CEMENT !!! Part II

Well , as already said ... preparation of cement is a two step process .
Firstly , Beneficiation of cement rock , and
then the actual method of preparation of cement .



BENEFICIATION OF  CEMENT ROCK :- 

What is " Beneficiation" in the first place ?? 
Simply , It is the process of improving the physical and chemical properties of the raw materials so that we can recover the final product with more efficiency , and thus , more profit !!! It is the process of separating the gangue from the required ore . It is also known as "mineral dressing" . These beneficiation methods  are based on the properties of fluid mechanics and adsorption . 
The limestone obtained from the mines is not pure and efficient enough for use in the production of cement , hence the need to beneficiate it . 
The operations used can be grinding , classification , flotation , thickening and much more accordingly , keeping the quality of the ore in mind .  

The beneficiation can be done by two methods - wet and dry methods . Dry methods are more efficient preventing wastage , but more care has to be taken in separation . Nowadays , wet processes are more in vogue . 

The process consists of the following steps : 
1) Firstly , the ore is examined , magnetic impurities are removed easily by respective methods and the ore is  then pulverized to a fine mixture . Pulverizers are mechanical devices , including ball mills , tube mills , etc , which are used for grinding the mixture into a fine powder . 

A TYPICAL PULVERIZER

2) If the ore is usable enough , then it is directly sent into the "Hydro separator" . The part of the ore which is not so suitable enough is further processed , they are sent into "Rake Classifiers" .
Hydro separators are devices in which solids in suspension are agitated by hydraulic pressure or stirring devices , thus separating the ore . It is normally used to separate the ore from water . Speaking in common sense terms - HYDRO = water , SEPERATOR = device to separate . :P
Rake Classifiers are a type of mechanical classifier which utilize reciprocal rakes on an inclined plane to separate coarse particles from the fine ore . The fine material is overflowed , while the coarse waste material is discharged by means of the inclined plane . 

A TYPICAL HYDRO-SEPARATOR

3) The over-flown product from the rake classifier is then sent into a "Homogenizer" , which allows only one part of the ore , for us , the useful part and from there , it is sent into 3 Flotation Cells - namely Beater , Enriching and Stripping cells . 

A TYPICAL FLOTATION CELL

 Froth Flotation method takes place at these flotation cells . 
The BEATER cell is the place at which the cross-currents of the ore and the Frothing agent meet .
Then , the STRIPPING cell removes the sedimented ore .
The  ENRICHING cell enriches the ore with the froth and thus we obtain pure ore particles in the ore . For more efficiency , the froth reagent water is continuously recovered . 


4)  This product meets the already sent pure product at the hydro-separator , where the suspended ore particles in water are recovered , thus obtaining pure limestone slurry which can be used for cement production .
Note that in wet process we obtain a slurry , while in the dry process we get a powdery mixture itself . 




The reagent water is removed by the hydro-separator , thus giving us PURE BENEFICIATED LIMESTONE ROCK SLURRY , which is ready to be used in the next stage .........Keep logged in !!!

CEMENT !!! Part I

By no means complicated , cement is simply a material to hold together materials !!!  Technically speaking , Cement is the generic name of all those materials which initially have plastic flow , but when it is mixed with water or any other suitable liquid , forms a rigid - continuous mixture which solidifies on standing and when solidified has the capability to resist high compressive strengths . 

The most common type of cement is PORTLAND CEMENT !!! Way back in 1824 , an Englishman named JOSEPH ASPDIN patented portland cement . He obtained it by the calcination of an argillaceous limestone . He named it PORTLAND as synonymous to a type of rock found at the Isle Of Portland ,  famous for it's strength . One to think that this was the start for mankind's construction glue :P is wrong , cause centuries ago Romans built the famous "Colosseum" using a cement like material called POZZOLANS !!! pretty impressive huh ;) 

Basically , Cement can be summerised as a mixture of finely ground calcium silicates and aluminates of varying compositions , which decide the properties of that particular variety of cement . The main constituents of cement can be summed up into four varieties :
1)  C₂S
2)  C₃S
3)  C₃A
4)  C₄AF
Where , 
C = CaO
S = SiO₂
A = Al₂O₃
F = Fe₂O₃

Varying these % 's can lead to different types of Portland cements namely :- 


A ) TYPE - I :  REGULAR
      It has the following composition : 
      55% (C₃S), 19% (C₂S), 10% (C₃A), 7% (C₄AF), 2.8% MgO, 2.9% (SO₃), 1.0% Ignition loss, 
      and 1.0% free CaO. 
      It is used for general construction purposes . It gains it's full strength in 28 days . 

B ) TYPE - II : MODIFIED 
      It has the following composition : 
      51% (C₃S), 24% (C₂S), 6% (C₃A), 11% (C₄AF), 2.9% MgO, 2.5% (SO₃), 0.8% Ignition loss, 
      and 1.0% free CaO.
      The higher C₂S composition makes the cement moderately sulfate resistant and also 
      it has a moderate heat- of-hydration value .
      It is used specifically in places where the sulfur content in the soil is high .   

 C)  TYPE - III : HIGH EARLY STRENGTH 
        It has the following composition : 
        57% (C₃S), 19% (C₂S), 10% (C₃A), 7% (C₄AF), 3.0% MgO, 3.1% (SO₃), 0.9% Ignition loss, 
        and 1.3% free CaO.
        It has the ability to attain the strength of Type - I cement in just 3 days , but due 
       to the high % of C₃S and C₃A " together" can be devastating and can cause high 
       values of Heat-of-Hydration , thus long-time strength has to be sacrificed . Thus , it 
       is useless for massive construction works .
       Used only for emergency  constructions where we do not have much time to wait 
       for it to stand to gain strength .

  D) TYPE - IV : LOW HEAT 
        It has the following composition : 
      28% (C₃S), 49% (C₂S), 4% (C₃A), 12% (C₄AF), 1.8% MgO, 1.9% (SO₃), 0.9% Ignition loss, 
      and 0.8% free CaO.
      Notice the lower % of C₃S and C₃A , which are the major contributors of heat-of-
      hydration . Consequently , the % of C₄AF and other aggregates have to be increased.  
      Only drawback is that the time required to gain full strength is high when compared 
      to normal cement . 
      It is used for massive construction works like dams , etc .  

E ) TYPE - V : SULFATE RESISTANT 
       It has the following composition : 
     38% (C₃S), 43% (C₂S), 4% (C₃A), 9% (C₄AF), 1.9% MgO, 1.8% (SO₃), 0.9% Ignition loss, 
     and 0.8% free CaO.
     This kind of cement has the highest % composition of C₂S , thus making it highly 
     sulfate resistant .
     Used in places nearby to the sea , as it resists sea contact very well . 

Preparation of cement is a two step process ...The real game's still on......Keep logged into this site for an overview into it soon ;)

** CLOSED FOR MAINTENANCE **

EXAM TYM !!!!!!!!!!!!!! :O :O :O

PLATE HEAT EXCHANGERS !!!

Well guys..., today it will be PLATE HEAT EXCHANGERS ( PHE ) .

What exactly is a PHE ??
hmmmm

A Plate Heat Exchanger , or PHE as it is more commonly called as , is a type of heat exchanger that uses metal plates instead of the conventional pipes as in a Shell and Tube Heat Exchanger .

It was invented by Dr. Richard Seligman way back in 1923 .
                                                  

    

The plate heat exchanger revolutionized the concept of indirect heating or cooling of fluids . 

CONSTRUCTION :

The PHE consists of metal plates which are separated by rubber gaskets . The metal plates consist of holes at it's edges to facilitate the movement of the liquid .

The above picture illustrates the construction of a traditional PHE . The RED arrows represent the flow of the fluid which is hot , while the BLUE one represents the flow of the fluid which is relatively cooler. The metal plate can be either welded or semi-welded or brazen , accordingly to the industry in which the PHE is going to be incorporated into.

In place of pipes passing through a chamber , we have metal chambers , usually thin in depth and seperated by gaskets . 

Notice the flow of the liquids in the PHE , you will notice that the RED and BLUE fluid flow into alternating chambers !!! Thats the beauty of the idea !!! The gaskets are so designed as to allow the two fluids into successively alternating metal chambers , facilitating more surface area contact and thus , more heat transfer efficiency !!! BINGO !!!

Now the question why PHE when we already have shell and tube heat exchanger ??? Well , here's the complication : 

Shell and Tube Heat Exchangers cannot actually perform in par when we have a low-temperature or a low-pressure application , the design of the PHE is such that it is best suited for medium and low-pressure fluids because the driving factor in the concept is surface-area !!!

" Stainless- Steel " is the most commonly used metal to manufacture the plates in a PHE because of it's high strength , high corrosion resistance and it's ability to withstand high temperatures . 

There are again types of PHE :

1) PLATE AND FRAME HEAT EXCHANGER

2) PLATE AND FIN HEAT EXCHANGER

They have been classified based on the modifications done to the PHE for better feasibility in industrial processes.

ADVANTAGES :

1) High Heat Transfer Efficiency because it provides Large Surface Area

2) The thin layer ensures that the majority of the volume of the fluid flows through the plate cavities , facilitating more heat exchange

3) We can get High Degree of Turbulence at even Low Flow Rates 

4) We can control the amount of heat to be transferred between the fluids by changing the distance between the plates , i.e. by changing the volume of the cavities 

5) Compact , Low Cost and Easy to Clean

DISADVANTAGES :

1) Potential For Leakage 

2) Blocking of gaskets can occur due to the particulate impurities present in the fluids

3) After repeated use , particles may settle down in the metal cavities , thus decreasing the effective surface area of contact between the two fluids

USES :

1) In the petroleum industry - Lube Oil Cooling

2) As effective Condensers in pharmaceutical industries

3) In Combination Boilers

4) HVAC - Heating , Ventilating & Air-Conditioning ; It is used in this technology of indoor and automotive environmental comfort . 

Thats about the all important PHE guys !!! 

And ya !! From today am going to keep a problem as my poll !! I will give you " ONE DAY " to solve it out and click the answer !!! In that way we can also effectively develop our mathematical prowess in the subject !!!

THANKS GUYS FOR ALL THE SUPPORT !!! 

HAIL CHEMMIES !!!

HEAT EXCHANGERS !!!! Shell and Tube !!!

Ssup guys !!! Am so sorry to keep you all waiting ... but this stupid Windows Live Writer ceased to work :( ...Anywayz , am back in business , stronger as ever , so lets get into business right away !!!

Today it's about HEAT EXCHANGERS !!!
The most basic and common machine used in industries nowadays .

A Heat Exchanger , speaking in general terms is a device which " EXCHANGES HEAT " , simple right . Now as engineers we must complicate it :P .....so...A Heat Exchanger is a device *ahem* , which is used for effective heat transfer operations between two mediums , effectively , two fluids during industrial processes !!! Normally , there is no direct contact between the two media , but a thermally conductive wall exists separating them .


There are two primary classifications of heat exchangers -
1) The Parallel Flow Heat Exchanger

2) The Counter Flow Heat Exchanger

In the former , the fluids flow parallel to each other ; they enter the heat exchanger from  the same side and exit it from a common side . The latter is exactly opposite .
Always the Rebel wins the lot ;) , not surprisingly , the counter flow "rebel" Heat Exchanger is the one which gives more heat efficiency !!!

There are many types of heat exchangers , slowly and slowly i am going to highlight each one of them everyday ;)  .... today it will be The " SHELL AND TUBE " Heat Exchanger !!!

As the name itself declares , a Shell and Tube Heat Exchanger consists of an "outer" SHELL inside which a bundle of TUBES are arranged . This set of tubes is named a "Tube Bundle" . One fluid runs through these tubes , while the other flows outside the tubes BUT inside the shell . The heat is transferred from one fluid to the another through the walls of the tubes , either from tube side to shell side , or vice-versa .

But the tubes are not so simple as the one above guys :P ..... There are numerous tubes , for larger heat-exchange are , which are arranged inside the shell in patterns , either straight or in a U-shape , accordingly to the amount of heat it must exchange .

We can easily control the fluid in the tubes , but what about the one which is free-flowing in the shell ??? Hence , things called " BAFFLES" are used to direct the flow in the shell , so that the fluid in the shell is not flowing in a gingerly fashion creating pressure differences in the shell fluid .

The void like things in the right of the above picture are called "PLENUMS" , also called as "Water Boxes" , these help in pumping equal amount of the fluid in equal intervals of time in an orderly fashion .
Also depending on the number of times the fluids go around the heat exchanger , it can be diversified into ONE PASS or TWO PASS , the latter being the more efficient one .

Also they can be classified based on the phase of the fluids used in the shell and tubes . If the fluid used in each of them is in the same phase it is christened as a " SINGLE PHASE " Heat Exchanger . If the fluid in the shell is in a different phase than that of the tubes , it is called a " TWO PHASE " Heat Exchanger .

For an Heat Exchanger to be an efficient one , it must transfer heat well . Thus , the tube material in particular must have good thermal conductivity . Also , it must be able to resist thermal stresses which arise due to the difference in the temperatures of the two fluids in contact with the walls of the tube , thus repeatedly expanding and contracting .
Hence , the material must be Strong , Thermally Conductive and Corrosion resistant . Here comes the concept of " SUPER-ALLOYS " . These are used to make the tubes of the heat exchanger.
Ex:- Inconel , Hastelloy ,etc .
Stainless Steel and Carbon Steel can also be used , but they cannot compete with the above super-alloys in terms of efficiency developed .


ADVANTAGES :
1) used in oil refineries , and other large scale industrial processes

2) the BOILER used in locomotive engines is actually a modified heat exchanger , so is the CONDENSER used in refrigeration. They are essentially  TWO PHASE SHELL AND TUBE HEAT EXCHANGERS !!!

3) used in waste water treatment

4) the nuclear power plant's "Pressurized Water Reactors" is actually a TWO PHASE , U TUBE , SHELL AND TUBE HEAT EXCHANGER .

5) used in aircrafts . The Heat Exchanger takes the heat from the engine's oil system and showers it on the fuel , thus , leading to better fuel economy and an absence of using expensive anti-refrigerants in the fuel .

6) maybe the most common use of an heat exchanger is the RADIATOR !!!


Well people , thats about heat exchangers , or i must say a part of it :P ... there is more to come about the other types in the following posts !!!
BUT , i would want to say that the world's most efficient heat exchanger is INSIDE you !!!!
Believe me , thats true !!!



your LUNGS !!!!



just finished reading THE LOST SYMBOL !!! maybe this is what Dan Brown meant by saying YOUR BODY IS YOUR TEMPLE !!! Isn't nature wonderful !!!

SPRAY DRYER !!!

Hey guys , lets throw some light into the concept of Drying today !!!

Generally speaking , Drying refers to the removal of minute amount of water vapour from the feed . There are many types of Drying , the most prominent of them being Rotary Drying , Tunnel Drying , Spray Drying , etc .

In all of these basic UNIT OPERATIONS , Spray Drying holds a numero uno status from quite some time . What’s so special in this process that it survived the turmoil of humanity right from the 1870s , when new process come and then sink without a trace  ??? Lets know then !!!

First of all …..WHY SPRAY DRYING WHEN WE CAN JUST EVAPORATE ???   no great energy wastage from our side too …then why ??

The answer’s SIMPLE  ---- In the world there are a galore of thermally sensitive and thermally resistant  materials . We simply cannot dry them in the open sun …The former might just evaporate without a trace while the latter stubbornly sits there all day no matter you dry it for weeks on a trot !!! Tadaa !! Hence , Spray Drying

Lucidly speaking , Spray Drying involves the production of a dry , granular , free-flowing powder from a liquid or a slurry by the rapid cooling with hot gases .

It is a CONTINUOUS , PARTICLE PROCESSING , MASS-TRANSFER operation !!!

In the process of Spray Drying , the liquid stream or feed  , as we chemmies call it , is first atomized using a suitable Atomizer and is then sprayed at a high speed over hot gases present in the apparatus . The hot gas normally is Air , but if the feed is oxygen reacting we use Nitrogen . Next the hot gases dry up the stream , which is then taken into a Cyclone for separation of the particles produced . In addition , a bag filter can also be used to get finer particles .

Spray Drying mainly involves four stages :-

a) Concentration of the feed

b) Atomization of the slurry

c) Droplet drying

d) Separation using cyclones

 

Don’t get confused with the stages , but Spray Drying is a SINGLE-STEP process . The above stages occur at blinding velocity that they all are considered one continuous entity .

ADVANTAGES :

1) It is continuous.

2) Can be made Fully – Automated easily

3) It can be used irrespective of the feed capacity .

4) We can produce nearly-perfect spherical particles .

5) The weight and volume of feed can be reduced . As a matter of fact , Spray Drying reached it’s full glory during WW2 , where the need to reduce the weight of food for the army was enormous .

 

USES :

Used in the FOOD industry extensively , especially in the Dairy Industry .

The Pharmaceutical Industry found a great way to make powders for tablets .

In recent times the Ceramic field is catching up with this concept too !!!

 

DISADVANTAGES :

1) Very energy extensive

2)  High operating cost

3) Ineffective in producing a constant granular size of particles

Hence , the concept of NANO SPRAY DRYERS is the talk of the town nowadays .We will discuss about it sometime later in the future for sure !!!

Well , for the never ending practical thirst for the geek community of the world , here’s a special gift just for you

check out

http://www.gbm.dk/gbm/SD-e.htm for the working model of a common spray dryer !!!

au revoir guys !!!

BATCH PROCESS !!!

First of all lets discuss DISTILLATION !!! Distillation is a method of separating two liquid from a  mixture based in the difference in their boiling points or simply , Volatility .

Distillation is a pure UNIT OPERATION , which may as well be the oldest known operation used for the separation of liquid mixtures .

Distillation is many types , now letz throw some light into the most basic one , called BATCH DISTILLATION or BATCH PROCESS generally .

BATCH DISTILLATION , as the name suggests is a form of distillation where the mixture is distilled in “ BATCHES ” , or small volumes.
It means the distillation is carried out separately for different batches . First a batch is distilled , then the second and then the third and so on .

This is in total contrast to the CONTINUOUS  DISTILLATION where the distillation goes on continuously , the feed is continuously fed and the distillate product is continuously collected .

In Batch Distillation ,  as in the case of simple distillation , the liquid mixture is fed into the distillation column where it is vaporised . The lower boiling liquid evaporates first leaving behind the higher boiling liquid , thus effectively separating the mixture . The only difference is it is done in batches .

Batch process is used :

a) for “intermittent” processes ( which alternatively cease and start ) .

b) for small volumes of feed , as it is feasible or say economical for only small volumes . Continuous Distillation does not work out well when we have to distillate only a domestic amount of mixture .

c) when we desire for “flexible” methods , yes , we can easily change the components of the mixture and obtain the same successful distillation process without applying any changes to the operation . No wonder it is called a Unit Operation !!!

BENZENE !!!

Well….this compound one must say totally changed the way we understand chemistry !!! , especially ORGANIC CHEMISTRY .

It behaves differently , is structurally different , chemically different …… shortly totally different from any of the organic chemicals encountered by chemists in the history of chemicals .

The basic abnormality was it’s molecular formula….It did not fit itself into any of the known homologous series !!! It was a world in itself .

So , the total credit of the extension of the field of organic chemistry into new heights must go to KEKULE aka Friedrich August Kekule von Stradonitz !!! Phew !! that’s a mouthful !!  yet , this person is the PRINCIPAL founder of the total theory of CHEMICAL STRUCTURE !!!

He dreaming abt benzene’s structure is the best known story among chemists !!! Was it luck or must we salute his highly intellectuality which his sub-conscious mind possesses which we all together lack in real life !!!

Benzene is the stone-stepping break-through in organic chemistry cause this is where the concept of aromaticity all starts !!!

Structurally , benzene is a wonder !!! but rhetorically , it is quite inflammable and carcinogenic !!! Hence , it’s use as a industry solvent is being questioned further !!!

Whatever may be the conclusion….Benzene has become what we called the heart-throb of every school going child who is just fascinated by the mystery of it’s structure and is blown over by the history surrounding it !!!

Well , I was ….Benzene is simply …MY BABY !!!

happy new year guys and gals !!!!