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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)
Coal61%
Gas8%
Oil0%
Hydro(Renewable)14%
Nuclear2%
RES**(MNRE)15%
Coal Gas Oil Hydro(Renewable) Nuclear RES**(MNRE)
2 16th Dec 2016
BHEL’s Contribution In Indian Power Sector
0
20000
40000
60000
80000
100000
120000
140000
160000
180000
200000
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
187802.88
5780
25282.13
918.89
43133.43 46326.82
MW
CA
PA
CIT
Y
TYPE OF POWER PLANTS
All India BHEL
16th Dec 20163
Indian Renewable Energy Sector (46326.82 MW)Source: MNRE
Wind Power 62%
Small Hydro11%
Biomass/Cogneneration9%
Solar Power18%
Waste to Power0%
Wind Power Small Hydro Biomass/Cogneneration Solar Power Waste to Power
4 16th Dec 2016
Installed RE Capacity Vs. Revised RE TargetsA Long Way To Go…..
8727.64 MW
28279.4 MW
4882.33 MW 4323.37 MW
100000 MW
60000 MW
10000 MW5000 MW
0
20000
40000
60000
80000
100000
120000
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
7
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
16th Dec 2016
8
Integration of Renewable Energy in Grid
Balancing by conventional energy sources (large part of which isthermal) is required
Greater the penetration of RE in Grid greater is the requirementof balancing
16th Dec 2016
Expected All India Duck curve with 20GW Solar Power in Grid
9 16th Dec 2016
10
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.
16th Dec 2016
11
Start-up of Steam turbines (BHEL make)
Start type Outage hours Mean HP Rotor
temperature
(deg C)
Start-up time
(Rolling to full
load in min.
approx)
Cold Start 190 hr 150 deg C 255
Warm Start 48 hr 380 deg C 155
Hot Start 8 hr 500 deg C 55
Normal Mode : 2000-2200 starts
Slow Mode : 8000 starts
Fast Mode : 800 starts
16th Dec 2016
Effect of Load Cycling on Power Plant Components
12
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
16th Dec 2016
13
Life Expenditure of Components
Operating Steam
Pressure
Life Time Consumption
Creep Damage
Stress
Fatigue Damage
Creep Rupture Strength
Mechanical Stress Thermal StressType of
Material
Operating
Stress
Operating Steam
temperature
Steam Pressure
inside a thick –
walled
component
Physical properties of a
material
Geometrical
Dimensions of a thick
walled components
Temperature
Difference inside a
thick –walled
component
16th Dec 2016
14
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
16th Dec 2016
15
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 Sumindicates that the life of the component has reached its limit.
16th Dec 2016
Life Expenditure Computation
16
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
16th Dec 2016
17
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
16th Dec 2016
Age of Thermal Power Plants In India(in Years)
0
5000
10000
15000
20000
25000
30000
35000
40000
45000
0-5 years 6-10 years 10-15 years 15-20 years 20-25 years > 25years
43357 MW
22610 MW
8359 MW 7780 MW5630 MW
> 25years, 29549 MW
MW
CA
PA
CIT
Y
AGE GROUP
19
Assumed Load Demand Curve on Thermal Machines
16th Dec 2016
0
20
40
60
80
100
120
55%
80%
100%
80%
2%/min 3%/min
20
Impact Assessment of Load Cycling
Impact of cyclic operation on BHEL supplied equipment withassumed load curve has been investigated.
Lower load is limited to 55% of rated and a ramp down rate of2%/min and ramp up rate of 3%/ min. is considered.
It is assumed that main steam and HRH temperatures are keptconstant and Unit is operated in sliding pressure mode.
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 significantimpact on life consumption of Turbine, Boiler, Generator & ESP.
However this mode of operation will have additional cost interms of lower efficiency at part loads.
16th Dec 201620
Backing down below 55% load and/or increase in ramp rates willhave effect on the fatigue life of the equipment.
Backing down below 55% load will also have other negativeimpacts on the equipment as discussed earlier and need furtherinvestigation in detail.
22
Mitigating the Effect of Cycling
Additional Condition monitoring systems/ Sensors
Improved design of Boiler and Turbine to allow faster ramping 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
16th Dec 2016
23
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
16th Dec 2016
24
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
16th Dec 2016
25
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
26
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
16th Dec 2016