COMMISSIONING DEPARTMENT NTPC-SIPAT POINTS OF DISCUSSION Ø

COMMISSIONING DEPARTMENT, NTPC-SIPAT

POINTS OF DISCUSSION Ø SUB CRITICAL & SUPER CRITICAL BOILER Ø SIPAT BOILER DESIGN Ø BOILER DESIGN PARAMETERS Ø CHEMICAL TREATMENT SYSTEM Ø OPERATION Ø FEED WATER SYSTEM Ø BOILER CONTROL Ø BOILER LIGHT UP Ø START UP CURVES COMMISSIONING DEPARTMENT, NTPC-SIPAT

WHY SUPER CRITICAL TECHNOLOGY ü To Reduce emission for each Kwh of electricity generated : Superior Environmental 1% rise in efficiency reduce the CO 2 emission by 2 -3% ü The Most Economical way to enhance efficiency ü To Achieve Fuel cost saving : Economical ü Operating Flexibility ü Reduces the Boiler size / MW ü To Reduce Start-Up Time COMMISSIONING DEPARTMENT, NTPC-SIPAT

UNDERSTANDING SUB CRITICAL TECHNOLOGY ü Water when heated to sub critical pressure, Temperature increases until it starts boiling ü This temperature remain constant till all the water converted to steam ü When all liquid converted to steam than again temperature starts rising. ü Sub critical boiler typically have a mean ( Boiler Drum) to separate Steam And Water ü The mass of this boiler drum, which limits the rate at which the sub critical boiler responds to the load changes ü Too great a firing rate will result in high thermal stresses in the boiler drum COMMISSIONING DEPARTMENT, NTPC-SIPAT

Role of SG in Rankine Cycle Perform Using Natural resources of energy …….

UNDERSTANDING SUPER CRITICAL TECHNOLOGY ü When Water is heated at constant pressure above the critical pressure, its temperature will never be constant ü No distinction between the Liquid and Gas, the mass density of the two phases remain same ü No Stage where the water exist as two phases and require separation : No Drum ü The actual location of the transition from liquid to steam in a once through super critical boiler is free to move with different condition : Sliding Pressure Operation ü For changing boiler loads and pressure, the process is able to optimize the amount of liquid and gas regions for effective heat transfer. COMMISSIONING DEPARTMENT, NTPC-SIPAT

Circulation Vs Once Through COMMISSIONING DEPARTMENT, NTPC-SIPAT

No Religious Attitude COMMISSIONING DEPARTMENT, NTPC-SIPAT

540°C, 255 Ksc 568°C, 47 Ksc 492°C, 260 Ksc 457°C, 49 Ksc FUR ROOF I/L HDR ECO HGR O/L HDR HRH LINE MS LINE 411°C, 277 Ksc 411°C, 275 Ksc SEPARATOR G LPT C O N D E N S E R LPT FINAL SH FINAL RH DIV PANELS SH LTRH PLATEN SH VERTICAL WW ECO JUNCTION HDR 305°C, 49 Ksc S T O R A G E T A N K IPT HPT ECONOMISER ECO I/L lls a rw S al pir te wa FEED WATER BWRP 290°C, 302 KSC FUR LOWER HDR FRS

Steam Partial Steam Generation Steam Complete or Once-through Generation Water Heat Input Water Boiling process in Tubular Geometries

SEPARATOR TANK COMMISSIONING DEPARTMENT, NTPC-SIPAT

PENTHOUSE Eco. O/L hdr (E 7) LTRH O/L hdr (R 8) 2 nd pass top hdrs (S 11) Back pass Roof o/l hdr (S 5) SH final I/L hdr (S 34) 1 st SH final O/L hdr (S 36) F 19 pass top hdrs RH O/L hdr (R 12) RH I/L hdr (R 10) Platen O/L hdr (S 30) F 28 Platen I/L hdr (S 28) F 28 Div. Pan. O/L hdrs (S 24) Div. Pan. I/L hdrs (S 20) Back pass Roof i/l hdr Separator (F 31) F 8 S 2 1 st pass top hdrs Storage Tank (F 33)

SIPAT SUPER CRITICAL BOILER Ø BOILER DESIGN PARAMETER Ø DRUM LESS BOILER : START-UP SYSTEM Ø TYPE OF TUBE Ø Vertical Ø Spiral Ø SPIRAL WATER WALL TUBING v Advantage v Disadvantage over Vertical water wall COMMISSIONING DEPARTMENT, NTPC-SIPAT

Vertical Tube Furnace Ø To provide sufficient flow per tube, constant pressure furnaces employ vertically oriented tubes. Ø Tubes are appropriately sized and arranged in multiple passes in the lower furnace where the burners are located and the heat input is high. Ø By passing the flow twice through the lower furnace periphery (two passes), the mass flow per tube can be kept high enough to ensure sufficient cooling. Ø In addition, the fluid is mixed between passes to reduce the upset fluid temperature. COMMISSIONING DEPARTMENT, NTPC-SIPAT

Spiral Tube Furnace Ø The spiral design, on the other hand, utilizes fewer tubes to obtain the desired flow per tube by wrapping them around the furnace to create the enclosure. Ø This also has the benefit of passing all tubes through all heat zones to maintain a nearly even fluid temperature at the outlet of the lower portion of the furnace. Ø Because the tubes are “wrapped” around the furnace to form the enclosure, fabrication and erection are considerably more complicated and costly. COMMISSIONING DEPARTMENT, NTPC-SIPAT

COMMISSIONING DEPARTMENT, NTPC-SIPAT

SPIRAL WATER WALL ADVANTAGE ü Benefits from averaging of heat absorption variation : Less tube leakages ü Simplified inlet header arrangement ü Use of smooth bore tubing ü No individual tube orifice ü Reduced Number of evaporator wall tubes & Ensures minimum water flow ü Minimizes Peak Tube Metal Temperature ü Minimizes Tube to Tube Metal Temperature difference DISADVANTAGE ü Complex wind-box opening ü Complex water wall support system ü tube leakage identification : a tough task ü More the water wall pressure drop : increases Boiler Feed Pump Power ü Adherence of Ash on the shelf of tube fin

BOILER OPERATING PARAMETER FD FAN 2 No’S ( AXIAL ) 11 kv / 1950 KW 228 mmwc 1732 T / Hr PA FAN 2 No’s ( AXIAL) 11 KV / 3920 KW 884 mmwc 947 T / Hr ID FAN 2 No’s ( AXIAL) 11 KV / 5820 KW TOTAL AIR 2535 T / Hr SH OUT LET PRESSURE / TEMPERATURE / FLOW 256 Ksc / 540 C 2225 T / Hr RH OUTLET PRESSURE/ TEMPERATURE / FLOW 46 Ksc / 568 C 1742 T / Hr SEPARATOR OUT LET PRESSURE/ TEMPERATURE 277 Ksc / 412 C ECONOMISER INLET 304 Ksc / 270 C MILL OPERATION 7 / 10 COAL REQUIREMENT 471 T / Hr SH / RH SPRAY 89 / 0. 0 T / Hr BOILER EFFICIENCY 3020 T / Hr 87 % COMMISSIONING DEPARTMENT, NTPC-SIPAT

Coal Analysis 1. High erosion potential for pulverizer and backpass tube is expected due to high ash content. 2. Combustibility Index is relatively low but combustion characteristic is good owing to high volatile content. COMMISSIONING DEPARTMENT, NTPC-SIPAT

Ash Analysis 1. Lower slagging potential is expected due to low ash fusion temp. and low basic / acid ratio. 2. Lower fouling potential is expected due to low Na 2 O and Ca. O content.

AIR AND FLUE GAS SYSTEM AIR PATH : Similar as 500 MW Unit FLUE GAS PATH : No Of ESP Passes : 6 Pass No Of Fields / Pass : 18 1 -7 fields 70 KV. 8&9 field 90 KV No Of Hopper / Pass : 36 Flue Gas Flow / Pass : 1058 T/ Hr COMMISSIONING DEPARTMENT, NTPC-SIPAT

M M M PA FAN # A M M HOT PRIMARY AIR DUCT PAPH # A M TO PULVERISER SYSTEM AIR MOTOR M M M FD FAN # A M M M SAPH # B M AIR MOTOR M M FD FAN # B M M M PA FAN # B M PAPH # B HOT PRIMARY AIR DUCT M M TO PULVERISER SYSTEM LHS WIND BOX RHS WIND BOX ECONOMISER BACK PASS LTRH FINAL SUPERHEATER FINAL REHEATER PLATEN COILS DIVISIONAL PANEL FURNACE AIR PATH COMMISSIONING DEPARTMENT, NTPC-SIPAT

FUEL OIL SYSTEM Type Of Oil : LDO / HFO Boiler Load Attainable With All Oil Burner In Service : 30 % Oil Consumption / Burner : 2123 Kg / Hr Capacity Of HFO / Coal : 42. 1 % Capacity Of LDO / Coal : 52. 5 % HFO Temperature : 192 C All Data Are At 30 % BMCR COMMISSIONING DEPARTMENT, NTPC-SIPAT

DESIGN BASIS FOR SAFETY VALVES : 1. Minimum Discharge Capacities. Safety valves on Separator and SH Combined capacity 105%BMCR (excluding power operated impulse safety valve) Safety valves on RH system Combined capacity 105% of Reheat flow at BMCR (excluding power operated impulse safety valve) Power operated impulse safety valve 40%BMCR at super-heater outlet 60% of Reheat flow at BMCR at RH outlet 2. Blow down 4% (max. )b COMMISSIONING DEPARTMENT, NTPC-SIPAT

COMMISSIONING DEPARTMENT, NTPC-SIPAT

COMMISSIONING DEPARTMENT, NTPC-SIPAT

COMMISSIONING DEPARTMENT, NTPC-SIPAT

COMMISSIONING DEPARTMENT, NTPC-SIPAT

COMMISSIONING DEPARTMENT, NTPC-SIPAT

BOILER FILL WATER REQUIREMENT Main Feed Water Pipe ( FW Shut Off Valve to ECO I/L HDR) 28. 8 m 3 Economizer 253. 2 m 3 Furnace ( Eco Check Valve to Separator Link) 41. 5 m 3 Separators & Link 13. 8 m 3 COMMISSIONING DEPARTMENT, NTPC-SIPAT

OXYGENATED TREATMENT OF FEED WATER “WATER CHEMISTRY CONTROL MAINTAINS PLANT HEALTH. ” ØDosing of oxygen(O 2) or Hydrogen peroxide (H 2 O 2) in to feed water system. ØConcentration in the range of 50 to 300 µg/L. ØFormation of a thin, tightly adherent ferric oxide (Fe. OOH) hydrate layer. ØThis layer is much more dense and tight than that of Magnetite layer. 39

All Volatile Treatment Oxygenated Water Treatment 40

DOSING POINTS 41

“AVT” Dosing Auto Control 42

“OWT” Dosing Auto Control 43

U#1 FUR ROOF I/L HDR VENT HDR WATER LINE N 2 FILLING LINE VENT LINE SAMPLE COOLER SEPRATOR #1 1 2 DRAIN LINE SAMPLE COOLER LINE SEPRATOR #2 1 2 1 2 VENT HDR FUR WW HDR FUR INTERMITTENT HDR STORAGE TANK DRAIN HDR FUR BOTTOM RING HDR FLASH TANK DRAIN HDR MIXING PIECE WR VENT HDR ZR BACK PASS ECO O/L HDR N 2 FILL LINE ECO JUNCTION HDR BRP ECO MIXING LINK BACK PASS ECO I/L HDR BLR FILL PUMP FROM FEED WATER TO DRAIN HDR WATER CIRCULATION SYSTEM

FEED WATER SYSTEM MODES OF OPERATION 1. BOILER FILLING 2. CLEAN UP CYCLE 3. WET MODE OPERATION (LOAD < 30 %) 4. DRY MODE OPERATION (LOAD > 30 %) 5. DRY TO WET MODE OPERATION ( WHEN START UP SYSTEM NOT AVAILABLE) COMMISSIONING DEPARTMENT, NTPC-SIPAT

BOILER FILLING LOGIC ü If the water system of the boiler is empty (economizer, furnace walls, separators), then the system is filled with approximately 10% TMCR ( 223 T/Hr) feed water flow. ü When the level in the separator reaches set-point, the WR valve will begin to open. ü When the WR valve reaches >30% open for approximately one minute, then increase feed water flow set-point to 30% TMCR ( approx 660 T/Hr). ü As the flow increases, WR valve will reach full open and ZR valve will begin to open. ü The water system is considered full when: ü The separator water level remains stable for two(2) minutes and ü The WR valve is fully opened and ZR valve is >15% open for two(2) minutes After completion of Filling, the feed water flow is again adjusted to 10 % TMCR for Clean up cycle operation COMMISSIONING DEPARTMENT, NTPC-SIPAT

BOILER INITIAL WATER LEVEL CONTROL (UG VALVE) ü The boiler circulating pump is started following the start of a feed water pump and the final clean-up cycle. ü This pump circulates feed water from the evaporator outlet back to the economizer inlet. ü Located at the outlet of this pump is the UG valve which controls economizer inlet flow during the start-up phase of operation. ü Demand for this recirculation, control valve is established based on measured economizer inlet flow compared to a minimum boiler flow set point. COMMISSIONING DEPARTMENT, NTPC-SIPAT

Boiler Clean-up ØWhen the feedwater quality at the outlet of deaerator and separator is not within the specified limits, a feedwater clean-up recirculation via the boiler is necessary. ØDuring this time, constant feedwater flow of 10% TMCR ( 223 T/Hr) or more is maintained. ØWater flows through the economizer and evaporator, and discharges the boiler through the WR valve to the flash tank and via connecting pipe to the condenser. ØFrom the condenser, the water flows through the condensate polishing plant, which is in service to remove impurities ( Like Iron & its Oxide, Silica, Sodium and its salts ), then returns to the feed water tank. ØThe recirculation is continued until the water quality is within the specified limits. COMMISSIONING DEPARTMENT, NTPC-SIPAT

FEED WATER QUALITY PARAMETER FOR START UP COMMISSIONING DEPARTMENT, NTPC-SIPAT

MODE OF OPERATION WET MODE : ü Initial Operation Of Boiler Light Up. When Economizer Flow is maintained by BCP. ü Boiler Will Operate till 30 % TMCR on Wet Mode. DRY MODE : ü At 30 % TMCR Separator water level will become disappear and Boiler Operation mode will change to Dry ü BCP Will shut at this load ü Warm Up system for Boiler Start Up System will get armed ü Boiler will turn to once through Boiler ü ECO Water flow will be controlled by Feed Water Pump in service COMMISSIONING DEPARTMENT, NTPC-SIPAT

SYSTEM DESCRIPTION ( WET MODE OPERATION) 1. Flow Control Valve ( 30 % Control Valve ) Ø Ensures minimum pressure fluctuation in Feed Water Header Ø It measures Flow at BFP Booster Pump Discharge and compare it with a calculated flow from its downstream pressure via a function and maintains the difference “ 0 “ 2. 100 % Flow Valve To Boiler Ø Remains Closed 3. BFP Recirculation Valve Ø It Measures Flow at BFP Booster Pump Discharge Ø Ensures minimum Flow through BFP Booster Pump ü ü Closes when Flow through BFP Booster Pump discharge > 2. 1 Cum Open When Flow through BFP Booster Pump Discharge < 1. 05 Cum ( Minimum Flow will be determined by BFP Speed via BFP Set limitation Curve) 4. BFP Scoop Ø It measures value from Storage tank level Transmitter Ø Maintain Separator Storage Tank Level COMMISSIONING DEPARTMENT, NTPC-SIPAT

5. UG Valve Ø Maintain Minimum Economizer Inlet Flow ( 30 % TMCR = Approx 660 T/Hr) Ø Maintain DP across the BRP ( Approx 4. 0 Ksc) Ø It Measures Flow Value from Economizer Inlet Flow Transmitter 6. WR / ZR Valve Ø Maintains Separator Storage Tank Level Ø It Measures value from the Storage tank Level 7. Storage Tank Level Ø 3 No’s Level Transmitter has been provided for Storage tank level measurement Ø 1 No HH Level Transmitter has been provided ü Ø At 17. 9 Mtr level it will trip all FW Pumps also MFT will act 1 No LL Level Transmitter has been provided ü At 1. 1 Mtr level MFT will Act COMMISSIONING DEPARTMENT, NTPC-SIPAT

SYSTEM DESCRIPTION ( DRY MODE OPERATION) 1. Following System will be isolated during Dry Mode Operation Ø FCV ( 30 % ) Ø Start Up System Of Boiler ü ü Ø WR / ZR Valve Storage Tank BRP Recirculation System BFP Recirculation Valve 2. Following System will be in service Ø UG Valve ( Full Open) Ø 100 % FW Valve ( Full Open) Ø Platen / Final Super-heater spray control Ø Start Up System Warming Lines ü Separator Storage Tank Wet Leg Level Control COMMISSIONING DEPARTMENT, NTPC-SIPAT

SYSTEM OPERATION ( DRY MODE OPERATION) 1. START UP SYSTEM Ø Ø Warming System for Boiler Start Up system will be charged Ø 2. In Dry Mode Start Up System Of Boiler will become isolated Separator Storage Tank level will be monitored by Separator storage tank wet leg level control valve ( 3 Mtr) TRANSITION PHASE : - Changeover of FW Control valve (30 % to 100 % Control ) Ø Ø During the transition phase system pressure fluctuates Ø 3. 100 % FW Flow valve will wide open The system pressure fluctuation will be controlled by 30 % FW Valve. After stabilization of system 30 % CV Will become Full Close FEED WATER CONTROL Ø It will be controlled in three steps ü ü ü Feed Water demand to maintain Unit Load Maintain Separator O/L Temperature Maintain acceptable Platen Spray Control Range COMMISSIONING DEPARTMENT, NTPC-SIPAT

FEED WATER DEMAND ( DRY MODE OPERATION) 1. FINAL SUPER HEATER SPRAY CONTROL Ø 2. Maintain the Final Steam Outlet Temperature ( 540 C) PLATEN SUPER HEATER SPRAY CONTROL Ø Primary purpose is to keep the final super heaer spray control valve in the desired operating range ü ü ü 3. Measures the final spray control station differential temperature It Compares this difference with Load dependent differential temperature setpoint Output of this is the required temperature entering the Platen Super Heater Section (Approx 450 C) FEED WATER DEMAND 1. FEED FORWARD DEMAND Ø It is established by Boiler Master Demand. Ø This Demand goes through Boiler Transfer Function where it is matched with the actual Evaporator Heat Transfer to minimize the temperature fluctuations 2. FEED BACK DEMAND Ø Work With two controller in cascade mode COMMISSIONING DEPARTMENT, NTPC-SIPAT

FEED WATER DEMAND ( DRY MODE OPERATION) 2. FEED BACK DEMAND Ø Work With two controller in cascade mode Ø FIRST CONTROLLER ü ü Ø One Controller acts on Load dependent average platen spray differential temperature Its Output represents the desired heat transfer / steam generation to maintain the desired steam parameters and Flue gas parameters entering the Platen section SECOND CONTROLLER ü Second Controller acts on the load dependent Separator Outlet Temperature adjusted by Platen spray differential temperature ü This controller adjust the feed water in response to firing disturbances to achieve the separator O/L Temperature THE RESULTING DEMAND FROM THE COMBINED FEEDFORWARD AND FEEDBACK DEMANDSIGNAL DETERMINED THE SETPOINT TO THE FEED WATER MASTER CONTROL SETPOINT COMMISSIONING DEPARTMENT, NTPC-SIPAT

DRY TO WET MODE OPERATION ( START UP SYSTEM NOT AVAILABLE) 1. The combined Feed Forward and Feed back demand ( as calculated in dry mode operation) will be compared with minimum Economizer Flow This ensures the minimum flow through Economizer during the period when start up system is unavailable 2. Output of the first controller is subjected to the second controller which monitors the Separator Storage tank level ( Since the system is in Wet Mode now) 3. The output of the second controller is the set point of Feed water master controller. 4. The Feed back to this controller is the minimum value measured before the start up system and Economizer inlet. COMMISSIONING DEPARTMENT, NTPC-SIPAT

WATER & STEAM PATH BLR PATH ( WHEN WET MODE) Separator - Backpass Wall & Extended Wall - SH Division - Platen SH - Final SH HP By-pass - Cold R/H Line - Primary R/H (Lower Temp R/H) - Final R/H - LP Bypass - Condenser BLR Path (When Dry Mode) Primary Eco - Secondary Eco - Ring HDR - Spiral W/W - W/W Intermediate HDR Vertical W/W - Separator - Backpass Wall & Extended Wall - SH Division - Platen SH - Final SH - HP TBN - Cold R/H Line - Primary R/H (Lower Temp R/H)- Final R/H - IP and LP TBN - Condenser COMMISSIONING DEPARTMENT, NTPC-SIPAT

Wet Mode and Dry Mode of Operation

DIV SH 406 451 PLATEN SH 440 FINAL SH 480 486 DSH 1 15% DSH 2 3% 540

BOILER LOAD CONDITION Constant Pressure Control ü Above 90% TMCR The MS Pressure remains constant at rated pressure ü The Load is controlled by throttling the steam flow ü Below 30% TMCR the MS Pressure remains constant at minimum Pressure Sliding Pressure Control ü Boiler Operate at Sliding pressure between 30% and 90% TMCR ü The Steam Pressure And Flow rate is controlled by the load directly COMMISSIONING DEPARTMENT, NTPC-SIPAT

CONSTANT PRESSURE VS SLIDING PRESSURE Ø Valve throttling losses occur because the boiler operates at constant pressure while the turbine doesn't. Ø The most obvious way to avoid throttling losses therefore is to stop operating the boiler at constant pressure! Ø Instead, try to match the stop valve pressure to that existing inside the turbine at any given load. Ø Since the turbine internal pressure varies linearly with load, this means that the boiler pressure must vary with load similarly. Ø This is called. sliding pressure operation. . Ø If the boiler pressure is matched to the pressure inside the turbine, then there are no valve throttling losses to worry about! While sliding pressure is beneficial for the turbine, it can cause difficulties for the boiler. Ø ADVERSE AFFECT v As the pressure falls, the boiling temperature (boiling point) changes. The boiler is divided into zones in which the fluid is expected to be entirely water, mixed steam / water or dry steam. A change in the boiling point can change the conditions in each zone. v The heat transfer coefficient in each zone depends upon the pressure. As the pressure falls, the heat transfer coefficient reduces. This means that the steam may not reach the correct temperature. Also, if heat is not carried away by the steam, the boiler tubes will run hotter and may suffer damage. COMMISSIONING DEPARTMENT, NTPC-SIPAT

CHALLANGES Ø The heat transfer coefficient also depends upon the velocity of the steam in the boiler tubes. Ø Any change in pressure causes a change in steam density and so alters the steam velocities and heat transfer rate in each zone. Ø Pressure and temperature cause the boiler tubes to expand. If conditions change, the tubes will move. The tube supports must be capable of accommodating this movement. Ø The expansion movements must not lead to adverse stresses. Ø The ability to use sliding pressure operation is determined by the boiler Boilers can be designed to accommodate sliding pressure. Ø When it is used, coal fired boilers in the 500 to 1000 MW class normally restrict sliding pressure to a limited load range, typically 70% to 100% load, to minimize the design challenge. Below this range, the boiler is operated at a fixed pressure. Ø This achieves an acceptable result because large units are normally operated at high load for economic reasons. Ø In contrast, when sliding pressure is used in combined cycle plant, the steam pressure is varied over a wider load range, typically 50% to 100% load or more COMMISSIONING DEPARTMENT, NTPC-SIPAT

Ø As stated, in coal-fired plant, sliding pressure is normally restricted to a limited load range to reduce design difficulties. Ø In this range, the boiler pressure is held at a value 5% to 10% above the turbine internal pressure. Consequently, the governor valves throttle slightly. Ø The offset is provided so that the unit can respond quickly to a sudden increase in load demand simply by pulling the valves wide open. Ø This produces a faster load response than raising the boiler firing rate alone. The step in load which can be achieved equals the specified margin ie 5% to 10%. Ø The throttling margin is agreed during the tendering phase and then fixed. Ø A margin of 5% to 10% is usually satisfactory because most customers rely upon gas turbines, hydroelectric or pumped storage units to meet large peak loads. Ø The throttling margin means that the full potential gain of sliding pressure is not achieved. Ø Nevertheless, most of the throttling losses which would otherwise occur are recovered. COMMISSIONING DEPARTMENT, NTPC-SIPAT

ADVANTAGES Ø Temperature changes occur in the boiler and in the turbine during load changes. These can cause thermal stresses in thick walled components. Ø These are especially high in the turbine during constant-pressure operation. They therefore limit the maximum load transient for the unit. Ø By contrast, in sliding pressure operation, the temperature changes are in the evaporator section. However, the resulting thermal stresses are not limiting in the Once through boiler due to its thermo elastic design. In fixed pressure operation , temperature change in the turbine when load changes, while in sliding-pressure operation , they change in the boiler COMMISSIONING DEPARTMENT, NTPC-SIPAT

Ø The enthalpy increase in the boiler for preheating, evaporation and superheating changes with pressure. Ø However, pressure is proportional to output in sliding pressure operation Ø In a uniformly heated tube, the transitions from preheat to evaporation and from evaporation to superheat shift automatically with load such that the main steam temperature always remains constant. COMMISSIONING DEPARTMENT, NTPC-SIPAT

Sliding Pressure v At loads over 25% of rated load, the water fed by a feed-water pump flows through the high pressure feed-water heater, economizer , furnace water wall, steam-water separator, rear-wall tubes at the ceiling, and super heaters, The super heaters steam produced is supplied to the turbine. v At rated and relatively high loads the boiler is operated as a purely once through type. At partial loads, however, the boiler is operated by sliding the pressure as a function of load. 24. 1 Mpa 9. 0 Mpa COMMISSIONING DEPARTMENT, NTPC-SIPAT

COMMISSIONING DEPARTMENT, NTPC-SIPAT

CONSTANT PRESSURE Vs VARIABLE PRESSURE BOILER CHARACTERSTIC Boiler Load % 20 60 40 80 100 Efficiency Change % +1 0 Variable Pressure -1 -2 e ur s s t n ta s e Pr n Co -3 -4 COMMISSIONING DEPARTMENT, NTPC-SIPAT

Benefits Of Sliding Pressure Operation ( S. P. O) ü Able to maintain constant first stage turbine temperature ü Reducing thermal stresses on the component : Low Maintenance & Higher Availability ü No additional pressure loss between boiler and turbine. ü low Boiler Pr. at low loads. WHY NOT S. P. O. IN NATURAL/CONTROL CIRCULATION BOILERS ü Circulation Problem : instabilities in circulation system due to steam formation in down comers. ü Drum Level Control : water surface in drum disturbed. ü Drum : (most critical thick walled component) under highest thermal stresses COMMISSIONING DEPARTMENT, NTPC-SIPAT

The Basis of Boiler Start-up Mode Basis Restart Hot Warm Cold Stopped time 2 Hr Within 6~12 Hr 56 Hr Within 96 Hr Above SH Outlet Temp 465℃ above 300℃ above 100℃ below Separator Tank pr 120～ 200㎏ /㎠ 30～ 120㎏ /㎠ 30㎏ /㎠ below 0㎏ /㎠ Starting Time STARTING TIME Startup Mode Light off →TBN Rolling(minutes) Light off → Full Load(minutes) Cold 120 420 Except Rotor and Chest Warming Time Warm 90 180 " Hot - - ․ Restart 30 90 ․ COMMISSIONING DEPARTMENT, NTPC-SIPAT

PURGE CONDITIONS Ø No Boiler Trip Condition Exists Ø All System Power Supply Available Ø Unit Air Flow > 30 % BMCR Ø Nozzle Tilt Horizontal and Air Flow < 40 % Ø Both PA Fans Off Ø The Following Condition Exist At Oil Firing System ü The HOTV / LOTV Should Be Closed ü All Oil Nozzle Valve Closed Ø The Following Condition Exists at Coal Firing System ü All Pulverisers are Off ü All Feeders are Off ü All Hot Air Gates Of Pulverisers are closed Ø All Flame Scanner on all elevation shows no Flame Ø Aux Air Damper At All Elevation should be modulating After Purging Boiler Light Up activites are same as in 500 MW plant COMMISSIONING DEPARTMENT, NTPC-SIPAT

MFT CONDITIONS Ø Both ID Fans Off Ø Both FD Fans Off Ø Unit Air Flow < 30 % TMCR Ø All Feed Water Pumps Are Off For More Than 40 Sec Ø 2 / 3 Pressure Transmitter indicate the furnace pressure High / Low for more than 8 sec ( 150 mmwc / -180 mmwc)) Ø 2 / 3 Pressure Transmitter indicate the furnace pressure High – High / Low - Low ( 250 mmwc / - 250 mmwc) Ø Loss Of Re-heater Protection Ø EPB Pressed Ø All SAPH Off Ø Economizer Inlet Flow Low For More Than 10 Sec (223 T/Hr) Ø Furnace Vertical Wall Temperature High For more than 3 Sec (479 C) Ø SH Pressure High On Both Side (314 KSc) Ø SH Temperature High For More Than 20 Sec ( 590 C) Ø RH O/L Temperature High For More Than 20 Sec ( 590 C) Ø Separator Level Low-Low During Wet Mode ( 1. 1 M) Ø Separator Level High-High During Wet Mode ( 17. 7 M) COMMISSIONING DEPARTMENT, NTPC-SIPAT

Ø MFT Relay Tripped Ø Loss Of Fuel Trip : It Arms when any oil burner proven. it occurs when all of the following satisfied Ø All Feeders Are Off Ø HOTV Not Open or all HONV Closed Ø LOTV Not Open or all LONV Closed Ø Unit Flame Failure Trip : It Arms when any Feeder Proves it occurs when all 11 scanner elevation indicates flame failure as listed below ( Example is for only elevation A) Ø Feeder A & Feeder B is Off with in 2 Sec Time Delay Ø following condition satisfied Ø Any oil valve not closed on AB Elevation Ø 3 /4 valves not proven on AB Elevation Ø Less Than 2 / 4 Scanner Shows Flame Ø Both Of The Following Condition Satisfied Ø Less Than 2 / 4 Scanner Flame Shows Flame Ø 2 / 4 Oil Valves not open at AB Elevation COMMISSIONING DEPARTMENT, NTPC-SIPAT

Boiler Light Up Steps ü Start the Secondary Air Preheater ü Start one ID fan, then the corresponding FD fan and adjust air flow to a min. of 30% TMCR ü Start the scanner air fan. ü Adjust fan and SADC to permit a purge air flow of atleast 30% of TMCR and furnace draft of approx. -12. 7 mm. WC. ü When fans are started, SADC should modulate the aux. air dampers to maintain WB to furnace DP at 102 mm. WC(g). ü Check that all other purge permissives are satisfied. ü Place FTPs in service. ü Check The MFT Conditions ü For First Time Boiler Light Up do the Oil Leak Test ü Initiate a furnace purge. COMMISSIONING DEPARTMENT, NTPC-SIPAT

SYSTEM / EQUIPMENT REQUIRED FOR BOILER LIGHT UP FURNACE READINESS ü PRESSURE PARTS ü SCANNER AIR FAN ü BOTTOM ASH HOPPER READINESS ü FUEL FIRING SYSTEM ü START UP SYSTEM SEC AIR PATH READINESS ü FD FAN ü SAPH ü WIND BOX / SADC FLUE GAS SYSTEM ü ESP PASS A , B ü ID FAN COMMISSIONING DEPARTMENT, NTPC-SIPAT

SYSTEM / EQUIPMENT REQUIRED FOR BOILER LIGHT UP CONDENSATE SYSTEM ü CONDENSER ü CEP ü CPU FEED WATER SYSTEM ü D/A ü MDBFP # A VACCUME SYSTEM SEAL STEAM SYSTEM TURBINE ON BARRING COMMISSIONING DEPARTMENT, NTPC-SIPAT

Evaporator – heat absorption

Reduced number of evaporator wall tubes. Ensures minimum water wall flow.

SPIRAL WALL ARRAMGEMENT AT BURNER BLOCK AREA :

Support System for Evaporator Wall • Spiral wall Horizontal and vertical buck stay with tension strip • Vertical wall Horizontal buck stay