aar webiner presentation 9 july 2020 h. egashira rev.2

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Ultra low temperature freezing plant using Ammonia

Hiroyuki EgashiraMayekawa Mfg. Co., Ltd.

AAR WEB Series-III9th, July., 2020

9 July 2020AAR WEBINAR SERIES -3 1

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1. The temperature ranges of Ammonia vapor compression refrigeration systems

2. Applications3. Ammonia low temperature refrigeration

systems4. Case Study


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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



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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.



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Substances change its phases:• Solid• Liquid• Vapor

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

Change of Phase


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P-H Diagram and Phase

Example of phases (CO2)9 July 2020AAR WEBINAR SERIES -3 8

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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.


Phase of the material

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• Vapor compression refrigeration system operate between vapor and liquid.

Vapor compression refrigeration Cycle

Condenser

Compressor

Evaporator

1

23

4

Heat Absorption

Heat Rejection

Expansion Valve


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Vapor Compression Refrigeration Cycle on P-H Diagram

Example of phases (CO2)9 July 2020AAR WEBINAR SERIES -3 11

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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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P-H Diagram NH3

100kg/hr+12.3kg/hr 35.5kW

112.3kg/hr



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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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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 systemEvaporating temperature limits

Of various substance


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I selected

1. the atmospheric pressure as a bench mark.

2. -0.8barG, as economical limit3. freezing point as the limit set by the law

of physics.

.




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Please note:1. -0.8 barG pressure, I consider as the

operational limit of standard rotating equipment.

2. Freezing point is where vapor compression system cannot work because there is no liquid.




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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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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.


Vapor compression refrigeration system

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Vapor compression refrigeration systemComparison of NH3 and CO2 (Booster)

NH3 CO2Tc deg.C -5 -5Te deg.C -50 -50Swept Volume m3/hr 659 659Pd kg/cm2 3.62 31.1Ps kg/cm2 0.42 6.96Weight flow kg/hr 186.1 9409Capacity kW 64.0 638.8BkW 30.2 272.4COP 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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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 systemComparison of NH3 and Propane (Booster)

NH3 PROPANETc -5 -5Te -60 -60

Swept Volume(m3/hr) 1210 1210Pd kg/cm2 3.62 4.11Ps kg/cm2 0.22 0.44Weight flow kg/hr 222.5 1157

Capacity(kW) 75.3 104.4BkW 57.1 69.2COP 1.32 1.51


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For the low temperature application with cascade system, Propane is a better option.However, Propane is an explosive gas and system as well as the handling of the gas would cost dearly.


Vapor compression refrigeration systemComparison of Propane and CO2 (Booster)

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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 PreservationMost 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 FreezingBefore 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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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 of 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 of 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

Impinging Jet

Slit

Cold Air

Cold AirImpinging Jet

Coanda Effect


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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 FreezingThis 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


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


Impingement technology IQFs make the quality of 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

Impinging Jet

Slit

Cold Air

Cold AirImpinging 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


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

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Cryogenic


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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1. Ammonia low temperature refrigeration systems


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P-H Diagram NH3

Single Stage Te=-5 deg.C.


112.3kg/hr


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P-H Diagram NH3

Single Stage Te=-40 deg.C. (Imaginary)

136.5kg/hr



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Idea of System A


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P-H Diagram NH3

System A on P-H Diagram


162.3kg/hr

25.8kg/hr


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P-H Diagram NH3

Screw Single Stage Te=-40 deg.C.

136.5kg/hr



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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

115k

g/hr

136.

5kg/

hr


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Effect of Economizer


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Idea of System C


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P-H Diagram NH3


135.4kg/hr

22.6kg/hr

112.

8kg/

hr13

5.4k

g/hr

System C on P-H Diagram


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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/h

r13

5.5k

g/hr

System D on P-H Diagram


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Gas compression in kg/hr

Booster High StageSingle 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. 9 July 2020AAR WEBINAR SERIES -3 58

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)


Te-30 -35 -40 -45 -50 -55 -60

Volu

me

ratio

1 0.54 0.401.19 1.01 0.80 0.61 0.461.49 1.91 1.64 1.37 1.12 0.90 0.69 0.521.95 2.04 1.74 1.52 1.27 1.03 0.81 0.612.31 2.09 1.81 1.57 1.33 1.09 0.87 0.662.91 2.08 1.82 1.57 1.36 1.14 0.92 0.723.79 1.82 1.60 1.38 1.19 0.99 0.814.55 1.73 1.56 1.36 1.17 1.00 0.845.69 1.45 1.30 1.13 0.97 0.85

Max 2.09 1.82 1.60 1.38 1.19 1.00 0.85Min 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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Volume ratio

Effic

ienc

y



0

0.5

1

1.5

2

2.5

0 1 2 3 4 5 6

Efficency of various volume ratio

-30 -35 -40 -45 -50 -55 -60

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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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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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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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Volume ratio

Effic

ienc

y

0

0.5

1

1.5

2

2.5

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

-30 -35 -40 -45 -50 -55

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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Screw compressor ports


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Tc=35deg.C

Tc=45deg.C

Adiabatic Compression Efficiency of Ammonia Compressors at volume ration 2.6 and evaporating temperature fixed at -5 deg.C.

(5)(3.8)

-5 14 27 37 45 52 58 63 68 73 77 81 85 Condensing temp

Screw compressor ports for high stage


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Te=-30deg.CTe=-45deg.C

Adiabatic Compression Efficiency of Ammonia Compressors at volume ration 2.6 and condensing temperature fixed at -5 deg.C.

(5)(3.0)

-5 -22 -30 -36 -40 -44 -46 -49 -51 -52 -54 -55 -57 Evaporating 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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4. Case StudyCryogenic cooling

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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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aar webiner presentation 9 july 2020 h. egashira rev.2

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