Turbine Bypass System

Overview Over the years, turbine-bypass technology has advanced along with that of the power industry.

F turbine-bypass systems have grown in sophistication to enhance

operational flexibility and to protect power plant components during a variety of transient modes. With more than 1500 bypass valves supplied over the last 40 years and a strong worldwide service network, our leadership has been proven time and time again.

Turbine-bypass systems are not only essential for the flexible operation of large coalfired power plants but play an equally important role in advanced combined-cycle power plants. Turbine-bypass systems permit operation of the steam-generator independently of the turbine during start-up, commissioning, shutdown and load disturbances. This enhances operational flexibility during transient operating conditions. As a result, startup and reloading times are reduced. In addition, equipment life and overall plant availability are increased.

To achieve the desired results, turbine-bypass systems must be adequately sized to meet the needs of transient operating modes.

F can effectively support plant designers

and plant operators in selecting and integrating a bypass system into an overall plant design. In addition to providing original-equipment, we have extensive experience in integrating bypass systems into existing plants and in retrofitting existing bypass valves that have failed in service. Our worldwide sales and service organization and local engineering centers are ready to support customers in their evaluation and engineering efforts.

F turbine-bypass systems meet the requirements of all governing boiler and valve codes, including ANSI, ASME, TRD and many others.

Examples of CCI/Sulzer Bypass Systems: 1967 1975 1982 1988 1991

1993 1993 1993 1995 1996

1965-98 1971-98

1972-98 1981-98 1988 1990

RWE Frimmersdorf, Germany (combined bypass and safety function) TEAS, Elbistan A, Turkey (once through boiler) Chubu Electric, Kawagoe 1&2, Japan (ultra-supercritical plant) HIPDC Shidongku, China (supercritical power plant) Korea Electric Power Corp., Korea (twenty supercritical units, Poryong, Taean, Hadong & others) Shanghai Municipal Electric Power Bureau, WaiGaoQiao 1-4, China China Light and Power, Black Point, China (eight combined cycle plants) Kansai Electric, Himeji Units 1-5/1-6, Japan (combined cycle units) Shell Australia Ltd., Geolong Refinery, Australia (system redesign and valve replacement) VEAG, Schwarze Pumpe, Germany (supercritical, combined bypass and safety function) Various plants, Japan (over 40 bypass systems) Neyvilly Lignite 1-3, NTPC Rihand STPP, NTPC Talcher, CESC Budge Budge and other plants, India (over 100 bypass systems) Various plants, China (over 130 bypass systems with all utilities) EGAT, Mae Moh 4-13, Rayong, Ratchaburi, Thailand (drum, combined cycle, and supercritical plants) Pacific Gas & Electric, Moss Landing, USA (supercritical, cyclic operation) New England Power Service Co., Brayton Point, USA (supercritical, cyclic operation)

WaiGaoQiao Power Plant, China

F turbine-bypass systems are recognized around

“

startup, preventing needless energy loss, lengthening

Heat Recovery Steam Generator

Deaerator

HP-Bypass Steam Turbine Gas Turbine HP

GT

IP

LP

G

LP-Bypass HP-System IP-System LP-System Typical combined cycle power plant schematic

IP-Bypass

Purpose Faster Start-up and Minimized Thermal Stress A good turbine-bypass system reduces start-up time under cold, warm, and hot conditions. The turbinebypass system provides continuous flow through the superheater and the reheater, and allows for higher firing rates which result in quicker boiler warm-up. It also controls superheater and reheater pressure during the entire startup, keeping thermal transients in the boiler to a minimum. Operating experience shows that power plants equipped with

F turbine-bypass systems experience reduced start-up times and

much less solid particle erosion of the turbine blades,reducing the need for expensive repair and replacement.

Temperature Matching A

F turbine-bypass system allows optimum steam to metal temperature matching for all start-

up modes. The boiler load can be selected to reach the desired superheater and reheater conditions for turbine start. This results in reduced start-up time and extented life for main turbine components.

the world as the best turbine-bypass systems for faster trouble-free plant life and increasing plant reliability.” Steam Turbine HP

p Safety System

HP-Bypass Controller

IP

LP

G

p

Safety System

Superheater

HP-Bypass

T

p T

Safety System Reheater

LP-Bypass Controller Condenser

RH-Safety Valve

LP-Bypass

Evaporator Preheater

Deaerator

Economizer

Typical coal fired supercritical plant schematic

Avoid Boiler Trip after Load Rejections A fast-acting

F turbine-bypass system allows boiler operation to continue at an optimal

standby load while demand for turbine load is re-established after a load rejection. The turbine can cover house load requirements. Pressure and temperature transients invariably associated with boiler trip and restart are avoided.

Eliminate HP-Safety Valves A

F HP-bypass valve sized for 100% MCR capacity can serve as an HP-safety valve

when equipped with the necessary safe opening devices. This eliminates the need for separate

spring-loaded HP-Safety valves, associated piping, and silencers and can save millions of dollars in equipment and maintenance costs. Our engineering staff is qualified to review applicable codes and system designs.

Preventing Energy and Feedwater Loss Even when regulations require spring-loaded safety valves, a large capacity

F turbine-

bypass system with fast acting actuators can avoid lifting of the safety valves and the resulting energy and water losses under almost all upset conditions.

Sizing of the

F Turbine-Bypass System

Turbine-bypass system sizing considerations must take into account all plant operating conditions such as the number of warm starts, hot starts and requirements for house load operation. Later in plant life, cyclic operation may become common. Sizing of low pressure turbine-bypass valves must take into account the desired reheater pressure for turbine start as well as condenser capacity.

F turbine-bypass systems are custom designed to meet the specific capacity

requirements of the individual plant. Capacity can range up to 100 percent of the maximum continuous rating (MCR) boiler steam flow for the HP-bypass as well as for the LP-bypass.

Integrating Turbine-Bypass Systems

F turbine-bypass systems can be supplied for any type of fossil-fired power plant. The schematics on pages 4-5 show the integration of a turbine-bypass system into a combined-cycle power plant (CCPP) and a 500 MW fossil-fuel-fired supercritical plant.

The chart to the right shows a typical hot-startup characteristic for a supercritical, fossilfuel-fired, 500 MW unit using a

F turbine bypass system. Forty minutes after

lighting the steam generator, the steam temperature is matched to the turbine metal

temperature. The bypass system flow rate equals the difference between steamgenerator and turbine flows. In this case it is 22 percent of full flow. The corresponding steam-generator pressure is 30 percent of full-load pressure (80 bar [1160 psig] at 40 minutes compared to 260 bar [3800 psig] at full load).

The result is a required turbine bypass system capacity of approximately 70 percent MCR at full load (percent-steam-flow divided by percent-pressure). Because of the large bypass system designed into this particular plant, coal firing can be initiated earlier, thus reducing the amount and cost of oil necessary in the start-up cycle.

Steam temp press flow bar ˚C % 500

300

4.2

400

4.1

300 200 200 100 0

100

100

3.1

3.2 50

2.1

2.2 1.1 2.3 2.4

0

100 minutes

50

0 Light up

Full Load

Synchr.

Start-Up Time Pulverizers 1.1 2.1 2.2 2.3 2.4

Firing Rate Feedwater Flow Waterwall Flow Steam Flow (Superheater) Steam Flow (Turbine)

3.1 3.2 4.1 4.2

Superheater Pressure Reheater Pressure Superheater Temperature Reheater Temperature

Hot start of a supercritical 500 MW unit

F has developed a wide range of technologies for supplier of turbine-bypass systems, F supplies researched “

Valves

Duty of a Turbine-Bypass System The primary job of any turbine-bypass system is steam conditioning — high-pressure throttling integrated with desuperheating. Bypass valves must be able to perform these functions and achieve the desired pressures and temperatures without undue noise and vibration and without destructive valve-trim wear. In addition, bypass valves must perform these functions under severe temperature cycling.

Depending upon plant design, bypass systems must also perform additional functions such as safe HP-bypass opening and LP-bypass closing for condenser protection during transient operating periods.

F offers the advanced valve technology to meet these severe service requirements. With its distinctive body design, F is recognized as the lasting turbine bypass valve technology around the world.

Lower Noise and Vibration Excessive vibration in a turbine bypass valve can break pipe hangers and shake accessories off actuators, resulting in high maintenance costs and unscheduled downtime.

Using wave-principle theory,

F developed the unique WING-type stem with

contoured cage design for use in high pressure bypass systems. Unlike conventional plug designs, the WING-type stem has a specially contoured profile to produce wave

valves, desuperheating, actuators and controls. As the original and proven solutions to suit the needs of any type of plant.”

F

WING-type trim

interference. This effectively “cancels out” some of the aerodynamic effects as they impact valve parts. This design incorporates specially engineered channels that divide the steam flow into discrete paths and increase generated noise frequency. This higher frequency noise is more easily absorbed by the adjacent piping and results in noise-level reduction of more than 10 dBA as compared to conventional designs.

In addition, the WING-type stem with contoured cage creates a highly turbulent zone immediately down-stream of the valve seat in drum and supercritical plants. This turbulent zone is ideally suited for the in-body injection of desuperheating spraywater. Also, noise is attenuated by water injection inside the valve. This valve design ensures that this turbulent zone is removed from any valve surface to eliminate a source of vibration.

For installations requiring strict noise control,

F offers a low noise DRAG

®

solution.

DRAG® solutions provide the lowest noise for any turbine-bypass available in the industry. Noise generated by the valve can be kept to below 85 dBA throughout the entire operating range without the use of back pressure diffusers and acoustic insulation.

CCI DRAG® Disk Stack

F are recognized as the benchmark of turbine bypass systems — Distinctive, Complete, Proud, Swiss — F

With their distinctive body design,

Thermally Efficient Design

F turbine bypass systems feature unique thermally efficient bodies designed to eliminate the stresses from thermal transients associated with cycling duty. The body designs incorporate thin-walled spherical sections to produce compact, strong valves that are easily recognized as the distinctive

F style.

Thermographic analysis of a bypass valve during start-up showing complete water atomisation inside a DRE valve

F

Isolation Valves Specifications often call for steam-isolation valves upstream of the LP-bypass valve for condenser protection.

F supplies LP-bypass valves which combine the

control function with a safe-closing function. However, if the specification requires a bypass system with separate control and isolation valves for reasons of a different plant safety philosophy, we an also supply steam isolation valves.

Reheater Safety Valves

“The desuperheating function in a

F turbine-bypass

and quick evaporation of the injected water without Desuperheating

F has developed many different

controls,

technologies for desuperheating. The

arrangement can affect the quality of

primary job for any type of desuperheater

atomisation. Finally, good atomisation can

is the complete evaporation of the

only be achieved when the proper

injected

be

spraywater valve is selected. A good

accomplished without any water droplets

spraywater valve will have multi-stage

hitting the pressure boundary walls of the

pressure letdown to eliminate cavitation

valve or downstream piping. Key factors

and trim erosion in order to maintain fine

affecting desuperheater performance are

temperature control at all steam flows.

water

—

this

must

the degree of atomisation of the injected

flow

range

and

piping

water and the mixing with the steam, and

F experience and technology

second, quick evaporation with proper

ensures the optimal solution of complete

location and direction of the spray water

atomisation every time.

jet. Complete evaporation must be attained before the first pipe bend to

In-Body Desuperheating

prevent any erosion caused by high-speed

For HP bypass applications in a drum or

droplets contacting the pipe walls.

supercritical power plant,

F

recommends in-body desuperheating. The degree of spraywater atomization

In-body desuperheating makes the best

attained is determined by the relative

use of the principle of water injection into

speed of steam flow to that of injection

a zone of high steam-flow turbulence. The

water flow. Full atomisation is the result of

spraywater is fully atomised before the

high water injection speed and injection

steam exits the valve body, thereby

of the desuperheating water into a zone

providing the shortest evaporation length.

of turbulent, high-speed steam flow. In

In-body desuperheating provides the

addition, factors such as accuracy of

best atomisation available.

must provide for excellent steam and spraywater mixing creating thermal stress that can cause system damage.”

Proper design of in-body desuperheating requires a detailed understanding of the flow pattern inside the valve at all load conditions.

F has done extensive

research into these flow patterns, including spraywater injection and atomisation with the help of dynamic numerical calculations. Optimum arrangement of the injection nozzles, material selection, and shape and hole pattern of the cage around the injection zone is the result of this extensive research.

F is the only turbine bypass system supplier that has perfected in-body desuperheating technology to provide long lasting, fully integrated steamconditioning within the valve body. With this technology, we recommend only a ver y shor t straight length of piping downstream of the valve. In addition, piping material downstream of the valve may be switched to carbon steel instead of alloy material.

Steam conditioning valve type DRE using inbody desuperheating technology

Spring-Loaded Injection Nozzles Spring-loaded nozzles are typically used for LP bypass applications, but can be used in all types of combined cycle power plant applications. The atomizing principle of springloaded injection nozzles is based on highspeed injection. Due to the design of the spring-loaded nozzles, a sufficient injection pressure and injection speed exists at minimum load.The injection speed results not only in good atomisation but also in a sufficient penetration of the spraywater into the steam flow.

In addition, the

F spring-loaded

nozzle incorporates a unique swirl pattern which provides rotational energy to the spraywater over the entire range of flow conditions. This insures an even distribution which produces good mixing of steam and spraywater with extremely good rangeability. Steam conditioning valve type NBSE using spring loaded spray nozzles

Ring-Type Desuperheater For LP bypass applications,

F

recommends separate desuperheating downstream of pressure reduction. In a ringtype desuperheater, which is used primarily in drum and supercritical power plants, steam turbulence is created by the shape of the steam-flow. The steam velocity is increased by a contraction of the flow path, and the injection takes place where the flow path abruptly expands. Mixing takes place in this Ring type desuperheater EK

region of turbulence to produce the shortest distance required for atomisation.

Steam-Assisted Desuperheaters

F has developed the STEAMJET desuperheater for steam conditioning applications requiring the best possible atomisation outside of the body. The STEAMJET provides significantly better atomisation than the ring-type and springloaded nozzle desuperheaters currently available in the industr y. The design is based on a combination of high-speed water injection into a high-velocity , venturi steam flow. The "compound swirl" nozzle provides high injection speed while the atomising steam provides a velocity which is virtually independent of the main steam flow. The spray pattern is centered in the piping to produce even temperature distribution at all flow conditions.

F STEAMJET produces the shortest distance required for atomisation of all downstream desuperheaters.

Sparger Tubes

F provides custom-engineered condenser sparger (dump) tubes for the introduction of steam from the bypass valves to the condenser. These optional sparger tubes are custom designed to meet the space constraints of the specific condenser and to protect the internals of the condenser.

As required, we will engineer the sparger tubes to meet low-noise requirements.

F

DRAG ® steam conditioning valve

using steam assisted STEAMJET desuperheating technology. The desuperheater is also available as a separate downstream component.

“Turbine-bypass valves and their actuators and controls Actuators and Controls Reliable system operation is based on the proper selection and design of all of the system components . Using advanced technology developed by

F over years of testing and

experience, our expertise has produced the best pneumatic and hydraulic actuation technology in the industry.

Pneumatic Actuators

F pneumatic actuators feature a doubleacting piston designed to meet the application requirements for stroke, speed, actuating force, and positional accuracy. The actuator is equipped with quick acting components to achieve stroke speeds for bypass applications of one second.

Pneumatic actuator

F is the only supplier in the industry to provide high speed pneumatic actuation with stable control.

Hydraulic Actuators Hydraulic actuators are well suited for applications requiring high force and high stroking speeds with precise control.

F provides the complete

system consisting of hydraulic cylinders, control devices, positioners and hydraulic power units. The hydraulic power units meet all safety requirements and consist of a fluid tank, pumps, filters, accumulators, and the necessary monitoring and controls. Hydraulic power unit for a bypass system

must be matched for optimum system performance.” Our hydraulic actuation systems and controls are recognized as the original, long-lasting technology for hydraulic actuation.

Safety Systems for HP Bypass valves In countries where regulations allow the use of HPbypass valves as safety valves against superheater overpressure,

F can provide bypass valves,

actuators , and the necessar y safety control equipment. Safe trip devices can be easily mounted on hydraulic actuators permitting the use of bypass systems in place of safety valves. The complete safety system has a type approval according to the German TRD421 code.

F Turbine-bypass Controller A well-designed bypass controller is important for smooth plant operation, especially during plant

Hydraulic actuator

start-up, shut down, and load disturbances. We have more than 25 years’ experience in designing and supplying turbine-bypass controllers.

Our latest AV6 series turbine-bypass controller uses advanced control strategies. The state controller with observer (SCO) provides more precise control than standard systems, thereby producing less thermal cycling stresses on valves and pipings.

The AV6 series controllers can easily interface to any boiler and turbine control system.

F

AV6 series bypass controller

F a product of CCI

CCI World Headquarters Telephone: (949) 858-1877 Fax: (949) 858-1878 22591 Avenida Empresa Rancho Santa Margarita California 92688 USA

F are manufactured in a state of the art facility centrally located in Switzerland. We welcome you as a visitor to our factory and beautiful country.

CCI Switzerland formerly SULZER THERMTEC Telephone: 41 52 262 11 66 Fax: 41 52 262 01 65 P.O. Box Hegifeldstrasse 10 CH-8404 Winterthur, Switzerland CCI Japan Telephone: 81 726 41 7197 Fax: 81 726 41 7198 194-2, Shukunosho Ibaraki-City, Osaka 567 Japan CCI Korea Telephone: 82 341 85 9430 Fax: 82 341 85 0552 26-17, Pungmu-Ri Kimpo-Eup, Kimpo Gun Kyunggi-Do, South Korea CCI UK Technology Centre North Europe Sharp Street Worsley, Manchester M2B 3NA, England

“We Solve Control Valve Problems” Sales & Service Locations Throughout The World E-Mail: [email protected] Web Site: http://www.ccivalve.com

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