TECHNICAL PAPER & MODEL PRESENTED BY ASHOK SARKAR Management Consultant, Consultant – Energy.

1. MATHEMATICAL MODELLING OF TUBULAR AIR HEATERS OF KhSTPP AND UNIQUE STRATEGY FOR APH PERFORMANCE OPTIMISATION TECHNICAL PAPER & MODEL PRESENTED BY ASHOK SARKAR Management Consultant, Consultant – Energy.

2. MATHEMATICAL MODELLING OF TUBULAR AIR HEATERS OF KhSTPP AND UNIQUE STRATEGY FOR APH PERFORMANCE OPTIMISATION TECHNICAL PAPER & MODEL PRESENTED BY ASHOK SARKAR

3. APH – AN OVERVIEW • Air Pre Heater • is a heat transfer surface, for transferring heat from other media such as flue gas. • Reclaims heat from flue gas at low temperature levels than is possible with economiser, • Enhances the efficiency of the boiler. • For every 20 deg.C drop in flue exit temperature , the boiler efficiency increases by about 1%.

4. APH – TYPES & SPECIFIC USE • Regenerative or Ljungstrom (RAPH),Regenerative type Air Pre Heater; is a rotating type. This may be horizontal (now very common in power generation utilities) or vertical. • Recuperative type, • Tubular type built into the boiler outlet Flue gas ducting • Either gas or air may be designed to flow through the tubes

5. TUBULAR APHS OF KHSTPP • 4 x 210 MW Boilers, TYPE 690-13.8-540, are designed for firing of coal from Rajmahal coalfields of ECL. • This coal is having high ash content with high abrasiveness and relatively low heat value of volatile matters. • This signifies the low reactivity of the coal. • HIGH FURNACE VOLUME & HEEIGHT, SIDE WALL FIRING • One more distinguished feature of said boilers is use of tubular air heaters in place of commonly used Regenerative Air Heaters.

6. TUBULAR APH - CONSTRUCTIONAL FEATURES

7. GENERAL ARRANGEMENT OF DIFFRERENT HEAT TRANSFER SURFACES IN THE SECOND PASS

10. PROBLEMS IN GENERAL • General problems faced: • Spool piece damage: leading to increase in I.D. FAN current & loss of ID FAN margin. • Action Taken: During Overhaul, the APH tightness test is conducted, leaking tubes and eroded spool pieces are identified and are replaced. • Choking of tubes:which leads to increase in loss of margin of I.D. fan • Action taken: Cleaning of choked APH tubes are done by water jetting in lower tier & by Air jetting in Top tiers. • Leakage of Tubes: leading to increase in I.D. FAN current & loss of ID FAN margin • Action Taken: During Overhaul, the APH tightness test is conducted, leaking tubes are identified and are replaced.

11. PRESENT PRACTICE OF PERFORMANCE ASSESSMENT • Temperatures • Roadblock: The unavailability of the flue gas temperature at the APH stage-II outlet. • Boiler pressure Survey: • APH leakage Survey: • IMPROVEMENT NEEDED - WHY? • Due to unavailability of a specific temperature measurement and uniqueness of construction, • A combination of the information cited above provided a qualitative information about the APH condition. • More direct & comprehensive information regarding the APH condition, with more emphasis on quantitative aspects - NEED OF THE HOUR.

12. MATHEMATICAL MODEL – NEED & STRATEGIC TOOL FOR PERFORMANCE IMPROVEMENT • Unique Strategic tool for APH performance Improvement • Prediction of number of tubes choked; as a value addition to MIS and feedback to Mech. Maintenance • Indirect estimation of Tramp Air Ingress in the Boiler without resorting to HVT test. • Estimation of APH stage – II, outlet Flue gas temperature.

13. THE MODEL – IN BRIEF • To start with, a simplified model of the APH was made with the assumption of no or negligible fouling. • Initial roadblock was: • The unavailability of the flue gas temperature at the APH stage-II outlet. The availability of the same was necessary for any effective model. • First stage of the Economiser was placed in between APH stage – I and Stage – II. • The airflow & fluid flow calculations were arrived through flue gas analysis and excess air evaluations.

14. THE MODEL – IN BRIEF • Data required: Data required for the complete analysis by the model: • Full set of data as required for the Boiler efficiency test • Flue gas analysis, across APH., obtained through ORSAT TEST, dry gas basis. • As fired coal Analysis. • Additional Temperature measurements across the two stages of the Air Pre Heater, Air & Flue gas. • The feed water flow to economiser & feed water temperature at economiser inlet were required.

15. INPUT Configuration of APH Geometry Proximate Analysis of coal Flue gas composition at Inlet & Outlet of APH Temp. of flue gas & Air at Inlet & Outlet of APH OUTPUT Flue gas temp. at outlet of APH stage-II Effectiveness / gas side efficiency at diff. Stages Tramp Air estimate No. of tubes not taking part in Heat Transfer WHAT GOES IN & COMES OUT OF THE MODEL

16. VALIDATION OF THE MODEL - WITH DESIGN DATA

17. MORE DIRCT VALIDATION – AT SITE • RECOMMISSIONING GROUP’S APPROX. ASSESSEMENT OF THE NUMBER OF TUBES NOT TAKING PART IN HEAT TRANSFER, PHYSISCALLY; JUST AFTER STOPPING OF UNIT # 4, WAS 24.0%.

26. APPLICATION OF THE MODEL – BEFORE OVERHAUL • For assessment of number of tubes not taking part in heat transfer • which is equivalent to number of tubes, having leakage and choking • a valuable feedback to mechanical maintenance and MIS • Useful aid for overhauling preparedness

27. Quantitative assessment of number of tubes not taking part in heat transfer

28. APPLICATION OF THE MODEL – AFTER OVERHAUL • THUS IT CAN BE SEEN THAT THE MODEL USED FOR FINDING THE EFFECTIVENESS OF THE O/H. • GIVES A USEFUL FEEDBACK REGARDING THE EFFICIACY OF THE JOBS / PROCESSES UNDERTAKEN IN THE OVERHAUL. • FOR FORMULATING STRATEGIES FOR BETTERMENT OF THE SAME

30. MODEL – AN USEFUL TOOL FOR BETTER FEEL OF EQPT. • MODEL CAN BE UTILISED FOR UNDERSTANDING OBSERVATIONS & FOR DEVELOPING BETTER FEEL OF THE EQPT. • THE MODEL WAS UTILISED TO FIND AN EXPLANATION FOR SUDDEN RISE IN ID FAN CURRENT AFETR A ECONOMISER TUBE LEAK IN ONE OF THE UNITS.

32. UNIT - 3 , NUMBER OF TUBES CHOKED +LEAKING

33. TRENDING & OSERVATIONS

34. TRENDING & OSERVATIONS

35. TRENDING & OSERVATIONS

36. TRENDING & OSERVATIONS

37. TRENDING & OSERVATIONS

38. TRENDING & OSERVATIONS

39. TRAMP AIR DETERMINATION – INDIRECTLY WIHTOUT HVT TEST • AN INDIRECT WAY, FOR TRAMP AIR DETERMINATION WITHOUT ACTUALLY RESORTING TO HVT TEST, WHICH REQUIRES: • A LOT OF PHYSICAL EFFORT • PREPARATION & TIME • LIMITATION FACED: • COAL PROXIMATE ANALYSIS, SOURCE OF ERROR; WHEN COAL FROM DIFFERENT SOURCES ARE FIRED. • NEEDS VALIDATION WITH INSTRUMNETS .

40. THE MODEL PREDICTS TRAMP AIR, APPROX.

41. FORMULATION OF UNIQUE STRATEGY FOR OPTIMISATION OF APH PERFORMANCE • With the availability of the trending facility through the programme and the understanding (being developed), of the various factors responsible for choking & leakage of tubes, the rate of choking & leakage of tubes can be controlled with success to certain extent. • The same can therefore lead to substantial saving in terms of energy consumption of ID fan. Moreover, if losses in boiler efficiency due unavailability of ID fan margin is considered, the gains can be much higher. • Direct Gains: substantial saving in energy consumption of ID & FD fans • Indirect Gains: No loss of Boiler Efficiency due to loss of ID fan margin.

42. SAVINGS GENERATED - USING THE MODEL AS A TOOL • FOR A CASE, WHEN REDUCTION IN ID FAN CURRENT IS ABOUT 30 Amps. AND THE SAME IS MAINTAINED OVER THE YEAR, USING THE MODEL AS A TOOL, CAN BE • 0.4 MU PER MONTH • RS 8.0 LAKH PER MONTH IN ONE UNIT. • INDIRECT GAIN, NO LOSS OF BOILER EFFICIENCY DUE TO LOSS OF ID FAN MARGIN.

43. SUGGESTIONS & QUERIES ARE WELCOME THEY WILL ONLY ENRICH THE MODEL

44. THANK YOU FOR PATIENT LISTENING