Devdeep Bose DGM ( Commng & Testing) INTRODUCTION TO SUPER - - PowerPoint PPT Presentation

Devdeep Bose DGM ( Commng & Testing)

• INTRODUCTION TO SUPER CRITICAL

UNI -

POINTS OF DISCUSSION

• SUB CRITICAL & SUPER CRITICAL BOILER
• SIPAT BOILER DESIGN
• SIPAT TURBINE DESIGN
• DESIGN PARAMETERS
• COMMISSIONING
• PRE COMMISSIONING PROBLEMS
• POST COMMISSIONING PROBLEM

Description unit 660 500

S/H STEAM FLOW T/HR 2225 1625 SH STEAM PR KG/CM2 256 179 SH STEAM TEMP

0C

540 540 RH STEAM FLOW T/HR 1742 1397.4 RH STEAM TEMP INLET

0C

303.7 338.5 RH STEAM TEMP OUTLET

0C

568 540 RH STEAM PRESS INLET KG/CM2 51.17 46.1 FEED WATER TEMP

0C

291.4 255.2

COMPARISION OF 660 MW Vs 500 MW BOILER

Description 660 MW 500 MW Structural Steel Erection 7383

9200

Boiler Proper & Accessories (Pre. Parts) 7080

5300

Refractory, Insulation & Cladding 1410

2000

Power Cycle Piping 3032

2200

Soot Blowing System 54

76

Coal Firing System 3573

2000

Draft System 5275

5200

Fuel oil system 62

200

Miscellaneous System 130

280

Electrical & Instrumentation 282

380

TOTAL

28281 26836

Tonnage Comparison

Material Comparison

Description 660 MW 500 MW Structural Steel Alloy Steel

Carbon Steel

Water wall T22

Carbon Steel

SH Coil T23, T91

T11, T22

RH Coil T91,Super 304 H

T22, T91,T11

LTSH T12

T11

Economizer SA106-C

Carbon Steel

Welding Joints (Pressure Parts) 42,000 Nos

24,000 Nos

Structural Comparison

Slno 660 MW 500 MW Remarks 1 STRUCTURALS a

Entire structural is bolting type- entire structure is bolted. Holes are drilled on the columns and gusset plates, and supplied with matching plates. Structural is assembled at site with welding Advantages (660MW) of Bolting structure:

• Fast in erection.
• Clean environment
• No Welding network required
• Safety at site
• Painting finish is good
• ( No Weld surface)

b.

No Welding work involved in assembly/ Erection , except Walkway rail post welding Assembly is carried

• ut with Welding

Can be dismantled if required ( For Maintenance purpose)

c

Material supply is tier wise including staircases, railing, gratings etc. Material is supplied as per the erection sequence. Erection completion tier wise, including gratings, platforms , staircases etc.

1 Cost of SG Package 1970.73 Cr 1020.54 Cr with ESP 2 Cost of ESP 183.54Cr 3 Total cost of Boiler + ESP 2154.27 Cr 1020.54 Cr 4

Cost of Boiler per MW with ESP

1.09 Cr 1.02 Cr

5 Cost of TG for entire stage 1204.72 Cr 634.31 Cr 6 TG cost per MW

0.6Cr 0.63 Cr

COST COMPARISON

BOILER SPECIFICATION

Description unit

S/H STEAM FLOW T/HR 2225 SH STEAM PR KG/CM2 256 SH STEAM TEMP

0C

540 RH STEAM FLOW T/HR 1742 RH STEAM TEMP INLET

0C

303.7 RH STEAM TEMP OUTLET

0C

568 RH STEAM PRESS INLET KG/CM2 51.17 FEED WATER TEMP

0C

291.4

Quoted Turbine Heat Rate 100% Load 1904 Kcal / KWH 80% Load 1924 Kcal / KWH 60% Load 1973 Kcal / KWH 50% Load 2065 Kcal / KWH Net Plant Heat Rate = NTRH = 2207 KCal / KWHR ( at 100% TMCR) 80% TMCR = 2222 Kcal / KWHR 60% TMCR = 2276 Kcal / KWHR 50% TMCR = 2376 Kcal / KWHR Plant Efficiency at 100% TMCR = 38.96% 80% TMCR = 38.7 % 60% TMCR= 37.78% 50% TMCR = 36.19% = Boiler Efficiency 100% TMCR 86.27% 80% TMCR 86.60% 60% TMCR 86.68% 50% TMCR 86.91%



Supplier : M/s DOOSAN  Erection By : M/s L&T

 When Water is heated at constant pressure above the critical pressure, its temperature will never be constant  No distinction between the Liquid and Gas, the mass density of the two phases remain same  No Stage where the water exist as two phases and require separation : No Drum  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  For changing boiler loads and pressure, the process is able to optimize the amount of liquid and gas regions for effective heat transfer. UNDERSTANDING SUPER CRITICAL TECHNOLOGY

SUPER CRITICAL BOILER CYCLE WITH SH, RH & Regeneration

Steam flow :2225 T/Hr Steam temp : 540 ‘c Steam Pres : 256 kg/cm2 RH pre : 51.6 Kg/cm2 RH Temp : 568’c Feed water Temp : 291’c

100 200 300 400 500 600

540’C 568’C ENTROPY TEMP 1 2 3 4 5

HPT IPT LPT

C O N D E N S E R

FEED WATER FRS

S T O R A G E T A N K

SEPARATOR

BWRP MS LINE HRH LINE VERTICAL WW

ECO I/L ECO JUNCTION HDR ECO HGR O/L HDR FUR LOWER HDR

FUR ROOF I/L HDR DIV PANELS SH PLATEN SH FINAL RH FINAL SH LTRH ECONOMISER

290°C, 302 KSC 411°C, 277Ksc 411°C, 275 Ksc 492°C, 260 Ksc 540°C, 255 Ksc 305°C, 49 Ksc 457°C, 49 Ksc 568°C, 47 Ksc

G

LPT

Boiling process in Tubular Geometries

Heat Input Heat Input Water Water Water Steam Steam Partial Steam Generation Complete or Once-through Generation

SIPAT SUPER CRITICAL BOILER

• BOILER DESIGN PARAMETER
• DRUM LESS BOILER : START-UP SYSTEM
• TYPE OF TUBE
• Vertical
• Spiral
• SPIRAL WATER WALL TUBING

 Advantage  Disadvantage over Vertical water wall

Vertical Tube Furnace

• To provide sufficient flow per tube, constant pressure furnaces

employ vertically oriented tubes.

• Tubes are appropriately sized and arranged in multiple passes in

the lower furnace where the burners are located and the heat input is high.

• 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.

• In addition, the fluid is mixed between passes to reduce the upset

fluid temperature.

Spiral Tube Furnace

• 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.

• 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.

• Because the tubes are “wrapped” around the furnace to form the

enclosure, fabrication and erection are considerably more complicated and costly.

SPIRAL WATER WALL

ADVANTAGE  Benefits from averaging of heat absorption variation : Less tube leakages  Simplified inlet header arrangement  Use of smooth bore tubing  No individual tube orifice  Reduced Number of evaporator wall tubes & Ensures minimum water flow  Minimizes Peak Tube Metal Temperature  Minimizes Tube to Tube Metal Temperature difference DISADVANTAGE  Complex wind-box opening  Complex water wall support system  tube leakage identification : a tough task  More the water wall pressure drop : increases Boiler Feed Pump Power  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 3020 T / Hr 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 87 %

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.

Parameter Unit Design Coal Worst Coal Best Coal Young Hung #1,2(800MW) Tangjin #5,6(500MW) High Heating Value kcal/kg 3,300 3,000 3,750 6,020 6,080 Total Moisture % 12.0 15.0 11.0 10.0 10.0 Volatile Matter % 21.0 20.0 24.0 23.20 26.53 Fixed Carbon % 24.0 20.0 29.0 52.89 49.26 Proximate Analysis Ash % 43.0 45.0 36.0 13.92 14.21 Fuel Ratio (FC/VM)

• 1.14

1.00 1.21 2.28 1.86 Combustibility Index

• 2,067

2,353 2,476 2,781 3,492 Carbon % 39.53 31.35 40.24 63.03 62.15 Hydrogen % 2.43 2.30 2.68 3.60 3.87 Nitrogen % 0.69 0.60 0.83 1.53 1.29 Oxygen % 6.64 5.35 8.65 7.20 7.80 Sulfur % 0.45 0.40 0.60 0.72 0.68 Ash % 43.00 45.00 36.00 13.92 14.21 Ultimate Analysis Moisture % 12.00 15.00 11.00 10.00 10.00 Grindability HGI 50 47 52 45 48 ASTM Coal Classification

• Hi–Vol. ‘C’

Bituminous Hi–Vol. ‘C’ Bituminous Hi–Vol. ‘C’ Bituminous Midium Vol. Bituminous Hi–Vol. ‘C’ Bituminous

Coal 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 Na2O and CaO content.

Parameter Unit Design Coal Worst Coal Best Coal Young Hung #1,2(800MW) Tangjin #5,6(500MW) SiO2 % 61.85 62.40 61.20 57.40 57.40 Al2O3 % 27.36 27.31 27.32 29.20 29.20 Fe2O3 % 5.18 4.96 5.40 4.40 4.40 CaO % 1.47 1.42 1.52 2.70 2.70 MgO % 1.00 1.03 0.97 0.90 0.90 Na2O % 0.08 0.08 0.08 0.30 0.30 K2O % 0.63 0.32 1.22 0.70 0.70 TiO2 % 1.84 1.88 1.80 1.30 1.30 P2O5 % 0.54 0.55 0.44

• SO3

% 0.05 0.05 0.05

• Ash

Analysis Others %

• 3.10

3.10 Initial Deformation

• C

1150 1100 1250 1200 1200 Softening

• C
• Hemispheric
• C

1400 1280 1400 Ash Fusion

• Temp. (oC)

(Reducing Atmos.) Flow

• C

1400 1280 1400 Ash Content kg/Gcal 130.3 150.0 96.0 23.12 23.37 Basic / Acid B/A 0.09 0.09 0.10 1.63 1.63

Ash Analysis

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

+1

• 1
• 2
• 3
• 4

20 40 60 80 100 Efficiency Change % Boiler Load % Variable Pressure CONSTANT PRESSURE Vs VARIABLE PRESSURE BOILER CHARACTERSTIC

Benefits Of Sliding Pressure Operation ( S.P.O)

 Able to maintain constant first stage turbine temperature  Reducing the thermal stresses on the component : Low Maintenance & Higher Availability  No additional pressure loss between boiler and turbine.  low Boiler Pr. at low loads.

WHY NOT S.P.O. IN NATURAL/CONTROL CIRCULATION BOILERS

 Circulation Problem : instabilities in circulation system due to steam formation in down comers.  Drum Level Control : water surface in drum disturbed.  Drum : (most critical thick walled component) under highest thermal stresses

 LMZ (LENINGRADSKY METALLICHESKY ZAVOD)  K STANDS FOR KLAPAN LTD.,BULGARIA WHICH SUPPLIES TURBINE,NOZZLES,DIAPHRAGMS, SEALS,BLADES ETC.

1.TG DECK IS VIS SUPPORTED AND HAS 26 CONCRETE COLUMNS (T1 – T26). 2.TG HALL IS CONSTITUTED OF 3 MAINS ROWS OF COLUMNS – A,B ,C ROW AND TWO BAYS – AB BAY AND BC BAY. THE WIDTH OF AB BAY IS 36m AND BC BAY IS 12m 3.CONDENSER TUBE BANKS (CW PATH) HAS AN INCLINATION OF 40. 4.THERE ARE TWO MAIN EOT CRANES FOR TG HALL.EACH EOT CRANE IS HAVING A CAPACITY OF 200t FOR MAIN HOIST AND 20t FOR AUXILIARY HOIST. 35.5m IS THE MAXIMUM VERTCAL DISTANCE A HOIST CAN TRAVEL.TANDEM OPERATION OF TWO EOT CRANES ARE ALLOWED.

IP Turbine

LP Turbine

Ext. No Source Of Extraction Destination Equipments

1 13th stage of HPT HPH-8 2 CRH HPH-7 3 3rd stage of IPT HPH-6 * 3 3rd stage of IPT TDBFP 4 6th stage of IPT DEAERATOR 5 8th stage of IPT LPH-4 6 11th stage of IPT LPH-3 7 2nd stage of LPT LPH-2 8 4th stage of LPT LPH-1

Condenser

• Design

LMZ

• Design CW Flow

64000 m3/hr

• Vacuum

77 mm Hg (abs) at 33 0C 89 mm Hg (abs) at 36 0C

• No. of passes

1

• Total no. of tubes

22.225 (OD)x0.71 (t) - 29920 22.225 (OD)x1.00 (t) - 2080

• Tube material

ASTM A-249 TP 304

• Rated TTD

3.40C

• DT of CW

100C

Condensate Extraction Pump

• Design flow rate

238.75 Kg/s

• Discharge pressure

32.15 Ksc

• Shut off head

395 m

• Pump speed

1480 rpm

• Power input

972.3 KW

• No. of stages

6

• Type of first stage impeller

double entry

• Depth

7.43 m

MDBFP

• Pump flow

769.950 TPH

• Suction temp

186.2

0C

• BP Suction pr.

14.05 ata

• BFP Suction pr. 21.01

ata

• BFP Discharge pr.

335.78 ata

• BFP Discharge temp.

187.9

0C

• BP Discharge pr.

22.01 ata

• Shut off head

4830 m

• BFP Speed

6275 rpm

• BP Speed

1490 rpm

• Normal R/C flow220

TPH

• HC Rated O/P Speed

6505 rpm

• Outer casing type

barrel

• No. of stages

7

• BFP warm up flow

15 TPH

TDBFP

• Pump flow

1283.14 TPH

• Suction temp

186.2 0C

• BP Suction pr.

14.10 ata

• BFP Suction pr.

28.24 ata

• BFP Discharge pr.

335.83 ata

• BFP Discharge temp.

187.8 0C

• BP Discharge pr.

29.06 ata

• Shut off head

4580 m

• BFP Speed

4678 rpm

• BP Speed

2098 rpm

• Normal R/C flow

365 TPH

• HC Rated O/P Speed

6505 rpm

• Outer casing type

barrel

• No. of stages

7

• BFP warm up flow

20 TPH

Drip Pump

• Design flow rate

324.509 TPH

• Discharge pressure

43 ata

• Shut off head

306.7 m

• Pump speed

1486 rpm

• Power input

310.1 KW

• No. of stages

5

• Type of first stage impeller

centrifugal, single entry

• Depth

1090 mm

RATED CONDITIONS

• LOAD

: 660MW

• BEFORE HP STOP VALVE
• STEAM PRESSURE

: 247KSC

• STEAM TEMPERATURE

: 5370C

• STEAM FLOW

: 2023.75T/HR

• AFTER HPC
• STEAM PRESSURE

: 48KSC

• STEAM PRESSURE

: 298.710C

• BEFORE IP STOP VALVE
• STEAM PRESSURE

: 43.2KSC

• STEAM TEMPERATURE

: 5650C

• STEAM FLOW TO REHEATER

: 1681.12T/HR.

• DESIGN CONDENSER PRESSURE

: 0.105KSC (abs.)

• COOLING WATER FLOW

: 64000M3/HR

• FINAL FEED WATER TEMP.

: 286.350C

• FREQUENCY RANGE

: 47.5 – 51.5 Hz

STEAM TURBINE

• Generator rated speed

3000 rpm

• Generator manufacturer

Electrosila

• No. of bleedings

8

• Length of the turbine

36.362 m

• No. of stages

 HPT 17  IPT 11x2  LPT-1 5x2  LPT-2 5x2  Total 59

• Turbine Governing system

 Mode of Governing Nozzle  Type E/H  Control fluid Firequel-L make Supresta-USA  Normal Operating Pr. 50 Ksc  Capacity 600 lpm  Fluid pump motor rating 200 KW  Filter material Ultipor  Mesh size 25 µ

Turbine Protections

Turbine protection system consists of Two Independent channels, each operating the corresponding solenoid (220V DC) to trip the Turbine in case of actuation of remote protection Hydraulic Protection: Apart from the Electrical Trip, Turbine is equipped with the following Hydraulic Protections:

• 1. Local Manual Trip (1V2)
• 2. Over speed Trip #1 at 110% of rated speed
• 3. Over speed Trip #2 at 111% of rated speed
• 4. Governing oil pressure < 20 Ksc

Contd..

5.Axial shift Very High (2V3) [-1.7mm, +1.2mm] 6.Turbine bearing vibration : Very High (2V10 including X & Y directions)* >11.2mm/sec (Td=2 sec) 7.Lube oil tank level very Low (2V3)* Td=3sec (Arming with two stop valves open) 8.Lub oil pressure Very Low (2V3) < 0.3 Ksc; Td =3 sec (Arming with two stop valves open) 9.Condenser pressure Very High (2V3) > - 0.7ksc (Arming with condenser press < 0.15 ksc Abs) Contd

10.M.S. temp Very Low (2V3) < 470 deg C (arming > 512 deg C)* 11.M.S. temp Very High (2V3) > 565 deg C* 12.HRH temp Very Low (2V3) < 500deg C (arming > 535 deg C)* 13.HRH temp Very High (2V3) > 593deg C* 14.HPT outlet temperature Very High (2V4) > 420 deg C Contd…

15.Gen seal oil level of any seal oil tank Very Low (2V3)* < 0 mm;Td=15 sec (Arming with any two stop valves open) 16.All Generator seal oil pumps OFF (3V3)* Td: 9 sec (Arming with any two stop valves open) 17.Generator Stator winding flow Very Low (2v3) < 17.3 m3/hr; Td =120 sec (Arming with any two stop valves open) 18.Generator hot gas coolers flow Very LOW (2V3)* : <180m3/hr; Td=300sec(Arming with any two stop valves open) 19.Generator cooler hot gas temp. Very High(2V4) > 85 deg (Td = 300sec Contd

20.MFT operated: (2V3) 21.Deareator level Very High (2V3) > 3400 mm* 22.HP heater level protection operated (2V3)* 23.Generator Electrical protection operated (2V3) 25.Turbine over speed protection operated (114%) 26.Turbine Controller failure protection operated (2V3)

OF SIPAT SUPER CRITICAL UNIT

1ST UNIT SYNCHRONIZED AT : 18.02.2011 1ST UNIT FULL LOAD ACHIEVED AT : 2nd UNIT SYNCHRONIZED AT : 03.12.2012 2ND UNIT FULL LOAD ACHIEVED AT : 24.12.2012

PRE – COMMISSIONING ACTIVITIES 

CHEMICAL CLEANING OF BOILER :

REQUIRED FOR Maintaining steam quality at the turbine inlet. Minimizing corrosion of the metal surface of boiler.

 DETERGENT FLUSHING OF PRE-BOILER SYSTEM

To remove dirt ,oil ,grease etc., from Condensate ,Feed water, Drip and Extraction steam lines of HP and LP heaters prior to putting these systems in regular service. This is to ensure flow of clean condensate and feed water to the boiler.

 STEAM BLOWING OF POWER CYCLE PIPING :

The purpose of steam line blowing is to remove pipe slag, weld bead deposits and other foreign material from the main and reheat steam systems prior to turbine operation. The cleaning is accomplished by subjecting the piping systems to heating, blowing steam and cooling cycles in sufficient number and duration until clean steam is

• btained.

 SAFETY VALVE FLOATING

PRE – COMMISSIONING CHECKS  All commissioning procedure should be finalized.  P&I Drawings should be finalized and available with site engineer  Different systems check list should be finalized with all concerned agencies  All Field quality checks should be completed.  P&I Checks should be finalized.  Start – Up procedure should be finalized

COMMISSIONING SEQUENCE OF TG SIDE 1.Commissioning of stator water cooling system for HV testing before generator rotor insertion. a) Stator water pump trial run. b) Flushing of the system bypassing winding. c) Flushing of the system through the winding. 2.Commissioning of MCW,ACW and DMCW system. a) Trial run of pumps. b) Flushing of the system. 3.Detergent Flushing of pre boiler system (Feed water ,condensate ,HPH and LPH drip system) a) Cold water flushing until turbidity comes below 5NTU. b) Hot water flushing (600C) with 2 hrs circulation of each circuit. c) Raising water temperature to 600C and addition of Detergent d) (Coronil 100%)

e) Circulation through each circuit for 2 hrs. f) Hot draining of the system g) DM water rinsing of each circuit until conductivity comes below 5µs/cm and oil content BDL. h) Passivation with ammonia and hydrogen peroxide solution at a temperature of 400C. i) Draining of the system.

• 4. Lube oil flushing of MDBFP lube oil system.

5.Trial run of MDBFP. 6.Lube oil and seal oil flushing of main TG. 7.CF system flushing. 8.Condenser flood test. 9.Trial run of CEPs 10.Commissioning of generator gas system. 11.Generator ATT. 12.Calibration of HPCVs and IPCVs 13.Putting turbine on barring. 14.Vacuum pumps trial run.

15.Commissioning of seal steam system. 16.Commissioning of HP and LPBP system.

• 17. Vacuum pulling.

18.Lube oil flushing of TDBFP. 19.Steam blowing of TDBFP steam line. 20.Commissioning of TDBFP.

FUR DRAFT SYSTEM SEC AIR SYSTEM TG ON BARRING BRP TRIAL RUN TG LUBE OIL / GEN SEAL OIL SYSTEM FURNACE READINESS FUEL OIL SYSTEM READINESS DDCMIS FSSS READINESS MFT CHECKING GATES, DAMPERS / VALVES TG : SG : (13 / 190 ) STATOR COOLING WATER CW SYSTEM READINESS CHEMICAL CLEANING OF BOILER MS Line Welding Completion ( 30 Pen) CRH Line Welding Completion ( 12 Pen) HRH Line Welding Completion (34 Pen) MS Line Hanger Erection Cold Setting CRH Line hangers Cold Setting HRH Line Hangers Cold Setting MS Line Insulation CRH Line Insulation HRH Line Insulation MS Line HT CRH Line HT HRH Line HT COMPRESSED AIR SYSTEM READINESS AUX PRDS READINESS CONDENSER VACCUM SYSTEM

POWER CYCLE PIPING STEAM BLOWING

UNIT SYNCHRONIZTION

MDBFP Trial CEP Trial TG SEAL STEAM SYSTEM TG CONTROL FLUID SYS TG GOV SYSTEM GEN GAS SYSTEM

Questions Please Enlighten Us Discussion

Evapor aporator ator – heat at absorp rpti tion

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

SPIRAL WALL ARRAMGEMENT AT BURNER BLOCK AREA :

Suppor port t System em for Evapor aporat ator

• r Wall

all

• Spiral wall

 Horizontal and vertical buck stay with tension strip

• Vertical wall

 Horizontal buck stay