Energy Conservation in

Transcription

1 Energy Efficiency Summit Sep 2010, Chennai Energy Conservation in Air Compressors & Compressed Air System Mr Mahesh Puranam Life Cycle Cost For A Compressor Initial Cost 5% Maintenance Cost 5% Energy Cost 90% 1

2 National Energy Saving Potential in Compressed air systems Energy Saving Potential - Atleast 1250 MW Annual Saving Potential - Rs 2000 Crores Investment potential - Rs 3000 Crores Sample case study 1 Optimal utilization of compressors 2

3 Optimal Utilization of Compressors v Air requirement cfm normal running v In case of yarn breakage, sudden demand of 600 cfm Compressor Capacity : Screw type : 600 cfm Avg. loading : 17% (during normal running) Optimal Utilization of Compressors Action v Installed new air compressor of 125 cfm capacity for normal operation v When pressure falls in receiver, screw compressor to start automatically Annual Savings Investment Payback period : Rs lakhs : Rs lakhs : 3 months 3

4 Optimal Utilization of Compressors In sum v Size the compressor correctly v Minimize / avoid unload power consumption v Screw : Unload Power is 30-40% of load power v Recip : Unload power is 15-20% of load power Sample case study 2 Heat Recovery from the Compressors (a nylon yarn manufacturing plant) 4

5 Recover thermal energy from the heat of compression De aerator DM Tank 80 TPD K 10/11 Compressor C Heat 30 0 C Exchanger 80 0 C 80 0 C Increase the temperature of the DM water makeup to the boiler v DM water make up to the boiler -220 m 3 /day DM water is supplied for the lactam condenser cooling q Temp is increased to 85 C q 140 m 3 /day is circulated back to the deaerator Another 80 m 3 /day is directly sent to the de aerator at ambient temp Good potential to heat the DM water which is directly supplied to the De-aerator q FO savings of 200 lit/day for one compressor heat recovery 5

6 Single Acting, Two Stage Reciprocating Compressor Motor starter Inlet filter *Filter Dryer Inter cooler After cooler Pressure switch Motor Valve Relief valve Trap (Drain) Trap (Drain) Receiver Trap (Drain) heat recovery from Compressor v Heat available for removal Inter-cooler After-cooler Jacket cooling (compressor body cooling) Oil coolers v Not straight forward Design of heat recovery units can affect the performance of the compressed air system 6

7 After cooler for a 100 cfm Compressor T LMTD = 50 o C Q = 5500 kcal/hr Cooling Tower 37 o C 40 C 180 C After cooler 30 C Compressor Cooling water heat recovery from after cooler Boiler / deaerator 80 C Heat exchange area should increase by 30 % T LMTD = 39 o C Q = 5500 kcal/hr 40 C 180 C Heat recovery unit 30 C Compressor Boiler Feed Water pressure drop of compressed air across the heat exchanger should not increase 7

8 Temperature of air downstream of after/inter coolers v Maintain same temperature After cooler : In case of refrigeration driers q Other wise, power consumption will increase Intercooler reduces the compression power requirement in the subsequent stage q Other wise shaft power will increase q Capacity of compressor reduces Sample case study 3 Usage of Centrifugal compressor for compressed air generation National Best practice from Pulp & paper Industry (Hindustan Newsprint Limted, Tamil Nadu Newsprint and Papers Ltd, ITC PSPD Bhadrachalam) 8

9 TNPL integrated Paper plant v Pulp mill Bagasse Wood chips v Chemical recovery section Evaporators Recovery boiler Caustisizing section Rotary lime kiln v Paper Machines 3 nos v Finishing section Compressed air system at TNPL v One of the most expensive utilities Most systems have typical efficiencies of 15 25% v Proper selection of compressor is one of the ways of reducing energy consumption Reciprocating Rotary screw Centrifugal 9

10 Compressed air system at TNPL v Case 1 (August 2007) Centralised compressed air generation Reciprocating compressors 7 nos q Single/double stages v Case 2 (October 2007) Centralised compressed air generation Centrifugal compressors 2 nos q Three stages with intercoolers Installation at TNPL cfm (0.165 kw/cfm) (0.135 kw/cfm) Case study available in National Best Practices Manual Pulp & Paper Industry Free download from 10

11 v Benefit accrued Centrifugal compressors installation at TNPL Because of more stages (with inter-cooling) q Higher isothermal efficiency Compressor itself is efficient q higher polytropic efficiency q Lesser conversion to heat q Lesser temperature at the outlet of each stage Annual Energy Savings Investment Payback period : Rs lakhs : Rs lakhs : 18 months Performance of compressor 11

12 Standard methods available v Specific energy consumption Measure power consumed by motor q Using standard electrical measuring instrument Measure Flow of Compressed air q Online flow meters q Receiver pump up method q Nozzle test method Online flow meters v Very handy while analyzing the system v Calibration!? Should be done regularly Else they can be misleading v Not very popular as yet 12

13 Receiver Pump-up method Average Compressor Delivery = P 2 - P 1 1. V R. P Dt P 1 = Initial pressure in receiver P 2 = Final pressure in receiver P = Atmospheric pressure V R = Volume of air receiver plus connecting lines Dt = Time taken for charging the receiver from P 1 to P 2 Receiver Pump-up method v Reasonably accurate Accuracy depends on size on receiver, pressure range selected etc.. v Needs to have a compressor and receiver isolated from the main system Either Provision should be made by design or during shutdown Conduct during non-operation hours Not practical in many cases of continuous running plants 13

14 Nozzle test method v Good accuracy v Need to take the standby compressor off line A matter of concern for some plants v In one of the plants Any other method Online flow meters were available q Capacity of compressor q Meter reading q Meters were not calibrated Receiver pump up method : 3500 cfm : 4700 cfm q No provision to segregate a compressor and receiver from the rest of the system Nozzle test q Pipelines had to be modified - Time consuming q No stand by available Air Compressors consumed 1.2 MW out of 7 MW load q SEC of the compressor had to be established 14

15 Overall energy balance concept Energy balance concept v Compressed air passes through after cooler Heat exchange occurs Heat delivered by compressed air = heat picked up by the cooling water WATER INLET 30 C AIR IN 180 C AIR OUT 45 C WATER OUTLET 39 C 15

16 Energy balance concept v Heat picked up by the cooling water Measure flow of water q Using ultrasonic flow meter for fluids Measure the temperature rise of cooling water across the compressor Calculate enthalpy rise (m x C p x T) v Heat delivered by air = heat taken by CTW Measure the temperature drop of air across the compressor Calculate using the formula q Q = M air x Cp x T air Precautions for accuracy v Ensure full loading of compressor As steady pressure band as possible v Error analysis was conducted Accuracy of water flow : ±3% Accuracy of T (water / air) : 0.2 o C Accuracy of temperature of water is most crucial v Overall accuracy ± 10% Accuracy can be improved q by increasing the temp drop across the water by reducing flow of cooling water, temporarily q Multiple measurements 16

17 SEC of compressors v Importance of SEC monitoring A direct indication of efficiency of compressed air generation In case of multiple compressors, which compressor to run When to go for overhaul q Set limits 8 Eg: when SEC increases to 0.17 kw/cfm then overhaul Thank You 17

18 OVER-ALL ROAD MAP Conduct an awareness program: PAPER TECH 2007 Formation of Core working group (Paper Mills, Consultants, Equipment Suppliers) Inter plant visits and sharing of best practices Development of National Best Practices Manual - within a year Implementation by Plants June 2007 Completed Dec 2007 Completed June 208 Completed Dec 2008 Studying best practices in overseas installations International Best Practices Manual European mills studied Released in July 2009 Implementation & at-least 3 World Class paper plants - within 3 years 18

19 National Best Practices List of Mills visited (Alphabetical) 1. APPM, Rajahmundry 2. BILT, Bhigwan Unit 3. Delta Paper Mills Ltd., Vendra 4. Hindustan Newsprint Ltd., Kottayam 5. ITC PSPD, Bhadrachalam 6. JKPM, Rayagada 7. Naini Tissues Limited, Kashipur 8. Rama Newsprints and Paper Ltd. 9. Shreyans Industries Ltd. 10. TNPL, Kagithapuram 19