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7/10/20 AAR WEB Series-III 9 th , July., 2020 1. The temperature - - PDF document

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7/10/20 AAR WEB Series-III 9 th , July., 2020 1. The temperature ranges of Ammonia Ultra low temperature freezing plant vapor compression refrigeration systems using Ammonia 2. Applications 3. Ammonia low temperature refrigeration systems

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SLIDE 1

7/10/20 1

Ultra low temperature freezing plant using Ammonia

Hiroyuki Egashira Mayekawa Mfg. Co., Ltd.

AAR WEB Series-III

9th, July., 2020

9 July 2020 AAR WEBINAR SERIES -3 1

1

  • 1. The temperature ranges of Ammonia

vapor compression refrigeration systems

  • 2. Applications
  • 3. Ammonia low temperature refrigeration

systems

  • 4. Case Study

9 July 2020 AAR WEBINAR SERIES -3 2

2

  • 1. The temperature ranges of vapor

compression refrigeration systems

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  • 1. Temperature is a kinetic energy of

molecules that make a substance.

  • Energy level is low, the molecules stick

together, and form Solid.

What is temperature?

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  • When the energy level increase and the

bonding of the molecules loosen, solid melts and becomes liquid.

  • When the energy level goes higher, and

the molecule starts to move freely, the substance become gas/vapor

What is temperature?

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  • This process requires the

absorption of energy by the molecule, and the level of energy in the molecule is measured as temperature of the substance.

  • State of no energy at all in the

substance is absolute 0 temperature, or 0K(Kelvin). In terms of Celsius,- 273.15deg.C.

What is temperature?

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SLIDE 2

7/10/20 2

Substances change its phases:

  • Solid
  • Liquid
  • Vapor

Each substance has specific temperature , pressure and specific energy level to change phases This can be visualized in P-H Diagram

Change of Phase

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P-H Diagram and Phase

Example of phases (CO2)

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Previous slide is CO2 P-H diagram, that shows the 3 phases of CO2. I could not find Ammonia P-H diagram to show the same phase changes, but in the same manner, vapor, liquid and solid states exist for Ammonia.

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Phase of the material 9

  • Vapor compression refrigeration

system operate between vapor and liquid.

Vapor compression refrigeration Cycle

Condenser Compressor Evaporator 1 2 3 4 Heat Absorption Heat Rejection Expansion Valve

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Vapor Compression Refrigeration Cycle on P-H Diagram Example of phases (CO2)

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As shown in the previous slide, the vapor compression refrigeration cycle operate where the liquid and gas co-exist.

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Vapor compression refrigeration Cycle 12

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SLIDE 3

7/10/20 3

P-H Diagram NH3

100kg/hr+12.3kg/hr 35.5kW 112.3kg/hr 9 July 2020 AAR WEBINAR SERIES -3 13

Vapor compression refrigeration Cycle 13

We usually operate at the very high pressure side of Ammonia, so we do not think about the solid state of Ammonia. However, Ammonia also reaches solid state at -77.72 deg.C., at around 0.06bar A.

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Vapor compression refrigeration Cycle 14

Mol Weight Te at 0barG Te at -0.8barG Freezing Point Ammonia NH3 17

  • 33.6
  • 61.6
  • 77.73

Carbon Dioxide CO2 44

  • 56.6

Propane C3H8 44

  • 42.4
  • 73.6
  • 187.7

Nitrogen N2 28

  • 196.0
  • 206.3
  • 210

Vapor compression refrigeration system Evaporating temperature limits Of various substance

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I selected

  • 1. the atmospheric pressure as a bench

mark.

  • 2. -0.8barG, as economical limit
  • 3. freezing point as the limit set by the law
  • f physics.

.

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Vapor compression refrigeration system Evaporating temperature limits Of various substance

16

Please note:

  • 1. -0.8 barG pressure, I consider as the
  • perational limit of standard rotating

equipment.

  • 2. Freezing point is where vapor

compression system cannot work because there is no liquid.

9 July 2020 AAR WEBINAR SERIES -3 17

Vapor compression refrigeration system Evaporating temperature limits Of various substance

17

CO2 has a peculiar characteristics. CO2 freezes at -56.6deg.C., at 5.2bar.A. The temperature limit of CO2 vapor compression system is much higher than Ammonia. Considering CO2’s efficiency does not match Ammonia below -40deg.C., the application of CO2 is limited between -40 and -50deg.C only.

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Vapor compression refrigeration system Evaporating temperature limits Of various substance

18

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SLIDE 4

7/10/20 4

Propane’s evaporating temperature is -73.6 deg.C. at -0.8barG. So as it can achieve

  • approx. 10 deg.C. lower than Ammonia.

In this case, the problem is, Propane is highly explosive substance.

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Vapor compression refrigeration system

19

Vapor compression refrigeration system Comparison of NH3 and CO2 (Booster)

NH3 CO2 Tc deg.C

  • 5
  • 5

Te deg.C

  • 50
  • 50

Swept Volume m3/hr 659 659 Pd kg/cm2 3.62 31.1 Ps kg/cm2 0.42 6.96 Weight flow kg/hr 186.1 9409 Capacity kW 64.0 638.8 BkW 30.2 272.4 COP 2.12 2.35

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As you can see, for the temperature of

  • 50deg.C evaporation and -5 deg.C.

condensing, CO2 have 10 times the capacity at 9 times the power. This shows that it requires 1/10 the size of compressor for CO2 cascade system, but in terms of power saving, 10% of the booster. In the tropical climate, high stage has to be Ammonia.

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Vapor compression refrigeration system Comparison of NH3 and CO2 (Booster)

21

Saving of 10% of booster power is negligible for the entire system. Also consider the high pressure design for the discharge side of CO2 and the limited application range of -45 to -55. Down to -60deg.C. can be achieved by Ammonia, there is no reason for us to invest for CO2 cascade system.

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Vapor compression refrigeration system Comparison of NH3 and CO2 (Booster)

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Vapor compression refrigeration system Comparison of NH3 and Propane (Booster)

NH3 PROPANE Tc

  • 5
  • 5

Te

  • 60
  • 60

Swept Volume(m3/hr) 1210 1210 Pd kg/cm2 3.62 4.11 Ps kg/cm2 0.22 0.44 Weight flow kg/hr 222.5 1157 Capacity(kW) 75.3 104.4 BkW 57.1 69.2 COP 1.32 1.51

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For the low temperature application with cascade system, Propane is a better

  • ption.

However, Propane is an explosive gas and system as well as the handling of the gas would cost dearly.

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Vapor compression refrigeration system Comparison of Propane and CO2 (Booster)

24

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SLIDE 5

7/10/20 5

Down to -60deg.C. Ammonia is the best refrigerant, since we can achieve the temperature with the equipment we already have. What are the specific application for this kind of temperature?

Ammonia low temperature application

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  • 1. Applications

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  • 1. Food Preservation

Most of the products can be stored for months at -25 deg.C.

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Great exceptions are:

  • Premium Grade Ice Cream -30deg.C.
  • Premium Grade Tuna
  • 60deg.C.
  • 1. Food Preservation

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For the food freezing, the faster the better.

Freezing of Food

Quick Freezing

Faster the freezing, ice crystal formed in the cell is smaller, and less damages to the cell membrane. With damaged cell membrane, cytoplasm flows out at the time of defrost.

Normal Freezing Before Freezing

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Low temperature is essential for the fast freezing. However, the low temperature alone does not insure the fast freezing.

Freezing of Food

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SLIDE 6

7/10/20 6

Typical temperature pattern of freezing. Initial temperature is high. It quickly goes near freezing point, then stay there.

Freezing of Food

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Only after the freezing, the temperature goes

  • down. The refrigeration system designed for low

temperature operate at higher temperature most

  • f the time.

Freezing of Food

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Typical temperature pattern of freezing. Surface freezes immediately ,but it will take longer for the center to freeze.

Freezing of Food

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Since the lower the temperature, the cost of freezing is higher, it is always the balance between the cost of freezing and cost of storage against market price.

Freezing of Food

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IQF is a solution that make a consistent low temperature operation and quick freezing possible

Freezing of Food

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Impingement freezer improve the heat transfer

  • f surface to shorten the freezing time.

Freezing of Food

Conventional Air Flow Impingement Air Flow Uniform Flow One Side Two Sice Product Cold Air Slit Cold Air Slit Coanda Effect Im pinging Jet Slit Cold Air Cold Air Im pinging Jet Coanda Effect

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SLIDE 7

7/10/20 7

The direction of the research and development is how to make a same quality at the temperature easily available by Ammonia, that is down to -40 deg.C.

Freezing of Food

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Cryogenic Freezing This is the process where inert gas, such as N2 and CO2 are directly sprayed on the products. N2: -196.9 deg.C. CO2: -78.5 deg.C.(Solid)

Freezing of Food

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.

Freezing of Food

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Even though the low temperature freezing is possible with Cryogenic, it requires continuous supply of N2 or CO2.

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.

Freezing of Food

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Impingement technology IQFs make the quality

  • f freezing equal for most of the products.

So when the production scale goes up and continuous operation is required, they are replaced with impingement IQFs.

Conventional Air Flow Impingement Air Flow Uniform Flow One Side Two Sice Product Cold Air Slit Cold Air Slit Coanda Effect Im pinging Jet Slit Cold Air Cold Air Im pinging Jet Coanda Effect

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Cryogenic is one method of keeping the temperature of the chemical reactions in pharmaceutical and chemical process.

Cryogenic

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It is an inexpensive method of low temperature cooling for research and development. .

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Cryogenic

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Often, -196.9deg.C. is over spec for the process. Continuous supply of N2 is required. For higher quantity with relatively higher temperature requirement, it can be replaced with Ammonia refrigeration system. We will see this in our case study.

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SLIDE 8

7/10/20 8

  • 1. Ammonia low temperature refrigeration

systems

9 July 2020 AAR WEBINAR SERIES -3 43

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P-H Diagram NH3 Single Stage Te=-5 deg.C.

100kg/hr+12.3kg/hr 35.5kW 112.3kg/hr 9 July 2020 AAR WEBINAR SERIES -3 44

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P-H Diagram NH3 Single Stage Te=-40 deg.C. (Imaginary)

136.5kg/hr 100kg/hr+36.5kg/hr 38.6kW 9 July 2020 AAR WEBINAR SERIES -3 45

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Idea of System A

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P-H Diagram NH3 System A on P-H Diagram

100kg/hr+36.5kg/hr 38.6kW 162.3kg/hr 25.8kg/hr 9 July 2020 AAR WEBINAR SERIES -3 47

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P-H Diagram NH3 Screw Single Stage Te=-40 deg.C.

136.5kg/hr 100kg/hr+36.5kg/hr 38.6kW 9 July 2020 AAR WEBINAR SERIES -3 48

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SLIDE 9

7/10/20 9

Screw Single Stage Te=-40 deg.C. Economizer-Single stage liquid sub cooling

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System of Economizer

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P-H Diagram NH3 Single Stage Te=-40 deg.C. With Economizer

136.5kg/hr 100kg/hr+15kg/hr 38.6kW 20.5kg/hr 1 1 5 k g / h r 1 3 6 . 5 k g / h r 9 July 2020 AAR WEBINAR SERIES -3 51

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Effect of Economizer

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Idea of System C

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P-H Diagram NH3

100kg/hr+12.8kg/hr 38.6kW 135.4kg/hr 22.6kg/hr 112.8kg/hr 135.4kg/hr

System C on P-H Diagram

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SLIDE 10

7/10/20 10

Idea of System D

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P-H Diagram NH3

100kg/hr+15kg/hr 38.6kW 135.5kg/hr 20.5kg/hr 115 kg/hr 135.5kg/hr

System D on P-H Diagram

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Gas compression in kg/hr Booster High Stage Single Stage 136.5 System A 136.5 162.3 Single Stage with liquid cooler 115.0 136.5 System C 112.8 135.4 System D 115.0 135.5

Compression gas weight of each system

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The comparison of the previous sheet put the economizer and two stage on the same level. The above calculations do not take into the account the effect of gas cooling to the capacity of high stage. In two stages, the low stage discharge gas is cooled at intercooler and this enhance the capacity of high stage. This enable the lower intermediate pressure with the same set of the compressors.

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Efficiency of Two stage systems

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Two Stage Refrigeration System

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Efficiency of Two stage system with various volume ratio (Screw)

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Te

  • 30
  • 35
  • 40
  • 45
  • 50
  • 55
  • 60

Volume ratio 1 0.54 0.40 1.19 1.01 0.80 0.61 0.46 1.49 1.91 1.64 1.37 1.12 0.90 0.69 0.52 1.95 2.04 1.74 1.52 1.27 1.03 0.81 0.61 2.31 2.09 1.81 1.57 1.33 1.09 0.87 0.66 2.91 2.08 1.82 1.57 1.36 1.14 0.92 0.72 3.79 1.82 1.60 1.38 1.19 0.99 0.81 4.55 1.73 1.56 1.36 1.17 1.00 0.84 5.69 1.45 1.30 1.13 0.97 0.85 Max 2.09 1.82 1.60 1.38 1.19 1.00 0.85 Min 1.91 1.64 1.37 1.01 0.80 0.54 0.40 9% 10% 14% 27% 33% 46% 53% Ratio 2.31 2.31 3.79 3.79 3.79 4.55 5.69 Ti 1.01

  • 4.42
  • 4.79
  • 10.7
  • 16.8
  • 14.1
  • 16.8

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SLIDE 11

7/10/20 11

Volume ratio Efficiency

Efficiency of Two stage system with various volume ratio (Screw)

9 July 2020 AAR WEBINAR SERIES -3 61 0.5 1 1.5 2 2.5 1 2 3 4 5 6

Efficency of various volume ratio

  • 3
  • 3

5

  • 4
  • 4

5

  • 5
  • 5

5

  • 6

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Overall efficiency goes down as the temperature goes down. Effect of Volume ratio increases as the evaporative temperature goes down. Up to

  • 40 deg.C. the highest and lowest

efficiency has only 10 %, but at -60deg.C, there are more than 50% difference.

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Efficiency of Two stage system with various volume ratio (Screw)

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From Te -30 to -40 deg.C. , selecting intermediate temperature of -5 deg.C. gives maximum performance. The common intercooler works good in this range. For the lower temperature separate intercoolers are required.

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Efficiency of Two stage system with various volume ratio (Screw)

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The efficiency goes down as the evaporating temperature goes down. Between Te=-40deg.C. and Te=-60deg.C., the power consumption increases by 60%. The bottom line is, you must get 60% more yield or 60% higher price if you want to run the system at -60 deg.C.

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Efficiency of Two stage system with various volume ratio (Screw)

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Volume ratio Efficiency

0.5 1 1.5 2 2.5 0.5 1 1.5 2 2.5 3 3.5 4 4.5

  • 3
  • 3

5

  • 4
  • 4

5

  • 5
  • 5

5

Efficiency of Two stage system with various volume ratio (Reciprocating)

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Effect of high compression ratio to the volumetric efficiency of reciprocating compressors.

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SLIDE 12

7/10/20 12

Screw compressor ports

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Tc Tc=35d 35deg.C

Tc=45deg.C

Ad Adiabatic Compression Efficiency of Am Ammonia Compressors at volume ration 2.6 an and evap aporat ating temperat ature fixed at at -5 5 de deg.C.

(5) (3.8)

  • 5

14 27 37 45 52 58 63 68 73 77 81 85

Co Condensing temp

Screw compressor ports for high stage

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Te Te=-30d 30deg.C

Te=-45deg.C

Ad Adiabatic Compression Efficiency of Am Ammonia Compressors at volume ration 2.6 and and co condensing te temperatu ture fixed at t -5 5 de deg.C.

(5) (3.0)

  • 5
  • 22
  • 30
  • 36 -40
  • 44
  • 46
  • 49
  • 51
  • 52
  • 54
  • 55 -57 Ev

Evap aporat ating te temp

Screw compressor ports for low stage

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Role of selection of low pressure receiver is more significant for low temperature applications because.

  • 1. Any sizes of the vessels cannot completely

eliminate the liquid drop.

  • 2. Impact of liquid particle to the efficiency is

more significant in low temperature

  • At -5deg.C., the liquid expand to the gas with

233time volume.

  • At -40deg.C. 1071times.
  • At -60 deg.C. 3364 times

Significance of Selection of low pressure receivers

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  • You cannot

completely remove the liquid drops from the gas.

  • There are only

some guide lines. Selection Criteria

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The low pressure receiver liquid level changes during the defrost and change of freezing cycle. This is more significant in low temperature, and especially for the freezing applications. Sizes, designs and the decision of control and high level alarm for the low pressure receiver and surge drum should take this in consideration. At high level, the gas speed should not exceed the design.

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SLIDE 13

7/10/20 13

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  • 4. Case Study

Cryogenic cooling

73

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Tc deg.C. Te deg.C. TR BkW High Stage 15

  • 40

64.9 100 Booster

  • 40
  • 60

39.2 42

Cryogenic cooling

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This customer was using N2 for the process cooling. Product temperature required is -40 deg.C. N2 are released in atmosphere at -30 to -80 deg.C. after the evaporation. This was changed by the closed circuit Ammonia refrigeration. Cryogenic cooling

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Original reactor limpet coil and jacket was used for the cooling. N2 temperature at 0 bar G is -195.8deg.C. It is replaced with Ammonia at -60 deg.C. with forced circulation of 6 times the evaporation. Cryogenic cooling

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