Flooded Evaporation Application Expert Refrigeration ... M6-MW M10-BW MK15-BW TK20-BW T20-BW MA30-W

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  • www.alfalaval.com

    October 15th , 2020

    | © Alfa Laval 1 |

    Lets talk about…

    Flooded Evaporation How to build an efficient flooded ammonia system with a semi-welded Alfa Laval unit, and a liquid separator

    15/10/2020

    NH3

    Jesper Olsen

    Application Expert Refrigeration at Alfa Laval

    jesper.olsen@alfalaval.com

  • www.alfalaval.comwww.alfalaval.com15/10/2020 | © Alfa Laval 2 |

    Energy efficiency

    NH3

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    3 |

    Energy efficiency − Reason for using Ammonia

    Why Ammonia?

    Main benefits using ammonia as a refrigerant are:

    - Unique thermal properties – very efficient - Stable physical properties - 100% environmentally correct

    - low GWP (Global Warming Potential) low - ODP (Ozone Depletion Potential) - ZERO impact

    - Easy to handle

    - Low cost - Inbuilt detection – self alarming

    Some disadvantages though:

    - Toxicity - Fear, caused by misinformation and rarely related to the

    use as a refrigerant

    NH3

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    M6-MW

    M10-BW MK15-BW

    TK20-BW

    T20-BW MA30-W

    T10-EW

    15/10/2020 | © Alfa Laval

    4 |

    Energy efficiency − Reason for using Semi-Welded technology

    Why Alfa Laval Semi-Welded technology?

    Main benefits using SWPHE’s as a heat exchanger are:

    - Very high heat transfer efficiency. Close approach*) is possible to reach, 2K or less in evaporators, 0K or less in condensers

    - Forgiving construction, the gaskets will take the forces

    - High fatigue resistance - Freezing causes no damages - As we brought the technology to the market already

    in the last century, we have a long experience in

    ammonia applications. Market standard since the mid 1990’s

    *) Difference between e.g. the evaporating temperature and the leaving cooled water temperature or the difference between the condensing temperature and the leaving heated water temperature.

    NH3

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    Flooded evaporation

    NH3

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    6 |

    Flooded evaporation − Reason for using flooded evaporation

    Why Flooded Evaporation?

    Main benefits using flooded evaporation are:

    - A simple system using the laws of physics - laws of nature

    - A constant wet surface will enhance the

    efficiency in the evaporator - It will allow close approach - less compressor

    power needed - Just a few control devices are needed if the

    condenser is water cooled - If used in a well-designed thermosyphon

    system, the waste energy can be eliminated

    CO2

    NH3 Cascade Heat Exchanger

    NH3

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    7 |

    Flooded evaporation − The thermosyphon system

    NH3 Cascade Heat Exchanger

    NH3

    1. ΔPfriction

    2. ΔPstatic

    3. ΔPcomponents

    4. Expansion & contraction

    5. ΔPPHE

    1

    1

    3

    3

    3

    4

    4

    5

    2

    Driving head

    =∑ΔP

    ∆� � � ∗ � ∗ ℎ � � ∗ � ∗ ℎ � � ℎ ���

  • www.alfalaval.com10/15/2020

    | © Alfa Laval

    8 |

    Flooded evaporation − Optimum heat transfer

    • Adopt outlet vapour fraction for optimum heat transfer

    – Minimum pressure drop in wet return line => high outlet vapour

    quality

    – Vapour quality 0.7 to 0.85 => CR 1.2 to 1.4

    • Highest Tevap possible

    • Optimum efficiency at all loads

    NH3

    Source: Prof. Thome, Wolverine engineering data book

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    | © Alfa Laval

    9 |

    Flooded evaporation − Design to avoid trouble with the performance…or maybe cause the trouble

    ► The pre-heating zone will be shorter, which means an increase of the MTD.

    This is especially pronounced the lower the temperature is.

    ► The driving head does not need to produce a lift of the liquid in the return leg.

    ► The separator must not be placed that low that the circulation is affected. Driving force?

    ► An evaporator with a horizontal exit to the separator, will have excellent part load properties.

    ► An elevated separator will have a very large return leg pressure drop, i.e. a large difference between the evaporator and separator temperatures.

    ► Keep the separator design as simple as possible. Avoid extra baffles, distributors, guide vans, etc.

    ► The danger of backflow and hunting is diminished.

    NH3The separator should be placed as low as possible and with a return leg as short and straight as possible and preferably with no valves or other fittings:

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    | © Alfa Laval

    10 |

    Flooded evaporation with Alfa Laval U-turn − Termosyphon system in the Alfa Laval way

    NH3

    Self-supporting

    construction

    Small diameter

    surge drum

    Standard oil-pot

    included

    Drop leg:

    Integrated piping for liquid

    level sensors and high

    level shut-off devices

    Advantages

    • Very energy efficient • Very high separation

    efficiency • Low charge in the

    evaporator part of the

    system • Low weight • Compact, compared to

    traditional separators

    • “Plug’n’play”

    Disadvantages

    • Very small volume for

    liquid hold up

    Wet return – Low

    pressure drop

    Liquid injection with

    “ejector function” to

    reduce wet return dP

    Backflow preventer +

    Drip nose to prevent oil to enter.

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    M6-MW

    M10-BW MK15-BW

    TK20-BW

    T20-BW MA30-W

    T10-EW

    15/10/2020 | © Alfa Laval 11 |

    Reliable R717 Heat Exchangers − Available as standard from our factory in Lund Sweden

    Industry can increasingly benefit the advantages of this kind of system for

    industrial refrigeration with:

    - A no global warming refrigerant, R-717

    - High energy efficiency

    - High reliability

    - High safety

    - Future safe

    NH3

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    THANK YOU FOR LISTEN IN!

    Ready to go…

    …any questions?

    | © Alfa Laval15/10/2020 12 |

    NH3

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