todayâ€™s presentation advances in the technologies for severe

Advances in the Technologies for Severe Service Control Valves

and Desuperheating

VECTOR™ - The most cost effective valve solutions

Power Plant Summit 2008, New Delhi, November 5-8, 2008: “Make Indian thermal power plants world class – Development of service providers

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Sanjay V. Sherikar and Markandey Rai,Nihon Koso Co., Ltd.

11-Nov-08 ©2007 - KOSO. All rights reserved. 2

Today’s presentation

• Severe service control valves (10 minutes)

– Impact on plant performance– Common problems– Advances in technology

• Desuperheating (6 minutes)

– Common problems– Advances in technology

• Nihon KOSO Co. Ltd. (3 minutes)

Severe service control valves

Process performance = f(control valve performance)

• Control valve is the weakest link in most cases … it limits performance of the whole process!

• Desuperheating, where required, can make any problems worse.


Impact of control valves on plant performance ( 1 of 2)

• Control valves are the most under-rated in terms of their impact on plant performance.

• Poor performance of control valves cause heat rate penalty of 100 – 500 Btu/kW-hour.– Even 100 Btu/kw-hour penalty in heat rate means an

additional fuel cost of IR 25 crore (USD 500K) annually for a 500 MW Unit (@USD 1 per M-Btu)

– Hidden costs of poor control valve performance:o damage to expensive components in the plantomaintenanceo reduced output capacity

THESE ARE AVOIDABLE LOSSES!11-Nov-08 ©2007 - KOSO. All rights reserved. 5

Impact of control valves on plant performance ( 2 of 2)

• Most common root cause of poor control valve performance → misapplication of technology

• Remedy → retrofit, or replace, the control valves with the correct technology.o Cost of remedy → typically between USD 50 – 200 per

kW (INR 2500 – 10,000 per kW) … very economic for recouping the lost performance.

• Conclusion: Power plants can not afford not to have the correct technology in their control valves!


Example of valve-related losses (case study)


Source: Experience of Moneypoint Power Station in Recovering Plant Heat Rate: Focus on Control Valves, 12th EPRI Heat Rate Improvement Conference, 2001.


Applications in fossil power plants

• Main & booster feedpump recirculation

• Start-up & main feedwater regulation

• Deaerator level control• Sootblower control• Spray control• High level heater drains• Turbine bypass• Auxiliary steam• Start-up system: B&W, CE, FW

& licensees• Sampling


Common problems


Definition of severe service for control valves

Severe service • high pressure drop • high velocity • Enemy


Common categories of threats

• High pressure drops• Two-phase flows• Corrosion• Wear• Vibration• Blockage by solids


Damage from erosion


Damage from cavitation


Conventional control valve (liquid)


Solution: Velocity control principle


Velocity control valveeliminates cavitation


Fluid energy - acceptance criteria

Acceptable velocity* Acceptable energy

Location ft/s m/s psi bar

Main flow piping 10 3 0.7 0.05

Valve inlet & outlet 60 18.3 24.2 1.7

Valve trim outlet 100 30.5 70 4.8

*assumes ambient temperature water


Fluid energy - acceptance criteria

Trim outlet kinetic energy criteria =

Service conditionsKinetic energy criteria Equivalent water

velocity

psi bar ft/s m/s

Continuous service, single-phase fluids 70 4.8 100 30

Cavitating & multi-phase fluid flow 40 2.75 75 23

Vibration-sensitive system 11 0.75 40 12

KE = V2

2gc

ρ


VECTOR™ disk flow patternunder the plug


VECTOR™ disk stack sectionover the plug


VECTOR ™ disk stack installed


Under the plug flow (gas or steam)


Over the plug flow (liquid or water)


Summary of advances in the technology for severe service control valves

• Cost-effective, multi-stage pressure let-down (“velocity control”) trim solutions for severe service applications are available. Payback for solving problematic severe service valves is generally less than few months.

• There is a better, physics-based understanding of the problematic phenomenon in valves (vibrations and noise, premature erosion, cavitation, leakage etc)– Quantitative criteria to solve these problems are developed– These criteria are easily understood, can be used in

specifications and are verifiable by power plant engineers• Physical understanding of the processes has been correlated

with field experiences over many years. This is reflected in the robustness of Vector technolgy.

Desuperheating


Koso and Desuperheating

Koso’s strengths:• Experience of over 25 years in

turbine bypass systems and desuperheaters

• The most cost effective solutions resulting from a unique combination of:– knowledge of systems, – engineering expertise, and,– customer support.

Common problems in desuperheating

• Poor temperature control• Water hammer• Cracking of internals• Cracking of pipes

– high thermal stresses


Root causes

• Cold water contacts hot metal causing high thermal stresses locally• Heavy droplets falling out of the steam & forms a river at the bottom

of the pipe• This a result of:

– Poor control of spray-water placement in steam• Spray penetration• Mixing

– Large droplet sizes


Estimate of thermal stresses

• Range of thermal stress can be estimated fromσ = E.α.∆T

• Using typical values for steel, for ∆T of 400 oC between metal pipe (steam) and water,

σ = (1.8 x 105 MPa)(14 x 10-6 / oC)(400 oC)

= 1000 MPa (145,000psi) … !

- This is much higher than yield strength of pipe materials– Metal boundaries can subjected repeatedly to such high level of

thermal stress in operation

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Physical processes in desuperheating

The key physical processes in desuperheating are:1. Atomization of spraywater

– Primary … depends on spray nozzle characteristics– Secondary … resulting form the momentum of the steam

2. Dispersion (mixing) of spraywater in steam3. Evaporation

All these processes are predictable based on known physics!

Primary atomization

• Primary atomization is initiated by shear between the liquid and gas streams

• The liquid stream to be unstable and eventually breaks up into droplets of different sizes

• Mean droplet size after primary break-up from typical high capacity desuperheating nozzles is typically in 200 -800 micron range.


Primary break-up of a liquid jet

Secondary atomization

• When We > 14, a drop breaks up by aerodynamic forces of the gas stream• Droplet size after secondary break-up is typically in micron range (fog), less

than 100 microns, when the vapor stream has sufficient energy• Demonstrates that velocity head is the key parameter in desuperheating

– the key is to make use of it correctly.


number Weber

2

=

=

We

dUWeσ

ρ

Too many options?

• “There are many options – what are the rules for selection? …”… next slide!


Desuperheater design & selection• RULE #1: Average droplet size should be less than 250 µm.

– Fixed area orifices/nozzles– Spring loaded nozzles, variable area– Steam assisted

• RULE #2: Eliminate direct spraywater hit on hot metal

– Spray penetration should be between 15% and 85%

• RULE #3: For control near saturation, feed-forward control logic

• RULE #4: Provide sufficient distances to bends & temp sensors

• RULE #0: AVOID IN-BODY DESUPERHEATING The risk is high … i.e. the risk of cold water impinging on hot metal, leading to cracking at the pressure boundary.


Good practices lead to good results

Cost effective solutions for desuperheating require:• A good specification which includes -

– Velocity control technology for high DP control valves– Droplet size and penetration criterion for

desuperheaters• Correct control logic• Proper system layout, which includes considerations

for warming and drainage of condensate

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Advances in technology for desuperheaters – a summary

• Development of physics-based understanding of the phenomenon in desuperheaters

• Better understanding of different desuperheating application requirements– Better understanding of root causes of problems– Development of solutions/ hardware to solve problems

• Development of acceptance criteria for:– droplet size (less than 250 microns)– dispersion of spraywater (15% < spray penetration < 85%)

• Availability of user-friendly engineering tools for physics-based prediction of desuperheater performance– applicable for selection, sizing and analysis of problems

About Nihon KOSO Co. Ltd.


Koso service organization

Boston, Mass

Brighouse, UK

Wuxi, China

Fukushima, Japan

Osaka, Japan

Palakkad, India

Singapore

Nasik, India

Tokyo, Japan

Dallas, Texas

Houston, Texas

Chicago

Atlanta

Calgary, Canada

Shenyang

Amsterdam, Holland

Sidney, Australia

Baku, Azerbaizan

Oslo, Norway

UAE

Taipei, Taiwan

Major service Locations

Satellite Locations

Factory Certified independents

Beijing Anshan

Chengdu

Xi’an

Wuhan

Maoming

Nanjing

Saudi Arabia

Tangshan

Xinjiang

Kunming

Fuzhou


India factories

• Palakkad factory– Palakkad, India– Main products: Control valves

• India – Nashik factory– Nashik, India– Main products: Control valves


Our power customers


Our oil & gas customers


Four+ decades of quality valve & control components development

• 1965: Business established as control valve manufacturing company in Japan

• 1979: Established manufacturing company in Korea• 1986: DRAG® technology license with Control

Components Inc. (USA)• 1987: Established manufacturing & foundry in China• 1993: Acquired Rexa Inc. hydraulic actuators, USA• 2001: Established Koso manufacturing in India• 2002: Acquired Hammel-Dahl valves, USA• 2005: Acquired Kent Introl choke & control valves, UK


KOSO velocity control

• Designed and manufactured severe service valves since 1983

• Over 10,000 valves installed• Meets ISA specifications of velocity

control• Innovative disk designs added• Only valve supplier that does

everything - manufacturing of disk stacks including EDM, laser cutting of disks & vacuum brazing of disk stack


Standardized velocity control valves


Customized velocity control valvesConclusions

• Advanced, and cost-effective, technology is available now for control valves and desuperheaters.

• Power plants today can not afford not to have multi-stage pressure letdown technology for their severe service control valves.

• Pay back on the investment in the correct technology of control valves is very quick.



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Advances in the Technologies for Severe Service Control Valves and Desuperheating


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Thank you for your kind attention!

Sanjay V. Sherikar and Markandey Rai,Nihon Koso Co., Ltd.

todayâ€™s presentation advances in the technologies for severe

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