vegetables, milk etc) to room temperature

before placing on the gas stove for heating

Ø Use Solar Water Heater – a good replacement for a electric water heater

Electronic Devices

Ø Do not switch on the power when TV and Audio Systems are not in use i.e. idle operation

leads to an energy loss of 10 watts/device

Computers

Ø Turn off your home office equipment when not in use. A computer that runs 24 hours a

day, for instance, uses - more power than an energy-efficient refrigerator.

Ø If your computer must be left on, turn off the monitor; this device alone uses more than half

the system's energy.

Ø Setting computers, monitors, and copiers to use sleep-mode when not in use helps cut

energy costs by approximately 40%.

Ø Battery chargers, such as those for laptops, cell phones and digital cameras, draw power

whenever they are plugged in and are very inefficient. Pull the plug and save.

Ø Screen savers save computer screens, not energy. Start-ups and shutdowns do not use

any extra energy, nor are they hard on your computer components. In fact, shutting

computers down when you are finished using them actually reduces system wear - and

saves energy

Refrigerator

Ø Regularly defrost manual-defrost refrigerators and freezers; frost buildup increases the

amount of energy needed to keep the motor running.

Ø Leave enough space between your refrigerator and the walls so that air can easily

circulate around the refrigerator

Ø Don't keep your refrigerator or freezer too cold.

Ø Make sure your refrigerator door seals are airtight

Ø Cover liquids and wrap foods stored in the refrigerator. Uncovered foods release moisture

and make the compressor work harder.

Ø Do not open the doors of the refrigerators frequently

Ø Don't leave the fridge door open for longer than necessary, as cold air will escape.

Ø Use smaller cabinets for storing frequently used items

Ø Avoid putting hot or warm food straight into the fridge

Tips on Energy Savings Page 4 of 5

Washing machines

Ø Always wash only with full loads

Ø Use optimal quantity of water

Ø Use timer facility to save energy

Ø Use the correct amount of detergent

Ø Use hot water only for very dirty clothes

Ø Always use cold water in the rinse cycle

Ø Prefer natural drying over electric dryers

Air Conditioners

Ø Prefer air conditioners having automatic temperature cut off

Ø Keep regulators at “low cool” position

Ø Operate the ceiling fan in conjunction with your window air conditioner to spread the

cooled air more effectively throughout the room and operate the air conditioner at higher

temperature

Ø Seal the doors and windows properly

Ø Leave enough space between your air conditioner and the walls to allow better air

circulation

Ø A roof garden can reduce the load on Air Conditioner

Ø Use windows with sun films/curtains

Ø Set your thermostat as high as comfortably possible in the summer. The less difference

between the indoor and outdoor temperatures, the lower will be energy consumption.

Ø Don't set your thermostat at a colder setting than normal when you turn on your air

conditioner. It will not cool your home any faster and could result in excessive cooling.

Ø Don't place lamps or TV sets near your air-conditioning thermostat. The thermostat senses

heat from these appliances, which can cause the air conditioner to run longer than

necessary.

Ø Plant trees or shrubs to shade air-conditioning units but not to block the airflow. A unit

operating in the shade uses as much as 10% less electricity than the same one operating

in the sun.

Tips on Energy Savings Page 5 of 5

Electrical Safety Tips for Homes

Electrical Hazards

Ø Shocks

§ Electric Shock causes an involuntary grip which prolongs the period of contact.

§ More the period of contact, more the damage

§ Passage of current through the heart , stops the blood supply to the brain , resulting in

loss of consciousness and termination of breathing

§ When a person standing at a height receives an electrical shock , it is most likely that

he will fall

§ Personal sensitivity to electrical shock varies from person to person

Ø Burns

§ Whenever an electrical flash appears, and if a part of a body comes within flashing

distance, burns can be caused

§ Burns may be caused by short circuits as well, because a short circuit could create an

electrical fire

Preventive Measures

Ø Allow only a qualified person to attend to your electrical repairs

Ø Service your electrical equipment at frequent intervals through a competent electrician

Ø In case of a short circuit or a fire, switch off the mains instantly Make sure that you have

easy access to switch off the supply source quickly, in case of an emergency

Ø Make sure your extension cords are free from cuts, improper insulation, or joints

Ø Ensure pins of your plugs are tight and not loose

Ø Use switches of the correct current rating and preferably with indicators to indicate whether

the switch is ON/OFF

Ø Use appliances with 3 pin plugs and connect them to 3 pin sockets

Ø Do not overload electrical outlets or use extension cords in place of additional outlets

Ø Switch off electrical appliances when not in use

Ø Provide proper earthing for the building/house

CALCULATION OF AIR QUANTITY POWER ENGINEERING

CALCULATION OF AIR QUANTITY


1. Law of definite proportion: Substances always combine in definite proportions and these proportions are determined by the molecular masses of reactants consumed and the products formed.



C (g) + O2(g) == CO2 (g)

12 32 44



2. The law of gaseous volumes ( Gay Lussac 1808): according to this law When gas combine they do so in volumes which bear a simple ratio to each other and also to the product formed, provided all gases are measured under similar conditions



H2(g) + ½ O2(g) = H2O(v)

1 vol 0.5 vol 1 vol



3. Avogadros law ; Equal volumes of gases under similar conditions of pressure and temperature posses equal no of moles or molecules



At 1 atm pressure and 0 deg C I mol of gas contains 6.023 X 10 23 molecules of gas



One mole of an ideal gas at 0 deg C and 1 Atm pressure occupies 22.4 litre volume.



Significance of these laws

A combustion equation



CH4 (g) + 2 O2 (g) = CO2 (g) + 2 H2O (L)



1) Weight ratio . 16 gm 64 gm 44 gm 36 gm

2) Volume ratio 1 vol 2 vol 1 vol 2 vol

3) Mol ratio 1 mol 2 mol 1 mol 2 mol

4)Molecule ratio 6.023x 10 23 2x6.023x 10 23 6.023x 10 23 2x6.023x 10 23





In actual practice the combustion is carried out in presence of air. Therefore amount of air is calculated

1) Air contains 21 % of oxygen by volume, and 23% of Oxygen by mass. Hence from the amount of Oxygen required by the fuel the amount of air can be calculated



I kg of oxygen is supplied by 1x 100/23= 4.35 kg of air

1 M3 of oxygen is supplied by 1x100/21= 4.76 M3 of air



Mean molecular mass of air is taken as 28.94 g/mol



Minimum oxygen required for combustion = Theoritical oxygen reqd- O2 present in the fuel

Minimum O2 required should be calculated on the basis of complete combustion. If the combustion product contain CO and O2 then excess O2 is found by subtracting the amount of O2 required to burn CO to CO2



The mass of any gas can be converted to its volume at certain temp. and pressure by assuming that the gas behaves ideally and using the gas equation

PV= nRT



The volume of a gas at a given temp. and pressure can be redused to the corresponding volume at any other specified conditions of temp. and pressure with the help of



P1V1/T1 = P2V2/T2



CONVERSION OF VOLUME OF AIR INTO WEIGHT OR VICEVERSA



Density of Air ( d air) = Molar mass of air(M)/ Molar volume of air (V)

28.94 g/mol

= ---------------

22.4 L/mol

28.94

= --------------

22.4 g/L

Let us assume that for the combustion of a particular fuel m gm of air is reqd



The corresponding volume of air ( let v litre) requirement can be calculated by assumimg that the density of air remains constant.

Thus m/v = M/V



m/v = 28.94/22.4

v= 22.4/28.94 m



Guide line for combustion calculation

1) Determine the amounts of various combustibles present in a given fuel

2) Write the balanced combustion equation for all the combustibles

3) Calculate the requirement of oxygen for complete combustion of fuel constituents either by weight or by volume or by moles.

4) Find the total oxygen required by adding up the oxygen requirement for individual combustibles substance of the given fuel .

5) Calculate net oxygen required by subtracting from the total oxygen required the amount of oxygen already present in the fuel

6) Convert net oxygen requirement into total air requirement.











Combustion calculation by weight



S no Fuel constituent Amount of constituent in fuel (gm) Combustion equation Weight of oxygen

1



2



3



4



5 C



CO



H



S



O a



b



c



d



e C + O2 = CO2

12 32

CO + ½ O2= CO2

28 16

H2 + ½ O2

2 16

S + O2 = SO2

32 32

-----------------------



32/12 * a = A



16/28 * b = B





16/2 * c = C



32/32 * d = D

------------------

Total weight of oxygen needed for combustion A+ B+ C+D = T ( LET)

Weight of oxygen already present in fuel = e gm



Thus net weight of Oxygen required for combustion T-e gm = N gm (LET)



Theoretical weight of air required for combustion = N * 100/23 gms



COMBUSTION CALCULATION BY VOLUME



S No Fuel constituent Amount of constituent in fuel (M3) Combustion equation Volume of oxygen needed for combustion (M 3)

1



2 CH4



C2H6 A



B CH4 + 2O2 = CO2 + 2 H2O

1 M3 2 M3

C2H6 + 3.5 O2 = 2 CO2 +3 H2O 2/1* A



3.5/1 * B

Total volume of oxygen needed for combustion A+B+C+……… = T (M3)

Volume of Oxygen already present = H (M3)



Thus net volume of Oxygen required = T- H ( M3)



Theoretical volume of air required = ( T- H) * 100/21 M3





COMBUSTION CALCULATION BY MOLES



S No Fuel constituent Amount of constituent in fuel Combustion equation Moles of oxygen needed for combustion

1



2



3 C



H



S A gm = A/12 mol



B gm = B/2 mol



C gm= C/32 mol C + O2 = CO2

1 Mole 1 Mole

H2 + 0.5 O2 = H2O

1 mol 0.5 mol

S + O2 = SO2

1 mole 1 mole A/12 *1= A1



B/2* 0.5 = B1



C/32 *1=C1



Total moles of oxygen needed for combustion A1+B1+C1+ ……. + = T Moles (LET)

As moles of oxygen already present in fuel = G Moles



Net moles of Oxygen needed for combustion = T-G moles= N Moles



Weight of oxygen needed for combustion = N * 32 Gm = N1 gm



Thus weight of Air required for complete combustion of fuel = N1 *100/23



Now volume of air required for complete combustion of fuel = N1 * (22.4 L/mol/ 28.94 g/mol)



















A hydro carbon fuel on combustion gave a flue gas of the following volume % composition CO2= 13.53%, N2 = 82.91% and O2 = 3.56 . Determine composition of fuel by weight b) the % of excess air and c) volume of air supplied per kg of the fuel

Solution:

a) As the flue gas contains CO2 so one of the constituents in fuel must be carbon



C + O2 = CO2

That indicates that moles of CO2=Moles of O2= Moles of C

Assuming total amount of dry flue gas = 100 Kmol

So mols of CO2= 13.53 K mol

Thus amount of O2 in flue gas = 13.53 Kmol + 3.56 Kmol = 17.09 Kmol



Given amount of N2 in flue gas = 82.91 kmol



As in 100 Kmol of air 79 Kmol N2 is present

Thus, Amount of air supplied for combustion = 100/79* 82.91 = 104.95 Kmol

Therefore amount of oxygen supplied = 104.95 *21/100= 22.039 kmol



Amount of O2 combined with H2= 22.04- 17.09= 4.95 Kmol

Combustion equation of H2= H2 + ½ O2 = H20



So amount of H2 burnt= 2X4.95= 9.90 Kmol

And weight of H2 burnt= 9.9x2= 19.8 Kg



As 100 Kmol of flue gas containg 13.53 Kmol of CO2 = 13.53 Kmol of C

Therefore weight of C in fuel 13.53 X12= 162.36 Kg



Now % of C= [162.36/( 162.36+ 19.80)] *100=89.130

And % of H= [19.80/( 162.36+ 19.80) ]* 100= 10.87



b) Theoretically amount of O2 required for producing 13.53 kmol of Co2= 13.53 kmol of O2



And amount of O2 required for burning H2 = 4.95 Kmol



So total O2 theoretically required = 13.53+4.95= 18.48 Kmol



Oxygen supplied 22.04 kmol

So % of excess air = [(22.04-18.48)/18.48]*100 = 19.264



c) Total air supplied = 104.95 Kmol



Volume of air supplied= 104.95x 22.4= 2350.93 M3



Thus volume of air supplied per kg of fuel= 12.91 M3/kg


in doubt ask at      kaacconsultant@gmail.com 

YOU could be one of those finicky sorts, determined to have a day cream and a night one too. You spend plenty on special skin care products such as astringents, toners and eye gels. Even though your friends laugh at you, you believe you are on the right track. After all so many celebs are endorsing your favourite products.




But are so many products really neccessary? We help you decide which of those bottles and jars are really essential.



BODY WASH OR SOAP BAR



THE IDEA of using a bar of soap when there are so many fancy bottles body wash lining the shelves is surely unfashionable.



But which is more effective? Promoters of liquid cleansers claim that these are gentler than bathing bars as they contain large amounts of petrolatum – an ingredient that moisturises and lubricates the skin.



Undoubtedly soap bars are more alkaline and have a dehydrating impact on the skin. "Body washes are a more convenient and hygienic option for bathing and they spread easily over the skin. They have hydrating and nourishing ingredients too,” says Dr Chiranjeev Chabra, dermatologist and cosmetic laser surgeon, Skin Alive Clinic.



On the flip side, conservatives claim that the moisturising property of liquid cleansers makes them less effective at removing dirt and reducing body odour.



"The reality is that both soap bars and body wash are equally good in cleaning the body. The selection should be based on individual skin requirements and the season," says Dr Anil Malik, senior consultant, dermatology, Sitaram Bhartia.



Moreover, many mild soap bars are now available in the market, which have a neutral pH of 7- 10 and don’t have the same drying effect. "Earlier soaps had high per cent of caustic and this left the skin dry and stretchy. Things have changed now. Special soaps are available too for acne skin which are antiseptic and help to dry the acne," says Dr Chabra.



EXPERT TAKE: Body wash is ideal for winter or hot and dry weather. Use soap bars on hot and humid days, during the rainy season or if you have oily skin.



DAY CREAM OR NIGHT CREAM



DO WE really need different creams for the days and night? Can’t day creams be used at night too? Experts say no. Our skin needs different products as the skin’s requirement varies according to the body clock. "During the day our skin needs protection from pollution and harmful rays. At night, the skin needs to rejuvenate itself and repair all the damage that goes during the day,” says Dr Sachin Dhawan, head, department of dermatology, Artemis.



Day creams contain antioxidants and titanium dioxide (or other sunscreens), which serve as proper shield for the skin. Night creams, on the other hand, have higher levels of active ingredients such as vitamin C, retinol and alpha hydroxy acids ( AHAs) that repair the skin and also moisturise it. Moreover, night creams are highly concentrated, thicker and stronger than day creams because the skin dries out more quickly while you sleep.



In fact, different categories of creams should be used by individuals of different skin types. In her book, The Skin Type Solution , Dr Leslie Baumann suggests that if your skin is dry, you need a hydrating night cream. Sensitive skin needs an anti- inflammatory night cream, while those with wrinkles should opt for a night cream with retinol or antioxidants.



EXPERT TAKE:If you use night cream during the day, the active ingredients can either get oxidised by the UV rays or cause skin reaction.



ASTRINGENT OR TONER



ASTRINGENTS and toners were earlier part of female domain but are now popular among men too. “ Our face needs intense cleaning to remove the proteins produced by the skin. These will otherwise block the pores, causing blackheads and acne,” says Dr Dhawan. The purpose of an astringent and toner is the same – cleaning the skin, destroying bacteria that cause acne and adjusting the pH level in the skin.



But astringent is for oily skin while toner is for dry skin. Essentially astringent has an anti- bacterial quality that reduces oil, blackheads and cares for acne prone skin types. Toners, on the other hand, are milder and are meant for those who produce less oil on their face and older skins.



EXPERT TAKE: Astringents are alcohol based and intended for oily skin. Toners hydrate and tone the skin and are ideal for dry or normal skin.



EYE GEL OR EYE CREAM



NO ONE wants under eye pouches, dark circles or wrinkles and the solution seems to lie in over-the-counter eye gels and creams. People assume these fulfil the same purpose.



But the reality is that eye gels and creams work differently. "Wrinkles are removed with a compound called matrixyl, which works best when delivered in the form of cream. Eye bags and dark circles, on the other hand, respond well to a chemical called haloxyl, effective when delivered in the form of a gel rather than cream," says Dr Urvashi Kaw, consultant, dermatology and cosmetology, B L Kapur Memorial Hospital.



Creams and gels are oil particles in water used in different proportions. Gels are less oily and tend to be absorbed faster by the skin. "Unlike creams, gels neither block the skin pores nor do they leave behind a greasy residual effect," says Dr Malik. "The skin under our eyes is 4-5 times thinner than facial skin and is more porous. Therefore, the chances of pores getting blocked are higher under the eye," he adds. Hence, in general it’s advisable to use eye gels as against eye creams in general.



EXPERT TAKE: Eye gels are intended to reduce puffiness, dark circles and eye sags, while creams may reduce wrinkling.

modern age MODERN AGE

Modern age is referred to as the science age because of the changes qualitative and q2uantitative

THE QUANTUM MACHINE
Until MARCH 2010 all man made objects had moved according to the laws of classical mechanics. Back in MARCH a group of researchers

http://www.archive.org/details

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Performance Evaluation of New and In-Service Turbine Oils


•



For any power generation facility, the turbine is considered the lifeblood of the operation. Any problem requiring an unexpected shutdown of the main turbine is likely to cause a significant unplanned outage, potentially resulting in millions of dollars of downtime costs. According to a 1991 study by General Electric (GE), turbines contribute on average 20 percent of all forced outages in a conventional power plant. Among this 20 percent, GE noted that 19 percent of turbine/generator problems were associated with the lube oil system. For this reason, monitoring turbine oils has become commonplace in the power generation industry.

Figure 1. Contributors to Costly Forced Outage

Turbine oils, particularly those used in steam turbines, are expected to last around 10 to 20 years. For this reason, careful monitoring of both lube oil physical and chemical properties is required, together with common contaminants such as water and solid particles. This is true not just of in-service oils, but also for new oils, which must meet rigorous performance specifications prior to selection and use in a new application.

The testing of turbine oils is of such significance that ASTM has developed a standard devoted exclusively to this area, specifically ASTM D4378-97 “Standard Practice for In-Service Monitoring of Mineral Turbine Oils for Steam and Gas Turbines.” Some of the tests important to the evaluation of new and used turbine oils are detailed in the following discussion.

Viscosity ASTM D445 and Viscosity Index D2270

Viscosity is the most important characteristic of a turbine oil because the oil film thickness under hydrodynamic lubrication conditions is critically dependent on the oil’s viscosity characteristics. Turbine blade clearances are critical to power plant efficiency and reliability. These blade clearances are directly impacted by lubricant viscosity. Changes in oil viscosity can result in unwanted rotor positioning, both axially and radially. Axial movements directly impact turbine blade efficiency and in extreme cases can lead to blade damage. Radial movements caused by changes in viscosity can result in oil whip, where the rotor does not settle into one radial position. Oil whip can often be identified from vibration analysis, but is often a direct result of high viscosity.

For in-service turbine oils, the viscosity should remain consistent over years of service, unless the oil has become contaminated or severely oxidized. ASTM D4378-97 identifies a five percent change from the initial viscosity as a warning limit. It is important to note that this is a change with respect to a new oil baseline, not the typical value reported on the lube oil supplier’s spec-sheet. Testing for viscosity should be conducted on a quarterly basis, at a minimum.

The Viscosity Index (VI) is an indication of the oil’s change in viscosity with a change in temperature. Most gas and steam turbine OEMs require a turbine oil with a VI of

at least 90, which is met by most turbine oil suppliers. The VI for turbine oils should not vary in-service, because turbine oils typically do not contain VI improvers and therefore do not need to be tested routinely.

Rotating Pressure Vessel Oxidation

Test (RPVOT) - ASTM D2272

Formerly known as the RBOT test, the RPVOT test (Figure 2) was developed for the monitoring of in-service oils to warn of a loss in oxidation resistance. Oxidation is driven by heat and exposure to contaminants like water, entrained air and catalytic metals. As a turbine oil degrades, it forms weak organic acids and insoluble oxidation products that adhere to governor parts, bearing surfaces and lube oil coolers. After a period of time, these oxidation by-products and carbon insolubles cure on surfaces causing a significant change in critical clearances, and in some instances prevent the oil from providing adequate cooling to the bearings and fouling turbine control elements and heat exchangers.

This accelerated oxidation test is an industry standard for identifying oxidation stability problems with in-service turbine oils. ASTM D4378-97 identifies an RPVOT drop to 25 percent of the new oil RPVOT value with a concurrent increase in Acid Number (AN) as a warning limit. Many turbine OEMs simplify this by using the 25 percent of initial RPVOT without reference to AN, while others list a 100-minute RPVOT minimum. It should be noted that the RPVOT test is designed to determine a lubricant’s suitability for continued use, not to compare competitive oils. Competitive oil comparisons should be evaluated on the basis of RPVOT longevity, rather then the absolute RPVOT value.

In gas turbines that utilize a common lube oil sump for bearings and system hydraulics the use of ultra centrifuge testing should be used in conjunction with RPVOT as a means to determine varnish formation.

Typically, an oil that has reached its minimum allowable RPVOT values needs to be changed. However, as a short-term measure, the so-called “bleed and feed” method of turbine oil rejuvenation is suitable to extend the life of the turbine oil for a limited time.

Efforts to readditize a severely oxidized turbine oil with oxidation inhibitor can put equipment at risk. An oil that has a RPVOT value below 100 minutes more than likely has diminished its inherent base stock oxidation stability, making readditizing a nonpractical solution. In such cases, readditization may temporarily boost the RPVOT value but given the diminished nature of the base stock may sharply reduce the time frame before heavy varnishes and sludges are formed. Without the use of special filters such as Fuller’s Earth, to strip all polar materials, contaminants and additives, followed by complete readditization, the rejuvenation of a degraded turbine oil is inadvisable.

In steam and gas turbines, RPVOT testing should be conducted on an annual basis with an increased frequency as the turbine oil approaches 25 percent of its initial value. Some utilities time the test just before scheduled outages, to allow time to plan for an oil change if necessary.

Turbine Oil Stability Test (TOST) ASTM D943

The TOST test attempts to determine the expected turbine oil life by subjecting the test oil to oxidative stress using oxygen, high temperatures, water and metal catalysts, all of which increase sludge and acid formation. This test was developed to evaluate the anticipated new turbine oil performance. However, because it is impossible to simulate actual in-service conditions in a lab, correlation between test results and actual field performance is difficult. Most turbine OEMs utilize TOST in their specifications to screen out high-risk turbine oils.

Current gas turbine OEM specifications for TOST range from 2,000 to 4,000 hours with new gas turbine technology specifications at 7,000 hours. All TOST reporting above 10,000 is done through non-ASTM test modifications that may not correctly represent a turbine oil’s performance. Reporting of TOST values greater than 10,000 hours is not possible within ASTM D943 procedures due to the limited initial 300 ml test oil sample volume that is depleted during AN testing.

Because a TOST test can take up to a year or more to complete, it is impractical as an in-service oil test and is rarely performed for this reason.

Water by Karl Fischer

Titration - ASTM D6304

Testing for water, particularly in steam turbines, is important because water is a precursor to oil oxidation and rust formation (Figure 3).




Figure 3. Laboratory Moisture Test - Karl Fischer

Excessive water will also alter an oil’s viscosity, which reduces its load-carrying capacity. Studies also warn that water levels above 250 ppm in hydrogen-cooled generator windings may lead to stress corrosion cracking of generator rotor retainer rings. Water in a turbine oil in warm storage tanks, where the oil is typically stagnant, can promote the spread of microbial growth that will foul system filters and small-diameter gauge and transducer line extensions.

ASTM D4378-97 identifies 1000 ppm or 0.1 percent of water as a warning level, while some gas and steam turbine OEMs have identified 500 ppm. In hydrogen-cooled generators, an upper limit of 250 ppm should be maintained. Because free and emulsified water are the most harmful, it is advisable to keep water levels below saturation, typically 100 to 200 ppm depending on base oil types, additive formulation and age. Testing for water should be conducted on a quarterly basis, at a minimum using coulometric Karl Fischer Titration (ASTM D6304), complete with codistillation.

Acid Number (AN) - ASTM D664

Sharp increases in AN may indicate contamination or a severely oxidized oil. Organic acids formed by oxidation can corrode bearing surfaces and should be addressed in a timely manner. ASTM D4378-97 offers guidelines of 0.3 to 0.4 mg KOH/g above the initial value as an upper warning level. However, many oil analysts view an upward movement in AN as small as 0.1 as worthy of concern.

Testing for AN should be conducted at least on a quarterly basis using the potentiometric titration method (ASTM D664).

ISO 4406:99 Cleanliness Code

Turbine journal bearing clearances (10 to 20 microns) and hydraulic servovalve clearances (3 to 5 microns) dictate the need for clean oil. Excessive bearing wear and servovalve sticking can result if tight cleanliness standards are not maintained.

Typical OEM recommended turbine oil cleanliness levels are ISO (4406:99) 18/16/13 or an NAS 1638 cleanliness level of 7, although significant component life extension can be achieved by keeping cleanliness levels significantly lower than these limits.

Testing for ISO cleanliness should be conducted on a quarterly basis at the very least.

Rust ASTM D665 A

Rust particles act as oxidation catalysts and can cause abrasive wear in journal bearings. Rust inhibitors are normally kept at proper levels through the addition of makeup oil. Rust inhibitors can impact water separation so field readditization is generally not recommended.

In-service oil testing should be conducted with distilled water as identified in D665 A. ASTM D4378-97 considers a light fail as a warning limit.

Testing for rust should be conducted on an annual basis, or if the lube oil system is exposed to water.

Demulsibility ASTM D1401

Water shedding characteristics are important to lube oil systems that have had direct contact with water. This is particularly true for steam turbines where gland seal leakage is inevitable. The ability of the oil to shed water will have a direct impact on its long-term oxidation stability. Demulsibility can be compromised by excessive water contamination or the presence of polar contaminants and impurities. Demulsibility can be tested using ASTM D1401, in which a known volume of oil is mixed with water, and the time taken for the two to separate measured in minutes; the faster the separation, the better the demulsibility.

ASTM D4378-97 does not offer warning limits for demulsibility although some turbine OEMs identify levels of 3 ml emulsion after 30 minutes on new oils. In-service oil warning limits of 15 ml or greater of emulsion after 30 minutes should serve as a warning limit.

The impact of demulsibility depends on the system residence time and anticipated levels of water contam-ination. Demulsibility testing can show failure in the lab, but with sufficient residence time, the turbine oil may shed water at an acceptable rate that does not impact turbine oil performance. Small sumps with lower residence times will require better demulsibility performance than larger sumps. Testing for demulsibility should be conducted on an annual basis, or if the lube oil system is exposed to water.

Foam ASTM D892

A turbine oil sample will often test for foam higher than turbine OEM initial suggested levels, but typically present no field foaming issues because of the position of the suction line relative to the lube oil surface, where foam accumulates. If the foam level in the turbine sump is six inches or less and does not overflow the sump or cause level-monitoring issues, then turbine oil foaming is not usually a major cause for concern, although a sudden increase in foaming may indicate a more serious problem.

Lube oil at the turbine sump surface should show at least one clear area (no bubbles) and larger breaking bubbles should be seen at this interface.

ASTM D4378-97 offers warning limits for Sequence I of the foam test of 450 ml for foaming tendency, defined as the volume of foam generated after blowing for 5 minutes at 75°F (24°C), and a foam stability of 10 ml, defined as the residual foam left after a 10-minute settling period. A foam stability of less than 5 ml is a good indication that foam bubbles are breaking and the turbine should not experience foam operational problems.

When addressing a foam problem, cleanliness, contamination or mechanical causes should be investigated before field defoamant readditization can be considered. Excessive readditization can result in an even greater problem with increased air entrainment. Dirt is a leading cause of foam, so ISO cleanliness should be tested as a likely cause.

Testing for foam should be conducted only when foaming presents an operational problem and for product compatibility testing.

Air Release ASTM D3427

Some steam and gas turbine OEMs specify air release limits in their new oil specification requirements. These limits can be as low as four minutes, defined as the time for the air entrained during the test procedure to detrain to 0.2 percent by volume. This is typically not a problem for most ISO VG 32 turbine oils, but can be an obstacle for ISO VG 46 oils, due to the higher viscosity. In turbines with small sumps and minimal residence time, entrained air mixtures could be sent to bearings and critical hydraulic control elements causing film strength failure problems, loss of system control, particularly in EHC systems and an increased rate of oxidation.

Air release of turbine oils should not vary with in-service time and therefore may not need to be tested for condition assessments routinely, unless a specific problem is suspected.

FZG Gear Test - ASTM D5182

Turbines with geared shaft connections to the generator often require antiwear or extreme pressure additives to support gear tooth loading. Industry standard testing for gear load performance is the FZG Gear Test, with results reported as Failure Load Stage (FLS). Typical R&O ISO 32 turbine oils carry an FZG failure load stage of 6 or 7. ISO VG 32 R&O oils with antiwear or extreme pressure additives can give an FZG failure load stage of 10, which meets all major turbine OEM specifications.

FZG Gear Tests on turbine oils should not vary with in-service time and do not need to be tested for condition routinely unless a specific wear related problem is encountered.

Flash Point - ASTM D92

Flash point testing is done primarily to confirm product integrity from contamination.

Figure 4. Flash Point Testers

ASTM D4378-97 identifies a drop in 30°F (17°C) from the new oil flashpoint as a warning limit.

Flash point testing is required only if product contamination from a different oil or solvent is suspected.

Lube Oil Analysis Test Packages

Turbine oil lube oil analysis test packages should be assembled in a manner that provides pertinent, cost-effective information. Specific turbine oil test packages for regular trend analysis and suitability for continued use are described as follows:

Regular Trend Analysis (Monthly/Quarterly)

• Viscosity ASTM D445

• Water by Karl Fischer Titration ASTM D1744 (or D6304)

• Acid Number ASTM D664

• Cleanliness Code ISO 4406:99

• Elemental analysis

Suitability for Continued Use (“Turbine Annual”)

• Viscosity ASTM D445

• RPVOT ASTM D2272

• Water by Karl Fischer Titration ASTM D1744 (or D6304)

• Acid Number ASTM D664

• Cleanliness Code ISO 4406:99

• Rust ASTM D665 A (if exposed to water)

• Demulsibility ASTM D1401 (if exposed to water)

• Foam ASTM D892 Sequence I

• Elemental analysis

Figure 5. Laboratory Kinematic Viscometers



Onsite Checks

Often the most valuable and timely information is right in your hand at the time of sampling. Don’t pass up a great opportunity to assess key performance parameters on turbine oils. The use of clear, clean sample containers will allow for quick and easy quality checks as identified below:

• Color - Unusual and rapid darkening can indicate contamination or excessive degradation.

• Odor - Sour smelling oil can indicate contamination or excessive degradation.

• Air entrainment - Air bubbles in the body of the lube oil sample should clear within 15 minutes.

• Foam - After a vigorous shake, foam from the surface should clear within 10 minutes.

• Water - Turbine oil samples should be transparent. If you cannot read printing through a clear sample container, then water levels above 300 ppm may be present. A simple crackle test can also prove useful in determining if any free or emulsified water is present.

• Solids - Look for solids settling out as signs of external and internal contamination.

Additional onsite lube oil checks can be conducted by a lubricant supplier. These tests might include viscosity, filter patch for particulate, water concentration and thermography.

Knowledge of your turbine oil and its limitations will set the stage for years of reliable service. Keys to this knowledge include having the right tool for the job, and a solid understanding of lube oil analysis for new turbine oil evaluation and in-service oil condition monitoring. By following a few simple rules, like keeping the oil cool, dry and clean and by monitoring with regular, routine oil analysis, turbines oils should provide many years of continued service.

References

1. AISE Association of Iron and Steel Engineers. (1996). The Lubrication Engineers Manual - Second Edition. Pittsburgh, PA.

2. Bloch, H. P. (2000). Practical Lubrication for Industrial Facilities. The Fairmont Press. Lithburn, GA.

3. ExxonMobil Corporation. Turbine Inspection Manual. Fairfax, VA.

4. Swift, S.T., Butler, D.K., and Dewald, W. (2001). Turbine Oil Quality and Field Applications Requirements. Turbine Lubrication in the 21st Century ASTM STP 1407. West Conshohocken, PA.

5. ASTM. (1997). Standard Practice for In-Service Monitoring of Mineral Turbine Oils for Steam and Gas Turbines ASTM D4378-97. Annual Book of ASTM Standards Vol. 05.01.

Practicing Oil Analysis (3/2002)

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EMF EQUATION OF THREE PHASE SYNCHRONOUS MACHINE

EMF EQUATION


Let P= No of Poles F= Flux per pole in webers, N= speed in RPM, f= frequency in Hz


Z ph = No of conductors connected in series in phase


Tph= No of turns connected in series per phase


Kc= Coil span factor Kd= Distribution factor


Flux cut by each conductor during one revolution=PF webers


Time taken to complete one revolution= 60/N sec


Average emf induced per conductor= PF/60/N= PFN/60 volts


Averagw emf induced per phase= (PFN/60)*Zph= PFN/60x 2 Tph= 4 Ff Tph


RMS value of EMF induced per phase= average value x form factor = 4.44 FTpf f


Form factor = 1.11


Taking into consideration the coil span factor and distribution factor of the winding Actual EMF induced per phase
E ph= 4.44 Kc Kd f F Tph

Coil span factor K c
The ratio of induced emf in a coil when the winding is short pitched to the induced emf in the same coil when it is full pitched is called a coil span factor or pitch factor or chorded factor. It is generally denoted by Kc and its value is always less than unity

Distribution factor Kd
The ratio of induced emf in the coil group when the winding is distributed in number of slots to the induced emf in the coil group when the winding is concentrated in one slot is called a distribution factor or breadth factor.