Adoption of Supercritical Technology in India- A `Rationale`
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Transcript Adoption of Supercritical Technology in India- A `Rationale`
Adoption of
Supercritical
Technology in IndiaA ‘Rationale’
India have a considerable potential for adding up new power generation
capacity based on coal, having proven reserves of over 202 billion tones.
¨ Substantial demand for adoption of supercritical steam technology is
developing, driven largely by the need to minimize the environmental impact
of power generation by achieving higher efficiencies of energy conversion.
¨ In Asia, particularly in India and the Far East, environmental requirements
are tightening and look set to tighten further. The conventional power plant
will not be able to meet the environmental norms and efficiency demands of
the future.
The principal advantages of
supercritical steam cycles are:
•
Reduced fuel costs due to improved thermal efficiency
•
CO2 emissions reduced by about 15%, per unit of electricity generated, when
compared with typical existing sub-critical plant
•
Well-proven technology with excellent availability, comparable with that of
existing sub-critical plant
•
Very good part-load efficiencies, typically half the drop in efficiency experienced
by sub-critical plant
•
Plant costs comparable with sub-critical technology and less than other clean coal
technologies
•
Very low emissions of nitrogen oxides (NOx) sulfur oxides (SOx) and particulates
achievable using modern flue gas clean-up equipment.
Front line issues
Development of high temperature creep resistant alloy steels.
Turbine material development
Alternative boiler technology for gasification cycles. like FBCs etc.,
Advanced controls & Instrumentation
Stringent Boiler Water Quality Control
Transfer of Technology (TOT)
MATERIALS AND METTALLURGY
The steam conditions and hence the thermal efficiency of advanced
supercritical steam cycles are primarily limited by the available
materials. The trend towards progressively higher thermal efficiencies
can only be achieved if better materials can be identified for a number of
critical components.
The recently developed high creep strength martensitic 9 to 12 percent
Cr steels, such as P91, P92 (NF616) and P122 (HCM12A), used for thick
section boiler components and steam pipes, are the key new materials
that have driven forward the supercritical technology to steam
temperatures over 565 degrees Centigrade into the USC range.
•
High strength ferritic 9-12Cr steels for use in thick section components
are now commercially available for temperatures up to 620 degrees
Celsius. Field tests are in progress, but long-term performance data are
not yet available
MATERIALS AND METTALLURGY…Contd
.
•
Initial data on two experimental 12 Cr ferritic steels indicate that they
may be capable of long-term service up to 650 degrees Celsius, but more
data are required to confirm this.
•
Advanced austenitic stainless steels for reheater and super-heater tubing
are available for service temperatures up to 650 degrees Celsius and
possibly 700 degrees Celsius. The ASME Boiler Code Group has
approved none of these steels so far.
•
Higher strength materials are needed for upper water construction of
plants with steam pressures above 24 Mpa. A high strength 1-1/2
percent Cr steel recently ASME Code approved as T-23 is the preferred
candidate material for this application. Field trials are in progress.
USC/SC TECHNOLOGY WORLD WIDE
Several USC, PC plants of 400-1000 MW have entered service in Japan
and Europe over the past five years with design heat rates 5 to 7 percent
lower than standard sub-critical plants. The longer-term reliability of
these USC plants in Europe and Japan is of key importance to the future
of this technology.
AFBC plants are particularly suitable for lower quality and high ash
coals. In the smaller sizes 50-150 MW they have shown reliabilities
similar to PC plants of the same size.
Several units of 250 MW size have been deployed in Europe and the U.S.
Larger units of 400-600 MW have been designed and could potentially
make use of the higher efficiency super critical steam cycles.
R&D IN METALLURGY
The main R&D efforts are in Japan, the USA (funded by the
US Department of Energy, USDOE) and Germany (including the
MARCKO Program). Japanese manufacturers claim to have already
demonstrated materials suitable for 650C steam temperatures.
Furnace wall tubing, T23, developed by Sumitomo Metal
industries and MHI, and 7Cr. Mo.V.Ti.B1010 (Ti: titanium; B:
boron), developed by Mannesmann and Valourec, are the most likely
materials to be selected for steam conditions up to 625C/325 bar.
Short-term creep rupture data suggest that these steels may
have equivalent creep properties to T91 steel whilst requiring no
post-weld heat treatment. For steam conditions >625C/325bar
stronger materials will be required.
Candidate materials currently at the most advanced stage of
development are P92, P122 and E911. All three steels offer
considerably enhanced creep-rupture properties over more
conventional equivalent steels, T91 and X20Cr.Mo.V121, but all
require post-weld heat treatment during fabrication
R&D IN METALLURGY
Contd...
More highly alloyed steels under development, such as NF709,
HRBC and HR6W, may allow operation at steam temperatures of
630C, but again more advanced work is needed.
The recent ASTM/ASME-approved P92 and P122 steels
should allow construction of thick-section components and steam
lines for PF plant operating with steam parameters up to
325bar/610C.
Circumferential water wall cracking has been the major
source of boiler tube failures for supercritical units. The objective of
EPRI project on this aspect was to determine the root cause(s) of the
circumferential cracking experienced on the fireside of water wall
tubes of supercritical steam boilers in the United States. Information
is now available from detailed monitoring to provide guidance on
controlling these failures.
Boiler Design
Considerable research effort into plant damage,
including thermal fatigue has been under way, aimed
at supporting existing operating plant. This is leading
to new designs of, for example, headers and steam
chests that are much more resistant to thermal fatigue
and where thermal fatigue can be better predicted. To
prevent problems, multiple components can be used to
reduce component sizes and hence wall thickness.
Turbine Material
Development
New alloys based upon 10% Cr. Mo.W.V.Nb.Ni B (W: tungsten; Nb:
niobium) are becoming available for turbine rotors and casings for construction
of 300-325bar/600-610C steam turbines. Creep testing to 40,000h, together with
large-scale fabrication trails, has so far demonstrated reliable results. Hence,
turbine parameters of 600C/325bar can be considered achievable.
By the addition of cobalt to 12%Cr.W steel (i.e. NF 12 and HR 1200), Japan
expects to be able to manufacture steam turbines capable of handling final steam
conditions of 650C/325bar.
A number of design changes are also being developed to allow higher temperatures
and pressures to be used are
(a)
(b)
(c)
(d)
Partial triple-casing on turbines or use of inlet guide vanes to reduce the
peak pressures seen by the HP cylinder
Steam inlets and valves welded rather than flanged to give reduced leakage
and fewer maintenance problems
Use of heat shields and cooling steam in the IP turbine inlet
New blade coatings to reduce solid particle erosion where high-velocity
inlets are used to minimize pressure effects
Turbine Cycle Development
Some of the highlights of the development are:
•
•
Improved blading profiles making use of modern CFD techniques
Higher final feed temperatures and bled-steam temperatures
bled-steam tapping off the HP cylinder
Improved efficiency of auxiliaries
Lower condenser pressures using larger condensers and larger LP exhaust
areas (this requires site-specific cost optimization for each project)
OTHER OPTIONS
• Trend to larger unit sizes improving turbine efficiencies
• Increasing automation and levels of control
• Optimizing plant layout, e.g. to shorten pipe runs and ductwork.
Control & Instrumentation
Advanced control techniques should be developed to optimize plant operation
and maintenance. These include intelligent control systems to:
Maintain uniform temperatures across the boiler by control of burner
parameters
Minimize carbon-in-ash or NOx formation in the same way
Better match of load and firing during load changes, to avoid temperature
excursions and improve ramp rates
Improve reliability and repeatability of cycling procedures
Condition-monitor both boiler and turbine components
Forecast damages accumulation and allows targeted preventative maintenance.
Ensure higher reliability of temperature sensors
Monitor high temperature fire side corrosion in super-heater section
March towards maximum allowable operating point from metallurgical point of
view requires use of advanced control, as normal PID control is intolerable. These
are; Fuzzy logic control, State Variable Control, Predictive Adaptive Control etc.
Intelligent soot blower control
Alternative Boiler Technology
In principle, supercritical steam cycles can be used for any technology
using a steam cycle to generate electricity. Supercritical plant can
therefore be incorporated into:
gasification cycles
FBCs
any process involving an HRSG to power a turbine generator
However, in order to be commercially viable, supercritical cycles
need to be of a certain size, and also to be able to generate hightemperature steam.
For all the above cycles, one or both of these factors have been
missing to date, so no supercritical version has been constructed.
Transfer of Supercritical / Ultra- Supercritical
(SC/ USC) Technology from a developed
economy to India vis-à-vis an imported SC/USC
Methodology
Production Technologies & value addition to each of the component
of the production chain
An exercise of breaking down each major component/sub system
into constituent Production technology/Production chain has been
undertaken for Supercritical Power Project firing high ash Indian coal,
as summarized at Table below This table also shows the Value addition to
the production chain.
Tables 1 & 2
Cost structure in the countries of origin and
absorption
The cost data has been obtained through literature survey for the following four
main variants of SC / USC plants.
PF 540…Sub-critical PF fired unit with 169 kg/Cm2, 538/ 5380C
PF 580…Super-critical PF fired unit with 246 kg/Cm2, 538/ 5650C
PF 610…Super-critical PF fired unit with 246 kg/Cm2, 566/ 5930C
PF 710…Ultra-supercritical PF fired unit with 300 kg/Cm2,
temperature up to 7100C
Cost Data …contd
The cost figures in $/kW is worked out in table below for the
components available in India. Average figures indicating cost of all
major components/ sub systems in case of import from USA, Europe &
Japan i.e. the countries of origin for the above three variants of SC /
USC are also calculated at this table.
Availability of various components of supercritical / ultrasupercritical Technologies suitable for high ash Indian coals is given at
this Table. Country wise (USA, Europe, Japan) variation in cost
structure of major components of SC / USC technology is also worked
out at the following Table
Tables 3&4
VELOCITY OF TRANSFER OF TECHNOLOGY
Determination of Velocity of Transfer of Technology (TOT) from a developed
economy to India
Using the program TOT the velocity of the transfer of technology, both at normal
pace and at an accelerated pace is worked out as under:
PF 580…Super-critical PF fired unit with 246 kg/Cm2, 538/ 5650C…(Refer
Fig. 4.1)
Normal pace…2 and ½ years
Accelerated TOT…2 years
PF 610…Super-critical PF fired unit with 246 kg/Cm2, 566/ 5930C…(Refer
Fig. 4.2)
Normal pace…3 and ½ years
Accelerated TOT…3 years
PF 710…Ultra-supercritical PF fired unit with 300 kg/Cm2, temperature up
to 7100C… (Refer Fig. 4.3)
Normal pace…6 and ½ years
Accelerated TOT…5 years
TRANSPARANCIES
Overall SC/ USC Power plant cost analysis –
results and discussions
An analysis of the results of the table 3 shows that specific cost ( Rs. Cr. per
MW @ Rs.45/ US $ ) of the following variance of a Sub-critical and
three types of Imported SCU / USC units may be worked out as under:
PF 540…5.058
PF 580…5.396
PF 610…5.454
PF 710…9.635
…
CONTD
For the indigenous development through a systematic transfer of technology
(TOT), the corresponding figures are:
PF 540…2.713
PF 580…2.988
PF 610…3.114
PF 710 …6.687
This cost does not include the cost of transfer of technology and the
time required for TOT and consequent add on to the cost. In case of
partial import, the cost shall lie between above two sets of figures.
CONTD…
Country wise variation in cost structure of imported SC / USC plants
suitable for using above referred technologies. The same is summarized
as below:
Country
USA
Europe (Germany)
Japan
SC Plant PF 580
5.985 Cr. / MW
5.396 Cr. / MW
5.130 Cr. / MW
Cost of indigenous SC plant (PF 580…246 b and 538/565 C) suitable for
Indian coals using about 70% indigenous materials, would be of the
order of 3 Cr./MW at today’s exchange rate (Cost of TOT shall be extra)
TECHNO-ECONOMIC ANALYSIS
Techno-economic studies were carried out by EPDC of Japan for:
(a)
(b)
Pit head station specifically Sipat STPP of NTPC
Load-centered station (coastal), about 1200 km from coal source
Following five cases based on steam conditions were analyzed:
Case 1: 169 kg/Cm2 & 538/5380C
Case 2: 246 kg/Cm2 & 538/5380C
Case 3: 246 kg/Cm2 & 538/5660C
Case 4: 246 kg/Cm2 & 566/5660C
Case 5: 246 kg/Cm2 & 566/5930C
Tables 5&6
FINDINGS FROM LEAST COST
OPTIMIZATION STUDY
Project cost decreases by about 1.8% through use of washed coal,
mainly due to reduction in boiler and its auxiliary plant size for a Super
Critical Unit as compared to ROM coal fired Sub critical unit of Case 1
(both being Pit- head Units). The corresponding Heat Rate improvement
is by about 2.42% in this case.
Maximum cost impact is found for a load center SCU station firing
ROM coal, both for land and land-cum-sea transport between above two
Cases. This is of the order of 288 Crores. Heat rate improvement is also
highest in this case.
Cost of generation is least for a Pit- head Washed coal fired Unit
amongst all other Super Critical Units.
Cost of generation is highest for ROM coal fired load center SCU
with land transport of coal.
Parameters selected for super critical unit firing ROM coal at
Pithead station as the most optimum for Indian conditions is that of
Case 3: 246 kg/Cm2 & 538/5660C.