NTPC (DOC) by RaghothamNandam

VIEWS: 702 PAGES: 36

       The Simhadri Thermal Power Plant, Visakhapatnam is the first coastal coal fired
thermal power project of NTPC. The capacity of the NTPC Simhadri is 1000MW
(2*500). This plant is operating on Modified Rankine Cycle. The main components of
Rankine Cycle are Boiler, Turbine, Condenser and a pump.

       The primary objective of the air pre heater or air heater is to increase the thermal
efficiency of the process. The purpose of the air pre heater is to recover heat from the
boiler flue gas, which increases the thermal efficiency of the boiler by reducing the useful
heat lost in the flue gas. For every 200 C drop in the flue gas exit temperature, the boiler
efficiency increases by 1%.

       Air heater performance procedure provides a systematic approach for conducting
routine air heater performance tests on tubular and rotary regenerative air heater. Various
performances indices like air heater leakage, gas-side efficiency, x-ratio etc can be
determined using this procedure.

                                           1. NTPC
1.1 Introduction
        NTPC was incorporated in 1975. In the last 30 years, it has grown into the largest
power utility of India. NTPC is the sixth largest thermal power generator in the World
and the Second most efficient utility in terms of capacity utilization based on data of
1998. NTPC delivers power at minimal environment cost, and achieves it. Right from the
stage of its project conceptualization, technology selection to operations, care is taken to
preserve the natural ecology and minimize environmental impact.

        NTPC comes to the rescue of about 20 million units of power consumed even
day in Visakhapatnam. NTPC Simhadri is providing the ever growing power needs of
A.P. the total power generation capacity of NTPC has reached to 3600 MW in A.P with
NTPC Ramagundam already generating 2600 MW a day. Location of Simhadri project is
near Parawada Village, Visakhapatnam District A.P.

        Coal is being drawn from Mahanadi Coal Fields in Orissa drawing over 5 million
tons of coal every year. The Coal comes to the plant with a rail fine. The water intake for
the plant for cooling is done by sea water drawn from 8.9 km away from Bay of Bengal
through an intake well sized 9100 m3/hr. The plant also gets sweet water from the Eluru
canal. The power generated at NTPC Simhadri is bought by A.P. Transco- the power
distribution arm of the electricity board in the state. The height of chimney is 275 meter-a
record in Asia for being the tallest factory chimney. Near to this there are two 165 meter
cooling towers. The intake well is again the biggest well constructed in the entire India.
The National Thermal Power Corporation (NTPC) Simhadri plant has generated 7000
million units so far during the last financial year at a plant load factor of 92.7%.
1.2 Unique Features of NTPC

   First costal-based coal fired thermal power plant of NTPC.

   Biggest seawater intake-well in India.

   Use of seawater for condenser cooling and ash disposal.

   Asia‟s tallest natural cooling towers and 6th in the world 165m.

   Use of fly ash bricks in the construction of the buildings.

   Coal based plant of NTPC whose entire power is allocated to home state(A.P).

   Use of Monitors as Man Machine interface (MMIs) for operating the plant.

   Use of Process Analysis, Diagnosis and Optimization (PADO) for the 1st time.

   Flame analysis of boiler by dedicated scanners for all coal burners.

   Boiler mapping by Acoustic Pyrometers.

   Use of Distributed Digital Control and Management Information System

   Totally spring loaded floating foundation for all major equipment including
    transformers generator.

   Use of INERGEN as fire protection system for the 1st time in NTPC.

   Commissioning of 1st unit in record 39 months.
1.3 Facts about NTPC- Simhadri

Govt. approved date                         24.07.1997(Zero date 08.07.1997)

Plant Capacity                              1000MW

Plant configuration                          2 * 500MW

Land availability                            3384.24 acres

International assistance                     32.011 Billions (JBIC)
                                             Japan Bank for International

Approved investment                          Rs.3650.79 Cr

Source of finance                            JBIC loan and Internal Resources

Associated transmission system               Being executed by APSEB

1.4 Basic Power Plant Cycle

       The thermal (steam) power plant uses a dual (vapor + liquid) phase cycle. It is a
closed cycle to enable the working fluid (water) to be used again and again. The cycle
used is “Rankine Cycle” modified to include super heating of steam, regenerative feed
water heating and reheating of steam as shown Fig.1.
       On large turbines, it becomes economical to increase the cycle efficiency by using
reheat, which is a way of partially overcoming temperature limitations. By returning
partially expanded steam to reheat, the average temperature at which heat is added and
increased by expanding this reheated steam to the remaining stages of turbine. For
regenerative system, numbers of non-regulated extractions are taken from HP, IP turbine.
Regenerative heating of the boiler feed water is widely used in modern power plants, the
effect being to increase the average temperature at which heat is added to the cycle, thus
improving the cycle efficiency.
                                 Figure 1:Power Plant Cycle

1.5 Basic functioning of NTPC:

1.5.1 Coal to Steam

       Coal from the wagons is unloaded in the coal handling plant. The coal is
transported up to the raw coal bunkers with the help of belt conveyors. Coal is
transported to bowl mills by coal feeders the coal is pulverized in the bowl mills, where it
is ground to a powdered form. The mill consists of a round metallic table on which coal
particles fall. This table is rotated with the help of a monitor. There are three large steel
rollers which are spaced 1200C apart. When there is no coal, these rollers does not rotate
but when the coal is fed to the table it packs up between roller and the table this forces
the rollers to rotate. Coal is crushed by the crushing action between the rollers and the
table. This crushed coal is taken away to the furnace through coal pipes with the help of
hot and cold air mixture from Primary Air fan. Primary Air fan taken atmospheric air, a
part of which is sent to air pre heaters for heating while apart goes directly to the mill for
temperature control. Atmosphere air from forced draught (F.D) fan is heated in the air
heaters and sent to the furnace as combustion air.

                               Fig. 2: Overview of the cycle

       Water from the boiler feed pump passes through economizer and the boiler drum
water from the drum passes through down comers and goes to bottom ring header. Water
from the ring header is divided to all four sides of the furnace. Due to heat and the
density difference the water rises up in the water wall tubes. Water is partly converted to
steam as the furnace is heated. This steam and water mixture is again taken to the boiler
drum where the steam is separated from water. Water follows the same path while the
steam is sent to superheating. The super heaters are located inside the furnace and the
steam is super heated (540oC) and finally it goes to turbine.
       Flue gases from the furnace is extracted by induced draft fan, which maintains
balance Draft in the furnace (-5 to -10mmwc) with forced draft fan. These flue gases
emits their heat energy to various super heaters in the pant house and finally passes
through air pre heaters and goes to electrostatic precipitator where the ash particles are
       Electrostatic precipitator consists of metal plates which are electrically charged.
Ash particles are attracted on to these plates, so that they do not pass through the chimney
to pollute the atmosphere. Regular mechanical hammers blows cause the accumulation of
ash to fall to the bottom of the precipitator where they are collected in a hopper for
disposal. This ash is mixed with water to from slurry and is pumped to ash pond.

1.5.2 Steam to mechanical energy

       Steam from the control valves enters the high pressure cylinder of the turbine,
where it pass through a ring of stationary blades fixed to cylinder wall. These acts as a
nozzle and direct the steam into a second ring of moving blades mounted on the disc
secured to the turbine shaft. The stationary and moving blades together constitute a stage
of the turbine and in practice many stages are necessary. The steam passes through the
each stage in turn until it reaches the end of the high pressure cylinders and in its passage
some of its heat energy is changed into mechanical energy.

       The steam leaving the high pressure cylinder goes back to the boiler for reheating
and returns by a further pipe to the intermediate pressure cylinder. Here it passes through
another series of moving blades. Finally the steam is taken into low pressure cylinders,
each of which it enters at the center flowing outwards in opposite directions the rows of
Turbine blades. This arrangement is known as double flow to the extremities of the

1.5.3 Mechanical energy to Electrical energy

       The turbine shaft is coupled directly to generator, where the mechanical energy is
gets converted to electrical energy. A two pole generator with cooling for stator winding
and hydrogen cooling for rotor winding is used. A generator essentially consists of stator,
stator frame and shielded stator winding, hydrogen coolers, rotor, rotor shaft, rotor
Winding rotor retaining rings, field connections, bearing shaft seals.
                                  2. AIR PRE-HEATER

       An air pre heater or air heater is a general term to describe designated to heat air
before another process with the primary objectives of increasing the thermal efficiency of
the process. Air heater is a heat transfer surface in which air temperature is raised by
transferring heat from other media such as flue gas. Since air heater can be successfully
employed to reclaim heat from flue gas at low temperatures than is possible with
Economizer, the heat rejected to chimney can be reduced to higher extent thus increasing
the efficiency of the boiler. For every 200C drop in the flue gas exist temperature, the
Boiler efficiency increases by about 1%.
       The purpose of air pre heater is to recover the heat from the flue gas which
increases the thermal efficiency of the boiler by reducing the useful heat lost in the flue
gas. As a consequence, the gases are also sent to the flue gas stack at a lower temperature,
allowing simplified design of the ducting and the flue gas stack. It also allows control
over the temperature of gases leaving the stack.
       The most common way to preheat the air is with a heat exchanger on the flue
exhaust. The heat exchanger can be either air-air or air-liquid-air. The design of air pre
heaters today requires weighing often, conflicting demands for high heat transfer, small
pressure drop, reduced fouling, and ease of cleaning. The schematic representation of air
and flue gases path is shown.
                            Fig:3 Air and flue gases path


Air heaters can be classified as:

                 a) Recuperative air heaters

                 b) Regenerative air heaters

       In recuperative type, heating medium is on one side and air is on the other side of
the tube or plate and heat transfer is by conduction through the material which separates
the media.
       In regenerative type, the heating medium flows through a closely packed matrix
to raise its temperature and then air is passed through the matrix to pick up the heat.


These are further classified as follows:

               i.   Tubular air heater

             ii.    Plate type air heater

             iii.   Steam type air pre heater

       This is usually consists of large number of steel tubes of 40 to 65 mm dia. either
welded or expanded into the plates at the end. Either gas or air will be designated to flow
through the tubes. Gas through the normally requires higher size tubes and vertical flow
to reduce fouling. Air heater portion at low temperature is designated normally with a
shorter tube length so as to facilitate maintenance of surface due to corrosion and fouling.
In some cases instead of using boiler flue gases, separate external firing is used
particularly during starting.

                                Fig:4 Tubular Type Air Preheater

       These comprise of parallel plates which provide alternate passage for air and gas.
This type is simple and compact compared to that of tubular type. The narrow passes
between plates make the cleaning tedious but with shot cleaning method it is improved.
But replacement is a major task.

                                Fig5: Plate Type Air Heater


       This does not utilize the heat from the boiler flue gas and hence does not improve
boiler efficiency. Normally this is used only during starting when flue gas temperature
entering the regular air heater is low and hence further heat extraction is not possible and
low temperature corrosion prevails.
   b) Regenerative air heaters

       There are two types of regenerative air pre-heaters:

              I.   Rotating-plate regenerative air pre-heaters (RAPH)

             II.   Stationary-plate regenerative air pre-heaters (Rothmuhle)

   I. Rotating-plate regenerative air pre-heaters (RAPH)

       The rotating plate regenerative air pre-heaters are classified as follows:

              i.   Ljungstrom or bi-sector type regenerative air heater

             ii.   Tri-sector type regenerative air heater

            iii.   quad-sector type regenerative air heater

   i. Ljungstrom Regenerative Air Heater

       The Ljungstrom regenerative air heater is more widely used than any other type of
heat exchanger for comparable services in the steam generating industry. The reasons for
this world wide acceptance are its high thermal effectiveness, proven performance and
reliability, effective leakage control, compactness of its design, and its adaptability to
most any fuel burning process. Simplicity of the design also makes it easy and
economical to maintain in operation and scheduled outages.
   ii. Tri-sector type regenerative air pre heater

       The design has three sectors- one for the flue gas, one for the primary air that
dries the coal in the pulverizer, and one for the secondary air that goes to the boiler for

                                   Fig6: Tri-Sector Type
   iii. Quad-sector type

       This type of air pre-heater is a further development of the tri-sector type. The
secondary air section is divided in to two sections embracing the primary air section. The
advantages of the quad sector type compared with the tri-sector is reduced leakage. The
quad-sector takes the family one step further, with four flow streams through the rotor.

                                 Fig7: Quad Sector Type
    II. Stationary-plate regenerative air pre-heater

        This type is same as Ljungstrom except that the matrix element is stationary and
the air or gas hoods rotate again axis of rotation may be horizontal or vertical. The
heating plate elements in this type of regenerative air heater are also installed in a casing,
but the heating plate elements are stationary rather than rotating. Instead the air ducts in
the pre-heater are rotated so as to alternatively expose sections of the heating plate
elements to the up flowing cool air. As indicated in the adjacent drawing, there are
rotating inlet air ducts at the bottom of the stationary plates similarly to the rotating outlet
air ducts at the stationary plates. These are also known as Rothemuhle pre-heaters.

                        Fig8: Typical stationary plate air pre-heaters

          In NTPC-Simhadri plant we are using Bi-sector type air pre-heater
                           3. ADVANTAGES OF AIR HEATERS

       In addition to increase the boiler efficiency the other advantages are:

      Stability of combustion is improved by the use of hot air.

      Intensified and improved combustion.

      Permitting to burn poor quality coal.

      High heat transfer rate in the furnace and hence lesser heat transfer area

      Less number of unburnt fuel particles in flue gas, there by combustion and boiler
       efficiency is improved.

      Intensified combustion permits faster load variation and fluctuation.

      In case of pulverized coal combustion, hot air can be used for drying the coal as
       well as for transporting the pulverized coal to burners.

                            4. ELEMENTS OF AIR PREHEATERS


       The heating elements are a compact arrangement of formed metal sheets
contained in the rotor in two/more layers. The bracketed elements at the cold end, where
air is admitted and flue gases are discharged, can be removed through and access door in
the air pre-heater housing without disturbing sealing members of the pre-heater
components. When one edge of the cold end element has thinned to approximately 1/3 rd
of its original thickness, the basket can be reversed for extended element life. Similarly,
when the top edge of the hot end elements close to the rotor periphery have eroded
resulting in loss of height by 50mm, the baskets can be reversed. Special care should be
taken to see that the heating elements remain free from the deposits buildup, particularly
during start up periods.

4.2 Oil circulating systems

       The oil circulating systems are designed to supply the bearing with a bath of
continuously cleaned oil at proper viscosity. To accomplish this, the bearing oil is
circulated by means of a motor driven pump through an external filtering system. The
system components consist of pump, motor, thermometer, pressure gauge coolers and
filters. The oil selected must have a minimum viscosity of 100ssu at maximum of
operating temperature.

4.3 Sealing systems

       Seals are provided at both ends of air pre-heaters to minimize leakage between the
air side and gas side.
The various sealing systems used are:

           a. Radial sealing system

           b. Axial sealing system

           c. Circumferential sealing system

           d. Shaft sealing system

                                 Fig9: Sealing System
4.3(a) Radial sealing system

        The function of the radial sealing system is to minimize the leakage from the air
side to the flue gas side. The radial seals are arranged between the rotor and the sector
beams both at the top and bottom comprises a horizontally spaced construction that is
suspended from the sector beams via movable rod system.

4.3(b) Axial sealing system

        The function of the axial sealing system is to minimize the leakage from the air
side to the flue gas side. The seals are mounted vertically in the rotor housing in the
sector beams at the top and in the bottom and from the sealing between rotor housing and
and vertical sealing ribs on the rotor shell.

4.3(c) Circumferential sealing system

        The function of the Circumferential sealing system is to minimize the by-pass air
and flue gas flows around the rotor with out heat exchanger with the exchanger elements.
The circumferential seal are mounted on the external encircling console in the rotor
housing at the upper rim and lower rim of the rotor periphery.

4.3(d) Shaft sealing system

        The shaft seals are mounted above and below the rotor at the shaft penetration for
guiding and supporting shaft in the sector beams. Each shaft seals comprise housing with
three sealing rings that “Swim” in the sealing housing to allow certain moment between
the sector beams and the rotor shafts.
                            5. ADDITIONAL CONSIDERATIONS
5.1 Lubrication

        All Air pre-heaters support and guide bearings are both lubricated regardless of
whether are not a circulating system is provide. The purpose of circulating system is for
viscosity control of filtering oil.
The lubricating oil used must meet the following specification

           High quality well refined petroleum oil.
           Non-corrosive to gears, ball, roller or sleeve bearings and free from dirt and
           Good de-foaming properties and good resistance to oxidation.
           Straight mineral type.

5.2 Cleaning devices

        Cleaning devices is provided at the cold end gas side to remove soot deposits on
the heating elements. Single nozzle or twin nozzle is used to cleaning devices. The
effective cleaning action will not be obtained if the pressure too low. For normal
operation the recommended pressure is 14 kg/sq cm at 1500 C superheat for steam and
6.4 kg/sq cm for compressed air with the inlet valve wide open.

5.3 Water washing of air pre-heater

        In cases when the residual deposit accumulations cannot be removed readily by
soot blowing, it sometimes becomes necessary to water wash the heating surfaces to
maintain acceptable draft losses through air pre-heater. In some insistences, this may be
required more frequently than during the scheduled boiled out stages. Most deposit
accumulations forming on the air pre-heater heat transfer surface are highly soluble in
water and therefore, are easily removed by washing provided by washing provided a
sufficient quantity of water is used.

5.4 Water Sources

        Fresh water is ordinarily used air pre-heaters. The most commonly used sources
of water for washing air pre-heaters are rivers, lakes, ponds although well water and
house service water also used extensively.
5.5 Pre-Commissioning Checks

      Check gas inlet, gas outlet, air inlet and air outlet to air pre-heater to find whether
       expansion bellows are provided and temporary shipping braces of such bellows
       removed and ready for operation. And duct weights should not bare upon pre-
       heater flanges.
      Check whether the pre-heater is insulated properly.
      Check all the instruments connected at air pre-heater terminal to measure
       pressure, temperature, oxygen etc, are working conditions
      Check all the electrical wiring to pre-heater installation is properly made and
       require supply voltages are available at the terminals.
      Check steam supply to air pre-heater soot blower is connected properly and
      Check water washing manifolds are connected to the piping system properly.
      Check the drainage facility also.
                                   6. AIR PRE-HEATER FIRES
       Air pre-heater fires are rear. A fire may occur during cold start up on oil or start-
up following hot stand-by because of poor combustion of oil fuel. The improper
combustion results in burnt or partially burnt oil condensing and depositing on the air
pre-heater increases, this deposit is baked to a hot varnish like material. These deposits
can ignite as temperature increases to 315-370 oC range. If this ignited deposit remains
undetected it will continue to generate heat until he metal heat transfer element reaches
730-7650C. At this point, metal may ignite with temperatures reaching 16500C and higher
in a matter of minutes.

6.1 Fire Sensing Devices

       The primary purpose of this accessory to the air pre-heater is to detect small areas
of hot metal surfaces with in the rotating heating elements.
       Types of hot spot detectors
               a. Thermocouples
               b. Ultra violet detector
               c.   Infra red systems

6.2 Requirements of a fire detector

              Rapid response time.
              Ability to discern metal temperature not more than 150 0C above the
              Heating element metal temperature under normal conditions.
              Ability to detect small fires that are deep with in the heating element pack.
              High reliability.
              Ease of installation on existing as well as new air pre-heaters.
              Simplicity of maintenance and servicing.
              Ability to provide signal for operating personal and monitor the entire
               rotating surface.
                                7. Maintenance
       This section contains the procedure necessary to maintain the air pre-heater in
proper condition. The following precautions should be observed before and maintenance
on the air pre heaters. Precautions before maintenance
      Obtain a work permit.
      Ensure that the air pre-heater is electrically isolated and will remain isolated while
       maintenance is being performed.
      Open inspection and access doors from the ducts to ensure adequate ventilation.
      Check for poisonous gases.
      Ensure that the air pre-heater is adequately cooled down.
      Ensure that the supplies to the soot blowers and water washing devices are shut-
       off and will remain off .
      A check must be kept on the oil temperature in the bearing housing when the air
       pre-heater is running with no oil circulation.
      Check air inlet dampers are closed in primary and secondary.

7.1 Precautions after maintenance
      Ensure that all tools and extraneous equipment are from air pre-heater.
      Check that any components, which have been serviced, are properly re-lubricated.
      Rotate the rotor slowly by air motor for one complete revolution to prove freeness
       of rotation.
      Secure all access and inspection doors
      Ensure all electrical power is restored.

7.2 Air Pre-Heater Performance Test

       This procedure provides a systematic approach for conducting routine air heater
performance tests on tubular and rotary regenerative air heater. Various performance
indices like
       1. Air heater leakage
       2. Gas side efficiency
       3. X-ratio
can be determined using this procedure.
   1. To determine air pre-heater performances indices-leakage, gas-side efficiency and
   2. To provide information for performance analysis and identify the causes of
       performance degradation.
   3. To cross-check the readings of online instruments around air heaters.

                               8. TEST PROCEDURE

8.1 Test set up-operating conditions of test runs
       The operating conditions of each test run are as follows.
      No furnace or air heater soot blowing is done during the test.
      Unit operation is kept steady for at least 60 minutes prior to the test.
      Steam coil air heaters (SCAPH) steam supply is kept isolated and gas re-
       circulation dampers if any, are tightly shut.
      No mill change over is done during the test.
      All air and gas side dampers positions should be checked and recorded.
      The test is abandoned in case of any oil support during the test period.
      Eco hopper de-ashing or bottom hopper de-ashing is not done during the test.
      Regenerative heaters should be in service with normal drip cascading.

8.2 Test duration
       The test run duration will be the time required to complete two transverse for
temperature and flue gas analysis. Two separate test crews should sample the gas inlet
and outlet ducts simultaneously.
8.3 Measurement locations

       The number and type of instruments required for conducting this test depend on
the unit being tested. The following table lists the measurement locations.

Measurement                   Temperature Gas Analysis              Pressure

AH Gas Inlet                  Yes            Yes                      Yes

AH Gas outlet                 Yes            Yes                      Yes

AH Air Inlet                  Yes                                      Yes

AH Air Outlet                 Yes                                      Yes
                                 9. AIR HEATER PERFORMANCE INDICES

9.1 Air Heater Leakage
         Air heater leakage is expressed as a percentage of gas flow entering the air heater.
It‟s determined by following equation.
         AIR HEATER LEAKAGE (AH) = {(CO2 ge-CO2 gl)/CO2 gl}*100
         CO2 ge = % CO2 in gas entering air heater
         CO2 gl = % CO2 in gas leaving air heater
         Alternatively, the air heater leakage may also be determined from the following

AIR HEATER LEAKAGE (AH) = {(CO2 gl-O2 ge)/(21-O2 gl}*100O2 gl}*100

         O2 gl = % O2 in gas entering air heater

         O2 ge = % O2 in gas leaving air heater

         Air heater leakage dilutes the flue gases and lowers the measured exit gas

temperature. Gas outlet temperature corrected to no leakage condition is calculated using

the formula.

         Tgnl    = {AL*Cpa*(Tgl-Tae)/(100*Cpg)}+Tgl


         Tgnl   =    Gas outlet temperature corrected to no leakage.

         Cpa    =    The mean specific heat between Tae and Tgl

         Tae    =    Temperature of the air entering air heater

         Tgl    =    Temperature of the air leaving air heater

         Cpg    =    Mean specific heat between Tgl and Tgnl
9.2 Air Heater Gas-Side Efficiency

         Air heater gas-side efficiency is defined as the ratio of the temperature drop,

corrected for leakage, to the temperature head, expressed as a percentage. Temperature

Drop is obtained by subtracting the corrected gas outlet temperature from the gas inlet

temperature. Temperature head is obtained by subtracting air inlet temperature from the

gas inlet temperature. The corrected gas outlet temperature is defined as the outlet gas

temperature calculated for „No Air Heater Leakage‟.

   Gas-side efficiency ( GSE):

         GSE          = (temperature drop/ temperature head)*100

         GSE          = {(Tgl-Tgnl)/(Tge-Tae)}*100


         Tae      = Temperature of the air entering air heater

         Tgnl     =     Gas outlet temperature corrected to no leakage.


         Air heater X-ratio is the ratio of heat capacity of passing through the air heater to
the heat capacity of the flue gas passing through the air heater and is calculated using the
following formula.

     AIR HEATER X-RATIO                 =     (WAIR OUT *Cpa)/(W gas in*Cpg)

     AIR HEATER X-RATIO                 = (Tgas in-Tgas out (no leakage))/(Tair out Tair in)

Flue gas temperature drop across air heater

         The difference of flue gas temperature at air heater inlet and outlet.

Air Side Temperature Rise

         The difference of air temperature at air heater inlet and outlet.

10.1 For Primary Air Pre-Heater-A

      PARAMETER                         UNIT        DESIGN       ACTUAL
                                                    VALUES       VALUES

AIR INLET TEMPERATURE                       C        36            39.36

AI OUTLET TEMPERATURE                       C       318           320.13

FLUE GAS INLET TEMPERATURE                  C        343          368.38

FLUE GAS OUTLET TEMPERATURE                 C        125          139.91

AIR DIFFERENTIAL PRESSURE               mmwc           47          49.61

FLUE GAS DIFFERENTIAL PRESSURE          mmwc           90          100.6

OXYGEN AT FLUE GAS INLET                        %         3.50     3.58

OXYGEN AT FLUE GAS OUTLET                       %         5.35     5.71
10.2 For Primary Air Pre-Heater- B

      PARAMETER                      UNIT        DESIGN    ACTUAL
                                                 VALUES    VALUES

AIR INLET TEMPERATURE                    C        31        37.08

AI OUTLET TEMPERATURE                    C        318       317.93

FLUE GAS INLET TEMPERATURE               C        343       369.28

FLUE GAS OUTLET TEMPERATURE              C        125      134.15

AIR DIFFERENTIAL PRESSURE            mmwc          47       56.44

FLUE GAS DIFFERENTIAL PRESSURE       mmwc           90      110.25

OXYGEN AT FLUE GAS INLET                     %      3.50     3.60

OXYGEN AT FLUE GAS OUTLET                    %      5.35     5.63
10.3 For Secondary Air Pre-Heater-A

      PARAMETER                       UNIT        DESIGN       ACTUAL
                                                  VALUES       VALUES

AIR INLET TEMPERATURE                     C       31           30.48

AI OUTLET TEMPERATURE                     C       317          355.7

FLUE GAS INLET TEMPERATURE                C        343         390.73

FLUE GAS OUTLET TEMPERATURE               C        125         142.18

AIR DIFFERENTIAL PRESSURE             mmwc             41        55.73

FLUE GAS DIFFERENTIAL PRESSURE        mmwc              90       103.82

OXYGEN AT FLUE GAS INLET                      %         3.50     3.52

OXYGEN AT FLUE GAS OUTLET                     %         4.85      5.13
10.4 For Secondary Air Pre-Heater- B

      PARAMETER                        UNIT        DESIGN       ACTUAL
                                                   VALUES       VALUES

AIR INLET TEMPERATURE                      C       28           30.44

AI OUTLET TEMPERATURE                      C       317          351.68

FLUE GAS INLET TEMPERATURE                 C        343          376.02

FLUE GAS OUTLET TEMPERATURE                C        125          141.08

AIR DIFFERENTIAL PRESSURE              mmwc          41          55.66

FLUE GAS DIFFERENTIAL PRESSURE         mmwc             90       105.73

OXYGEN AT FLUE GAS INLET                       %         3.50      3.42

OXYGEN AT FLUE GAS OUTLET                      %         4.85      5.02
                                 11. RESULTS

               The following results are obtained from the above observations

11.1 For Primary Air Pre-Heater-A

               Description                 Units    Design values   Actual values

       Air heater leakage                       %        11.82            13.93

Air heater gas side efficiency                  %        67.75           65.39

       Air heater X- ratio                               0.7376         0.7663

Flue gas temperature drop across
       Air heater                               C        218             235.13

Air side temperature rise                       C        282            280.85
   11.2 For Primary Air Pre-Heater-B

               Description             Units    Design values   Actual values

       Air heater leakage              %            11.82           13.207

Air heater gas side efficiency         %           67.75           67.11

       Air heater X- ratio                         0.7376          0.7938

Flue gas temperature drop across
       Air heater                          C         218            235.13

Air side temperature rise                   C       287             280.85
11.3 For Secondary Air Pre-Heater-A:

               Description             Units   Design values   Actual values

       Air heater leakage                  %       8.359           10.144

Air heater gas side efficiency             %       67.479           66

       Air heater X- ratio                         0.736           0.7311

Flue gas temperature drop across
       Air heater                          C       218             248.55

Air side temperature rise                  C      286.77           321.24
11.4 For Secondary Air Pre-Heater-B

               Description            Units   Design values   Actual values

       Air heater leakage             %          8.359             10.01

Air heater gas side efficiency        %         66.76              64.93

       Air heater X- ratio                       0.727             0.698

Flue gas temperature drop across
       Air heater                         C       218             234.94

Air side temperature rise                 C       289             321.24

        From the above tabulated values it indicates that the actual air heater leakage is
more when compared with the designated values. The air heater leakage is an indication
of the condition of the air heater seals.

       The following books we referred to analyze the project:

13.1 BOOKS

1.   POWER PLANT ENGINEERING                           P.K.NAG

2. POWER PLANT ENGINEERING                             ARORA & DOMKUNDWAR

3. AIR PRE-HEATER MANNUAL                               NTPC-SIMHADRI

4. POWER PLANT ENGINEERING                              R.K.RAJPUT

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