bhel cfbc experience

8/18/2019 BHEL CFBC Experience

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2 JUNE 2011 TS TIDINGS

TECHNICAL SERVICES / PSSR

INSIDE

1. STATUS OF PROJECTS COMMISSIONED / TO BE COMMISSIONED DURING2009 - 2012.

2. SERVICE RENDERED TO OTHER REGIONS/SAS/PROJECTS AFTER

CONTRACT CLOSING/ CUSTOMER TRAINING.

3. APPRECIATION FROM CUSTOMER FOR SERVICES RENDERED.

4. FEED BACK ON EQUIPMENTS FROM SITES.

5. LET US KNOW. 100% PETCOKE FIRED CFBC BOILER – UNIQUE DESIGNCHALLENGES

Feed backs and suggestions from all departments of BHEL for improvement of TSTIDINGS are welcome and may please be addressed to ADDL. GENERAL MANAGER(TSX)/BHEL-PSSR/CHENNAI


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Condenser water fill test was carried out and identified leaks wereattended.

Wall blowers and LRSBs electrical commissioning is in progress. Unit was synchronized on 11.06.11. Unit was hand tripped on 17.06.11due to

tube leakage in the divisional panel.

Load shedding relay was commissioned.

UNIT REACHED FULL LOAD FOR THE FIRST TIME ON 26.06.11 ANDMAXIMUM LOAD REACHED WAS 515 MW.

Unit is presently running around 305 MW.

KUTTIYADI 2 x 50 MW UNIT 1:

Unit is in service as per the requirement of customer.

LGB oil leakage through oil vapour seal assembly was attended.

KUTTIYADI 2 x 50 MW UNIT 2:

Nozzle 2 modification work was completed and unit was synchronized on18.06.2011.

Unit is in service as per the requirement of customer.

NALCO -120 MW UNIT 9:

Unit was running at 90-115 MW as per requirement of customer.

NALCO – 120 MW UNIT 10:

Unit was under shut down since 27.05.11 for carrying out maintenancework.

TG PG Test flow nozzle in HPH drip line and condensate line erection wascompleted.


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TG PG test pressure points and temperature points erection is in progress.

Condenser on load tube cleaning system (COLTCS) erection work (piping) is in

progress.

NALCO – DAMANJODI UNIT 5:

Boiler was lighted up on 03.06.11 and stopped due to water wall leakages.

Water wall tube leakage works were completed and subsequently hydro test wascarried out.

Boiler Drum Safety valves 2 nos floating was completed.

COAL FIRING WAS CARRIED OUT FOR THE FIRST TIME ON 08.06.11.

Unit was stopped due to bunker choking ( customer scope ) and HFO pumpmechanical seal damage, which was attended, pump was run and theperformance was found to be alright.

BFP – B trial run was carried out.

Boiler was boxed up on 20.06.2011 for attending the coal leakages.

NEYVELI TS II EXP CFBC, 2 X 250 MW, UNIT 1:

Unit is under shut down since 18.05.11. Preparatory works for lignitefiring is in progress.

Emergency BFP: suction and discharge piping flushing was completed, oilflushing was completed and lines were normalised. 2 hrs trial run of emergencyBFP was completed.

All the six nos. of spies valve operation was checked. ESP – GD test was completed .

Ash cooler - rear bed ash feeder motor trial run was completed.

Transport feeders B,C& D trial run was completed.

Self Cleaning air-lock feeders B& C trial run was completed.


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RAYALASEEMA – 1 x 210 MW - UNIT 5:

Unit is running around 200 MW.

SIMHADRI STAGE II, 2 X 500 MW, UNIT 3:

Unit is under shut down after full load operation on 31/03/2011 for attendingto pending jobs and balance system commissioning.

SH safety valve 02nos, ERV 04nos floating was completed.

ECO hoppers flue gas duct air tightness test was carried out.

TDBFP B: Emergency governor problem was attended.

TDBFP A : Governing system checking, control valve calibration and hydro testof lines was completed. Feed water line flushing was completed.

Drum safety valves assembly was completed after rectification byBHEL/Trichy representative.

Turbine ATT: Checking of control valves was completed.

ESP C pass: Dummy load test of BAPCON panels was carried out. SCCand OCC test of HVRs was completed . All 20 nos of fields were charged.EERMs 20 nos trial run was completed.

CC pump –C trial run was done after replacement with unit 4 CC Pump.

FD Fan 3A blades were replaced with anodised blades.

Boiler hydro test was carried out and identified leaks were attended.

Furnace ATT was carried out and identified leaks were attended

HPH, LPH and TDBFP A&B MOVs commissioning is in progress.

Wall blowers remote commissioning is in progress. 78/88 was completed.


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SERVICES RENDERED TO CUSTOMER /SAS/MUs:

Shri S. Elangovan, AE-I/TSX, PSSR, Chennai was deputed to Bellary TPS –Unit 1 on 04.06.11 for attending to Generator hydrogen pressure droppingproblem. The hydrogen leakage was observed from liquid detector rack valveand same was replaced by new one. The Generator air tightness test wasconducted from 07.06.11 to 08.06.11 and found that the drop rate waswithin limits. Generator was released for hydrogen filling on 08.06.11.

CUSTOMER TRAINING & TECHNICAL PAPER PRESENTED:

--- NIL ---

APPRECIATION FROM CUSTOMER FOR SERVICES RENDERED :

--- NIL ---


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FEED BACK NO.1

Project: NTPC Simhadri, stage II, unit 3, 500 MW

Problem: Repeated Failure of pin in tripping device while conducting oil injectiontest and overspeed test of Drive Turbine of TDBFP-B

Problem detail and analysis:

TDBFP-B drive turbine was rolled to 5400 rpm (Rated operating speed) on27/03/2011.Oil injection test was attempted to check the freeness of over speedtripping device before going for actual over speed test. But oil injection test was notsuccessful. The following are the observations during the test:

1. At test position of tester, the hand tripping knob of over speed trip device iscoming out instead of going inside.

2. Hand tripping was also attempted but could not be achieved as the trip lever wasextremely tight.

3. During releasing of the lever of over speed tester, turbine is getting tripped andthe trip device was not coming to reset position.

4. The Trip device assembly was dismantled in presence of technicians from BHEL,Hyderabad and it was observed that the Pin (shown in the attached figure:1 ) hassheared off.

5. This pin was replaced and the Drive turbine was put on Barring gear. Afterreplacement of the pin resetting and hand tripping of the turbine was normal. Due

to lack of time (March end), the actual over speed testing was not attempted andpump was taken in service.


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TDBFP-B drive turbine was re-rolled to 5400 rpm on 29.05.2011. Oil injection testwas attempted and could not be achieved at 4KSC test oil pressure. Hand tripping wasalso attempted but without any success. Suspecting jamming, the trip device wasopened and serviced; the pin was again found to be sheared. The pin was replaced andthe Drive turbine was cleared for rolling. After rolling the same phenomena wereobserved again for the third time and the turbine was stopped and kept on BarringGear for analysis:

1. Hand trip knob was pressed in test position and it did not operate. It wasobserved that holding/reset oil line is getting heated up during testing process.

2. Doubting generation of reset oil pressure during testing a dummy was provided to

block reset oil.3. The turbine was reset. Lever of over speed tester is pressed down and hand wheel

is tightened to test position. Trip device knob was pressed and found to bebehaving normally (with the dummy in reset oil line).

4. It was suspected that the overspeed tester pilot position is not correct, which maybe causing the build up of reset oil pressure in the tester.

5. Over speed governor tester is dismantled. It was observed that in test conditionpilot piston is moving 12 mm (instead of 5 mm) downwards and oil above piston isgetting connected to holding oil port due to over travel of piston which is leading tobuild up of reset oil. Shown in figures: 2 & 3.

6. The hand wheel position of tester in TDBFP A was checked and compared withTDBFP B for establishing the overtravel.It was found that the TDBFP-B testerhand wheel position was up by 6mm (approx) when compared to TDBFP A. Thetester was kept at intermediate position by partially closing the hand wheel and

Trip device knob was pressed and found to be behaving normally. Shown infigure:4.

7. The downward movement of the pilot is stopped by the hand wheel after requiredtravel of 5 mm as per drawing. This over travel confirmed the improper fixing ofHand wheel at works. It was also observed that locking pin of over speed testerhand wheel has partially come out, as a result holding oil path is not getting


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12 JUNE 2011

Figure: 1 Figure:2


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13 JUNE 2011

Figure:3 Figure:4


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FEED BACK NO. 2

Project: KTPS, Stage VI, Kothagudam, unit 11, 500 MW

Problem: Fouling of IP rotor with the Oil guard ring (Turbine side) of IP Rearpedestal (pedestal no-3)

Problem detail:

Kothagudam unit 11 was synchronized for the first time with grid on 30/03/2011.Subsequently unit was restarted on 27/05/2011 at 13:55 hrs. Unit was loaded upto120 MW with four mills taken into service. The main steam temperature of almostrated parameter was reached. At 16:00 hours sparks were observed at IP rear oilguard area for few seconds and disappeared. Again at 21:00 hrs similar observationwas made. Close monitoring of all parameters were made and there were vibrationchanges during this period. Unit tripped at 01:30 hrs due to tripping of 80mvatransformer causing tripping of auxiliaries. After trip out, during machine on barringgear oil leakages and smoke were observed in IP rear area. It was planned forinspection of IP rear pedestal.

Analysis and rectification:

The expansion achieved in IP rotor was 15mm during these above observations. Axialrubbing marks of IP Rotor collar with the oil guard ring (Turbine side) at bearingpedestal number 3 were observed. On further inspection & dimensional measurement itwas observed that the maximum axial clearance available for expansion of IP rotortowards +VE side (Gen side) in front of pedestal no-3, in present condition, is only15mm instead of the required gap of 25mm approx as per design/drawing. Damagewas noticed on oil guard ring (Turbine side) of pedestal – 3 after axial expansion of IP

rotor (refer photo I and II). This is due to the IP rotor dimension which is physicallymaintained as 80 mm in manufacturing instead of 70 mm as shown in the section EE ofdrg no 0-10201-41000 “IP ROTOR” (refer sketch – I and II). All other dimensionsare found to be as per drawing and shown in the SKETCH– I. Damage to oil guard ring(Turbine side) of pedestal no– 3 and its outermost sealing strip due to axial rubbing isbeyond repair and the oil guard needed replacement (refer attached photos).BHEL/Hardwar was referred to analyze the failure. Team from BHEL,Hardwar wasdeputed and the dimensions of the rotor was verified and it was decided to carry out


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in situ machining of the rotor. The rotor was machined by grinding by BHEL hardwartechnicians with machine in barring gear. As the gap available for machining was small,it could be done with pedestal top half removed condition only. For putting themachine on barring gear with pedestal No.3 top half open condition, the oil flow tothe bearing was reduced to minimum by adjusting the lub oil inlet throttle. The speedof barring gear was maintained around 35 RPM during machining by throttling ofbarring gear inlet valve. The final diameter of the rotor to the tolerance limit of0.02 mm was achieved by polishing with emery paper during machine on barring gear.The damaged oil guard was replaced with new one.

Conclusion:After machining of the rotor, unit was restarted and full load of the unit wasachieved and rubbing problem was resolved. The axial dimensional check of machines inother projects were also carried out as per advice of BHEL,Hardwar for suchdeviations and it was found in few of the units machining was required to avoid axialrubbing. This dimension was not in Quality checklist for production and it wassuggested to BHEL, Hardwar to introduce the same to avoid such occurrence infuture.


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Photo 1


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Photo 2

Courtesy : 1. Shri B. Murmu, SDGM, BHEL PSSR, Chennai2. Shri. Sandip Mondal, Engineer, Kothagudam Site.


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100% PETCOKE FIRED CFBC BOILER – UNIQUE DESIGN CHALLENGES

Abstract

The role of power in driving growth of country and any industry is now establishedbeyond doubt. In developing countries, fuel security and environmental issues aretaking centre stage of public concern.

In this present environment, the design of power equipments for utilizing newer fuelsoffers unique challenges for design. Petcoke is a by product of the oil refiningprocess. Ongoing advances in refining technologies enchanced conversion of bottom ofcrude and increased global demand for oil has increased the quantum of cokeproduction. Petcoke in addition, to being used for needle or anode grade cokeproduction, is used as primary fuel or for co-firing with other fuels. Petcoke fuelwith low volatile and high sulphur content poses a significant design challenge forensuring good combustion and minimal impact on environment.

The paper outlines the unique issues arising out of designing Circulating Fluidised BedCombustion boiler for exclusive Petcoke firing along with process involved in CFBcombustor, The design for ensuring good carbon burnout and high sulphur capture iskey in utilization of Petcoke as fuel. CFB process by nature is best suited forcombustion of petcoke as it offers sulphur capture option at the combustion stageitself.

BHEL’s experience in CFB technology is also brought out with reference to two majorboiler installations at BILT Graphics, Pune and SLPP, Mangrol. The experience gainedin designing, erecting, commissioning, and running these boilers have given immenseunderstanding of CFB technology. This along with continuous trials being undertaken atCFBC test facility at BHEL, Trichy are key to developing technology to utilize newerchallenging fuels like Petcoke.


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Design issues arising out of adapting for low volatile fuel are discussed and pathforward is elucidated.

Key Words :Bharat Heavy Electricals Limited (BHEL); Circulating Fluidised Bed (CFB); CirculatingFluidised Bed Combustion (CFBC); Petcoke; Cofiring; FBHE (Fluidised Bed HeatExchangers); Oxides of sulphur Sox; Oxides of Nitrogen NOx; Selective CatalyticReduction (SCR); Flue Gas Desulphurisation (FGD).

Introduction to CFB Technology:

The fluid bed combustion process facilitates power production firing a wide range offuels while meeting stringent required emissions limits. CFB technology has

demonstrated an unparalleled ability to achieve low NOx production without the needfor post- combustion temperatures (850-900 * C) and the staging of air by applicationof secondary air admission zones. Furthermore, CFB technology has exhibited fuelflexibility with an ability to burn waste materials and fuels previously deemeduneconomical and/or impossible to handle by conventional boiler firing systemtechnologies.

A large mass of solid particles, once heated, help in maintaining combustiontemperature and stabilize combustion over wide ranges of heating values of fuels thusallowing a range of poor quality and waste fuels, as well as usual fuels, to becombusted.

In a fluidizing bed, gas is passed upward through a bed of solid particles. At lowflow, solid particles remain in contact with one another and the bed solid particles arestagnant. As the gas flow increases, a point is reached at which the forces aresufficient to separate the solid particles, and the beds acts much like a fluid.

Large portions of the fuel and limestone are suspended in the gas stream and thegas-solid phase extends throughout the furnace. Even though the velocity in thecombustor is sufficient to entrain most of the particles, the dynamics of solids in thecombustor is such that suspended particles tend to form clusters. The size of theseclusters increases to sizes for which velocity of the gas is below entrainment velocitycausing the material to fall down the furnace. On their way down, these clusterscollide with rising material, breakup, and the smaller particles travel up again. Thisaction promotes mixing and gas to solid contact in the bed. Some of the material inthe bed is too large to be entrained until it is reduced in size by combustion andattrition. Fresh feed of coal and limestone maintains the bed condition. In a typical


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combustor, bed velocity is maintained at approx. 4-6 m/s. At this velocity. Erosionrates are low and heat transfer rates are reasonable. The circulating inventory wouldnormally consist of particles of size ranges of 0.03 to 2 mm, depending on the fuel.In general, fuels with low volatile content. Low volatile matter fuels would requirefiner sizes and high recycle rates, in the range of 10:1 to 100:1 to ensure goodcarbon burn out. The size of the particles is critical, if the feed is too fine,excessive material will remain in the gas leaving the cyclones resulting in aninsufficient material in circulation.

A combustor temperature between 850 0 C and 900 0 C is usually selected in CFBC.Combustion stability is provided by the high thermal inertia of the large mass of fueland inert material in the bed. Acceptable burnout of fuel results from the longresidence time of fuel in the bed and by recycles of material captured. A wide rangeof fuels may be fired in fluidized bed boilers because the design is for combustiontemperatures that are lower than the ash softening temperatures of most of thefuels. The use of a scrubber may not be required for S0 X control. The potential forhigh temperature corrosion due to high vanadium content in the fuel and lowtemperature corrosion due to high sulphur in the fuel is reduced by bed absorption. Inthe combustor, limestone continuously reacts and, therefore, it is necessary tocontinuously feed limestone with the fuel. The Sulphation reaction requires that thereis always an excess amount of limestone present. The amount of excess limestone thatis required is dependent on a number of factors such as the amount of sulphur in thefuel, the temperature of the bed, and the physical and chemical characteristics ofthe limestone. Sulphur capture by mixing higher percentage of limestone.

Fuel characteristics & Impact on Emission.

The uncontrolled SO X emission from the combussion of a coal with 1.0% - (weight%)sulphur with a heating value of 3800kcal/kg under normal combustion conditions isabout 2000 mg/nm 3 In number of countries with 3% (wt) sulphur removal would be

required for environmental compliance. Sulphur dioxide emissions can be reasonablypredicted given the sulphur content in the fuel, however NO X emissions are not soeasy to predict, because the amount of NO X produced in a combustor depends not onlyon the type of fuel being burned but also on the process conditions observed in aparticular combustion device.


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Uncontrolled NO X emissions from coal combustion in CFBC ranges from 200-400mg/nm3. In conventional pulverized Combustion Boilers, it could be even upto 200 mg/nm3

In power plants particulate emissions arise mostly from combustion of solid fuels e.g.fly ash and bottom ash, Current technology options like ESPs, bag filters provideeffective means of controlling emissions of particulate from combustion sources.

Petcoke is unique fuel because of low volatile component and high sulphur contentwhich makes it difficult to burn in conventional pulverized boilers.

Low volatile content makes it difficult to sustain the combussion. High sulphur contentmakes it economically unviable for employment of downstream FGD equipments tocontrol SO X emission. Lower grindability index makes the fuel difficult for theprocessing in pulveriser.

Constituents Average RangeCarbon 79.74 75.0-85.0Hydrogen 3.31 3.0-3.6Nitrogen 1.61 1.3-1.9Sulphur 4.47 3.4-5.3Ash 0.27 0.0-0.6Oxygen 0.00 0.0-0.1Moisture 10.60 5.5-15.0HHV kcal/kg 7475 7000-8050HGI 55 35-55Ash Properties, ppmVanadium


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raised higher and longer residence time are provided. Both the requirements increasesthe NO X generation potential.Petcoke is produced from virgin crude residues by precipitation reactions of highmolecular weight compounds, asphaltenes, and resins or from highly aromatic tar ordecanted oil stokes by condensation and polymerization of aromatic compounds.

Delayed Petcoke is produced by a semi continuous process, which can be carriedthrough in one of the following ways: ultimate, once-through, or intermediate coking.The sulphur content of the Petcoke strongly depends on the nature of the cokinffeedstock (crude oil) and its sulphur content. The sulphur content of the feed stocksincrease with increasing the concentration of asphaltenes and conradson carboncontent. For instance, higher sulphur contents were found in “sponge” coke (producedfrom high-resin asphaltene feed stocks) than in “honeycomb” coke (produced fromlow-resin asphaltene feed stocks) or “needle” coke (produced from highly-aromaticfeed stocks).

The sulphur content in petcoke varies widely mainly depending on the sulphur contentof feedstock, Typically sponge coke contains between 1% and 6% Sulphur sponge cokecontaining 4% Sulphur is used for fuel whereas that of less than 4% sulphur content isused in anode manufacturing. Needle cokes used for electode manufacturing, arerequired to have less than 1% sulphur content.

Coking temperature also affects the sulphur content of petcoke, though in lessdegree, mainly due to the vaporization and removal of the low sulphur containingvolatile matter, which result in a reduction of the total sulphur content in the coke.Most of the sulphur in Petcoke exists as organic sulphur bound to the carbon matrixof the coke. Some sulphur could also exist as sulphates and as pyretic sulphur, butthese do not in general make up more than 0.02% of the total sulphur in coke.

Hence, it is more critical to ensure a fair degree of desulphurization to capture the

SOX emanating from combustion of petcoke.Advantages of CFB process for Petcoke Firing:

The following list of process advantages in combination with unique design innovationshave enabled the 100% firing of Petcoke – Large amount of ignition energy in the bedmakes up for the delayed combustion characteristics of the fuel. Pulverisers are notemployed as the process support combussion of larger particles of millimeterdiameter.


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In back pass, heat is removed from the flue gas through superheater and economizersurfaces and an air preheater.

The entire combustor as well as the grate is enclosed by water walls and the lowerwater wall section is refractory lined to prevent corrosion and attack of the metalsurfaces.The upper water wall section is not refractory lined and provides the majority of theevaporative duty of the boiler.

Flue gas resulting from the combustion of the fuel along with the entrained solids exitthe combustor via gas outlet located in the upper portion of the water wall and isducted to the recycling cyclone designed to remove more than 99% of the solidsentrained by the gas from the combustion chamber. The flue gas exiting the cyclonefollows a path some what similar to a conventional boiler system namely:

A) Steam Cooled EnclosureB) Superheat surfacesC) Economizer SurfacesD) Air Pre-Heater for Primary, Secondary and FBHE airE) Electrostatic precipitator for removing finely entrained dustF) Induced draft fanG) Stack

Unique Advatage of Using FBHE Surfaces

The solids separated by the recycling cyclone is collected and returned directly intothe combustor via seal pots fed with a small amount of fluidizing air, This isnecessary because the pressure at the base of the cyclone is less than in thecmbustor. The solids returning via this route to the combustor are at essentially thecombustor exit temperature.

Part of the solids from the seal pot are directed at a controlled rate to the FBHEfor heat removal and subsequently returned to the combustor at lower temperature.The fluid bed exchanger replaces the need for additional heat transfer surface in thecombustor. The heat exchanger facilitates turndown because part of the steamproduction is de-coupled from the combustion process. In the absence of the FBHE,turndown has to be achieved by simultaneously balancing combustion and heat transferrequirements in the combustor. This would require adjustment of excess air,


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temperature, and solids concentration to arrive at a compromise between combustionand heat transfer requirements. The FBHE, on the other hand, provides an additionaldegree of freedom allowing combustion and heat transfer to be controlledindependently. Being in low velocity regime, the heat transfer surfaces are notaffected by erosion (as opposed to heat transfer surfaces in Combustor where highvelocity fluidization regime is employed). As the FBHE is supported with separatefluidization air from high-pressure blowers through efficient distribution nozzles, theprocess also avoids potential agglomeration problems. As a result, the use of theFBHE simplifies plant operation and provides better efficiency at turndown conditions.

Start Up System

An oil system consisting of a set of over bed burners for start-up for initial heat-upof the combustion system and oil lances for support fuel firing to bring the CFBcombustion system up to fuel ignition temperature during start-up and to maintainproper combustion temperatures during shortage or loss of solid fuel. The optimumtemperature for ensuring petcoke combustion sustenance was determined during trialsundertaken at CFBC test facility. Start Up System design was developed to meet thiscriteria.

Operating Experience Gained at Bilt Graphics & SLPP

The unit at BILT Graphics was started in 1998. The boiler has been burning amixture of Indian and Indonesian coal though it was designed for firing high ashIndian coal. The boiler has been in operation, meeting the full load requirements ofthe turbine and paper plant. The load response has been good considering the highlyfluctuating demand of the paper plant.

Initially the boiler was operating at low loads till the turbine became ready, and thelow laod capability of the uint has been excellent. The plant had operated at a load

of25% MCR (45 t/h) without oil support.

The combustor temperatures were uniform and the combustibles in the bottom and flyash have been consistently low, indicating good fluidization and circulation of solids,resulting in high efficiency of the unit

The unit has been in continuous operation throughout last year till the annual overallof the unit was taken.


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The units at SLPP were started up in November 1999 and after resolving teethingproblems, commercial operation of the units began in February 2000, The unitsunderwent a reliability trial for a month (May 2000), and this included a full load trialfor 10 days during which they were operated continuously at rated load.

Although the units were designed for lignite of HHV of 4240 kcal/kg the units arenow being fired with lignite having heat value of close to 3000 kcal/kg. The unitsperformance matches design predictions quite well. The operational and erectionfeedbacks has been captured and incorporated in subsequent CFBC designs.

Unique Design Challenges Involved for 100% Petcoke Firing

Petcoke is a difficuilt fuel for combustion and offered for the first time for 100%firing in CFBC boiler in India. This fuel contains very low volatiles (in range of 10%viz a viz >25% for lignite), higher sulphur (in range of 6% viz a viz 1% for lignite) ascompared with other coals like lignite.

Other coals such as Lignite has more volatiles and the ash is more friable than thatfrom Petcoke. Petcoke is devoid of its volatile content as it has already been exposedto high temperatures in the refinery process and is of high Carbon content (>70%),The absence of volatiles makes the combustion of carbon in Petcoke difficult. Thecombustion characteristic of Petcoke is such that the heat release is delayed by acouple of minutes after entering the combustor.

Sulphur capture reaction is a complex gas-solid reaction, which is highly dependent onsurface property and size of the solid under reaction (limestone). The sulphur-di-oxide formed from combustion of fuel sulphur has to penetrate the pores in thecalcium sulphate. This capture is further critical in Petcoke, which has higher sulphurcontent in comparison to other coal like lignite.

The design development of CFBC boiler firing 100% Petcoke involved extensive trialsat CFBC test facility to evaluate fuel characteristics in CFBC environment. Fixing twolevels of secondary air elevation to ensure better control over NOX and combustionprocess are other unique features employed in the design. The trials were also usedto arrive at optimum level of Ca/S ratio to reduce SOX to desired levels


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A) Low Ash Content

Utilising a low ash content exclusively in CFBC boiler poses a significant challenge asthe process is highly dependent on the bed material for heat transfer to walls,maintenance of lower dense bed etc.

In absence of continuous generation of adequate ash quantity from fuel (whichgenerally is the major source of bed material) additional features such continuous bedmaterial addition are envisaged in the design to ensure adequate combustor inventorywith optimizing the ash contribution from limestone and better uitlisation of thebottom ash generated.

B) Effective NOx Control

Fuel characteristics of delayed heat release and higher carbon content would entailmaintenance of higher combustor temperature, which has the tendency to increaseNOx generation potential. This feature of fuel has also been accommodated byincreasing the quantum of refactory lined zone to provide ample time for the fuel tomaintain bed temperatures conducive for better carbon utilization.The innovative location of secondary nozzles aids in effective NOx control strategy ofstaging the oxygen available while promoting good turbulence and mixing of the bed.

C) FBHE Sizing

One of critical challenges in sizing the combustor considering the conflictingrequirement arising out of inherent fuel characteristics of delayed heat release due tolow volatiles and higher carbon content . The former demanded that maintenance ofsufficient temperature and inventory (Quality & Quantity of Ignition Energy) where asthe latter demanded a very good residence time which lead to taller furnace. Therequirement of latter leads to larger area leading to depression of operating

temperatures at part loads thereby affecting the combustion characteristics.

Envisaging higher refractory zone and reduction of evaporative duty to provide optimumcombustor loading at part loads formed part of the design problem. The current designenvisages three evaporative FBHE circuit to optimize the boiler performance at partloads while providing sufficient residence time.


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Additionally, one more FBHE surface is envisaged to provide superheat duty tomaintain superheat temperature at part loads also thus meeting the specified processparameters.

Conclusion

The Petcoke generated in Refineries are difficult to burn in conventional boilers due tolow volatiles and very high sulphur content.

The CFBC boiler has been designed to fire Petcoke exclusively taking care of specificfuel characteristics.

References

1. Challengers and Economics of UsingPetroleum Coke for Power GenerationNarula, Ram G. Bechtel PowerCorporation, USA

2. Gasification in Petroleum Refinery of 21 st Century – E. Fuminsky

3. Review of fluid bed coking technologiesDG Hammond Exxonmobil Research andEngineering Company.

Courtesy : 1. Shri. M. Lakshminarasimhan, BHEL, Trichy2. Shri. B. Ravikumar, BHEL, Trichy3. Shri. S. Sundararajan, BHEL, Trichy


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UNITS WHICH HAVE ACHIEVED 100% OA

THERMAL

500 MWRAMAGUNDAM UNITS – 4, 5, 6 & 7

SIMHADRI UNIT – 1 & 2SIPAT UNIT – 5VTPS UNIT - 7

250 MW

KOTHAGUDEM UNIT - 10

210 MW

VIJAYAWADA UNIT – 1 & 6MUDDANUR UNITS - 2 & 4

RAICHUR UNIT - 6METTUR UNIT – 3 & 4

NORTH CHENNAI UNIT - 2NEYVELI UNIT – 4 & 6

UNITS WHICH HAVE ACHIEVED PLF MORE THAN 100%

500 MW

RAMAGUNDAM UNITS - 4, 5, 6 & 7SIMHADRI UNIT – 1 & 2

SIPAT UNIT – 4 & 5


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UNITS WHICH HAVE ACHIEVED PLF BETWEEN 90 & 100%

THERMAL500 MW

TALCHER UNITS – 4, 5 & 6VTPS UNIT – 7

250 MWKOTHAGUDAM UNIT – 10

210 MW

VIJAYAWADA UNITS – 1, 2, 4, 5 & 6MUDDANUR UNITS – 1, 2 & 4

RAICHUR UNIT – 6METTUR UNITS – 1, 2, 3 & 4

TUTICORIN UNITS - 1, 4 & 5NORTH CHENNAI UNITS – 2 & 3NEYVELI UNITS - 4, 5, 6 & 7

AMARKANTAK UNIT - 5


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N e y v e l i

R a i c h u r

T u t i c o r i n

R a m a g u n d a m

M u d d a n u r

K o t h a g u d a m

V i j a y a w a d a

V T P S - 7

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A m a r k a n t a k

2010 - 11 2011 - 12

STATION 2010-11 2011-12North Chennai 69.95 90.91

Neyveli 89.12 95.10Raichur 57.45 81.58

Tuticorin 89.60 87.94Ramagundam 101.03 89.52

Muddanur 92.77 89.53Kothagudam 81.75 89.30Vijayawada 78.53 93.44VTPS - 7 62.37 98.46

Mettur 90.08 98.07Talcher 93.69 91.44

Simhadri 100.35 101.62Sipat 96.55 91.18

Amarkantak -- 95.10

PERFORMANCE OF BHEL THERMAL SETS IN SR (210 MW AND ABOVE)FOR THE PERIOD FROM 01/04/2011 TO 30/06/2011 COMPARED WITH THE

CORRESPONDING PERIOD IN THE PREVIOUS YEAR.( PLF IN PERCENTAGE )

bhel cfbc experience

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