introduction to ammonia refrigeration systems · ammonia as a refrigerant 2. recognize materials...
TRANSCRIPT
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Douglas Reindl, Ph.D., P.E.
ASHRAE Fellow
Director, IRC
Professor, University of Wisconsin-Madison
An Introduction to Ammonia Refrigeration Systems
ASHRAE is a Registered Provider with The American Institute of Architects
Continuing Education Systems. Credit earned on completion of this program will be reported to CES Records for AIA members. Certificates of
Completion for non-AIA members are available on request.
This program is registered with the AIA/CES for continuing professional education. As such, it does not include content that may be deemed or
construed to be an approval or endorsement by the AIA of any material of construction or any method or manner of handling, using, distributing, or dealing in any material or product. Questions related to specific materials,
methods, and services will be addressed at the conclusion of this presentation.
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However, any course found to be in violation of
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Course ID: 0090010881
COURSE TITLE
By Provider’s Name
Approved for:
x General CE hours
x LEED-specific hours
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Course description
Industrial refrigeration systems have used anhydrous ammonia for more than a sesquicentennial. Although ammonia has a long history of use in the industrial sector, the interest in ammonia as a potential refrigerant for non-industrial applications has grown recently.
This presentation will provide an overview of the ammonia refrigeration systems that have been the mainstay in the industrial sector and emphasize unique characteristics that differentiate ammonia systems from traditional halocarbon refrigeration systems. An emphasis will be placed on safety.
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Learning objectives
1. Identify key safety considerations when using ammonia as a refrigerant
2. Recognize materials used in halocarbon refrigeration systems that are not appropriate for use with ammonia due to material incompatibilities
3. Differentiate direct-expansion, gravity flooded, and liquid overfeed evaporator arrangements
4. Describe the difference between single stage and two stage compression systems
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During this presentation, we will discuss
• Ammonia and its uses
• Ammonia as a refrigerant
• Ammonia refrigeration, the technology
– Single stage: DX, flooded, overfeed
– Two-stage
• How is ammonia different compared to other refrigerants?
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Where is ammonia used?
87%
11%
2%**
Annual ammonia use in U.S.
Agriculture Other Refrigerant
Annual US consumption in 2012 was 14.4 million metric tons*.
• Source: US Geological Survey (2013).
** Source: ASHRAE Position Document on ammonia (RA 2013)
NH3
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Anhydrous ammonia as a refrigerant
•Where is ammonia used as a refrigerant?
– Industrial systems: large cold storage and process systems
– Some HVAC systems (requires a central plant)
– Where no ODP and low/no GWP is desirable/needed
• Distinct characteristics
– Usually a custom engineered system vs. packaged systems for halocarbons
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Anhydrous ammonia characteristics
• Refrigerant grade
– 99.95% Purity
– 75 PPM H2O (max)
• Vapor tends to be lighter than air
• Liquid specific gravity ~ 0.65
• Alkaline – pH of 11.6
• Pungent odor makes it self-alarming
• Highly soluble in water
• Very corrosive to human tissue upon exposure!
• Toxic at elevated concentrations
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Flammability characteristics
• ASHRAE 34 flammability classification: 2L
• DOT classified as non-flammable
• Autoignition temperature: 1204F
• Lower flammability limit (vol.%)1 15-16
• Upper flammability limit (vol. %)1 25-28
• Combustion products: oxides of nitrogen
• Fire hazard: slight
1 IIAR Ammonia Data Book, (2009).
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Materials compatibility for ammonia
• Not permitted
– Copper and copper alloys such as brass are prohibited (but allowed for bearing materials)
– Zinc (in continuous contact with ammonia)
– Non-metallic materials that degrade upon exposure
• Permitted
– Carbon steel
– Stainless steel
– Aluminum
– Other nonmetallic materials such as PTFE are permitted (if they will not break down)
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• Why is ammonia widely used in food processing
and storage facilities?
• Because it is a good refrigerant!
– High heat transfer coefficients in equipment
– Efficient compressor operation
– Low refrigerant cost
– No ozone depletion & no/low global warming impact
– Sustainable
– Self-alarming
Anhydrous ammonia
Let’s now look at the technology
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Ammonia refrigeration technology
• Single stage compression with evaporators configured as
– direct-expansion
– flooded
– overfeed
• Multi-stage compression systems
• Cascade systems
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Simple vapor compression system
Qevap
Qcond
Wcomp
Expansion
Device
Superheated vapor,
high pressure
Saturated vapor,
low pressure liquid+vapor,
low pressure
Saturated liquid,
high pressure
Condenser
1 2
3
4
high-side
low-side
Evaporator
Comp
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Single stage – Direct-eXpansion (DX)
Eq
ua
lize
r lin
e
High
Pressure
Receiver
High pressure gas
King valve (automatic)
Condenser Evaporative Condenser
Compressor(s)
T T
High pressure liquid
DX Evap 1
Protected suction
…
Suction
Trap
Solenoid valve Thermostatic
expansion valve
Equalizing line
T T
DX Evap n
Refrigerant
Transfer
System
To HPR
Dis
ch
arg
e lin
e
Condenser Evaporative Condenser
Single stage – Direct-eXpansion (DX)
Eq
ua
lize
r lin
e
High
Pressure
Receiver
High pressure gas
King valve (automatic)
Condenser Evaporative Condenser
Compressor(s)
T T
High pressure liquid
DX Evap 1
Protected suction
…
Suction
Trap
Solenoid valve Thermostatic
expansion valve
Equalizing line
T T
DX Evap n
Refrigerant
Transfer
System
To HPR
Dis
ch
arg
e lin
e
Condenser Evaporative Condenser
25 psig (~11F)
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Single stage – Direct-eXpansion (DX)
Eq
ua
lize
r lin
e
High
Pressure
Receiver
High pressure gas
King valve (automatic)
Condenser Evaporative Condenser
Compressor(s)
T T
High pressure liquid
DX Evap 1
Protected suction
…
Suction
Trap
Solenoid valve Thermostatic
expansion valve
Equalizing line
T T
DX Evap n
Refrigerant
Transfer
System
To HPR
Dis
ch
arg
e lin
e
Condenser Evaporative Condenser
25 psig (~11F)
40 psig (~26F)
Single stage – Direct-eXpansion (DX)
Eq
ua
lize
r lin
e
High
Pressure
Receiver
High pressure gas
King valve (automatic)
Condenser Evaporative Condenser
Compressor(s)
T T
High pressure liquid
DX Evap 1
Protected suction
…
Suction
Trap
Solenoid valve Thermostatic
expansion valve
Equalizing line
T T
DX Evap n
Refrigerant
Transfer
System
To HPR
Dis
ch
arg
e lin
e
Condenser Evaporative Condenser
25 psig (~11F)
40 psig (~26F) 60 psig (~41F)
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Single stage – Direct-eXpansion (DX)
Eq
ua
lize
r lin
e
High
Pressure
Receiver
High pressure gas
King valve (automatic)
Condenser Evaporative Condenser
Compressor(s)
T T
High pressure liquid
DX Evap 1
Protected suction
…
Suction
Trap
Solenoid valve Thermostatic
expansion valve
Equalizing line
T T
DX Evap n
Refrigerant
Transfer
System
To HPR
Dis
ch
arg
e lin
e
Condenser Evaporative Condenser
25 psig (~11F)
40 psig (~26F) 60 psig (~41F)
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Compressor, rotary screw
Oil Separator
Compressor Motor
Motor
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Oil Separator
Oil
Compressor discharge
Motor Compressor
1st Stage Oil Separation 2nd Stage Oil Separation
Discharge
vapor
Oil Separator
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Compressors, reciprocating
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Single stage – Direct-eXpansion (DX)
Eq
ua
lize
r lin
e
High
Pressure
Receiver
High pressure gas
King valve (automatic)
Condenser Evaporative Condenser
Compressor(s)
T T
High pressure liquid
DX Evap 1
Protected suction
…
Suction
Trap
T T
DX Evap n
Refrigerant
Transfer
System
To HPR
Dis
ch
arg
e lin
e
Condenser Evaporative Condenser
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Condensers, evaporative
Ambient Air
Eliminators
Spray header
Makeup water
Moist, hot air out
Ambient Air
High pressure
vapor refrigerant, in
High pressure
liquid refrigerant, out
Remote sump
Condenser water
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Condensers, evaporative
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Evaporative condenser coil
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Single stage – Direct-eXpansion (DX)
Eq
ua
lize
r lin
e
High
Pressure
Receiver
High pressure gas
King valve (automatic)
Condenser Evaporative Condenser
Compressor(s)
T T
High pressure liquid
DX Evap 1
Protected suction
…
Suction
Trap
T T
DX Evap n
Refrigerant
Transfer
System
To HPR
Dis
ch
arg
e lin
e
Condenser Evaporative Condenser
30
Receivers, high pressure
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Single stage – Direct-eXpansion (DX)
Eq
ua
lize
r lin
e
High
Pressure
Receiver
High pressure gas
King valve (automatic)
Condenser Evaporative Condenser
Compressor(s)
T T
High pressure liquid
DX Evap 1
Protected suction
…
Suction
Trap
T T
DX Evap n
Refrigerant
Transfer
System
To HPR
Dis
ch
arg
e lin
e
Condenser Evaporative Condenser
32
King valve
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Single stage – Direct-eXpansion (DX)
Eq
ua
lize
r lin
e
High
Pressure
Receiver
High pressure gas
King valve (automatic)
Condenser Evaporative Condenser
Compressor(s)
T T
High pressure liquid
DX Evap 1
Protected suction
…
Suction
Trap
T T
DX Evap n
Refrigerant
Transfer
System
To HPR
Dis
ch
arg
e lin
e
Condenser Evaporative Condenser
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Evaporator, air-cooling
Ceiling-hung evaporator in a dock area
Penthouse evaporator in a freezer
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Evaporator technologies
• Air-cooling
– Very low temperature blast freezing
– Low temperature holding freezers
– Higher temperature storage coolers, production areas, air-conditioning
• Liquid-cooling (secondary fluids and products)
– Shell-and-tube
– Plate-and-frame
– Falling film
– Scraped surface
Plate-and-frame liquid chiller Shell-and-tube liquid chiller
Single stage – Direct-eXpansion (DX)
Eq
ua
lize
r lin
e
High
Pressure
Receiver
High pressure gas
King valve (automatic)
Condenser Evaporative Condenser
Compressor(s)
T T
High pressure liquid
DX Evap 1
Protected suction
…
Suction
Trap
T T
DX Evap n
Refrigerant
Transfer
System
To HPR
Dis
ch
arg
e lin
e
Condenser Evaporative Condenser
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Transfer system
Suction trap
Transfer drums
Oil pot
Evaporative Condenser(s )
Equalize line
High Pressure Receiver
High pressure liquid
High pressure gas
Flooded evap 1
“Protected” suction
To HPR
Suction
trap
King valve
Flooded evap, n
Solenoid
valve
Flooded evaporator
Hand expansion
valve
Float
Transfer
Station
Dis
ch
arg
e lin
e
Gravity flooded recirculation system
Compressor(s)
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Su
rge
Dru
m
Gravity flooded evaporator
Evaporator, liquid supply
Evaporator, vapor return
Float
Hand-expansion
valve
Solenoid valve
Evaporative Condenser Evaporative
Condenser
Eq
ua
lize
lin
e
Dry suction
High pressure liquid
High pressure gas
1
2
3
King valve
Pumped recirculator
4’ Overfed
evaporator(s)
4
T
4”’
Wet
return
3
Evaporative Condenser Evaporative
Condenser
Dis
ch
arg
e lin
e
Pumped liquid overfeed
Compressor(s)
High Pressure Receiver
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Liquid overfeed system
Recirculator
Float column
Liquid refrigerant pumps
Pumped liquid
line
42
Liquid overfeed system components
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• Lower evaporator temperatures
– Requires lower evaporator pressures
– Leading to increased compressor compression ratios
• Limitations of specific compression technologies
• Increased refrigerant discharge superheat
Two-stage compression systems
Equalize
line
Evaporative
Condenser(s)
Low
temperature
Evaporator(s)
Intercooler
Low
temperature
recirculator
Booster
Compressor(s)
High-Stage Compressor(s)
High Pressure Receiver
1 2
3
5
5’
6
5’’
4’
King valve
4’
4
7
Medium Temperature Recirculator/ Intercooler
T
DX Evap
Two-stage compression (two temperature level with two stages of liquid expansion)
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Equalize
line
Evaporative
Condenser(s)
Low
temperature
Evaporator(s)
Intercooler
Low
temperature
recirculator
Booster
Compressor(s)
High-Stage Compressor(s)
High Pressure Receiver
1 2
3
5
5’
6
5’’
4’
King valve
4’
4
7
Medium Temperature Recirculator/ Intercooler
T
DX Evap
Two-stage compression (two temperature level with two stages of liquid expansion)
10.4 psia or 8.8” Hg (~40F)
Equalize
line
Evaporative
Condenser(s)
Low
temperature
Evaporator(s)
Intercooler
Low
temperature
recirculator
Booster
Compressor(s)
High-Stage Compressor(s)
High Pressure Receiver
1 2
3
5
5’
6
5’’
4’
King valve
4’
4
7
Medium Temperature Recirculator/ Intercooler
T
DX Evap
Two-stage compression (two temperature level with two stages of liquid expansion)
10.4 psia or 8.8” Hg (~40F)
196 psia or 181 psig (~95F)
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Equalize
line
Evaporative
Condenser(s)
Low
temperature
Evaporator(s)
Intercooler
Low
temperature
recirculator
Booster
Compressor(s)
High-Stage Compressor(s)
High Pressure Receiver
1 2
3
5
5’
6
5’’
4’
King valve
4’
4
7
Medium Temperature Recirculator/ Intercooler
T
DX Evap
Two-stage compression (two temperature level with two stages of liquid expansion)
10.4 psia or 8.8” Hg (~40F)
196 psia or 181 psig (~95F)
45 psia
(~17F)
Equalize
line
Evaporative
Condenser(s)
Low
temperature
Evaporator(s)
Intercooler
Low
temperature
recirculator
Booster
Compressor(s)
High-Stage Compressor(s)
High Pressure Receiver
1 2
3
5
5’
6
5’’
4’
King valve
4’
4
7
Medium Temperature Recirculator/ Intercooler
T
DX Evap
Two-stage compression (two temperature level with two stages of liquid expansion)
10.4 psia or 8.8” Hg (~40F)
196 psia or 181 psig (~95F)
45 psia
(~17F)
𝐶𝑅𝐻𝑆 =196
45= 4.3: 1 𝐶𝑅𝐵 =
45
10.4= 4.3: 1
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Evaporative Condenser Evaporative
Condenser
Eq
ua
lize
r lin
e
Dry suction
High Pressure Receiver
Hig
h p
ressu
re liq
uid
High pressure gas
1
2
3
King valve (automatic)
3
Evaporative Condenser Evaporative
Condenser
Pumped
recirculator
4’
Overfed evaporator(s)
4
T 4”’
Wet
return
Compressor(s)
Suction
Trap
Compressor(s)
T T
DX evaporator
Flooded
Evaporator
What’s a “typical” system?
Transfer
Station
To HPR
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Conclusions
• Ammonia has been the mainstay refrigerant in the industrial sector
• Must be aware of its safety considerations
• As low GWP refrigerants continue to be pursued, ammonia applications are expanding
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QUESTIONS?
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What did you learn?
1. Where does the vast majority of ammonia originate from?
2. Which of the following materials is not compatible with
ammonia: carbon steel, stainless steel, copper,
aluminum?
3. Ammonia is considered highly flammable:
True or False?
4. The “suction trap” is needed to prevent compressors from
ingesting liquid refrigerant:
True or False?
5. Which of the following is not an industrial ammonia
system configuration: direct-expansion, liquid underfeed,
gravity flooded, two-stage?