Compressed air and refrigeration system

3,779 views

Published on

Published in: Business, Technology
1 Comment
4 Likes
Statistics
Notes
No Downloads
Views
Total views
3,779
On SlideShare
0
From Embeds
0
Number of Embeds
4
Actions
Shares
0
Downloads
272
Comments
1
Likes
4
Embeds 0
No embeds

No notes for slide
  • A reciprocating compressor is a positive displacement machine that uses a piston contained within a cylinder to produce compression. The piston traverses the cylinder, sucking in atmospheric air at one end of its stroke, then compressing the air when it reaches the other end of its stroke. This type of machine is available as an 'oil-free' compressor or as a 'lubricated' compressor.The reciprocating compressor probably accounts for largest number of compressors used worldwide
  • A screw compressor is a positive displacement machine that uses a pair of intermeshing rotors instead of a piston to produce compression. The rotors comprise of helical lobes affixed to a shaft. One rotor is called the male rotor and it will typically have four bulbous lobes. The other rotor is the female rotor and this has valleys machined into it that match the curvature of the male lobes. Typically the female rotor will have six valleys. This means that for one revolution of the male rotor, the female rotor will only turn through 240 deg. For the female rotor to complete one cycle, the male rotor will have to rotate 1 1/2 times. Screw compressors are available as oil-free machines, oil-lubricated machines and more recently as water lubricated machines.
  • As mentioned earlier, we can see the difference in power consumption between various cooling mediums. The lower the temperature to be attained the higher is the power consumption.
  • Energy savings in refrigeration needs application of common sense. The first thing to look for is in the process. There may be a stream which is cooled from 50 O C to 25 O C. In this case the stream can first be cooled by cooling water upto say 30 O C and further cooling can be effected by chilled water. Chilled water is costlier than cooling water. There could also be process streams to be cooled and other stream requiring heating. In such cases proces to process heat exchange can reduce chilled water requirements as well as steam. Similarly in an air conditioning application, minimising/ eliminating unwanted loads can bring down energy consumption. Once load reduction options have been explored, we can move to refrigeration plant to try and optimise the system.
  • Compressed air and refrigeration system

    1. 1. ENERGY EFFICIENCY IN ELECTRICAL Utilities D.PAWAN KUMAR
    2. 2. ENERGY EFFICIENCY IN COMPRESSED AIR SYSTEM
    3. 3. Air Is Free !!! Compressed Air Is Free !!! Not
    4. 4. <ul><li>Compressed Air Efficiency: </li></ul><ul><ul><li>60 to 80% of the power of the prime mover is converted into an unusable form of energy (HEAT) </li></ul></ul><ul><ul><li>And to a lesser extent, into friction, misuse and noise </li></ul></ul>Approximately 10% gets to the point of use!!
    5. 5. A TYPICAL COMPRESSED AIR SYSTEM
    6. 6. COMPRESSOR FAMILY TREE
    7. 7. TYPES OF AIR COMPRESSORS <ul><li>There are three basic types of air compressors: </li></ul><ul><ul><li>Reciprocating (Recip) </li></ul></ul><ul><ul><li>Rotary Screw (Screw) </li></ul></ul><ul><ul><li>Rotary Centrifugal (Centrifugal) </li></ul></ul><ul><li>These types are further defined by: </li></ul><ul><ul><li>the number of compression stages </li></ul></ul><ul><ul><li>method of cooling (air, water, oil) </li></ul></ul><ul><ul><li>drive method (motor, engine, steam, other) </li></ul></ul><ul><ul><li>how they are lubricated (oil, oil-free) </li></ul></ul><ul><ul><li>packaged or custom-built </li></ul></ul>
    8. 8. RECIPROCATING COMPRESSOR
    9. 9. STAGES OF RECIPROCATING COMPRESSOR
    10. 10. STAGES OF RECIPROCATING COMPRESSOR
    11. 11. SCREW COMPRESSOR
    12. 12. CENTRIFUGAL COMPRESSOR
    13. 13. GENERAL SELECTION CRITERIA FOR COMPRESSORS
    14. 14. SYSTEM COMPONENTS <ul><li>Intake Air Filters : Prevent dust and atmospheric impurities from entering compressor. Dust causes sticking valves, scored cylinders, excessive wear etc. </li></ul><ul><li>Inter-stage Coolers : Reduce the temperature of the air (gas) before it enters the next stage to reduce the work of compression and increase efficiency. They can be water-or air-cooled. </li></ul><ul><li>After Coolers : Reduce the temperature of the discharge air, and thereby reduce the moisture carrying capacity of air. </li></ul><ul><li>Air-dryers : Air dryers are used to remove moisture, as air for instrument and pneumatic equipment needs to be relatively free of any moisture. The moisture is removed by suing adsorbents or refrigerant dryers, or state of the art heatless dryers. </li></ul><ul><li>Moisture Traps : Air traps are used for removal of moisture in the compressed air distribution lines. They resemble steam traps wherein the air is trapped and moisture is removed. </li></ul><ul><li>Receivers : Depending on the system requirements, one or more air receivers are generally provided to reduce output pulsations and pressure variations. </li></ul>
    15. 15. AIR DISTRIBUTION SYSTEMS <ul><li>The air distribution system links the various components of the compressed air system to deliver air to the points of use with minimal pressure loss. </li></ul><ul><li>The specific configuration of a distribution system depends on the needs of the individual plant, but frequently consists of an extended network of main lines, branch lines, valves, and air hoses. </li></ul><ul><li>The length of the network should be kept to a minimum to reduce pressure drop. </li></ul><ul><li>Air distribution piping should be large enough in diameter to minimize pressure drop. </li></ul><ul><li>A loop system is generally recommended, with all piping sloped to accessible drop legs and drain points </li></ul><ul><li>When designing an air distribution system layout, it is best to place the air compressor and its related accessories where temperature inside the plant is the lowest. </li></ul><ul><li>A projection of future demands and tie-ins to the existing distribution system should also be considered. </li></ul>
    16. 16. COMPRESSOR EFFICIENCY N = No. of stages K = Ratio of specific heats (1.35 for air) Ps = suction pressure in kg/cm2 Pd = Discharge pressure in kg/cm2 Q = Actual air flow (m3/min.) Actual kW =  3 V I  PF as measured Efficiency of compressor and motor combination = Theoretical kW =
    17. 17. EFFECT OF INTAKE AIR TEMPERATURE ON POWER CONSUMPTION Every 4 0 C rise in inlet air temperature results in a higher energy consumption by 1 % to achieve equivalent output. Hence, cool air intake leads to a more efficient compression.
    18. 18. EFFECT OF PRESSURE DROP ACROSS AIR INLET FILTER ON POWER CONSUMPTION For every 25 mbar pressure lost at the inlet due to choked filters, the compressor performance is reduced by about 2 percent.
    19. 19. ELEVATION It is evident that compressors located at higher altitudes consume more power to achieve a particular delivery pressure than those at sea level, as the compression ratio is higher.
    20. 20. EFFICACY OF INTER AND AFTER COOLERS It can be seen from the table that an increase of 5.5 0 C in the inlet to the second stage results in a 2 % increase in the specific energy consumption. Use of cold water reduces power consumption
    21. 21. COOLING WATER REQUIREMENT
    22. 22. POWER REDUCTION THROUGH PRESSURE REDUCTION A reduction in the delivery pressure of a compressor would reduce the power consumption.
    23. 23. EXPECTED SPECIFIC POWER CONSUMPTION OF RECIPROCATING COMPRESSORS (BASED ON MOTOR INPUT)
    24. 24. ENERGY WASTAGE DUE TO SMALLER PIPE DIAMETER Typical acceptable pressure drop in industrial practice is 0.3 bar in mains header at the farthest point and 0.5 bar in distribution system
    25. 25. DISCHARGE OF AIR THROUGH ORIFICE
    26. 26. COST OF AIR LEAKAGE Based on Rs. 5 / kWh ; 8000 operating hours; air at 7.0 bar
    27. 27. HEAT RECOVERY <ul><li>As noted earlier, compressing air generates heat. In fact, industrial-sized air compressors generate a substantial amount of heat that can be recovered and put to useful work. More than 80% of the electrical energy going to a compressor becomes heat. Much of this heat can be recovered and used for producing hot water or hot air. </li></ul><ul><li>Typical uses for recovered heat include supplemental space heating, industrial process heating, water heating, makeup air heating, and boiler makeup water preheating. Recoverable heat from a compressed air system is not, however, normally hot enough to be used to produce steam directly.  </li></ul><ul><li>As much as 80-93% of the electrical energy used by an industrial air compressor is converted into heat. In many cases, a properly designed heat recovery unit can recover anywhere from 50-90% of this available thermal energy and put it to useful work heating air or water </li></ul>
    28. 28. HEAT RECOVERY WITH AIR-COOLED ROTARY SCREW COMPRESSORS <ul><li>Air-cooled packaged rotary screw compressors are very amenable to heat recovery for space heating or other hot air uses. Ambient atmospheric air is heated by passing it across the system's aftercooler and lubricant cooler, where it extracts heat from both the compressed air and the lubricant that is used to lubricate and cool the compressor </li></ul><ul><li>  </li></ul><ul><li>Since packaged compressors are typically enclosed in cabinets and already include heat exchangers and fans, the only system modifications needed are the addition of ducting and another fan to handle the duct loading and to eliminate any back pressure on the compressor cooling fan. These heat recovery systems can be modulated with a simple thermostatically-controlled hinged vent. When heating is not required -- such as in the summer months -- the hot air can be ducted outside the building. The vent can also be thermostatically regulated to provide a constant temperature for a heated area. </li></ul><ul><li>Hot air can be used for space heating, industrial drying, preheating aspirated air for oil burners, or any other application requiring warm air. As a rule of thumb, approximately 50,000 Btu/hour of energy is available for each 100 cfm of capacity (at full-load). Air temperatures of 30 to 40 o F above the cooling air inlet temperature can be obtained. Recovery efficiencies of 80-90% are common </li></ul>
    29. 29. AIR AMPLIFIERS Compressed air flows through the inlet (1) into an annular chamber (2). It is then throttled through a small ring nozzle (3) at high velocity. This primary air stream adheres to the coanda profile (4), which directs it toward the outlet. A low pressure area is created at the center (5) inducing a high volume flow of surrounding air into the primary air stream. The combined flow of primary and surrounding air exhausts from the Air Amplifier in a high volume, high velocity flow.
    30. 30. STEPS IN SIMPLE SHOP-FLOOR METHOD FOR LEAK QUANTIFICATION <ul><li>Shut off compressed air operated equipments (or conduct test when no equipment is using compressed air). </li></ul><ul><li>Run the compressor to charge the system to set pressure of operation </li></ul><ul><li>Note the sub-sequent time taken for ‘on load’ and ‘off load’ cycles of the compressors. For accuracy, take ON & OFF times for 8 – 10 cycles continuously. Then calculate total ‘ON’ Time (T) and Total ‘OFF’ time (t). </li></ul><ul><li>The system leakage is calculated as </li></ul><ul><li>System leakage (cmm) = Q  T / (T + t) </li></ul><ul><li>Where, </li></ul><ul><li>Q = Actual free air being supplied during trial, in cubic meters per minute </li></ul><ul><li>T = Time on load in minutes </li></ul><ul><li>t = Time unload in minutes </li></ul>
    31. 31. LEAK TEST: EXAMPLE <ul><li>Compressor capacity (CMM) = 35 </li></ul><ul><li>Cut in pressure kg/SQCMG = 6.8 </li></ul><ul><li>Cut out pressure kg/SQCMG = 7.5 </li></ul><ul><li>On load kW drawn = 188 kW </li></ul><ul><li>Unload kW drawn = 54 kW </li></ul><ul><li>Average ‘On-load’ time = 1.5 minutes </li></ul><ul><li>Average ‘Unload’ time = 10.5 minutes </li></ul><ul><li>Comment on leakage quantity and avoidable loss of power due to air leakages. </li></ul><ul><li>a)      Leakage quantity (CMM) = </li></ul><ul><li>= 4.375 CMM </li></ul><ul><li>b) Leakage per day = 6300 CM/day </li></ul><ul><li>c) Specific power for compressed air generation= </li></ul><ul><li>= 0.0895 kwh/m 3 </li></ul><ul><li>d) Power lost due to leakages/day = 563.85 kWh </li></ul>
    32. 32. CAPACITY ASSESSMENT IN SHOP-FLOOR <ul><li>Isolate the compressor along with its individual receiver being taken for test from main compressed air system by tightly closing the isolation valve or blanking it, thus closing the receiver outlet. </li></ul><ul><li>Open water drain valve and drain out water fully and empty the receiver and the pipe line. Make sure that water trap line is tightly closed once again to start the test. </li></ul><ul><li>Start the compressor and activate the stop watch. </li></ul><ul><li>Note the time taken to attain the normal operational pressure P 2 (in the receiver) from initial pressure P 1 . </li></ul><ul><li>Calculate the capacity as per the formulae given below : </li></ul>Actual Free air discharge
    33. 33. EXAMPLE <ul><li>Piston displacement : 16.88 CMM </li></ul><ul><li>Theoretical compressor capacity : 14.75 CMM @ 7 kg/SQCMG </li></ul><ul><li>Compressor rated rpm 750 : Motor rated rpm : 1445 </li></ul><ul><li>Receiver Volume : 7.79 CM </li></ul><ul><li>Additional hold up volume, i.e., pipe / water cooler, etc., is : 0.4974 CM </li></ul><ul><li>Total volume : 8.322 CM </li></ul><ul><li>Initial pressure P 1 : 0.5 Kgf / SQCMG </li></ul><ul><li>Final pressure P 2 : 7.03 Kgf / SQCMG </li></ul><ul><li>Atmospheric pressure : 1.026 Kgf/cm 2 A </li></ul><ul><li>Compressor output CMM : </li></ul>= 13.17 CMM
    34. 34. ENERGY EFFICIENCY IN REFRIGERATION SYSTEM
    35. 35. INTRODUCTION <ul><li>Refrigeration deals with the transfer of heat from a low temperature level at the heat source to a high temperature level at the heat sink. </li></ul><ul><ul><li>Air conditioning for comfort </li></ul></ul><ul><ul><li>Refrigeration for process </li></ul></ul>
    36. 36. TON OF REFRIGERATION 1 ton of refrigeration = 3024 kCal/hr heat rejected. The cooling effect produced is quantified as tons of refrigeration.
    37. 37. VAPOUR-COMPRESSION REFRIGERATION SYSTEM (R-22)
    38. 38. VAPOUR – ABSORPTION REFRIGERATION SYSTEM EVAPORATOR CONDENSOR PUMP GENERATOR ABSORBER STRONG SOLUTION WEAK SOLUTION COOLING WATER IN HOT WATER OUT THROTTLING VALVE Regulating Valve Waste Heat/ Direct Fired Heat load In
    39. 39. PERFORMANCE ASSESSMENT The specific power consumption kW/TR is a useful indicator of the performance of refrigeration system. By messing refrigeration duty performed in TR and the Kilo Watt inputs measured, kW/TR is used as a reference energy performance indicator. The refrigeration TR is assessed as TR = Q  C p  (T i – T o ) / 3024 Where TR is cooling TR duty Q is mass flow rate of coolant in kg/hr C p is coolant specific heat in kCal /kg / 0 C T i is inlet. Temperature of coolant to evaporator (chiller) in 0 C. T o is outlet temperature of coolant from evaporator (chiller) in 0 C.
    40. 40. OVERALL ENERGY CONSUMPTION <ul><li>Compressor kW </li></ul><ul><li>Chilled water pump kW </li></ul><ul><li>Condenser water pump kW </li></ul><ul><li>Cooling tower fan kW </li></ul>Overall kW/TR = sum of all above kW/ TR
    41. 41. EFFECT OF VARIATION IN EVAPORATOR TEMPERATURE ON COMPRESSOR POWER CONSUMPTION A 1 0 C raise in evaporator temperature can help to save almost 3 % on power consumption.
    42. 42. EFFECT OF VARIATION IN CONDENSER TEMPERATURE ON COMPRESSOR POWER CONSUMPTION
    43. 43. EFFECT OF POOR MAINTENANCE ON COMPRESSOR POWER CONSUMPTION
    44. 44. ENERGY SAVINGS OPPORTUNITIES <ul><li>Cold Insulation </li></ul><ul><li>Process Heat Loads Minimisation </li></ul><ul><ul><li>Flow optimization and Heat transfer area increase to accept higher temperature coolant </li></ul></ul><ul><ul><li>Avoiding wastages like heat gains, loss of chilled water, idle flows </li></ul></ul><ul><ul><li>Frequent cleaning / de-scaling of all heat exchangers </li></ul></ul><ul><li>. </li></ul>
    45. 45. AT THE REFRIGERATION PLANT AREA <ul><li>Ensure adequacy of chilled water and cooling water flows, avoidance of bypass flows by valving off the idle equipment. </li></ul><ul><li>Minimize part load operations by matching loads and plant capacity on line, adopting variable speed drives for varying process load. </li></ul><ul><li>Ensure efforts to continuously optimize condenser and evaporator parameters for minimizing specific energy consumption and maximizing capacity. </li></ul><ul><li>Adopt VAR system where economics permit as a non CFC solution </li></ul>
    46. 46. SELECT THE RIGHT COOLING MEDIUM <ul><li>Type of cooling Power Consumption </li></ul><ul><li>1. Cooling tower water 0.1 KW/TR </li></ul><ul><li>2. Chilled water System at 10 o C 0.7 KW/TR </li></ul><ul><li>3. Brine System at -20 o C 1.8 KW/TR </li></ul><ul><li>Order of preference </li></ul><ul><li>Cooling water ChilledWater Brine </li></ul>
    47. 47. ENERGY SAVINGS IN REFRIGERATION SYSTEMS <ul><li>There are two broad ways by which energy can be conserved </li></ul><ul><li>By decreasing the load </li></ul><ul><li>By optimising the refrigeration system </li></ul>
    48. 48. CALCULATING THE OPERATING LOAD OF A CHILLER PLANT Refrigeration plant Hot well 12 O C Cold well 8 O C Process Chilled water flow – 100 m 3 /hr Refrigeration TR - 100,000 kg/hr x 1 x 4 3000 - 133.33 TR Efficiency - Power drawn by compressor, kW TR m C p 120 133.33 - = 0.9 DT
    49. 49. EFFICIENT OPERATION & MAINTENANCE <ul><li>The suction temperature, pressure delivery pressure of compressors should be kept at optimum level </li></ul><ul><ul><li>Ensure all indicators are working properly </li></ul></ul><ul><ul><li>Keep record of oil consumption </li></ul></ul><ul><li>Condensers </li></ul><ul><ul><li>Remove scale and algae and adopt suitable water treatment </li></ul></ul><ul><ul><li>Give periodic purging of non-condensable gases </li></ul></ul><ul><ul><li>Lesser the water temperature more the COP </li></ul></ul><ul><ul><li>Routine defrosting of Cooling coils </li></ul></ul><ul><ul><li>Stop condenser water pump when compressor not working </li></ul></ul><ul><ul><li>5 O C rise in condensing temperature increases 10 % power consumption </li></ul></ul><ul><ul><li>5 O C rise in evaporating temperature increases 10 % power consumption </li></ul></ul>
    50. 50. ENERGY SAVING MEASURES IN REFRIGERATION <ul><li>Look for process modifications to reduce the cooling load </li></ul><ul><li>Use cooling water to remove the maximum heat before using chilled water </li></ul><ul><li>Provide VSD for condenser water pumps </li></ul><ul><ul><li>to vary the cooling water flow to maintain 4 o C difference across the condensers </li></ul></ul><ul><li>Avoid primary pump operation </li></ul><ul><ul><li>Normally two pumps are operation (Chilled water supply pump from cold well and return water pump from hot well) </li></ul></ul><ul><ul><li>Modify to operate only return water pump </li></ul></ul><ul><ul><li>Provide VSD for efficient part load operation </li></ul></ul><ul><li>Explore ‘Ice-bank’ system for Maximum demand reduction </li></ul><ul><li>Explore application of vapour absorption with cost economics </li></ul><ul><li>Replace old systems with modern energy efficient systems </li></ul>
    51. 51. COLD INSULATION <ul><li>Thumb rules for cold Insulation </li></ul><ul><ul><li>Chilled water pipe insulation (Provide 2 to 3 inch thickness) </li></ul></ul><ul><ul><li>Duct insulation (Provide 1 to 2 inch thickness) </li></ul></ul><ul><ul><li>Suction line refrigerant pipe insulation(Provide 2 to3 inch thickness) </li></ul></ul>Difference in temperature between ambient and surface Heat ingress kCal/m 2 /hr Exposed area per tonne of refrigeration 5 35 86 10 73 41 15 113 27 20 154 19 Basis: Ambient temperature - 35 O C, emissivity – 0.8, still air conditions Allowable heat ingress – 10 –15 Kcal/m 2 /hr
    52. 52. THANK YOU

    ×