4. yazd-system description for lp section

MINISTRY OF ENERGY IRAN POWER DEVELOPMENT CO.

I P D C

PROJECT : 22 COMBINED CYCLE POWER PLANTS YAZD COMBINED CYCLE POWER PLANT

System Description

For HRSG LP Section

C Revised according to P22-1621 04.08.13 D.S KIM 04.08.13 B.J PARK 04.08.13 S.G JUNG 04.08.13

B Revised according to P22-828 04.07.07 D.S KIM 04.07.07 B.J PARK 04.07.07 S.G JUNG 04.07.07

A Revised according to P22-557 ‘04.03.10 D.S KIM ‘04.03.10 B.J PARK ‘04.03.10 S.G JUNG ‘04.03.10

0 FIRST ISSUE 03.12.02 D.S KIM 03.12.02 B.J PARK 03.12.02 S.G JUNG 03.12.02

REV DESIGNATION DATE DESIGN DATE CHKD DATE APPROVED DATE

DOCUMENT NO. : MP-YZC-BA-04-HG0-002-C REV. C MAPNA C o . ( PRIVATE JOINT STOCK )

IRAN POWER PLANT PROJECTS MANAGEMENT Co. CONTRACT NO. : 22-0701/BA/TL PAGE 1 OF 13

ORIGINATOR NO. : YZC-A-SP-201-SDE-002-3 A4 ORIGINATOR

DOOSAN HEAVY INDUSTRIES & CONSTRUCTION CO.,LTD. ORIG

LOC. ORIG. DEPT.

PROJ. NAME

DISC.

DOC. TYPE

AREA TYPE

SYS. FA.N

SEQ. N.

SH. N. REV. C

FOR APPROVAL

MINISTRY OF ENERGY IRAN POWER DEVELOPMENT CO.

I P D C

PROJECT : 22 COMBINED CYCLE POWER PLANTS YAZD COMBINED CYCLE POWER PLANT

REVISION REVISION

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DOCUMENT NO. : MP-YZC-BA-04-HG0-002-C REV. C MAPNA C o . ( PRIVATE JOINT STOCK )

IRAN POWER PLANT PROJECTS MANAGEMENT Co. CONTRACT NO. : 22-0701/BA/TL PAGE 2 OF 13

ORIGINATOR NO. : YZC-A-SP-201-SDE-002-3 A4 ORIGINATOR

DOOSAN HEAVY INDUSTRIES & CONSTRUCTION CO.,LTD. ORIG

LOC. ORIG. DEPT.

PROJ. NAME

DISC.

DOC. TYPE

AREA TYPE

SYS. FA.N

SEQ. N.

SH. N. REV. C

22 Units Combined Cycle

SYSTEM DESCRIPTION FOR HRSG LP SECTION

DOOSAN Changwon, KOREA

Contract No. : 22-0701/BA/TL

Originator No. : YZC-A-SP-201-SDE-002-3 Appendix :

Revision : C Date : Aug 13.’04

Page: 3 of 13

CONTENTS CLAUSE NO. DESCRIPTION PAGE NO.

1.0 GENERAL DESIGN CONCEPT 4 2.0 OPERATING CONCEPT 6 2.1 Preparations 6 2.2 Start-up and Shutdown 6 2.3 Operation, Closed and Open Loop Controls 8 2.4 Abnormal Operational Occurrences 9 3.0 DRUM LEVEL CONTROL CONCEPT 10 4.0 DRAIN CONTROL CONCEPT 11 5.0 REFERENCE FILE 13







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1.0 GENERAL DESIGN CONCEPT

The low pressure steam system products LP steam of specific quality, which means of correct pressure and temperature, from the thermal energy contained in the GT exhaust gas including supplementary firing at duct firing case.. The steam is produced in the heat recovery steam generator (HRSG) with connections between the feedwater system and main steam system. Besides it fulfils the following objective;

l Delivers feedwater to the low pressure drum during start-up, shutdown and power operation of the combined-cycle unit

l Supplies LP steam produced by the HRSG to the LP main steam system during normal operation.

l Shuts off feedwater supply during feedwater control malfunction in order to prevent overfeeding of the HRSG.

The low pressure system is located downstream of the exhaust gas inlet of the heat recovery steam generator behind the HP part. The heating surfaces are fabricated from mainly finned tubes. The low pressure system is subdivided into the following sections, listed in the order in which exhaust gas flows through them: l LP superheater l LP evaporator

The LP evaporator generates steam through a natural circulation loop from LP boiler drum and to LP boiler drum. The LP superheater heats the saturated steam from drum temperature up to the required conditions. The LP superheater is cross counter flow heat exchangers and the LP evaporator flow is cross to the exhaust gas flow. The HRSG is of horizontal design. The feedwater is fed by LP feedwater pumps from F.W. storage tank(HAD80BB001) to the LP drum(HAD50BB001). Water is fed from the LP drum(HAD50BB001) through downcomers to the inlet header of the LP evaporator. Water partly evaporates in the LP evaporator and the water/steam mixture is fed via natural convection in tube risers from the outlet header back to the LP drum(HAD50BB001). The connecting piping between the outlet header and drum are distributed uniformly over the length of the drum.







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The boiler drum has the following functions: - ensure good mixing of feedwater and boiler water - constitute a water reserve required for the circulation system - allow water expansion during start-up - ensure a thorough water and steam separation. The drum capacity is selected to ensure safe and stable operation under all normal operating conditions. The drum is installed outside of casing thus not heated by exhaust gas. The steam water separation is achieved by means of a water/steam separation system, which restricts carryover to the superheater within the limits as specified in the ABMA guidelines. Saturated steam flows from the LP drum(HAD50BB001) through connected piping to the LP superheater. Two safety valves(HAD50AA191,192) are installed on the LP drum(HAD50BB001) to protect the system against over pressure. Sampling connections are provided in the system for sampling of superheated & saturated steam during operation. Continuous blowdown, blowdown lines are routed from the LP drum(HAD50BB001) and LP evaporator manifolds to the blowdown tank(LCQ60BB001). The intermittent blowdown line from the LP drum(HAD50BB001) to the boiler blowdown system HAN is equipped with motorized valve. Connections for chemical dosing are installed in the LP drum. pH control The purpose of pH limits of feedwater and boiler water is to prevent the corrosion of the pre-boiler, and the boiler and its appurtenances, and to reduce as far as possible the picked-up matters delivered into the boiler after dissolving in the pre-boiler, and also the prevent the contamination of the boiler and the troubles caused to the heat transfer surfaces due to scaling. The pH limits are considered to the most suitable for various units. The most suitable pH value depends upon the particular characteristics of the plant, and the chemist in charge, should select the most suitable pH after checking the Fe and Cu dissolved in the feedwater at the highest, lowest and middle points, (9.2-9.7 and 9.5) during plant operation.







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1.1 Applicable Code 1.1.1 US STANDARDS

AISI, ANSI, API, ASME, ASNT, ASTM, AWS, EIA, HEI, HIS, IES, IEEE, ISA, MSS, NEMA, NFPA, OSHA, PFI, SAMA, SSPC, TEMA

1.1.2 Other International Standards

DIN, NG, IFC, ISO, JIS, UL, WHO







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2.0 OPERATION CONCEPT 2.1 Preparations The filling of the system coincides with the start-up procedures described below. 2.2 Start-up and Shutdown Start-up from a cold piping state The motorized drains(LBB20AA051,LBB20AA053) and vents (LBB20AA052) of the LP system are opened. The feedwater control valve is opened and the LP drum(HAD50BB001) is filled to start-up level with the fill rate. The start-up valve level is switched over to start-up level and some water maybe discharged to the blowdown tank(LCQ60BB001). If the condenser is ready for service, the steam generator is started. The start-up level is maintained in LP drum(HAD50BB001) by means of the start-up valve(HAD60AA051). During water ejection out of the evaporator the start-up valve(HAD60AA051). of the LP drum(HAD50BB001) is switched over to overflow water level, if a pressure or level increase in the drum is detected. If the water level in the drum rises above overflow water level and the operating pressure in the drum is below a preset value, the start-up valve(HAD60AA051) opens and the excess volume of water is discharged to the atmospheric blowdown tank(LCQ60BB001). After the water has been discharged and steam production has reached at least the feedwater minimum flow, the LP feedwater control station is switched over to 3-component control. When the pressure in the LP system has risen to about 3 barg, the motorized venting valves(LBB20AA052) are closed. The drains are closed as soon as the steam is slightly superheated.







Page: 8 of 13

Warm start The same logical sequences as for the cold start apply for preparation for a warm start. As a matter of principle, however, motorized venting valves(LBB20AA052) remain closed if a pressure ＞3 barg prevails in the system. The drain valves(LBB20AA051,LBB20AA053) may be opened only after it has been assured that the HRSG is heated and a positive pressure rise has been detected. The motorized drains(LBB20AA051,LBB20AA053) are closed according the same criteria as with cold start. The gas turbine is then run up corresponding to the steam conditions required by the steam turbine in accordance with the allowable gradients for the heat recovery steam generator and the steam turbine. Shutdown and Part-Load Behavior The main steam temperature starts to rise slightly in the first phase of the GT load reduction. The main steam temperature drops proportionally to the GT exhaust gas temperature only when the GT power is reduced further. The LP system is shut down simultaneously to the GT run down or the closing of the diverter damper. For the shutdown of the steam turbine, the turbine inlet valves are closed.







Page: 9 of 13

2.3 Operation, Closed and Open Loop Controls The HRSG will be subject to the prevailing gas turbine exhaust gas conditions. The HRSG will be on-load generating steam in accordance with the heat available in the gas turbine exhaust gas. The quantity of feedwater to low pressure system will be controlled by the feed water control system utilizing the three element control loop.







Page: 10 of 13

2.4 Abnormal Operational Occurrences The LP system is protected against exceeding design pressure by spring loaded safety valves(HAD50AA191,192) positioned on the drum and spring loaded(LBB20AA191) & power actuated (LBB20AA192) safety valve positioned on Superheater outlet pipe, in accordance with the code requirements. The low pressure circulating system is protected against loss of water by monitoring the drum water level. If the drum water level rises to High-High level, the HRSG and feedwater pump will be tripped. The design of the system is based on the applicable codes and standards. The design pressure is based on the thermodynamic condition of the steam turbine the safety valve has a fixed setpoint. Design temperature of the system is based on the maximum possible heat transfer in the LP superheater of the HRSG.







Page: 11 of 13

3.0 DRUM LEVEL CONTROL CONCEPT The task of the LP-feedwater level controls is: l To switch-over to the required LP drum(HAD50BB001) level setpoint, depending

on the HRSG operation status (e.q. start-up, normal operation) l To coordinate the automatic switch-over between level control (during start-up) and

3-element control (during normal operation) l To maintain the correct LP-feedwater flow to the LP drum(HAD50BB001) at all time

as per selected setpoint The task of the blowdown level control is: l To switch-over to the required LP drum(HAD50BB001) level setpoint, depending

on the HRSG operation status (e.q. start-up, normal operation) l To maintain the required start level (slightly higher then setpoint) during start-up in

cooperation with the feedwater level control valves (slightly lower then setpoint) l To avoid water carry-over into the LP superheater by draining water from the LP

drum(HAD50BB001) to the blow down tank, in case the LP drum(HAD50BB001) level would rise above overflow level.







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4.0 DRAIN CONTROL CONCEPT An open sub-loop control operates the motor-actuated drain valves. Based on the measured steam pressure, the reference saturation-steam temperature is calculated and compared with the actual steam temperature. When the actual steam temperature exceeds the saturation temperature for more than 30℃ in the LP line, the drain valves close(LBB20AA051,053). If the steam is superheated less than 30℃, the drain valves open(LBB20AA051,053). It will be sure that these temperature difference between superheated steam and saturated steam will be indicated 100% of superheated steam.







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5.0 Reference File

1. MP-YZC-GA-02-HL0-002 : P&ID DIAGRAM FOR LOW PRESSURE SECTION. 2. MP-YZC-GA-04-HN0-001:SYSTEM DESCRIPTION for HP/LP SYSTEM 3. MP-YZC-IM-04-IG0-001 : PROTECTION, LOOP AND LOGIC DESCRIPTION 4. MP-YZC-MA-04-PE0-001 : DESIGN BASIS REPORT 5. MP-YZC-IM-04-IGO-002 : START-UP/SHUT DOWN DESCRIPTION 6. MP-YZC-GA-04-SA0-001 : SYSTEM DESCRIPTION FOR AUXILIARY STEAM

SYSTEM 7. MP-YZC-I1-05-IG0-004 : ALARM / TRIP LIST 8. MP-YZC-MA-08-HA0-001 : SPECIFICATION AND DRAWING FOR DUCT

BURNER 9. MP-YZC-MA-08-HP0002 : SPECIFICATION AND DRAWING FOR DIVERT

DAMPER 10. MP-YZC-BA-09-PGD-001 : O/M MANUAL

C

4. yazd-system description for lp section

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