Dahanu Thermal Power Station

2X250 MW DAHANU THERMAL POWER STATION

RELIANCE ENERGY LTD., INDIA

1.0 UNIT PROFILE

Reliance Energy Limited is a fully integrated utility engaged in the generation, transmission and distribution of electricity. Today it is India’s leading private sector Utility group with aggregate group revenue of around Rs. 99 billion and gross fixed assets of Rs. 108 billion. Reliance Energy is also India's one of the most valuable private sector company with market capitalization of over Rs. 99 billion.

With a vision to be amongst the most admired and most trusted integrated utility companies in the world, the company is committed to be world class utility company benchmarked to the international standards of quality, operational performance, efficiency and customer care.

2 x 250 MW Dahanu Thermal Power Station (DTPS) is one of company’s generating facilities at Dahanu near Mumbai, India. Power generated from DTPS is transmitted to Mumbai, the business capital of India and is further distributed to more than 2.5 million retails consumers in Mumbai Suburbs. DTPS units are the first 250 MW sets in the country supplied by BHEL, India and are in operation since 1995. Over the years DTPS has established best practices in all its Operation and Maintenance areas, which resulted in continuous improvement in its performance.

Since last five years DTPS enjoyed the top slot amongst the best performing Indian Coal based Power stations. Its performance is recognized at national as well as international forums, the latest one being selected amongst the ‘Top Plant of 2004‘ by Platts Power magazine and first prize for meritorious performance award by CEA . But DTPS is not complacent about these achievements and in line with Reliance’s ambition; the quest for excellence is on, forever.

2.0 ENERGY CONSUMPTION The plant achieved newer heights in most of the key operating and Energy management performance parameters over the period as tabulated below.

Financial Year

PLF (%)

Availability (%)

Heat Rate

(Kcal/kwh)

Sp. Oil (ml/KHW)

Aux. Power

(%)

DM Makeup

(%)

No of trips /

1000 hrs1996-97 73.19 80.25 2372 1.739 8.269 1.41 3.2714 1997-98 85.00 90.49 2336 0.515 8.24 1.38 1.8293 1998-99 76.55 92.24 2337 0.478 7.44 1.25 1.2376 1999-00 88.68 98.42 2313 0.167 7.04 0.90 0.2892 2000-01 82.68 92.33 2313 0.274 7.2 0.69 1.2982 2001-02 87.83 93.02 2320 0.166 7.82 0.74 0.2455 2002-03 90.53 91.03 2312 0.309 7.43 0.68 0.627 2003-04 100.34 96.84 2265 0.115 7.34 0.39 0.117 2004-05 101.35 96.88 2261 0.139 7.53 0.37 0.412 2005-06 98.70 94.71 2286 0.182 7.59 0.38 0.301

Sp. Energy Consumption:

DESCRIPTION UNIT 2003-04 2004-05 2005-06

Annual Generation Lakhs kWh 44068.31 44391.9 43230.7 Total Electrical Energy Consumption

Lakhs kWh/ year

3234.97 3342.86 3282.04

Sp. Energy Consumption- Electrical

KWh / kWh 0.0734 0.0753 0.0759

Total Thermal (Fuel) Consumption

Million KCal / year

9998145 10037402 9897476

Sp. Energy Consumption- Thermal

Kcal / Kwh 2265 2261 2286

YEAR ELECTRICITY THERMAL

Consum.

(Lakh kWh)

%Reduction(Saving achieved / consum. Of pre. Yr.)

Consum.

(MKcal)

%Reduction(Saving achieved / consum. Of pre. Yr.)

2003-04 3234.97 0.610 9998145 0.928

2004-05 3342.86 2.279 10037402 1.060

2005-06 3282.04 0.541 9897476 1.169

Benchmarking in Indian Power Sector 2005-06:

DTPS has sustained and excelled in its performance and set benchmark for consecutive second year amongst Indian Power sector on key performance indicators related to Energy Management. 3.0 Energy Commitment, Policy and Set Up: During the period several best practice initiatives were undertaken for overall improvement in all round performance.

• Integrated Energy Conservation One of the most important aspects of the operation of a power station is the energy consumption. With this in view various programmes were implemented during the Financial Year (F.Y.) 2003 -2004, 2005 & 2006 so as to

1. Improve the Heat Rate. And 2. Reduce the Auxiliary power consumption

The benefits gained from the implementation of the programmes taken up which have a direct bearing on the environmental performance of the power plant as reduction in both results in:

Reduced coal consumption and thus Reduced emissions from the plant Reduced waste generation

In order to improve the identified aspects, the process areas with potential for Improvement were identified. Some areas where improved technology could be beneficial were also identified where the capital costs involved were justified with respect to the gains. In order to achieve the above the overall reliability of the process also needs to be improved as higher the reliability the lesser are the starts and stops in the process thus reducing the unstable behavior of the process leading to reduced emissions. Programmes to achieve the same were also taken up during the year, which resulted in achieving very high PLF with higher loading factor and availability during the year. This has also contributed in improving the Heat Rate of the plant as expected against design.

All the above-mentioned programmes led to overall environmental benefits, which can be quantified and summarized as follows against 2002-03 is as below:

Sr. No.

Reduction Cost Saving / Result Gain

1. 3.2% coal consumption i.e. 75,000 MT per annum

Rs. 153 million

2. 27% in the particulate emissions Reduced emission by 20 mg/Nm3

3. 3.2% ash (Waste) generation 25,000 MT Ash less generated quantity

4. Green House Gas (CO2) by about 1,37,500 MT

5 2.5% SO2 emissions 2.05 MT per day (on a emission limit of 80.4 T/day)

6. 1.2% Aux. Power Consumption 4.94 MUs (Rs. 17.55 million).

• Six sigma and Quality improvement programs (QIP)

The plant undertook massive awareness drive for initiation of Six Sigma, which shall effectively bring down waste generation, better energy management and defect elimination. Employees are now trained to use techniques like Five-S, FMEA (Failure mode effective Analysis), cost of poor quality, Pareto chart, control chart and 8-D analysis etc and achieve break through results. The program resulted in identification of 123 QIPs against expenditure of Rs. 6.3 million giving cost benefit of Rs. 185.65 million in 03-04. During last

year 32 QIPs against expenditure of Rs.15.30 million, this resulted in saving of Rs. 63.90 million spread over the last two years and many other intangible benefits.

• Environment Management Program (EMP) on Particulate Matter

As part of continual improvement of Environmental performance, many Environmental Management Programme (EMPs) were also undertaken. Most significant EMP is being the Total Particulate Matter emission eduction (from 51 mg/Nmr 3 to 29 mg/Nm3) from stack.

MAJOR EMP for Waste disposal Utilization of process waste i.e Ash generated after power generation is a major environmental aspect in coal fired thermal power station. 100% Ash Utilisation is one of major EMP at Dahanu TPS, which will be active during the lifetime of the Plant. To achieve this new Dry Fly Ash Evacuation System has been installed and commissioned with investment of Rs. 82 million using Strutvent, USA Classifier technology, which shall make maximum ash available for utilisation. The system is commissioned and under operation and is helping the plant to gradually increase Ash utilization. This is the first installation of such classifier in the country for adding values to the fly ash there by increasing to market utilization. And today other power plants are implementing the same.

ENERGY MANAGEMENT POLICY

Reliance Energy Limited is committed to be the most efficient integrated energy utility in the world. Our mission is to use all energy resources most efficiently and thereby minimizing the impact of our operations on environment and conserving the scarce natural resources. This we plan to achieve by,

• Adopting appropriate energy efficient and clean technologies in process

design, procurement, implementation and also continually upgrade our

performance

• Managing efficient use of all forms of energy by adopting industry wide best

practices

• Continually benchmarking our energy performance against the best in the

world and improving our competitiveness by training and knowledge

sharing.

• Creating awareness about efficient use of energy and conservation

methods amongst all our stakeholders

• Carrying out regular energy audits to identify areas for improvement

• Complying with all relevant state regulatory and statutory requirements on

energy management.

ENERGY MANAGEMENT CELL

Manager (C&I)

Manager (Mech.)

Dy. Manager (Operation)

Addl. Manager (Operation)

Addl. Manager (Electrical)

Addl. Manager (Operation)

Manager (CHP)

Dy. Manager (Off site)

Chief Engineer (CTS)

Energy Manager

Vice President

4.0 Energy Conservation Achievements:

07 nos. of ENCON projects implemented and resulting in savings of Rs. 7.6 Crores annually.

5.0 Energy Conservation Plans & Targets:

Anticipated savings in

Energy Value

Energy Conservation Measures (Planned)

(Specify units) Rs. Lakhs/ year

Approx. investment (Rs.

lakhs)

Project Commencement & Completion year

Optimise overall voltage in StationTransformers 100KW 29 0 Mar-07 Optimise operation of Distribution Transformers in of site areas 1.59 0 Completed Reduce cable loss in MCA-1 & 2 Feeders

0.36 0.25 Install auto Star Delta Star converter in identified motors

0.76 1.20 Mar-07 Replace copper ballast with electronic ballast

6.86 9.90 Replace 125 Mercury vapour lamps with 70 W metal Halide Lamps

1.60 5.00 Trial in progress Replace the existing ECW pumps with new correct size pumps 250KW 73.75 90.00 Reduce one stage of impeller in condensate extraction pump 170 KW 50.45 32.00 Trial in progress Utilise ECW for air condition unit condensor water requirement 22KW 6.31 2.00 Install VFD for chilled water pumps

4.5KW 1.31 2.00 Mar-07 Install vapour absorption machine for air conditioning unit 11.90 45.00 Utilise cold reheat steam for auxiliary steam rquirement

37.50 0.00 Trial in progress Avoid steam drain in turbine sealing system. 83.40 0.00 Mar-07

Install VFD for raw water pump house 3 0.86 1.00 Install high efficiency separators for the coal mill

540 KW 154.98 450.00 Mar-07 Install VFD for seal air fans

200KW 48.21 50.00 In progress Install VFD for fly ash silo vent fan 18 KW 5.94 7.00 Completed Install VFD for ID fans

800KW 315.70 560.00 Mar-08

Install high efficiency fans for FD & PA fans 1600KW 459.00 600.00 Install intermediate controller in compressed air system 15.75 15.00 Mar-08 6.0 Environment & Safety: 6.1 Environmental performance: DTPS has also substantially improved its environmental performance as well and today it is recognized as one of the best environmentally performing plant in the country. 6.2 Health and Safety performance: During this year the plant implemented British Safety Council’s Five Star Health and Safety Management System Audit, which are beyond OHSAS standards which in turn set benchmark of Occupational Health and Safety Performance for Coal fired power plant in the country.

The plant could achieve Four Stars rating in its maiden attempt. DTPS has got distinction for longest accident free period of 1073 days from last reportable accident of till end of this financial year. 7.0 AWARDS AND RECOGNITIONS: In the last 10 years of operation DTPS has won many Awards and has been recognized at various forums for its sustained and excellent performance in plant operation-maintenance, environment and OHS management. Environmental Awards: 1997 International Greenland Society National Award. 1998 The G-51 Millennium Award in the field of Mother Earth protection. 1998 Dr.R.J.Rathi Environmental Award.

1999 “Environment Performance Award” by Council of Power Utilities (CPU ) as a

part of Thermal Centenary Celebration-1999. 2000 “Millennium Business Award for Environmental Achievement” by United

Nations (UN) and International Chamber of Commerce (ICC) at BUDAPEST.

2000 Federation of Indian Chambers of Commerce & Industry (FICCI) Award. 2000 “Indo-German Environmental Excellence Award ” by Greentech Foundation 2001 “Indo-German Environmental Excellence Award ” by Greentech

Foundation. 2005 “Greentech Environmental Excellence Award” for 2004-05. 2006 “Greentech Environmental Excellence Award” for 2006 Safety Awards: 1999 “National Safety Council-Maharashtra Chapter ” for longest accident free

period during the year 1999.

2001 “Safety Award-2001” by “National Safety Council of India” for good

performance in OSH for 1998 to 2000 2004 “National Safety Award-2003” Govt. of India. 2004 National Safety Council-Maharashtra Chapter. 2004 “Four Stars” Ranking by British Safety Council, UK for Occupational Health

and Safety Management System. 2005 NSC -Maharashtra Chapter-- Safety Awards-2004

· For longest accident free period and · For lowest accident frequency

2006 NSC -Maharashtra Chapter-- Safety Awards-2005 for “Lowest Accident Frequency Rate During the year 2005”

Operational Performance Awards: 2004 Dahanu TPS was named as one of the worlds top 12 power plants of 2004

by platts Power Magazine, in its July/August 2004 edition based on several

selection criteria such as operational efficiency, minimal environmental impact, technology use, financing structure, etc.

2004 Reliance Energy was presented the prestigious “QIMPRO Benchmark 2004”

award by the QIMPRO Foundation in the “Service Category” on the basis of its performance in 15 parameters including attributes such as Leadership, Strategic planning, Communication, Quality Management System, and Customer Interaction Management, among others.

2005 “CII National Award for Excellence in Energy Management ” for 2005 by

Confederation of Indian Society (C I I ) 2005 “CII National Award for excellence in Water Management ” for 2005 by

Confederation of Indian Society (C I I ) 2005 Vishwakarma Rashtriya Purasakar - 2004 (Eight Employees) by Ministry of

Labour and Employment., Govt. of India, 2005 Maharastra Energy Development Agency (MEDA) Award for Excellence in

Energy Conservation & Management in Thermal Power Station sector for the year 2005.

2006 First Prize National Award for Meritorious Performance by Central

Electricity Authority (CEA), Govt. of India for its Excellent PERFORMANCE amongst Indian Thermal Power Plants in the year 2004-05.

2006 “CII National Award for Excellence in Energy Management” for 2006 by

Confederation of Indian Society (C I I )

5.0 THE JOURNEY TOWARDS EXCELLENCE: The plant has many success stories to share. A dedicated team of employee is working behind the scene untiringly to make this power plant a ‘Show Piece’ in the state, in the country and in the world.. Today all other utilities in the country are benchmarking DTPS and trying to emulate its performance. Together, the Indian power sector is moving ahead fast and greater challenges are lying ahead. Sustaining performance at highest level is the key issue and for Reliance Energy it is our journey towards excellence. By participating in NATIONAL LEVEL ENERGY CONSERVATION AWARD –2006 organized by BEE we can share our practices in the field of Energy Efficiency in the Industry. At the same time any recognition from esteemed NATIONAL level nodal agency like BEE shall go a long way in motivating the organization to perform better and bring laurel to the organization and to the country.

1. Installation Of Fabric Expansion Compensator At Primary, Secondary

Air Duct And Furnace-Wind Box Duct

Background In a coal based power plant PA & FD fans supply primary and secondary air required for combustion. This air is heated in air pre heater to a temperature of 300°C. The hot secondary air is supplied to the boiler from wind box. The joints of air preheater with primary and secondary air ducts and joints of the windbox are exposed to high wear and tear and results in heavy leakage of hot dust laden air. The surroundings become very hot and difficult to work. There is huge heat loss also. Observations There was severe ash / hot Air leakages in all four corners from wind box & primary, secondary hot air leakages from expansion bellows. Technical & Financial analysis

1. MS plate of 3 mm thickness welded from inside the wind box to cover the metallic expansion bellow to avoid direct contact of hot secondary air.

2. Fabric expansion bellow provided from outside the wind box to cover metallic

expansion bellow. 3. Fabric expansion bellow provided at APH outlet duct in primary & secondary metallic

expansion bellow.

4. Investment of Rs. 12.34 Lakhs Energy Saving Rs. 112 .12 Lakhs/year. Impact of implementation

1. To reduce respective fan loading. Saving Energy. 2. To reduced the ash accumulation around furnace and APH guide bearing area,

thereby improving equipment life and reliability. 3. To reduce hot air leakages around furnace and APH guide bearing area, thereby

preventing loss of energy. 4. Cost savings of Rs 112.12 lakhs. Per year for both units.

Fabric Expansion C

ompensator

Page 1 of 18

2. To Achieve Feed Water Temperature At High Pressure Heaters Outlet

Near Design Value

Background

In thermal power plants heaters are used for regenerative heating to increase cycle efficiency. At DTPS there are five shell and tube type heater and one contact heater (Deaerator). Out of five heaters three are LP heaters and two are HP heaters. Steam bled from different stages of turbine are used for heating condensate and feed water. The inlet and outlet water box of high pressure heaters are separated by a thick partition plate. Observations Feed water temperature at HPH-6 outlet was maintaining 06 °C less than design value. Technical & Financial analysis It was observed that the parting plate of feed water inlet and outlet was short-circuiting the inlet and outlet water. This was the reason for the low temperature at the outlet of the HP heaters. Parting plate design modified from bolted type to welded type and the chronic problem was eliminated. No investment was made. Impact of implementation

1. The modification has resulted in improving heat rate by 4.674 Kcal/KWh for 6 °C gain in temperature. This has saved 6 tons of coal consumption per day. The modification carried out in both the units.

2. The cost savings of Rs 88.71 Lakhs has been achieved per year

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3. Modification In Hopper And Shaft Support Insulator Background In any Thermal Power Plant electrostatic precipitation (ESP) forms an integral part of fly ash collecting system, which plays a vital role in control of TPM present in the flue gases. For the smooth functioning of ESP, the heating elements provided at hopper and support & shaft insulators play an important role. The heater in ESP hoppers are provided to avoid clinker formation of the ash being collected at bottom of ESP. Whereas the heaters provided at support and shaft insulators are required to maintain the temperature above acid dew point which lies between 80 to 1150C. If temperature fall below the range as mentioned, there will be continuous tracking of electrical field over the surface of insulator which will result into the damage of insulator and non-availability of field for collecting the fly ash. Observation There was a frequent problem of the T.B. of the heaters circuit and cables getting burnt. This was observed mainly in the TBs and cables of the incoming junction boxes. After constant monitoring, it was observed that the heaters remained in service continuously and as a result there was a continuous flow of current. Whereas heaters are supposed to be in intermittent duty cycle and designed for controlled operation through thermostat. The heat generated due to continuous flow of current in the J.B. did not get dissipated, resulting into the burning of cable, lugs and the terminal blocks, as JBs were only designed for controlled operation through thermostat.

Location of thermost before at modification

Location of thermostat after modification

Technical & Financial analysis The reason for non switching off of the heaters were evaluated and it was concluded that due to the wrong positioning of thermostat, the circuit used to never switch off. The OEM had provided thermostat in support insulator of HVR transformer duct at a height of 1380 mm above support insulator heater. The improper sensing of the temperature by thermostat probe kept heaters continuously on. The temperature recorded were 750C and 1300C at thermostat and heater elevations respectively. Then it was decided to shift the location of thermostat at near the support insulator whose temperature was actually supposed to be sensed. The matter was also referred to BHEL (OEM) who also recommended for this modification. Accordingly the thermostat were removed from its current position and installed near the vicinity of support insulator for efficient control of heater circuit . No. Investment done.

Page 3 of 18

Impact of implementation As a result of modification following results were achieved. The energy consumption drastically fell to about 50 %. As earlier, the heaters were never to get switch off whereas after modification, the heaters are in service for less than 50% of time in order to maintain the required temperature.

a) The recurring problem of burning of cable, lugs and TB stopped. b) Energy consumption by support insulator heaters before modification was 24 KW X [4

passes X 2 units] X 24 Hrs. X 365 days = 16,81,920 Units. c) Energy Consumption after modification. The energy consumption after modification was

measured for a month and it was found that the consumption reduced to around 50% of its earlier consumption.

d) Hence financial saving on account of reduced energy consumption @ Rs. 3.50 per unit

comes to be Rs. 30,00,000/- Per annum (Recurring). e) Same modification was accepted by BHEL and incorporated in design and further supply to other units.

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4. Change In Boiler Feed Pump Changeover Philosophy Background One of the major auxiliaries of DTPS is Boiler Feed Pump (9000 KW). The purpose of Boiler Feed Pump is to pump feed water to boiler drum, provide spray water to HPBP, APRDS, De-superheater station. One BFP caters to entire requirement of the process. The second pump remains as an auto stand by equipment. A scheduled change over philosophy is followed for following reasons.

• To improve reliability by ensuring emergency standby of equipment • Preventive maintenance (Quarterly and half yearly) • Emergency changeover to attend any serious defect that has developed

Observation It was observed that the change over process was consuming a lot of time. During the change over process both the BFPs were remaining in service for a long duration. This was causing extra power consumption. Technical & Financial analysis During changeover the standby pump has to be taken in service and gradually loaded up to 30% load and wait for sometime keeping pump in recirculation mode for normalization of all parameter related to pump and visual inspection of pump and parameter to check whether everything is normal. Then, gradual loading of pump and simultaneous unloading of other pump, all these process takes lot of time and consume extra power during parallel running of pump. To reduce power consumption proper time management and faster loading of standby pump reduce time of changeover. Time of change over in past was 56 min Impact of implementation Average increase of pump current during changeover= 400amp Saving in power consumption due to time saved= 400*1.73*6.6*.85*22/60= Saving in power consumption due to time saved=1423 KWH Saving in cost=1423*3.5= Rs 4980 Cost saving due to total 52 change over per year in station=4980*52=258960 Now time of change over reduced to 34 min. Time saved= 22min

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5. Interconnection Of Air-Conditioning Units Of U-1 And U-2

Background In a power plant air conditioning system is provided to maintain the controlled condition of temperature and humidity. Such a condition is required for trouble free and reliable operation of DDC and other electronic equipments. At DTPS both the units were provided with independent air conditioning system without any interconnection. Observation There are two air conditioning units at DTPS. Capacity of U-1 AC unit is 3 X 110 T/HR and U-2 is 3 X 55 T/HR. the normal way of operation of air conditioning system was not optimised. This was resulting in running of both the systems simultaneously at full load even when the atmospheric temperatures were low. Technical & Financial analysis Two units were independent and were catering to different loads. It was decided to optimise the load of both AC units by interconnecting the chiller piping. Power consumption of ac units prior to interconnection AC U-1 power consumption- 6303 KW/day AC U-2 power consumption- 3680 KW/day Total power consumption of both units- 9989 KW/day Impact of implementation Total power consumption of both units after interconnection- 7728 KW/day Net saving due to interconnection- 2260 KW/day Saving of power per year – 825424 KW/year Saving in Rupees (cost of power Rs 3.50) - 825424*3.5 = 2888984 Investment for interconnection- Rs 162779 Simple payback period- 21 days.

Page 6 of 18

6. Optimised Ball Loading In Coal Mill Background Coal mills are required in Power Plant for grinding or pulverisation of coal before firing in Furnace. At DTPS we have three Ball and Tube Mill for each unit. Grinding inside the mill takes place due to impact of alloy steel balls on liners of the Mill shell and due to friction and attrition. Observation In a ball and tube mill for proper grinding certain quantity of balls has to be loaded in mill. The practice at DTPS was to charge the balls till approximately 160 Amp of current that is drawn by Mill motor at full load. It was observed that due to ball-to-ball attrition the balls were getting worn out. And after certain running hours certain balls were not taking part in the grinding process but these balls were increasing the loading of the coal mill. Technical & Financial analysis Since the power consumed by mill is very high so to optimise the loading of mill it was decided to reduce the ball charging in mill so as to reduce loading of mill motor by 10 amp. There was no difference in output and performance of Mill after reducing ball-charging quantity. Impact of implementation Power saved = 1.73*10*6.6*.85*24=2329 KWH Cost saved per year= 2329*3.5*365=Rs 2975644

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7. Replacement Of Cartridge Of Boiler Feed Pump Background One of the major auxiliaries of DTPS is Boiler Feed Pump (9000 KW). The purpose of Boiler Feed Pump is to pump feed water to boiler drum, provide spray water to HPBP, APRDS, De-superheater station. One BFP caters to entire requirement of the process. The second pump remains as an auto stand by equipment. Observation The Boiler Feed Pump at DTPS is of multistage (three stage) type. It was observed that the BFP-2B is taking much higher current than other BFPs. From performance curve of the pump also it was clear that it is consuming much higher power corresponding to the flow. Technical & Financial analysis It was concluded that loss is taking place due to interstage leakage or recirculation. Hence decision was taken to replace the cartridge of pump. Impact of Implementation After replacing the cat ridge the current drawn by current reduced by 70 Amp. Power saved per day= 1.73*6.6*70*.85*24=16304 KWH Power saved per year=5951290 KWH Saving of cost= 5951290*3.5=Rs20829515

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8. Replacement Of Recirculation Valve Of Boiler Feed Pump

Background One of the major auxiliaries of DTPS is Boiler Feed Pump (9000 KW). The purpose of Boiler Feed Pump is to pump feed water to boiler drum, provide spray water to HPBP, APRDS, De-superheater station. To maintain a minimum flow from the pump a pneumatic recirculation valve is provided. This valve avoids dry run and overheating of pump. Observation It was observed that after certain running hours the suction flow of a loaded pump was much higher than the discharge feed water flow. Technical & Financial analysis When recirculation valve of the BFP was further closed, the difference got reduced. Hence the manual isolating valve was closed and it resulted in drastic reduction of suction flow . Now the suction flow was matching with the discharge feed water flow. Hence it was suspected that some flow is passing through valve seat. After due maintenance of the existing valve not much improvement was observed. Hence it was decided to replace the existing valve with an advanced class of drag technology valve. Impact of Implementation After replacement of valve the current drawn by the motor of pump reduced by 60 amp. Power saved due to the reduction current drawn by motor = 6.6*60*1.73*0.85 Power saved= 582 KWH/HR Saving in cost/hr= 582*3.5= Rs 2037 Saving/year=2037*24*365=17844120 Investment= Rs 2500000 Payback period= 51days Same valve replaced in all the 4 BFP with an investment of 1 crore which resulted in saving of Rs 71376480.

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9. Increased Reliability & Availability Of CW Debris Filter System Background At DTPS cooling water used in condenser is seawater. Condenser is two pass once through cooling type. With seawater floating debris, shells, foreign materials may come and choke the condenser tubes. To avoid choking of condenser tubes a Debris filter is provided at the inlet of each pass of condenser cooling water inlet. The floating debris, shells, foreign materials gets filtered in Debris filter screen and gets cleaned by filter online cleaning system which gets started as filter DP increases. Observation Debris filter cleaning system was failing frequently for which there was falling of vacuum in condenser, which led to generation loss. Technical & Financial analysis The following modification has been carried out in the Debris filter system. Modified cleat design of screen basket for firm fixing with shell.

• Introducing special non-metallic, non-corrosive high wear resistance polymer bearing material in place of aluminium Bronze.

• Modified design of gear sealing support to have more rigidity to rotary mechanism. • Introducing smart type debris extraction arm to have excellent debris extraction. • Introducing one quicker opening manhole at the rear end of the Debris filter shell for

easy maintenance. Introduction of simplified DP System. The modified Debris Filter was installed in Unit # I & II during July-August 01 and June-July 02 captive overhaul respectively. No defects were raised for U # I from August 2001 to Dec2002. Internal inspection could not be done during the period as Unit was continuously running. Hence problems had come subsequently after Dec-02.It clearly indicates that the inspection & repair if any had to be done in every available opportunity. Inspection is not included in PM, as opportunity cannot be predicted. Secondly every Inspection will cause Generation Loss. The inspection and servicing of Debris filter was done during unit # I shutdown in Nov-Dec-03 and no defects were raised. No defects were raised for U # II after installation of Modified Debris Filter in June-July 02.The Debris filter inspection & servicing done during unit # II shutdown in Dec-03.

Page 10 of 18

Impact of Implementation

1. The graph clearly indicates that the defects due to Debris Filter were reduced drastically. This has saved partial generation loss, which otherwise would have been taken up to attend the Debris filter problem. This has also helped in reducing the inventory & manpower cost.

2. The cost savings of Rs 2201lacs has been achieved

Condenser inlet pressure zero

0 0 0 0

7 8

36

10

0 0 0 0 0

20

6

0 0 0

6

Dec-00

Jun-01

Jul-0

1Dec

-01Ju

n-02Ju

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Dec-02

Nov-03

Dec-03

Feb-04

year

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UNIT # I

UNIT # I MODIFIED DEBRIS FILTER REPLACED IN JULY-AUGUST-2001

UNIT # II

UNIT # II MODIFIED DEBRIS FILTER REPLACED IN JUNE-JULY-2002

UNIT # I SERVICING DONE IN NOV-DEC-03

UNIT # II SERVICING DONE IN DEC-03

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10. Use Of Variable Frequency Drive For HFO Pump

Background A coal based boiler requires to fire oil to support coal combustion. So as to keep the availability of the support fuel, an HFO firing pump is provided. The HFO firing pump is provided with a minimum recirculation valve so as to ensure minimum oil flow from the pump. Observation

During the normal operation of both the units, the HFO consumption is zero. The HFO gets re-circulated through short and long re-circulation line of both boilers to maintain the HFO temperature. Flow through short & long re-circulation is very less & maximum quantity of HFO is re-circulated through Pressure Control Valve (PCV), located near the HFO firing pumps, to HFO tank. PCV maintains the HFO discharge header pressure at 21-23 Kg/cm2 & remains approx. 50% open during normal operation of both units. Technical & Financial analysis Hence it was decided to install VFD for HFO firing pump motor rated 415V, 37 KW, to control and maintain the required flow and pressure of HFO by varying the speed of motor. Impact of implementation

Energy consumption by pump will reduce considerably after installation of VFD. The proposed payback period is less than one year.

Energy consumption by pump will reduce considerably after installation of VFD. The proposed payback period is less than one year. Installation and commissioning of suitable VFD for the 37 KW, 415 V HFO pump to have optimum performance with considerable energy saving During normal re-circulation mode average power measurement is •Without VFD @ 18.10KW •With VFD @ 8.36KW •Difference @ 9.74 Saving in KWH = KW *HR *DAYS = 9.74*24*365 KWH = 85322 KWH Saving in rupees @ Rs. 3.50 = 298628. Cost of VFD = Rs.1, 63,223 Simple Pay back period is 200 days or 6.65 month

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11. Installation Of Fabric Expansion Compensator

at Air Through Mill Ducts.

Background In a coal based power plant PA fans supply Hot and Cold air required for pulverised coal to Dry and transportation from mill to boiler. This air is heated in air pre heater to a temperature of 300°C. The hot primary air is supplied to the mill through ducts. The joints of air ducts and joints are exposed to high wear and tear and results in heavy leakage of hot dust laden air. The surroundings become very hot and difficult to work. Observations There was severe ash / hot Air leakages from expansion bellows. Technical & Financial analysis

1. MS plate of 3 mm thickness welded from inside the duct to cover the metallic expansion bellow to avoid direct contact of hot secondary air.

5. Fabric expansion bellow provided from outside to cover metallic expansion bellow. 6. Fabric expansion bellow provided at APH metallic expansion bellow.

Impact of implementation

5. To reduce respective fan loading by about 5 Amp of PA fan ”thereby saving of RS. 17.34 Lakhs/ year”.

6. To reduced the ash accumulation around furnace and APH guide bearing area. 7. To reduced hot air leakages around mill area.

.

Fabric Expansion Compensator

Page 13 of 18

12. Condenser leak test with Helium

Background

On 30th March -06 Unit-1 & Unit # 2 were running at 264 MW & 261MW respectively.

Suddenly at 12:03 Hrs both the Units tripped on “Generator negative sequence current –

high”

Technical & Financial analysis: After synchronisation of Units it was reported that UNIT#2 Vacuum was maintaining on lower

side i.e it had deteriorated from –0.9193 Ksc to –0.9023 Ksc.

To establish the reason for drop in the vacuum

1) Following valves were checked for air ingress

• All MAL valve & it’s isolating valves

• LPH & HPH drain valves

• LP Heater Drip valves (DR-22, DR-28 & their isolating valve glands i.e.

sealing water side)

• HP Heater Drip valves (DR-9, DR-16 From steam & sealing water side)

& flash tank flange joints were checked visually & no leakage was

noticed

• CW pass & debris filter were isolated to for any suspected leakage.

• Air flow measurement at discharge of Vacuum pump was measured

which was on higher side 110 kg/hr with two vacuum pumps in service

against normal value of 40 kg/hr with one pump in service .

• Air flow measurement at discharge of Vacuum pump was measured

which was on higher side (110 kg/hr against normal value of 40 kg/hr )

From above measures it was suspected that reason for deterioration in vacuum was due

to air leakage into the condenser. Condenser test was carried out Results of condenser

test indicated increase in Back pressure variation due to air ingress from “–20.39 mm

Hg To - 0.72 mm Hg”

To identify the location of air ingress M/s Arudhara Engineers Pvt. Ltd was invited to carry

out Helium leak detection test

Helium leak detection test was carried from 9th APRIL-06 to 15th APRIL-06 in Unit #2.

Page 14 of 18

Impact of implementation

Leakages were found in location as per pictures shown below.

Major leakages were attended after which vacuum has improved from –0.876 Ksc to –

0.914 Ksc. & back pressure variation due to air leakage & dirty tube has improved

from 3.97 MM of Hg to –6.92 MM of Hg as seen from trends attached herewith

It can be seen that there is gain of 10-15 Kcal/Kwh which would result in saving

of Rs.14,17,998/- in one month (due decrease in coal consumption by

651.44

TN of coal ( 15 *263.17 *1000*24*30 /4363/ 1000)

Benefit of attending leakage : . It can be seen from Annexture that there is gain of

10-15 Kcal/Kwh which would result in saving of Rs.14,17,998/- (650* due decrease

in coal consumption by 651.44 TN of coal ( 15 *263.17 *1000*24*30 /4363/ 1000)

Page 15 of 18

TREND OF CONDENSER VACUUM & BACK PRESSURE VARIATION

-14.74

-20.39

-11.32

1.46

-6.560

2.24

14.41

-1.77 -2.16 -2.79

-4.93

-1.24

4.88

0.480 -0.2-0.2-0.6

4.2

1.1

8.3

4.2

-0.8

3.4

9.9

4.53.97

-0.72 -0.38

-5.4-6.59 -5.81

-6.73-6.92

-0.876

-0.904

-0.893

-0.9204

-0.9022

-0.913-0.9111

-0.8857

-0.9198

-0.914

-0.901

-25

-20

-15

-10

-5

0

5

10

15

20

15-Mar-06 22-Mar-06 29-Mar-06 05-Apr-06 10-Apr-06 12-Apr-06 12-Apr-06 12-Apr-06 13-Apr-06 14-Apr-06 15-Apr-06

MM

OF

Hg

-0.93

-0.92

-0.91

-0.9

-0.89

-0.88

Ksc

B.P VAR.- CW I/L TEMP - U # II B.P VAR. DUE TO FLOW -U # II

B.P .VAR. DUE TO DIRTY TUBE-U # II VAC. MM

Improvements after the leakages were plugged

Page 16 of 18

13. Developed bootable floppies for PMS PPSV initialization

Background: In plant operation • Bootable floppies, which are essential for PMS system, are rapidly becoming defective due to aging. • Only two nos. of bootable floppies are available for six systems. The PPSV (Pre-processing Station has provision to boot Process Management System) from 3-1/2 inch floppy drive. (Make: TEAC- FD235HF). The floppy drive is bundled with SCSI controller (MAKE: OMIT 3500). The drive and controller are unique and not available in the market. The bootable floppy contains the critical boot program. We have contacted BHEL, Motorola (OEM) and various other vendor globally but replacement is not available for the defective part. Nowadays these components are not being manufactured. Also no support is available from Motorola on VERSADos operating system, which has become obsolete. Impact: •Non availability of Process Management System to the operator. •Operator will not be able to do effective process control as well as operation. •Jeopardise the safety of plant equipment. Root Cause: •Aging of bootable floppies on account of continuous us for 10 years. •Operating system VERSADos residing in the has become obsolete. Corrective Action: •Sufficient nos. of bootable floppies developed jointly with BHEL. •Successful efforts made to find method of making Effectiveness Of Corrective Action: •Sufficient nos. of bootable floppies are available & availability of PMS is ensured.

Measurable Benefits: • 100% Availability of PMS, which is vital for O & M, is ensured. • Deferred the expenditure in the order of Rs. 2.5 crore till reasonable solution is found.

Page 17 of 18

14. Operation of ACW / ACW Pumps through DDC Logic along with Auto pickup scheme.

Background: Operation Of ACW / ECW Pumps Is Possible Only From The Local Panel. Local Panel Is At 0 Mtr. While Control Room Is Located At 13.5 Mtr. Impact: During Emergency Of Tripping Of Ecw Pump, It Is Not Possible For Control Room Operator To Start The Pump Immediately. This May Lead To Unit Tripping And Loss Of Generation. Reasons for taking up the plan: • ACW / ECW Pumps are critical auxiliaries of plant. • To save the units from tripping in case of failure of ACW /ECW pump. • Parallel operation was provided in PCR-2 from local panel, which involved abundant cabling. • These pump were operating through relay logic. • These systems require regular maintenance. • Auto pickup facility of standby pump was not available. ROOT CAUSE ANALYSIS: 1.Operation Of ECW / ACW Pumps Is Not Available From Control Room. 2.Vendor Does Not Supply The Scheme Of Remote Operation Since Commissioning. Corrective Action: Scheme Has To Be Prepared And Approved. Implementation Shall Be Done During Opportunity. Signals Like “MCC Disturbance ”, Pump Auto Selection, Command “On” To Pumps Are Configured In SOE or Each Pump. Purpose / envisaged benefits: Auto pickup facility of standby pump is provided through DDC. • All cabling is done directly from individual breaker of each pump to control panel in PCR-2. This has reduced the cabling, which in turn shall reduce maintenance and increase reliability of system. • Protections and permissive like MCC disturbance are provided through DDC which will ensure safe operation of pumps. • Critical events like “MCC Disturb” / Command “ON” of each pump is hooked to SOE for monitoring and event analysis. •Existing spare cable from local panel to PCR-2 can be utilized for same modification in U-1. •Avoidance to one unit trip can lead to direct savings of Rs. 20 Lakhs. and preventing to inconvenience to customer Measurable Benefits:

1. Operator Shall Have The Operational Control Of The Pumps From Remote. 2. In Case Of Emergency Operator Can Take Appropriate Action. Immediately.

3. Possible Unit Trip On ECW / ACW System Failure Shall Be averted.

Page 18 of 18

(Trend Setter Project 1) Reduction in Boiler Tube Failures

1.0 Introduction:

The power sector demand and supply balance in the country is always t i l ted towards demand. The demand outstrips supply by a substantial margin. And the peak demand supply gap is substantial ly higher than base demand – supply posit ion. In such a condit ion the availabil i ty of a generating capacity is very vital. A generating station in healthy condit ion not only supplies electricity to end-users but also provides stabil ity to regional grid system for i ts proper functioning.

In Indian power sector, coal based thermal power generating stations operate as base load stations and they provide major chunk of the demand. Hence their availabil i ty is highly desirable. These power plants have to undergo certain regulatory outages as well as outages for necessary maintenance. These outages are termed as planned outages. And all the other outages, which cause unit outage, are forced or unplanned outage. A typical classif ication of forced outage is shown below (Refer Fig: 1). As it is clear that the major reason for forced outage is tube leakage in boiler pressure parts.

Forced Outage Analysis

71%

24% 4% 1%

Tube Leakage Turbine problemsTransmission & Grid C & I

(FIG: 1)

Page 1 of 24

A coal based thermal power plant of the size of DTPS would loss its availabil i ty by about 1.65 %, if i t experiences one tube leakage every 6 months in each of i ts unit. This would be equivalent to a direct generation loss of 72 MUs and a direct revenue loss of Rs.215 Mil l ion for DTPS.

Each start up of boiler / turbine after attending the problem would result in consumption of large quantity of oi l , coal and DM water. The start / stop due to the frequent tube leakages would affect the long-term l i fe and performance of boiler and turbine. And in case of frequent leakages boiler parameters may also be need to be restricted to lower value compared to design parameters and this would result in continuous loss in heat rate.

2.0 Root Cause of Tube Failures:

The boiler pressure parts are subjected to very high steam pressures and flow internally and high temperatures and abrasive environment externally. Hence they are l ikely to fai l and cause a forced outage.

India has huge reserves of coal that can be used for power generation. But the quality of coal is poor due to very high proportion of highly abrasive ash content. The ash content is as high as 45 % in Indian coals. The inherent nature of power generation process is such that the boiler pressure parts get a continuous exposure towards high temperature f lue gases containing abrasive ash. This erosion leads to tube thinning process, which ult imately results in boiler tube rupture causing a forced outage.

3.0 Classification of Tube Failure Causes:

A typical classif ication of boiler tube fai lure causes is shown below (Refer Fig: 2). This picture shows clear majority of tube failure cases due to erosion and welding failures.

Page 2 of 24

Tube Failure Classification

Erosion44%

Welding failure44%

Overheating6%

Material Defect

6%

(FIG: 2)

But the welding fai lures for the jobs done during erection work in past is not preventable during the O & M phase. So we have taken preventive measures for welding joints being made at our end. We ensure 100 % radiography and use of highly skil led high-pressure welders. This has resulted in no welding joint fai lure of the joint made at our site since 1997. Hence the focus gets shifted towards prevention and control of erosion related failures.

4.0 Initial Innovative Strategy for Erosion Reduction:

The cause of erosion is known and we undertook some preventive measures right at the beginning of the operations of DTPS. We pioneered the concept of blending the low quality-high ash Indian coal with high quality imported coal having very low ash proportion. Thereafter we also improved the quality of available Indian coal by establishing a coal washery near pithead and washing the low quality Indian coal and reducing its ash proportion by about 10 %. And again blended this better quality Indian coal with high GCV – Low ash imported coal.

Page 3 of 24

These efforts gave us good results and this is evident from the statistics of tube fai lure cases for DTPS vis-à-vis that of NTPC – a leader in Indian power generation sector. NTPC mainly uses indigenous coal having high ash content. And even after r igorous preventive measures the rate of tube failures is high (refer f ig: 3). This clearly shows advantage of use of blended coal over the use of Indian coal. And now the practice of coal blending is being adopted by progressive uti l i t ies all over the country. The innovative practice of coal blending was started way back in 1996 and it has given very good results for DTPS.

Rate of Boiler Tube Failures

00.10.20.30.4

97-'9

898

-'99

99-'0

000

-'01

01-'0

202

-'03

03-'0

404

-05

Year

TF /

1000

Hrs

DTPSNTPC

(Fig: 3)

5.0 Continuous Improvement through further Innovation:

But after year 2002 we thought of having further improvement in the boiler performance and wanted more reliabil i ty / availabil i ty. As the demand of Mumbai suburban region was growing at a faster rate, high availabil i ty and reliabil i ty of boilers at a much higher loading was becoming a necessity.

The blended coal has sti l l an ash content of @ 25% and that again causes erosion but at a lower rate. This erosion also ult imately leads to boiler tube leakage and unplanned forced outage. The use of 100 % imported coals of 1-2 % ash content is techno economically unviable as the boilers are not designed accordingly and cost of generation also would be highly subjected to cost of imported coal.

Page 4 of 24

5.1 Prevention of Erosion – Conventional Techniques:

There are prevalent industry wide practices of erosion prevention or reduction.

1. Thicker tubes 2. Shielding

But these techniques have disadvantages. All the areas of boiler are not easily approachable. Hence in such areas it is diff icult to provide shielding. Also provision of shielding in some areas would disturb the established gas flow pattern. And more f low may get directed towards newer zones making them more erosion prone. Provision of thicker tubes need to be done right at the design stage for erosion prone zones. But these would result in comparative ineff icient heat transfer process.

Hence discussions with industry experts, recommendations of OEM and our own past experiences led us to thinking about having some protective layer over the tubes exposed to highly abrasive, high temperature and high velocity ash laden flue gases.

Our past experiences and those of NTPC showed some clear trends of vulnerable zones of boiler. The boiler tubes in these zones were subjected to more erosion compared to rest of the internals. The areas may be different from one boiler to another due to different f low patterns, gas distribution, misalignments in tube rows, vicinity of soot blowers, etc. As having a protective layer over complete boiler internals would not be technically and economically feasible, the vulnerable zones of the boiler were identif ied and decided to give a protective anti erosion layer. As an improved practice to monitor vulnerable areas of the boiler, we started doing a regular extensive tube thickness survey for the boiler. The results of these surveys and failures of boiler tubes due to erosion were showing similar trends (refer Fig: 4 & 5).

Page 5 of 24

Area wise classification of Tube Failures due to Erosion

010203040506070

DTPS NTPC

% o

f Tub

e Fa

ilure

s

Water wall EconomiserSuperheaterReheter

(Fig: 4)

Tube Thickness Survey - Erosion Pattern

70

10 155

01020304050607080

Water wall Soot blowerzone

Economiser LTSH

Boiler Locations

% E

rosi

on

(Fig: 5)

Page 6 of 24

5.2 Technology of HVOF Process: Selection of the process: In market there are many technologies available for surface coating. 1. Wire Flame spray 2. Arc wire spray 3. Powder Flame spray 4. Plasma spray But, in the above-mentioned surface coating technologies, temperature used for the spraying as well as base metal temperature goes more than 600° C, which may lead to change in microstructure of the metal. 5.3 High Velocity Oxy Fuel (HVOF) Process: The process is designed to give high level of coating density and adhesion to the substrate and can handle coating materials in powder form such as tungsten carbide / cobalt, chromium carbide / nickel chrome, tr iballoy and inconel. This process gives very dense and high adhesion deposits, and has application in space, defense, chemical, petrochemical, and power generation and aircraft industries. As, in this HVOF process, temperature of base metal is not crossing more than 300 deg C, hence microstructure of the base metal is retained. Also, advantage of this process is that porosity is very low & adhesion is very good. And hence the technology of HVOF for anti erosion coating was selected. 5.4 Implementation: We have decided to replace the eroded tubes by surface coated tubes in phased manner. The reason for carrying out the replacement job in phase manner was some selective replacement could be done due to l imited time span of the O / H and it would also provide an opportunity to evaluate the performance of the coated tubes.

Page 7 of 24

Phase I: In DTPS, water wall tubes near burner panel are the most erosion prone area. Of the total number of tube leakages due to erosion, 60% occur in water wall tubes. Hence we replaced these eroded tubes by surface coated tubes during overhaul of U # 1and 2 during their respective overhauls. Cost incurred during the implementation of Phase-I was Rs 2.3 Mil l ion. Phase II: The second most erosion prone area is economiser tube. Of the total number of tube leakages due to erosion, 15% occur in economiser tubes. As above phase – 1 replacement is showing very good results, we are planning to replace eroded economiser tubes by surface coated tubes during the next proposed overhaul.

Page 8 of 24

Location of Erosion prone areas in DTPS Boiler

Reheater Coils

Radiant Roof Tubes

Eco Upper & Lower coils

Water wall burner Panels.

Steam Cooled Wall Tubes

LTSH Coils

Fig: 6

Page 9 of 24

6.0 Conclusion: From the trend shown (Fig-7) here it is very clear that there has not been a single tube leakage since 2003 in the areas where it was highly probable due to high erosion patterns observed in past. The strategy of tube coatings has helped us with improving our availabil i ty(Fig-9) and also maintaining the high loading factor(Fig-10).

Erosion Vs. Total failures

01234567

96-97

98-99

00-01

02-03

04-05

year

No.

of f

ailu

res

ErosionTotal failure

(Fig: 7) We have been able to operate DTPS units at a record availabil i ty and loading factor and maintain yearly plant loading factor at more than 100 % with lowest heat rate(Fig-8) in India since 2003-04. The resultant heat rate is lower by 2.54 % from the base value of 2320 Kcal/ KWH in 2001-02. The project of providing addit ional protection to boiler tubes in vulnerable areas can be very easily replicated across the industry. It can be applied to large util i ty boilers as well as smaller industrial boiler the benefits to the consumer would be immense as mentioned earl ier.

Page 10 of 24

Direct Benefits: (a) In case of a tube leakage DTPS looses revenues of Rs. 18 Mil l ion for this loss of generation. This loss of generation needs to be bought from external sources at a much higher rate than the generation cost of DTPS. Hence prevention of one tube leakage helps the company to continue to provide subsidy or lower tariff to retail consumers.

(b) Also start up after each tube leakage consumes on an average

1. 75 Kilo Litters oil 2. 50 Tonnes of coal

These resources are consumed without generating electricity. Hence it is a direct loss. This direct loss costs are more than Rs 1 mil l ion for DTPS. Also these processes generate addit ional green house gases. Hence prevention of one tube leakage provides benefit in terms of

1. Lower tariff to consumers 2. Lesser pollution & resource conservation to society at large

Fig: 8

Page 11 of 24

Fig: 9 Fig: 10

Page 12 of 24

(Trend Setter Project 2)

Reduction of Boiler Exit Flue Gas Temperature

The Indian power sector has always been operating in the deficit regime. The customer has been facing the brunt of the impact. The power costs and availabil i ty of quality power are the major issues for the customer. And the suppliers have been charging for availabil i ty and reliabil i ty. In the regions where players other than state electricity boards are supplying the power directly to the end user, they have been charging a premium for the consistent supply. Hence the power availabil i ty, quality and ult imately the cost are the three issues, which the customer has been dealing with to control his own costs. In India, the coal based thermal power plants are the backbone of the power generation sector. Out of total generation more than 70 % is being met by the coal based thermal plants. The soaring cost, unreliabil i ty of supply, dependency on other countries has made oil and gas power plants not viable. Almost all of existing oil and gas-based power plants are either idle or running with reduced capacity. Non-fossil / renewable energy based power is considered an alternate due to its environmentally clean power and non-exhaustive primary energy source. But commercially and economically it is not viable due to high capital investment. Hence eff iciency of the coal-based power plant plays a major role in the costs of power available for consumption. The basic coal based power generation plants operate on the modified Rankine cycle. Here there is a lot of scope for ineff iciencies. Or inversely there is a lot of scope for improvement in the operating eff iciency.

Page 13 of 24

Analysis of Boiler Efficiency: - The steam generator is the heart of any coal based thermal power station. The boiler operat ions play a major role in maintaining and improving the eff iciency of the power generation cycle and they affect the power costs. Following graph shows a breakup of design eff iciency of DTPS boiler. And the 2nd f igure shows the typical breakup of actual boiler operation for DTPS.

Figure: 1 Design losses

39%

8%4%2%

1%

46%

UNBURNT CARBON

DRY FLUE GASLOSS

WET FLUE GASLOSS

MOISTURE IN AIR

SURFACERADIATION &CONVECTIONUNACCOUNTEDLOSSES

Figure: 2 Actual losses

53%

3%2%

1%37%

4%

UNBURNT CARBON

DRY FLUE GASLOSS

WET FLUE GASLOSS

MOISTURE IN AIR

SURFACERADIATION &CONVECTION

UNACCOUNTEDLOSSES

As it can be seen from the figure that that dry & wet f lue gas losses and the unburnt carbon losses are the major losses. The efforts of DTPS O & M team were focused on these losses as the boiler eff iciency can be greatly improved by reducing these losses.

Page 14 of 24

The wet f lue gas losses are mainly dependent on the characteristic of the fuel and they cannot be controlled. While the dry f lue gas losses are controllable as they mainly depend upon

• Flue gas volume • Flue gas temperature

The innovative strategy for boiler eff iciency enhancement was implemented in two phases. 1s t phase involved control of excess air. All the boiler engineers know that every percent reduction in residual Oxygen (after air preheater) improves the heat rate by 0.3%. But this thumb rule cannot be applied blindly. The combustion of coal in huge quantity is needs a highly controlled environment for safe and eff icient result. DTPS operations concentrated in controll ing oxygen by checking CO in exit f lue gas. The investment was done in CO measurement equipment. The CO measurement also posed a great challenge not only in measurement but also in sustaining the validity of these measurements. The original location of the sensing elements, as suggested by the OEM, was highly prone to problems. Hence it was shifted to 70-meter height in the f lue gas stack. This helped in establishing the reliabil i ty of the measurement of f lue gas CO content an eventually the reduction in excess air to an acceptable level. The next step was to improve the measurement of residual Oxygen in the f lue gasses. The flue gas duct of a 250 MW boiler is huge equipment. And to control the combustion on the basis of a single point measurement of Oxygen cannot give accurate results. So to start with addit ional investments were made for procuring and commissioning addit ional Oxygen sensors. So the residual Oxygen measurement was done based on multiple sensors. DTPS boiler operators have been given a target to maintain the excess air level < 12% with CO levels at < 50PPM in hourly average as a part of their own functional level objectives. This strategy of involving desk engineers has given very good results. For the whole of last f inancial year 2005-06 the average excess air was maintained at 12.3 %. The trend of monthly average excess air as measured by online instrumentation is shown below.

Page 15 of 24

Excess Air - Monthly Average %

12.412.1

10.8

11.7

12.5

16.6

13.112.6

11.2

12.211.9

11.3

10.0

13.0

16.0

A/05 M/05 J/05

J/05

A/05 S/05 O/05 N/05 D/05 J/06

F/06 M/06

% E

xces

s A

ir

The Problem: -

The other factor affecting the flue gas losses is the temperature of exit f lue gases. For every 1 °C rise in exit f lue gas temperature the heat rate deteriorates by 1 Kcal / Kwh. Almost all the coal based thermal power stations have a problem of high exit f lue gas temperature. The APH exchanges heat between the flue gasses coming out of the boiler and gives it to primary/secondary out of the boiler and gives it to primary/secondary air. But this is not the only equipment, which affects the exit f lue gas temperature. The flue gas temperature is affected by

• Condit ion of air pre heater. • Condition of furnace heat transfer surface cleanliness • Condit ion of fuel f ir ing equipment

The problems of these equipments are generally dealt with during overhauls and rectif ied to an extent. These losses can be controlled by way of use of good O & M practices l ike

• Regular soot blowing of Air preheater • Soot blowing of furnace heat transfer surfaces by use

of water wall & long range soot blowers • Replacement of air heater baskets • Recondit ioning / replacement of coal burners • Regular cleaning of furnace

Page 16 of 24

But the problem sti l l cannot be eliminated and it becomes a part of day-to-day O & M activity. DTPS also has been facing the problem of high exit f lue gas temperature.

Analysis of the Problem at DTPS: - The following schematic diagram shows the coal mil l ing system of DTPS.

Figure 3: Coal Mill Schematic

DTPS has ball & tube type of coal mil ls for coal pulverization. These systems have a provision of special “ON / OFF” type damper for purging of PC (Pulverised coal) pipes. The basic purpose of purging dampers is to remove any residual pulverized fuel from the piping and push it into the furnace. The PC pipe purging system uses high-pressure cold primary air. This damper plays a very crit ical role in APH performance. The problem of the high f lue gas temperature had following complicated symptoms. • The heat / energy balancing of APH was showing that

the heat accounting was not proper as per the measured values.

Page 17 of 24

Figure 4 : Air Pre-Heater

• The theoretical air requirement for combustion was on higher side and actual measured air was less than the required.

• The PA fan loading was on higher side than the measured airf low.

• The oxygen (on l ine & off l ine) and CO measurements were OK and showing that the total air requirements were being properly met.

• Also the physical condit ion of the f lame as seen in the boiler and shown by the f lame monitors was ok.

After investigating it was observed that the dampers for pulverised coal pipe purging were passing. As this system is used only for a very short span of t ime, mainly during starting and shut down of coal mil l , i t did not have any airf low measurement provision. So the airf low was from this piping was not gett ing reflected in the total air measurement. But the oxygen requirements were being met with lesser amount of measured air. The rest of the airf low was being supplied from the passing of these dampers. As this airl ine was tapped from the cold primary air header, the loading of PA fans was on higher side against the measured airf low. Also as this l ine

Page 18 of 24

was bypassing the APH, the heat transfer was not taking place. And in fact, cold primary air was working l ike cold secondary air. The following thermo graphic image of the purge air duct shows the region where the cold primary air mixes with the hot pulverised fuel f lowing out of coal mil l. The marked area shows the low temperature zone where the cold air mixes with the hot PC pipe and cools it to a lesser temperature.

PC p ipes a t > 65°C

Co ld pu rge a i r p ipes 35°C

Leakage f rom purge a i r damper ` 45°C

Purge Air Damper area Thermography before modification.

Immediate / Short Term Solution for the Problem: - So first immediate step was to close the manual isolation valves provided prior to the damper. The function of these manual valves is to regulate the flow being used at the t ime of purging. The isolation of purging pipeline gave us good result, which can be seen from the following trend.

Page 19 of 24

Flue gas Temperature °C

148

147147 147

152151

155

153

146 146146

147

150

153 152

150

145145

144

146

149

150149

149

142

141 141

142

145

146 146 146

140

142

144

146

148

150

152

154

156

0 2 4 6 8 10 12 14Time of Day

Tem

pera

ture

°C

All Dampers Normal Average Flue Gas Temperature °C AB mill DampersAB & CD mill Dampers isolated AB, CD & EF mi

Figure 5: Effect of Purge Air Line Isolation

But this immediate and simple solution posed anoThe flow of hot pulverized fuel in the adjoining PCdeposit ion in the purging pipeline. Previously the was open and the purge air dampers were passing.cold & high-pressure primary air was not allowingfuel to enter the purging l ine. But now after isolatiovalves, the pulverized fuel laden air entered the il ine from the very same damper that was passing. Oabout 10 – 12 days of operation in this condit ion,coal started burning spontaneously. And we facedfire, which could have resulted in a major damaawareness of operators a major f ire was detectecontrolled.

Page 20 of 24

Al l dampers are open

151

150150

150149

149

147

149149

148

146

147

145145

144144

Al l dampers are c losed

16 18 20 22

isolatedll Dampers isolated

ther challenge. pipes caused

manual damper So the passing the pulverized n of the manual solated purging ver a period of

this deposited an incident of ge. But due to d in t ime and

But this setback was overcome by the realisation that our theory of damper passing is a reality. The damper was checked for the physical condit ion during an available opportunity and it revealed a minor gap for air to pass. To avoid another f ire, a system of monitoring of purge air duct was put in place. A handheld temperature-scanning device was used to monitor the temperature of al l the purge air piping. The strategy was also modified and closure of the manual purge damper of the mil l that was not in service was ensured. And for the rest of the mil ls the damper was kept open. This gave partial gains without affecting the reliabil i ty of operations by f ire risks.

Final Solution: -

Damaged purge a i r damper

PC p ip ing

PC P ipe

Purge A i r Damper

The OEM was referred with this problem. But the response from the OEM was such that DTPS had to l ive with the problem. As the design of f lue gas piping was such that any stoppage of purge air wil l result in pulverised coal deposit ion and eventually a f ire. This was corroborated by our own experience. Hence this design deficiency was taken up as a challenge, and our engineers came up with several solutions. 1. Provide high-pressure seal air to block primary air. This was

dropped in this would result in loading of seal air fans and

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purpose wil l not serve as instead of primary air fans, seal air fans wil l supply the addit ional air.

2. Provide a tapping of cold P.A l ike an integral bypass valve. This was also dropped as this wil l only reduce the losses but we wanted to eliminate the losses. Hence it was decided to procure an advanced class t ight shut-off gates for purging l ine. The problem of coal deposit ion was overcome by locating the damper just 100 mm away from PC pipe. This reduced the volume of the pipeline where the coal deposit ion can take place. And the tight shut-off wil l ensure that the deposited coal wil l not travel towards the cold purging l ine. The commissioning of this damper in 1st mil l has resulted in drop in temperature of f lue gas by 4°C as shown in the trend. The result is obvious that the dry f lue gas losses have reduced by 4 kcal / KWH. The thermographic image of the piping after the modification also shows the effect of the damper very clearly.

APH O/L EXIT FLUE GAS TEMP. (Avg.)

145

146

147

148

149

150

151

152

153

154

1-May

3-May

5-May

7-May

9-May

11-M

ay

13-M

ay

15-M

ay

17-M

ay

19-M

ay

21-M

ay

23-M

ay

25-M

ay

27-M

ay

29-M

ay

31-M

ay2-J

un

Ef fect of modi f ied purge a i r damper on ex i t gas temperature

F lue gas tempera tu re has inc reased a f te r m i l l changeover

F lue gas temperature is h igh as defect ive damper is in

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Hot PC p ipes >65 °C

PC p ipe to Purge a i r l i ne j o in t – No Pass ing Tempera tu re > 60°C

Mod i f i ed Damper < 35°C

Purge Air Damper area Thermography After modification.

Benefits: - The benefits of this project are very obvious. As the suggested modification directly aims to improve the temperature of the exit f lue gasses by improving the heat transfer in air preheater. The heat rate wil l improve by 10 Kcal / Kwh. This wil l result not only in the coal consumption, but also reduce the emissions of TPM, carbon dioxide – a GHG gas. The benefits are summarised in the table below.

Improvement Quantity Reduction in coal consumption By 10000 Tonnes per annum Reduction in CO2 emission 12085 T of CO2 per annum Reduction in TPM emission Reduction in 2.616 T / annum

of ash dispersion from stack Monetary benefit (Rs. 2500 /- per tonne of coal)

Rs. 25 mil l ion

Reduction in Ash generation Approximately 2899 Tonnes per annum

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Conclusion: -

For many coal based power stations the problem of chocked air heaters and resultant high exit f lue gas temperatures are chronic problems. Many captive power plants are also coal based and they also face similar problem with their air heaters. Of course the air preheater have generic nature of problems due to inherent nature of i ts constructional features. But it may also happen that entire problem may not be with the air preheater only. There may be a problem in other elements – invisible elements that are out of measuring circuits – and finding such elements and rectifying them wil l give substantial benefits. This project can be easily replicated across the power sector.

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