Availability of Generators:

Reliability and Efficiency in the

Present Operating Regime

Workshop on “Regulatory Framework in Electricity Industry

in India – Challenges, Governance & Future Roadmap” Ranchi, 7th Dec’2018

Power Scenario

Coal, 195992,

57%

Gas, 24937,

7%

Nuclear, 6780, 2%

Hydro, 45487, 13%

Renewables, 72013, 21%

Others, 838, 0%

Installed Capacity, MWAs on 31.10.2018

3,46,048 MW

Growth in Demand: CAGR- 5%

Growth in Renewable Supply: CAGR- 24%

Growth in Overall Capacity: CAGR- 8%

Growth in Renewable Capacity: CAGR- 19%

Renewables planned to be ramped up to 175GW by 2022

Grid Operating RegimeTypical Demand & Renewable Supply Curve

• Evening Peak coincides with low Renewable availability

• Day Lean coincides with High Solar; Night Lean coincides with High Wind

• This creates additional Cycling Requirements from Conventional Generators

• Seasonal Variation

– Peak Demand 175GW in

Oct’18

– Peak Demand as low as

135GW in Jan’18

• Daily Variation

– Peak to Off-Peak: upto 1.25

• Hourly Variation

– Hourly Ramp rates: around

6000 MW/hr

– In 2022, max net Load Ramp

expected to be 92GW over 6

hours

Evening Peak

Morning Peak

Day Lean

Night Lean

NTPC Operating Fleet- 52+ GW

• By Size/ Technology• By Fuel Type/ Vintage

122

44.1035

5.985 0.8113.0 0.91

No of Units Capacity (GW)Coal Gas/Liquid Hydro Solar Wind

111

36.4

11 7.7

No of units Capacity (GW)

Sub Critical Super Critical

33

4.6

28

6.8

50

25.0

11 7.7

No of units Capacity (GW)

<200 200 Series 500 Series 660 & 800

33

9.69

27

7.16

36

14.614

27

12.635

No of units Capacity (GW)

>25 15~ 25 5 ~ 15 <5

Availability, Reliability & Efficiency

• Availability: Capability to deliver

– Readiness of machine

– Adequate Availability of inputs- coal, water

– Operating conditions- quality of inputs, ambient

conditions

• Reliability: Available when required

– Also as required- matching demand characteristics?

• Efficiency- at best cost- normalised for inputs?

– How do we measure efficiency? Cost? M/c efficiency

Parameters?

– Since there are asymmetries in inputs, machine

efficiency alone may not define merit order

NTPC’s Fleet Characteristics

• NTPC’s fleet predominantly Thermal

– Coal Plants comprise 85% of NTPC’s portfolio

– Gas Capacity 9%; however effectively 2%

• APM gas availability around 20%

• 50% GTs generally not on bar

• Capacity set up as Base Load units

– Both as Designed & as Contracted

• 60 units (~17GW) more than 15 years old

– Technological Limitations of Cycling, Ramping and Low load

operations

– Impact on Safe, Reliable and Efficient Operations

The Above Scenario of NTPC largely representative of the Scenario in the CountryThe country is looking to the Thermal Generators to match the net demand

variation characteristics that are now incident on the system

• Start up/Shut down

(Hot/Warm/Cold)

• On load cycling

(LL1,LL2,LL3)

• High frequency load

variations

(RGMO/AGC/Condensate

throttling)

Type of Cycling

Cyclic Operation-Safety Concern

• Sub-optimised combustion can lead to

frequent tripping on flame failure, furnace

pressurisation, slagging and clinkering

• Low flue gas temp below Acid Dew point

can lead to duct , APH basket and ESP

fields corrosion. Even chances of Collapse

of ESP

• Due to corrosion boiler drains may also

burst leading to unsafe situation

Cyclic Operation- Impacts

• Fast & Frequent thermal cycling of

components lead to fatigue, creep

• Stresses on components and turbine shells

resulting from changing pressure & temp

• Failures of boiler tubes caused by cyclic

fatigue, corrosion fatigue and pitting.

• Cracking in dissimilar metal welds,

headers and valves, and other thick-walled

components due to rapid changes in steam

temperature.

• Cracking of generator rotors due to the

movement between the rotor and casing

during “barring”.

• LPT last stage blade is prone failure due to

handling of Wet steam

Shorter Component life expectancies result in higher EFOR- Reduced Reliability

Cycling and Fast Ramping- Cycle Chemistry

• Corrosion caused by oxygen entering the system (e.g.,

during start-up), and changes to water quality and

chemistry, resulting from, e.g. falling pH

• Condensation from cooling steam, which in turn can

cause corrosion of parts, leakage of water, and an

increased need for drainage.

• Oxidation, e.g, from exposure to air on start-up and

draining; oxides in boiler tubes can dislodge due to

thermal changes.

• Corrosion of turbine parts, not only from oxides but

also from wet steam that occurs on start-up, during low-

load operations

Cycling and Fast Ramping- Impact on η and

environment

• Heat rates typically degrade at partial load

due to lower steam parameter (Pr and temp) and Low Feed water temp at ECO inlet.

• NOX and SO2 rates are also affected by loading. Startup emissions of CO2, NOX, and SO2 may be significantly higher than steady-state emissions rates.

• Ramp ups in power output may also result in higher than steady-state emissions.

• Low flue gas temp below acid Dew point can damage APH basket and flue gas duct.

Cycling of Coal Plants- Effects

In Indian conditions there is limited data

Boiler Component Failure due to Cycling

(Intertek Global Benchmarking study)

Failure due to Cycling operation in thermal plants

(Siemens European study)

Case Study

A team of experts from EEC, Siemens and VGB carried out test runs in unit

6 of the NTPC Dadri power plant jointly with the local operations team.

The aim of the tests to run 500 MW block with a minimum load of 40% & it

was successfully demonstrated by running the unit safely for five hours with

a load of 200 MW.

The test team was also able to drive load ramps of 15 MW/min (3% ramp

rate) successfully in the range of 200 to 500 MW and ramp down to 200MW

Copyright © 2016 Your Company All Rights Reserved. 14

LOAD(%)

RAMP

DOWN

MAJOR ACTION

TAKEN

OBSERVATION REMARK

420

MW(84%)

One Mill Cut Out MS TEMP maintaining high

Eco outlet o2% =3.1%

Steam temp fluctuation

330MW(66

%)

2ND Mill Cut out HRH steam temp maintaining low Steam temp fluctuation

280MW(55

%)

4 Mill in service One TDBFP recirculation valve opened

and due to Feed water flow imbalance

Drum level dipped

HRH steam temp maintaining low

Flame intensity <35%

Drum level fluctuation

Steam temp fluctuation

250MW(50

%)

One TDBFP was

withdrawn

Super heater temp after de-superheater

is less than Sat temp(alarm)

Delta T left and right after de-

superheater >20degc

Flame intensity stable

Steam temp fluctuation

230MW(46

%)

3RD Mill was cut out Flame intensity improved,

Flue gas temp after APH was <113 deg

C at SAH and <108degc at PAH outlet

Flue gas temp of 108°C is below the

acid dew point which is approx. at

122°C as per a sulfur content of 0.3%.

This situation will lead to corrosion

within the flue gas duct and ESP

200

MW(40%)

O2% increased to 4.3%

to improve mill outlet

temp and windbox to

furnace DP

Single BFP and 3 mills in

service

Mill outlet temp improved >70 degc

Flame intensity remaining the same

FW Flow and drum level fluctuation

, flue gas temp running below acid

dew point causing potential for

corrosion

Steam temp parameter fluctuating

Systematic Ramp down

Cost Implications for Generators

• All of the effects of Low Load Operations, Cycling, fast

ramping etc. are imposing additional costs on the

generators

• Capex Costs: For modifications in equipment, processes

& systems- one time costs

– Automatic Mill Operation (Mill Scheduler)

– Smarter Main Steam Temperature Control

– Reheat Temperature Control

– Automated Start of Fans and Pumps

– Flue Gas Temperature Control

– Modulating Recirculation Valve Across Boiler Feed Pump

These Modification may require an additional Capex

requirement to the tune of Rs 50 Crores. However this will

vary from unit to unit

Cost Implications for Generators …contd.Recurring Cost

– Additional O&M Cost

– Reduction in Efficiency

– Emissions management

– Reduced Availability

• Modified Availability targets for such units- linked to resonse

Regulatory framework to address these cost implications

Thank You