Nestle USA - Ron Worley: Lessons learned from a low temperature food production facility
Looking at the history, Ron Worley stated that already since 1995 there has been a renaissance of CO2/NH3 refrigeration with, for example, more than 30 shock freezing plants in Germany, 5 ice rinks in Switzerland and Austria and numerous projects also in other European countries today. Already in 1998/99, Nestlé started to evaluate possible applications and commissioned its first CO2/NH3 refrigeration plant in France in 2000 and one year later in the UK. By using the example of a CO2/NH3 cascade project in the US, Worley explained the lessons learned in regards to the CO2 auto purger, the cascade condenser purge design, moisture clean up CO2 evaporator water defrost design, plate freezer liquid flow design, the heat exchangers and more. However, the conclusion he drew from this project and others he had been working on is that “CO2 always surprises because it over performs.”
Andy Pearson - Star Refrigeration: “Safety considerations for carbon dioxide systems”
Talking about safety issues when handling CO2 systems, Andy Pearson started off by pointing out that CO2 is not more or less safe than any other refrigerant, but that it is different. Especially the higher pressure in which it operates should not be seen as a drawback, considering CO2 gets all its major advantages from this. Pearson added “if the designer does his job right then the system will be as safe as any other”.
Pearson outlined the main safety issues to be considered when working with CO2:
- Physiological effects: CO2 in high concentration might cause hyperventilation, numbness or, in extreme cases, also coma. Fresh air helps a speedy recovery and to prevent this, good ventilation systems and infra gas detectors are very reliable.
- Pressure and temperature: The pressure/temperature relationship is important. Transcritical systems require at least 100bar to operate correctly, although its probably more like 120bar.
- Precautions when venting a CO2 systems: Only vent to open air
- Precautions when pumping out CO2 liquid: Never apply heat to blockages
- Considerations when charging a CO2 system either from a cylinder or from a tanker
- Material and components: Combination of high pressure and low temperature mean that standard steels are not always suitable. High pressure shut off valves are needed.
- Chemical reactions with ammonia: Putting CO2 and ammonia together forms ammonium carbamate. This can block pressure tappings and relief valve ports. Deal with leaks quickly to prevent additional damage.
- Chemical reactions with water: Corrosion is not a risk if the water content is low enough.
This can of course, be only a short summary of his presentation, but R744.com will soon publish a more detailed article from Andy Pearson about safety considerations for CO2 systems.
Michael Lynch - United State Cold Storage (USCS): CO2/NH3 cascade refrigeration, lessons learned in public refrigerated warehousing
Michael Lynch started by saying that USCS is operating 6 locations with CO2/NH3 cascade refrigeration systems, with 2 additional ones currently under construction. One reason for the company to invest in these systems that combine the benefits of both CO2 and ammonia, are safety issues, as such a system moves ammonia away from the storage area and reduces the ammonia charge. A second very important reason is also the energy efficiency. Average US public refrigerated warehouse energy efficiency lies at 1.54 kwh/ft3 per year. However, the USCS facilities using CO2/NH3 can score with a much higher efficiency ranging between 0.7 and 1.0 kwh/ft3. Lynch concluded his presentation by mentioning future considerations for the USCS CO2/NH3 plants that will include: Hot gas defrost, single stage ammonia with CO2 as a volatile brine and high pressure CO2 screw compressors (instead of reciprocating).
Hernan Hidalgo, Danfoss: Transcritical CO2 in industrial refrigeration
Hernan Hidalgo concluded the IIAR training programme with examples and technical information about the use of CO2 transcritical refrigeration systems in industrial applications. As one of the biggest challenges for industrial refrigeration he stated the size and number of compressors available to operate in transcritical refrigeration. In addition, Hernan summarised the following:
- Current set up for large supermarkets is manageable, but larger installations would require in excess of 40 reciprocating compressors depending on the medium and low temperature load.
- Transcritical systems, compared to traditional HFC systems, offer large opportunities in colder climates for large air conditioning systems (schools, government buildings, etc.) and cooling of data centers CO2 in cascade arrangements is most efficient for low temperature evaporators.
- NH3/CO2 cascade systems are most efficient in moderate hot climates for low and medium temperature applications.
- CO2 booster systems are most efficient in cold to moderate climates and low and medium temperatures.
About IIAR Conference & Exhibition 2013
The Industrial Refrigeration Conference and Exhibition (IIAR) took place on March 17-20, 2013 in Colorado Springs, USA. Apart from the over 100 exhibitor booths, the IIAR is the largest event dedicated exclusively to industrial refrigeration offering exhibitor sponsored technomercials, technical presentations, panel discussions and workshops. More than 1200 industrial refrigeration professionals attended this year for the opportunity to network with engineers, manufacturers and end-users throughout the four-day event.