Geared variable speed coupling / Geared Hydrodynamic coupling

The principle:
The geared variable speed coupling combines the hydro dynamic coupling and Mechanica Gear in one compact unit.
The geared variable speed coupling controls the speed of the driven machine precisely, quickly.

Uses:
It is used to control the speed of the Driven Machine,Vary the power transmitted Reduce the power consuption, Increases the productivity of operation. Motor can start at no load

Design and function:
*The hydrodynamic geared coupling consist of double helical gear integrated in a housing with a split   horizontal body.
*The gear box is located before the hydrodynamica coupling.
*In hydrodynamic coupling there are two wheels, pump wheel abd turbine wheel. pump wheel is          conected to the drive machine. and the turbine wheel is conected to the driven machine.
*The pump wheel rotates at constant motor speed  and the turbine wheel rotates atvariable speed.
*Using the hydro dynamic principle the fluid is transmitted from the pump wheel to the turbine wheel at variable output speed.
*The scoop varies the coupling filling. The filling amount determines the power transmitted and the    speed of the driven machine.
*An actuator varies the speed of the scoop tube, in this way speed can be controlled.
*Working oil is supplied to the hydrodynamic coupling for varying the speed
*lube oil is supplied to the gear box.
*working and lube oil circuits are seperate.

The actuator is Electro hydraulic actuator for quick and precision operation of the scoop. A simple 4-20 MA is requires to control the scoop position.

The motor will start with no load conditions and smoothly accelerate even with machines with large moment of inertia. This happens because the hydrodynamic coupling is empty during the motor starting, so it seperates the motor from the driven machine so that the motor runs at no load condition.
starting the motor at no load conditions are important for equipments having large moment of inertia or with processes with initially large load.

Classification Steel Pipes and Tubes

Steel pipe & tubes are classified by the following methods:

1. Manufacture: Method Broadly Classified as Seamless & Welded.
• Seamless method is further classified as Hot Finished & Cold Drawn.  
• Welded are classified as ERW, SAW, CDW, SW, MMAW.
2. Steel Chemistry: Carbon steel, Alloy steel, Stainless Steel.
• Carbon Steel are further classified as low, Medium, high carbon, manganese steel.
• Alloy steel are further classified by composition of chrome & moly.
• Stainless steel are classified by their various composition of Nickel, crome, moly etc.   
3. End Use;
• Tubes are used to transferred heat load through its walls (Thickness) 
• Pipes are used to transfer heat loads through its Bore

Precautions to be taken before entering Electrostatic precipitator for maintenance

Following are the safety precautions must be taken before enering the esp
1.Valid work permit must be taken for working
2.Switch off the High voltage power supply using disconnecting switch and lock the disconneting          switch in off position
3.when the disconnecting switch is in off position the emmitting electrode of respective field gets          earthed directly
4.Then discharge the static charge of Electrostatic precipitator field using earthing rods
5.The earthing rod clamps must be properly connected to the earth
6.The ESP internals must be cooled down sufficiently
7.Rapping motors are switched off and power should be isolated.
8.The Oxygen level must be measured before entering the ESP
9. If dust is accumulated, it must be removed and area must be clean                                           10.Hand lamps and tools for work must be connected to 24v supply
11.It is always safe to carry out work atlest with a team of two persons inside ESP.

Proximate and Ultimate Analysis of coal

Coal can be analysed by two methods
(i) Proximate Analysis
(ii) Ultimate Analysis

(i) Proximate Analysis
The analysis of moisture content, fixed carbon, volatile matter and Ash content of coal is called proximate Analysis of coal

Analysis of Moisture Control in coal:
1-2 gms of powdered coal is taken in a dry crucible and heated for 105deg c for 1 hour is cooled over concentrated h2so4.

% of moisture content =( (W-W1)/W) x 100

where W is the 1-2 gms weight of coal powder before heating
W1 - Weight of coal powder after heating at 105 for 1 hour

Analysis of volatile Matter in coal
1-2 gms of coal is taken in a platinum crucible and heated in a furnace at 950 deg c for 7 min and it is cooled over as explained earlier

% of volatile matter in coal (W1-W2)/W1  x100

W1 - Weight of coal powder after heating at 105 for 1 hour
W2 - Weight of coal powder after heating at 950deg for 7min

Analysis of fixed carbon and Ash
1-2 gms powedered coal is taken in a platinum crucible with lid and carefully heated until to remove all volatile matter and then the lid is removed and stongly heated at 750deg c until all carbanaeous content are reonved then it is cooled

% of ash = (ash weight / coal powder weight) x 100
% of fixed carbon = 100 -(% moisture content+ % of volatile matter + % of  ash content)

ULTIMATE ANALYSIS
It is the analysis of element wise coal composition. It is helpful in finding the % of carbon, hydrogen, nitrogen,sulphur and oxygen content.

STEAM DRUM CONTROL ELEMENTS

The purpose of the drum level controller is to bring drum level upto a level during the startup and to maintain the level at the constant load.The decrease in the level will uncover the boiler tubes and expose them to high temperature and leads them to failure. Increase in the level may interfere the steam and moisture separation and will lead to moisture carry over to turbine and reduce boiler efficiency.

Steam flow is the rate of steam leaving the boiler- the demand. water flow is the rate of feed water flow in to the drum- the supply. Drum level reflects the amount of water in the boiler - the invetory

when there is change in the boiler load , suppose boiler load increases, the steam flow demand will be higher than the supply feed water and so the drum water level reduces. so in such a event the controller opens the feed control valve and increases the drum level.

There are types of drum level control.

single element drum level control
Two Element drum level control
Three element drum level control

The use of one of these method will depend upon boiler size and the load changes.

Single element drum level control:

This is the simplest and least effective form of control

Two Element Drum level Control

The two element drum level control can be best applied to single drum boiler where the feed water is at constant pressure. It gets rwo proportional signal from drum trasmitter and mainsteam transmitter.

The steam flow from the boiler transmitts the output signal which acts as a set point for the feed water controller. so that there will be balance between the steam flow and feed water flow. If the steam flow increases due to the load increases, The controller compares the setpoint of the steam flow with the feed flow and to match the set point it opens the feed control valve to increase the feed flow this is called feed forward flow.

The drum level transmitter sends signals to the drum controller which further trims the setpoint of the feed water flow set by the steam flow. Because the drum controller can compensate for the flow measurement errors and unmeasured load disturbances like blow down or steam circuit leakage. this is called cascade controll.

Three Element Drum level control

The three element drum level control maintains the drum level by monitoring the drum level, feed water flow  and steam flow.It provides tighter control for drum level with fluctuating steam load and ideal for a system which suffers from fluctuating feed water pressure or flow.

The three level controller uses three transmitter or process variables to maintain the drum level.

Three Element Drum level control is used in plant where multiple boiler feed water pumps run in parallel to meet the pressure rating of the steam drum, so that it can fill the water in the drum.. 

When the steam flow from the boiler increases , it sets a setpoint to the feed water controller so that the feed water control valve opens according to it. further the drum level controller further trims the set point as mentioned earlier in the two element drum control. If any of the pump pressure reduces and as the feed water valve opens to maintain the water in the drum , the feed water pressure reduces as the valve opens so in order to avois this the valve must be opened gradually for decreasing the feed water pressure this is achieved by taking the feed water pressure transmitter and comparing with the drum and feed water controller set point

water Level gauges in super critical boiler

In plant where steam is used primarily for generating power, water and steam cycle becomes more complicated. Some of these are reffered to supercritical boiler where steam is produced in the pressure exceeding 220 bar. At this pressure the density of water and steam are same. Because there is no difference in density these boilers does not require water level  guages because there is no water level. the supercritical boiler is also called once through boiler as it does not have drum.  After the water is converted into steam in the boiler it passes through the superheater coil, more tubes are exposed to the flue gases to increase the temperature of steam. As steam passes through these tubes the temperature of steam further increases and forms superheated steam. (If the saturated steam which is heated again is converted into supersatured steam.)

Mechanical Seal

Parts of a mechanical seal
1.Rotary seal ring
2.Stationary seal ring
3.Rotary seal ring secondary seal
4.stationary seal ring secondary seal
5.spring
6.Gland Plate
7.Clamp Ring

Mechanical Seal 4 main points sealing system.
Primary Seal:
The sealing Between Rotating and stationary Faces is know as primary seal

Secondary Seal
The seal between the rotary part and shaft with o ring
The seal between the statioary part and gland seal plate
The seal between gland plate and stuffing box is usally o ring or gasket

Stationary seal ring
The stationary seal ring is usually attached to the gland plate and is made of softer material like carbon graphite

Rotary seal Ring
The Rotay seal ring is fixed to the rotating shaft and is made of harder material usally tungsten carbide and silicon carbide.

The fluid film:
In mechanical seal faces are lubricated by thin film between rotating and stationary

The distance between the stationary and Rotary Faces are 0.0001mm

Essential Requirement of proper operation of MechanicSeal
1.Seal faces must be flat and polished.
2.seal faces must be perpendicular to the shaft.
3.sufficient spring force for maintaining the contact
4.sufficient lubrication between seal faces

Flatness of seal faces 0.0008mm obtained by lapping

Mechanical seal faces material:
Usually dissimilar materials are used for seal faces. one face will be soft material like carbon and another material will be harder like silicon carbide and tungsten carbine. However for abrasive fluids both faces are harder materials are used.

Requirement of spring in mechanical seal
A spring member is used to maintain the contact between the faces.It pushes one face to contact with the other.
1.single spring
2.multiple springs
3.metal bellows

Types of Mechanical seal:
Pusher
Non pusher or bellow seals
Balanced
Unbalance seal
inside mounted
outside mounted
catridge design

Seal Orientation
1.face to back used in tandem un pressurized dual seals
2.Back to back: both flexible seal elements between seal faces used in pressurized dual seal
3.face to Face : Both seal faces are between flexible elements used in pressurized dual seal

Codification Based on API 682
Based on API 682 all mechanical seal shall be cartridge type
C2 A1 C 11 62

C2  category
A1  seal arrangment
C   Type
11   Flush Plan
62   Quench Plan 62

Category 1 seal chamber temperature from -40 to 260c and pr upto 22kg2
category 2 seal chamber temperature from -40 to 400c and pr upto 42kg2

A1 Single seal
A2 Dual un pressurized seal
A3 Dual pressurized seal

Dual pressurised seal
On this kind of seal the lubricating fluid is generated by the barrier fluid, which is 1.5 - 2kg  more than the product pressure. If there is any leakage the barrier fluid penetrates the product.

Dual Mechanical seal Application:
In high pressure and temperature aggresive fluids
acid fluids
vaccum lines
chemical
food processing industry.

Mechanical Seal selection Basis
Metal parts: must be corrosion resistant steel, stainless steel , haste alloy, bronze.
Mating Faces: Must also be corrosion and wear resistant ceramic, carbon ,tungustun carbide, silicon carbide
pressure: Depending on pressure seal may be balanced or unbalanced.

Seal flushing
Seal Flushing is based on the operating condition of the pump. commonly used seal flushing plan are plan 11 and 23
Plan 11 - seal flush from pump discharge through orifice
plan 23 - seal flush plan from internal pumping device in seal chamber through cooler. its is used in hot water service
plan 32 - seal flush plan of injecting cool and clean water from external source.

seal flushing:
It prevents abrasive particles from entering seal faces.
It prevents sediments build up in seal faces.

seal quenching:
It prevent leaked water from contacting the atmosphere
It lubricates and cools the seal faces.

Identification of mechanical Seal Failure:
There is excessive loss of sealed product
Excessive loss of barrier fluid
There is excess process contamination

Common causes of Mechanical Seal Failure
Incorrect Fitting and Alignment
Loss of barrier fluid for lurication
incorrect seal selection
Most of mechanical seal fail due to process change or fault.
Shaft runout
Bearing failure

Single Mechanical Seal:
A single mechanical seal has one mating surfaces which is pressurized and lubricated by the sealing product. Its is the preferred solution for many applications.

Tandem Mechanical seal
It consist of two mechanical seal arranged in succession. seal near product is called primary seal or inboard seal.primary seal is lubricated and pressurized by product fluid. The seal near atmosphere is called outboard or secondary seal.The outboard seal is lubricated by unpressurized buffer fluid.If primary seal fails , secondary seal will protect the leakage.The secondary seal is used only for additional protection

Tandem mechanical seal Application:
Volatile liquids, chemicals, hazardous liquids, food processing and pharmaceutical field.


Double Mechanical Seal:
It consist of two Mechanical seal with presurized barrier fluid circulating between them.The barrier fluid is always higher than the product fluid.The inboard and outboard seal are pressuried and lubricated by barrier fluid.IF inner seal fails barrier fluid leaks into product . If outer seal fails barrier fluid leaks to the atmosphere, In both cases the product never leaks. This type of seal is used in hazourdous products.

Double Mechanical Seal application
High toxic and Explosive Hazardous fluids.

Most commonly used seal faces:
Carbon & silicon carbide

Where carbon faces cannot be used;
In most areas carbon faces are used. but in some areas two mating faces are metal like silicon and tungsten carbide.seal faces are selected according to the product characteristics.In abrasive and acidic area, volatile fluids areas carbon cannot be used.

Reasons for selecting two hard faces:
carbon faces are succeptable to acid attacks
carbon faces cannot be used in abrasive applications like slurry, sea water,crude oil
food processing and pharmaceutical were carbon wear are not accepted
Duty temperature exceeding the carbon temperature range
Higher viscosity will tend to bond the faces together.

Causes of component Damage:
Mechanical Damage to seal face due wrong alignment and installations.
Chemical and corrosion attack due to incompability
cracks may devolpe in seal ring and o ring may get harder and brittle due to high temperature.
wear due to excessive misalignment and abrasives

Mechanical Seal life:
Normally a mechanical seal life will be five years when operated in clean stable media , service life may exceed five years, when operated in viscous and abrasive media it may fail within few months

Springs used in mechanical seal:
Single spring
Multi spring
Wave spring
bellows

mechanical seal types by arrangment
single seal:
inside mounted
outside mounted

Dual seal
pressurised (double seals)
un presurized seal( tandem seals)

hot cyclone & cold cyclone in CFBC Boiler

 In hot cyclone super heaters located before cyclone. 

In cold cyclone superheaters located ofter cyclone.

Thermal Power plant Questions & Answers

1-The following is the correct order of energy conversion in thermal power plants

(A) Chemical energy – Mechanical energy – Electrical energy

(B) Mechanical energy – Chemical energy – Electrical energy

(C) Wind energy – Mechanical energy – Electrical energy

(D) Heat energy – Electrical energy – Mechanical energy

(Ans: A)

2-In thermal power plant, turbine is placed

(A) before boiler

(B) in between boiler and generator

(C) after generator

(D) any of the above

(Ans: B)

3-In the steam condensing power plants

(A) The amount of energy extracted per kg of steam is increased

(B) the steam, converted into water, can be re-circulated with the help of pump

(C) Both (A) and (B)

(D) None of the above

(Ans: C)

4-In thermal power plants, the dust of flue gases is trapped by

(A) Precipitator

(B) Economizer

(C) Superheater

(D) Air preheater

(Ans: A)

5-The path of flue gases in Thermal power plant is

(A) Boiler – Economizer – Superheater– Air preheater

(B) Boiler – Superheater – Air preheater – Economizer

(C) Boiler – Air preheater – Superheater – Economizer

(D) Boiler – Superheater – Economizer – Air preheater

(Ans: D)

6-The following is not a component of Thermal power plant

(A) Condenser

(B) Cooling tower

(C) Turbine

(D) Fuel tank

(Ans: D)

7-With the increase in _____ the efficiency obeys the ‘law of diminishing returns’

(A) Pressure

(B) Temperature

(C) Volume

(D) All of the above

(Ans: A)

8- With the increase in _____ the efficiency obeys the ‘straight line law’

(A) Pressure

(B) Temperature

(C) Volume

(D) All of the above

(Ans: B)

9-Fluid fuels are handled by

(A) burners

(B) stokers

(C) both (A) and (B)

(D) None of the above

(Ans: C)

10-For steam boilers, the fuel(s) is (are) mainly

(A) Bituminous coal

(B) Fuel oil

(C) Natural gas

(D) All of the above

(Ans: D)

11-The most common method(s) used for burning of coal is (are)

(A) Stroker firing

(B) Pulverized fuel firing

(C) both (A) and (B)

(D) None of the above

(Ans: C)

12-A ‘stroker’ is a power operated fuel ___ mechanism

(A) Burning

(B) Feeding

(C) Handling

(D) Storage

(Ans: B)

13-The spreader stroker, secondary air is supplied

(A) through holes

(B) through nozzles

(C) from bottom side

(D) any of the above

(Ans: B)

14-The following is not a pulverized fuel burner.

(A) Tangential burner

(B) Turbulent burner

(C) Cyclone burner

(D) Radial burner

(Ans: D)

15-In which of the following type of burner, liquid fuel is raised by capillary action?

(A) Wick burners

(B) Re-circulating burner

(C) Rotating cup burner

(D) All of the above

(Ans: A)

16-A Fluidised bed may be defined as the bed of ______ particles

(A) Liquid

(B) Solid

(C) Both (A) and (B)

(D) None of the above

(Ans: B)

17-The following is (are) ash handling system(s)

(A) Hydraulic system

(B) Pneumatic system

(C) Steam jet system

(D) All of the above

(Ans: D)

18-The following is dry type dust collectors

(A) Spray type

(B) Packed type

(C) Impingement type

(D) cyclone separator

(Ans: D)

19-The major constituent of fly ash is

(A) Silicon dioxide

(B) Aluminium oxide

(C) Calcium oxide

(D) Magnesium oxide

(Ans: A)

20-The draught produced by the chimney if due to the ____ difference between the column of hot gases inside the chimney and the cold air outside.

(A) Temperature

(B) Potential

(C) Density

(D) None of the above

(Ans: C)

Forging Types

Forging operations:

1: Drawing:

This is the operation in which metal gets elongated with a reduction in the cross sedation area. For this, a force is to be applied in a direction perpendiaulant to the length axis. 

2:Up setting:

This is applied to increase the cross seat ional area of the stock at the expanse of the length. To achieve the length of upsetting force is applied in a direction parallel to the length axis, For example forming of a bolt head.  

3: Fullering:

It a similar to material cross-section is decreased and length increased. To do this; the bottom fuller is kept in angle hole with the heated stock over the fuller .the top fuller is then kept above the stock and then with the sledge hammer, and the force is applied on the top fuller.  

                           

4:Edging:

It is a process in which the metal piece is displaced to the desired shape by striking between two dies edging is frequently as primary drop forging operation.

5:Bending:

Bending is very common forging operation. It is an operation to give a turn to metal rod or plate. This is required for those which have bends shapes.

6:Punching:

It is a process of producing holes in motel plate is placed over the hollow cylindrical die. By pressing the punch over the plate the hole is made.

7:Forged welding:                                                                                               It is a process of joining two metal pieces to increase the length. By the pressing or hammering then when they are at for ging temperature.Itis performed in forging shop and hence is called forged welding.

8:Cutting:

It is a process in which a metal rod or plate cut out into two pieces, with the help of chisel and hammer, when the metal is in red hot condition.

9: Flating and setting down:

Fullering leaves a corrugated surface on the job. Even after a job is forged into shape with a hammer, the marks of the hammer remains on the upper surface of the job. To remove hammer marks and corrugation and in order to obtain a smooth surface on the job, a flatter or set hammer is used.

 10: Swaging:

Swaging is done to reduce and finish work for desire size and shape, usually either round or hexagonal. For small jobs top and bottom swage pair is employed, where as for large work swage block can be used.