Adoption of Supercritical Technology in India- A ‘Rationale’

Adoption of Supercritical Technology in India- A ‘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 625C/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 >625C/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 630C, 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/610C. • 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/600-610C steam turbines. Creep testing to 40,000h, together with large-scale fabrication trails, has so far demonstrated reliable results. Hence, turbine parameters of 600C/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 650C/325bar. A number of design changes are also being developed to allow higher temperatures and pressures to be used are (a) Partial triple-casing on turbines or use of inlet guide vanes to reduce the peak pressures seen by the HP cylinder • (b) Steam inlets and valves welded rather than flanged to give reduced leakage and fewer maintenance problems • (c) Use of heat shields and cooling steam in the IP turbine inlet • (d) 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 high-temperature 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. • ØPF 540…Sub-critical PF fired unit with 169 kg/Cm2, 538/ 5380C • ØPF 580…Super-critical PF fired unit with 246 kg/Cm2, 538/ 5650C • ØPF 610…Super-critical PF fired unit with 246 kg/Cm2, 566/ 5930C • ØPF 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 / ultra- supercritical 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: • ØPF 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 • ØPF 610…Super-critical PF fired unit with 246 kg/Cm2, 566/ 5930C…(ReferFig. 4.2) Normal pace…3 and ½ years Accelerated TOT…3 years • ØPF 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 3shows 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 SC Plant PF 580 USA 5.985 Cr. / MW Europe (Germany) 5.396 Cr. / MW Japan 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)Pit head station specifically Sipat STPP of NTPC (b) 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 • ØProject 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. ØMaximum 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. ØCost of generation is least for a Pit- head Washed coal fired Unit amongst all other Super Critical Units. • ØCost of generation is highest for ROM coal fired load center SCU with land transport of coal. • ØParameters 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.

Adoption of Supercritical Technology in India- A ‘Rationale’