Deaerator

 

                                          DEAERATOR

As discussed in the previous page, boiler feed water form suspended solids, minerals, and other dissolve impurities and gases. DM water is used in a boiler as for steam generation

      Deaerator are commonly used remove oxygen and other dissolve gases in the boiler feed water because oxygen is mainly responsible for corrosion in boiler tube and other equipment forming of oxide like rust.

In case of steam generation in a power plant, the steam is drive turbine , then condensed in a condenser and this condensate steam use again as feed water in a boiler . so the feed water path work as a close loop path . only some make up is required to make up the blow down and leakage losses. Feed water used in the boiler should be free from any dissolved gasses and oxygen. Deaerator is used for this propose. Dissolve carbon dioxide combine with water and make carbonic acid and that may cause of corrosion but mostly deaerator are design to remove oxygen in the feed water. Also, it serves the purpose of a storage tank from where feedwater is pump into the boiler by the BFP( boiler feed pump). L.P( low pressure ) dosing is also done here for removing the dissolved oxygen from the water.

There are many type of deaerator but commonly two type of deaerator are use in a power plant .

·      Tray type , direct contact deaerator

·      Spray type deaerator

Tray type deaerator- In this type of deaerator, water enters from the top of deaerator . water is distributed through a set of nozzles. Water collect into the bottom storage tank from the deareator column through the perforated trays and small droplets are formed. Low pressure steam is supplied to the steam distributor. This steam moves up in the boiling point corresponding to the deaerator pressure. Due to the formation of small water droplets, the contact surface exposed to increase which result in complete removal of dissolved gasses.

by heating the water dissolving capacity of gases in the water decrease. So, dissolved gasses are remove from the water easily.

 Spray type deaerator- Spray Type deaerator is a cylindrical vessel used for the removal of dissolved gases from the feed water. The feed water fed into the deaerator will pass on through the vented section where the water will experience high steam which allows the feed water to remove dissolved gases. The spray type deaerator diagram is shown below

 

 

 

 

 

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Waste heat recovery boiler (WHRB)

 

WHRB

WHRB (waste heat recovery boiler) are used to utilize the heat energy from the system which would otherwise go waste.

     This  boilers are make use of the waste heat of the exhaust gases at the outlet of furnace , gas turbine and other factories when the waste exhaust gases have on a required temperature.

          Waste heat recovery boiler is a system which recovery various kind of waste heat generated from the production process of steel, chemicals etc. then lot of gas is produced. This hot gases is utilized in the boiler for steam generation. This hot gases contain significant amount of abrasive dust, these dust particles may be damage the boiler tube due to erosion. This problem is minimum by lowering the gas velocity providing the M.D.C( mechanical dust collector) .in m.d.c hot gasses passes though and the abrupt change in the direction of flue gases flow, dust partials settle down and remove by suitable ash ash handling system.

There are  some basic requirement or input calculation your waste heat form the soure . these are

·      Type of fuel and its composition

·      Amount of flue gasses leaving the exhaust in per hour in kg/hr or nm³/hr

·      The temperature of flue gases at the exhaust in ^oc

·      The process where you want to utilize this heat.The amount of steam generation or steam boiler of heat transfer is controlled by the quantity of heat available in the flue gasses. In this water tube and fire tube both are available as per the design requirement.

Waste heat recovery boiler benefit:

·      High reliable in operation and robust in construction

·      Quick payback return are achieved

·      One time investment and long time return

·      No combustion, no emission hence eco-friendly

·      Energy being put to use which was getting wasted anyway     

 Whrb boiler efficiency formula-

Efficiency = 100-(q₁+q₂₊q₃+q₄+q₅+q₆)

When, q₂ is flue gas losses

            q₃ is complete combustion losses

            q₄ is solid incomplete combustion losses

            q₅  is heat radiation  losses

            q₆ is slag gas physical losses

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Electric motor

 

                           Electric motors

Introduction-An electric motor is an electrical machine that convert electrical energy into mechanical energy those use in pump , fan and other equipment .

Type of motors-mostly two type motor use in electrical field .

·      A.C motors

·      D.C motors

Today we are discuss about a.c motors

                              A.C motors

 An a.c motor is the most commonly used in industrial application. Its is work on alternating current. Its using an electromagnetic induction phenomenon. The motor may be single phase or three phase. The three phase motor are mostly applied in the industry for bulk power conversion. For small power conversion the single phase a.c motor are used. In motor all part cover in main housing. In a front of motor a shaft is available those provide mechanical energy, in end  of motor fan is available for cooling propose because the induction motor can produce a lot of heat when in operation. So fan blown ambient air over the casing to cool down. If the induction motor becomes to hot the winding insulation melts , causing a short circuit and fire.fins increase surface area allowing more unwanted heat to be removed .motor shaft is  run with the help of bearing smoothly , that bearing install in the front shield and end shield of motor.

            In housing there are two main part .

·      Stator

·      Rotor

stator is static part of the motor it is installed in the motor casing. It is make with copper wire, copper wire wrapped and make a coil that is called stator winding. It is positioned around inner perimeter, this copper wire is cover with enameled. In a electric motor , the stator provide a rotating magnetic field .

          rotor is a rotating component of an electromagnetic system in the electric motor.

There are two type of rotor in a.c machine

    Squirrel cage rotor

    Wound type rotor or slip ring type rotor

 In a three phase induction motor every coil have two end point those connect with electrical terminal box at the top and output rotating shaft on the left ,when current flow through in wire, wire generates electromagnetic field . The magnetic field of the wire interacts with the magnetic causing movement. wire move upward or downward depending on direction of current and polarity of current then the rotor is start to run,

Its rotation is due to the interaction between the winding and the magnetic field which produces a torque around the rotor’s axis.

Advantages of a.c motors- three-phase induction motor is the most commonly used motor in industrial application because of the advantage listed below:

Simple design

Rugged construction

Reliable operation

Low initial cost

High efficiency

Easy operation and simple maintenance

 

 

 

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What is steam turbine?

 

Intoduction-Steam turbine is mechanical device that convert kinetic energy from pressurised steam into useful mechanical work. It is generate rotary motion directly.

            Sir Charles Algemon Parson , a British engineer, patented modern steam turbine in 1884. The crude from of a steam turbine was made by Hero Alexandra during 1^st century AD, called Hero ball or Aeolipile .It was the first from of reaction steam turbine. This device was consisting of an airtight chamber(sphere) with bent or curved pipes, the sphere starts rotating.

Now days, large steam turbine are used to generate 100MW electricity. Interior of a turbine consists of several sets of blades. The blades fixed on the casing are called fixed blades and some blades are fixed on rotor shaft is called rotating or moving blades. Clearance between these two blades sets is very minimum. steam is allowed to expand in these blades.

Fixed blades convert the potential energy of the steam into kinetic energy and directs the flow to the moving blades . Moving blades convert this kinetic energy into force and rotate the turbine shaft. Steam turbine are mostly axial flow type it means steam flow over the blades in the direction parallel to axis of rotor.                                 

Steam turbine blade- turbine blades classified in two type.

·      Moving blades

·      Fixed blades( daiphragm)

Moving blades-we are discussed in earlier section those blades are fixed on rotor shaft it is called moving blades and This blades are convert kinetic energy into force. In each stage of the turbine, there are moving and fixed blades. At each stage the pressure of steam are drop .

       A blades has to withstand higher pressure and temperature at the inlet stage. The pressure and temperature of steam decrease gradually. Toward the last stage of blade, the steam becomes wet and its volume become more. So, the blade size at the exit stage is large and it has to withstand erosion.

v Properties of a good blades- These are some properties are available in a turbine blades.

·      Good tensile and fatigue.

·      Toughness and ductility at working temperature.

·      Resistance to corrosion and erosion.

·      Good machinability.

·      Low ductility.

·      Good vibration damping property.

 Fixed blades(Diaphragm)- The partitions between pressure stage in a turbine’s casing are called diaphragm. They hold the vane-shaped fixed blades which facilitate the expansion of steam and guide it to flow over the subsequent moving blade row. One-half of diaphragm is fitted to the top casing and second half diaphragm is fitted into the button casing.

         Diaphragm is comprises of following three main section

·      Outer ring

·      Blade ring

·      Inner ring or web

 

 

 

 

 

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Steam generation in a boiler

 AS discusses earlier section boiler is a machine that generated steam at a desires pressure and temperature. In a boiler fuel burn in a furnace to get heat energy which is convert chemical energy in a heat energy store in fuel. This heat is utilised to produce steam from the water. Different type of fuel use in a boiler and according , the boiler designed. In water tube boiler water tube is arranged around the furnace and the path the flue gasses. In this tube feed water is circulated. Water tube is arranged in close system by the boiler drum. Feed water come in tube by water drum and after take heat energy to vaporize and went in drum. Due to different density , water is circulated in these tube naturally

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                                               Water circulation is divide into two type first is natural circulation and second is force circulation.                    

              In a force circulation circulation is given by

                                                    F = ρcH₁ - ρcH₂

Where, ρc = density of cold water, ρc = density of hold water
A force circulation boiler is a boiler where a pump is used to circulate water inside the boiler.
               The force circulation boiler being the same as a natural circulation boiler, at the feed water pump water is introduced into the steam drum and is circulation around the boiler, leaving only as steam what makes the force circulation boiler different its use of a secondary pump that circulation water through the boiler. The secondary pump takes the feed water going to the boiler and rises the pressure of the water going in.

A boiler drum filled with a fresh feedwater. The feed water before entering into the drum is heat at the economiser which placed at the flue gas path. Most of the heat of flue gas is utilised inside the boiler . still considerable amount of heat energy is available in it. This heat is utilised in economiser to heat up the feed water. it is increase the efficiency of boiler.
                  For burning of fuel, the required oxygen is obtain from atmospheric air. air is supplied by force draught (F.D) fan . this air is heat by air heat before sent into the boiler furnace . if cold air is used , then there will be loss of energy. Air heater is place the path of the flue gasses.

 

 

Boiler system arrangement

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Boiler feed water chemistry

Introduction

  Steam is convert by the water those water is used in boiler is called boiler feed water. The water is available from different source like river, sea, pond, ground water but this water is not use directly in the boiler of the purpose of steam generation .

    Before using this water in a boiler, these impurities are remove by different method.

Water impurities remove method -water impurities are responsible to decrease boiler efficiency .Water impurities are solidify in tube so the heat is not transfer properly and then the boiler efficiency decrease. Before transfer the water in boiler tube this impurities are remove. There are mainly two type of impurities available in the water first is undissolved impurities and second is dissolved impurities. We are discuss about how to remove this impurities 

*Undissolved impurities- There are three process to remove undissolved impurities. 

:: Sedimentation- In this method the raw water is collected in the tank with which the sand ,mud and other heavy suspended material are settle down by the gravity of force and the clean water is on the tank . Then the is decant a other tank, this water is clear but it is not useful for drank. 

 

:: Filtration-In filtration process water is pass through a bed, this bed  is made by  porous material ( sand ,gravel ,charcoal). when water is passed through this bed then suspended material are collected in the bed and clean water is collected in the bottom of the filter bed , after some quantity of water are pass through this bed it is wash with water, water are normally  flow in reverse direction and the sediments are remove in the filter bed ,this process is called backwash .  after remove this sediments filter is used again.

               In water treatment plant , pressure sand filter and active carbon filter are also used to make the water completely free form suspended solids. 

Pressure sand filter- The pressure sand filter  is consists a multiple layer of sand with a verity of  size  and special gravel . This filter is designed to remove the turbidity and suspended particles present in feed water with a minimum pressure drop.

 

                                           

Active carbon filter- Active carbon and charcoal is used at active carbon filter. Active carbon is a black solid substance resembling granular or powdered charcoal . active carbon reduces organic chemicals , chlorine, lead and tastes and odours

                                            

                                                                                   

                                                            

  A   Multi Grade Filters (MGF) is also used in water treatment but it is used only low turbidity water , this filter is consists by a multiple layer of gravel , sand and active carbon , it a combination for PSF and ACF filter .

 

 

        :: Coagulation- In coagulation , colloidal impurities are remove in water by the conglomeration of small colloidal particles to the bigger particles having more mass to settle by the gravity of force.                                                                                                             colloidal particles have some electric charge developed on the surface , so repel each other and cannot conglomerate into large particles ,  we add some chemical such as alum which are produces positive charge to neutralization  the negative charge of particles then the particles can be stick together, forming a bigger particles, then these particles can be settle down by gravity of force and the colloidal impurities are remove in boiler water .

                          

                                   

        After this process water is used to drinking but this water is not transfer in boiler for the purpose of steam generation (chlorination is done to kill bacteria) . Only undissolved impurities are remove by above process . The water still contains dissolved salt and minerals. Present this salt and minerals are responsible  for hardness of water. Their are two type of hardness in water.                                                                               

       First temporary hardness and second is permanent hardness. Temporary hardness are remove by boiling the water bicarbonates and magnesium are responsible for temporary hardness. permanent hardness remove by many method.

         *Dissolved impurities- after remove undissolved impurities in water ,its it use drinking but their don't sent in boiler for steam generation because some salt of calcium , iron,  aluminum,  magnesium  and other gas etc are present in water then as it form a sludge.                       

                 Natural source of water contain silica. Present of silica is not desirable in feed water, as its form hard scale. Sometime silica is evaporated and carried out in steam which form an insoluble deposit on the turbine blades  , then the efficiency of turbine is decrease.                                         So some treatment are apply to remove the salt in boiler feed water . 

 Those treatments are apply inside the boiler it is called internal treatment and those treatment are apply outside the boiler it is called external treatment.

:: Internal  treatment- In internal treatment ,chemical are added in boiler water. these chemical are react with water salts and convert a harmful sludge after some time this sludge settle down by gravity for force .later then this sludge remove by blow down .

Some internal treatment are basically use in boiler.

* Soda ash (sodium carbonate Na₂) treatment - soda ash treatment is also use in low pressure boiler . In this process soda ash is added in boiler water , it react with chlorides and sulphates of magnesium and calcium to convert into insoluble sludge .  

Cacl₂ + Na₂Co₃ → CaCo₃ + 2NaCl  

MgSo₄ + Na₂Co₃   →MgCo₃  + Na₂So₄

* Phosphate treatment or Hp dosing ( high pressure dosing) – In high pressure boiler soda ash treatment is not used ,  it  is form caustic soda and increase  with the increase in temperature. Hence it is very difficult to maintain the ph valve of boiler water .Also , at higher PH solubility of calcium carbonate increase . so ,in high pressure boiler phosphate treatment is preferred as internal treatment.  

                HP dosing is only use in drum type boiler , chemicals are added in boiler in  boiler drum because phosphate work on absolute temperature and create a harmful sludge , this sludge are remove by CBD(continuous blow down).

Trisodium phosphate (Na₃PO₄), Disodium phosphate(Na₂HPO₄), Monosodium phosphate(NaH₂PO₄) are use in hp dosing. TSP is highly alkaline , DSP is less alkaline and MSP is slightly alkaline . It is use to different purpose. This chemical is also called orthophosphates.

 :: External treatment – we are discussed internal treatment method for remove the dissolve impurity in boiler feed water but there are not sufficient in a high pressure boiler.

Feed water treated externally before sending in boiler. By using external treated water, the quality of the boiler water can be maintain with little blowdown. Particularly   , in case of once though boiler the feed water is treated externally , as no further internal treatment is possible.

We are used some process to remove the dissolved salts and minerals in boiler feed water

*Softener process

*RO ( reverse osmosis )

* Demineralization process/ Cation and anion exchanger

Some process are used to remove the dissolve gases in feed water

* LP dosing

* Degasser

* Deaerator

We are discussed in following process in details.

SOFTNER- In softener is make hard water into soft water. softener is used for low pressure boiler. It is easily remove scale forming calcium and magnesium iron from water by iron exchange process using resin. Hard water contains salts of magnesium and calcium. Water hardness is measured in grains per gallon or milligrams per liter(mg/liter) or equivalent part per million(ppm).

          In this process, softener vessel is filled with negatively charge resin these resin is react with positively charge calcium and magnesium iron and it is exchange, sodium into water because resin is in a sodium form. The water is come out is soft form. After some time resin is discharge so first resin bed is backwashed to remove any filtered particles and recharge with sodium chloride or NaCl.

Chemical reaction

RCa + NaCL→ RNa + CaCl₂

RMg + NaCL→ RNa + MgCl₂

 

 

                                         

Softener working process

Demineralization process– In industrial water treated by demineralization process, in this process dissolved impurities are remove form feed water and process to steam generation. Demineralised water complete (almost) free of dissolved minerals like calcium, magnesium, iron, copper etc.  

* Principle of demineralization process –Water free from undissolved  suspend  solids(from  pressures filter and active carbon filter) passes through a cation  exchange containing a bed of cross-linked polymers called cation resin. This resin containing hydrogen ions (H⁺) .When water passes through the bed , earlier mentioned cation are substituted by these H⁺ ions of the resin.

Water coming out form cation exchange is acidic in nature which passes through another exchange, i.e anion exchanger ,anion exchanger contains another type of resin called anion resin containing hydroxide ions OH^- . When water from the cation passed through anion resin, earlier discussed anion are substituted by OH^- ions of resin.

In between the cation and anion exchanger, there is a degasifier unit .Here, carbonate and bicarbonates are removed. 

 

                             

DM water treatment process

Degasser- As state in earlier section, when carbonates and bicarbonates are passed though the cation and anion exchanger, carbonic acid (H₂CO₃) is formed . carbonic is a weak acid. Soft drinks available in market contain carbonic acid. This can easily be broken into water and carbon dioxide gas.

                               H₂CO₃  ^→ H₂O +CO₃

 

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what is boiler

Boiler is a machine that is generate steam on a designer pressure and temperature .A boiler is a machine that used to create steam by applying heat energy to water. This steam is use as a mechanical energy.

   

In a power plant boiler is use to produce steam , this steam can be generate electricity.

 

Type of boiler- Boiler  are classified depending upon the flue , pressure of steam, mode of flow of heat carrying substance etc. Mostly boilers are classified on basis of following considerations. 

*

 Fire tube boiler and water tube boiler

 

•  fire tube boiler - In this boiler hot gasses is flow in the tube and water is run outer surface of the tube . In this boiler the fuel is burnt inside the furnace and hot gasses produced in it, then passes through the fire tube . The fire tube are immersed in water inside the main vessel of the boiler . As the hot gasses is passes through these tubes and water is flow  outer surface of these tube and the heat is transfer through it and water is convert into steam by the naturally circulation. The water is convert into steam and the new cool water is come in the vessel through water feed inlet path , as the steam and the water is stored is the same vessel, and high pressure  steam is pass through the main steam valve this steam valve is called mssv valve . Main steam safety valve (mssv) is use the safety of the boiler. 

 

 

                                                  Fire tube boiler

  Example- lancashire,cornish ,locomotive ,scotch etc.

 

Water tube boiler-  In this boiler water is pass thought in-side the tube and hot flue gasses pass outside the tube .The heat is transfer thought the wall of the tubes by thermal condition , heating the water and ultimately creating steam . This steam is use to utilize to generate the electricity and other work. Water tube boiler is a high pressure boiler that is operate at a pressure. Water tube boiler efficiency is high greater than fire tube

       

 

Water tube boiler

Example- la-mont, bensen, stirling, babcock and wilcox ect.

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