1) Semi-welded plate heat exchangers are increasingly being used in R717 (ammonia) / R744 (CO2) cascade systems due to their safety and efficiency.
2) Two case studies are presented of semi-welded plate heat exchangers in the Netherlands that have operated reliably for over 10 years in coffee and poultry processing plants.
3) The semi-welded design eliminates the risk of media intermixing and has very high fatigue resistance, making it the most reliable solution for R717/R744 cascade applications.
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Semi welded plate heat exchanger as efficient R717/R744 cascade solution
1.
2. Semi welded plate heat exchanger as
R717/R744 cascade heat exchanger
Alfa Laval
3. Why we see an increasing number of R717 Ammonia /
R744 CO2 Cascade installations
1) Benefit the use of the very efficient natural refrigerant ammonia R717 :
- using a secondary fluid in the refrigeration system limiting the ammonia
charge to increase safety
2) Increasing efficiency in low temperature two stage cascade applications
- benefitting the relatively better thermal properties of CO2 at low temperature
side and of Ammonia at high temperature (ambient) side
3) Benefit the advantages of CO2 R744 compared to glycol or chloride brines
- requiring smaller pipe and pump dimensions to reduce cost
Two cases of installations currently in operation in Netherlands will be
presented.
4. The Cascade Heat Exchanger – one of the most
important components*
Is handling a challenging duty of high
importance and must deliver:
1) efficient close temperatures approach
2) high design pressure CO2 side
3) resistance against high fatigue forces
from cyclical patterns of temperature
and pressure.
4) low risk of intermixing R744 and R717.
>It is a well-known fact that ammonia and carbon dioxide
mixing results in an ammonium carbamate powder*
Ammonia
Condensor
CO2
Evaporator
R717/R744 Cascade Heat Exchanger
CO2
Receiver
CO2
Compressor
Ammonia
Compressor
*Source: Zahid Ayub, M. Sultan Khan, Amir Jokar, Tariq S. Khan & Niel Hayes (2013) Recent Developments in Plate Exchangers—
Ammonia/Carbon Dioxide Cascade Condensers, Heat Transfer Engineering, 34:5-6, 401-408,
5. Plate Heat exchanger –efficient alternatives
Factor Fully Welded
Plate HEX
Semi Welded
Plate HEX
Temperature approach 2-3 K Yes Yes
Design Pressure min 40 Bar Yes Yes
Fatigue resistance Depends Very high
Risk of intermixing Yes* Very low
Reliability factors
* Source: Zahid Ayub, M. Sultan Khan, Amir Jokar, Tariq S. Khan & Niel Hayes (2013) Recent Developments in Plate Exchangers—
Ammonia/Carbon Dioxide Cascade Condensers, Heat Transfer Engineering, 34:5-6, 401-408,
6. Semi welded plate heat exchanger - the most reliable
solution*
- The Gaskets absorbs metal plate or
frame movements, eliminating any risk
of fatigue failures.
… and in case of sealing failure, all the
gaskets and welds are facing the external
atmosphere
à Eliminating the risk of fatal media
intermixing
*Source: Alfa Laval,
9. Reliable R717/R744 Cascade Heat Exchangers –
Available as standard
Customers can increasingly benefit the
advantages of this kind of system for industrial
refrigeration with:
- No global warming refrigerants
- High efficiency
- High safety