It's all about HP heaters (Feed water heaters) in Power plants

 1-Why do you use HP heaters in power plants?

HP heaters are used for heating the feed water, which will contribute in increasing cycle efficiency as well as reduction in fuel consumption

2-What is the design code of HP heaters?

HEI, ASME SEC VIII Div-I IBR

3-What are the advantages of using feed water heaters in power plants?

• Fuel consumption reduces
•  Reduce heat losses in the condenser
•  Lower emissions as fuel use is reduced due to improved heat rate
• Decreases the plant heat rate & hence increases the plant efficiency

4-What are the different types of feed water heaters?

Open type feed water heaters & closed type feed water heaters

5-What do you mean by open type of feed water heaters?

In open type feed water heaters steam directly mixes with feed water. Steam pressure used is lower < 5 kg/cm2

6-What do you mean by closed type of feed water heaters?

In closed type feed water heaters steam directly mixes with feed water. Steam pressure used is high > 5 kg/cm2, these are shell & tube type heat exchangers

7-What are the pipe lines connected to HP heaters?

• Bleed steam inlet line
• Feed water inlet line
• Condensate outlet line
• Feed water outlet line
• Feed water box drain & vent lines
• Shell zone drain & vent

Procedure for Boiler gauge glass line up

8-What are the MOCs of Tubes & shells used in closed type of HP heaters?

Tubes: SA 213 TP 304 (Feed water pressure up to 170 kg/cm2)

Shell: SA 516 Gr.70

9-What are the different zones of HP heaters?

• Desuper heating zone
• Condensing zone
• Sub cooling zone

10-Where does the maximum heat transfer occur out of all zones?

Maximum heat transfer occurs at condensing zones

11-Why the name Sub-cooling has come?

Here condensed steam from condensing zone is cooled by feed water entering by convective heat transfer method.

12-What is the function of drain coolers in HP heaters?

Drain Coolers are employed because of heat consumption improvement in case of drain introduction into the lower heater through the control valve.

13-Why the feed water inlet line connection is at the bottom & outlet line is at the top?

          

Feed water inlet line & outlet line are connected in such a way that to separate desuperheating zone, condensing zones & sub cooling (drain cooler) zones

14-Where do the fixed & sliding supports of HP heaters are located?

Fixed support: Towards feed water inlet & outlet line

Sliding support: Opposite side of feed water line connections

15-What would be the velocity of feed water in HP heaters tubes?

It’s around 0.6 to 0.8 m/sec

16-What is the effect of high/low condensate level in heaters shell?

Higher the condensate level lower is the performance of heater and vice versa. Heater level is always maintained in between 30–50%.

17-Briefly explain the condensate level control in HP heaters?

One of the most common causes of tube failures in a feed water heater (FWH) is the improper control of the internal liquid level, which also can cause operational and maintenance costs that might lead to premature replacement. These problems are not new, they have been experienced by many utility plants throughout the industry during the past 50 years. However in many cases, the resulting damaging phenomenon has seldom been totally understood and the loss of corporate knowledge and failure of some utilities to identify and rectify level control problems continues to bring this issue to the forefront of root causes of FWH operational failures.

In general, the performance of the Drain Cooler (DC) Zone is tied to the operational parameter of Drain Cooler Approach (DCA). DCA is a good indication of whether the DC Zone is operating properly or not, it is not the only parameter that should be considered. DCA is a measurement of temperatures

The pressure of the drains also must be known in order to determine the degree of sub cooling and whether there is a potential for flashing, either within the DC itself or the downstream piping before the level control valve. Flashing and two-phase flow in either of these areas can cause significant damage to the heater.

It is important to remember that the drain cooler is designed to be a water-to-water exchanger. It must remain that way to function properly. Any admission of vapour into the zone typically results in problems. This might be a result of a low liquid level in which steam is admitted directly from the condensing zone into the DC zone, the result of flashing within the DC zone itself, or can be the result of leakage into the zone via the endplate or shroud cracks.

18-What do you mean by drain cooler approach (DCA) in HP heaters?

DCA is the temperature difference between the drains (steam condensate) leaving the heater and the temperature of feed water entering the heater. For more cycle efficiency DCA value should be small.

19-A HP heater is used to heat the feed water from 160 °C to 180 °C by using turbine bleed steam at 15 kg/cm2 and 320 °C. The condensate returning from heater is at 170 °C, calculate the DCA of heater.

We have,

DCA = Temperature of condensate leaving the heater – Temperature of feed water entering the heater

DCA = 170 - 160 = 10 °C

Note: For best performance, heaters are designed to get DCA 3 to 5 °C at full operation capacity.

20-What do you understand by Terminal Temperature Difference (TTD)?

It is the difference between the saturation temperature at the operating pressure of the inlet steam to the heater and the temperature of the feed water leaving the heater. For more cycle efficiency TTD value should be small.

21-A HP heater is used to heat the feed water from 110 °C to 160 °C by using MP steam at pressure 13 kg/cm2 at temperature 280 °C, calculate the TTD.

We have,

TTD = Saturation temperature of inlet steam - Feed water outlet temperature

Saturation temperature of inlet steam at 13 kg/cm2g pressure = 195.6 °C

TTD = 195.6 - 160 = 35.6 °C

Note: For best performance, heaters are designed to get TTD 3 to 5 °C at full operation capacity.

22-How the DCA does affects condensate level of HP heaters?

An increase in DCA,HP heater level decreases & vice versa

23-What is flashing in heaters? How does it occur?

Flashing, by definition, is the change in state of liquid to vapour. While in most cases this change of state results from the addition of heat (as in the boiler) in a FWH the most common cause of flashing is a result of a reduction in pressure (or pressure drop). Pressure drop might be a result of the geometry of the Drain Cooler Entrance window, the fact that the drains must travel around the tubes and change direction many times due to the baffling arrangement and also due to changes in elevation and elbows in the downstream piping. If the liquid drains are not sub cooled enough, any one of these pressure drops could result in flashing and two-phase flow. Two-phase flow is known to cause problems to piping, tubing, the cage and the shell, especially in the case of carbon steel components.

24-What do you mean by fouling in heat exchangers?

Deposition of any undesired material on heat transfer surfaces is called fouling. Fouling may significantly impact the thermal and mechanical performance of heat exchangers. Fouling is a dynamic phenomenon which changes with time. Fouling increases the overall thermal resistance and lowers the overall heat transfer coefficient of heat exchangers. Fouling also impedes fluid flow, accelerates corrosion and increases pressure drop across heat exchangers.

Different types of fouling mechanisms have been identified. They can occur individually but often occur simultaneously.

Scaling:

• Particulate/Sedimentation Fouling
• Corrosion Fouling
• Chemical Fouling
• Freezing Fouling

25-What are the problems associated with HP heaters?

•  Initial two phase mixture & hammering
• Tubes failure due to wrong operation
• Level fluctuation & leakages
• Overfeeding of steam & feed water
• Operating the heaters above the operating & design parameters

Read Power plant standard operating procedure

26-Write down the initial charging process of feed water heater (HP heater)

Steps:

• Ensure all the maintenance activities on HP heaters are completed
• Ensure all inlet & outlet valves of heaters are healthy
• Ensure all field instruments are healthy
• Keep open all water box & shell side vents & drains are  open
• Ensure steam condensate outlet valve is open

Water side

• Crack Open the feed water outlet valve
• Then crack open the feed water inlet valve
• Allow to vent out the air
• Then gradually open the outlet & inlet feed water valves
• Then close the water box vents & drain valves

Steam side

• Ensure steam line drains are in opened condition
• Ensure steam parameters are as per desired values
• Ensure no water in steam line drains
• Crack open the steam inlet valve to HP heater
• Ensure there are no water particles in drain & vent line of shell. If found clear, then close the valves
• Then gradually open steam inlet valves & allow for stabilization

27-A HP heater is used to heat the 200 TPH feed water from 160 °C to 180 °C by using turbine bleed steam at 15 kg/cm2 and 320 °C. The condensate returning from heater is at 170 °C, calculate the quantity of steam used.

 Given that,

Qf = 200 TPH

Tf1 = 160 °C

Tf2 = 180 °C

Hg  at pressure 15 kg/cm2 & temperature 320 °C =735.3 kcal/kg

Enthalpy of condensate water Hf = 171 kcal/kg

Heat lost by the steam = Heat gained by feed water

Ms X (Hg-Hf) = Mw X (Tf2-Tf1)

Ms X (735.3-171) = 200 X (180-160)

Ms = 7.08 TPH

28-What are the precautions to be taken for safe operation of HP heaters?

Precautions:

• Operate the HP heaters as per SOP
• Take utmost care during initial charging
• Do not operate the heaters beyond the operating pressure & temperature
• Bypass the HP heaters during Boilers Hydraulic tests
• Conduct routine preventive maintenance

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Boiler calculations for Boiler operation engineer (BOE) exam

Various IBR forms, acts & regulations for a power plant engineers

Sl No.	IBR Form No.	Details of forms
1	I	Memorandum for Boiler inspection or registration
2	II	Issued by inspection authority during new construction
3	II A	Issued by inspection authority during new construction for foreign code boilers
4	III	Certificate of manufacture issued by constructor
5	III A	Steam pipe line test certificate  issued by manufacturer
6	III B	Tubes  test certificate issued by manufacturer
7	III C	Test certificates for  fittings & mountings (Valves,bend,elbow,tee etc)
8	III F	Test certificates of casting & forging issued by manufacturer
9	V	Boiler use provisional order issued by Boiler inspector authority
10	VI	Certificate issued by  directorate of steam boiler for boiler use
11	VII	Inspecting authority (directorate of steam boiler) certificate for constructional Boiler
12	XI	Certificate for the use of an Economiser
14	XII	Welder qualification record
15	XIII	IBR welder certificate
16	XVI-F	Certificate for approval of tube maker
17	XVI-G	Certificate for approval of pipe maker
18	XVI-H	Certificate for approval of material testing laboratory
19	XV-I	Certificate for approval for RLA organisation
20	Form No.C	Certificate for 2nd class Boiler attendant issued by Directorate of steam Boilers under rule-41
21	Form No.B	Certificate for 1st class Boiler attendant issued by Directorate of steam Boilers under rule-41
22	Form No.B	Certificate for BOE  issued by Directorate of steam Boilers under rule-40 Boiler operation engineer-2011

Power plant consruction materials & welding electrodes used

Various sections and their significance of IBR act 1923.

Sl. No.	Section No.	Used for
1.	Section-7	New boiler registration
2.	Section-8	Renewal of boiler on form VI
3.	Section-9	Provisional order on form V
4.	Section-12	Boiler alteration, modification
5.	Section-23	Penalties on illegal use of boilers

Power plant maintenance Questions & Answers

Various regulations and their significance of IBR regulation 1950.

Sl. No.	Regulations	Used for
1.	376	Preparation for boiler inspection
2.	379	Boiler hydraulic test
3.	390	Boiler open inspection
4.	391A	Boiler RLA test or NDT tests

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Batteries & troubleshooting

  

1-List down the applications of auxiliary DC power supply system in Power plants?

•  Protections relays
• Circuit breakers
• DCS
• Trip circuits
• Signaling
• Telephone system & communication
• Emergency lighting
• Transmitters & Positioners
• Emergency oil pumps
• Metering panels

2-List down the various DC voltages & their applications in power plants

Sl No.	Voltage	Applications
1	220 VDC & 110 VDC	Protection system Emergency lighting Trip & closing coil of circuit breakers Operating mechanisms
2	48 VDC	Telephone communication
3	+/- 24 VDC	Control circuits Measuring instruments Static relays

3-What is the power source for DC supply?

Main power source is lead-acid storage battery & AC/DC rectifier set

4-What are the installation requirements for lead acid battery ?

• The room should be isolated from other system
• Room should have adequate lighting & ventilation
• The room walls & floor should have acid proof tiles
• Battery cells should be installed on insulated racks
• Racks should be placed on insulator generally porcelain insulators
• Cables should be acid proof
• The DC bus bars should be of round or flat copper materials
• Bus bars connections are made by soldering or brazing
• The positive terminal of the battery is Red & negative terminal should be blue

30-selected QnA on power Transformers

5-How do you calculate the maximum discharge current of batteries?

Maximum discharge current = (Continuous load (W1) + Short time Load (W2)) / Rated Voltage

6-How do you specify the batteries?

Batteries have following specification:

• Rated voltage
• No.of cells
• AH capacity
• Arrangement of cells
• Details of charging equipment

7-What do you mean by AH of batteries?

AH (Ampere hour) is the capacity of battery. It is the product of current and total time required for discharge. It depends on the magnitude of discharge current.

8-How do you decide the number of batteries for a particular battery bank?

No. of battery cells = Bus bar voltage / Voltage of one cell

9-What are the various charging methods employed for batteries?

• Initial charging
• Quick charging
• Trickle charging

60-Basic questions & Answers on power plant electrical system

10-What do you mean by trickle charging? & what is its significance?

Trickle charging is constant charging current that is supplied to battery to compensate its discharge current.

Batteries get discharge when not in use. Hence to avoid sulphating, the batteries should be kept continuous charging by trickle charging.

11-What do you mean by primary cells (dry cell) & secondary cells?

Primary cells are non rechargeable cells & Secondary cells are storage batteries

12-What are anode, cathode & electrolyte in Lead-acid batteries?

• Cathode: Sponge lead
• Anode: Lead Peroxide (PbO2)
• Electrolyte: Sulphuric acid & water

13-What is the voltage level of lead acid batteries that are generally employed?

It is 2 V

14-What is the voltage level of fully charged & fully discharged lead acid battery?

Voltage of fully charged cell is 2.5 V & 1.75 V for fully discharged cell

15-What will happen during battery discharge & charging of lead acid battery?

During discharging process, the lead & lead peroxide het change into lead sulphate. And during charging lead sulphate gets convert into lead & lead peroxide

16-How do you check the specific gravity (SG) of electrolyte of lead acid battery?

Specific gravity (SG) is checked with the help of Hydrometer

17-What is the SG of fully charged & fully discharged electrolyte

SG Fully charged electrolyte: 1.28 & 1.12 for fully discharged electrolyte

18-What is the proportion of Sulphuric acid & water in Lead acid batteries?

Sulphuric acid: 64% & Distilled water: 36%

19-How do make up electrolyte level in lead-acid batteries?

Lower level of electrolyte is due to evaporation of water.

If the lower electrolyte level is due to evaporation of water, then add distilled water. And if If the lower electrolyte level is due to spilling over bubbling, then add acid & water solution.

20-Explain the charging method of lead-acid battery?

During charging process current forced into battery from opposite direction to its normal direction of current flow.

That is during normal use current leaves from positive terminal & enters through negative terminal. During charging current enters through positive terminal & leaves through negative terminal

21-Why do the lead-acid batteries get discharge when they are not in use?

This is because internal discharge current due to impurities in the electrolyte

22-What electrolyte is used in Nickel-Iron batteries?

Potassium hydroxide

23-What is the voltage level & density of electrolyte of Nickel-Iron battery?

It is 1.2 V & 1.2

24-Which electrolyte is used for Nickel Cadmium batteries?

Potassium hydroxide

25-What precautions do you take to avoid over discharging of battery?

• Over discharging can be avoided by
• Regular charging of battery
• Avoid excessive discharge rate
• Avoid short-circuit currents & leakage current
• Schedule charging & discharging
• When not in use, battery terminals should be considered

Basics of power plant instrumentations

26-What do you mean by sulphated Battery?

Discharge battery with abnormal hardened lead sulphate on its plate is a Sulphated battery

27-What actions you will take if Battery is charging slowly?

• Check battery connections & rectify if there are loose connections
• Check charger capacity
• Add distilled water or acid water solution if electrolyte is low
• Check sulphatation of battery & rectify it
• Increase current rating
• Check connection that is positive lead of charger to positive of battery & negative to negative

28-What are the reasons for overheating of battery while charging?

• Poor ventilation
• High charging rate

Lower specific gravity of electrolyte

29- What are the reasons for overheating of battery while discharging?

High discharge rate

Separators between plates have damaged

30-What are the reasons for cells having unequal voltages?

• Over discharge
• Lower electrolytes level
• Foreign material in electrolyte
• Positive plate worn out

Valves: DO you know these..???

•  Valve is a Mechanical or electromechanical device which is used to control the flow, pressure & temperature of fluid.
• Generally Globe valve, Gate valves, Butterfly valve, diaphragm valve, needle valve, Non return valves etc used in power plant various applications.
• The materials which are directly in contact with high pressure & temperature fluid are called trim materials.
• IBR Valves materials are manufactured according to the ASME class 16.34 B
• “Y” type globe valves have minimum pressure drop as compared to normal globe valves
• WCB indicates cast carbon steel, includes the standard A 216 . Used for fluid temperature up to 425 deg C
• WC-6 indicates Chromium Molybdenum steel, includes the standard A 217. Used for fluid temperature up to 575 deg C
• WC-9 indicates Cast alloy steel, includes the standard A 217. Used for fluid temperature up to 593 deg C
• SA 105 indicates forged & SA 182 indicates forged alloy steels

Equivalent grades of valves:

1. SA 216 WCB/WCC: SA 105N
2. SA 217 WC6: SA 182 F11
3. SA 217 WC9: SA 182 F22
4. SA 217 C12A : SA 182 F91

Safety valves QnA

• The MOC of Stud & nut materials of high pressure valves are SA 194 Gr.B7 & SA 194-2H
• Stem nuts of all high pressure valves is of Aluminium bronze materials
• The yoke of all high pressure valves are made up of material A-216 WCB
• Hand wheel of all HP valves are made up of SG iron 400/12
• Stems of all HP valves are made up of A 479-410-2

IBR acts, regulations & forms used

Comparison between Gate valve & Gate valve

• For a same size of valves, the size & weight of gate valves is more as compared to globe valves
• Time required for operating the gate valve is more as compared to globe valve
• Effort required to operate the gate valve is less as compared to globe valve
• Complicated maintenance procedure for larger size gate valves & simple maintenance procedure for globe valves
• In gate valve pressure drop of fluid is very less as compared to globe valve
• Gate valves cannot be used for flow regulating valves whereas globe valves can be used
• Very less or no turbulence of fluid in gate valves whereas there is much turbulence in globe valves
• Upon prolonged exposure of cast carbon steel or forged carbon steel valves to temperatures above 425°C, the carbide phase of steel may be converted to graphite. Permissible but not recommended for prolonged use above 425°C.

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