What do you mean by Turbine supervisory system???

 

What do you mean by Turbovisory or Turbine supervisory system?

Turbovisory or Turbine supervisory system is the monitoring of a Turbine. It supervises the condition of turbine and informs to an operating person. It also ensures the parameters do not exceed maximum allowable limit.

What is the significance of Turbine supervisory system?

Turbines are heavy & high speed machines, failures of machine lead into unrecoverable losses. So in case of any abnormality turbine should stop automatically. This is taken care by Turbine supervisory system.

What are the equipments or systems used in Turbine supervisory system?

Vibration probes: These probes are used for sensing shaft or bearing casing vibrations. Generally two probes are fitted at 90⁰ apart at X & Y-directions to measure the shaft vibrations. These vibrations are measured in microns, mills or mm/sec.

Speed probes: Speed sensors are generally Magnetic Pick up unit (MPU) type. These are fitted at teethed portion of turbine shaft for measurement. Generally 2 MPUs are used to measure the shaft speed, one for speed sensing & other for controlling.

Axial shift probes: This probe is fitted at the turbine front end to measure the axial displacement of shaft. Axial displacement probe of the shaft is generally set between +/- 0.4 to +/- 0.6 mm.

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Bearing temperature measuring sensors: These are used to sense the bearing metal temperature or bearing drain oil temperature. For measuring bearing metal temperature, RTD is inserted into drilled hole & touches the white metal & to measure the oil temperature RTD sensor touches the drain oil only.

Differential expansion probes: During abnormal operation conditions like quick start up, wrong SOP & uninform temperature distribution in casing & turbine rotor there could be the possibility of rubbing among turbine internals. To measure & monitor these gaps differential expansion probes are used & trips the turbine if these gaps increase beyond set values.

Casing temperature measuring sensors: Generally turbine casing thickness is very large around 150 mm &it depends on turbine operating parameters. So it is very much necessary of uniform distribution of temperature throughout the casing thickness.

And also the difference between top & bottom casing temperature of turbine should be very less.

Casing expansion measurement probes/sensors: These sensors are used to measure absolute expansion of casing. During startup &subsequent loading conditions turbine casing thermal expansion is must. Generally LVDTs are used for casing expansion measurement.

ESV opening indication: This is used to indicate the actual position of valves.

Eccentricity: This is very important supervision system. This is used to measure the mechanical bow. This may happen due to sudden trip of turbine & unavailability of barring device. Standstill position of turbine rotor for long time

Why do vacuum breaker valves are provided on steam condensers?

During tripping of turbine due to any of the above reasons like bearing vibration, temperature, axial shift, differential expansion etc, the vacuum breaker valve opens to bring down the turbine rotor speed to zero at the earliest time

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 Turbine oil flushing procedure

 

Questions & Answers on Coal analysis & related calculations

 

1-What are the various coal analysis are carried out in plant lab?

• Surface moisture
• Inherent moisture
• Total moisture
• Volatile matter
• Ash
• Fixed carbon
• Unburned carbon
• Moisture in ash
• GCV by Bomb calorimeter & by calculation
• Sieve analysis

2-How do you calculate the surface moisture (SM) of coal?

Take 100 gram of coal sample whose size is < 12.5 mm & keep this sample in lab for 24 hours at atmospheric condition.

Then calculate the surface moisture = Loss in weight X 100 / Weight of the sample (100 gram)

For example: After drying the 100 gram coal in lab for 24 hours its total becomes 92 gram then,

Surface moisture = (100-92) X 100 / 100 = 8%

3- How do you calculate the Inherent moisture (IM) of coal?

After analysis of surface moisture, take 5 gram of coal sample & powder it to 212 microns or 0.212 mm & keep it in oven at temperature 108 deg C for 1 Hr

Sample is then cooled & is weighed & IM is calculated as

Inherent Moisture = = Loss in weight X 100 / Weight of the sample (5 gram)

4-What do you mean by Total moisture (TM) of coal? & how do you calculate the Total Moisture of coal?

Coal containing free visible & non visible water is called total moisture of coal. The total moisture of coal is due to rain or coal in contact with water.

TM is calculation:

Take 100 gram of coal sample of size < 12.5mm & keep it in oven for 1 hour at 108 deg C

Sample is then cooled & is weighed & TM is calculated as

Total Moisture = Loss in weight X 100 / Weight of the sample (100 gram)

Total moisture is the sum of IM & SM

5-How do you calculate Volatile matter present in coal?

Take 2 gram of moisture free coal sample & keep it in muffle furnace for 7 minutes at 900 deg C temperature. Then cool it in desiccator for 15 minutes. Then sample is again weighed for final weight.

Volatile matter = Loss in weight X 100 / Weight of the sample (2 gram)

6-How do you calculate the percentage of ash present in coal?

Take 1 gram of coal sample & keep it in muffle furnace for 1 Hr at 900 deg C temperature. Then cool it in desiccator for 15 minutes. Then sample is again weighed for final weight.

Ash % = Residual weight X 100 / Total weight of the sample (1 gram)

7-Write down the formula for calculating Fixed Carbon (FC)

Fixed carbon FC = 100-(TM+VM+Ash)

8-How do you calculate the unburned carbon in ash sample?

Take 1 gram of ash sample & burn it in muffle furnace for 1 hr at temperature 900 deg c. Then cool it in desiccator for 15 minutes. Then sample is again weighed for final weight.

% of unburned carbon = Loss in weight X 100 / Weight of the sample (1 gram)

9-How do you convert GCV of coal from Air dried basis (ADB) to As received basis (ARB) & Vice versa?

GCV ADB to ARB =GCVADB X (100-TM) / (100-IM)

GCV ARB to ADB =GCVARB X (100-IM) / (100-TM)

10-How do you convert coal GCV from ADB to Dried basis?

ADB to DB = GCVADB X 100 / (100-IM)

11-What are the two different types of coal analysis?

Proximate Analysis & Ultimate analysis

12-What parameters of coal are analysed in proximate analysis of coal?

Moisture, Volatile matter, Ash & Fixed carbon

13- What parameters of coal are analysed in Ultimate analysis of coal?

Total Carbon, Hydrogen, Nitrogen, Oxygen & Sulphur

14-How do you convert Higher Calorific value of coal into Lower calorific Value coal?

LCV = HCV - (9 X H2 X 586)

15-A coal sample of HCV 5100 kcal/kg having 3.5% of hydrogen in it, then calculate the LCV

LCV = HCV - (9 X H2 X 586) = 5100 – (9 X 3.5% X 586) = 4915.41 kcal/kg

16-A coal sample of GCV 4800 kcal/kg having total moisture 18%, then calculate the Net calorific value (NCV) of coal

NCV = GCV-(10.02 X Moisture) = 4800 – (10.02 X 18) = 4619.64 kcal/kg

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9-steps for Steam Turbine commissioning

 

1. What do you mean by Turbine commissioning?

Turbine commissioning is the process of start-up of newly installed Turbine auxiliaries & Turbine up to satisfactory level.

2. When and how do one shall conduct commissioning of Turbine?

Turbine & their auxiliaries are commissioned after proper install, checking & trials. And it is commissioned under the guidance of OEM (Original Equipment Manufacturer)

3. Write down the sequential steps involved in Turbine commissioning

• Steam blowing
• Oil flushing
• Cooling water system commissioning
• Evacuation or vacuum pulling system commissioning
• Condensate lines flushing
• Calibration of servomotor, interlocks checking
• Turbine rolling
• Over speed trip setting
• Synchronization & loading

4. Write down the various steps involved in steam blowing

• Hope Boiler is commissioned
• Steam blowing line is installed properly with required supports
• Start to increase Boiler pressure up to 40% of operating or 40 kg/cm2 whichever is lower
• Heat up the line by opening Boiler Main bypass valve, heat up is done at steam temperature around 400 deg C
• Blow the steam line from steam pressure 40 kg/cm2 to 25-20 kg/cm2
• Again steam line is cooled up to 100-150 deg C or 3 hours if main steam line from Boiler to Turbine is insulated & 1 hour if line is uninsulated
• Continue this process for around 20-30 blows
• Then put the target plate aluminium or steel & continue the blow
• Blowing is continued till

For Target Plate Made of Aluminum:

The piping considered clean if there are not more than 3 (Three) pitting of 0.5 mm to 1mm dia. in center area of 25 mm X 25 mm and shall not have any deformed edges. Besides this there shall be no pitting in the rim zone. Pitting below 0.5 mm may be ignored.

 For Target Plate Made of Stainless Steel:

The piping is considered clean if there are not more than five pitting of 0.1 mm dia to 0.5 mm dia. in centre area of 50 mm X 50 mm & shall not have any deformed edges. Pitting below 0.1 mm may be ignored

Then normalize the steam line

Connect main steam line flange to ESV (Ensure MS line flange & ESV flange’s prallelity is done)

What do you mean by Turbine supervisory system???

5. Write down the sequential steps for Steam line charging.

 Following steps shall be followed during steam line charging:

•  Ensure all the maintenance works related to steam lines are finished.
•  Ensure the clearance from process or Turbine side for charging the steam line.
• Ensure all the drain and trap valves are opened. 
• Slowly open the steam line bypass valve and allow for heat up of line.
• After ensuring line proper heat up, cracks open the main valve and allow for condensate drain.
• After ensuring no condensate in drain line, open the main valve gradually and observe the hammering. (If hammering occurs suddenly close the main valve). 
• After opening the valve 100%, wait till line stabilization. 
• After ensuring no condensate in drain lines, close all the drain valves

6. What is the significance of steam blowing?

Steam blowing allows power station boilers and pipelines to ensure that during normal operation no adhering material in the super heaters, reheaters, and steam pipelines will become dislodged, reach the turbine blades, and damage them. The steam blowing operation cleans all the debris in the super heater, reheater and the steam pipe line connecting the turbine.

7. What are the sequential steps involved in Turbine oil flushing?

Following are the steps

• Ensure OEM recommended oil is being selected for oil flushing
• Oil tank is filled with oil
• Flushing loops are prepared as per OEM recommendations
• Ensure return oil line is fitted with OEM recommended strainers
• Ensure oil centrifuge is in place & ready for operation
• Flush oil by starting lube oil pump & ensure oil is circulating through cooler
• Keep oil centrifuge ON with heater ON
• Maintain oil temperature up to 70 deg C for 4-5 hours
• Charge oil cooler & bring down the oil temperature up to 35-40 deg C
• Then hammer the oil lines to dislodge the sludge, bur or any other foreign materials
• Continue oil flushing till return line strainer is clean by 24 microns filter
• Oil flushing shall be deemed as completed, If Lube oil filter does not choke for more than 24 hours

8-What are the steps involved in cooling water system commissioning?

Following activities are involved in cooling water system commissioning

• Ensure all erection activities are completed on cooling water system
• Ensure all instruments are fitted on CW system
• Ensure cooling tower level is filled with required quality water
• Check the Cooling water pumps physical condition, if found ok take no load trial Or Ensure CW pumps are commissioned under the guidance of OEM
• Connect cooling water line with flushing line & leave to open areas (DO not connect return cooling water line to cooling tower)
• Then start the cooling water pumps & flush all the lines
• This activity shall be done -5 times & keep on making up cooling tower level every time

Read Generator and Turbine inter tripping

9-List down the sequential steps involved in condensate line flushing

• Condensate system consists of Condenser, CEP, Ejector, GSC
• Ensure all condensate system is ready for flushing
• Condensate line should be left open at deaerator floor
• Ensure hot well level is normal & provision is made to make up the level of hot well
• Ensure CEP is ready to start or CEP is commissioned under the guidance of OEM
• Then start CEP & flush the line
• This activity shall be dine for 8-10 times & every time up hot well level

10-What are the sequential steps for turbine rolling?

• Ensure Lube oil system is commissioned & is in service
• Ensure cooling water system is commissioned & is being charged
• Ensure condensate system is in service
• Ensure main steam line is charged as per standard process
• Vacuum pulling is done
• Reset turbine protections
• ESV opens & Turbine rolling is done s per OEM guidance

 

 Questions & Answers on steam blowing

 

 

 

 

 

14 unknowns you must know in Boilers

 1-How do you decide Right hand side & Left hand side of a Boiler?

Boiler front is decided based on boiler outlet duct.

If you stand by facing towards boiler out let duct, then the most front part of you is deemed as Boiler front , next to that is boiler rear & LHS & RHS side of you is deemed as Boiler left hand side & right hand side.

2-Why in Some HP boilers drums are aligned at an angle 2 to 4⁰ towards right or left?

Drum slanting side depends on the connection of CBD line. If CBD line is connected at LHS side of the drum then the drum is slanted towards LHS side that is it is made down by an angle 2 to 4^0. This is because to avoid the blow down of excess water throughout the drum length & for such drums CBD line is extended for only for short distance only .And also it is been ensured that all the sludge will collect at slant position only.

3-How it is been decided that RHS or LHS safety valve of steam drum is set at higher pressure?

It is decided based on the slanting angle of steam, drums & CBD line connection.

If drum is aligned horizontally then you can set any side of the Safety valve at higher pressure as there is uniform spreading of sludge in drum.

Whereas if drum is slanted (made down)towards right or left from where CBD line is connected then it is needed to set that side safety valve at higher pressure to avoid carryover of sludge into the safety valve if t blows first. Such sludge will deposit on safety valves disc & seat which again leads into leakages & wrong operation related issues. So safety valve of such location is always set at higher pressure.

4-Why thickness of steam drum dish end is somewhat lesser than other area

Because dish end has spherical shape, so there develop hoop or circumferential stresses & on the other part of the drum longitudinal stress.

 For Hoop stresses

σc =  Pd/2tη

Thickness t = Pd/(2 ησ)

& For longitudinal stresses σl = Pd/4tη

Thickness t = Pd/(4 ησ)

Where P = Pressure acting & d is internal diameter of the drum

Based on above relations thickness for spherical part of the drum that is dish end, the thickness is lesser than other part of the drum.

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5-Why the start up vent is used in Boilers?

Start up vent is used for

• To provide minimum steam flow from the boiler during start up, shutdown & sudden load cut off
• It is used to manual relieve of excess pressure
• Used to give excess flow for temperature rising during start up or partial loads
• Used to take excess load on boilers during peak load test

6-Why the super heater safety valve is set at lower pressure than drum safety valve

If drum safety valves set at lower pressure, then there will be very less or no steam flow to super heaters.

In order to save super heater coils from starvation due to no flow of steam during steam blow from drum safety valves, the super heater safety valves are always set at lower pressure than drum safety.

7-Why LHS/RHS water wall panels expand more (towards down) than front & rear water wall panels?

Side water panels are usually straight hence expansion readings show more value  where as front & rear water wall panel will have bends.

8-Why pressure gauges fitted at boiler firing floors show more pressure than actual (that of fitted at steam drum EL.level)

Pressure gauges show 2 to 3 kg/cm2 higher pressure due to addition of hydraulic head in PG impulse line laid from actual location to firing floor

9-Why there is a pressure difference between main steam line pressure & drum pressure?

Main steam line pressure shows lower pressure than drum pressure due to pressure loss in super heater coils. And this pressure difference increases as the number of super heater coils & steam flow increase.

10-Why do high pressure Boilers have higher efficiency & lower fuel consumption?

Because:

1-High pressure boilers have higher  saturation temperature

2-High pressure boilers have higher feed water temperature at economiser inlet

3-High pressure boiler have lower enthalpy of evaporation (latent heat)will be less

H = Hf + Hfg + Cps x (Tsup-Tsat) -

Where,

Hf = Enthalpy of liquid at operating pressure

Hfg = Latent heat

Tsup = Suepr heated steam temperature

Tsat = Saturated temperature of steam

Example:What amount of heat would be required to produce 5000 kg of steam at a pressure of 65 kg/cm2 and temperature 485 °C from water at temperature 175 °C?

Steam pressure P = 65 kg/cm2

Steam temperature Tsup = 485 °C

At above parameters, saturated temperature Ts = 282.7 °C

hf = 298.82 kcal/kg, hfg = 364.47 kcal/kg

Now, enthalpy of 1 kg of superheated steam

Hsup= hf + hfg + Cps (Tsup - Ts)

hsup = 298.82 + 364.47 + 0.5 X (485 - 282.7)

hsup = 764.44 kcal/kg

Amount of heat already associated with 1 kg of water = 1 X 1 X (175 – 0) X 175 kcal/kg

Therefore net heat to be supplied per kg is 764.44 – 175 = 589.44 kcal/kg

11-Why there is more CO in flue gas?

More CO in flue gas is due to improper combustion, that is due to

• Less excess air
• In adequate turbulent
• Lower furnace/bed temperature
• Higher FC in fuel

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12-Why Does boiler furnace pressure fluctuate?

• Interrupted fuel flow
• Leakage in boiler pressure parts
• Furnace combustion controller not working properly
• Malfunctioning of fans pneumatic dampers
• Higher moisture in fuel

13-Why there is more NOX in flue gas?

• Higher NOx is due to
• Higher bed temperature or furnace temperature
• Higher excess air
• More N2 in fuel

14-Why there is no Temperature gauge (TG) is fitted on steam drum of any Boiler?
In steam dream the phase of water is at saturated state, so no any necessary of providing TG. However temperature gauges are provided at drum inlet feed water line & drum outlet saturated line.

In some drums whose thickness is > 100 mm, there you may find thermo couples for measuring skit temperature. So in order to avoid  weakening of steam drums due to making number of drill holes for unnecessary instruments, the TG is not generally provided for drums.

For example if  drum PG showing  pressure 110 kg/cm2, then its temperature will be around 320 deg c. (Refer steam table for saturation temperature). And generally not used in any calculation or performance analysis, if required one can refer steam tables for saturated water

The temperature gauge or thermo couple provided at the drum outlet lines is used during plant start up.

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