Combined Cycle (CCGT) Power Plant
Process Overview
Combined Cycle (CCGT) Power Plant — Process Overview
In a combined cycle gas turbine (CCGT) plant, hot exhaust from the gas turbine raises steam in a heat recovery steam generator (HRSG), usually at HP, IP and LP pressure levels, and the steam drives a steam turbine. Pumping duties sit mainly in the water–steam cycle (boiler feed, condensate extraction and cooling water), plus liquid fuel forwarding on dual-fuel units.
Many CCGT units start and stop daily or follow grid load, so seals see repeated thermal transients that a base-load coal unit does not. For coal-fired units see Coal-Fired Thermal Power; for bagasse and biomass boilers see Co-Generation & Biomass.
Key Sealing Challenges
- Cycling duty: frequent starts expose faces and elastomers to thermal shock; the Plan 23 loop must be vented and kept in service through standby.
- HP / IP boiler feed pumps: hot feedwater close to saturation. The seal is sized for seal-chamber pressure, not HP discharge.
- Condensate extraction: vacuum suction, so air ingress across the seal faces must be prevented.
- Liquid fuel: hydrocarbon service needs FKM elastomers and leak-tight cartridge seals.
What mechanical seal is used on HRSG boiler feed pumps?
HRSG boiler feed pumps typically use a balanced cartridge seal with stationary springs (e.g. Gipfel HP760) on an API Plan 23 cooling circuit, with silicon carbide vs. carbon faces. Stationary springs do not rotate with the shaft, so the seal is less sensitive to speed and to small misalignment from thermal growth during frequent starts, and carbon handles thermal shock better than a hard-on-hard face pair. The seal is sized for seal-chamber pressure, not HP discharge pressure.
Root-Cause Failure Analysis — Field Example
Symptom: HP boiler feed pump seal leaks after warm and cold starts, but runs dry at steady load.
├── Incorrect Response: "Increase spring load."
├── Diagnostic Evidence Required:
│ ├── Trend seal-chamber temperature through a start: does it overshoot the seal datasheet limit?
│ ├── Check the Plan 23 loop for trapped air: was it vented at the high point after maintenance?
│ └── Inspect faces for radial heat-check cracks (thermal shock).
└── Engineered Solution:
├── Vent the Plan 23 loop and keep cooling water on during standby.
├── Use SiC vs carbon faces for thermal-shock tolerance.
└── Follow the pump OEM warm-up procedure before loading the pump.
Frequently Asked Questions
Do CCGT plants need different seals from coal plants?
The water–steam duties are similar, so the same seal families apply. The difference is cycling: CCGT seals need reliable Plan 23 cooling through starts and standby, and face pairs that tolerate thermal shock.
Which seal suits a liquid fuel forwarding pump?
A balanced cartridge seal with silicon carbide vs. carbon faces and FKM elastomers on an API Plan 11 flush is typical for diesel. Where local rules require secondary containment, a dual seal can be supplied.
Related: Coal-Fired Thermal Power · Co-Generation & Biomass · Oil & Gas.
Request a Seal Selection
Send your pump make and model, fluid, temperature, pressure, shaft size and speed to info@gipfelengg.com or use our enquiry form. Gipfel Engineering (ISO 9001:2015, NSIC-registered MSME, Mumbai) designs and manufactures mechanical seals, seal support systems and process pumps.
Equipment solutions: Boiler Feed & Multistage Pumps · Vertical & Sump Pumps · Turbines.
Pump Duty & Mechanical Seal Selection Matrix
Typical values for selection guidance only. Final selection is made against the customer duty sheet.
| Pump duty | Fluid | Typical temp. | Typical pressure (bar) | Seal arrangement | Faces / elastomer | API piping plan |
|---|---|---|---|---|---|---|
| HP / IP Boiler Feed Pump (HRSG) | Deaerated feedwater | 140–170 °C | HP discharge 120–180 bar; IP supply from an interstage tapping. The seal sees seal-chamber (suction / balance-line) pressure, not discharge — confirm per pump | High-pressure balanced cartridge, stationary springs (catalogue ref. HP760) | Reaction-bonded SiC vs electro-graphite carbon / EPDM (peroxide-cured) or FEPM (Aflas) | API Plan 23 (pumping ring + seal cooler) |
| LP Boiler Feed Pump (where fitted) | Feedwater | Up to 160 °C | 5–25 bar | Balanced multi-spring cartridge | SiC vs carbon / EPDM (peroxide-cured) or FEPM | API Plan 23 |
| Condensate Extraction Pump (CEP) | Turbine condensate | 35–55 °C | Suction under condenser vacuum — confirm seal-chamber pressure per pump | Balanced multi-spring cartridge; Double cartridge, back-to-back (pressurised) where air ingress is critical | SiC vs carbon / EPDM | API Plan 32 (condensate injection) + Plan 62 quench, or dual seal with Plan 53A |
| Main Cooling Water (CW) Pump | Cooling tower or raw water | 25–40 °C | 2–4 bar | Balanced multi-spring cartridge | SiC vs SiC / EPDM or FKM | API Plan 11 (clarified water) or Plan 32 (silt-laden water) |
| Closed Cooling Water (CCW) Pump | Inhibited DM water or glycol mixture | 30–45 °C | 3–8 bar | Wave-spring semi-cartridge | SiC vs carbon / EPDM | API Plan 11 |
| Liquid Fuel Forwarding Pump (dual-fuel units) | Diesel / high-speed diesel (HSD) | Ambient | 5–15 bar | Balanced multi-spring cartridge | SiC vs carbon / FKM | API Plan 11 |
| DM Water Transfer / Make-up Pump | Demineralised water | Ambient | 3–8 bar | Single-spring seal | SiC vs carbon / EPDM | API Plan 11 |
| HRSG Blowdown / Drain Pump | Hot blowdown water | 100–140 °C | 2–6 bar | Balanced multi-spring cartridge | SiC vs carbon / EPDM (peroxide-cured) or FEPM | API Plan 23 |
Reviewed by Gipfel Engineering’s technical team.
Technical Information Disclaimer
The information on this page, including process descriptions, flow diagrams, operating ranges, seal arrangements, materials and piping plans, is general technical guidance for information only. Values shown are typical industry ranges, not guaranteed ratings or specifications of any Gipfel Engineering product. Each application differs. Seal selection, material compatibility, installation and operation must be verified by qualified personnel against the specific equipment data sheet, process conditions, applicable codes and the pump manufacturer’s instructions. A binding recommendation is given only in a written quotation or technical offer from Gipfel Engineering.
References to standards (such as API 682, ISO 21049, ISO 3069, FDA 21 CFR 177.2600 and NACE MR0175 / ISO 15156) describe common industry practice. They do not mean that any product is certified, qualified or approved to that standard unless this is confirmed in writing for a specific order. Third-party company and product names, including “equivalent to” references, are used for identification only and remain the trademarks of their owners. No affiliation, endorsement or OEM approval is implied.
Compliance with safety, hazardous-area, environmental and statutory requirements at the user’s site remains the responsibility of the plant owner or operator. To the extent permitted by law, Gipfel Engineering accepts no liability for loss or damage arising from reliance on this general information without a confirmed written recommendation. Content may change without notice.