Boiler feed pumps (BFP) questions & answers for interview


Boiler feed pumps (BFP) questions & answers for interview:



1-What is the function of Boiler feed pumps (BFP) in power plant?
Functions:
To supply the feed water to boilers
To conduct the Boiler hydraulic tests
To supply the desuperheating & attemperator water required for process steam lines & boilers respectively

TOP-6 BEST POWER PLANT O&M BOOKS

Boiler calculations for Boiler operation engineer (BOE) exam

Viva Questions & answers for preparation of BOE exam & interview

 2-What are the type of prime movers (drives) used for BFPs?
Prime movers:
  • LT drive (415 V)
  • HT drive (11 KV)
  • Turbo drive (Steam driven)
3-What are the auxiliaries associated with BFP?
BFP auxiliaries
  • Cooling water pump & lines
  • Lube oil system
  • ARC valve
  • Mechanical seal flushing system
  • Balance leak off line & its PRV
4-What are the various pipe lines connected to BFP?

 Questions & Answers on AFBC Boilers



  • Suction pipe line
  • Discharge pipe line
  • Bearing cooling water lines
  • Jacket cooling water lines
  • Mechanical seal flushing line
  • ARC line (Minimum re circulation line)
  • Impulse lines for instrumentation measurements (Suction pressure, discharge pressure, Differential pressure, balance leak off pressure)
  • Balance leak off line

5-What is the size of suction strainer of a BFP
It is generally 30 to 40 mesh, that is 30 or 40 hole openings in 1 linear inch on strainer.
A SS 30 wire mesh is generally wrapped on SS mesh having hole openings around 3 to 4 mm
6-What are the different protection devices given for boiler feed pumps?
  • Pressure relief valve
  • Balance leak off line
  • Auto re circulation valve

7-What is the function minimum re circulation line or Automatic re circulation valve (ARC VALVE?)
Minimum re circulation line is provided mainly for centrifugal pump with constant speed drive based on the system and vendor information. There are two types of minimum continuous flow required by the pump (Stable and Thermal). Pump is designed to operate at the flow greater than this flow rate. If pump is operated at less flow than the minimum continuous stable flow, it will damage bearing and internals and may abnormal vibration occur. Below the minimum continuous thermal flow, temperature of fluid will rise at faster rate. To avoid these problems, minimum re circulation line is provided. If the demand of the fluid is decreased below minimum continuous flow, then the auto re circulation valve of the pump will open and maintains the required flow and if flow increased more than minimum flow then auto re circulation valve closes. Generally for higher head flow like 1500 meter head pump the minimum circulation will be 20–25% of total capacity.
8-What is the function of balance leak off line?

Balance leak off line is used to balance the centrifugal pump shaft from axial thrust. During centrifugal pump operation, especially in multistage centrifugal, suction side will have relatively very less pressure as compared to the discharge side. Because of this, there are lot of possibilities that impeller along with the shaft and bearing will be pushed from discharge end to suction end which is also known as axial thrust. Balance line is used to balance the centrifugal pump shaft from axial thrust. Due to the axial thrust, pump bearings and internals will get damaged. To nullify this effect, a tapping from discharge end (between balancing & counter balancing disc) is connected to a balancing drum.
33-Frequently asked QnA on air compressors
9-Why the balance leak off line water is not connected to suction line to save the pump hydraulic power instead of directing it into Deaerator?

Balance leak off water temperature is little bit higher than pump operating temperature which may lead cavitations if it mixes with suction water. For some pumps where there is no risk of cavitations, in such cases this line is connected to suction side of the pump.
10-What is the operating pressure of balance leak off line ?
It is just 0.5 to 1 kg/cm2 more than pump’s suction pressure
10a-What is the standard  gap maintained between balance & counter balance discs?
It is around 0.8 to 1.2mm

10-tips to reduce LOI in Boilers

11-What does it indicate if balance pressure is increasing gradually?
It indicates the wear out of balance or counter balance disc. That is gap or clearance between these two discs has increased
12-How do you calculate the maximum allowable balance leak off pressure?
Maximum allowable balance leak off pressure = 0.03X (Shut off pressure-Suction pressure)+ Suction pressure.
13-What is the velocity of water in the balance leak off line?
It should not exceed 5 m/sec on any account
14-Why the BFP discharge water & balance leak off temperature is slightly more than that of suction water temperature?
15-Due to the compression action of water inside the pump, the water pressure rises around 2 to 3 deg C more than the suction water. Water is an in compressible fluid
15-What do you mean by the shut off pressure in centrifugal pumps?
Shut-off head is a condition, when a centrifugal pump runs with discharge valve closed. It is the maximum head generated by a centrifugal pump with zero flow and relatively less power.
16-How do cavitations occur? What are the abnormal effects of cavitations?

 

Boy's Watch (Multi Colored Strap)





50-QUESTIONS & ANSWERS ON CENTRIFUGAL PUMPS
Pump cavitation occurs when the pressure in the pump inlet drops below the vapour pressure of the liquid. Vapour bubbles form at the inlet of the pump and are moved to the discharge of the pump where they collapse and make high sound and vibrations often taking small pieces of the pump with them.
Cavitation is often characterized by:
Loud noise often described as a grinding or “marbles” in the pump.
Loss of capacity (bubbles are now taking up space where liquid should be).
Pitting damage to parts as material is removed by the collapsing bubbles.

 IBR acts, regulations & forms used

17-What do you mean by NPSHA & NPSHR in BFPs?
NPSHA: Net positive suction head available is the absolute pressure at the suction port of the pump.

NPSHR: Net positive suction head required is the minimum pressure required at the suction port of the pump to prevent the pump from cavitations.
NPSHA should be always greater than NPSHR (NPSHA >  NPSHR)
18-What is the significance of NPSH in BFPS?
If BFPs do not have required NPSH, then there will be more chances for formation of cavitations.
How the pump speed is related to NPSH
NPSHR varies approximately with the square of pump speed.
NPSHR = N2
19-How do you calculate the NPSHA ?
NPSHA = Absolute pressure in
NPSHa = Ha +- HZ - Hf + Hv - Hvp
Where, Ha is the absolute pressure on the surface of the liquid in the supply tank.
HZ is vertical distance between the surface of the liquid in the supply tank and the center line of the pump.
Hf is friction losses in the suction piping.
Hv is Velocity head at the pump suction port.
Hvp Absolute vapour pressure of the liquid at the pumping temperature of the pump, it could lead to cavitations of pump.

Boiler Feed Pumps Design factors & Pump Capacity calculation

20-What is the significance of vortex breakers in pumps?
A vortex breaker is a device/arrangement in pumps to stop the formation of a vortex when a fluid (liquid or gas) enters into pump suction. The formation of vortices can entrain vapour in the liquid stream, leading to poor separation in process steps such as distillation or excessive pressure drop, or causing cavitations.
21-What are the reasons for Vortexing in pumps?
Vortexing can occur if any of the following conditions are present:
  • Low liquid levels.
  • Liquid level falling greater than 1 Meter/sec.
  • There is a large concentration of dissolved gases in the liquid.
  • High outlet velocities in pipes leaving vessels. Generally greater than 3 meters/sec.
  • Liquids near their vapour point.
  • High circulation caused by asymmetrical inlet or outlet conditions.
  • Inlet piping too close to the wall or bottom of the tank.


22-What are the protection interlocks given for BFPs.
Protection interlocks: That is BFP will trip/stop on following conditions
  • Low Deaerator level
  • High bearing vibrations
  • High bearing temperature
  • Low cooling water pressure
  • More differential pressure of suction strainer
  • High load
  • Higher balance leak off pressure
  • Low speed (<40% of rated speed)

23-Write down the BFP start permissive interlocks
  • Start permissive interlocks
  • Deaerator level normal
  • Bearing temperature normal
  • Bearings vibrations normal
  • Cooling water pressure normal
  • Motor bearing temperature, winding temperatures normal
  • Discharge valve close
  • Suction valve open
  • Suction pressure normal
  • Differential pressure normal
  • Arc Valve open
24-How do you start the BFP?
BFP start up  sequence
  • Ensure all the start permissive are healthy
  • Ensure no maintenance activities are going on BFP & pump is ready to start with all respect
  • Start the pump from DCS by giving >80% command to VFD
  • Observe the bearing temperature, vibration & speed ramp rate
  • Ensure pump has reached its 50% speed within 10-15 seconds
  • If all parameters (discharge pressure, bearing temperature & vibrations, motor current, winding temperatures etc) are normal
  • Then open the discharge valve slowly
  • After 100% opening of discharge valve rise the speed as per your requirement
  • Note: Ensure all the parameters are normal on every operation on BFP
25-Why it is not allowed to run the BFPS at speed lesser than 50% of rated speed?
For journal bearing BFPS at speed < 50%  the oil splash rings will not flash oil in bearings, leading to the damage to the bearings due to low lubricating oil.
26-What will happen if BFPs run in reverse direction?
If pump runs in reverse direction for more than 5 seconds, there will be the more chances of pumps to seize
27-How do you stop the BFP?
  • Pump stop sequences:
  • Reduce the pump speed slowly up to 60% of rated
  • Close the discharge valve
  • Shut down the pump
28-What is the recommended minimum head for BFP operation?
Should not be less than 10% of its rated head except in start-up & shutdown conditions?
29-What will happen if pump is started and stopped with discharge valve open?
  • Pump may trip due to sudden motor over load
  • Alignment may get disturb
  • Shaft coupling may damage
  • May harm to bearings of pumps and motor
  • Piping supports may get disturbed
  • Pump foundation fasteners may get loose
  • So it is always recommended to start and stop the pump with discharge valve close.


29-What are the reasons for pump to seize?
Following conditions can cause pump to seize:
  • No suction or less liquid flow to suction
  • Operating pump continuously at lesser NPSH
  • Reverse direction rotation of pump
  • Damaged strainer
  • Foreign materials in impellers
  • Uneven thermal expansion of pump internals
30-What is the recommended acceptable value for a BFP shaft run out?


It is around 0.03 mm (Max. 0.05 mm)

31-When should one can carry out alignment on BFP?

Why do the Boilers explode???

Alignment on BFP shall be done when the temperature of the pump is <50 Deg C or in atmospheric temperature.
32-Why do you use 2 dial gauges for axial alignment of BFP?



BFP has more axial float that is 8 to 9 mm without bearings & seal & 0.8 to 1 mm with bearings & seal, so in order to get accurate readings 2 dial gauges are used for angular alignment & 1 dial gauge for parallel alignment. Refer above figure

33-What are the shutdown preservation methods for BFP?

Shutdown preservation method
  • Depressurize the pump
  • Drain all the water
  • Fill the pump with 1:2 or 1:1  Glycol water mixture.
  • Rotate the pump shaft twice in a week
34-What is the recommended bearing temperature for BFPs?
It should be less than 75 deg C (Max 90 deg c)
35-What are the recommended bearing vibrations for BFPs?
It should be less than 3 mm/sec (Max 5 mm/sec)
36-What is the allowable leakage drops for BFP mechanical seal
15 drops/minute
37-What should be allowable the DP across strainer
0.1   to 0.3 kg/cm2 (1000 to 3000 mmwc)
38-What is the filter mesh size for BFP oil replacement
Mesh size is 30 micro meters
39-What preventive maintenance activities that you are going to carryout on BFPS?
Preventive maintenance activities:
  • Pump cleaning
  • Oil level checking & top up if required
  • Alignment correction
  • Suction strainer cleaning
  • Cooling water lines flushing
  • Foundation bolts tightness checking
40-What is the acceptable impeller & wear ring clearance in BFP




BUY....QnA for power plant O&M

Power plant Maintenance Calculations




15 comments:
Labels:

25 most frequently asked viva questions & answers on Boiler safety valves

Boiler safety valves question & answers:
1-Which type of safety valves are used in modern high pressure Boilers?
Open yoke, spring loaded, Semi Nozzle & full lift type
2-What is the over pressure range for safety valves?
It is around 6 to 7% of operating pressure of particular line/vessel
3-What is the recommended % of blow down for Boiler safety valves?
It is around 2 to 3%
4-How do you calculate safety valves blow down?
Blow down = SV (Set pressure – Reseat pressure) X 100 / Set pressure
5-What is the MOC of safety valve disc & spindle?
Disc: Stain less steel with 13% chromium & Spindle: SS 316
6-What happens if drum safety valve set at lower pressure than super heater safety valves?
Upon blowing of drum safety valve first, all the steam formed will blows out through the drum safety valves causing less or no steam flow to the super heater coils. This situation will lead to the failure of super heater coils.
7-When should be gags for safety valves applied & removed?
Safety valve gags should be applied & removed at 80-85% of the pressure of the low set valve, even at safety valve setting & during hydro. Test.
8-Why safety valve gags should not be applied in cold condition?
Spindle of the safety valves expands considerably with increase in temperature as pressure is raised. Due to constraint to the expansion may cause spindle bend & also cause damage to the seating surface.
9-How do you adjust the set pressure of a safety valve?
Safety valve is set by adjusting the compression of spring
10-How do you adjust the blow down of a safety valve?
By turning up/down of upper ring.
To reduce the blow down: Upper ring is taken down & to increase the blow down upper wring is turned up.
11-How do you reduce the simmering sound of safety valve?
By adjusting the lower ring
12-What will happen if a safety valve has higher blow down than required?
Higher blow down of safety valve causes

1-Fluctuation steam demand & drum level
2-Increase in super heater steam temperature
3-Sudden & fast dropping of boiler pressure
4-Insufficient steam flow to super heater coils (In case of drum safety valve)
5-Loss of high temperature steam eventually leads loss of fuel

Basic concepts of Boiler safety valves

13-What will happen if a safety valve has lower blow down than required?
Lower blow down setting of safety valve leads to the pressurizing of boiler eventually damages to the pressure parts.
14-What are the potential reasons for failure/damage of safety valves?
Potential reasons for safety valve failure are:
  • Crossing the quantity of steam to be discharged
  • Quality of the steam is not up to the mark
  • Higher back pressure
  • Stress in discharge piping
  • Improper gagging & bolting
  • Foreign materials in steam
  • Damages during disassembly & assembly in field

15-Why drum safety valves are set first instead of super heater safety valve?
Possibilities of valve part damage because of “girl blasting” are greater on the super heated valves in contrast to the drum valves. If a super heater valve is gagged after seat damage while testing of other valves continues, the total valve damage will most likely be increased.
And also steam temperature is more while testing the drum safety valves; hence more temperature for setting super heater valve will be available producing accurate results.
16-Why the drum level should be maintained lower in the range of 30-40% during SV setting?
Higher drum level will cause stugging of valves with water causing long blow down & damages to the disc & seat.
17-What is the pressure rising rate during safety valve setting?
Usually 2 to 3 kg/cm2 per minute. Slow rising may cause simmering & valve to lift very erratically
18-What precautions shall be taken for lifting the safety valves several times?
A cooling off period around 25-30 minutes should be given between every lift to get accurate results & to avoid damages to the valve
19-What are the reasons for simmering in safety valves?

Know about valves
  • Improperly set lower ring
  • Holding the boiler pressure at or nearer to the set pressure of valve
  • Maintaining higher drum level during lifting of SV

20-Why it is necessary to drop the pressure of boiler after setting a safety valve before removing gags?
Boiler pressure should be dropped 20% of valve set pressure to avoid valve lifting prematurely
21-Why it is been recommended that SH safety valve to be set at higher blow down rate if the steam temperature available is less?
Yes, as the steam temperature increase SH safety valve’s blow down decreases, hence at lower temperature it is always set at higher blow down.
22-What are the criteria for selecting the safety valves?
  • Super heater safety valve should have blowing (relieving capacity) 30-35% Boiler MCR
  • Drum safety valves (Including 1 &2) should have relieving capacity 90 to 95% of Boiler MCR
  • All safety valves (SH & Drum) should have relieving capacity 125 to 130% of Boiler MCR
  • Solenoid operated electromatic safety valves are generally deigned to relieve steam 12-15% of Boiler MCR.
23-On which side of steam drum higher pressure set safety valve is to be fitted?
It depends on the inclination of the drum & CBD line layout. Actually HP boiler drums are made inclined at an angle 2-3 for enabling collection of internal treated sludge. So in order to not to lift that side SV , that SV is set at higher pressure
24-What is meant by back pressure in safety valves? & how does it affect SV performance?
Back pressure is the static pressure existing at the outlet of a pressure relief device due to pressure in the discharge system.
If pressure in the valve outlet varies while the valve is closed, the valve set pressure will change. If back pressure varies while the valve is open and flowing, valve lift and flow rate through the valve can be affected.
25-What is meant by accumulating test pressure?
The accumulation test is done on boilers to limit the excessive pressure rising while the safety valve is in open. The test is carried on new boilers or new safety valves with full firing condition with MSSV and feed water valves closed. It is conducted as long as water in drum permits generally 7 minutes for water tube boilers.

Best Practices to reduce auxilary power consumption of power plant

Questions & Answers on ESP Troubleshooting

Reasons for Boiler Back fire

Know about IBR forms

For questions & ans`wers on Power plant. visit the site powerplantandcalculations.com

No comments:
Labels:

40 important question & answers on belt conveyor for power plant engineers & operators

1-What are the equipments used in coal handling plant (CHP)?
Starting from coal shed
  • Coal elevator
  • Coal grizzly hopper
  • Coal vibro feeder
  • Coal conveyors (belt conveyor)
  • Coal vibro screen
  • Coal crusher
  • Coal dust extraction system
  • Shuttle conveyor
2-Name the various parts of the belt conveyors?
  • Belt
  • Carrying idlers
  • Return idlers
  • Impact idlers
  • Transoms
  • Pulleys
  • Vertical gravity take up system
  • Power transmission system (Motor, Gear box, couplings)
  • Main structure & trestles
Tools & tackles used in power plant maintenance


3-How do you specify the conveyor belt?
Belt is specified based on
  • Its material of composition
  • Number of ply
  • Belt rating
  • Belt width

4-What are the various materials used for manufacturing of belts
Nylon, Polyester, Aramide, Polyester-Nylon, Steel fabric
5-What are the various pulleys used in belt conveyors?
  • Head pulley
  • Tail pulley
  • Snub pulley
  • Bend pulley
  • Take up pulley
6-Which is the largest and smallest pulley among above all pulley?
  • Largest pulley : Head pulley
  • Smallest pulley : Snub pulley
7-What are the different troughing angles used for transoms?
Depending on application and load carrying capacity, different troughing angles transoms are used namely
  • 180 degree: For flat belts and low loads
  • 45 degree: Higher capacity
  • 35 degree: Medium capacity
  • 20 degree: Low capacity
  • 10 and 15 degrees.
8-What are the different protection systems provided for belt conveyors?
  • Pull Cord Switch (PCS): Used for emergency stopping of the belt.
  • Belt Sway Switch (BSS): Protects belt from swaying or restricts over side movement
  • Zero Speed Switches (ZSS): This arrangement is fitted to tail pulley or snub pulley to protect the belt from further damage during belt cut. 

9-What  do you mean by the transoms in belt conveyors?
Transoms: Transoms are the brackets on which idlers are fitted to locate them properly.
Following types of transoms are noticed in general belt conveyor system.
  • Carrying idler transom
  • Return idler transom
  • Self aligning carrying transom
  • Self aligning return transom
  • Garland idler transom (refer below image)
10-What are the functions of carrying idler, return idler, impact idler & side guide idler
  • Carrying idlers: Fitted on carrying side of the belt (top side of the belt)
  • Return idler: Fitted on return side of the conveyor (bottom side). It is the largest idler among all the idlers used in conveyors
  • Impact idlers: It is same as carrying idler, it is fitted on carrying side of the conveyor below the discharge chute of preceding conveyor
  • Side guide idler: Fitted to the self aligning transoms to avoid the belt swaying at one side

10a-What are the various grades of belts, explain their applications
  • M Grade: Heavy duty resistant to abrasion, sharp and rugged materials. Work in normal atmosphere temperature. Generally used for coal, bagasse and other biomass fuel applications.
  • N Grade: Used for coal, bagasse and biomass, low resistant to abrasion, sharp and rugged materials.
  • B (G) Grade: Work in normal temperature used only for low duty.
  • HRS: Used for high temperature applications up to 100 °C surface temperature and 200 °C material temperature.
  • HRE Grade: Used for high temperature applications up to 150 °C surface temperature and 400 °C material temperature.
11-List down the various problems that you face in belt conveyors.
  • Belt running off at head pulley due to improper alignment of troughing idlers near head pulley.
  • Belt running off at tail pulley due to build up of material on return idlers.
  • Excessive wear on bottom side of belt.
  • Excessive wear on carrying and return side of belt.
  • Overstretch of belt due to excessive tension.
  • Belt slipping on tail pulley.
  • Pulley hub key way damage.
  • Belt moving on one side only.
  • Fuel leakage and spillage due to improper arrangement of scrapers and skirting.
  • Conveyor Drive Problem: Vibrations in gear box and motors, abnormal sound in gear box, coupling bolts loose.
12-What are the reasons for operating ZSS?
Zero speed switches operate on following conditions:
  • Belt cut
  • Belt slip on head pulley
13-What are the reasons for excessive wear out of belt on carrying side?
  • Excessive wear out on carrying side of belt is due to:
  • Dirt, frozen or misaligned return idlers
  • Excessive sag between troughing idlers causing load to move and shift on belt as it passes over idlers
  • Abrasive skirt boards
  • Poor loading
14-What is the reason for excessive wear on bottom side of belt?
  • Slippage Between Belt and Drive Pulley or Pulleys: Check the wear out of pulley rubber lagging.
  • Sticking Troughing Idlers: Check the operation of belt cleaners (scrapers).
  • Material Ground Between Pulley and Belt: Arrest fuel leakage and remove the collected fuel regularly.
15-What are the possible reasons for belt running off at head pulley?
  • Build up of material on return idlers.
  • Unequal loading.
  • Improper alignment of head pulley.
  • Not working of self aligning transums situated near head pulley.
16-What is the reason for a conveyor belt runs to one side for some distance along conveyor length?
It is due to Improper loading of belt and failure of self aligning transoms.
 17-What actions will you take if you found conveyor carrying side wearout occurs continuously?
Following actions should be taken to avoid wear out:
  • Install belt-cleaning plows at head end and tail end.
  • Clean, repair and align return idlers.
  • Increase belt tension if too low.
  • Reduce idler spacing.
  • Repair and inspect skirt board rubbers regularly.
  • Feed load on belt in same direction at same speed.
18-What actions will you take if belt has excessive tension?
If belt has excessive tension, then following actions shall be taken:
  • Decrease the belt tension by lagging on drive pulleys.
  • Increase arc of contact of drive pulley.
  • Increase speed, if possible, keeping shift tonnage the same.
  • Reduce tonnage at slower speed.
  • Tighten screw take-up just enough to keep belt from slipping.
  • On a gravity take-up reduce counter weight to minimum amount sufficient to keep belt from slipping.
19-What is the preferred speed of coal belt conveyors in power plants?
For medium capacity power plants 10 to 50 MW : 0.9 to 1 m/sec
For Higher thermal power plants = 0.9 to 1.5 m/sec
20-What is meant by transition distance?
Transition distance is traditionally defined as the distance from the center line of the first fully troughed idler roll to the centre line of either the head or tail pulley
21-Tell briefly about belt cleaners/scrapers.
Belt cleaning techniques are aimed at removing the greatest possible percentage of carryover at the source i.e. at the head/discharge pulley. Belt cleaners must not however cause damage to the belt in the course of operation.
Types of Belt Cleaners:
Contact Type:
Generally primary, secondary and tertiary belt cleaners are used.
Primary belt scraper is installed inside the head chute at a point below the natural material trajectory where the belt is in contact with the pulley. Primary scrapers are usually contact scrapers.
Secondary belt scraper is usually installed within the head chute however this scraper is positioned to contact the belt once it leaves the head pulley. Secondary scrapers are usually contact scrapers and are either blade-type scrapers or rotating brushes although the latter is not common.
Tertiary scrapers are sometimes installed although this is not common practice. In this case the scraper is outside the head chute and scrapings must be returned to the head chute by a mechanical chain conveyor or similar. Tertiary scrapers are usually contact scrapers.

Belt washing systems are also used in cases where the material carried over is extremely difficult to remove from the belt and/or where the disposal or handling of the washing water plus spillage can be done easily or conveniently. Washing systems are usually considered to be non-contact cleaners in as much as water is used to clean the belt and squeeze rollers provide a drying function.
 22-What is the function of Take up unit (TU)?
The role of the take-up device is to create and maintain adequate pre-tension to allow the conveyor drive pulley to drive the belt under all running conditions (empty or loaded).
23-What are the main two types of Take up unit (TU)?
1-Fixed type : screw take up unit (STU)
2-Vertical gravity take up (VGTU)
24-What is the percentage of belt tension adjustment in normal running condition?
It is 0.8 to 1.2% of total length
25-What is the minimum length of the take up system ?
Minimum length of take up is  the 1.5% of Conveyor length (Center to Center)  
26-A belt conveyor of length 100 meter need to install VGTU system calculates the minimum length of take up.
Minimum length of take up = 1.5% X 100 = 1.5 X 100/100 =1.5 meters
27-A conveyor length is 200 meters and speed is 1 meter/sec, then calculate the time taken for this conveyor for one complete rotation
Total appx.length of the belt = 2 X conveyor length + Conveyor length X 1.5%

                                              =2 X 200 + 200 X 1.5% = 403 meters


Time taken for one complete rotation of the belt 
= 403 m X 1 sec =403 seconds =403/60 = 6.71 minutes.

28-What is meant by transition distance?


Transition distance is defined as the distance from the centre line of the first fully troughed idler roll to the centre line of either the head or tail pulley.

29-Explain VGTU system in belt conveyors.


The role of the take-up device is to create and maintain adequate pre-tension to allow the conveyor drive pulley to drive the belt under all running conditions (empty or loaded). Generally there are two main types of take-up. The fixed type normally referred to as a screw take-up STU and the automatic or Gravity take-up (GTU). The screw take-up is normally used on short conveyors up to a length of 50 meters. Over 50 meter an automatic take-up system should be used to ensure constant pre-tension. The length of the take-up depends on the both the center distance of the conveyor and the type of belt. The screw take-up on shorter belts is normally located at the tail end. Tracking of the belt with the screw take-up should only be performed as a last resort as it may cause permanent belt stretch.

The GTU performs best located close to the drive pulley. The GTU bend pulleys will have a minimum diameter based on the belt specification. Movement of the GTU on both the vertical and horizontal axis should be limited to avoid excessive movement and associated tracking problems. The GTU should be protected with a return belt plough and must be adequately guarded.

30-What is the significance of counter weight?



The weight of the GTU should maintain a constant belt sag between the idlers (normally H/L 5 1–2% of length of take up) hence calculating the correct weight is important. A GTU underweight will lead to excessive belt sag thus increasing belt bend resistance and reducing overall belt and idler life. A GTU over weight will lead to excessive belt tension resulting in belt and joint stretch.
31-What is the significance of covers in belt?
Covers are used in conveyor belt constructions in order to protect the base conveyor belt carcass and to extend its service life. In addition, covers do provide the finished belt with a wide variety of desirable properties, including the following:
32-A belt conveyor of length 100 meter need to install VGTU system calculate the minimum length of take up.

Minimum length of take up = Conveyor length (centre to Centre) X 1.5%
                                              = 100 X 1.5/100 = 1.5 meters

33-A 200 metre length conveyor belt has a drive pulley size OD 510 mm 3 Length 1800 mm, this pulley is directly coupled to planetary reduction gear box having reduction ratio 40:1 and 1475 rpm motor is used to drive this gear box. Then calculate the time required for conveyor for one complete rotation.

We have,
Conveyor length: 200 meters
Pulley OD: 510 mm = 0.51 m
Motor output speed = 1475 rpm
Gear box reduction ratio = 40:1
Gear box output speed N = 1475/40 = 36.87 rpm
Head pulley speed = Gear box output speed (As head pulley is directly coupled to gear box)
Pulley speed in m/sec. = V = Pi X D X N/60
                                          = (3.142 X 0.51 X 36.87/60) = 0.98 m/sec

Belt speed is 0.98 m/sec, given that conveyor total length is 200 meters.
Then the length of the belt = 2 X conveyor C/C length + Conveyor C/C length X 2 X 1.5% (VGTU) + 0.5 X No. of pulleys (Pulley and belt contact radius length is considered 0.5 meter for each pulleys)
= 2 X 200 + 200 X 2 X (1.5/100) + 0.5 X 6 (6 Nos of pulleys)
= 409 meters
Time required for one complete revolution = Belt length/Speed
                                                                     = 409/(0.98 X 60) = 6.95 minutes
34-A conveyor of 7.5 KW having belt width 800 mm and speed 0.95 m/sec., calculate the maximum tension at the start of the belt.

Belt rated power P = 7.5 KW
Belt speed V = 0.95 m/sec.
Belt width W = 800 mm = 0.8 meters
Maximum tension at the start of the belt = (3.2 X P)/(V X W)
                                                                 = (3.2 X 7.5)/(0.95 3 0.8)
                                                                 = 31.5 KN/M

Read SOP on CHP & Dust extraction system

35-A 1400 mm width inclined belt conveyor has its head pulley at the elevation of 22 meter from ground, is used to convey 45 TPH coal. The head pulley is coupled to motor of RPM 1450 through planetary gear box of efficiency 80%. Then calculate the motor rated power to drive the conveyor. Consider motor efficiency 90%.

Belt width W =1400 mm
Vertical lift = L = 22 meter
Conveyor capacity Q = 45 TPH
Gear box efficiency = 80%
Motor efficiency = 90%
We have power required to drive the inclined belt P = 4.7 X L X Q/1000
                                                                                   = 4.7 X 22 X 45/1000
                                                                                   = 4.65 KW
Motor input power = 4.65/(Gear box eff. 3 Motor eff.)
                               = 4.65/(0.8 X 0.9) = 6.45 KW

Motor rated power = Motor input power X 1.15 = 6.45 X 1.15 = 7.42 KW (Take 15% margin)
Select 7.5 KW motor

36-Calculate the length of a 3 ply 1600 mm width conveyor belt, which is coiled on a 100 mm pipe. The thickness of the belt is 10 mm and belt is coiled around 65 turns.

We have,

Diameter of centre hole of coiled belt, d = 100 mm X 0.1 m

Thickness of the belt T = 10 mm = 0.01 m

No. of turns N = 65

Outer diameter of belt, D= 2 X 65 X 0.01 = 1.9 m

Length of belt = (d + (D - d)/2) X π X N

                        = (0.1 + (1.9 - 0.1)/2) X 3.142 X 65

                        = 204.23 meters

37-Write a short note on operation checks of conveyor belt?
Belts:
Watch out for spillage of material onto the return strand, where it can get between the belt and pulleys.
See that the belt is properly aligned and does not contact steel structure. This is especially important on the return strand that is generally not as easy to see.
Mark breaks, damaged and worn spots and report them for early repair.
Keep large lumps (coal lumps, stones, other foreign materials) of material off belts. If they do get on, remove them carefully.
Idlers and Pulleys:
Note and mark “frozen” or damaged idlers for repair or replacement.
Check troughing and return training/self aligning idlers for proper operation.
Check scrapers and plows for proper operation.
Watch for material to build up on decking or floor under idlers or pulleys. This is especially important at training/self aligning idlers.
 Chutes and Hoppers:
Note and correct clogged or “bridged” material.
Prevent large lumps from dropping onto unprotected belt.

Check to see that the material is centred on the belt and that the belt is not overloaded.
Replace all damaged impact idlers; do not replace impact idlers with regular idler.
38-What is the significance of pulley lagging?
Lagging is done to improve Pulley traction, either bolt or vulcanize the lagging to the pulley face. The lagging will prevent slipping at the head pulley and also cushion the wear between the belt and the pulley surface. In wet conditions, grooved lagging works best.

39-What is the function of hold back device in conveyor belts?
Hold back is a device used to restrict the reverse/back movement of belt during sudden stop or trip of conveyor.

40-What is belt splicing? What are the different types of splicing?
Splicing is the process of joining up of two trimmed ends of a conveyor belt utilizing a defined chemical or mechanical procedure.

Vulcanized Splicing (cold and hot) and Mechanical Splicing are generally used for belt jointing.

Available @ Flipcart/Amazon/Notion press



Factors considered for Boiler Engineering/Design

Power plant maintenance calculations

Turbine oil and transformer oil standard testing parameters

6 comments:
Labels:
Subscribe to: Posts (Atom)

15-Emergencies in power plant operation

Most visited posts