Natural Refrigerants Meet Global Warming Challenge
The world must identify existing sustainable technologies that are ready for immediate and wide-scale adoption.
As the search for those technologies intensifies, ammonia and other natural refrigerants are emerging as the most viable solutions for industrial refrigeration, thanks to international treaties that put pressure on countries to phase down CFCs and identify alternatives. At the same time, advances in system design are expanding the applications for ammonia systems around the world.
“Our ability to overcome our global warming challenges will depend on our ability to accelerate the use of technologies that do not contribute to global warming,” said IIAR president Dave Rule. “Ammonia and other natural refrigerants are the most practical and efficient refrigerants available to meet those challenges right now within the global cold chain.”
In the United States, the recent decision to join the Montreal Protocol – an international agreement to phase down the consumption and production of HFCs and other halocarbon refrigerants – and a renewed commitment from the White House to accelerate existing green technologies, represents “a significant step forward,” said John Thomson, Deputy Director of Environmental Quality for the Department of State. Ammonia is currently on the Environmental Protection Agency’s list of four hundred prioritized green technologies, he said.
At the same time, rapidly evolving small-package, low-charge ammonia systems may be changing the way the world looks at ammonia refrigeration, especially in emerging markets. Large-scale refrigeration facilities, traditionally run by ammonia systems, have long been the hallmark of industrial refrigeration in countries like the U.S. with the space and infrastructure to support them.
“The mega-structures that exist in places like the U.S. are not common in much of the world,” said Richard Tracy, Vice President of International Programs for the Global Cold Chain Alliance, adding that because smallsize facilities are easily charged by freon, those systems are more common in places where the cold chain is still developing. “The prevailing idea is that ammonia isn’t considered unless a system is much bigger in scale. The ability to compete with smaller-scale systems would open up the door to the rest of the world for ammonia in places it has not been applied before.”
Nevertheless, regardless of facility size, ammonia and other natural refrigerants have always been particularly well-suited to meet environmental needs while preserving efficiency, said Rule.
“In the United States, and many other parts of the world, natural refrigerants are beginning to get more attention as the best potential solution to many of today’s problems, but the advantages posed by thermal performance, low cost, low environmental impact and simple technology have always made it one of the most efficient and practical solutions,” he said.
Now that the focus is shifting to ammonia and other natural refrigerants, governments and standards-writing bodies around the world are looking for information on how to design, operate and maintain safe systems.
That’s a need that IIAR is particularly well positioned to meet, said Rule, adding that the organization is taking on a greater role as a recognized international source for information about almost every facet of ammonia refrigeration, from design to safe operation.
“Because of the efforts of IIAR and other organizations around the world, there are detailed codes and standards that have been developed which provide industry vetted guidelines,” he said. “These standards address equipment and system design, installation, maintenance and process safety guidelines to ensure that management and operators are prepared for any emergency.” “There is an abundance of information and training materials available, so anyone anywhere can understand how to use ammonia, and how to use it safely.” Two countries that have recently turned to IIAR for information are Brazil and Colombia.
In Brazil, the national standards organization, ABNT, is working in conjunction with the Brazilian Association of Refrigeration, Air Conditioning, Ventilation, or ABRAVA, to write a national standard for ammonia. “ABRAVA has asked IIAR to supply an IIAR standard, IIAR-2, as a reference for their own ammonia standard,” said IIAR Chairman-elected, Marcos Braz. “That standard, once it is formed, will then be proposed to the Brazilian government, which will use it as a reference for future regulations referencing ammonia.”
Nevertheless, the use of IIAR standards as models for other countries and international organizations looking to create their own standards is just one example of the growing focus on the industry and the organization that represents it, said Braz.
Recently, the Colombian government requested – through ACAIRE the Colombian Association of Air Conditioning and Refrigeration – that IIAR give a presentation on the sustainability of ammonia refrigeration at the XII CIAR Convention, Spanish Ibero American Congress for Air Conditioning and Refrigeration, sponsored by FAIAR members including ASHRAE.
The purpose of the request, said Braz, was to outline the basic process of the design and construction of a facility that would deliver efficiency and maximize environmental gains.
The invitation was significant, he added, because it was the first time the well-established international convention on its twenty-second year focused specifically on natural refrigerants.
“This was one of the most important conventions in that area to allow that much space for ammonia,” said Braz. “There’s interest now where there wasn’t a focus before.”
“The Department of the Environment and Sustainable Development in Colombia was asking IIAR to be there. It’s significant that this was an invitation from the government through ACAIRE. It’s an example of how other countries are starting to take note of this industry and look to IIAR as a valuable reference.”
As for the technical presentation he gave to the organization, Braz said his primary goal was to provide a simple guideline for the best way to design a process plant to achieve environmental sustainability.
“The purpose was really to help them understand the applications of ammonia as a sustainable refrigerant for industrial use,” he said.
However, the presentation was also a way to outline the implementation of some of the best standardized processes for a meat process plant and how they might be expanded for application on a global level.
As international focus on natural refrigerants continues to grow, there will be many more opportunities for the industrial refrigeration industry to make its standards available and lend its experience to those organizations and countries that will be looking for guidance, said Braz. “Industrial refrigeration is positioned to grow around the world, and it will be able to expand, thanks to the large body of information we’ve cultivated in the form of standards, reference materials, training and our own real world experience. IIAR, and the industry at large, is ready and well prepared to share that knowledge.”
The technical paper re-printed below was produced at the request of the Colombian Association of Air Conditioning and Refrigeration and the Colombian Department of the Environment and Sustainable Development to illustrate the design and construction of a meat processing plant. In this paper, author Marcos Braz, outlines the factors that should be considered in creating a design that meets the goals of environmental sustainability while maintaining efficiency and safety.
SUSTAINABLE REFRIGERATION OF PROCESS PLANTS UNDER SANITARY STANDARDS
BY MARCOS R. BRAZ, PE
NOTE: This paper was presented at the XII CIAR 2013 convention in Cartagena Colombia on July 23rd, 2013. The participation of Marcos Braz, PE, Chair Elect of IIAR, was sponsored by the Unidad Tecnica Ozono – UTO, from the Colombian Department of Environment and Sustainable Development. The UTO is the office in charge of implementing the Montreal Protocol in Colombia.
SUSTAINABLE EXPECTATIONS
An era of global interaction, fueled by advances in communication and transportation, has revolutionized the way food is produced, transported and distributed, and the food industry must meet the challenge of providing nutritious and fresh, but perishable, products at an affordable cost while minimizing or neutralizing any direct impact on the environment. While the problems presented by airborne bacteria, including E.coli, Listeria and Salmonella have been minimized by a globally advanced cold chain, they still deserve a great deal of attention from a design perspective.
At the early stages of a meat process plant design, the real estate-required production rates, equipment and the number of people necessary to produce the work are the main factors in obtaining real financial results. Moreover, the economic plan for the growth of such a plant needs to meet the global demand for quality and competitive costs. This paper will outline the ways in which those challenges may be met.
SPOILAGE AND ENVIRONMENTAL IMPACT
The growth of harmful microorganisms in food production and its environment have a direct impact on our daily lives. These days, thanks to global advances in technology and logistics, we are eating fruits, drinking juices and obtaining diverse protein products from distant countries, thanks to the ease of transporting refrigerated food across the globe.
Nevertheless, we are vulnerable to the related hazards that account for thousands of deaths per year (estimated at 9,000 per year in the USA) while food spoilage is estimated at 20 to 40 percent on average worldwide. These problems deserve attention if we are going to achieve the final product quality required by international standards.
How do these important aspects of global interaction relate to the design of a process plant? Or, in the case of this paper, a slaughter and meat packaging plant?
To answer that question, design must be considered first. All the facets of design should be made to work together to achieve results from an economic, environmental and health perspective.
REFRIGERANT SELECTION
The refrigeration system of a slaughter and meat processing plant is responsible for integrating the sanitary requirements for production, including process environment temperatures. Additionally the refrigeration system accounts for 60 to 80 percent of the electrical energy consumption and consequent environmental impact in relation to its carbon foot print.
Ammonia has been chosen by the vast majority of industrial plants in the world as reliable and efficient – due to its spectacular thermal properties (see Appendix A) – refrigerant, noted for its resilience by keeping somewhat workable efficiency under the undesirable presence of impurities such as water and air. This is a very important factor that allows the industry to operate in less than ideal conditions until corrective actions are taken.
Ammonia is produced by the human body from the metabolism of protein, amino acids and other nitrogen-containing chemicals. The human body produces ammonia at a rate of 50 mg per day. Although essential, ammonia can be a toxic agent to the extent to which its concentration in the air rises.
Ammonia can cause burns on exposed human tissue, including the respiratory tract, eyes and skin when its concentration reaches lethal levels (5,000 to 10,000 ppm, or parts per million) in short periods of exposure. The level of concentration known as Immediately Dangerous to Life and Health, or IDLH, is 500 ppm. This level is determined as the level at which a worker can be exposed for 30 minutes without suffering irreversible health effects.
The irritating and pungent odor of ammonia makes this refrigerant easily detected at much less than 25 ppm. Therefore, it is self-alarming. The concentrations from 25 to 35 ppm do not represent an immediate health risk, even for prolonged periods of exposure.
It is very important to note that only at concentrations of 15 percent to 25 percent is ammonia flammable by deflagration and not by violent explosion. This means that its flame velocity, at these concentrations, is much lower than other flammable substances. There are no reported cases of ammonia ignition at any concentration in an open environment.
Therefore, it is necessary to respect this natural inorganic substance with safety procedures that include operator training, proper equipment and maintenance.
Leaks of ammonia in the environment require as much attention to the protection of people as to nature. Having been used as a refrigerant for more than 100 years, ammonia’s characteristics are well known and this means the design engineer has all the information needed to design a safe and stable system, and to be prepared for any emergencies.
SUSTAINABLE AMMONIA PRODUCTION:
Steam reforming, sometimes called fossil fuel reforming, is a method for the production of hydrogen, or other useful products from hydrocarbon fuels such as natural gas. This is achieved in a processing device called a reformer which reacts steam at high temperature with the fossil fuel. The steam methane reformer is widely used in the industry to make hydrogen.
To produce the desired end-product ammonia, the hydrogen is then catalytically reacted with nitrogen (derived from process air) to form anhydrous liquid ammonia. This step is known as the ammonia synthesis loop (also referred to as the HaberBosch process):
3H2 + N2 = 2NH3
Ammonia production depends on plentiful supplies of natural gas, a finite but abundant resource, to provide hydrogen. Due to its critical role in intensive agriculture and other processes, sustainable production is desirable. This is can be achieved by using renewable energy to generate hydrogen by electrolysis of water. Electrolysis of water is the decomposition of water (H2 O) into oxygen (O2 ) and hydrogen gas (H2 ) due to an electric current being passed through the water. In practice, natural gas will remain the major source of hydrogen for ammonia production as long as it is cheapest.
Waste water is also often high in ammonia. Because discharging ammonia laden water into the environment can cause problems, nitrification is often necessary to remove the ammonia. This may be a potentially sustainable source of ammonia in the future because of its abundance and the need to remove it from the water anyway.
AMMONIA REFRIGERATION:
In general, the Slaughter Process Plant is composed of a slaughter area, hanging, bleeding and offal evisceration, followed by rapid cooling, staging, deboning, special cuts, vacuum and packaging areas.
Typically one could estimate for a slaughter plant with frozen and refrigerated packaging: a 17 to 20 TR/ Head Hour of refrigeration capacity at 1.2 hp/ TR which, at 100 heads per hour, can result in a refrigeration system consuming upwards of 2,400 HP of power. This translates into a 0.016 KW/ pound to 0.021 KW/ pound range of energy usage.
It is imperative, then, to utilize a refrigerant that results in the most sustainable refrigeration system with the lowest carbon footprint considering the magnitude of power consumption.
For a Two Stage Refrigeration System with SST -30 F (-34.4°C) / SST 20 F (-6.7 °C) TO DST 96 F (35.5°C)
- R717 (ammonia) COP 4.11/4.48
- R22 COP 3.80 /4.15
- R404a COP 3.36/4.52
- R134a COP 3.33/2.52
- Ammonia/CO2 COP 3.8 / 5.83 * cascade system at 15 F
- Hydrocarbon 3.79/4.27
The numbers above are achieved with ammonia on low and high temperature stages. It is important to note that new technologies are being developed with CO2 as the refrigerant of choice for low suction temperatures (below -40 F), mainly due to the reduced pressure drop and estimated energy efficiency. There are factors yet to be overcome that require careful analysis or special design for CO2 refrigeration systems given limitations with higher pressures, defrost, screw type compressors performance, triple point at 75 psig (“dry ice’) , oil type and other system management issues.
INTERTWINING INDUSTRIAL REFRIGERATION EFFICIENCY WITH PRODUCT PROCESS QUALITY
Facility Programming:
At the very early stage of the project, several factors could significantly reduce the final energy bill of a given facility. For example, factors resulting from the site selection include:
- Prevailing Winds
- Traffic in Paved Areas
- Rendering Plants or Wastewater Treatment
- Machinery Room Location
- Process Flow
Hazard Analysis and Critical Control Points:
HACCP is a management system in which food safety is addressed through the analysis and control of biological, chemical, and physical hazards from raw material production, procurement and handling, to manufacturing, distribution and consumption of the finished product.
The HACCP was developed to ensure that Process Plants address the continued monitoring of food processed with regard to its quality, and therefore, lack of contamination. It can be summarized in two main principles:
Principle 1: Conduct a hazard analysis.
Plans determine the food safety hazards and identify the preventive measures the plan can apply to control these hazards. A food safety hazard is any biological, chemical, or physical property that may cause food to become unsafe for human consumption.
Principle 2: Identify critical control points.
A critical control point (CCP) is a point, step, or procedure in a food manufacturing process at which control can be applied and, as a result, a food safety hazard can be prevented, eliminated, or reduced to an acceptable level.
One of the main objectives of a process plant is to reach product quality while decreasing the energy consumption, or costs, to produce it.
In this paper, we address the impact of sanitary design of a slaughter meat plant and its consequences for the refrigeration system energy consumption, meaning that you can be saving energy while complying with the highest sanitary standard required.
For example, the control of odor, dust and particulates should start as a higher priority since the plant location with prevailing winds and surrounding industries could have a negative or positive impact on the plant’s final electrical bill and product quality. The upwind location of a rendering plant near the process areas could be easily avoided during the planning phase. See appendix A.
Mitigating these effects afterwards impacts the installed refrigeration system directly, that now has to cope with reduced air intake and increased consumption of energy during cleaning and drying mode since it cannot bring fresh air in.
Infiltration of outside air is one of the most important factors in energy consumption. It is easily estimated that 1,000 CFM of outside air on a warm day (96°F [36°C]/ 45% RH) brings 10 TR of extra load to a 35°F [2°C]/ 70 % RH environment. A 50°F [10°C]/ 70 % RH environment will be penalized at 8 TR.
The air coming from outside should always be filtered and should be limited to what would be required to keep the process area environment under correct pressurization and, or, to provide enough fresh air to production areas. However, it must be kept to a minimum to avoid the thermal penalty described above.
In a slaughter process area, it is very common to produce negative pressure with the exhaust fans where the goal is to achieve humidity control and create a counter flow of contaminated air against the product process.
Although desirable from the perspective of sanitary control, an unmeasured amount of air extraction will provoke a huge amount of refrigeration load since it will carry most of the air conditioned air from adjacent areas. The solution to this problem is achieved by balancing supply and exhaust fans to produce just the desired amount of negative pressure while moving the moisture and contaminants away.
From AMI (American Meat Institute) the principles of Sanitary Design include:
Establish Distinct Hygienic Zones in the Facility
Maintain strict physical separations that reduce the likelihood of transfer of hazards from one area of the plant, or from one process, to another area of the plant, or process, respectively. Facilitate necessary storage and management of equipment, waste, and temporary clothing to reduce the likelihood of transfer of hazards.
Temperature and Humidity Control in Process Areas
Controlling Relative Humidity should be prioritized instead of just lowering the temperature of the room. The correct control of relative humidity translates in avoiding condensation dripping over the product as well as avoiding condensation over the product that was cooled, chilled or frozen.
From 24 to 26 hours after sacrifice at the Slaughter plant, the meat carcass goes from 105 degrees to close to 38 degrees F [41°C to 3°C] where it will be processed in the deboning room. The control of relative humidity in the de-boning area should create a dew point higher than the product (meat) surface temperature.
This is accomplished by keeping the 50°F [10°C] room at 60% RH. This will produce a dew point of 37 degrees F [2.8°C] which will prevent the meat from condensing moisture over its surface.
Condensation control not only achieves the sanitary goals of a meat process plant, but also creates savings from having to lower the room temperatures to avoid microbial growth. It is more economical and safe to control the relative humidity of the air than to reduce the temperature of the room with additional thermal load removal.
Usually, lowering the room temperature will penalize the energy consumption and accomplish more moisture migration to the room due its greater differential temperature and potential to provoke condensation. Besides that, the comfort of the workers will be impaired when you impose close to freezing temperatures in the room for manual labor.
From AMI sanitary design principles for the design, construction, and renovation of food processing facilities to reduce food safety hazards.
Room Temperature and Humidity Control
Control room temperature and humidity to facilitate control of microbial growth. Keeping process areas cold and dry will reduce the likelihood of growth of potential food borne pathogens. Ensure that the HVAC/ refrigeration systems serving process areas will maintain specified room temperatures and control room air dew point to prevent condensation. Ensure that control systems include a cleanup purge cycle (heated air makeup and exhaust) to manage fog during sanitation and to dry out the room after sanitation.
There are different types of equipment and approaches to provide the correct temperature and humidity control to a given area at the plant. There are three main types of Air Handling Units available, each with its own moisture and temperature control capabilities such as:
- Mechanical Cooling with Reheat Coil
- Dry Desiccant Wheel
- Liquid Desiccant
It is important to note the safety aspects of these units assisting the processing areas.
The following are recommended “must haves” for all processing areas in the plant as a minimum:
- Ammonia alarm at air handling units discharge (before the final filter downstream of the cooling coil)
- Integral flow exhaust fan to be used to exhaust the room to atmosphere, usually at 12 to 15 air renovations per hour
- Stainless steel coils with aluminum fins
- Interlocked controls with valve groups, machinery room and other roof ventilation equipment
Pressurization of Packaging and Deboning Processing Areas
Almost as obvious as the correct separation of the hygienic areas with a focus on traffic and a decreased amount of openings (read as doors), is the correct pressurization that will allow minimum cross contamination potential as well as a reduction in energy consumption, as explained before. It is important to note the implication of fresh air brought into pressurization areas and how it relates to the energy consumption of the plant. Pressurization costs are closely related to the amount and quality of the openings to adjacent areas. Remember that we showed that 1,000 CFM will easily produce an extra 10 TR requirement on the refrigeration system. See Appendix C.
From AMI sanitary design principles for the design, construction, and renovation of food processing facilities to reduce food safety hazards.
Room Air Flow and Room Air Quality Control
Design, install and maintain HVAC/ refrigeration systems serving process areas to ensure air flow will be from cleaner to less clean areas, adequately filter air to control contaminants, provide outdoor makeup air to maintain specified airflow, minimize condensation on exposed surfaces, and capture high concentrations of heat, moisture and particulates at their source.
Walls, Roof and Floor Insulation
The separation of areas is accomplished physically through insulated walls that also act as barriers to contamination from adjacent areas. It is very important to assure proper vapor barrier at the warm side to avoid the migration of moisture by a difference in vapor pressures that will bring moisture to the insulation with detriment of the insulation values. This will result in increased heat conduction with energy losses and condensation occurring at the warm side due to the loss of insulation R-value.
The floor insulation must be considered since an un-insulated floor will conduct 15 to 20 times more than an insulated floor with R=32.
Doors
The selection of doors for the differential of temperature and traffic frequency is of extreme importance to maintain the correct pressurization in the process areas as well as to avoid air infiltration between these areas. There are numerous types and models of doors that will work for the traffic and temperatures between the adjacent areas. The choice should be always for fast acting doors and preferably easily reparable after impact.
Air curtain doors must be selected with care since they have to match the frequency of openings and differential temperature between the separated areas. Refer to Appendix D.
Interstitial Space Ventilation
The ambient temperature we find above the ceiling is of great importance to ventilate and create enough convection to avoid condensation over the insulated ceiling due to stagnated air. It is also important to decrease the temperature differential caused by ancillary equipment load (air compressors, vacuum pumps, etc.) using proper ventilation.
Wash Down / Cleaning and Pre-Operational Time
The Cleaning Cycle must be addressed correctly. Use outside air when the outside temperature allows for removing the excessive steam produced during the wash-down. It will remove most of the moisture with a 100 percent exhaust flow provided by the air handling unit or exhaust system. It is important that the cooling and dehumidification mode should be utilized after the air renovation is accomplished. The use of burners to heat the air is advised when temperatures outside are lower than room operating conditions. The objective is always to remove the excessive moisture of the cleaning cycle using an economized mode of outside air.
It should be noted that the cleaning cycle could happen when nearby areas are still in production mode. The relevance of doors insulating the wash down process from production is then highly augmented.
From AMI sanitary design principles for the design, construction, and renovation of food processing facilities to reduce food safety hazards.
Water Accumulation Controlled Inside Facility
Design and construct a building system (floors, walls, ceilings, and, supporting infrastructure) that prevents the development and accumulation of water. Ensure that all water positively drains from the process area and that these areas will dry during the allotted time frames.
IN CONCLUSION:
Meeting international sanitary regulations creates energy savings and a competitive advantage for a welldesigned slaughter process plant.
Establishing a sanitary and energy efficient layout, while keeping the pressurization and infiltration controlled to optimum levels will minimize the energy consumption.
Complying with sanitary standards can be translated into optimized and efficient usage of energy from refrigeration systems with a consequent reduction of the carbon foot print. Ammonia, a natural, efficient and abundant refrigerant presents itself as a strong element in this industry to minimize environmental impact, while promoting sustainability for years to come.
