Flexible Operation - Challenges for Thermal

Power Plants

K B Batra
Technical Services, Noida
 Total Installed Capacity of India (309244MW)
As on 30.11.2016( Source: CEA and MNRE)

RES**(MNRE)
15%

Nuclear
2%

Hydro(Renewable)
14%

Oil Coal
0% 61%
Gas
8%

Coal Gas Oil Hydro(Renewable) Nuclear RES**(MNRE)

2 16th Dec 2016

 BHEL’s Contribution In Indian Power Sector

200000 187802.88

180000

160000

140000
MW CAPACITY

120000

100000

80000

60000 46326.82
43133.43
40000 25282.13
20000 5780
918.89
0
Thermal Nuclear CCPP Diesel Hydro RE
All India 187802.88 5780 25282.13 918.89 43133.43 46326.82
BHEL 113264 3340 7560.13 199.42 20149.41 175
TYPE OF POWER PLANTS

All India BHEL

3 16th Dec 2016

 Indian Renewable Energy Sector (46326.82 MW)
Source: MNRE
Waste to Power
Solar Power 0%
18%

Biomass/Cogneneration
9%

Wind Power
62%
Small Hydro
11%

Wind Power Small Hydro Biomass/Cogneneration Solar Power Waste to Power

4 16th Dec 2016

 Installed RE Capacity Vs. Revised RE Targets
A Long Way To Go…..
120000

100000 MW
100000

80000

60000 MW
60000

40000
28279.4 MW

20000
8727.64 MW 10000 MW
4882.33 MW 4323.37 MW5000 MW
0
Solar Power Wind Power Biomass Small Hydro

Installed Capacity (October 2016) Revised Targets(Till 2022)

5 16th Dec 2016

 Share of RE in Future Energy Mix
Source: MNRE

6 16th Dec 2016

 Renewable Generation - Challenges

} Intermittent and variable

} Season and Weather dependent
} Location and time of day dependent
} Does not match the load demand curve
} Wind generation is unpredictable
} Solar generation is predictable but non controllable

7 16th Dec 2016

 Integration of Renewable Energy in Grid

} Balancing by conventional energy sources (large part of which is

thermal) is required

} Greater the penetration of RE in Grid greater is the requirement

of balancing

8 16th Dec 2016

 Expected All India Duck curve with 20GW Solar Power
in Grid

9 16th Dec 2016

 Expectation from Thermal plants

} Backing down and cyclic loading

} Frequent start/stops may be required
} Higher ramping rates during loading and unloading

But base load conventional plants are not designed for such cyclic
loading.

10 16th Dec 2016

 Start-up of Steam turbines (BHEL make 500MW)

Start type Outage hours Start-up time

(Rolling to full
load in min.
approx)
Cold Start 192 hr 180
Warm Start 36 hr 60
Hot Start 8 hr 30

Normal Mode : 2000 starts

Slow Mode : 8000 starts
Fast Mode : 800 starts

11 16th Dec 2016

 Effect of Load Cycling on Power Plant Components

Creep – Slow and continuous deformation of materials due to high

temperature exposure even at constant load

Thermal Fatigue – Failure of metal when subjected to repeated or fluctuating

stresses due to thermal cycling of components

Components affected – HP/IP rotors, Blades, Casings, Valves, Header, Y-Piece,

T-piece, MS/HRH Pipelines

12 16th Dec 2016

 Life Expenditure of Components
Life Time Consumption

Creep Damage Fatigue Damage

Creep Rupture Strength Stress

Operating Steam Operating Type of Mechanical Stress Thermal Stress

temperature Stress Material

Temperature
Operating Steam Steam Pressure Difference inside a
Pressure inside a thick – thick –walled
walled component
component

Geometrical Physical properties of a

Dimensions of a thick material
walled components

13 16th Dec 2016

 Life Expenditure Computation

The consumed life of a component is the sum of the life

consumed by Creep & Low Cycle Fatigue

MINER SUM MC IS INDICATOR OF THE LIFE EXPENDED DUE TO

CREEP
&
MINER SUM MF IS INDICATOR OF THE LIFE EXPENDED DUE TO
LOW CYCLE FATIGUE

14 16th Dec 2016

 Life Expenditure Computation

FOR STATIONARY COMPONENTS :

M = MC + MF = 1 WARNING POINT

FOR ROTATING COMPONENTS :

M = M C + MF = 0.5 WARNING POINT

Approaching the Warning Point of Effective Miner Sum

indicates that the life of the component has reached its limit.

15 16th Dec 2016

 Impact of Cycling on Equipment and Operation
} Critical components are subjected to thermal stresses which are
cyclic in nature
} Higher fatigue rates leading to shorter life of components
} Advanced ageing of Generator insulation system due to increased
thermal stresses
} Efficiency degradation at part loads
} More wear and tear of components
} Damage to equipment if not replaced/attended in time
} Shorter inspection periods
} Increased fuel cost due to frequent start-ups
} Increased O&M cost

16 16th Dec 2016

 Other Operational Risks

} Ventilation in HP and LP Turbine at lower loads

} Droplet erosion of LP blades
} Excitation of LP blades due to ventilation
} Frequent start/stop of major auxiliaries (PA/FD/ID fans, BFP)
reduces their reliability
} Increased risk for pre-fatigued components

17 16th Dec 2016

 Age of Thermal Power Plants In India
(in Years)

45000 43357 MW

40000

35000
> 25years, 29549 MW
30000
MW CAPACITY

25000 22610 MW

20000

15000

10000 8359 MW 7780 MW

5630 MW
5000

0
0-5 years 6-10 years 10-15 years 15-20 years 20-25 years > 25years
AGE GROUP
 Age of Thermal Power Plants In India
(in Years)

160 > 25years, 151

140

120
101
NO OF SETS

100

80 72

60

33 35
40
23
20

0
0-5 years 6-10 years 10-15 years 15-20 years 20-25 years > 25years
AGE GROUP

Number of Sets
 Assumed Load Demand Curve on Thermal Machines
120

100%
100

80% 80%
80

2%/min 3%/min

60

55%

40

20

20 16th Dec 2016

 Impact Assessment of Load Cycling

Ø Impact of cyclic operation on BHEL supplied equipment with

assumed load curve has been investigated.

Ø Lower load is limited to 55% of rated and a ramp down rate of

2%/min and ramp up rate of 3%/ min. is considered.

Ø It is assumed that main steam and HRH temperatures are kept

constant and Unit is operated in sliding pressure mode.

21 16th Dec 2016

 Cyclic Operation - Findings

} Preliminary studies indicate that load backing from 100%-55%

load at a ramp rate of 2%-3% per minute will not have significant
impact on life consumption of Turbine, Boiler, Generator & ESP.
} However this mode of operation will have additional cost in
terms of lower efficiency at part loads.

} Backing down below 55% load and/or increase in ramp rates will
have effect on the fatigue life of the equipment.
} Backing down below 55% load will also have other negative
impacts on the equipment as discussed earlier and is under
further investigation
} 2 shift operation will significantly reduce the life of the
equipment.
20 16 Dec 2016
th
 Factors to be considered for Flexible Operation

} Load demand Scenario in 2022

} Daily demand curve and requirement of backing down
} Age of the machine
} Rating and operational history of the machine
} Residual life left (to be assessed)
} Replacement strategy to be decided
} Requirement of two shift operation. If yes, which machines?
} Backing down strategy, categorization of machines
} Maintenance planning and budgeting

23 16th Dec 2016

 Mitigating the Effect of Cycling

} Additional Condition monitoring systems/ Sensors

} Improved design of Boiler and Turbine to allow faster start-up
and increased number of cycles
} Adaptation of Control System
} Low cycling regime for older plants (may require RLA)
} Replacement of fatigued/ worn-out components
} Shorter inspection period

24 16th Dec 2016

 Condition Monitoring for Flexible operation

} Complete operation data is available

} Continuous online consumption of life expenditure
} Detection of highly stressed parts for inspection
} Scheduling of RLA
} Exploring the margins available for optimization of operating
modes
} Online monitoring of Generator components as early warning
system

25 16th Dec 2016

 Condition Monitoring Systems
} Turbine Stress Controller (TSC)
} Boiler Stress Monitoring System (BOSMON)
} Blade Vibration Monitoring System (BVMS)
} Stator End Winding Vibration Monitoring
} Rotor Flux Monitoring
} Partial Discharge Monitoring
} Additional sensors for health monitoring

26 16th Dec 2016

 Renewables integration - Overall impact

Thus increased penetration of renewables will lead to

} Increased cost due to cycling resulting in higher tariff from
conventional sources
} Reduced equipment life and thus earlier replacement of
plants

27
 Example WB- Scenario 2022

} Day peak demand = 8240 MW

q Minimum Solar generation = 4233 MW
q Backing down of Conv. generation during day time = 4017 MW

} Evening peak demand = 12084 MW (additional 8067MW)

v During evening
peak, Conv. Generation to ramp up by 6000 MW
v 1000MW by energy efficient lighting
v 1067 MW by Purulia pump storage

28
 WB Proposed backing down - 2022
} During evening 3010MW to be put to two shift operation (at 85%
availability it comes to 2558MW). Shutdown during daytime.
(>25 year old plants – Mejia 210)
} During daytime 1510MW backed down to 55%. Offloading =
577MW (>15 year old plants, Bakreshwar)
} 4382MW backed down to 70% = 1117MW (Newer plants, DPL,
Budge-Budge)

Total backing down = 3010 + 577 + 1117 = 4704MW

(availability 85%)

29
 Renewables integration - Overall impact

Thus increased penetration of renewables will lead to

} Increased cost due to cycling resulting in higher tariff from

conventional sources
} Reduced equipment life and thus earlier replacement of plants
} Increased CO emissions, partly offsetting the gains from
renewables

30 16th Dec 2016